Updated: 2021/Apr/14


GCC(1)                                GNU                               GCC(1)



NAME
       gcc - GNU project C and C++ compiler

SYNOPSIS
       gcc [-c|-S|-E] [-std=standard]
           [-g] [-pg] [-Olevel]
           [-Wwarn...] [-Wpedantic]
           [-Idir...] [-Ldir...]
           [-Dmacro[=defn]...] [-Umacro]
           [-foption...] [-mmachine-option...]
           [-o outfile] [@file] infile...

       Only the most useful options are listed here; see below for the
       remainder.  g++ accepts mostly the same options as gcc.

DESCRIPTION
       When you invoke GCC, it normally does preprocessing, compilation,
       assembly and linking.  The "overall options" allow you to stop this
       process at an intermediate stage.  For example, the -c option says not
       to run the linker.  Then the output consists of object files output by
       the assembler.

       Other options are passed on to one or more stages of processing.  Some
       options control the preprocessor and others the compiler itself.  Yet
       other options control the assembler and linker; most of these are not
       documented here, since you rarely need to use any of them.

       Most of the command-line options that you can use with GCC are useful
       for C programs; when an option is only useful with another language
       (usually C++), the explanation says so explicitly.  If the description
       for a particular option does not mention a source language, you can use
       that option with all supported languages.

       The usual way to run GCC is to run the executable called gcc, or
       machine-gcc when cross-compiling, or machine-gcc-version to run a
       specific version of GCC. When you compile C++ programs, you should
       invoke GCC as g++ instead.

       The gcc program accepts options and file names as operands.  Many
       options have multi-letter names; therefore multiple single-letter
       options may not be grouped: -dv is very different from -d -v.

       You can mix options and other arguments.  For the most part, the order
       you use doesn't matter.  Order does matter when you use several options
       of the same kind; for example, if you specify -L more than once, the
       directories are searched in the order specified.  Also, the placement
       of the -l option is significant.

       Many options have long names starting with -f or with -W---for example,
       -fmove-loop-invariants, -Wformat and so on.  Most of these have both
       positive and negative forms; the negative form of -ffoo is -fno-foo.
       This manual documents only one of these two forms, whichever one is not
       the default.

       Some options take one or more arguments typically separated either by a
       space or by the equals sign (=) from the option name.  Unless
       documented otherwise, an argument can be either numeric or a string.
       Numeric arguments must typically be small unsigned decimal or
       hexadecimal integers.  Hexadecimal arguments must begin with the 0x
       prefix.  Arguments to options that specify a size threshold of some
       sort may be arbitrarily large decimal or hexadecimal integers followed
       by a byte size suffix designating a multiple of bytes such as "kB" and
       "KiB" for kilobyte and kibibyte, respectively, "MB" and "MiB" for
       megabyte and mebibyte, "GB" and "GiB" for gigabyte and gigibyte, and so
       on.  Such arguments are designated by byte-size in the following text.
       Refer to the NIST, IEC, and other relevant national and international
       standards for the full listing and explanation of the binary and
       decimal byte size prefixes.

OPTIONS
   Option Summary
       Here is a summary of all the options, grouped by type.  Explanations
       are in the following sections.

       Overall Options
           -c  -S  -E  -o file  -x language -v  -###  --help[=class[,...]]
           --target-help  --version -pass-exit-codes  -pipe  -specs=file
           -wrapper @file  -ffile-prefix-map=old=new -fplugin=file
           -fplugin-arg-name=arg -fdump-ada-spec[-slim]
           -fada-spec-parent=unit  -fdump-go-spec=file

       C Language Options
           -ansi  -std=standard  -fgnu89-inline
           -fpermitted-flt-eval-methods=standard -aux-info filename
           -fallow-parameterless-variadic-functions -fno-asm  -fno-builtin
           -fno-builtin-function  -fgimple -fhosted  -ffreestanding -fopenacc
           -fopenacc-dim=geom -fopenmp  -fopenmp-simd -fms-extensions
           -fplan9-extensions  -fsso-struct=endianness
           -fallow-single-precision  -fcond-mismatch  -flax-vector-conversions
           -fsigned-bitfields  -fsigned-char -funsigned-bitfields
           -funsigned-char

       C++ Language Options
           -fabi-version=n  -fno-access-control -faligned-new=n
           -fargs-in-order=n  -fchar8_t  -fcheck-new -fconstexpr-depth=n
           -fconstexpr-cache-depth=n -fconstexpr-loop-limit=n
           -fconstexpr-ops-limit=n -fno-elide-constructors
           -fno-enforce-eh-specs -fno-gnu-keywords -fno-implicit-templates
           -fno-implicit-inline-templates -fno-implement-inlines
           -fms-extensions -fnew-inheriting-ctors -fnew-ttp-matching
           -fno-nonansi-builtins  -fnothrow-opt  -fno-operator-names
           -fno-optional-diags  -fpermissive -fno-pretty-templates -fno-rtti
           -fsized-deallocation -ftemplate-backtrace-limit=n
           -ftemplate-depth=n -fno-threadsafe-statics  -fuse-cxa-atexit
           -fno-weak  -nostdinc++ -fvisibility-inlines-hidden
           -fvisibility-ms-compat -fext-numeric-literals -Wabi-tag
           -Wcatch-value  -Wcatch-value=n -Wno-class-conversion
           -Wclass-memaccess -Wcomma-subscript  -Wconditionally-supported
           -Wno-conversion-null  -Wctor-dtor-privacy  -Wno-delete-incomplete
           -Wdelete-non-virtual-dtor  -Wdeprecated-copy
           -Wdeprecated-copy-dtor -Weffc++  -Wextra-semi
           -Wno-inaccessible-base -Wno-inherited-variadic-ctor
           -Wno-init-list-lifetime -Wno-invalid-offsetof  -Wno-literal-suffix
           -Wmismatched-tags -Wmultiple-inheritance  -Wnamespaces  -Wnarrowing
           -Wnoexcept  -Wnoexcept-type  -Wnon-virtual-dtor -Wpessimizing-move
           -Wno-placement-new  -Wplacement-new=n -Wredundant-move
           -Wredundant-tags -Wreorder  -Wregister -Wstrict-null-sentinel
           -Wno-subobject-linkage  -Wtemplates -Wno-non-template-friend
           -Wold-style-cast -Woverloaded-virtual  -Wno-pmf-conversions
           -Wsign-promo -Wsized-deallocation  -Wsuggest-final-methods
           -Wsuggest-final-types  -Wsuggest-override -Wno-terminate
           -Wuseless-cast  -Wvirtual-inheritance -Wno-virtual-move-assign
           -Wvolatile  -Wzero-as-null-pointer-constant

       Objective-C and Objective-C++ Language Options
           -fconstant-string-class=class-name -fgnu-runtime  -fnext-runtime
           -fno-nil-receivers -fobjc-abi-version=n -fobjc-call-cxx-cdtors
           -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck
           -fobjc-std=objc1 -fno-local-ivars
           -fivar-visibility=[public|protected|private|package]
           -freplace-objc-classes -fzero-link -gen-decls -Wassign-intercept
           -Wno-property-assign-default -Wno-protocol  -Wselector
           -Wstrict-selector-match -Wundeclared-selector

       Diagnostic Message Formatting Options
           -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
           -fdiagnostics-color=[auto|never|always]
           -fdiagnostics-urls=[auto|never|always]
           -fdiagnostics-format=[text|json] -fno-diagnostics-show-option
           -fno-diagnostics-show-caret -fno-diagnostics-show-labels
           -fno-diagnostics-show-line-numbers -fno-diagnostics-show-cwe
           -fdiagnostics-minimum-margin-width=width
           -fdiagnostics-parseable-fixits  -fdiagnostics-generate-patch
           -fdiagnostics-show-template-tree  -fno-elide-type
           -fdiagnostics-path-format=[none|separate-events|inline-events]
           -fdiagnostics-show-path-depths -fno-show-column

       Warning Options
           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors -w
           -Wextra  -Wall  -Wabi=n -Waddress  -Wno-address-of-packed-member
           -Waggregate-return -Walloc-size-larger-than=byte-size  -Walloc-zero
           -Walloca  -Walloca-larger-than=byte-size
           -Wno-aggressive-loop-optimizations -Warith-conversion
           -Warray-bounds  -Warray-bounds=n -Wno-attributes
           -Wattribute-alias=n -Wno-attribute-alias -Wno-attribute-warning
           -Wbool-compare  -Wbool-operation -Wno-builtin-declaration-mismatch
           -Wno-builtin-macro-redefined  -Wc90-c99-compat  -Wc99-c11-compat
           -Wc11-c2x-compat -Wc++-compat  -Wc++11-compat  -Wc++14-compat
           -Wc++17-compat -Wc++20-compat -Wcast-align  -Wcast-align=strict
           -Wcast-function-type  -Wcast-qual -Wchar-subscripts -Wclobbered
           -Wcomment -Wconversion  -Wno-coverage-mismatch  -Wno-cpp
           -Wdangling-else  -Wdate-time -Wno-deprecated
           -Wno-deprecated-declarations  -Wno-designated-init
           -Wdisabled-optimization -Wno-discarded-array-qualifiers
           -Wno-discarded-qualifiers -Wno-div-by-zero  -Wdouble-promotion
           -Wduplicated-branches  -Wduplicated-cond -Wempty-body
           -Wno-endif-labels  -Wenum-compare  -Wenum-conversion -Werror
           -Werror=*  -Wexpansion-to-defined  -Wfatal-errors
           -Wfloat-conversion  -Wfloat-equal  -Wformat  -Wformat=2
           -Wno-format-contains-nul  -Wno-format-extra-args
           -Wformat-nonliteral  -Wformat-overflow=n -Wformat-security
           -Wformat-signedness  -Wformat-truncation=n -Wformat-y2k
           -Wframe-address -Wframe-larger-than=byte-size
           -Wno-free-nonheap-object -Wno-hsa  -Wno-if-not-aligned
           -Wno-ignored-attributes -Wignored-qualifiers
           -Wno-incompatible-pointer-types -Wimplicit  -Wimplicit-fallthrough
           -Wimplicit-fallthrough=n -Wno-implicit-function-declaration
           -Wno-implicit-int -Winit-self  -Winline  -Wno-int-conversion
           -Wint-in-bool-context -Wno-int-to-pointer-cast
           -Wno-invalid-memory-model -Winvalid-pch  -Wjump-misses-init
           -Wlarger-than=byte-size -Wlogical-not-parentheses  -Wlogical-op
           -Wlong-long -Wno-lto-type-mismatch -Wmain  -Wmaybe-uninitialized
           -Wmemset-elt-size  -Wmemset-transposed-args
           -Wmisleading-indentation  -Wmissing-attributes  -Wmissing-braces
           -Wmissing-field-initializers  -Wmissing-format-attribute
           -Wmissing-include-dirs  -Wmissing-noreturn  -Wno-missing-profile
           -Wno-multichar  -Wmultistatement-macros  -Wnonnull
           -Wnonnull-compare -Wnormalized=[none|id|nfc|nfkc]
           -Wnull-dereference  -Wno-odr  -Wopenmp-simd -Wno-overflow
           -Woverlength-strings  -Wno-override-init-side-effects -Wpacked
           -Wno-packed-bitfield-compat  -Wpacked-not-aligned  -Wpadded
           -Wparentheses  -Wno-pedantic-ms-format -Wpointer-arith
           -Wno-pointer-compare  -Wno-pointer-to-int-cast -Wno-pragmas
           -Wno-prio-ctor-dtor  -Wredundant-decls -Wrestrict
           -Wno-return-local-addr  -Wreturn-type -Wno-scalar-storage-order
           -Wsequence-point -Wshadow  -Wshadow=global  -Wshadow=local
           -Wshadow=compatible-local -Wno-shadow-ivar
           -Wno-shift-count-negative  -Wno-shift-count-overflow
           -Wshift-negative-value -Wno-shift-overflow  -Wshift-overflow=n
           -Wsign-compare  -Wsign-conversion -Wno-sizeof-array-argument
           -Wsizeof-pointer-div  -Wsizeof-pointer-memaccess -Wstack-protector
           -Wstack-usage=byte-size  -Wstrict-aliasing -Wstrict-aliasing=n
           -Wstrict-overflow  -Wstrict-overflow=n -Wstring-compare
           -Wstringop-overflow=n  -Wno-stringop-truncation
           -Wsuggest-attribute=[pure|const|noreturn|format|malloc] -Wswitch
           -Wno-switch-bool  -Wswitch-default  -Wswitch-enum
           -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand
           -Wsystem-headers  -Wtautological-compare  -Wtrampolines
           -Wtrigraphs -Wtype-limits  -Wundef -Wuninitialized
           -Wunknown-pragmas -Wunsuffixed-float-constants  -Wunused
           -Wunused-but-set-parameter  -Wunused-but-set-variable
           -Wunused-const-variable  -Wunused-const-variable=n
           -Wunused-function  -Wunused-label  -Wunused-local-typedefs
           -Wunused-macros -Wunused-parameter  -Wno-unused-result
           -Wunused-value  -Wunused-variable -Wno-varargs  -Wvariadic-macros
           -Wvector-operation-performance -Wvla  -Wvla-larger-than=byte-size
           -Wno-vla-larger-than -Wvolatile-register-var  -Wwrite-strings
           -Wzero-length-bounds

       Static Analyzer Options
           -fanalyzer -fanalyzer-call-summaries -fanalyzer-checker=name
           -fanalyzer-fine-grained -fanalyzer-state-merge
           -fanalyzer-state-purge -fanalyzer-transitivity
           -fanalyzer-verbose-edges -fanalyzer-verbose-state-changes
           -fanalyzer-verbosity=level -fdump-analyzer -fdump-analyzer-stderr
           -fdump-analyzer-callgraph -fdump-analyzer-exploded-graph
           -fdump-analyzer-exploded-nodes -fdump-analyzer-exploded-nodes-2
           -fdump-analyzer-exploded-nodes-3 -fdump-analyzer-state-purge
           -fdump-analyzer-supergraph -Wno-analyzer-double-fclose
           -Wno-analyzer-double-free
           -Wno-analyzer-exposure-through-output-file -Wno-analyzer-file-leak
           -Wno-analyzer-free-of-non-heap -Wno-analyzer-malloc-leak
           -Wno-analyzer-null-argument -Wno-analyzer-null-dereference
           -Wno-analyzer-possible-null-argument
           -Wno-analyzer-possible-null-dereference
           -Wno-analyzer-stale-setjmp-buffer -Wno-analyzer-tainted-array-index
           -Wanalyzer-too-complex
           -Wno-analyzer-unsafe-call-within-signal-handler
           -Wno-analyzer-use-after-free
           -Wno-analyzer-use-of-pointer-in-stale-stack-frame
           -Wno-analyzer-use-of-uninitialized-value

       C and Objective-C-only Warning Options
           -Wbad-function-cast  -Wmissing-declarations
           -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
           -Wold-style-declaration  -Wold-style-definition -Wstrict-prototypes
           -Wtraditional  -Wtraditional-conversion
           -Wdeclaration-after-statement  -Wpointer-sign

       Debugging Options
           -g  -glevel  -gdwarf  -gdwarf-version -ggdb  -grecord-gcc-switches
           -gno-record-gcc-switches -gstabs  -gstabs+  -gstrict-dwarf
           -gno-strict-dwarf -gas-loc-support  -gno-as-loc-support
           -gas-locview-support  -gno-as-locview-support -gcolumn-info
           -gno-column-info -gstatement-frontiers  -gno-statement-frontiers
           -gvariable-location-views  -gno-variable-location-views
           -ginternal-reset-location-views  -gno-internal-reset-location-views
           -ginline-points  -gno-inline-points -gvms  -gxcoff  -gxcoff+
           -gz[=type] -gsplit-dwarf  -gdescribe-dies  -gno-describe-dies
           -fdebug-prefix-map=old=new  -fdebug-types-section
           -fno-eliminate-unused-debug-types -femit-struct-debug-baseonly
           -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-
           list] -fno-eliminate-unused-debug-symbols
           -femit-class-debug-always -fno-merge-debug-strings
           -fno-dwarf2-cfi-asm -fvar-tracking  -fvar-tracking-assignments

       Optimization Options
           -faggressive-loop-optimizations -falign-functions[=n[:m:[n2[:m2]]]]
           -falign-jumps[=n[:m:[n2[:m2]]]] -falign-labels[=n[:m:[n2[:m2]]]]
           -falign-loops[=n[:m:[n2[:m2]]]] -fno-allocation-dce
           -fallow-store-data-races -fassociative-math  -fauto-profile
           -fauto-profile[=path] -fauto-inc-dec  -fbranch-probabilities
           -fcaller-saves -fcombine-stack-adjustments  -fconserve-stack
           -fcompare-elim  -fcprop-registers  -fcrossjumping
           -fcse-follow-jumps  -fcse-skip-blocks  -fcx-fortran-rules
           -fcx-limited-range -fdata-sections  -fdce  -fdelayed-branch
           -fdelete-null-pointer-checks  -fdevirtualize
           -fdevirtualize-speculatively -fdevirtualize-at-ltrans  -fdse
           -fearly-inlining  -fipa-sra  -fexpensive-optimizations
           -ffat-lto-objects -ffast-math  -ffinite-math-only  -ffloat-store
           -fexcess-precision=style -ffinite-loops -fforward-propagate
           -ffp-contract=style  -ffunction-sections -fgcse
           -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity
           -fgcse-sm  -fhoist-adjacent-loads  -fif-conversion -fif-conversion2
           -findirect-inlining -finline-functions
           -finline-functions-called-once  -finline-limit=n
           -finline-small-functions  -fipa-cp  -fipa-cp-clone -fipa-bit-cp
           -fipa-vrp  -fipa-pta  -fipa-profile  -fipa-pure-const
           -fipa-reference  -fipa-reference-addressable -fipa-stack-alignment
           -fipa-icf  -fira-algorithm=algorithm -flive-patching=level
           -fira-region=region  -fira-hoist-pressure -fira-loop-pressure
           -fno-ira-share-save-slots -fno-ira-share-spill-slots
           -fisolate-erroneous-paths-dereference
           -fisolate-erroneous-paths-attribute -fivopts
           -fkeep-inline-functions  -fkeep-static-functions
           -fkeep-static-consts  -flimit-function-alignment
           -flive-range-shrinkage -floop-block  -floop-interchange
           -floop-strip-mine -floop-unroll-and-jam  -floop-nest-optimize
           -floop-parallelize-all  -flra-remat  -flto  -flto-compression-level
           -flto-partition=alg  -fmerge-all-constants -fmerge-constants
           -fmodulo-sched  -fmodulo-sched-allow-regmoves
           -fmove-loop-invariants  -fno-branch-count-reg -fno-defer-pop
           -fno-fp-int-builtin-inexact  -fno-function-cse
           -fno-guess-branch-probability  -fno-inline  -fno-math-errno
           -fno-peephole -fno-peephole2  -fno-printf-return-value
           -fno-sched-interblock -fno-sched-spec  -fno-signed-zeros
           -fno-toplevel-reorder  -fno-trapping-math
           -fno-zero-initialized-in-bss -fomit-frame-pointer
           -foptimize-sibling-calls -fpartial-inlining  -fpeel-loops
           -fpredictive-commoning -fprefetch-loop-arrays -fprofile-correction
           -fprofile-use  -fprofile-use=path -fprofile-partial-training
           -fprofile-values -fprofile-reorder-functions -freciprocal-math
           -free  -frename-registers  -freorder-blocks
           -freorder-blocks-algorithm=algorithm -freorder-blocks-and-partition
           -freorder-functions -frerun-cse-after-loop
           -freschedule-modulo-scheduled-loops -frounding-math
           -fsave-optimization-record -fsched2-use-superblocks
           -fsched-pressure -fsched-spec-load  -fsched-spec-load-dangerous
           -fsched-stalled-insns-dep[=n]  -fsched-stalled-insns[=n]
           -fsched-group-heuristic  -fsched-critical-path-heuristic
           -fsched-spec-insn-heuristic  -fsched-rank-heuristic
           -fsched-last-insn-heuristic  -fsched-dep-count-heuristic
           -fschedule-fusion -fschedule-insns  -fschedule-insns2
           -fsection-anchors -fselective-scheduling  -fselective-scheduling2
           -fsel-sched-pipelining  -fsel-sched-pipelining-outer-loops
           -fsemantic-interposition  -fshrink-wrap  -fshrink-wrap-separate
           -fsignaling-nans -fsingle-precision-constant
           -fsplit-ivs-in-unroller  -fsplit-loops -fsplit-paths
           -fsplit-wide-types  -fsplit-wide-types-early  -fssa-backprop
           -fssa-phiopt -fstdarg-opt  -fstore-merging  -fstrict-aliasing
           -fthread-jumps  -ftracer  -ftree-bit-ccp -ftree-builtin-call-dce
           -ftree-ccp  -ftree-ch -ftree-coalesce-vars  -ftree-copy-prop
           -ftree-dce  -ftree-dominator-opts -ftree-dse  -ftree-forwprop
           -ftree-fre  -fcode-hoisting -ftree-loop-if-convert  -ftree-loop-im
           -ftree-phiprop  -ftree-loop-distribution
           -ftree-loop-distribute-patterns -ftree-loop-ivcanon
           -ftree-loop-linear  -ftree-loop-optimize -ftree-loop-vectorize
           -ftree-parallelize-loops=n  -ftree-pre  -ftree-partial-pre
           -ftree-pta -ftree-reassoc  -ftree-scev-cprop  -ftree-sink
           -ftree-slsr  -ftree-sra -ftree-switch-conversion  -ftree-tail-merge
           -ftree-ter  -ftree-vectorize  -ftree-vrp  -funconstrained-commons
           -funit-at-a-time  -funroll-all-loops  -funroll-loops
           -funsafe-math-optimizations  -funswitch-loops -fipa-ra
           -fvariable-expansion-in-unroller  -fvect-cost-model  -fvpt -fweb
           -fwhole-program  -fwpa  -fuse-linker-plugin --param name=value -O
           -O0  -O1  -O2  -O3  -Os  -Ofast  -Og

       Program Instrumentation Options
           -p  -pg  -fprofile-arcs  --coverage  -ftest-coverage
           -fprofile-abs-path -fprofile-dir=path  -fprofile-generate
           -fprofile-generate=path -fprofile-note=path
           -fprofile-prefix-path=path -fprofile-update=method
           -fprofile-filter-files=regex -fprofile-exclude-files=regex
           -fprofile-reproducible=[multithreaded|parallel-runs|serial]
           -fsanitize=style  -fsanitize-recover  -fsanitize-recover=style
           -fasan-shadow-offset=number  -fsanitize-sections=s1,s2,...
           -fsanitize-undefined-trap-on-error  -fbounds-check
           -fcf-protection=[full|branch|return|none|check] -fstack-protector
           -fstack-protector-all  -fstack-protector-strong
           -fstack-protector-explicit  -fstack-check
           -fstack-limit-register=reg  -fstack-limit-symbol=sym
           -fno-stack-limit  -fsplit-stack -fvtable-verify=[std|preinit|none]
           -fvtv-counts  -fvtv-debug -finstrument-functions
           -finstrument-functions-exclude-function-list=sym,sym,...
           -finstrument-functions-exclude-file-list=file,file,...

       Preprocessor Options
           -Aquestion=answer -A-question[=answer] -C  -CC  -Dmacro[=defn] -dD
           -dI  -dM  -dN  -dU -fdebug-cpp  -fdirectives-only
           -fdollars-in-identifiers -fexec-charset=charset
           -fextended-identifiers -finput-charset=charset
           -fmacro-prefix-map=old=new -fmax-include-depth=depth
           -fno-canonical-system-headers  -fpch-deps  -fpch-preprocess
           -fpreprocessed  -ftabstop=width  -ftrack-macro-expansion
           -fwide-exec-charset=charset  -fworking-directory -H  -imacros file
           -include file -M  -MD  -MF  -MG  -MM  -MMD  -MP  -MQ  -MT
           -no-integrated-cpp  -P  -pthread  -remap -iprefix file
           -iwithprefix dir -traditional  -traditional-cpp  -trigraphs -Umacro
           -undef -Wp,option  -Xpreprocessor option

       Assembler Options
           -Wa,option  -Xassembler option

       Linker Options
           object-file-name  -fuse-ld=linker  -llibrary -nostartfiles
           -nodefaultlibs  -nolibc  -nostdlib -e entry  --entry=entry -pie
           -pthread  -r  -rdynamic -s  -static  -static-pie  -static-libgcc
           -static-libstdc++ -static-libasan  -static-libtsan  -static-liblsan
           -static-libubsan -shared  -shared-libgcc  -symbolic -T script
           -Wl,option  -Xlinker option -u symbol  -z keyword

       Directory Options
           -Bprefix  -Idir  -I- -idirafter dir -imacros file  -imultilib dir
           -iplugindir=dir -iquote dir  -isysroot dir  -isystem dir
           -iremapsrc:dst -cxx-isystem=dir -iwithprefix dir
           -iwithprefixbefore dir -Ldir  -no-canonical-prefixes
           --no-sysroot-suffix -nostdinc  -nostdinc++  --sysroot=dir

       Code Generation Options
           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions
           -fnon-call-exceptions  -fdelete-dead-exceptions  -funwind-tables
           -fasynchronous-unwind-tables -fno-gnu-unique
           -finhibit-size-directive  -fcommon  -fno-ident -fpcc-struct-return
           -fpic  -fPIC  -fpie  -fPIE  -fno-plt -fno-jump-tables
           -frecord-gcc-switches -freg-struct-return  -fshort-enums
           -fshort-wchar -fverbose-asm  -fpack-struct[=n] -fleading-underscore
           -ftls-model=model -fstack-reuse=reuse_level -ftrampolines  -ftrapv
           -fwrapv -fvisibility=[default|internal|hidden|protected]
           -fstrict-volatile-bitfields  -fsync-libcalls

       Developer Options
           -dletters  -dumpspecs  -dumpmachine  -dumpversion -dumpfullversion
           -fcallgraph-info[=su,da] -fchecking  -fchecking=n -fdbg-cnt-list
           -fdbg-cnt=counter-value-list -fdisable-ipa-pass_name
           -fdisable-rtl-pass_name -fdisable-rtl-pass-name=range-list
           -fdisable-tree-pass_name -fdisable-tree-pass-name=range-list
           -fdump-debug  -fdump-earlydebug -fdump-noaddr  -fdump-unnumbered
           -fdump-unnumbered-links -fdump-final-insns[=file] -fdump-ipa-all
           -fdump-ipa-cgraph  -fdump-ipa-inline -fdump-lang-all
           -fdump-lang-switch -fdump-lang-switch-options
           -fdump-lang-switch-options=filename -fdump-passes -fdump-rtl-pass
           -fdump-rtl-pass=filename -fdump-statistics -fdump-tree-all
           -fdump-tree-switch -fdump-tree-switch-options
           -fdump-tree-switch-options=filename -fcompare-debug[=opts]
           -fcompare-debug-second -fenable-kind-pass -fenable-kind-pass=range-
           list -fira-verbose=n -flto-report  -flto-report-wpa
           -fmem-report-wpa -fmem-report  -fpre-ipa-mem-report
           -fpost-ipa-mem-report -fopt-info  -fopt-info-options[=file]
           -fprofile-report -frandom-seed=string  -fsched-verbose=n
           -fsel-sched-verbose  -fsel-sched-dump-cfg
           -fsel-sched-pipelining-verbose -fstats  -fstack-usage
           -ftime-report  -ftime-report-details
           -fvar-tracking-assignments-toggle  -gtoggle
           -print-file-name=library  -print-libgcc-file-name
           -print-multi-directory  -print-multi-lib  -print-multi-os-directory
           -print-prog-name=program  -print-search-dirs  -Q -print-sysroot
           -print-sysroot-headers-suffix -save-temps  -save-temps=cwd
           -save-temps=obj  -time[=file]

       Machine-Dependent Options
           AArch64 Options -mabi=name  -mbig-endian  -mlittle-endian
           -mgeneral-regs-only -mcmodel=tiny  -mcmodel=small  -mcmodel=large
           -mstrict-align  -mno-strict-align -momit-leaf-frame-pointer
           -mtls-dialect=desc  -mtls-dialect=traditional -mtls-size=size
           -mfix-cortex-a53-835769  -mfix-cortex-a53-843419
           -mlow-precision-recip-sqrt  -mlow-precision-sqrt
           -mlow-precision-div -mpc-relative-literal-loads
           -msign-return-address=scope -mbranch-protection=none|standard|pac-
           ret[+leaf +b-key]|bti -mharden-sls=opts -march=name  -mcpu=name
           -mtune=name -moverride=string  -mverbose-cost-dump
           -mstack-protector-guard=guard -mstack-protector-guard-reg=sysreg
           -mstack-protector-guard-offset=offset -mtrack-speculation
           -moutline-atomics

           Adapteva Epiphany Options -mhalf-reg-file  -mprefer-short-insn-regs
           -mbranch-cost=num  -mcmove  -mnops=num  -msoft-cmpsf -msplit-lohi
           -mpost-inc  -mpost-modify  -mstack-offset=num -mround-nearest
           -mlong-calls  -mshort-calls  -msmall16 -mfp-mode=mode
           -mvect-double  -max-vect-align=num -msplit-vecmove-early
           -m1reg-reg

           AMD GCN Options -march=gpu -mtune=gpu -mstack-size=bytes

           ARC Options -mbarrel-shifter  -mjli-always -mcpu=cpu  -mA6
           -mARC600  -mA7  -mARC700 -mdpfp  -mdpfp-compact  -mdpfp-fast
           -mno-dpfp-lrsr -mea  -mno-mpy  -mmul32x16  -mmul64  -matomic -mnorm
           -mspfp  -mspfp-compact  -mspfp-fast  -msimd  -msoft-float  -mswap
           -mcrc  -mdsp-packa  -mdvbf  -mlock  -mmac-d16  -mmac-24  -mrtsc
           -mswape -mtelephony  -mxy  -misize  -mannotate-align  -marclinux
           -marclinux_prof -mlong-calls  -mmedium-calls  -msdata
           -mirq-ctrl-saved -mrgf-banked-regs  -mlpc-width=width  -G num
           -mvolatile-cache  -mtp-regno=regno -malign-call  -mauto-modify-reg
           -mbbit-peephole  -mno-brcc -mcase-vector-pcrel  -mcompact-casesi
           -mno-cond-exec  -mearly-cbranchsi -mexpand-adddi  -mindexed-loads
           -mlra  -mlra-priority-none -mlra-priority-compact mlra-priority-
           noncompact  -mmillicode -mmixed-code  -mq-class  -mRcq  -mRcw
           -msize-level=level -mtune=cpu  -mmultcost=num  -mcode-density-frame
           -munalign-prob-threshold=probability  -mmpy-option=multo -mdiv-rem
           -mcode-density  -mll64  -mfpu=fpu  -mrf16  -mbranch-index

           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-reentrant
           -mno-apcs-reentrant -mgeneral-regs-only -msched-prolog
           -mno-sched-prolog -mlittle-endian  -mbig-endian -mbe8  -mbe32
           -mfloat-abi=name -mfp16-format=name -mthumb-interwork
           -mno-thumb-interwork -mcpu=name  -march=name  -mfpu=name
           -mtune=name  -mprint-tune-info -mstructure-size-boundary=n
           -mabort-on-noreturn -mlong-calls  -mno-long-calls -msingle-pic-base
           -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport
           -mpoke-function-name -mthumb  -marm  -mflip-thumb -mtpcs-frame
           -mtpcs-leaf-frame -mcaller-super-interworking
           -mcallee-super-interworking -mtp=name  -mtls-dialect=dialect
           -mword-relocations -mfix-cortex-m3-ldrd -munaligned-access
           -mneon-for-64bits -mslow-flash-data -masm-syntax-unified
           -mrestrict-it -mverbose-cost-dump -mpure-code -mcmse -mfdpic

           AVR Options -mmcu=mcu  -mabsdata  -maccumulate-args
           -mbranch-cost=cost -mcall-prologues  -mgas-isr-prologues  -mint8
           -mdouble=bits -mlong-double=bits -mn_flash=size  -mno-interrupts
           -mmain-is-OS_task  -mrelax  -mrmw  -mstrict-X  -mtiny-stack
           -mfract-convert-truncate -mshort-calls  -nodevicelib
           -nodevicespecs -Waddr-space-convert  -Wmisspelled-isr

           Blackfin Options -mcpu=cpu[-sirevision] -msim
           -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
           -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly
           -mno-csync-anomaly -mlow-64k  -mno-low64k  -mstack-check-l1
           -mid-shared-library -mno-id-shared-library  -mshared-library-id=n
           -mleaf-id-shared-library  -mno-leaf-id-shared-library -msep-data
           -mno-sep-data  -mlong-calls  -mno-long-calls -mfast-fp
           -minline-plt  -mmulticore  -mcorea  -mcoreb  -msdram -micplb

           C6X Options -mbig-endian  -mlittle-endian  -march=cpu -msim
           -msdata=sdata-type

           CRIS Options -mcpu=cpu  -march=cpu  -mtune=cpu -mmax-stack-frame=n
           -melinux-stacksize=n -metrax4  -metrax100  -mpdebug  -mcc-init
           -mno-side-effects -mstack-align  -mdata-align  -mconst-align
           -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue  -mno-gotplt
           -melf  -maout  -melinux  -mlinux  -sim  -sim2 -mmul-bug-workaround
           -mno-mul-bug-workaround

           CR16 Options -mmac -mcr16cplus  -mcr16c -msim  -mint32  -mbit-ops
           -mdata-model=model

           C-SKY Options -march=arch  -mcpu=cpu -mbig-endian  -EB
           -mlittle-endian  -EL -mhard-float  -msoft-float  -mfpu=fpu
           -mdouble-float  -mfdivdu -melrw  -mistack  -mmp  -mcp  -mcache
           -msecurity  -mtrust -mdsp  -medsp  -mvdsp -mdiv  -msmart
           -mhigh-registers  -manchor -mpushpop  -mmultiple-stld  -mconstpool
           -mstack-size  -mccrt -mbranch-cost=n  -mcse-cc  -msched-prolog

           Darwin Options -all_load  -allowable_client  -arch
           -arch_errors_fatal -arch_only  -bind_at_load  -bundle
           -bundle_loader -client_name  -compatibility_version
           -current_version -dead_strip -dependency-file  -dylib_file
           -dylinker_install_name -dynamic  -dynamiclib
           -exported_symbols_list -filelist  -flat_namespace
           -force_cpusubtype_ALL -force_flat_namespace
           -headerpad_max_install_names -iframework -image_base  -init
           -install_name  -keep_private_externs -multi_module
           -multiply_defined  -multiply_defined_unused -noall_load
           -no_dead_strip_inits_and_terms -nofixprebinding  -nomultidefs
           -noprebind  -noseglinkedit -pagezero_size  -prebind
           -prebind_all_twolevel_modules -private_bundle  -read_only_relocs
           -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate
           -sectobjectsymbols  -sectorder -segaddr  -segs_read_only_addr
           -segs_read_write_addr -seg_addr_table  -seg_addr_table_filename
           -seglinkedit -segprot  -segs_read_only_addr  -segs_read_write_addr
           -single_module  -static  -sub_library  -sub_umbrella
           -twolevel_namespace  -umbrella  -undefined -unexported_symbols_list
           -weak_reference_mismatches -whatsloaded  -F  -gused  -gfull
           -mmacosx-version-min=version -mkernel  -mone-byte-bool

           DEC Alpha Options -mno-fp-regs  -msoft-float -mieee
           -mieee-with-inexact  -mieee-conformant -mfp-trap-mode=mode
           -mfp-rounding-mode=mode -mtrap-precision=mode  -mbuild-constants
           -mcpu=cpu-type  -mtune=cpu-type -mbwx  -mmax  -mfix  -mcix
           -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data
           -mlarge-data -msmall-text  -mlarge-text -mmemory-latency=time

           eBPF Options -mbig-endian -mlittle-endian -mkernel=version
           -mframe-limit=bytes -mxbpf

           FR30 Options -msmall-model  -mno-lsim

           FT32 Options -msim  -mlra  -mnodiv  -mft32b  -mcompress  -mnopm

           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float
           -msoft-float -malloc-cc  -mfixed-cc  -mdword  -mno-dword -mdouble
           -mno-double -mmedia  -mno-media  -mmuladd  -mno-muladd -mfdpic
           -minline-plt  -mgprel-ro  -multilib-library-pic -mlinked-fp
           -mlong-calls  -malign-labels -mlibrary-pic  -macc-4  -macc-8 -mpack
           -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
           -moptimize-membar  -mno-optimize-membar -mscc  -mno-scc
           -mcond-exec  -mno-cond-exec -mvliw-branch  -mno-vliw-branch
           -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
           -mno-nested-cond-exec  -mtomcat-stats -mTLS  -mtls -mcpu=cpu

           GNU/Linux Options -mglibc  -muclibc  -mmusl  -mbionic  -mandroid
           -tno-android-cc  -tno-android-ld

           H8/300 Options -mrelax  -mh  -ms  -mn  -mexr  -mno-exr  -mint32
           -malign-300

           HPPA Options -march=architecture-type -mcaller-copies
           -mdisable-fpregs  -mdisable-indexing -mfast-indirect-calls  -mgas
           -mgnu-ld   -mhp-ld -mfixed-range=register-range -mjump-in-delay
           -mlinker-opt  -mlong-calls -mlong-load-store  -mno-disable-fpregs
           -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
           -mno-jump-in-delay  -mno-long-load-store -mno-portable-runtime
           -mno-soft-float -mno-space-regs  -msoft-float  -mpa-risc-1-0
           -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime -mschedule=cpu-
           type  -mspace-regs  -msio  -mwsio -munix=unix-std  -nolibdld
           -static  -threads

           IA-64 Options -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld
           -mno-pic -mvolatile-asm-stop  -mregister-names  -msdata  -mno-sdata
           -mconstant-gp  -mauto-pic  -mfused-madd
           -minline-float-divide-min-latency
           -minline-float-divide-max-throughput -mno-inline-float-divide
           -minline-int-divide-min-latency -minline-int-divide-max-throughput
           -mno-inline-int-divide -minline-sqrt-min-latency
           -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm
           -mearly-stop-bits -mfixed-range=register-range  -mtls-size=tls-size
           -mtune=cpu-type  -milp32  -mlp64 -msched-br-data-spec
           -msched-ar-data-spec  -msched-control-spec -msched-br-in-data-spec
           -msched-ar-in-data-spec  -msched-in-control-spec -msched-spec-ldc
           -msched-spec-control-ldc -msched-prefer-non-data-spec-insns
           -msched-prefer-non-control-spec-insns
           -msched-stop-bits-after-every-cycle
           -msched-count-spec-in-critical-path
           -msel-sched-dont-check-control-spec  -msched-fp-mem-deps-zero-cost
           -msched-max-memory-insns-hard-limit  -msched-max-memory-insns=max-
           insns

           LM32 Options -mbarrel-shift-enabled  -mdivide-enabled
           -mmultiply-enabled -msign-extend-enabled  -muser-enabled

           M32R/D Options -m32r2  -m32rx  -m32r -mdebug -malign-loops
           -mno-align-loops -missue-rate=number -mbranch-cost=number
           -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func
           -mflush-func=name -mno-flush-trap  -mflush-trap=number -G num

           M32C Options -mcpu=cpu  -msim  -memregs=number

           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020
           -m68020-40  -m68020-60  -m68030  -m68040 -m68060  -mcpu32  -m5200
           -m5206e  -m528x  -m5307  -m5407 -mcfv4e  -mbitfield  -mno-bitfield
           -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div
           -mshort -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
           -malign-int  -mstrict-align  -msep-data  -mno-sep-data
           -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
           -mxgot  -mno-xgot  -mlong-jump-table-offsets

           MCore Options -mhardlit  -mno-hardlit  -mdiv  -mno-div
           -mrelax-immediates -mno-relax-immediates  -mwide-bitfields
           -mno-wide-bitfields -m4byte-functions  -mno-4byte-functions
           -mcallgraph-data -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes
           -mno-lsim -mlittle-endian  -mbig-endian  -m210  -m340
           -mstack-increment

           MeP Options -mabsdiff  -mall-opts  -maverage  -mbased=n  -mbitops
           -mc=n  -mclip  -mconfig=name  -mcop  -mcop32  -mcop64  -mivc2 -mdc
           -mdiv  -meb  -mel  -mio-volatile  -ml  -mleadz  -mm  -mminmax
           -mmult  -mno-opts  -mrepeat  -ms  -msatur  -msdram  -msim
           -msimnovec  -mtf -mtiny=n

           MicroBlaze Options -msoft-float  -mhard-float  -msmall-divides
           -mcpu=cpu -mmemcpy  -mxl-soft-mul  -mxl-soft-div  -mxl-barrel-shift
           -mxl-pattern-compare  -mxl-stack-check  -mxl-gp-opt  -mno-clearbss
           -mxl-multiply-high  -mxl-float-convert  -mxl-float-sqrt
           -mbig-endian  -mlittle-endian  -mxl-reorder  -mxl-mode-app-model
           -mpic-data-is-text-relative

           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2
           -mips3  -mips4  -mips32  -mips32r2  -mips32r3  -mips32r5 -mips32r6
           -mips64  -mips64r2  -mips64r3  -mips64r5  -mips64r6 -mips16
           -mno-mips16  -mflip-mips16 -minterlink-compressed
           -mno-interlink-compressed -minterlink-mips16  -mno-interlink-mips16
           -mabi=abi  -mabicalls  -mno-abicalls -mshared  -mno-shared  -mplt
           -mno-plt  -mxgot  -mno-xgot -mgp32  -mgp64  -mfp32  -mfpxx  -mfp64
           -mhard-float  -msoft-float -mno-float  -msingle-float
           -mdouble-float -modd-spreg  -mno-odd-spreg -mabs=mode
           -mnan=encoding -mdsp  -mno-dsp  -mdspr2  -mno-dspr2 -mmcu
           -mmno-mcu -meva  -mno-eva -mvirt  -mno-virt -mxpa  -mno-xpa -mcrc
           -mno-crc -mginv  -mno-ginv -mmicromips  -mno-micromips -mmsa
           -mno-msa -mloongson-mmi  -mno-loongson-mmi -mloongson-ext
           -mno-loongson-ext -mloongson-ext2  -mno-loongson-ext2 -mfpu=fpu-
           type -msmartmips  -mno-smartmips -mpaired-single
           -mno-paired-single  -mdmx  -mno-mdmx -mips3d  -mno-mips3d  -mmt
           -mno-mt  -mllsc  -mno-llsc -mlong64  -mlong32  -msym32  -mno-sym32
           -Gnum  -mlocal-sdata  -mno-local-sdata -mextern-sdata
           -mno-extern-sdata  -mgpopt  -mno-gopt -membedded-data
           -mno-embedded-data -muninit-const-in-rodata
           -mno-uninit-const-in-rodata -mcode-readable=setting
           -msplit-addresses  -mno-split-addresses -mexplicit-relocs
           -mno-explicit-relocs -mcheck-zero-division
           -mno-check-zero-division -mdivide-traps  -mdivide-breaks
           -mload-store-pairs  -mno-load-store-pairs -mmemcpy  -mno-memcpy
           -mlong-calls  -mno-long-calls -mmad  -mno-mad  -mimadd  -mno-imadd
           -mfused-madd  -mno-fused-madd  -nocpp -mfix-24k  -mno-fix-24k
           -mfix-r4000  -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400
           -mfix-r5900  -mno-fix-r5900 -mfix-r10000  -mno-fix-r10000
           -mfix-rm7000  -mno-fix-rm7000 -mfix-vr4120  -mno-fix-vr4120
           -mfix-vr4130  -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1
           -mflush-func=func  -mno-flush-func -mbranch-cost=num
           -mbranch-likely  -mno-branch-likely -mcompact-branches=policy
           -mfp-exceptions  -mno-fp-exceptions -mvr4130-align
           -mno-vr4130-align  -msynci  -mno-synci -mlxc1-sxc1  -mno-lxc1-sxc1
           -mmadd4  -mno-madd4 -mrelax-pic-calls  -mno-relax-pic-calls
           -mmcount-ra-address -mframe-header-opt  -mno-frame-header-opt

           MMIX Options -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon
           -mabi=gnu -mabi=mmixware  -mzero-extend  -mknuthdiv
           -mtoplevel-symbols -melf  -mbranch-predict  -mno-branch-predict
           -mbase-addresses -mno-base-addresses  -msingle-exit
           -mno-single-exit

           MN10300 Options -mmult-bug  -mno-mult-bug -mno-am33  -mam33
           -mam33-2  -mam34 -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0
           -mrelax  -mliw  -msetlb

           Moxie Options -meb  -mel  -mmul.x  -mno-crt0

           MSP430 Options -msim  -masm-hex  -mmcu=  -mcpu=  -mlarge  -msmall
           -mrelax -mwarn-mcu -mcode-region=  -mdata-region= -msilicon-errata=
           -msilicon-errata-warn= -mhwmult=  -minrt  -mtiny-printf

           NDS32 Options -mbig-endian  -mlittle-endian -mreduced-regs
           -mfull-regs -mcmov  -mno-cmov -mext-perf  -mno-ext-perf -mext-perf2
           -mno-ext-perf2 -mext-string  -mno-ext-string -mv3push  -mno-v3push
           -m16bit  -mno-16bit -misr-vector-size=num -mcache-block-size=num
           -march=arch -mcmodel=code-model -mctor-dtor  -mrelax

           Nios II Options -G num  -mgpopt=option  -mgpopt  -mno-gpopt
           -mgprel-sec=regexp  -mr0rel-sec=regexp -mel  -meb -mno-bypass-cache
           -mbypass-cache -mno-cache-volatile  -mcache-volatile
           -mno-fast-sw-div  -mfast-sw-div -mhw-mul  -mno-hw-mul  -mhw-mulx
           -mno-hw-mulx  -mno-hw-div  -mhw-div -mcustom-insn=N
           -mno-custom-insn -mcustom-fpu-cfg=name -mhal  -msmallc
           -msys-crt0=name  -msys-lib=name -march=arch  -mbmx  -mno-bmx  -mcdx
           -mno-cdx

           Nvidia PTX Options -m32  -m64  -mmainkernel  -moptimize

           OpenRISC Options -mboard=name  -mnewlib  -mhard-mul  -mhard-div
           -msoft-mul  -msoft-div -msoft-float  -mhard-float  -mdouble-float
           -munordered-float -mcmov  -mror  -mrori  -msext  -msfimm  -mshftimm

           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45
           -m10 -mint32  -mno-int16  -mint16  -mno-int32 -msplit  -munix-asm
           -mdec-asm  -mgnu-asm  -mlra

           picoChip Options -mae=ae_type  -mvliw-lookahead=N
           -msymbol-as-address  -mno-inefficient-warnings

           PowerPC Options See RS/6000 and PowerPC Options.

           PRU Options -mmcu=mcu  -minrt  -mno-relax  -mloop -mabi=variant

           RISC-V Options -mbranch-cost=N-instruction -mplt  -mno-plt
           -mabi=ABI-string -mfdiv  -mno-fdiv -mdiv  -mno-div -march=ISA-
           string -mtune=processor-string -mpreferred-stack-boundary=num
           -msmall-data-limit=N-bytes -msave-restore  -mno-save-restore
           -mstrict-align  -mno-strict-align -mcmodel=medlow  -mcmodel=medany
           -mexplicit-relocs  -mno-explicit-relocs -mrelax  -mno-relax
           -mriscv-attribute  -mmo-riscv-attribute -malign-data=type

           RL78 Options -msim  -mmul=none  -mmul=g13  -mmul=g14  -mallregs
           -mcpu=g10  -mcpu=g13  -mcpu=g14  -mg10  -mg13  -mg14
           -m64bit-doubles  -m32bit-doubles  -msave-mduc-in-interrupts

           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type
           -mcmodel=code-model -mpowerpc64 -maltivec  -mno-altivec
           -mpowerpc-gpopt  -mno-powerpc-gpopt -mpowerpc-gfxopt
           -mno-powerpc-gfxopt -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb
           -mpopcntd  -mno-popcntd -mfprnd  -mno-fprnd -mcmpb  -mno-cmpb
           -mhard-dfp  -mno-hard-dfp -mfull-toc   -mminimal-toc
           -mno-fp-in-toc  -mno-sum-in-toc -m64  -m32  -mxl-compat
           -mno-xl-compat  -mpe -malign-power  -malign-natural -msoft-float
           -mhard-float  -mmultiple  -mno-multiple -mupdate  -mno-update
           -mavoid-indexed-addresses  -mno-avoid-indexed-addresses
           -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
           -mstrict-align  -mno-strict-align  -mrelocatable -mno-relocatable
           -mrelocatable-lib  -mno-relocatable-lib -mtoc  -mno-toc  -mlittle
           -mlittle-endian  -mbig  -mbig-endian -mdynamic-no-pic  -mswdiv
           -msingle-pic-base -mprioritize-restricted-insns=priority
           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
           -mcall-aixdesc  -mcall-eabi  -mcall-freebsd -mcall-linux
           -mcall-netbsd  -mcall-openbsd -mcall-sysv  -mcall-sysv-eabi
           -mcall-sysv-noeabi -mtraceback=traceback_type -maix-struct-return
           -msvr4-struct-return -mabi=abi-type  -msecure-plt  -mbss-plt
           -mlongcall  -mno-longcall  -mpltseq  -mno-pltseq
           -mblock-move-inline-limit=num -mblock-compare-inline-limit=num
           -mblock-compare-inline-loop-limit=num
           -mstring-compare-inline-limit=num -misel  -mno-isel -mvrsave
           -mno-vrsave -mmulhw  -mno-mulhw -mdlmzb  -mno-dlmzb -mprototype
           -mno-prototype -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
           -msdata=opt  -mreadonly-in-sdata  -mvxworks  -G num -mrecip
           -mrecip=opt  -mno-recip  -mrecip-precision -mno-recip-precision
           -mveclibabi=type  -mfriz  -mno-friz -mpointers-to-nested-functions
           -mno-pointers-to-nested-functions -msave-toc-indirect
           -mno-save-toc-indirect -mpower8-fusion  -mno-mpower8-fusion
           -mpower8-vector  -mno-power8-vector -mcrypto  -mno-crypto  -mhtm
           -mno-htm -mquad-memory  -mno-quad-memory -mquad-memory-atomic
           -mno-quad-memory-atomic -mcompat-align-parm  -mno-compat-align-parm
           -mfloat128  -mno-float128  -mfloat128-hardware
           -mno-float128-hardware -mgnu-attribute  -mno-gnu-attribute
           -mstack-protector-guard=guard -mstack-protector-guard-reg=reg
           -mstack-protector-guard-offset=offset -mprefixed -mno-prefixed
           -mpcrel -mno-pcrel -mmma -mno-mmma

           RX Options -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu -mcpu=
           -mbig-endian-data  -mlittle-endian-data -msmall-data -msim
           -mno-sim -mas100-syntax  -mno-as100-syntax -mrelax
           -mmax-constant-size= -mint-register= -mpid -mallow-string-insns
           -mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts
           -msave-acc-in-interrupts

           S/390 and zSeries Options -mtune=cpu-type  -march=cpu-type
           -mhard-float  -msoft-float  -mhard-dfp  -mno-hard-dfp
           -mlong-double-64  -mlong-double-128 -mbackchain  -mno-backchain
           -mpacked-stack  -mno-packed-stack -msmall-exec  -mno-small-exec
           -mmvcle  -mno-mvcle -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
           -mhtm  -mvx  -mzvector -mtpf-trace  -mno-tpf-trace
           -mtpf-trace-skip  -mno-tpf-trace-skip -mfused-madd  -mno-fused-madd
           -mwarn-framesize  -mwarn-dynamicstack  -mstack-size  -mstack-guard
           -mhotpatch=halfwords,halfwords

           Score Options -meb  -mel -mnhwloop -muls -mmac -mscore5  -mscore5u
           -mscore7  -mscore7d

           SH Options -m1  -m2  -m2e -m2a-nofpu  -m2a-single-only  -m2a-single
           -m2a -m3  -m3e -m4-nofpu  -m4-single-only  -m4-single  -m4
           -m4a-nofpu  -m4a-single-only  -m4a-single  -m4a  -m4al -mb  -ml
           -mdalign  -mrelax -mbigtable  -mfmovd  -mrenesas  -mno-renesas
           -mnomacsave -mieee  -mno-ieee  -mbitops  -misize
           -minline-ic_invalidate  -mpadstruct -mprefergot  -musermode
           -multcost=number  -mdiv=strategy -mdivsi3_libfunc=name
           -mfixed-range=register-range -maccumulate-outgoing-args
           -matomic-model=atomic-model -mbranch-cost=num  -mzdcbranch
           -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd
           -mno-fused-madd  -mfsca  -mno-fsca  -mfsrra  -mno-fsrra
           -mpretend-cmove  -mtas

           Solaris 2 Options -mclear-hwcap  -mno-clear-hwcap  -mimpure-text
           -mno-impure-text -pthreads

           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model
           -mmemory-model=mem-model -m32  -m64  -mapp-regs  -mno-app-regs
           -mfaster-structs  -mno-faster-structs  -mflat  -mno-flat -mfpu
           -mno-fpu  -mhard-float  -msoft-float -mhard-quad-float
           -msoft-quad-float -mstack-bias  -mno-stack-bias -mstd-struct-return
           -mno-std-struct-return -munaligned-doubles  -mno-unaligned-doubles
           -muser-mode  -mno-user-mode -mv8plus  -mno-v8plus  -mvis  -mno-vis
           -mvis2  -mno-vis2  -mvis3  -mno-vis3 -mvis4  -mno-vis4  -mvis4b
           -mno-vis4b -mcbcond  -mno-cbcond  -mfmaf  -mno-fmaf  -mfsmuld
           -mno-fsmuld -mpopc  -mno-popc  -msubxc  -mno-subxc -mfix-at697f
           -mfix-ut699  -mfix-ut700  -mfix-gr712rc -mlra  -mno-lra

           System V Options -Qy  -Qn  -YP,paths  -Ym,dir

           TILE-Gx Options -mcpu=CPU  -m32  -m64  -mbig-endian
           -mlittle-endian -mcmodel=code-model

           TILEPro Options -mcpu=cpu  -m32

           V850 Options -mlong-calls  -mno-long-calls  -mep  -mno-ep
           -mprolog-function  -mno-prolog-function  -mspace -mtda=n  -msda=n
           -mzda=n -mapp-regs  -mno-app-regs -mdisable-callt
           -mno-disable-callt -mv850e2v3  -mv850e2  -mv850e1  -mv850es -mv850e
           -mv850  -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float
           -mhard-float -mgcc-abi -mrh850-abi -mbig-switch

           VAX Options -mg  -mgnu  -munix

           Visium Options -mdebug  -msim  -mfpu  -mno-fpu  -mhard-float
           -msoft-float -mcpu=cpu-type  -mtune=cpu-type  -msv-mode
           -muser-mode

           VMS Options -mvms-return-codes  -mdebug-main=prefix  -mmalloc64
           -mpointer-size=size

           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy
           -Xbind-now

           x86 Options -mtune=cpu-type  -march=cpu-type -mtune-ctrl=feature-
           list  -mdump-tune-features  -mno-default -mfpmath=unit
           -masm=dialect  -mno-fancy-math-387 -mno-fp-ret-in-387  -m80387
           -mhard-float  -msoft-float -mno-wide-multiply  -mrtd
           -malign-double -mpreferred-stack-boundary=num
           -mincoming-stack-boundary=num -mcld  -mcx16  -msahf  -mmovbe
           -mcrc32 -mrecip  -mrecip=opt -mvzeroupper  -mprefer-avx128
           -mprefer-vector-width=opt -mmmx  -msse  -msse2  -msse3  -mssse3
           -msse4.1  -msse4.2  -msse4  -mavx -mavx2  -mavx512f  -mavx512pf
           -mavx512er  -mavx512cd  -mavx512vl -mavx512bw  -mavx512dq
           -mavx512ifma  -mavx512vbmi  -msha  -maes -mpclmul  -mfsgsbase
           -mrdrnd  -mf16c  -mfma  -mpconfig  -mwbnoinvd -mptwrite
           -mprefetchwt1  -mclflushopt  -mclwb  -mxsavec  -mxsaves -msse4a
           -m3dnow  -m3dnowa  -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4  -mxop
           -madx  -mlzcnt  -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mhle
           -mlwp -mmwaitx  -mclzero  -mpku  -mthreads  -mgfni  -mvaes
           -mwaitpkg -mshstk -mmanual-endbr -mforce-indirect-call
           -mavx512vbmi2 -mavx512bf16 -menqcmd -mvpclmulqdq  -mavx512bitalg
           -mmovdiri  -mmovdir64b  -mavx512vpopcntdq -mavx5124fmaps
           -mavx512vnni  -mavx5124vnniw  -mprfchw  -mrdpid -mrdseed  -msgx
           -mavx512vp2intersect -mcldemote  -mms-bitfields
           -mno-align-stringops  -minline-all-stringops
           -minline-stringops-dynamically  -mstringop-strategy=alg
           -mmemcpy-strategy=strategy  -mmemset-strategy=strategy -mpush-args
           -maccumulate-outgoing-args  -m128bit-long-double
           -m96bit-long-double  -mlong-double-64  -mlong-double-80
           -mlong-double-128 -mregparm=num  -msseregparm -mveclibabi=type
           -mvect8-ret-in-mem -mpc32  -mpc64  -mpc80  -mstackrealign
           -momit-leaf-frame-pointer  -mno-red-zone  -mno-tls-direct-seg-refs
           -mcmodel=code-model  -mabi=name  -maddress-mode=mode -m32  -m64
           -mx32  -m16  -miamcu  -mlarge-data-threshold=num -msse2avx
           -mfentry  -mrecord-mcount  -mnop-mcount  -m8bit-idiv
           -minstrument-return=type -mfentry-name=name -mfentry-section=name
           -mavx256-split-unaligned-load  -mavx256-split-unaligned-store
           -malign-data=type  -mstack-protector-guard=guard
           -mstack-protector-guard-reg=reg
           -mstack-protector-guard-offset=offset
           -mstack-protector-guard-symbol=symbol -mgeneral-regs-only
           -mcall-ms2sysv-xlogues -mindirect-branch=choice
           -mfunction-return=choice -mindirect-branch-register

           x86 Windows Options -mconsole  -mcygwin  -mno-cygwin  -mdll
           -mnop-fun-dllimport  -mthread -municode  -mwin32  -mwindows
           -fno-set-stack-executable

           Xstormy16 Options -msim

           Xtensa Options -mconst16  -mno-const16 -mfused-madd
           -mno-fused-madd -mforce-no-pic -mserialize-volatile
           -mno-serialize-volatile -mtext-section-literals
           -mno-text-section-literals -mauto-litpools  -mno-auto-litpools
           -mtarget-align  -mno-target-align -mlongcalls  -mno-longcalls

           zSeries Options See S/390 and zSeries Options.

   Options Controlling the Kind of Output
       Compilation can involve up to four stages: preprocessing, compilation
       proper, assembly and linking, always in that order.  GCC is capable of
       preprocessing and compiling several files either into several assembler
       input files, or into one assembler input file; then each assembler
       input file produces an object file, and linking combines all the object
       files (those newly compiled, and those specified as input) into an
       executable file.

       For any given input file, the file name suffix determines what kind of
       compilation is done:

       file.c
           C source code that must be preprocessed.

       file.i
           C source code that should not be preprocessed.

       file.ii
           C++ source code that should not be preprocessed.

       file.m
           Objective-C source code.  Note that you must link with the libobjc
           library to make an Objective-C program work.

       file.mi
           Objective-C source code that should not be preprocessed.

       file.mm
       file.M
           Objective-C++ source code.  Note that you must link with the
           libobjc library to make an Objective-C++ program work.  Note that
           .M refers to a literal capital M.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.h
           C, C++, Objective-C or Objective-C++ header file to be turned into
           a precompiled header (default), or C, C++ header file to be turned
           into an Ada spec (via the -fdump-ada-spec switch).

       file.cc
       file.cp
       file.cxx
       file.cpp
       file.CPP
       file.c++
       file.C
           C++ source code that must be preprocessed.  Note that in .cxx, the
           last two letters must both be literally x.  Likewise, .C refers to
           a literal capital C.

       file.mm
       file.M
           Objective-C++ source code that must be preprocessed.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.hh
       file.H
       file.hp
       file.hxx
       file.hpp
       file.HPP
       file.h++
       file.tcc
           C++ header file to be turned into a precompiled header or Ada spec.

       file.f
       file.for
       file.ftn
           Fixed form Fortran source code that should not be preprocessed.

       file.F
       file.FOR
       file.fpp
       file.FPP
       file.FTN
           Fixed form Fortran source code that must be preprocessed (with the
           traditional preprocessor).

       file.f90
       file.f95
       file.f03
       file.f08
           Free form Fortran source code that should not be preprocessed.

       file.F90
       file.F95
       file.F03
       file.F08
           Free form Fortran source code that must be preprocessed (with the
           traditional preprocessor).

       file.go
           Go source code.

       file.brig
           BRIG files (binary representation of HSAIL).

       file.d
           D source code.

       file.di
           D interface file.

       file.dd
           D documentation code (Ddoc).

       file.ads
           Ada source code file that contains a library unit declaration (a
           declaration of a package, subprogram, or generic, or a generic
           instantiation), or a library unit renaming declaration (a package,
           generic, or subprogram renaming declaration).  Such files are also
           called specs.

       file.adb
           Ada source code file containing a library unit body (a subprogram
           or package body).  Such files are also called bodies.

       file.s
           Assembler code.

       file.S
       file.sx
           Assembler code that must be preprocessed.

       other
           An object file to be fed straight into linking.  Any file name with
           no recognized suffix is treated this way.

       You can specify the input language explicitly with the -x option:

       -x language
           Specify explicitly the language for the following input files
           (rather than letting the compiler choose a default based on the
           file name suffix).  This option applies to all following input
           files until the next -x option.  Possible values for language are:

                   c  c-header  cpp-output
                   c++  c++-header  c++-cpp-output
                   objective-c  objective-c-header  objective-c-cpp-output
                   objective-c++ objective-c++-header objective-c++-cpp-output
                   assembler  assembler-with-cpp
                   ada
                   d
                   f77  f77-cpp-input f95  f95-cpp-input
                   go
                   brig

       -x none
           Turn off any specification of a language, so that subsequent files
           are handled according to their file name suffixes (as they are if
           -x has not been used at all).

       If you only want some of the stages of compilation, you can use -x (or
       filename suffixes) to tell gcc where to start, and one of the options
       -c, -S, or -E to say where gcc is to stop.  Note that some combinations
       (for example, -x cpp-output -E) instruct gcc to do nothing at all.

       -c  Compile or assemble the source files, but do not link.  The linking
           stage simply is not done.  The ultimate output is in the form of an
           object file for each source file.

           By default, the object file name for a source file is made by
           replacing the suffix .c, .i, .s, etc., with .o.

           Unrecognized input files, not requiring compilation or assembly,
           are ignored.

       -S  Stop after the stage of compilation proper; do not assemble.  The
           output is in the form of an assembler code file for each non-
           assembler input file specified.

           By default, the assembler file name for a source file is made by
           replacing the suffix .c, .i, etc., with .s.

           Input files that don't require compilation are ignored.

       -E  Stop after the preprocessing stage; do not run the compiler proper.
           The output is in the form of preprocessed source code, which is
           sent to the standard output.

           Input files that don't require preprocessing are ignored.

       -o file
           Place output in file file.  This applies to whatever sort of output
           is being produced, whether it be an executable file, an object
           file, an assembler file or preprocessed C code.

           If -o is not specified, the default is to put an executable file in
           a.out, the object file for source.suffix in source.o, its assembler
           file in source.s, a precompiled header file in source.suffix.gch,
           and all preprocessed C source on standard output.

       -v  Print (on standard error output) the commands executed to run the
           stages of compilation.  Also print the version number of the
           compiler driver program and of the preprocessor and the compiler
           proper.

       -###
           Like -v except the commands are not executed and arguments are
           quoted unless they contain only alphanumeric characters or "./-_".
           This is useful for shell scripts to capture the driver-generated
           command lines.

       --help
           Print (on the standard output) a description of the command-line
           options understood by gcc.  If the -v option is also specified then
           --help is also passed on to the various processes invoked by gcc,
           so that they can display the command-line options they accept.  If
           the -Wextra option has also been specified (prior to the --help
           option), then command-line options that have no documentation
           associated with them are also displayed.

       --target-help
           Print (on the standard output) a description of target-specific
           command-line options for each tool.  For some targets extra target-
           specific information may also be printed.

       --help={class|[^]qualifier}[,...]
           Print (on the standard output) a description of the command-line
           options understood by the compiler that fit into all specified
           classes and qualifiers.  These are the supported classes:

           optimizers
               Display all of the optimization options supported by the
               compiler.

           warnings
               Display all of the options controlling warning messages
               produced by the compiler.

           target
               Display target-specific options.  Unlike the --target-help
               option however, target-specific options of the linker and
               assembler are not displayed.  This is because those tools do
               not currently support the extended --help= syntax.

           params
               Display the values recognized by the --param option.

           language
               Display the options supported for language, where language is
               the name of one of the languages supported in this version of
               GCC.  If an option is supported by all languages, one needs to
               select common class.

           common
               Display the options that are common to all languages.

           These are the supported qualifiers:

           undocumented
               Display only those options that are undocumented.

           joined
               Display options taking an argument that appears after an equal
               sign in the same continuous piece of text, such as:
               --help=target.

           separate
               Display options taking an argument that appears as a separate
               word following the original option, such as: -o output-file.

           Thus for example to display all the undocumented target-specific
           switches supported by the compiler, use:

                   --help=target,undocumented

           The sense of a qualifier can be inverted by prefixing it with the ^
           character, so for example to display all binary warning options
           (i.e., ones that are either on or off and that do not take an
           argument) that have a description, use:

                   --help=warnings,^joined,^undocumented

           The argument to --help= should not consist solely of inverted
           qualifiers.

           Combining several classes is possible, although this usually
           restricts the output so much that there is nothing to display.  One
           case where it does work, however, is when one of the classes is
           target.  For example, to display all the target-specific
           optimization options, use:

                   --help=target,optimizers

           The --help= option can be repeated on the command line.  Each
           successive use displays its requested class of options, skipping
           those that have already been displayed.  If --help is also
           specified anywhere on the command line then this takes precedence
           over any --help= option.

           If the -Q option appears on the command line before the --help=
           option, then the descriptive text displayed by --help= is changed.
           Instead of describing the displayed options, an indication is given
           as to whether the option is enabled, disabled or set to a specific
           value (assuming that the compiler knows this at the point where the
           --help= option is used).

           Here is a truncated example from the ARM port of gcc:

                     % gcc -Q -mabi=2 --help=target -c
                     The following options are target specific:
                     -mabi=                                2
                     -mabort-on-noreturn                   [disabled]
                     -mapcs                                [disabled]

           The output is sensitive to the effects of previous command-line
           options, so for example it is possible to find out which
           optimizations are enabled at -O2 by using:

                   -Q -O2 --help=optimizers

           Alternatively you can discover which binary optimizations are
           enabled by -O3 by using:

                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled

       --version
           Display the version number and copyrights of the invoked GCC.

       -pass-exit-codes
           Normally the gcc program exits with the code of 1 if any phase of
           the compiler returns a non-success return code.  If you specify
           -pass-exit-codes, the gcc program instead returns with the
           numerically highest error produced by any phase returning an error
           indication.  The C, C++, and Fortran front ends return 4 if an
           internal compiler error is encountered.

       -pipe
           Use pipes rather than temporary files for communication between the
           various stages of compilation.  This fails to work on some systems
           where the assembler is unable to read from a pipe; but the GNU
           assembler has no trouble.

       -specs=file
           Process file after the compiler reads in the standard specs file,
           in order to override the defaults which the gcc driver program uses
           when determining what switches to pass to cc1, cc1plus, as, ld,
           etc.  More than one -specs=file can be specified on the command
           line, and they are processed in order, from left to right.

       -wrapper
           Invoke all subcommands under a wrapper program.  The name of the
           wrapper program and its parameters are passed as a comma separated
           list.

                   gcc -c t.c -wrapper gdb,--args

           This invokes all subprograms of gcc under gdb --args, thus the
           invocation of cc1 is gdb --args cc1 ....

       -ffile-prefix-map=old=new
           When compiling files residing in directory old, record any
           references to them in the result of the compilation as if the files
           resided in directory new instead.  Specifying this option is
           equivalent to specifying all the individual -f*-prefix-map options.
           This can be used to make reproducible builds that are location
           independent.  See also -fmacro-prefix-map and -fdebug-prefix-map.

       -fplugin=name.so
           Load the plugin code in file name.so, assumed to be a shared object
           to be dlopen'd by the compiler.  The base name of the shared object
           file is used to identify the plugin for the purposes of argument
           parsing (See -fplugin-arg-name-key=value below).  Each plugin
           should define the callback functions specified in the Plugins API.

       -fplugin-arg-name-key=value
           Define an argument called key with a value of value for the plugin
           called name.

       -fdump-ada-spec[-slim]
           For C and C++ source and include files, generate corresponding Ada
           specs.

       -fada-spec-parent=unit
           In conjunction with -fdump-ada-spec[-slim] above, generate Ada
           specs as child units of parent unit.

       -fdump-go-spec=file
           For input files in any language, generate corresponding Go
           declarations in file.  This generates Go "const", "type", "var",
           and "func" declarations which may be a useful way to start writing
           a Go interface to code written in some other language.

       @file
           Read command-line options from file.  The options read are inserted
           in place of the original @file option.  If file does not exist, or
           cannot be read, then the option will be treated literally, and not
           removed.

           Options in file are separated by whitespace.  A whitespace
           character may be included in an option by surrounding the entire
           option in either single or double quotes.  Any character (including
           a backslash) may be included by prefixing the character to be
           included with a backslash.  The file may itself contain additional
           @file options; any such options will be processed recursively.

   Compiling C++ Programs
       C++ source files conventionally use one of the suffixes .C, .cc, .cpp,
       .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or
       (for shared template code) .tcc; and preprocessed C++ files use the
       suffix .ii.  GCC recognizes files with these names and compiles them as
       C++ programs even if you call the compiler the same way as for
       compiling C programs (usually with the name gcc).

       However, the use of gcc does not add the C++ library.  g++ is a program
       that calls GCC and automatically specifies linking against the C++
       library.  It treats .c, .h and .i files as C++ source files instead of
       C source files unless -x is used.  This program is also useful when
       precompiling a C header file with a .h extension for use in C++
       compilations.  On many systems, g++ is also installed with the name
       c++.

       When you compile C++ programs, you may specify many of the same
       command-line options that you use for compiling programs in any
       language; or command-line options meaningful for C and related
       languages; or options that are meaningful only for C++ programs.

   Options Controlling C Dialect
       The following options control the dialect of C (or languages derived
       from C, such as C++, Objective-C and Objective-C++) that the compiler
       accepts:

       -ansi
           In C mode, this is equivalent to -std=c90. In C++ mode, it is
           equivalent to -std=c++98.

           This turns off certain features of GCC that are incompatible with
           ISO C90 (when compiling C code), or of standard C++ (when compiling
           C++ code), such as the "asm" and "typeof" keywords, and predefined
           macros such as "unix" and "vax" that identify the type of system
           you are using.  It also enables the undesirable and rarely used ISO
           trigraph feature.  For the C compiler, it disables recognition of
           C++ style // comments as well as the "inline" keyword.

           The alternate keywords "__asm__", "__extension__", "__inline__" and
           "__typeof__" continue to work despite -ansi.  You would not want to
           use them in an ISO C program, of course, but it is useful to put
           them in header files that might be included in compilations done
           with -ansi.  Alternate predefined macros such as "__unix__" and
           "__vax__" are also available, with or without -ansi.

           The -ansi option does not cause non-ISO programs to be rejected
           gratuitously.  For that, -Wpedantic is required in addition to
           -ansi.

           The macro "__STRICT_ANSI__" is predefined when the -ansi option is
           used.  Some header files may notice this macro and refrain from
           declaring certain functions or defining certain macros that the ISO
           standard doesn't call for; this is to avoid interfering with any
           programs that might use these names for other things.

           Functions that are normally built in but do not have semantics
           defined by ISO C (such as "alloca" and "ffs") are not built-in
           functions when -ansi is used.

       -std=
           Determine the language standard.   This option is currently only
           supported when compiling C or C++.

           The compiler can accept several base standards, such as c90 or
           c++98, and GNU dialects of those standards, such as gnu90 or
           gnu++98.  When a base standard is specified, the compiler accepts
           all programs following that standard plus those using GNU
           extensions that do not contradict it.  For example, -std=c90 turns
           off certain features of GCC that are incompatible with ISO C90,
           such as the "asm" and "typeof" keywords, but not other GNU
           extensions that do not have a meaning in ISO C90, such as omitting
           the middle term of a "?:" expression. On the other hand, when a GNU
           dialect of a standard is specified, all features supported by the
           compiler are enabled, even when those features change the meaning
           of the base standard.  As a result, some strict-conforming programs
           may be rejected.  The particular standard is used by -Wpedantic to
           identify which features are GNU extensions given that version of
           the standard. For example -std=gnu90 -Wpedantic warns about C++
           style // comments, while -std=gnu99 -Wpedantic does not.

           A value for this option must be provided; possible values are

           c90
           c89
           iso9899:1990
               Support all ISO C90 programs (certain GNU extensions that
               conflict with ISO C90 are disabled). Same as -ansi for C code.

           iso9899:199409
               ISO C90 as modified in amendment 1.

           c99
           c9x
           iso9899:1999
           iso9899:199x
               ISO C99.  This standard is substantially completely supported,
               modulo bugs and floating-point issues (mainly but not entirely
               relating to optional C99 features from Annexes F and G).  See
               <http://gcc.gnu.org/c99status.html> for more information.  The
               names c9x and iso9899:199x are deprecated.

           c11
           c1x
           iso9899:2011
               ISO C11, the 2011 revision of the ISO C standard.  This
               standard is substantially completely supported, modulo bugs,
               floating-point issues (mainly but not entirely relating to
               optional C11 features from Annexes F and G) and the optional
               Annexes K (Bounds-checking interfaces) and L (Analyzability).
               The name c1x is deprecated.

           c17
           c18
           iso9899:2017
           iso9899:2018
               ISO C17, the 2017 revision of the ISO C standard (published in
               2018).  This standard is same as C11 except for corrections of
               defects (all of which are also applied with -std=c11) and a new
               value of "__STDC_VERSION__", and so is supported to the same
               extent as C11.

           c2x The next version of the ISO C standard, still under
               development.  The support for this version is experimental and
               incomplete.

           gnu90
           gnu89
               GNU dialect of ISO C90 (including some C99 features).

           gnu99
           gnu9x
               GNU dialect of ISO C99.  The name gnu9x is deprecated.

           gnu11
           gnu1x
               GNU dialect of ISO C11. The name gnu1x is deprecated.

           gnu17
           gnu18
               GNU dialect of ISO C17.  This is the default for C code.

           gnu2x
               The next version of the ISO C standard, still under
               development, plus GNU extensions.  The support for this version
               is experimental and incomplete.

           c++98
           c++03
               The 1998 ISO C++ standard plus the 2003 technical corrigendum
               and some additional defect reports. Same as -ansi for C++ code.

           gnu++98
           gnu++03
               GNU dialect of -std=c++98.

           c++11
           c++0x
               The 2011 ISO C++ standard plus amendments.  The name c++0x is
               deprecated.

           gnu++11
           gnu++0x
               GNU dialect of -std=c++11.  The name gnu++0x is deprecated.

           c++14
           c++1y
               The 2014 ISO C++ standard plus amendments.  The name c++1y is
               deprecated.

           gnu++14
           gnu++1y
               GNU dialect of -std=c++14.  This is the default for C++ code.
               The name gnu++1y is deprecated.

           c++17
           c++1z
               The 2017 ISO C++ standard plus amendments.  The name c++1z is
               deprecated.

           gnu++17
           gnu++1z
               GNU dialect of -std=c++17.  The name gnu++1z is deprecated.

           c++20
           c++2a
               The next revision of the ISO C++ standard, planned for 2020.
               Support is highly experimental, and will almost certainly
               change in incompatible ways in future releases.

           gnu++20
           gnu++2a
               GNU dialect of -std=c++20.  Support is highly experimental, and
               will almost certainly change in incompatible ways in future
               releases.

       -fgnu89-inline
           The option -fgnu89-inline tells GCC to use the traditional GNU
           semantics for "inline" functions when in C99 mode.

           Using this option is roughly equivalent to adding the "gnu_inline"
           function attribute to all inline functions.

           The option -fno-gnu89-inline explicitly tells GCC to use the C99
           semantics for "inline" when in C99 or gnu99 mode (i.e., it
           specifies the default behavior).  This option is not supported in
           -std=c90 or -std=gnu90 mode.

           The preprocessor macros "__GNUC_GNU_INLINE__" and
           "__GNUC_STDC_INLINE__" may be used to check which semantics are in
           effect for "inline" functions.

       -fpermitted-flt-eval-methods=style
           ISO/IEC TS 18661-3 defines new permissible values for
           "FLT_EVAL_METHOD" that indicate that operations and constants with
           a semantic type that is an interchange or extended format should be
           evaluated to the precision and range of that type.  These new
           values are a superset of those permitted under C99/C11, which does
           not specify the meaning of other positive values of
           "FLT_EVAL_METHOD".  As such, code conforming to C11 may not have
           been written expecting the possibility of the new values.

           -fpermitted-flt-eval-methods specifies whether the compiler should
           allow only the values of "FLT_EVAL_METHOD" specified in C99/C11, or
           the extended set of values specified in ISO/IEC TS 18661-3.

           style is either "c11" or "ts-18661-3" as appropriate.

           The default when in a standards compliant mode (-std=c11 or
           similar) is -fpermitted-flt-eval-methods=c11.  The default when in
           a GNU dialect (-std=gnu11 or similar) is
           -fpermitted-flt-eval-methods=ts-18661-3.

       -aux-info filename
           Output to the given filename prototyped declarations for all
           functions declared and/or defined in a translation unit, including
           those in header files.  This option is silently ignored in any
           language other than C.

           Besides declarations, the file indicates, in comments, the origin
           of each declaration (source file and line), whether the declaration
           was implicit, prototyped or unprototyped (I, N for new or O for
           old, respectively, in the first character after the line number and
           the colon), and whether it came from a declaration or a definition
           (C or F, respectively, in the following character).  In the case of
           function definitions, a K&R-style list of arguments followed by
           their declarations is also provided, inside comments, after the
           declaration.

       -fallow-parameterless-variadic-functions
           Accept variadic functions without named parameters.

           Although it is possible to define such a function, this is not very
           useful as it is not possible to read the arguments.  This is only
           supported for C as this construct is allowed by C++.

       -fno-asm
           Do not recognize "asm", "inline" or "typeof" as a keyword, so that
           code can use these words as identifiers.  You can use the keywords
           "__asm__", "__inline__" and "__typeof__" instead.  -ansi implies
           -fno-asm.

           In C++, this switch only affects the "typeof" keyword, since "asm"
           and "inline" are standard keywords.  You may want to use the
           -fno-gnu-keywords flag instead, which has the same effect.  In C99
           mode (-std=c99 or -std=gnu99), this switch only affects the "asm"
           and "typeof" keywords, since "inline" is a standard keyword in ISO
           C99.

       -fno-builtin
       -fno-builtin-function
           Don't recognize built-in functions that do not begin with
           __builtin_ as prefix.

           GCC normally generates special code to handle certain built-in
           functions more efficiently; for instance, calls to "alloca" may
           become single instructions which adjust the stack directly, and
           calls to "memcpy" may become inline copy loops.  The resulting code
           is often both smaller and faster, but since the function calls no
           longer appear as such, you cannot set a breakpoint on those calls,
           nor can you change the behavior of the functions by linking with a
           different library.  In addition, when a function is recognized as a
           built-in function, GCC may use information about that function to
           warn about problems with calls to that function, or to generate
           more efficient code, even if the resulting code still contains
           calls to that function.  For example, warnings are given with
           -Wformat for bad calls to "printf" when "printf" is built in and
           "strlen" is known not to modify global memory.

           With the -fno-builtin-function option only the built-in function
           function is disabled.  function must not begin with __builtin_.  If
           a function is named that is not built-in in this version of GCC,
           this option is ignored.  There is no corresponding
           -fbuiltin-function option; if you wish to enable built-in functions
           selectively when using -fno-builtin or -ffreestanding, you may
           define macros such as:

                   #define abs(n)          __builtin_abs ((n))
                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))

       -fgimple
           Enable parsing of function definitions marked with "__GIMPLE".
           This is an experimental feature that allows unit testing of GIMPLE
           passes.

       -fhosted
           Assert that compilation targets a hosted environment.  This implies
           -fbuiltin.  A hosted environment is one in which the entire
           standard library is available, and in which "main" has a return
           type of "int".  Examples are nearly everything except a kernel.
           This is equivalent to -fno-freestanding.

       -ffreestanding
           Assert that compilation targets a freestanding environment.  This
           implies -fno-builtin.  A freestanding environment is one in which
           the standard library may not exist, and program startup may not
           necessarily be at "main".  The most obvious example is an OS
           kernel.  This is equivalent to -fno-hosted.

       -fopenacc
           Enable handling of OpenACC directives "#pragma acc" in C/C++ and
           "!$acc" in Fortran.  When -fopenacc is specified, the compiler
           generates accelerated code according to the OpenACC Application
           Programming Interface v2.6 <https://www.openacc.org>.  This option
           implies -pthread, and thus is only supported on targets that have
           support for -pthread.

       -fopenacc-dim=geom
           Specify default compute dimensions for parallel offload regions
           that do not explicitly specify.  The geom value is a triple of
           ':'-separated sizes, in order 'gang', 'worker' and, 'vector'.  A
           size can be omitted, to use a target-specific default value.

       -fopenmp
           Enable handling of OpenMP directives "#pragma omp" in C/C++ and
           "!$omp" in Fortran.  When -fopenmp is specified, the compiler
           generates parallel code according to the OpenMP Application Program
           Interface v4.5 <https://www.openmp.org>.  This option implies
           -pthread, and thus is only supported on targets that have support
           for -pthread. -fopenmp implies -fopenmp-simd.

       -fopenmp-simd
           Enable handling of OpenMP's SIMD directives with "#pragma omp" in
           C/C++ and "!$omp" in Fortran. Other OpenMP directives are ignored.

       -fgnu-tm
           When the option -fgnu-tm is specified, the compiler generates code
           for the Linux variant of Intel's current Transactional Memory ABI
           specification document (Revision 1.1, May 6 2009).  This is an
           experimental feature whose interface may change in future versions
           of GCC, as the official specification changes.  Please note that
           not all architectures are supported for this feature.

           For more information on GCC's support for transactional memory,

           Note that the transactional memory feature is not supported with
           non-call exceptions (-fnon-call-exceptions).

       -fms-extensions
           Accept some non-standard constructs used in Microsoft header files.

           In C++ code, this allows member names in structures to be similar
           to previous types declarations.

                   typedef int UOW;
                   struct ABC {
                     UOW UOW;
                   };

           Some cases of unnamed fields in structures and unions are only
           accepted with this option.

           Note that this option is off for all targets except for x86 targets
           using ms-abi.

       -fplan9-extensions
           Accept some non-standard constructs used in Plan 9 code.

           This enables -fms-extensions, permits passing pointers to
           structures with anonymous fields to functions that expect pointers
           to elements of the type of the field, and permits referring to
           anonymous fields declared using a typedef.    This is only
           supported for C, not C++.

       -fcond-mismatch
           Allow conditional expressions with mismatched types in the second
           and third arguments.  The value of such an expression is void.
           This option is not supported for C++.

       -flax-vector-conversions
           Allow implicit conversions between vectors with differing numbers
           of elements and/or incompatible element types.  This option should
           not be used for new code.

       -funsigned-char
           Let the type "char" be unsigned, like "unsigned char".

           Each kind of machine has a default for what "char" should be.  It
           is either like "unsigned char" by default or like "signed char" by
           default.

           Ideally, a portable program should always use "signed char" or
           "unsigned char" when it depends on the signedness of an object.
           But many programs have been written to use plain "char" and expect
           it to be signed, or expect it to be unsigned, depending on the
           machines they were written for.  This option, and its inverse, let
           you make such a program work with the opposite default.

           The type "char" is always a distinct type from each of "signed
           char" or "unsigned char", even though its behavior is always just
           like one of those two.

       -fsigned-char
           Let the type "char" be signed, like "signed char".

           Note that this is equivalent to -fno-unsigned-char, which is the
           negative form of -funsigned-char.  Likewise, the option
           -fno-signed-char is equivalent to -funsigned-char.

       -fsigned-bitfields
       -funsigned-bitfields
       -fno-signed-bitfields
       -fno-unsigned-bitfields
           These options control whether a bit-field is signed or unsigned,
           when the declaration does not use either "signed" or "unsigned".
           By default, such a bit-field is signed, because this is consistent:
           the basic integer types such as "int" are signed types.

       -fsso-struct=endianness
           Set the default scalar storage order of structures and unions to
           the specified endianness.  The accepted values are big-endian,
           little-endian and native for the native endianness of the target
           (the default).  This option is not supported for C++.

           Warning: the -fsso-struct switch causes GCC to generate code that
           is not binary compatible with code generated without it if the
           specified endianness is not the native endianness of the target.

   Options Controlling C++ Dialect
       This section describes the command-line options that are only
       meaningful for C++ programs.  You can also use most of the GNU compiler
       options regardless of what language your program is in.  For example,
       you might compile a file firstClass.C like this:

               g++ -g -fstrict-enums -O -c firstClass.C

       In this example, only -fstrict-enums is an option meant only for C++
       programs; you can use the other options with any language supported by
       GCC.

       Some options for compiling C programs, such as -std, are also relevant
       for C++ programs.

       Here is a list of options that are only for compiling C++ programs:

       -fabi-version=n
           Use version n of the C++ ABI.  The default is version 0.

           Version 0 refers to the version conforming most closely to the C++
           ABI specification.  Therefore, the ABI obtained using version 0
           will change in different versions of G++ as ABI bugs are fixed.

           Version 1 is the version of the C++ ABI that first appeared in G++
           3.2.

           Version 2 is the version of the C++ ABI that first appeared in G++
           3.4, and was the default through G++ 4.9.

           Version 3 corrects an error in mangling a constant address as a
           template argument.

           Version 4, which first appeared in G++ 4.5, implements a standard
           mangling for vector types.

           Version 5, which first appeared in G++ 4.6, corrects the mangling
           of attribute const/volatile on function pointer types, decltype of
           a plain decl, and use of a function parameter in the declaration of
           another parameter.

           Version 6, which first appeared in G++ 4.7, corrects the promotion
           behavior of C++11 scoped enums and the mangling of template
           argument packs, const/static_cast, prefix ++ and --, and a class
           scope function used as a template argument.

           Version 7, which first appeared in G++ 4.8, that treats nullptr_t
           as a builtin type and corrects the mangling of lambdas in default
           argument scope.

           Version 8, which first appeared in G++ 4.9, corrects the
           substitution behavior of function types with function-cv-
           qualifiers.

           Version 9, which first appeared in G++ 5.2, corrects the alignment
           of "nullptr_t".

           Version 10, which first appeared in G++ 6.1, adds mangling of
           attributes that affect type identity, such as ia32 calling
           convention attributes (e.g. stdcall).

           Version 11, which first appeared in G++ 7, corrects the mangling of
           sizeof... expressions and operator names.  For multiple entities
           with the same name within a function, that are declared in
           different scopes, the mangling now changes starting with the
           twelfth occurrence.  It also implies -fnew-inheriting-ctors.

           Version 12, which first appeared in G++ 8, corrects the calling
           conventions for empty classes on the x86_64 target and for classes
           with only deleted copy/move constructors.  It accidentally changes
           the calling convention for classes with a deleted copy constructor
           and a trivial move constructor.

           Version 13, which first appeared in G++ 8.2, fixes the accidental
           change in version 12.

           Version 14, which first appeared in G++ 10, corrects the mangling
           of the nullptr expression.

           See also -Wabi.

       -fabi-compat-version=n
           On targets that support strong aliases, G++ works around mangling
           changes by creating an alias with the correct mangled name when
           defining a symbol with an incorrect mangled name.  This switch
           specifies which ABI version to use for the alias.

           With -fabi-version=0 (the default), this defaults to 11 (GCC 7
           compatibility).  If another ABI version is explicitly selected,
           this defaults to 0.  For compatibility with GCC versions 3.2
           through 4.9, use -fabi-compat-version=2.

           If this option is not provided but -Wabi=n is, that version is used
           for compatibility aliases.  If this option is provided along with
           -Wabi (without the version), the version from this option is used
           for the warning.

       -fno-access-control
           Turn off all access checking.  This switch is mainly useful for
           working around bugs in the access control code.

       -faligned-new
           Enable support for C++17 "new" of types that require more alignment
           than "void* ::operator new(std::size_t)" provides.  A numeric
           argument such as "-faligned-new=32" can be used to specify how much
           alignment (in bytes) is provided by that function, but few users
           will need to override the default of "alignof(std::max_align_t)".

           This flag is enabled by default for -std=c++17.

       -fchar8_t
       -fno-char8_t
           Enable support for "char8_t" as adopted for C++2a.  This includes
           the addition of a new "char8_t" fundamental type, changes to the
           types of UTF-8 string and character literals, new signatures for
           user-defined literals, associated standard library updates, and new
           "__cpp_char8_t" and "__cpp_lib_char8_t" feature test macros.

           This option enables functions to be overloaded for ordinary and
           UTF-8 strings:

                   int f(const char *);    // #1
                   int f(const char8_t *); // #2
                   int v1 = f("text");     // Calls #1
                   int v2 = f(u8"text");   // Calls #2

           and introduces new signatures for user-defined literals:

                   int operator""_udl1(char8_t);
                   int v3 = u8'x'_udl1;
                   int operator""_udl2(const char8_t*, std::size_t);
                   int v4 = u8"text"_udl2;
                   template<typename T, T...> int operator""_udl3();
                   int v5 = u8"text"_udl3;

           The change to the types of UTF-8 string and character literals
           introduces incompatibilities with ISO C++11 and later standards.
           For example, the following code is well-formed under ISO C++11, but
           is ill-formed when -fchar8_t is specified.

                   char ca[] = u8"xx";     // error: char-array initialized from wide
                                           //        string
                   const char *cp = u8"xx";// error: invalid conversion from
                                           //        `const char8_t*' to `const char*'
                   int f(const char*);
                   auto v = f(u8"xx");     // error: invalid conversion from
                                           //        `const char8_t*' to `const char*'
                   std::string s{u8"xx"};  // error: no matching function for call to
                                           //        `std::basic_string<char>::basic_string()'
                   using namespace std::literals;
                   s = u8"xx"s;            // error: conversion from
                                           //        `basic_string<char8_t>' to non-scalar
                                           //        type `basic_string<char>' requested

       -fcheck-new
           Check that the pointer returned by "operator new" is non-null
           before attempting to modify the storage allocated.  This check is
           normally unnecessary because the C++ standard specifies that
           "operator new" only returns 0 if it is declared "throw()", in which
           case the compiler always checks the return value even without this
           option.  In all other cases, when "operator new" has a non-empty
           exception specification, memory exhaustion is signalled by throwing
           "std::bad_alloc".  See also new (nothrow).

       -fconcepts
       -fconcepts-ts
           Below -std=c++2a, -fconcepts enables support for the C++ Extensions
           for Concepts Technical Specification, ISO 19217 (2015).

           With -std=c++2a and above, Concepts are part of the language
           standard, so -fconcepts defaults to on.  But the standard
           specification of Concepts differs significantly from the TS, so
           some constructs that were allowed in the TS but didn't make it into
           the standard can still be enabled by -fconcepts-ts.

       -fconstexpr-depth=n
           Set the maximum nested evaluation depth for C++11 constexpr
           functions to n.  A limit is needed to detect endless recursion
           during constant expression evaluation.  The minimum specified by
           the standard is 512.

       -fconstexpr-cache-depth=n
           Set the maximum level of nested evaluation depth for C++11
           constexpr functions that will be cached to n.  This is a heuristic
           that trades off compilation speed (when the cache avoids repeated
           calculations) against memory consumption (when the cache grows very
           large from highly recursive evaluations).  The default is 8.  Very
           few users are likely to want to adjust it, but if your code does
           heavy constexpr calculations you might want to experiment to find
           which value works best for you.

       -fconstexpr-loop-limit=n
           Set the maximum number of iterations for a loop in C++14 constexpr
           functions to n.  A limit is needed to detect infinite loops during
           constant expression evaluation.  The default is 262144 (1<<18).

       -fconstexpr-ops-limit=n
           Set the maximum number of operations during a single constexpr
           evaluation.  Even when number of iterations of a single loop is
           limited with the above limit, if there are several nested loops and
           each of them has many iterations but still smaller than the above
           limit, or if in a body of some loop or even outside of a loop too
           many expressions need to be evaluated, the resulting constexpr
           evaluation might take too long.  The default is 33554432 (1<<25).

       -fcoroutines
           Enable support for the C++ coroutines extension (experimental).

       -fno-elide-constructors
           The C++ standard allows an implementation to omit creating a
           temporary that is only used to initialize another object of the
           same type.  Specifying this option disables that optimization, and
           forces G++ to call the copy constructor in all cases.  This option
           also causes G++ to call trivial member functions which otherwise
           would be expanded inline.

           In C++17, the compiler is required to omit these temporaries, but
           this option still affects trivial member functions.

       -fno-enforce-eh-specs
           Don't generate code to check for violation of exception
           specifications at run time.  This option violates the C++ standard,
           but may be useful for reducing code size in production builds, much
           like defining "NDEBUG".  This does not give user code permission to
           throw exceptions in violation of the exception specifications; the
           compiler still optimizes based on the specifications, so throwing
           an unexpected exception results in undefined behavior at run time.

       -fextern-tls-init
       -fno-extern-tls-init
           The C++11 and OpenMP standards allow "thread_local" and
           "threadprivate" variables to have dynamic (runtime) initialization.
           To support this, any use of such a variable goes through a wrapper
           function that performs any necessary initialization.  When the use
           and definition of the variable are in the same translation unit,
           this overhead can be optimized away, but when the use is in a
           different translation unit there is significant overhead even if
           the variable doesn't actually need dynamic initialization.  If the
           programmer can be sure that no use of the variable in a non-
           defining TU needs to trigger dynamic initialization (either because
           the variable is statically initialized, or a use of the variable in
           the defining TU will be executed before any uses in another TU),
           they can avoid this overhead with the -fno-extern-tls-init option.

           On targets that support symbol aliases, the default is
           -fextern-tls-init.  On targets that do not support symbol aliases,
           the default is -fno-extern-tls-init.

       -fno-gnu-keywords
           Do not recognize "typeof" as a keyword, so that code can use this
           word as an identifier.  You can use the keyword "__typeof__"
           instead.  This option is implied by the strict ISO C++ dialects:
           -ansi, -std=c++98, -std=c++11, etc.

       -fno-implicit-templates
           Never emit code for non-inline templates that are instantiated
           implicitly (i.e. by use); only emit code for explicit
           instantiations.  If you use this option, you must take care to
           structure your code to include all the necessary explicit
           instantiations to avoid getting undefined symbols at link time.

       -fno-implicit-inline-templates
           Don't emit code for implicit instantiations of inline templates,
           either.  The default is to handle inlines differently so that
           compiles with and without optimization need the same set of
           explicit instantiations.

       -fno-implement-inlines
           To save space, do not emit out-of-line copies of inline functions
           controlled by "#pragma implementation".  This causes linker errors
           if these functions are not inlined everywhere they are called.

       -fms-extensions
           Disable Wpedantic warnings about constructs used in MFC, such as
           implicit int and getting a pointer to member function via non-
           standard syntax.

       -fnew-inheriting-ctors
           Enable the P0136 adjustment to the semantics of C++11 constructor
           inheritance.  This is part of C++17 but also considered to be a
           Defect Report against C++11 and C++14.  This flag is enabled by
           default unless -fabi-version=10 or lower is specified.

       -fnew-ttp-matching
           Enable the P0522 resolution to Core issue 150, template template
           parameters and default arguments: this allows a template with
           default template arguments as an argument for a template template
           parameter with fewer template parameters.  This flag is enabled by
           default for -std=c++17.

       -fno-nonansi-builtins
           Disable built-in declarations of functions that are not mandated by
           ANSI/ISO C.  These include "ffs", "alloca", "_exit", "index",
           "bzero", "conjf", and other related functions.

       -fnothrow-opt
           Treat a "throw()" exception specification as if it were a
           "noexcept" specification to reduce or eliminate the text size
           overhead relative to a function with no exception specification.
           If the function has local variables of types with non-trivial
           destructors, the exception specification actually makes the
           function smaller because the EH cleanups for those variables can be
           optimized away.  The semantic effect is that an exception thrown
           out of a function with such an exception specification results in a
           call to "terminate" rather than "unexpected".

       -fno-operator-names
           Do not treat the operator name keywords "and", "bitand", "bitor",
           "compl", "not", "or" and "xor" as synonyms as keywords.

       -fno-optional-diags
           Disable diagnostics that the standard says a compiler does not need
           to issue.  Currently, the only such diagnostic issued by G++ is the
           one for a name having multiple meanings within a class.

       -fpermissive
           Downgrade some diagnostics about nonconformant code from errors to
           warnings.  Thus, using -fpermissive allows some nonconforming code
           to compile.

       -fno-pretty-templates
           When an error message refers to a specialization of a function
           template, the compiler normally prints the signature of the
           template followed by the template arguments and any typedefs or
           typenames in the signature (e.g. "void f(T) [with T = int]" rather
           than "void f(int)") so that it's clear which template is involved.
           When an error message refers to a specialization of a class
           template, the compiler omits any template arguments that match the
           default template arguments for that template.  If either of these
           behaviors make it harder to understand the error message rather
           than easier, you can use -fno-pretty-templates to disable them.

       -fno-rtti
           Disable generation of information about every class with virtual
           functions for use by the C++ run-time type identification features
           ("dynamic_cast" and "typeid").  If you don't use those parts of the
           language, you can save some space by using this flag.  Note that
           exception handling uses the same information, but G++ generates it
           as needed. The "dynamic_cast" operator can still be used for casts
           that do not require run-time type information, i.e. casts to "void
           *" or to unambiguous base classes.

           Mixing code compiled with -frtti with that compiled with -fno-rtti
           may not work.  For example, programs may fail to link if a class
           compiled with -fno-rtti is used as a base for a class compiled with
           -frtti.

       -fsized-deallocation
           Enable the built-in global declarations

                   void operator delete (void *, std::size_t) noexcept;
                   void operator delete[] (void *, std::size_t) noexcept;

           as introduced in C++14.  This is useful for user-defined
           replacement deallocation functions that, for example, use the size
           of the object to make deallocation faster.  Enabled by default
           under -std=c++14 and above.  The flag -Wsized-deallocation warns
           about places that might want to add a definition.

       -fstrict-enums
           Allow the compiler to optimize using the assumption that a value of
           enumerated type can only be one of the values of the enumeration
           (as defined in the C++ standard; basically, a value that can be
           represented in the minimum number of bits needed to represent all
           the enumerators).  This assumption may not be valid if the program
           uses a cast to convert an arbitrary integer value to the enumerated
           type.

       -fstrong-eval-order
           Evaluate member access, array subscripting, and shift expressions
           in left-to-right order, and evaluate assignment in right-to-left
           order, as adopted for C++17.  Enabled by default with -std=c++17.
           -fstrong-eval-order=some enables just the ordering of member access
           and shift expressions, and is the default without -std=c++17.

       -ftemplate-backtrace-limit=n
           Set the maximum number of template instantiation notes for a single
           warning or error to n.  The default value is 10.

       -ftemplate-depth=n
           Set the maximum instantiation depth for template classes to n.  A
           limit on the template instantiation depth is needed to detect
           endless recursions during template class instantiation.  ANSI/ISO
           C++ conforming programs must not rely on a maximum depth greater
           than 17 (changed to 1024 in C++11).  The default value is 900, as
           the compiler can run out of stack space before hitting 1024 in some
           situations.

       -fno-threadsafe-statics
           Do not emit the extra code to use the routines specified in the C++
           ABI for thread-safe initialization of local statics.  You can use
           this option to reduce code size slightly in code that doesn't need
           to be thread-safe.

       -fuse-cxa-atexit
           Register destructors for objects with static storage duration with
           the "__cxa_atexit" function rather than the "atexit" function.
           This option is required for fully standards-compliant handling of
           static destructors, but only works if your C library supports
           "__cxa_atexit".

       -fno-use-cxa-get-exception-ptr
           Don't use the "__cxa_get_exception_ptr" runtime routine.  This
           causes "std::uncaught_exception" to be incorrect, but is necessary
           if the runtime routine is not available.

       -fvisibility-inlines-hidden
           This switch declares that the user does not attempt to compare
           pointers to inline functions or methods where the addresses of the
           two functions are taken in different shared objects.

           The effect of this is that GCC may, effectively, mark inline
           methods with "__attribute__ ((visibility ("hidden")))" so that they
           do not appear in the export table of a DSO and do not require a PLT
           indirection when used within the DSO.  Enabling this option can
           have a dramatic effect on load and link times of a DSO as it
           massively reduces the size of the dynamic export table when the
           library makes heavy use of templates.

           The behavior of this switch is not quite the same as marking the
           methods as hidden directly, because it does not affect static
           variables local to the function or cause the compiler to deduce
           that the function is defined in only one shared object.

           You may mark a method as having a visibility explicitly to negate
           the effect of the switch for that method.  For example, if you do
           want to compare pointers to a particular inline method, you might
           mark it as having default visibility.  Marking the enclosing class
           with explicit visibility has no effect.

           Explicitly instantiated inline methods are unaffected by this
           option as their linkage might otherwise cross a shared library
           boundary.

       -fvisibility-ms-compat
           This flag attempts to use visibility settings to make GCC's C++
           linkage model compatible with that of Microsoft Visual Studio.

           The flag makes these changes to GCC's linkage model:

           1.  It sets the default visibility to "hidden", like
               -fvisibility=hidden.

           2.  Types, but not their members, are not hidden by default.

           3.  The One Definition Rule is relaxed for types without explicit
               visibility specifications that are defined in more than one
               shared object: those declarations are permitted if they are
               permitted when this option is not used.

           In new code it is better to use -fvisibility=hidden and export
           those classes that are intended to be externally visible.
           Unfortunately it is possible for code to rely, perhaps
           accidentally, on the Visual Studio behavior.

           Among the consequences of these changes are that static data
           members of the same type with the same name but defined in
           different shared objects are different, so changing one does not
           change the other; and that pointers to function members defined in
           different shared objects may not compare equal.  When this flag is
           given, it is a violation of the ODR to define types with the same
           name differently.

       -fno-weak
           Do not use weak symbol support, even if it is provided by the
           linker.  By default, G++ uses weak symbols if they are available.
           This option exists only for testing, and should not be used by end-
           users; it results in inferior code and has no benefits.  This
           option may be removed in a future release of G++.

       -fext-numeric-literals (C++ and Objective-C++ only)
           Accept imaginary, fixed-point, or machine-defined literal number
           suffixes as GNU extensions.  When this option is turned off these
           suffixes are treated as C++11 user-defined literal numeric
           suffixes.  This is on by default for all pre-C++11 dialects and all
           GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14.
           This option is off by default for ISO C++11 onwards (-std=c++11,
           ...).

       -nostdinc++
           Do not search for header files in the standard directories specific
           to C++, but do still search the other standard directories.  (This
           option is used when building the C++ library.)

       In addition, these warning options have meanings only for C++ programs:

       -Wabi-tag (C++ and Objective-C++ only)
           Warn when a type with an ABI tag is used in a context that does not
           have that ABI tag.  See C++ Attributes for more information about
           ABI tags.

       -Wcomma-subscript (C++ and Objective-C++ only)
           Warn about uses of a comma expression within a subscripting
           expression.  This usage was deprecated in C++2a.  However, a comma
           expression wrapped in "( )" is not deprecated.  Example:

                   void f(int *a, int b, int c) {
                       a[b,c];     // deprecated
                       a[(b,c)];   // OK
                   }

           Enabled by default with -std=c++2a.

       -Wctor-dtor-privacy (C++ and Objective-C++ only)
           Warn when a class seems unusable because all the constructors or
           destructors in that class are private, and it has neither friends
           nor public static member functions.  Also warn if there are no non-
           private methods, and there's at least one private member function
           that isn't a constructor or destructor.

       -Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
           Warn when "delete" is used to destroy an instance of a class that
           has virtual functions and non-virtual destructor. It is unsafe to
           delete an instance of a derived class through a pointer to a base
           class if the base class does not have a virtual destructor.  This
           warning is enabled by -Wall.

       -Wdeprecated-copy (C++ and Objective-C++ only)
           Warn that the implicit declaration of a copy constructor or copy
           assignment operator is deprecated if the class has a user-provided
           copy constructor or copy assignment operator, in C++11 and up.
           This warning is enabled by -Wextra.  With -Wdeprecated-copy-dtor,
           also deprecate if the class has a user-provided destructor.

       -Wno-init-list-lifetime (C++ and Objective-C++ only)
           Do not warn about uses of "std::initializer_list" that are likely
           to result in dangling pointers.  Since the underlying array for an
           "initializer_list" is handled like a normal C++ temporary object,
           it is easy to inadvertently keep a pointer to the array past the
           end of the array's lifetime.  For example:

           *   If a function returns a temporary "initializer_list", or a
               local "initializer_list" variable, the array's lifetime ends at
               the end of the return statement, so the value returned has a
               dangling pointer.

           *   If a new-expression creates an "initializer_list", the array
               only lives until the end of the enclosing full-expression, so
               the "initializer_list" in the heap has a dangling pointer.

           *   When an "initializer_list" variable is assigned from a brace-
               enclosed initializer list, the temporary array created for the
               right side of the assignment only lives until the end of the
               full-expression, so at the next statement the
               "initializer_list" variable has a dangling pointer.

                       // li's initial underlying array lives as long as li
                       std::initializer_list<int> li = { 1,2,3 };
                       // assignment changes li to point to a temporary array
                       li = { 4, 5 };
                       // now the temporary is gone and li has a dangling pointer
                       int i = li.begin()[0] // undefined behavior

           *   When a list constructor stores the "begin" pointer from the
               "initializer_list" argument, this doesn't extend the lifetime
               of the array, so if a class variable is constructed from a
               temporary "initializer_list", the pointer is left dangling by
               the end of the variable declaration statement.

       -Wno-literal-suffix (C++ and Objective-C++ only)
           Do not warn when a string or character literal is followed by a ud-
           suffix which does not begin with an underscore.  As a conforming
           extension, GCC treats such suffixes as separate preprocessing
           tokens in order to maintain backwards compatibility with code that
           uses formatting macros from "<inttypes.h>".  For example:

                   #define __STDC_FORMAT_MACROS
                   #include <inttypes.h>
                   #include <stdio.h>

                   int main() {
                     int64_t i64 = 123;
                     printf("My int64: %" PRId64"\n", i64);
                   }

           In this case, "PRId64" is treated as a separate preprocessing
           token.

           This option also controls warnings when a user-defined literal
           operator is declared with a literal suffix identifier that doesn't
           begin with an underscore. Literal suffix identifiers that don't
           begin with an underscore are reserved for future standardization.

           These warnings are enabled by default.

       -Wno-narrowing (C++ and Objective-C++ only)
           For C++11 and later standards, narrowing conversions are diagnosed
           by default, as required by the standard.  A narrowing conversion
           from a constant produces an error, and a narrowing conversion from
           a non-constant produces a warning, but -Wno-narrowing suppresses
           the diagnostic.  Note that this does not affect the meaning of
           well-formed code; narrowing conversions are still considered ill-
           formed in SFINAE contexts.

           With -Wnarrowing in C++98, warn when a narrowing conversion
           prohibited by C++11 occurs within { }, e.g.

                   int i = { 2.2 }; // error: narrowing from double to int

           This flag is included in -Wall and -Wc++11-compat.

       -Wnoexcept (C++ and Objective-C++ only)
           Warn when a noexcept-expression evaluates to false because of a
           call to a function that does not have a non-throwing exception
           specification (i.e. "throw()" or "noexcept") but is known by the
           compiler to never throw an exception.

       -Wnoexcept-type (C++ and Objective-C++ only)
           Warn if the C++17 feature making "noexcept" part of a function type
           changes the mangled name of a symbol relative to C++14.  Enabled by
           -Wabi and -Wc++17-compat.

           As an example:

                   template <class T> void f(T t) { t(); };
                   void g() noexcept;
                   void h() { f(g); }

           In C++14, "f" calls "f<void(*)()>", but in C++17 it calls
           "f<void(*)()noexcept>".

       -Wclass-memaccess (C++ and Objective-C++ only)
           Warn when the destination of a call to a raw memory function such
           as "memset" or "memcpy" is an object of class type, and when
           writing into such an object might bypass the class non-trivial or
           deleted constructor or copy assignment, violate const-correctness
           or encapsulation, or corrupt virtual table pointers.  Modifying the
           representation of such objects may violate invariants maintained by
           member functions of the class.  For example, the call to "memset"
           below is undefined because it modifies a non-trivial class object
           and is, therefore, diagnosed.  The safe way to either initialize or
           clear the storage of objects of such types is by using the
           appropriate constructor or assignment operator, if one is
           available.

                   std::string str = "abc";
                   memset (&str, 0, sizeof str);

           The -Wclass-memaccess option is enabled by -Wall.  Explicitly
           casting the pointer to the class object to "void *" or to a type
           that can be safely accessed by the raw memory function suppresses
           the warning.

       -Wnon-virtual-dtor (C++ and Objective-C++ only)
           Warn when a class has virtual functions and an accessible non-
           virtual destructor itself or in an accessible polymorphic base
           class, in which case it is possible but unsafe to delete an
           instance of a derived class through a pointer to the class itself
           or base class.  This warning is automatically enabled if -Weffc++
           is specified.

       -Wregister (C++ and Objective-C++ only)
           Warn on uses of the "register" storage class specifier, except when
           it is part of the GNU Explicit Register Variables extension.  The
           use of the "register" keyword as storage class specifier has been
           deprecated in C++11 and removed in C++17.  Enabled by default with
           -std=c++17.

       -Wreorder (C++ and Objective-C++ only)
           Warn when the order of member initializers given in the code does
           not match the order in which they must be executed.  For instance:

                   struct A {
                     int i;
                     int j;
                     A(): j (0), i (1) { }
                   };

           The compiler rearranges the member initializers for "i" and "j" to
           match the declaration order of the members, emitting a warning to
           that effect.  This warning is enabled by -Wall.

       -Wno-pessimizing-move (C++ and Objective-C++ only)
           This warning warns when a call to "std::move" prevents copy
           elision.  A typical scenario when copy elision can occur is when
           returning in a function with a class return type, when the
           expression being returned is the name of a non-volatile automatic
           object, and is not a function parameter, and has the same type as
           the function return type.

                   struct T {
                   ...
                   };
                   T fn()
                   {
                     T t;
                     ...
                     return std::move (t);
                   }

           But in this example, the "std::move" call prevents copy elision.

           This warning is enabled by -Wall.

       -Wno-redundant-move (C++ and Objective-C++ only)
           This warning warns about redundant calls to "std::move"; that is,
           when a move operation would have been performed even without the
           "std::move" call.  This happens because the compiler is forced to
           treat the object as if it were an rvalue in certain situations such
           as returning a local variable, where copy elision isn't applicable.
           Consider:

                   struct T {
                   ...
                   };
                   T fn(T t)
                   {
                     ...
                     return std::move (t);
                   }

           Here, the "std::move" call is redundant.  Because G++ implements
           Core Issue 1579, another example is:

                   struct T { // convertible to U
                   ...
                   };
                   struct U {
                   ...
                   };
                   U fn()
                   {
                     T t;
                     ...
                     return std::move (t);
                   }

           In this example, copy elision isn't applicable because the type of
           the expression being returned and the function return type differ,
           yet G++ treats the return value as if it were designated by an
           rvalue.

           This warning is enabled by -Wextra.

       -Wredundant-tags (C++ and Objective-C++ only)
           Warn about redundant class-key and enum-key in references to class
           types and enumerated types in contexts where the key can be
           eliminated without causing an ambiguity.  For example:

                   struct foo;
                   struct foo *p;   // warn that keyword struct can be eliminated

           On the other hand, in this example there is no warning:

                   struct foo;
                   void foo ();   // "hides" struct foo
                   void bar (struct foo&);  // no warning, keyword struct is necessary

       -Wno-subobject-linkage (C++ and Objective-C++ only)
           Do not warn if a class type has a base or a field whose type uses
           the anonymous namespace or depends on a type with no linkage.  If a
           type A depends on a type B with no or internal linkage, defining it
           in multiple translation units would be an ODR violation because the
           meaning of B is different in each translation unit.  If A only
           appears in a single translation unit, the best way to silence the
           warning is to give it internal linkage by putting it in an
           anonymous namespace as well.  The compiler doesn't give this
           warning for types defined in the main .C file, as those are
           unlikely to have multiple definitions.  -Wsubobject-linkage is
           enabled by default.

       -Weffc++ (C++ and Objective-C++ only)
           Warn about violations of the following style guidelines from Scott
           Meyers' Effective C++ series of books:

           *   Define a copy constructor and an assignment operator for
               classes with dynamically-allocated memory.

           *   Prefer initialization to assignment in constructors.

           *   Have "operator=" return a reference to *this.

           *   Don't try to return a reference when you must return an object.

           *   Distinguish between prefix and postfix forms of increment and
               decrement operators.

           *   Never overload "&&", "||", or ",".

           This option also enables -Wnon-virtual-dtor, which is also one of
           the effective C++ recommendations.  However, the check is extended
           to warn about the lack of virtual destructor in accessible non-
           polymorphic bases classes too.

           When selecting this option, be aware that the standard library
           headers do not obey all of these guidelines; use grep -v to filter
           out those warnings.

       -Wstrict-null-sentinel (C++ and Objective-C++ only)
           Warn about the use of an uncasted "NULL" as sentinel.  When
           compiling only with GCC this is a valid sentinel, as "NULL" is
           defined to "__null".  Although it is a null pointer constant rather
           than a null pointer, it is guaranteed to be of the same size as a
           pointer.  But this use is not portable across different compilers.

       -Wno-non-template-friend (C++ and Objective-C++ only)
           Disable warnings when non-template friend functions are declared
           within a template.  In very old versions of GCC that predate
           implementation of the ISO standard, declarations such as friend int
           foo(int), where the name of the friend is an unqualified-id, could
           be interpreted as a particular specialization of a template
           function; the warning exists to diagnose compatibility problems,
           and is enabled by default.

       -Wold-style-cast (C++ and Objective-C++ only)
           Warn if an old-style (C-style) cast to a non-void type is used
           within a C++ program.  The new-style casts ("dynamic_cast",
           "static_cast", "reinterpret_cast", and "const_cast") are less
           vulnerable to unintended effects and much easier to search for.

       -Woverloaded-virtual (C++ and Objective-C++ only)
           Warn when a function declaration hides virtual functions from a
           base class.  For example, in:

                   struct A {
                     virtual void f();
                   };

                   struct B: public A {
                     void f(int);
                   };

           the "A" class version of "f" is hidden in "B", and code like:

                   B* b;
                   b->f();

           fails to compile.

       -Wno-pmf-conversions (C++ and Objective-C++ only)
           Disable the diagnostic for converting a bound pointer to member
           function to a plain pointer.

       -Wsign-promo (C++ and Objective-C++ only)
           Warn when overload resolution chooses a promotion from unsigned or
           enumerated type to a signed type, over a conversion to an unsigned
           type of the same size.  Previous versions of G++ tried to preserve
           unsignedness, but the standard mandates the current behavior.

       -Wtemplates (C++ and Objective-C++ only)
           Warn when a primary template declaration is encountered.  Some
           coding rules disallow templates, and this may be used to enforce
           that rule.  The warning is inactive inside a system header file,
           such as the STL, so one can still use the STL.  One may also
           instantiate or specialize templates.

       -Wmismatched-tags (C++ and Objective-C++ only)
           Warn for declarations of structs, classes, and class templates and
           their specializations with a class-key that does not match either
           the definition or the first declaration if no definition is
           provided.

           For example, the declaration of "struct Object" in the argument
           list of "draw" triggers the warning.  To avoid it, either remove
           the redundant class-key "struct" or replace it with "class" to
           match its definition.

                   class Object {
                   public:
                     virtual ~Object () = 0;
                   };
                   void draw (struct Object*);

           It is not wrong to declare a class with the class-key "struct" as
           the example above shows.  The -Wmismatched-tags option is intended
           to help achieve a consistent style of class declarations.  In code
           that is intended to be portable to Windows-based compilers the
           warning helps prevent unresolved references due to the difference
           in the mangling of symbols declared with different class-keys.  The
           option can be used either on its own or in conjunction with
           -Wredundant-tags.

       -Wmultiple-inheritance (C++ and Objective-C++ only)
           Warn when a class is defined with multiple direct base classes.
           Some coding rules disallow multiple inheritance, and this may be
           used to enforce that rule.  The warning is inactive inside a system
           header file, such as the STL, so one can still use the STL.  One
           may also define classes that indirectly use multiple inheritance.

       -Wvirtual-inheritance
           Warn when a class is defined with a virtual direct base class.
           Some coding rules disallow multiple inheritance, and this may be
           used to enforce that rule.  The warning is inactive inside a system
           header file, such as the STL, so one can still use the STL.  One
           may also define classes that indirectly use virtual inheritance.

       -Wno-virtual-move-assign
           Suppress warnings about inheriting from a virtual base with a non-
           trivial C++11 move assignment operator.  This is dangerous because
           if the virtual base is reachable along more than one path, it is
           moved multiple times, which can mean both objects end up in the
           moved-from state.  If the move assignment operator is written to
           avoid moving from a moved-from object, this warning can be
           disabled.

       -Wnamespaces
           Warn when a namespace definition is opened.  Some coding rules
           disallow namespaces, and this may be used to enforce that rule.
           The warning is inactive inside a system header file, such as the
           STL, so one can still use the STL.  One may also use using
           directives and qualified names.

       -Wno-terminate (C++ and Objective-C++ only)
           Disable the warning about a throw-expression that will immediately
           result in a call to "terminate".

       -Wno-class-conversion (C++ and Objective-C++ only)
           Do not warn when a conversion function converts an object to the
           same type, to a base class of that type, or to void; such a
           conversion function will never be called.

       -Wvolatile (C++ and Objective-C++ only)
           Warn about deprecated uses of the "volatile" qualifier.  This
           includes postfix and prefix "++" and "--" expressions of
           "volatile"-qualified types, using simple assignments where the left
           operand is a "volatile"-qualified non-class type for their value,
           compound assignments where the left operand is a
           "volatile"-qualified non-class type, "volatile"-qualified function
           return type, "volatile"-qualified parameter type, and structured
           bindings of a "volatile"-qualified type.  This usage was deprecated
           in C++20.

           Enabled by default with -std=c++2a.

       -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
           Warn when a literal 0 is used as null pointer constant.  This can
           be useful to facilitate the conversion to "nullptr" in C++11.

       -Waligned-new
           Warn about a new-expression of a type that requires greater
           alignment than the "alignof(std::max_align_t)" but uses an
           allocation function without an explicit alignment parameter. This
           option is enabled by -Wall.

           Normally this only warns about global allocation functions, but
           -Waligned-new=all also warns about class member allocation
           functions.

       -Wno-placement-new
       -Wplacement-new=n
           Warn about placement new expressions with undefined behavior, such
           as constructing an object in a buffer that is smaller than the type
           of the object.  For example, the placement new expression below is
           diagnosed because it attempts to construct an array of 64 integers
           in a buffer only 64 bytes large.

                   char buf [64];
                   new (buf) int[64];

           This warning is enabled by default.

           -Wplacement-new=1
               This is the default warning level of -Wplacement-new.  At this
               level the warning is not issued for some strictly undefined
               constructs that GCC allows as extensions for compatibility with
               legacy code.  For example, the following "new" expression is
               not diagnosed at this level even though it has undefined
               behavior according to the C++ standard because it writes past
               the end of the one-element array.

                       struct S { int n, a[1]; };
                       S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
                       new (s->a)int [32]();

           -Wplacement-new=2
               At this level, in addition to diagnosing all the same
               constructs as at level 1, a diagnostic is also issued for
               placement new expressions that construct an object in the last
               member of structure whose type is an array of a single element
               and whose size is less than the size of the object being
               constructed.  While the previous example would be diagnosed,
               the following construct makes use of the flexible member array
               extension to avoid the warning at level 2.

                       struct S { int n, a[]; };
                       S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
                       new (s->a)int [32]();

       -Wcatch-value
       -Wcatch-value=n (C++ and Objective-C++ only)
           Warn about catch handlers that do not catch via reference.  With
           -Wcatch-value=1 (or -Wcatch-value for short) warn about polymorphic
           class types that are caught by value.  With -Wcatch-value=2 warn
           about all class types that are caught by value. With
           -Wcatch-value=3 warn about all types that are not caught by
           reference. -Wcatch-value is enabled by -Wall.

       -Wconditionally-supported (C++ and Objective-C++ only)
           Warn for conditionally-supported (C++11 [intro.defs]) constructs.

       -Wno-delete-incomplete (C++ and Objective-C++ only)
           Do not warn when deleting a pointer to incomplete type, which may
           cause undefined behavior at runtime.  This warning is enabled by
           default.

       -Wextra-semi (C++, Objective-C++ only)
           Warn about redundant semicolons after in-class function
           definitions.

       -Wno-inaccessible-base (C++, Objective-C++ only)
           This option controls warnings when a base class is inaccessible in
           a class derived from it due to ambiguity.  The warning is enabled
           by default.  Note that the warning for ambiguous virtual bases is
           enabled by the -Wextra option.

                   struct A { int a; };

                   struct B : A { };

                   struct C : B, A { };

       -Wno-inherited-variadic-ctor
           Suppress warnings about use of C++11 inheriting constructors when
           the base class inherited from has a C variadic constructor; the
           warning is on by default because the ellipsis is not inherited.

       -Wno-invalid-offsetof (C++ and Objective-C++ only)
           Suppress warnings from applying the "offsetof" macro to a non-POD
           type.  According to the 2014 ISO C++ standard, applying "offsetof"
           to a non-standard-layout type is undefined.  In existing C++
           implementations, however, "offsetof" typically gives meaningful
           results.  This flag is for users who are aware that they are
           writing nonportable code and who have deliberately chosen to ignore
           the warning about it.

           The restrictions on "offsetof" may be relaxed in a future version
           of the C++ standard.

       -Wsized-deallocation (C++ and Objective-C++ only)
           Warn about a definition of an unsized deallocation function

                   void operator delete (void *) noexcept;
                   void operator delete[] (void *) noexcept;

           without a definition of the corresponding sized deallocation
           function

                   void operator delete (void *, std::size_t) noexcept;
                   void operator delete[] (void *, std::size_t) noexcept;

           or vice versa.  Enabled by -Wextra along with -fsized-deallocation.

       -Wsuggest-final-types
           Warn about types with virtual methods where code quality would be
           improved if the type were declared with the C++11 "final"
           specifier, or, if possible, declared in an anonymous namespace.
           This allows GCC to more aggressively devirtualize the polymorphic
           calls. This warning is more effective with link-time optimization,
           where the information about the class hierarchy graph is more
           complete.

       -Wsuggest-final-methods
           Warn about virtual methods where code quality would be improved if
           the method were declared with the C++11 "final" specifier, or, if
           possible, its type were declared in an anonymous namespace or with
           the "final" specifier.  This warning is more effective with link-
           time optimization, where the information about the class hierarchy
           graph is more complete. It is recommended to first consider
           suggestions of -Wsuggest-final-types and then rebuild with new
           annotations.

       -Wsuggest-override
           Warn about overriding virtual functions that are not marked with
           the "override" keyword.

       -Wuseless-cast (C++ and Objective-C++ only)
           Warn when an expression is casted to its own type.

       -Wno-conversion-null (C++ and Objective-C++ only)
           Do not warn for conversions between "NULL" and non-pointer types.
           -Wconversion-null is enabled by default.

   Options Controlling Objective-C and Objective-C++ Dialects
       (NOTE: This manual does not describe the Objective-C and Objective-C++
       languages themselves.

       This section describes the command-line options that are only
       meaningful for Objective-C and Objective-C++ programs.  You can also
       use most of the language-independent GNU compiler options.  For
       example, you might compile a file some_class.m like this:

               gcc -g -fgnu-runtime -O -c some_class.m

       In this example, -fgnu-runtime is an option meant only for Objective-C
       and Objective-C++ programs; you can use the other options with any
       language supported by GCC.

       Note that since Objective-C is an extension of the C language,
       Objective-C compilations may also use options specific to the C front-
       end (e.g., -Wtraditional).  Similarly, Objective-C++ compilations may
       use C++-specific options (e.g., -Wabi).

       Here is a list of options that are only for compiling Objective-C and
       Objective-C++ programs:

       -fconstant-string-class=class-name
           Use class-name as the name of the class to instantiate for each
           literal string specified with the syntax "@"..."".  The default
           class name is "NXConstantString" if the GNU runtime is being used,
           and "NSConstantString" if the NeXT runtime is being used (see
           below).  The -fconstant-cfstrings option, if also present,
           overrides the -fconstant-string-class setting and cause "@"...""
           literals to be laid out as constant CoreFoundation strings.

       -fgnu-runtime
           Generate object code compatible with the standard GNU Objective-C
           runtime.  This is the default for most types of systems.

       -fnext-runtime
           Generate output compatible with the NeXT runtime.  This is the
           default for NeXT-based systems, including Darwin and Mac OS X.  The
           macro "__NEXT_RUNTIME__" is predefined if (and only if) this option
           is used.

       -fno-nil-receivers
           Assume that all Objective-C message dispatches ("[receiver
           message:arg]") in this translation unit ensure that the receiver is
           not "nil".  This allows for more efficient entry points in the
           runtime to be used.  This option is only available in conjunction
           with the NeXT runtime and ABI version 0 or 1.

       -fobjc-abi-version=n
           Use version n of the Objective-C ABI for the selected runtime.
           This option is currently supported only for the NeXT runtime.  In
           that case, Version 0 is the traditional (32-bit) ABI without
           support for properties and other Objective-C 2.0 additions.
           Version 1 is the traditional (32-bit) ABI with support for
           properties and other Objective-C 2.0 additions.  Version 2 is the
           modern (64-bit) ABI.  If nothing is specified, the default is
           Version 0 on 32-bit target machines, and Version 2 on 64-bit target
           machines.

       -fobjc-call-cxx-cdtors
           For each Objective-C class, check if any of its instance variables
           is a C++ object with a non-trivial default constructor.  If so,
           synthesize a special "- (id) .cxx_construct" instance method which
           runs non-trivial default constructors on any such instance
           variables, in order, and then return "self".  Similarly, check if
           any instance variable is a C++ object with a non-trivial
           destructor, and if so, synthesize a special "- (void)
           .cxx_destruct" method which runs all such default destructors, in
           reverse order.

           The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods
           thusly generated only operate on instance variables declared in the
           current Objective-C class, and not those inherited from
           superclasses.  It is the responsibility of the Objective-C runtime
           to invoke all such methods in an object's inheritance hierarchy.
           The "- (id) .cxx_construct" methods are invoked by the runtime
           immediately after a new object instance is allocated; the "- (void)
           .cxx_destruct" methods are invoked immediately before the runtime
           deallocates an object instance.

           As of this writing, only the NeXT runtime on Mac OS X 10.4 and
           later has support for invoking the "- (id) .cxx_construct" and "-
           (void) .cxx_destruct" methods.

       -fobjc-direct-dispatch
           Allow fast jumps to the message dispatcher.  On Darwin this is
           accomplished via the comm page.

       -fobjc-exceptions
           Enable syntactic support for structured exception handling in
           Objective-C, similar to what is offered by C++.  This option is
           required to use the Objective-C keywords @try, @throw, @catch,
           @finally and @synchronized.  This option is available with both the
           GNU runtime and the NeXT runtime (but not available in conjunction
           with the NeXT runtime on Mac OS X 10.2 and earlier).

       -fobjc-gc
           Enable garbage collection (GC) in Objective-C and Objective-C++
           programs.  This option is only available with the NeXT runtime; the
           GNU runtime has a different garbage collection implementation that
           does not require special compiler flags.

       -fobjc-nilcheck
           For the NeXT runtime with version 2 of the ABI, check for a nil
           receiver in method invocations before doing the actual method call.
           This is the default and can be disabled using -fno-objc-nilcheck.
           Class methods and super calls are never checked for nil in this way
           no matter what this flag is set to.  Currently this flag does
           nothing when the GNU runtime, or an older version of the NeXT
           runtime ABI, is used.

       -fobjc-std=objc1
           Conform to the language syntax of Objective-C 1.0, the language
           recognized by GCC 4.0.  This only affects the Objective-C additions
           to the C/C++ language; it does not affect conformance to C/C++
           standards, which is controlled by the separate C/C++ dialect option
           flags.  When this option is used with the Objective-C or
           Objective-C++ compiler, any Objective-C syntax that is not
           recognized by GCC 4.0 is rejected.  This is useful if you need to
           make sure that your Objective-C code can be compiled with older
           versions of GCC.

       -freplace-objc-classes
           Emit a special marker instructing lldd(1) not to statically link in
           the resulting object file, and allow ddyylldd(1) to load it in at run
           time instead.  This is used in conjunction with the Fix-and-
           Continue debugging mode, where the object file in question may be
           recompiled and dynamically reloaded in the course of program
           execution, without the need to restart the program itself.
           Currently, Fix-and-Continue functionality is only available in
           conjunction with the NeXT runtime on Mac OS X 10.3 and later.

       -fzero-link
           When compiling for the NeXT runtime, the compiler ordinarily
           replaces calls to "objc_getClass("...")" (when the name of the
           class is known at compile time) with static class references that
           get initialized at load time, which improves run-time performance.
           Specifying the -fzero-link flag suppresses this behavior and causes
           calls to "objc_getClass("...")" to be retained.  This is useful in
           Zero-Link debugging mode, since it allows for individual class
           implementations to be modified during program execution.  The GNU
           runtime currently always retains calls to "objc_get_class("...")"
           regardless of command-line options.

       -fno-local-ivars
           By default instance variables in Objective-C can be accessed as if
           they were local variables from within the methods of the class
           they're declared in.  This can lead to shadowing between instance
           variables and other variables declared either locally inside a
           class method or globally with the same name.  Specifying the
           -fno-local-ivars flag disables this behavior thus avoiding variable
           shadowing issues.

       -fivar-visibility=[public|protected|private|package]
           Set the default instance variable visibility to the specified
           option so that instance variables declared outside the scope of any
           access modifier directives default to the specified visibility.

       -gen-decls
           Dump interface declarations for all classes seen in the source file
           to a file named sourcename.decl.

       -Wassign-intercept (Objective-C and Objective-C++ only)
           Warn whenever an Objective-C assignment is being intercepted by the
           garbage collector.

       -Wno-property-assign-default (Objective-C and Objective-C++ only)
           Do not warn if a property for an Objective-C object has no assign
           semantics specified.

       -Wno-protocol (Objective-C and Objective-C++ only)
           If a class is declared to implement a protocol, a warning is issued
           for every method in the protocol that is not implemented by the
           class.  The default behavior is to issue a warning for every method
           not explicitly implemented in the class, even if a method
           implementation is inherited from the superclass.  If you use the
           -Wno-protocol option, then methods inherited from the superclass
           are considered to be implemented, and no warning is issued for
           them.

       -Wselector (Objective-C and Objective-C++ only)
           Warn if multiple methods of different types for the same selector
           are found during compilation.  The check is performed on the list
           of methods in the final stage of compilation.  Additionally, a
           check is performed for each selector appearing in a
           "@selector(...)" expression, and a corresponding method for that
           selector has been found during compilation.  Because these checks
           scan the method table only at the end of compilation, these
           warnings are not produced if the final stage of compilation is not
           reached, for example because an error is found during compilation,
           or because the -fsyntax-only option is being used.

       -Wstrict-selector-match (Objective-C and Objective-C++ only)
           Warn if multiple methods with differing argument and/or return
           types are found for a given selector when attempting to send a
           message using this selector to a receiver of type "id" or "Class".
           When this flag is off (which is the default behavior), the compiler
           omits such warnings if any differences found are confined to types
           that share the same size and alignment.

       -Wundeclared-selector (Objective-C and Objective-C++ only)
           Warn if a "@selector(...)" expression referring to an undeclared
           selector is found.  A selector is considered undeclared if no
           method with that name has been declared before the "@selector(...)"
           expression, either explicitly in an @interface or @protocol
           declaration, or implicitly in an @implementation section.  This
           option always performs its checks as soon as a "@selector(...)"
           expression is found, while -Wselector only performs its checks in
           the final stage of compilation.  This also enforces the coding
           style convention that methods and selectors must be declared before
           being used.

       -print-objc-runtime-info
           Generate C header describing the largest structure that is passed
           by value, if any.

   Options to Control Diagnostic Messages Formatting
       Traditionally, diagnostic messages have been formatted irrespective of
       the output device's aspect (e.g. its width, ...).  You can use the
       options described below to control the formatting algorithm for
       diagnostic messages, e.g. how many characters per line, how often
       source location information should be reported.  Note that some
       language front ends may not honor these options.

       -fmessage-length=n
           Try to format error messages so that they fit on lines of about n
           characters.  If n is zero, then no line-wrapping is done; each
           error message appears on a single line.  This is the default for
           all front ends.

           Note - this option also affects the display of the #error and
           #warning pre-processor directives, and the deprecated
           function/type/variable attribute.  It does not however affect the
           pragma GCC warning and pragma GCC error pragmas.

       -fdiagnostics-show-location=once
           Only meaningful in line-wrapping mode.  Instructs the diagnostic
           messages reporter to emit source location information once; that
           is, in case the message is too long to fit on a single physical
           line and has to be wrapped, the source location won't be emitted
           (as prefix) again, over and over, in subsequent continuation lines.
           This is the default behavior.

       -fdiagnostics-show-location=every-line
           Only meaningful in line-wrapping mode.  Instructs the diagnostic
           messages reporter to emit the same source location information (as
           prefix) for physical lines that result from the process of breaking
           a message which is too long to fit on a single line.

       -fdiagnostics-color[=WHEN]
       -fno-diagnostics-color
           Use color in diagnostics.  WHEN is never, always, or auto.  The
           default depends on how the compiler has been configured, it can be
           any of the above WHEN options or also never if GCC_COLORS
           environment variable isn't present in the environment, and auto
           otherwise.  auto makes GCC use color only when the standard error
           is a terminal, and when not executing in an emacs shell.  The forms
           -fdiagnostics-color and -fno-diagnostics-color are aliases for
           -fdiagnostics-color=always and -fdiagnostics-color=never,
           respectively.

           The colors are defined by the environment variable GCC_COLORS.  Its
           value is a colon-separated list of capabilities and Select Graphic
           Rendition (SGR) substrings. SGR commands are interpreted by the
           terminal or terminal emulator.  (See the section in the
           documentation of your text terminal for permitted values and their
           meanings as character attributes.)  These substring values are
           integers in decimal representation and can be concatenated with
           semicolons.  Common values to concatenate include 1 for bold, 4 for
           underline, 5 for blink, 7 for inverse, 39 for default foreground
           color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode
           foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color
           modes foreground colors, 49 for default background color, 40 to 47
           for background colors, 100 to 107 for 16-color mode background
           colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes
           background colors.

           The default GCC_COLORS is

                   error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
                   quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\
                   diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
                   type-diff=01;32

           where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan,
           32 is green, 34 is blue, 01 is bold, and 31 is red.  Setting
           GCC_COLORS to the empty string disables colors.  Supported
           capabilities are as follows.

           "error="
               SGR substring for error: markers.

           "warning="
               SGR substring for warning: markers.

           "note="
               SGR substring for note: markers.

           "path="
               SGR substring for colorizing paths of control-flow events as
               printed via -fdiagnostics-path-format=, such as the identifiers
               of individual events and lines indicating interprocedural calls
               and returns.

           "range1="
               SGR substring for first additional range.

           "range2="
               SGR substring for second additional range.

           "locus="
               SGR substring for location information, file:line or
               file:line:column etc.

           "quote="
               SGR substring for information printed within quotes.

           "fixit-insert="
               SGR substring for fix-it hints suggesting text to be inserted
               or replaced.

           "fixit-delete="
               SGR substring for fix-it hints suggesting text to be deleted.

           "diff-filename="
               SGR substring for filename headers within generated patches.

           "diff-hunk="
               SGR substring for the starts of hunks within generated patches.

           "diff-delete="
               SGR substring for deleted lines within generated patches.

           "diff-insert="
               SGR substring for inserted lines within generated patches.

           "type-diff="
               SGR substring for highlighting mismatching types within
               template arguments in the C++ frontend.

       -fdiagnostics-urls[=WHEN]
           Use escape sequences to embed URLs in diagnostics.  For example,
           when -fdiagnostics-show-option emits text showing the command-line
           option controlling a diagnostic, embed a URL for documentation of
           that option.

           WHEN is never, always, or auto.  auto makes GCC use URL escape
           sequences only when the standard error is a terminal, and when not
           executing in an emacs shell or any graphical terminal which is
           known to be incompatible with this feature, see below.

           The default depends on how the compiler has been configured.  It
           can be any of the above WHEN options.

           GCC can also be configured (via the
           --with-diagnostics-urls=auto-if-env configure-time option) so that
           the default is affected by environment variables.  Under such a
           configuration, GCC defaults to using auto if either GCC_URLS or
           TERM_URLS environment variables are present and non-empty in the
           environment of the compiler, or never if neither are.

           However, even with -fdiagnostics-urls=always the behavior is
           dependent on those environment variables: If GCC_URLS is set to
           empty or no, do not embed URLs in diagnostics.  If set to st, URLs
           use ST escape sequences.  If set to bel, the default, URLs use BEL
           escape sequences.  Any other non-empty value enables the feature.
           If GCC_URLS is not set, use TERM_URLS as a fallback.  Note: ST is
           an ANSI escape sequence, string terminator ESC \, BEL is an ASCII
           character, CTRL-G that usually sounds like a beep.

           At this time GCC tries to detect also a few terminals that are
           known to not implement the URL feature, and have bugs or at least
           had bugs in some versions that are still in use, where the URL
           escapes are likely to misbehave, i.e. print garbage on the screen.
           That list is currently xfce4-terminal, certain known to be buggy
           gnome-terminal versions, the linux console, and mingw.  This check
           can be skipped with the -fdiagnostics-urls=always.

       -fno-diagnostics-show-option
           By default, each diagnostic emitted includes text indicating the
           command-line option that directly controls the diagnostic (if such
           an option is known to the diagnostic machinery).  Specifying the
           -fno-diagnostics-show-option flag suppresses that behavior.

       -fno-diagnostics-show-caret
           By default, each diagnostic emitted includes the original source
           line and a caret ^ indicating the column.  This option suppresses
           this information.  The source line is truncated to n characters, if
           the -fmessage-length=n option is given.  When the output is done to
           the terminal, the width is limited to the width given by the
           COLUMNS environment variable or, if not set, to the terminal width.

       -fno-diagnostics-show-labels
           By default, when printing source code (via
           -fdiagnostics-show-caret), diagnostics can label ranges of source
           code with pertinent information, such as the types of expressions:

                       printf ("foo %s bar", long_i + long_j);
                                    ~^       ~~~~~~~~~~~~~~~
                                     |              |
                                     char *         long int

           This option suppresses the printing of these labels (in the example
           above, the vertical bars and the "char *" and "long int" text).

       -fno-diagnostics-show-cwe
           Diagnostic messages can optionally have an associated
           @url{https://cwe.mitre.org/index.html, CWE} identifier.  GCC itself
           only provides such metadata for some of the -fanalyzer diagnostics.
           GCC plugins may also provide diagnostics with such metadata.  By
           default, if this information is present, it will be printed with
           the diagnostic.  This option suppresses the printing of this
           metadata.

       -fno-diagnostics-show-line-numbers
           By default, when printing source code (via
           -fdiagnostics-show-caret), a left margin is printed, showing line
           numbers.  This option suppresses this left margin.

       -fdiagnostics-minimum-margin-width=width
           This option controls the minimum width of the left margin printed
           by -fdiagnostics-show-line-numbers.  It defaults to 6.

       -fdiagnostics-parseable-fixits
           Emit fix-it hints in a machine-parseable format, suitable for
           consumption by IDEs.  For each fix-it, a line will be printed after
           the relevant diagnostic, starting with the string "fix-it:".  For
           example:

                   fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"

           The location is expressed as a half-open range, expressed as a
           count of bytes, starting at byte 1 for the initial column.  In the
           above example, bytes 3 through 20 of line 45 of "test.c" are to be
           replaced with the given string:

                   00000000011111111112222222222
                   12345678901234567890123456789
                     gtk_widget_showall (dlg);
                     ^^^^^^^^^^^^^^^^^^
                     gtk_widget_show_all

           The filename and replacement string escape backslash as "\\", tab
           as "\t", newline as "\n", double quotes as "\"", non-printable
           characters as octal (e.g. vertical tab as "\013").

           An empty replacement string indicates that the given range is to be
           removed.  An empty range (e.g. "45:3-45:3") indicates that the
           string is to be inserted at the given position.

       -fdiagnostics-generate-patch
           Print fix-it hints to stderr in unified diff format, after any
           diagnostics are printed.  For example:

                   --- test.c
                   +++ test.c
                   @ -42,5 +42,5 @

                    void show_cb(GtkDialog *dlg)
                    {
                   -  gtk_widget_showall(dlg);
                   +  gtk_widget_show_all(dlg);
                    }

           The diff may or may not be colorized, following the same rules as
           for diagnostics (see -fdiagnostics-color).

       -fdiagnostics-show-template-tree
           In the C++ frontend, when printing diagnostics showing mismatching
           template types, such as:

                     could not convert 'std::map<int, std::vector<double> >()'
                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

           the -fdiagnostics-show-template-tree flag enables printing a tree-
           like structure showing the common and differing parts of the types,
           such as:

                     map<
                       [...],
                       vector<
                         [double != float]>>

           The parts that differ are highlighted with color ("double" and
           "float" in this case).

       -fno-elide-type
           By default when the C++ frontend prints diagnostics showing
           mismatching template types, common parts of the types are printed
           as "[...]" to simplify the error message.  For example:

                     could not convert 'std::map<int, std::vector<double> >()'
                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

           Specifying the -fno-elide-type flag suppresses that behavior.  This
           flag also affects the output of the
           -fdiagnostics-show-template-tree flag.

       -fdiagnostics-path-format=KIND
           Specify how to print paths of control-flow events for diagnostics
           that have such a path associated with them.

           KIND is none, separate-events, or inline-events, the default.

           none means to not print diagnostic paths.

           separate-events means to print a separate "note" diagnostic for
           each event within the diagnostic.  For example:

                   test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter
                   test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL
                   test.c:27:3: note: (2) when 'i < count'
                   test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1

           inline-events means to print the events "inline" within the source
           code.  This view attempts to consolidate the events into runs of
           sufficiently-close events, printing them as labelled ranges within
           the source.

           For example, the same events as above might be printed as:

                     'test': events 1-3
                       |
                       |   25 |   list = PyList_New(0);
                       |      |          ^~~~~~~~~~~~~
                       |      |          |
                       |      |          (1) when 'PyList_New' fails, returning NULL
                       |   26 |
                       |   27 |   for (i = 0; i < count; i++) {
                       |      |   ~~~
                       |      |   |
                       |      |   (2) when 'i < count'
                       |   28 |     item = PyLong_FromLong(random());
                       |   29 |     PyList_Append(list, item);
                       |      |     ~~~~~~~~~~~~~~~~~~~~~~~~~
                       |      |     |
                       |      |     (3) when calling 'PyList_Append', passing NULL from (1) as argument 1
                       |

           Interprocedural control flow is shown by grouping the events by
           stack frame, and using indentation to show how stack frames are
           nested, pushed, and popped.

           For example:

                     'test': events 1-2
                       |
                       |  133 | {
                       |      | ^
                       |      | |
                       |      | (1) entering 'test'
                       |  134 |   boxed_int *obj = make_boxed_int (i);
                       |      |                    ~~~~~~~~~~~~~~~~~~
                       |      |                    |
                       |      |                    (2) calling 'make_boxed_int'
                       |
                       +--> 'make_boxed_int': events 3-4
                              |
                              |  120 | {
                              |      | ^
                              |      | |
                              |      | (3) entering 'make_boxed_int'
                              |  121 |   boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int));
                              |      |                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                              |      |                                    |
                              |      |                                    (4) calling 'wrapped_malloc'
                              |
                              +--> 'wrapped_malloc': events 5-6
                                     |
                                     |    7 | {
                                     |      | ^
                                     |      | |
                                     |      | (5) entering 'wrapped_malloc'
                                     |    8 |   return malloc (size);
                                     |      |          ~~~~~~~~~~~~~
                                     |      |          |
                                     |      |          (6) calling 'malloc'
                                     |
                       <-------------+
                       |
                    'test': event 7
                       |
                       |  138 |   free_boxed_int (obj);
                       |      |   ^~~~~~~~~~~~~~~~~~~~
                       |      |   |
                       |      |   (7) calling 'free_boxed_int'
                       |
                   (etc)

       -fdiagnostics-show-path-depths
           This option provides additional information when printing control-
           flow paths associated with a diagnostic.

           If this is option is provided then the stack depth will be printed
           for each run of events within
           -fdiagnostics-path-format=separate-events.

           This is intended for use by GCC developers and plugin developers
           when debugging diagnostics that report interprocedural control
           flow.

       -fno-show-column
           Do not print column numbers in diagnostics.  This may be necessary
           if diagnostics are being scanned by a program that does not
           understand the column numbers, such as dejagnu.

       -fdiagnostics-format=FORMAT
           Select a different format for printing diagnostics.  FORMAT is text
           or json.  The default is text.

           The json format consists of a top-level JSON array containing JSON
           objects representing the diagnostics.

           The JSON is emitted as one line, without formatting; the examples
           below have been formatted for clarity.

           Diagnostics can have child diagnostics.  For example, this error
           and note:

                   misleading-indentation.c:15:3: warning: this 'if' clause does not
                     guard... [-Wmisleading-indentation]
                      15 |   if (flag)
                         |   ^~
                   misleading-indentation.c:17:5: note: ...this statement, but the latter
                     is misleadingly indented as if it were guarded by the 'if'
                      17 |     y = 2;
                         |     ^

           might be printed in JSON form (after formatting) like this:

                   [
                       {
                           "kind": "warning",
                           "locations": [
                               {
                                   "caret": {
                                       "column": 3,
                                       "file": "misleading-indentation.c",
                                       "line": 15
                                   },
                                   "finish": {
                                       "column": 4,
                                       "file": "misleading-indentation.c",
                                       "line": 15
                                   }
                               }
                           ],
                           "message": "this \u2018if\u2019 clause does not guard...",
                           "option": "-Wmisleading-indentation",
                           "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation",
                           "children": [
                               {
                                   "kind": "note",
                                   "locations": [
                                       {
                                           "caret": {
                                               "column": 5,
                                               "file": "misleading-indentation.c",
                                               "line": 17
                                           }
                                       }
                                   ],
                                   "message": "...this statement, but the latter is ..."
                               }
                           ]
                       },
                       ...
                   ]

           where the "note" is a child of the "warning".

           A diagnostic has a "kind".  If this is "warning", then there is an
           "option" key describing the command-line option controlling the
           warning.

           A diagnostic can contain zero or more locations.  Each location has
           up to three positions within it: a "caret" position and optional
           "start" and "finish" positions.  A location can also have an
           optional "label" string.  For example, this error:

                   bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' {aka
                      'struct s'} and 'T' {aka 'struct t'})
                      64 |   return callee_4a () + callee_4b ();
                         |          ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
                         |          |              |
                         |          |              T {aka struct t}
                         |          S {aka struct s}

           has three locations.  Its primary location is at the "+" token at
           column 23.  It has two secondary locations, describing the left and
           right-hand sides of the expression, which have labels.  It might be
           printed in JSON form as:

                       {
                           "children": [],
                           "kind": "error",
                           "locations": [
                               {
                                   "caret": {
                                       "column": 23, "file": "bad-binary-ops.c", "line": 64
                                   }
                               },
                               {
                                   "caret": {
                                       "column": 10, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "finish": {
                                       "column": 21, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "label": "S {aka struct s}"
                               },
                               {
                                   "caret": {
                                       "column": 25, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "finish": {
                                       "column": 36, "file": "bad-binary-ops.c", "line": 64
                                   },
                                   "label": "T {aka struct t}"
                               }
                           ],
                           "message": "invalid operands to binary + ..."
                       }

           If a diagnostic contains fix-it hints, it has a "fixits" array,
           consisting of half-open intervals, similar to the output of
           -fdiagnostics-parseable-fixits.  For example, this diagnostic with
           a replacement fix-it hint:

                   demo.c:8:15: error: 'struct s' has no member named 'colour'; did you
                     mean 'color'?
                       8 |   return ptr->colour;
                         |               ^~~~~~
                         |               color

           might be printed in JSON form as:

                       {
                           "children": [],
                           "fixits": [
                               {
                                   "next": {
                                       "column": 21,
                                       "file": "demo.c",
                                       "line": 8
                                   },
                                   "start": {
                                       "column": 15,
                                       "file": "demo.c",
                                       "line": 8
                                   },
                                   "string": "color"
                               }
                           ],
                           "kind": "error",
                           "locations": [
                               {
                                   "caret": {
                                       "column": 15,
                                       "file": "demo.c",
                                       "line": 8
                                   },
                                   "finish": {
                                       "column": 20,
                                       "file": "demo.c",
                                       "line": 8
                                   }
                               }
                           ],
                           "message": "\u2018struct s\u2019 has no member named ..."
                       }

           where the fix-it hint suggests replacing the text from "start" up
           to but not including "next" with "string"'s value.  Deletions are
           expressed via an empty value for "string", insertions by having
           "start" equal "next".

           If the diagnostic has a path of control-flow events associated with
           it, it has a "path" array of objects representing the events.  Each
           event object has a "description" string, a "location" object, along
           with a "function" string and a "depth" number for representing
           interprocedural paths.  The "function" represents the current
           function at that event, and the "depth" represents the stack depth
           relative to some baseline: the higher, the more frames are within
           the stack.

           For example, the intraprocedural example shown for
           -fdiagnostics-path-format= might have this JSON for its path:

                       "path": [
                           {
                               "depth": 0,
                               "description": "when 'PyList_New' fails, returning NULL",
                               "function": "test",
                               "location": {
                                   "column": 10,
                                   "file": "test.c",
                                   "line": 25
                               }
                           },
                           {
                               "depth": 0,
                               "description": "when 'i < count'",
                               "function": "test",
                               "location": {
                                   "column": 3,
                                   "file": "test.c",
                                   "line": 27
                               }
                           },
                           {
                               "depth": 0,
                               "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1",
                               "function": "test",
                               "location": {
                                   "column": 5,
                                   "file": "test.c",
                                   "line": 29
                               }
                           }
                       ]

   Options to Request or Suppress Warnings
       Warnings are diagnostic messages that report constructions that are not
       inherently erroneous but that are risky or suggest there may have been
       an error.

       The following language-independent options do not enable specific
       warnings but control the kinds of diagnostics produced by GCC.

       -fsyntax-only
           Check the code for syntax errors, but don't do anything beyond
           that.

       -fmax-errors=n
           Limits the maximum number of error messages to n, at which point
           GCC bails out rather than attempting to continue processing the
           source code.  If n is 0 (the default), there is no limit on the
           number of error messages produced.  If -Wfatal-errors is also
           specified, then -Wfatal-errors takes precedence over this option.

       -w  Inhibit all warning messages.

       -Werror
           Make all warnings into errors.

       -Werror=
           Make the specified warning into an error.  The specifier for a
           warning is appended; for example -Werror=switch turns the warnings
           controlled by -Wswitch into errors.  This switch takes a negative
           form, to be used to negate -Werror for specific warnings; for
           example -Wno-error=switch makes -Wswitch warnings not be errors,
           even when -Werror is in effect.

           The warning message for each controllable warning includes the
           option that controls the warning.  That option can then be used
           with -Werror= and -Wno-error= as described above.  (Printing of the
           option in the warning message can be disabled using the
           -fno-diagnostics-show-option flag.)

           Note that specifying -Werror=foo automatically implies -Wfoo.
           However, -Wno-error=foo does not imply anything.

       -Wfatal-errors
           This option causes the compiler to abort compilation on the first
           error occurred rather than trying to keep going and printing
           further error messages.

       You can request many specific warnings with options beginning with -W,
       for example -Wimplicit to request warnings on implicit declarations.
       Each of these specific warning options also has a negative form
       beginning -Wno- to turn off warnings; for example, -Wno-implicit.  This
       manual lists only one of the two forms, whichever is not the default.
       For further language-specific options also refer to C++ Dialect Options
       and Objective-C and Objective-C++ Dialect Options.  Additional warnings
       can be produced by enabling the static analyzer;

       Some options, such as -Wall and -Wextra, turn on other options, such as
       -Wunused, which may turn on further options, such as -Wunused-value.
       The combined effect of positive and negative forms is that more
       specific options have priority over less specific ones, independently
       of their position in the command-line. For options of the same
       specificity, the last one takes effect. Options enabled or disabled via
       pragmas take effect as if they appeared at the end of the command-line.

       When an unrecognized warning option is requested (e.g.,
       -Wunknown-warning), GCC emits a diagnostic stating that the option is
       not recognized.  However, if the -Wno- form is used, the behavior is
       slightly different: no diagnostic is produced for -Wno-unknown-warning
       unless other diagnostics are being produced.  This allows the use of
       new -Wno- options with old compilers, but if something goes wrong, the
       compiler warns that an unrecognized option is present.

       The effectiveness of some warnings depends on optimizations also being
       enabled. For example -Wsuggest-final-types is more effective with link-
       time optimization and -Wmaybe-uninitialized does not warn at all unless
       optimization is enabled.

       -Wpedantic
       -pedantic
           Issue all the warnings demanded by strict ISO C and ISO C++; reject
           all programs that use forbidden extensions, and some other programs
           that do not follow ISO C and ISO C++.  For ISO C, follows the
           version of the ISO C standard specified by any -std option used.

           Valid ISO C and ISO C++ programs should compile properly with or
           without this option (though a rare few require -ansi or a -std
           option specifying the required version of ISO C).  However, without
           this option, certain GNU extensions and traditional C and C++
           features are supported as well.  With this option, they are
           rejected.

           -Wpedantic does not cause warning messages for use of the alternate
           keywords whose names begin and end with __.  This alternate format
           can also be used to disable warnings for non-ISO __intN types, i.e.
           __intN__.  Pedantic warnings are also disabled in the expression
           that follows "__extension__".  However, only system header files
           should use these escape routes; application programs should avoid
           them.

           Some users try to use -Wpedantic to check programs for strict ISO C
           conformance.  They soon find that it does not do quite what they
           want: it finds some non-ISO practices, but not all---only those for
           which ISO C requires a diagnostic, and some others for which
           diagnostics have been added.

           A feature to report any failure to conform to ISO C might be useful
           in some instances, but would require considerable additional work
           and would be quite different from -Wpedantic.  We don't have plans
           to support such a feature in the near future.

           Where the standard specified with -std represents a GNU extended
           dialect of C, such as gnu90 or gnu99, there is a corresponding base
           standard, the version of ISO C on which the GNU extended dialect is
           based.  Warnings from -Wpedantic are given where they are required
           by the base standard.  (It does not make sense for such warnings to
           be given only for features not in the specified GNU C dialect,
           since by definition the GNU dialects of C include all features the
           compiler supports with the given option, and there would be nothing
           to warn about.)

       -pedantic-errors
           Give an error whenever the base standard (see -Wpedantic) requires
           a diagnostic, in some cases where there is undefined behavior at
           compile-time and in some other cases that do not prevent
           compilation of programs that are valid according to the standard.
           This is not equivalent to -Werror=pedantic, since there are errors
           enabled by this option and not enabled by the latter and vice
           versa.

       -Wall
           This enables all the warnings about constructions that some users
           consider questionable, and that are easy to avoid (or modify to
           prevent the warning), even in conjunction with macros.  This also
           enables some language-specific warnings described in C++ Dialect
           Options and Objective-C and Objective-C++ Dialect Options.

           -Wall turns on the following warning flags:

           -Waddress -Warray-bounds=1 (only with -O2) -Wbool-compare
           -Wbool-operation -Wc++11-compat  -Wc++14-compat -Wcatch-value (C++
           and Objective-C++ only) -Wchar-subscripts -Wcomment
           -Wduplicate-decl-specifier (C and Objective-C only) -Wenum-compare
           (in C/ObjC; this is on by default in C++) -Wenum-conversion in
           C/ObjC; -Wformat -Wformat-overflow -Wformat-truncation
           -Wint-in-bool-context -Wimplicit (C and Objective-C only)
           -Wimplicit-int (C and Objective-C only)
           -Wimplicit-function-declaration (C and Objective-C only)
           -Winit-self (only for C++) -Wlogical-not-parentheses -Wmain (only
           for C/ObjC and unless -ffreestanding) -Wmaybe-uninitialized
           -Wmemset-elt-size -Wmemset-transposed-args -Wmisleading-indentation
           (only for C/C++) -Wmissing-attributes -Wmissing-braces (only for
           C/ObjC) -Wmultistatement-macros -Wnarrowing (only for C++)
           -Wnonnull -Wnonnull-compare -Wopenmp-simd -Wparentheses
           -Wpessimizing-move (only for C++) -Wpointer-sign -Wreorder
           -Wrestrict -Wreturn-type -Wsequence-point -Wsign-compare (only in
           C++) -Wsizeof-pointer-div -Wsizeof-pointer-memaccess
           -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch
           -Wtautological-compare -Wtrigraphs -Wuninitialized
           -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value
           -Wunused-variable -Wvolatile-register-var -Wzero-length-bounds

           Note that some warning flags are not implied by -Wall.  Some of
           them warn about constructions that users generally do not consider
           questionable, but which occasionally you might wish to check for;
           others warn about constructions that are necessary or hard to avoid
           in some cases, and there is no simple way to modify the code to
           suppress the warning. Some of them are enabled by -Wextra but many
           of them must be enabled individually.

       -Wextra
           This enables some extra warning flags that are not enabled by
           -Wall. (This option used to be called -W.  The older name is still
           supported, but the newer name is more descriptive.)

           -Wclobbered -Wcast-function-type -Wdeprecated-copy (C++ only)
           -Wempty-body -Wignored-qualifiers -Wimplicit-fallthrough=3
           -Wmissing-field-initializers -Wmissing-parameter-type (C only)
           -Wold-style-declaration (C only) -Woverride-init -Wsign-compare (C
           only) -Wstring-compare -Wredundant-move (only for C++)
           -Wtype-limits -Wuninitialized -Wshift-negative-value (in C++03 and
           in C99 and newer) -Wunused-parameter (only with -Wunused or -Wall)
           -Wunused-but-set-parameter (only with -Wunused or -Wall)

           The option -Wextra also prints warning messages for the following
           cases:

           *   A pointer is compared against integer zero with "<", "<=", ">",
               or ">=".

           *   (C++ only) An enumerator and a non-enumerator both appear in a
               conditional expression.

           *   (C++ only) Ambiguous virtual bases.

           *   (C++ only) Subscripting an array that has been declared
               "register".

           *   (C++ only) Taking the address of a variable that has been
               declared "register".

           *   (C++ only) A base class is not initialized in the copy
               constructor of a derived class.

       -Wabi (C, Objective-C, C++ and Objective-C++ only)
           Warn about code affected by ABI changes.  This includes code that
           may not be compatible with the vendor-neutral C++ ABI as well as
           the psABI for the particular target.

           Since G++ now defaults to updating the ABI with each major release,
           normally -Wabi warns only about C++ ABI compatibility problems if
           there is a check added later in a release series for an ABI issue
           discovered since the initial release.  -Wabi warns about more
           things if an older ABI version is selected (with -fabi-version=n).

           -Wabi can also be used with an explicit version number to warn
           about C++ ABI compatibility with a particular -fabi-version level,
           e.g. -Wabi=2 to warn about changes relative to -fabi-version=2.

           If an explicit version number is provided and -fabi-compat-version
           is not specified, the version number from this option is used for
           compatibility aliases.  If no explicit version number is provided
           with this option, but -fabi-compat-version is specified, that
           version number is used for C++ ABI warnings.

           Although an effort has been made to warn about all such cases,
           there are probably some cases that are not warned about, even
           though G++ is generating incompatible code.  There may also be
           cases where warnings are emitted even though the code that is
           generated is compatible.

           You should rewrite your code to avoid these warnings if you are
           concerned about the fact that code generated by G++ may not be
           binary compatible with code generated by other compilers.

           Known incompatibilities in -fabi-version=2 (which was the default
           from GCC 3.4 to 4.9) include:

           *   A template with a non-type template parameter of reference type
               was mangled incorrectly:

                       extern int N;
                       template <int &> struct S {};
                       void n (S<N>) {2}

               This was fixed in -fabi-version=3.

           *   SIMD vector types declared using "__attribute ((vector_size))"
               were mangled in a non-standard way that does not allow for
               overloading of functions taking vectors of different sizes.

               The mangling was changed in -fabi-version=4.

           *   "__attribute ((const))" and "noreturn" were mangled as type
               qualifiers, and "decltype" of a plain declaration was folded
               away.

               These mangling issues were fixed in -fabi-version=5.

           *   Scoped enumerators passed as arguments to a variadic function
               are promoted like unscoped enumerators, causing "va_arg" to
               complain.  On most targets this does not actually affect the
               parameter passing ABI, as there is no way to pass an argument
               smaller than "int".

               Also, the ABI changed the mangling of template argument packs,
               "const_cast", "static_cast", prefix increment/decrement, and a
               class scope function used as a template argument.

               These issues were corrected in -fabi-version=6.

           *   Lambdas in default argument scope were mangled incorrectly, and
               the ABI changed the mangling of "nullptr_t".

               These issues were corrected in -fabi-version=7.

           *   When mangling a function type with function-cv-qualifiers, the
               un-qualified function type was incorrectly treated as a
               substitution candidate.

               This was fixed in -fabi-version=8, the default for GCC 5.1.

           *   "decltype(nullptr)" incorrectly had an alignment of 1, leading
               to unaligned accesses.  Note that this did not affect the ABI
               of a function with a "nullptr_t" parameter, as parameters have
               a minimum alignment.

               This was fixed in -fabi-version=9, the default for GCC 5.2.

           *   Target-specific attributes that affect the identity of a type,
               such as ia32 calling conventions on a function type (stdcall,
               regparm, etc.), did not affect the mangled name, leading to
               name collisions when function pointers were used as template
               arguments.

               This was fixed in -fabi-version=10, the default for GCC 6.1.

           This option also enables warnings about psABI-related changes.  The
           known psABI changes at this point include:

           *   For SysV/x86-64, unions with "long double" members are passed
               in memory as specified in psABI.  Prior to GCC 4.4, this was
               not the case.  For example:

                       union U {
                         long double ld;
                         int i;
                       };

               "union U" is now always passed in memory.

       -Wchar-subscripts
           Warn if an array subscript has type "char".  This is a common cause
           of error, as programmers often forget that this type is signed on
           some machines.  This warning is enabled by -Wall.

       -Wno-coverage-mismatch
           Warn if feedback profiles do not match when using the -fprofile-use
           option.  If a source file is changed between compiling with
           -fprofile-generate and with -fprofile-use, the files with the
           profile feedback can fail to match the source file and GCC cannot
           use the profile feedback information.  By default, this warning is
           enabled and is treated as an error.  -Wno-coverage-mismatch can be
           used to disable the warning or -Wno-error=coverage-mismatch can be
           used to disable the error.  Disabling the error for this warning
           can result in poorly optimized code and is useful only in the case
           of very minor changes such as bug fixes to an existing code-base.
           Completely disabling the warning is not recommended.

       -Wno-cpp
           (C, Objective-C, C++, Objective-C++ and Fortran only) Suppress
           warning messages emitted by "#warning" directives.

       -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
           Give a warning when a value of type "float" is implicitly promoted
           to "double".  CPUs with a 32-bit "single-precision" floating-point
           unit implement "float" in hardware, but emulate "double" in
           software.  On such a machine, doing computations using "double"
           values is much more expensive because of the overhead required for
           software emulation.

           It is easy to accidentally do computations with "double" because
           floating-point literals are implicitly of type "double".  For
           example, in:

                   float area(float radius)
                   {
                      return 3.14159 * radius * radius;
                   }

           the compiler performs the entire computation with "double" because
           the floating-point literal is a "double".

       -Wduplicate-decl-specifier (C and Objective-C only)
           Warn if a declaration has duplicate "const", "volatile", "restrict"
           or "_Atomic" specifier.  This warning is enabled by -Wall.

       -Wformat
       -Wformat=n
           Check calls to "printf" and "scanf", etc., to make sure that the
           arguments supplied have types appropriate to the format string
           specified, and that the conversions specified in the format string
           make sense.  This includes standard functions, and others specified
           by format attributes, in the "printf", "scanf", "strftime" and
           "strfmon" (an X/Open extension, not in the C standard) families (or
           other target-specific families).  Which functions are checked
           without format attributes having been specified depends on the
           standard version selected, and such checks of functions without the
           attribute specified are disabled by -ffreestanding or -fno-builtin.

           The formats are checked against the format features supported by
           GNU libc version 2.2.  These include all ISO C90 and C99 features,
           as well as features from the Single Unix Specification and some BSD
           and GNU extensions.  Other library implementations may not support
           all these features; GCC does not support warning about features
           that go beyond a particular library's limitations.  However, if
           -Wpedantic is used with -Wformat, warnings are given about format
           features not in the selected standard version (but not for
           "strfmon" formats, since those are not in any version of the C
           standard).

           -Wformat=1
           -Wformat
               Option -Wformat is equivalent to -Wformat=1, and -Wno-format is
               equivalent to -Wformat=0.  Since -Wformat also checks for null
               format arguments for several functions, -Wformat also implies
               -Wnonnull.  Some aspects of this level of format checking can
               be disabled by the options: -Wno-format-contains-nul,
               -Wno-format-extra-args, and -Wno-format-zero-length.  -Wformat
               is enabled by -Wall.

           -Wformat=2
               Enable -Wformat plus additional format checks.  Currently
               equivalent to -Wformat -Wformat-nonliteral -Wformat-security
               -Wformat-y2k.

       -Wno-format-contains-nul
           If -Wformat is specified, do not warn about format strings that
           contain NUL bytes.

       -Wno-format-extra-args
           If -Wformat is specified, do not warn about excess arguments to a
           "printf" or "scanf" format function.  The C standard specifies that
           such arguments are ignored.

           Where the unused arguments lie between used arguments that are
           specified with $ operand number specifications, normally warnings
           are still given, since the implementation could not know what type
           to pass to "va_arg" to skip the unused arguments.  However, in the
           case of "scanf" formats, this option suppresses the warning if the
           unused arguments are all pointers, since the Single Unix
           Specification says that such unused arguments are allowed.

       -Wformat-overflow
       -Wformat-overflow=level
           Warn about calls to formatted input/output functions such as
           "sprintf" and "vsprintf" that might overflow the destination
           buffer.  When the exact number of bytes written by a format
           directive cannot be determined at compile-time it is estimated
           based on heuristics that depend on the level argument and on
           optimization.  While enabling optimization will in most cases
           improve the accuracy of the warning, it may also result in false
           positives.

           -Wformat-overflow
           -Wformat-overflow=1
               Level 1 of -Wformat-overflow enabled by -Wformat employs a
               conservative approach that warns only about calls that most
               likely overflow the buffer.  At this level, numeric arguments
               to format directives with unknown values are assumed to have
               the value of one, and strings of unknown length to be empty.
               Numeric arguments that are known to be bounded to a subrange of
               their type, or string arguments whose output is bounded either
               by their directive's precision or by a finite set of string
               literals, are assumed to take on the value within the range
               that results in the most bytes on output.  For example, the
               call to "sprintf" below is diagnosed because even with both a
               and b equal to zero, the terminating NUL character ('\0')
               appended by the function to the destination buffer will be
               written past its end.  Increasing the size of the buffer by a
               single byte is sufficient to avoid the warning, though it may
               not be sufficient to avoid the overflow.

                       void f (int a, int b)
                       {
                         char buf [13];
                         sprintf (buf, "a = %i, b = %i\n", a, b);
                       }

           -Wformat-overflow=2
               Level 2 warns also about calls that might overflow the
               destination buffer given an argument of sufficient length or
               magnitude.  At level 2, unknown numeric arguments are assumed
               to have the minimum representable value for signed types with a
               precision greater than 1, and the maximum representable value
               otherwise.  Unknown string arguments whose length cannot be
               assumed to be bounded either by the directive's precision, or
               by a finite set of string literals they may evaluate to, or the
               character array they may point to, are assumed to be 1
               character long.

               At level 2, the call in the example above is again diagnosed,
               but this time because with a equal to a 32-bit "INT_MIN" the
               first %i directive will write some of its digits beyond the end
               of the destination buffer.  To make the call safe regardless of
               the values of the two variables, the size of the destination
               buffer must be increased to at least 34 bytes.  GCC includes
               the minimum size of the buffer in an informational note
               following the warning.

               An alternative to increasing the size of the destination buffer
               is to constrain the range of formatted values.  The maximum
               length of string arguments can be bounded by specifying the
               precision in the format directive.  When numeric arguments of
               format directives can be assumed to be bounded by less than the
               precision of their type, choosing an appropriate length
               modifier to the format specifier will reduce the required
               buffer size.  For example, if a and b in the example above can
               be assumed to be within the precision of the "short int" type
               then using either the %hi format directive or casting the
               argument to "short" reduces the maximum required size of the
               buffer to 24 bytes.

                       void f (int a, int b)
                       {
                         char buf [23];
                         sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
                       }

       -Wno-format-zero-length
           If -Wformat is specified, do not warn about zero-length formats.
           The C standard specifies that zero-length formats are allowed.

       -Wformat-nonliteral
           If -Wformat is specified, also warn if the format string is not a
           string literal and so cannot be checked, unless the format function
           takes its format arguments as a "va_list".

       -Wformat-security
           If -Wformat is specified, also warn about uses of format functions
           that represent possible security problems.  At present, this warns
           about calls to "printf" and "scanf" functions where the format
           string is not a string literal and there are no format arguments,
           as in "printf (foo);".  This may be a security hole if the format
           string came from untrusted input and contains %n.  (This is
           currently a subset of what -Wformat-nonliteral warns about, but in
           future warnings may be added to -Wformat-security that are not
           included in -Wformat-nonliteral.)

       -Wformat-signedness
           If -Wformat is specified, also warn if the format string requires
           an unsigned argument and the argument is signed and vice versa.

       -Wformat-truncation
       -Wformat-truncation=level
           Warn about calls to formatted input/output functions such as
           "snprintf" and "vsnprintf" that might result in output truncation.
           When the exact number of bytes written by a format directive cannot
           be determined at compile-time it is estimated based on heuristics
           that depend on the level argument and on optimization.  While
           enabling optimization will in most cases improve the accuracy of
           the warning, it may also result in false positives.  Except as
           noted otherwise, the option uses the same logic -Wformat-overflow.

           -Wformat-truncation
           -Wformat-truncation=1
               Level 1 of -Wformat-truncation enabled by -Wformat employs a
               conservative approach that warns only about calls to bounded
               functions whose return value is unused and that will most
               likely result in output truncation.

           -Wformat-truncation=2
               Level 2 warns also about calls to bounded functions whose
               return value is used and that might result in truncation given
               an argument of sufficient length or magnitude.

       -Wformat-y2k
           If -Wformat is specified, also warn about "strftime" formats that
           may yield only a two-digit year.

       -Wnonnull
           Warn about passing a null pointer for arguments marked as requiring
           a non-null value by the "nonnull" function attribute.

           -Wnonnull is included in -Wall and -Wformat.  It can be disabled
           with the -Wno-nonnull option.

       -Wnonnull-compare
           Warn when comparing an argument marked with the "nonnull" function
           attribute against null inside the function.

           -Wnonnull-compare is included in -Wall.  It can be disabled with
           the -Wno-nonnull-compare option.

       -Wnull-dereference
           Warn if the compiler detects paths that trigger erroneous or
           undefined behavior due to dereferencing a null pointer.  This
           option is only active when -fdelete-null-pointer-checks is active,
           which is enabled by optimizations in most targets.  The precision
           of the warnings depends on the optimization options used.

       -Winit-self (C, C++, Objective-C and Objective-C++ only)
           Warn about uninitialized variables that are initialized with
           themselves.  Note this option can only be used with the
           -Wuninitialized option.

           For example, GCC warns about "i" being uninitialized in the
           following snippet only when -Winit-self has been specified:

                   int f()
                   {
                     int i = i;
                     return i;
                   }

           This warning is enabled by -Wall in C++.

       -Wno-implicit-int (C and Objective-C only)
           This option controls warnings when a declaration does not specify a
           type.  This warning is enabled by default in C99 and later dialects
           of C, and also by -Wall.

       -Wno-implicit-function-declaration (C and Objective-C only)
           This option controls warnings when a function is used before being
           declared.  This warning is enabled by default in C99 and later
           dialects of C, and also by -Wall.  The warning is made into an
           error by -pedantic-errors.

       -Wimplicit (C and Objective-C only)
           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This
           warning is enabled by -Wall.

       -Wimplicit-fallthrough
           -Wimplicit-fallthrough is the same as -Wimplicit-fallthrough=3 and
           -Wno-implicit-fallthrough is the same as -Wimplicit-fallthrough=0.

       -Wimplicit-fallthrough=n
           Warn when a switch case falls through.  For example:

                   switch (cond)
                     {
                     case 1:
                       a = 1;
                       break;
                     case 2:
                       a = 2;
                     case 3:
                       a = 3;
                       break;
                     }

           This warning does not warn when the last statement of a case cannot
           fall through, e.g. when there is a return statement or a call to
           function declared with the noreturn attribute.
           -Wimplicit-fallthrough= also takes into account control flow
           statements, such as ifs, and only warns when appropriate.  E.g.

                   switch (cond)
                     {
                     case 1:
                       if (i > 3) {
                         bar (5);
                         break;
                       } else if (i < 1) {
                         bar (0);
                       } else
                         return;
                     default:
                       ...
                     }

           Since there are occasions where a switch case fall through is
           desirable, GCC provides an attribute, "__attribute__
           ((fallthrough))", that is to be used along with a null statement to
           suppress this warning that would normally occur:

                   switch (cond)
                     {
                     case 1:
                       bar (0);
                       __attribute__ ((fallthrough));
                     default:
                       ...
                     }

           C++17 provides a standard way to suppress the
           -Wimplicit-fallthrough warning using "[[fallthrough]];" instead of
           the GNU attribute.  In C++11 or C++14 users can use
           "[[gnu::fallthrough]];", which is a GNU extension.  Instead of
           these attributes, it is also possible to add a fallthrough comment
           to silence the warning.  The whole body of the C or C++ style
           comment should match the given regular expressions listed below.
           The option argument n specifies what kind of comments are accepted:

           *<-Wimplicit-fallthrough=0 disables the warning altogether.>
           *<-Wimplicit-fallthrough=1 matches ".*" regular>
               expression, any comment is used as fallthrough comment.

           *<-Wimplicit-fallthrough=2 case insensitively matches>
               ".*falls?[ \t-]*thr(ough|u).*" regular expression.

           *<-Wimplicit-fallthrough=3 case sensitively matches one of the>
               following regular expressions:

               *<"-fallthrough">
               *<"@fallthrough@">
               *<"lint -fallthrough[ \t]*">
               *<"[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S |
               |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?">
               *<"[ \t.!]*(Else,? |Intentional(ly)? )?Fall((s |
               |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?">
               *<"[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s |
               |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?">
           *<-Wimplicit-fallthrough=4 case sensitively matches one of the>
               following regular expressions:

               *<"-fallthrough">
               *<"@fallthrough@">
               *<"lint -fallthrough[ \t]*">
               *<"[ \t]*FALLTHR(OUGH|U)[ \t]*">
           *<-Wimplicit-fallthrough=5 doesn't recognize any comments as>
               fallthrough comments, only attributes disable the warning.

           The comment needs to be followed after optional whitespace and
           other comments by "case" or "default" keywords or by a user label
           that precedes some "case" or "default" label.

                   switch (cond)
                     {
                     case 1:
                       bar (0);
                       /* FALLTHRU */
                     default:
                       ...
                     }

           The -Wimplicit-fallthrough=3 warning is enabled by -Wextra.

       -Wno-if-not-aligned (C, C++, Objective-C and Objective-C++ only)
           Control if warnings triggered by the "warn_if_not_aligned"
           attribute should be issued.  These warnings are enabled by default.

       -Wignored-qualifiers (C and C++ only)
           Warn if the return type of a function has a type qualifier such as
           "const".  For ISO C such a type qualifier has no effect, since the
           value returned by a function is not an lvalue.  For C++, the
           warning is only emitted for scalar types or "void".  ISO C
           prohibits qualified "void" return types on function definitions, so
           such return types always receive a warning even without this
           option.

           This warning is also enabled by -Wextra.

       -Wno-ignored-attributes (C and C++ only)
           This option controls warnings when an attribute is ignored.  This
           is different from the -Wattributes option in that it warns whenever
           the compiler decides to drop an attribute, not that the attribute
           is either unknown, used in a wrong place, etc.  This warning is
           enabled by default.

       -Wmain
           Warn if the type of "main" is suspicious.  "main" should be a
           function with external linkage, returning int, taking either zero
           arguments, two, or three arguments of appropriate types.  This
           warning is enabled by default in C++ and is enabled by either -Wall
           or -Wpedantic.

       -Wmisleading-indentation (C and C++ only)
           Warn when the indentation of the code does not reflect the block
           structure.  Specifically, a warning is issued for "if", "else",
           "while", and "for" clauses with a guarded statement that does not
           use braces, followed by an unguarded statement with the same
           indentation.

           In the following example, the call to "bar" is misleadingly
           indented as if it were guarded by the "if" conditional.

                     if (some_condition ())
                       foo ();
                       bar ();  /* Gotcha: this is not guarded by the "if".  */

           In the case of mixed tabs and spaces, the warning uses the
           -ftabstop= option to determine if the statements line up
           (defaulting to 8).

           The warning is not issued for code involving multiline preprocessor
           logic such as the following example.

                     if (flagA)
                       foo (0);
                   #if SOME_CONDITION_THAT_DOES_NOT_HOLD
                     if (flagB)
                   #endif
                       foo (1);

           The warning is not issued after a "#line" directive, since this
           typically indicates autogenerated code, and no assumptions can be
           made about the layout of the file that the directive references.

           This warning is enabled by -Wall in C and C++.

       -Wmissing-attributes
           Warn when a declaration of a function is missing one or more
           attributes that a related function is declared with and whose
           absence may adversely affect the correctness or efficiency of
           generated code.  For example, the warning is issued for
           declarations of aliases that use attributes to specify less
           restrictive requirements than those of their targets.  This
           typically represents a potential optimization opportunity.  By
           contrast, the -Wattribute-alias=2 option controls warnings issued
           when the alias is more restrictive than the target, which could
           lead to incorrect code generation.  Attributes considered include
           "alloc_align", "alloc_size", "cold", "const", "hot", "leaf",
           "malloc", "nonnull", "noreturn", "nothrow", "pure",
           "returns_nonnull", and "returns_twice".

           In C++, the warning is issued when an explicit specialization of a
           primary template declared with attribute "alloc_align",
           "alloc_size", "assume_aligned", "format", "format_arg", "malloc",
           or "nonnull" is declared without it.  Attributes "deprecated",
           "error", and "warning" suppress the warning..

           You can use the "copy" attribute to apply the same set of
           attributes to a declaration as that on another declaration without
           explicitly enumerating the attributes. This attribute can be
           applied to declarations of functions, variables, or types.

           -Wmissing-attributes is enabled by -Wall.

           For example, since the declaration of the primary function template
           below makes use of both attribute "malloc" and "alloc_size" the
           declaration of the explicit specialization of the template is
           diagnosed because it is missing one of the attributes.

                   template <class T>
                   T* __attribute__ ((malloc, alloc_size (1)))
                   allocate (size_t);

                   template <>
                   void* __attribute__ ((malloc))   // missing alloc_size
                   allocate<void> (size_t);

       -Wmissing-braces
           Warn if an aggregate or union initializer is not fully bracketed.
           In the following example, the initializer for "a" is not fully
           bracketed, but that for "b" is fully bracketed.

                   int a[2][2] = { 0, 1, 2, 3 };
                   int b[2][2] = { { 0, 1 }, { 2, 3 } };

           This warning is enabled by -Wall.

       -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
           Warn if a user-supplied include directory does not exist.

       -Wno-missing-profile
           This option controls warnings if feedback profiles are missing when
           using the -fprofile-use option.  This option diagnoses those cases
           where a new function or a new file is added between compiling with
           -fprofile-generate and with -fprofile-use, without regenerating the
           profiles.  In these cases, the profile feedback data files do not
           contain any profile feedback information for the newly added
           function or file respectively.  Also, in the case when profile
           count data (.gcda) files are removed, GCC cannot use any profile
           feedback information.  In all these cases, warnings are issued to
           inform you that a profile generation step is due.  Ignoring the
           warning can result in poorly optimized code.  -Wno-missing-profile
           can be used to disable the warning, but this is not recommended and
           should be done only when non-existent profile data is justified.

       -Wmultistatement-macros
           Warn about unsafe multiple statement macros that appear to be
           guarded by a clause such as "if", "else", "for", "switch", or
           "while", in which only the first statement is actually guarded
           after the macro is expanded.

           For example:

                   #define DOIT x++; y++
                   if (c)
                     DOIT;

           will increment "y" unconditionally, not just when "c" holds.  The
           can usually be fixed by wrapping the macro in a do-while loop:

                   #define DOIT do { x++; y++; } while (0)
                   if (c)
                     DOIT;

           This warning is enabled by -Wall in C and C++.

       -Wparentheses
           Warn if parentheses are omitted in certain contexts, such as when
           there is an assignment in a context where a truth value is
           expected, or when operators are nested whose precedence people
           often get confused about.

           Also warn if a comparison like "x<=y<=z" appears; this is
           equivalent to "(x<=y ? 1 : 0) <= z", which is a different
           interpretation from that of ordinary mathematical notation.

           Also warn for dangerous uses of the GNU extension to "?:" with
           omitted middle operand. When the condition in the "?": operator is
           a boolean expression, the omitted value is always 1.  Often
           programmers expect it to be a value computed inside the conditional
           expression instead.

           For C++ this also warns for some cases of unnecessary parentheses
           in declarations, which can indicate an attempt at a function call
           instead of a declaration:

                   {
                     // Declares a local variable called mymutex.
                     std::unique_lock<std::mutex> (mymutex);
                     // User meant std::unique_lock<std::mutex> lock (mymutex);
                   }

           This warning is enabled by -Wall.

       -Wsequence-point
           Warn about code that may have undefined semantics because of
           violations of sequence point rules in the C and C++ standards.

           The C and C++ standards define the order in which expressions in a
           C/C++ program are evaluated in terms of sequence points, which
           represent a partial ordering between the execution of parts of the
           program: those executed before the sequence point, and those
           executed after it.  These occur after the evaluation of a full
           expression (one which is not part of a larger expression), after
           the evaluation of the first operand of a "&&", "||", "? :" or ","
           (comma) operator, before a function is called (but after the
           evaluation of its arguments and the expression denoting the called
           function), and in certain other places.  Other than as expressed by
           the sequence point rules, the order of evaluation of subexpressions
           of an expression is not specified.  All these rules describe only a
           partial order rather than a total order, since, for example, if two
           functions are called within one expression with no sequence point
           between them, the order in which the functions are called is not
           specified.  However, the standards committee have ruled that
           function calls do not overlap.

           It is not specified when between sequence points modifications to
           the values of objects take effect.  Programs whose behavior depends
           on this have undefined behavior; the C and C++ standards specify
           that "Between the previous and next sequence point an object shall
           have its stored value modified at most once by the evaluation of an
           expression.  Furthermore, the prior value shall be read only to
           determine the value to be stored.".  If a program breaks these
           rules, the results on any particular implementation are entirely
           unpredictable.

           Examples of code with undefined behavior are "a = a++;", "a[n] =
           b[n++]" and "a[i++] = i;".  Some more complicated cases are not
           diagnosed by this option, and it may give an occasional false
           positive result, but in general it has been found fairly effective
           at detecting this sort of problem in programs.

           The C++17 standard will define the order of evaluation of operands
           in more cases: in particular it requires that the right-hand side
           of an assignment be evaluated before the left-hand side, so the
           above examples are no longer undefined.  But this option will still
           warn about them, to help people avoid writing code that is
           undefined in C and earlier revisions of C++.

           The standard is worded confusingly, therefore there is some debate
           over the precise meaning of the sequence point rules in subtle
           cases.  Links to discussions of the problem, including proposed
           formal definitions, may be found on the GCC readings page, at
           <http://gcc.gnu.org/readings.html>.

           This warning is enabled by -Wall for C and C++.

       -Wno-return-local-addr
           Do not warn about returning a pointer (or in C++, a reference) to a
           variable that goes out of scope after the function returns.

       -Wreturn-type
           Warn whenever a function is defined with a return type that
           defaults to "int".  Also warn about any "return" statement with no
           return value in a function whose return type is not "void" (falling
           off the end of the function body is considered returning without a
           value).

           For C only, warn about a "return" statement with an expression in a
           function whose return type is "void", unless the expression type is
           also "void".  As a GNU extension, the latter case is accepted
           without a warning unless -Wpedantic is used.  Attempting to use the
           return value of a non-"void" function other than "main" that flows
           off the end by reaching the closing curly brace that terminates the
           function is undefined.

           Unlike in C, in C++, flowing off the end of a non-"void" function
           other than "main" results in undefined behavior even when the value
           of the function is not used.

           This warning is enabled by default in C++ and by -Wall otherwise.

       -Wno-shift-count-negative
           Controls warnings if a shift count is negative.  This warning is
           enabled by default.

       -Wno-shift-count-overflow
           Controls warnings if a shift count is greater than or equal to the
           bit width of the type.  This warning is enabled by default.

       -Wshift-negative-value
           Warn if left shifting a negative value.  This warning is enabled by
           -Wextra in C99 and C++11 modes (and newer).

       -Wno-shift-overflow
       -Wshift-overflow=n
           These options control warnings about left shift overflows.

           -Wshift-overflow=1
               This is the warning level of -Wshift-overflow and is enabled by
               default in C99 and C++11 modes (and newer).  This warning level
               does not warn about left-shifting 1 into the sign bit.
               (However, in C, such an overflow is still rejected in contexts
               where an integer constant expression is required.)  No warning
               is emitted in C++2A mode (and newer), as signed left shifts
               always wrap.

           -Wshift-overflow=2
               This warning level also warns about left-shifting 1 into the
               sign bit, unless C++14 mode (or newer) is active.

       -Wswitch
           Warn whenever a "switch" statement has an index of enumerated type
           and lacks a "case" for one or more of the named codes of that
           enumeration.  (The presence of a "default" label prevents this
           warning.)  "case" labels outside the enumeration range also provoke
           warnings when this option is used (even if there is a "default"
           label).  This warning is enabled by -Wall.

       -Wswitch-default
           Warn whenever a "switch" statement does not have a "default" case.

       -Wswitch-enum
           Warn whenever a "switch" statement has an index of enumerated type
           and lacks a "case" for one or more of the named codes of that
           enumeration.  "case" labels outside the enumeration range also
           provoke warnings when this option is used.  The only difference
           between -Wswitch and this option is that this option gives a
           warning about an omitted enumeration code even if there is a
           "default" label.

       -Wno-switch-bool
           Do not warn when a "switch" statement has an index of boolean type
           and the case values are outside the range of a boolean type.  It is
           possible to suppress this warning by casting the controlling
           expression to a type other than "bool".  For example:

                   switch ((int) (a == 4))
                     {
                     ...
                     }

           This warning is enabled by default for C and C++ programs.

       -Wno-switch-outside-range
           This option controls warnings when a "switch" case has a value that
           is outside of its respective type range.  This warning is enabled
           by default for C and C++ programs.

       -Wno-switch-unreachable
           Do not warn when a "switch" statement contains statements between
           the controlling expression and the first case label, which will
           never be executed.  For example:

                   switch (cond)
                     {
                      i = 15;
                     ...
                      case 5:
                     ...
                     }

           -Wswitch-unreachable does not warn if the statement between the
           controlling expression and the first case label is just a
           declaration:

                   switch (cond)
                     {
                      int i;
                     ...
                      case 5:
                      i = 5;
                     ...
                     }

           This warning is enabled by default for C and C++ programs.

       -Wsync-nand (C and C++ only)
           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch"
           built-in functions are used.  These functions changed semantics in
           GCC 4.4.

       -Wunused-but-set-parameter
           Warn whenever a function parameter is assigned to, but otherwise
           unused (aside from its declaration).

           To suppress this warning use the "unused" attribute.

           This warning is also enabled by -Wunused together with -Wextra.

       -Wunused-but-set-variable
           Warn whenever a local variable is assigned to, but otherwise unused
           (aside from its declaration).  This warning is enabled by -Wall.

           To suppress this warning use the "unused" attribute.

           This warning is also enabled by -Wunused, which is enabled by
           -Wall.

       -Wunused-function
           Warn whenever a static function is declared but not defined or a
           non-inline static function is unused.  This warning is enabled by
           -Wall.

       -Wunused-label
           Warn whenever a label is declared but not used.  This warning is
           enabled by -Wall.

           To suppress this warning use the "unused" attribute.

       -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
           Warn when a typedef locally defined in a function is not used.
           This warning is enabled by -Wall.

       -Wunused-parameter
           Warn whenever a function parameter is unused aside from its
           declaration.

           To suppress this warning use the "unused" attribute.

       -Wno-unused-result
           Do not warn if a caller of a function marked with attribute
           "warn_unused_result" does not use its return value. The default is
           -Wunused-result.

       -Wunused-variable
           Warn whenever a local or static variable is unused aside from its
           declaration. This option implies -Wunused-const-variable=1 for C,
           but not for C++. This warning is enabled by -Wall.

           To suppress this warning use the "unused" attribute.

       -Wunused-const-variable
       -Wunused-const-variable=n
           Warn whenever a constant static variable is unused aside from its
           declaration.  -Wunused-const-variable=1 is enabled by
           -Wunused-variable for C, but not for C++. In C this declares
           variable storage, but in C++ this is not an error since const
           variables take the place of "#define"s.

           To suppress this warning use the "unused" attribute.

           -Wunused-const-variable=1
               This is the warning level that is enabled by -Wunused-variable
               for C.  It warns only about unused static const variables
               defined in the main compilation unit, but not about static
               const variables declared in any header included.

           -Wunused-const-variable=2
               This warning level also warns for unused constant static
               variables in headers (excluding system headers).  This is the
               warning level of -Wunused-const-variable and must be explicitly
               requested since in C++ this isn't an error and in C it might be
               harder to clean up all headers included.

       -Wunused-value
           Warn whenever a statement computes a result that is explicitly not
           used. To suppress this warning cast the unused expression to
           "void". This includes an expression-statement or the left-hand side
           of a comma expression that contains no side effects. For example,
           an expression such as "x[i,j]" causes a warning, while
           "x[(void)i,j]" does not.

           This warning is enabled by -Wall.

       -Wunused
           All the above -Wunused options combined.

           In order to get a warning about an unused function parameter, you
           must either specify -Wextra -Wunused (note that -Wall implies
           -Wunused), or separately specify -Wunused-parameter.

       -Wuninitialized
           Warn if an automatic variable is used without first being
           initialized.  In C++, warn if a non-static reference or non-static
           "const" member appears in a class without constructors.

           If you want to warn about code that uses the uninitialized value of
           the variable in its own initializer, use the -Winit-self option.

           These warnings occur for individual uninitialized elements of
           structure, union or array variables as well as for variables that
           are uninitialized as a whole.  They do not occur for variables or
           elements declared "volatile".  Because these warnings depend on
           optimization, the exact variables or elements for which there are
           warnings depend on the precise optimization options and version of
           GCC used.

           Note that there may be no warning about a variable that is used
           only to compute a value that itself is never used, because such
           computations may be deleted by data flow analysis before the
           warnings are printed.

       -Wno-invalid-memory-model
           This option controls warnings for invocations of __atomic Builtins,
           __sync Builtins, and the C11 atomic generic functions with a memory
           consistency argument that is either invalid for the operation or
           outside the range of values of the "memory_order" enumeration.  For
           example, since the "__atomic_store" and "__atomic_store_n" built-
           ins are only defined for the relaxed, release, and sequentially
           consistent memory orders the following code is diagnosed:

                   void store (int *i)
                   {
                     __atomic_store_n (i, 0, memory_order_consume);
                   }

           -Winvalid-memory-model is enabled by default.

       -Wmaybe-uninitialized
           For an automatic (i.e. local) variable, if there exists a path from
           the function entry to a use of the variable that is initialized,
           but there exist some other paths for which the variable is not
           initialized, the compiler emits a warning if it cannot prove the
           uninitialized paths are not executed at run time.

           These warnings are only possible in optimizing compilation, because
           otherwise GCC does not keep track of the state of variables.

           These warnings are made optional because GCC may not be able to
           determine when the code is correct in spite of appearing to have an
           error.  Here is one example of how this can happen:

                   {
                     int x;
                     switch (y)
                       {
                       case 1: x = 1;
                         break;
                       case 2: x = 4;
                         break;
                       case 3: x = 5;
                       }
                     foo (x);
                   }

           If the value of "y" is always 1, 2 or 3, then "x" is always
           initialized, but GCC doesn't know this. To suppress the warning,
           you need to provide a default case with assert(0) or similar code.

           This option also warns when a non-volatile automatic variable might
           be changed by a call to "longjmp".  The compiler sees only the
           calls to "setjmp".  It cannot know where "longjmp" will be called;
           in fact, a signal handler could call it at any point in the code.
           As a result, you may get a warning even when there is in fact no
           problem because "longjmp" cannot in fact be called at the place
           that would cause a problem.

           Some spurious warnings can be avoided if you declare all the
           functions you use that never return as "noreturn".

           This warning is enabled by -Wall or -Wextra.

       -Wunknown-pragmas
           Warn when a "#pragma" directive is encountered that is not
           understood by GCC.  If this command-line option is used, warnings
           are even issued for unknown pragmas in system header files.  This
           is not the case if the warnings are only enabled by the -Wall
           command-line option.

       -Wno-pragmas
           Do not warn about misuses of pragmas, such as incorrect parameters,
           invalid syntax, or conflicts between pragmas.  See also
           -Wunknown-pragmas.

       -Wno-prio-ctor-dtor
           Do not warn if a priority from 0 to 100 is used for constructor or
           destructor.  The use of constructor and destructor attributes allow
           you to assign a priority to the constructor/destructor to control
           its order of execution before "main" is called or after it returns.
           The priority values must be greater than 100 as the compiler
           reserves priority values between 0--100 for the implementation.

       -Wstrict-aliasing
           This option is only active when -fstrict-aliasing is active.  It
           warns about code that might break the strict aliasing rules that
           the compiler is using for optimization.  The warning does not catch
           all cases, but does attempt to catch the more common pitfalls.  It
           is included in -Wall.  It is equivalent to -Wstrict-aliasing=3

       -Wstrict-aliasing=n
           This option is only active when -fstrict-aliasing is active.  It
           warns about code that might break the strict aliasing rules that
           the compiler is using for optimization.  Higher levels correspond
           to higher accuracy (fewer false positives).  Higher levels also
           correspond to more effort, similar to the way -O works.
           -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3.

           Level 1: Most aggressive, quick, least accurate.  Possibly useful
           when higher levels do not warn but -fstrict-aliasing still breaks
           the code, as it has very few false negatives.  However, it has many
           false positives.  Warns for all pointer conversions between
           possibly incompatible types, even if never dereferenced.  Runs in
           the front end only.

           Level 2: Aggressive, quick, not too precise.  May still have many
           false positives (not as many as level 1 though), and few false
           negatives (but possibly more than level 1).  Unlike level 1, it
           only warns when an address is taken.  Warns about incomplete types.
           Runs in the front end only.

           Level 3 (default for -Wstrict-aliasing): Should have very few false
           positives and few false negatives.  Slightly slower than levels 1
           or 2 when optimization is enabled.  Takes care of the common
           pun+dereference pattern in the front end: "*(int*)&some_float".  If
           optimization is enabled, it also runs in the back end, where it
           deals with multiple statement cases using flow-sensitive points-to
           information.  Only warns when the converted pointer is
           dereferenced.  Does not warn about incomplete types.

       -Wstrict-overflow
       -Wstrict-overflow=n
           This option is only active when signed overflow is undefined.  It
           warns about cases where the compiler optimizes based on the
           assumption that signed overflow does not occur.  Note that it does
           not warn about all cases where the code might overflow: it only
           warns about cases where the compiler implements some optimization.
           Thus this warning depends on the optimization level.

           An optimization that assumes that signed overflow does not occur is
           perfectly safe if the values of the variables involved are such
           that overflow never does, in fact, occur.  Therefore this warning
           can easily give a false positive: a warning about code that is not
           actually a problem.  To help focus on important issues, several
           warning levels are defined.  No warnings are issued for the use of
           undefined signed overflow when estimating how many iterations a
           loop requires, in particular when determining whether a loop will
           be executed at all.

           -Wstrict-overflow=1
               Warn about cases that are both questionable and easy to avoid.
               For example the compiler simplifies "x + 1 > x" to 1.  This
               level of -Wstrict-overflow is enabled by -Wall; higher levels
               are not, and must be explicitly requested.

           -Wstrict-overflow=2
               Also warn about other cases where a comparison is simplified to
               a constant.  For example: "abs (x) >= 0".  This can only be
               simplified when signed integer overflow is undefined, because
               "abs (INT_MIN)" overflows to "INT_MIN", which is less than
               zero.  -Wstrict-overflow (with no level) is the same as
               -Wstrict-overflow=2.

           -Wstrict-overflow=3
               Also warn about other cases where a comparison is simplified.
               For example: "x + 1 > 1" is simplified to "x > 0".

           -Wstrict-overflow=4
               Also warn about other simplifications not covered by the above
               cases.  For example: "(x * 10) / 5" is simplified to "x * 2".

           -Wstrict-overflow=5
               Also warn about cases where the compiler reduces the magnitude
               of a constant involved in a comparison.  For example: "x + 2 >
               y" is simplified to "x + 1 >= y".  This is reported only at the
               highest warning level because this simplification applies to
               many comparisons, so this warning level gives a very large
               number of false positives.

       -Wstring-compare
           Warn for calls to "strcmp" and "strncmp" whose result is determined
           to be either zero or non-zero in tests for such equality owing to
           the length of one argument being greater than the size of the array
           the other argument is stored in (or the bound in the case of
           "strncmp").  Such calls could be mistakes.  For example, the call
           to "strcmp" below is diagnosed because its result is necessarily
           non-zero irrespective of the contents of the array "a".

                   extern char a[4];
                   void f (char *d)
                   {
                     strcpy (d, "string");
                     ...
                     if (0 == strcmp (a, d))   // cannot be true
                       puts ("a and d are the same");
                   }

           -Wstring-compare is enabled by -Wextra.

       -Wstringop-overflow
       -Wstringop-overflow=type
           Warn for calls to string manipulation functions such as "memcpy"
           and "strcpy" that are determined to overflow the destination
           buffer.  The optional argument is one greater than the type of
           Object Size Checking to perform to determine the size of the
           destination.  The argument is meaningful only for functions that
           operate on character arrays but not for raw memory functions like
           "memcpy" which always make use of Object Size type-0.  The option
           also warns for calls that specify a size in excess of the largest
           possible object or at most "SIZE_MAX / 2" bytes.  The option
           produces the best results with optimization enabled but can detect
           a small subset of simple buffer overflows even without optimization
           in calls to the GCC built-in functions like "__builtin_memcpy" that
           correspond to the standard functions.  In any case, the option
           warns about just a subset of buffer overflows detected by the
           corresponding overflow checking built-ins.  For example, the option
           issues a warning for the "strcpy" call below because it copies at
           least 5 characters (the string "blue" including the terminating
           NUL) into the buffer of size 4.

                   enum Color { blue, purple, yellow };
                   const char* f (enum Color clr)
                   {
                     static char buf [4];
                     const char *str;
                     switch (clr)
                       {
                         case blue: str = "blue"; break;
                         case purple: str = "purple"; break;
                         case yellow: str = "yellow"; break;
                       }

                     return strcpy (buf, str);   // warning here
                   }

           Option -Wstringop-overflow=2 is enabled by default.

           -Wstringop-overflow
           -Wstringop-overflow=1
               The -Wstringop-overflow=1 option uses type-zero Object Size
               Checking to determine the sizes of destination objects.  This
               is the default setting of the option.  At this setting the
               option does not warn for writes past the end of subobjects of
               larger objects accessed by pointers unless the size of the
               largest surrounding object is known.  When the destination may
               be one of several objects it is assumed to be the largest one
               of them.  On Linux systems, when optimization is enabled at
               this setting the option warns for the same code as when the
               "_FORTIFY_SOURCE" macro is defined to a non-zero value.

           -Wstringop-overflow=2
               The -Wstringop-overflow=2 option uses type-one Object Size
               Checking to determine the sizes of destination objects.  At
               this setting the option warna about overflows when writing to
               members of the largest complete objects whose exact size is
               known.  However, it does not warn for excessive writes to the
               same members of unknown objects referenced by pointers since
               they may point to arrays containing unknown numbers of
               elements.

           -Wstringop-overflow=3
               The -Wstringop-overflow=3 option uses type-two Object Size
               Checking to determine the sizes of destination objects.  At
               this setting the option warns about overflowing the smallest
               object or data member.  This is the most restrictive setting of
               the option that may result in warnings for safe code.

           -Wstringop-overflow=4
               The -Wstringop-overflow=4 option uses type-three Object Size
               Checking to determine the sizes of destination objects.  At
               this setting the option warns about overflowing any data
               members, and when the destination is one of several objects it
               uses the size of the largest of them to decide whether to issue
               a warning.  Similarly to -Wstringop-overflow=3 this setting of
               the option may result in warnings for benign code.

       -Wno-stringop-truncation
           Do not warn for calls to bounded string manipulation functions such
           as "strncat", "strncpy", and "stpncpy" that may either truncate the
           copied string or leave the destination unchanged.

           In the following example, the call to "strncat" specifies a bound
           that is less than the length of the source string.  As a result,
           the copy of the source will be truncated and so the call is
           diagnosed.  To avoid the warning use "bufsize - strlen (buf) - 1)"
           as the bound.

                   void append (char *buf, size_t bufsize)
                   {
                     strncat (buf, ".txt", 3);
                   }

           As another example, the following call to "strncpy" results in
           copying to "d" just the characters preceding the terminating NUL,
           without appending the NUL to the end.  Assuming the result of
           "strncpy" is necessarily a NUL-terminated string is a common
           mistake, and so the call is diagnosed.  To avoid the warning when
           the result is not expected to be NUL-terminated, call "memcpy"
           instead.

                   void copy (char *d, const char *s)
                   {
                     strncpy (d, s, strlen (s));
                   }

           In the following example, the call to "strncpy" specifies the size
           of the destination buffer as the bound.  If the length of the
           source string is equal to or greater than this size the result of
           the copy will not be NUL-terminated.  Therefore, the call is also
           diagnosed.  To avoid the warning, specify "sizeof buf - 1" as the
           bound and set the last element of the buffer to "NUL".

                   void copy (const char *s)
                   {
                     char buf[80];
                     strncpy (buf, s, sizeof buf);
                     ...
                   }

           In situations where a character array is intended to store a
           sequence of bytes with no terminating "NUL" such an array may be
           annotated with attribute "nonstring" to avoid this warning.  Such
           arrays, however, are not suitable arguments to functions that
           expect "NUL"-terminated strings.  To help detect accidental misuses
           of such arrays GCC issues warnings unless it can prove that the use
           is safe.

       -Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]
           Warn for cases where adding an attribute may be beneficial. The
           attributes currently supported are listed below.

           -Wsuggest-attribute=pure
           -Wsuggest-attribute=const
           -Wsuggest-attribute=noreturn
           -Wmissing-noreturn
           -Wsuggest-attribute=malloc
               Warn about functions that might be candidates for attributes
               "pure", "const" or "noreturn" or "malloc". The compiler only
               warns for functions visible in other compilation units or (in
               the case of "pure" and "const") if it cannot prove that the
               function returns normally. A function returns normally if it
               doesn't contain an infinite loop or return abnormally by
               throwing, calling "abort" or trapping.  This analysis requires
               option -fipa-pure-const, which is enabled by default at -O and
               higher.  Higher optimization levels improve the accuracy of the
               analysis.

           -Wsuggest-attribute=format
           -Wmissing-format-attribute
               Warn about function pointers that might be candidates for
               "format" attributes.  Note these are only possible candidates,
               not absolute ones.  GCC guesses that function pointers with
               "format" attributes that are used in assignment,
               initialization, parameter passing or return statements should
               have a corresponding "format" attribute in the resulting type.
               I.e. the left-hand side of the assignment or initialization,
               the type of the parameter variable, or the return type of the
               containing function respectively should also have a "format"
               attribute to avoid the warning.

               GCC also warns about function definitions that might be
               candidates for "format" attributes.  Again, these are only
               possible candidates.  GCC guesses that "format" attributes
               might be appropriate for any function that calls a function
               like "vprintf" or "vscanf", but this might not always be the
               case, and some functions for which "format" attributes are
               appropriate may not be detected.

           -Wsuggest-attribute=cold
               Warn about functions that might be candidates for "cold"
               attribute.  This is based on static detection and generally
               only warns about functions which always leads to a call to
               another "cold" function such as wrappers of C++ "throw" or
               fatal error reporting functions leading to "abort".

       -Walloc-zero
           Warn about calls to allocation functions decorated with attribute
           "alloc_size" that specify zero bytes, including those to the built-
           in forms of the functions "aligned_alloc", "alloca", "calloc",
           "malloc", and "realloc".  Because the behavior of these functions
           when called with a zero size differs among implementations (and in
           the case of "realloc" has been deprecated) relying on it may result
           in subtle portability bugs and should be avoided.

       -Walloc-size-larger-than=byte-size
           Warn about calls to functions decorated with attribute "alloc_size"
           that attempt to allocate objects larger than the specified number
           of bytes, or where the result of the size computation in an integer
           type with infinite precision would exceed the value of PTRDIFF_MAX
           on the target.  -Walloc-size-larger-than=PTRDIFF_MAX is enabled by
           default.  Warnings controlled by the option can be disabled either
           by specifying byte-size of SIZE_MAX or more or by
           -Wno-alloc-size-larger-than.

       -Wno-alloc-size-larger-than
           Disable -Walloc-size-larger-than= warnings.  The option is
           equivalent to -Walloc-size-larger-than=SIZE_MAX or larger.

       -Walloca
           This option warns on all uses of "alloca" in the source.

       -Walloca-larger-than=byte-size
           This option warns on calls to "alloca" with an integer argument
           whose value is either zero, or that is not bounded by a controlling
           predicate that limits its value to at most byte-size.  It also
           warns for calls to "alloca" where the bound value is unknown.
           Arguments of non-integer types are considered unbounded even if
           they appear to be constrained to the expected range.

           For example, a bounded case of "alloca" could be:

                   void func (size_t n)
                   {
                     void *p;
                     if (n <= 1000)
                       p = alloca (n);
                     else
                       p = malloc (n);
                     f (p);
                   }

           In the above example, passing "-Walloca-larger-than=1000" would not
           issue a warning because the call to "alloca" is known to be at most
           1000 bytes.  However, if "-Walloca-larger-than=500" were passed,
           the compiler would emit a warning.

           Unbounded uses, on the other hand, are uses of "alloca" with no
           controlling predicate constraining its integer argument.  For
           example:

                   void func ()
                   {
                     void *p = alloca (n);
                     f (p);
                   }

           If "-Walloca-larger-than=500" were passed, the above would trigger
           a warning, but this time because of the lack of bounds checking.

           Note, that even seemingly correct code involving signed integers
           could cause a warning:

                   void func (signed int n)
                   {
                     if (n < 500)
                       {
                         p = alloca (n);
                         f (p);
                       }
                   }

           In the above example, n could be negative, causing a larger than
           expected argument to be implicitly cast into the "alloca" call.

           This option also warns when "alloca" is used in a loop.

           -Walloca-larger-than=PTRDIFF_MAX is enabled by default but is
           usually only effective  when -ftree-vrp is active (default for -O2
           and above).

           See also -Wvla-larger-than=byte-size.

       -Wno-alloca-larger-than
           Disable -Walloca-larger-than= warnings.  The option is equivalent
           to -Walloca-larger-than=SIZE_MAX or larger.

       -Warith-conversion
           Do warn about implicit conversions from arithmetic operations even
           when conversion of the operands to the same type cannot change
           their values.  This affects warnings from -Wconversion,
           -Wfloat-conversion, and -Wsign-conversion.

                   void f (char c, int i)
                   {
                     c = c + i; // warns with B<-Wconversion>
                     c = c + 1; // only warns with B<-Warith-conversion>
                   }

       -Warray-bounds
       -Warray-bounds=n
           This option is only active when -ftree-vrp is active (default for
           -O2 and above). It warns about subscripts to arrays that are always
           out of bounds. This warning is enabled by -Wall.

           -Warray-bounds=1
               This is the warning level of -Warray-bounds and is enabled by
               -Wall; higher levels are not, and must be explicitly requested.

           -Warray-bounds=2
               This warning level also warns about out of bounds access for
               arrays at the end of a struct and for arrays accessed through
               pointers. This warning level may give a larger number of false
               positives and is deactivated by default.

       -Wattribute-alias=n
       -Wno-attribute-alias
           Warn about declarations using the "alias" and similar attributes
           whose target is incompatible with the type of the alias.

           -Wattribute-alias=1
               The default warning level of the -Wattribute-alias option
               diagnoses incompatibilities between the type of the alias
               declaration and that of its target.  Such incompatibilities are
               typically indicative of bugs.

           -Wattribute-alias=2
               At this level -Wattribute-alias also diagnoses cases where the
               attributes of the alias declaration are more restrictive than
               the attributes applied to its target.  These mismatches can
               potentially result in incorrect code generation.  In other
               cases they may be benign and could be resolved simply by adding
               the missing attribute to the target.  For comparison, see the
               -Wmissing-attributes option, which controls diagnostics when
               the alias declaration is less restrictive than the target,
               rather than more restrictive.

               Attributes considered include "alloc_align", "alloc_size",
               "cold", "const", "hot", "leaf", "malloc", "nonnull",
               "noreturn", "nothrow", "pure", "returns_nonnull", and
               "returns_twice".

           -Wattribute-alias is equivalent to -Wattribute-alias=1.  This is
           the default.  You can disable these warnings with either
           -Wno-attribute-alias or -Wattribute-alias=0.

       -Wbool-compare
           Warn about boolean expression compared with an integer value
           different from "true"/"false".  For instance, the following
           comparison is always false:

                   int n = 5;
                   ...
                   if ((n > 1) == 2) { ... }

           This warning is enabled by -Wall.

       -Wbool-operation
           Warn about suspicious operations on expressions of a boolean type.
           For instance, bitwise negation of a boolean is very likely a bug in
           the program.  For C, this warning also warns about incrementing or
           decrementing a boolean, which rarely makes sense.  (In C++,
           decrementing a boolean is always invalid.  Incrementing a boolean
           is invalid in C++17, and deprecated otherwise.)

           This warning is enabled by -Wall.

       -Wduplicated-branches
           Warn when an if-else has identical branches.  This warning detects
           cases like

                   if (p != NULL)
                     return 0;
                   else
                     return 0;

           It doesn't warn when both branches contain just a null statement.
           This warning also warn for conditional operators:

                     int i = x ? *p : *p;

       -Wduplicated-cond
           Warn about duplicated conditions in an if-else-if chain.  For
           instance, warn for the following code:

                   if (p->q != NULL) { ... }
                   else if (p->q != NULL) { ... }

       -Wframe-address
           Warn when the __builtin_frame_address or __builtin_return_address
           is called with an argument greater than 0.  Such calls may return
           indeterminate values or crash the program.  The warning is included
           in -Wall.

       -Wno-discarded-qualifiers (C and Objective-C only)
           Do not warn if type qualifiers on pointers are being discarded.
           Typically, the compiler warns if a "const char *" variable is
           passed to a function that takes a "char *" parameter.  This option
           can be used to suppress such a warning.

       -Wno-discarded-array-qualifiers (C and Objective-C only)
           Do not warn if type qualifiers on arrays which are pointer targets
           are being discarded.  Typically, the compiler warns if a "const int
           (*)[]" variable is passed to a function that takes a "int (*)[]"
           parameter.  This option can be used to suppress such a warning.

       -Wno-incompatible-pointer-types (C and Objective-C only)
           Do not warn when there is a conversion between pointers that have
           incompatible types.  This warning is for cases not covered by
           -Wno-pointer-sign, which warns for pointer argument passing or
           assignment with different signedness.

       -Wno-int-conversion (C and Objective-C only)
           Do not warn about incompatible integer to pointer and pointer to
           integer conversions.  This warning is about implicit conversions;
           for explicit conversions the warnings -Wno-int-to-pointer-cast and
           -Wno-pointer-to-int-cast may be used.

       -Wzero-length-bounds
           Warn about accesses to elements of zero-length array members that
           might overlap other members of the same object.  Declaring interior
           zero-length arrays is discouraged because accesses to them are
           undefined.  See

           For example, the first two stores in function "bad" are diagnosed
           because the array elements overlap the subsequent members "b" and
           "c".  The third store is diagnosed by -Warray-bounds because it is
           beyond the bounds of the enclosing object.

                   struct X { int a[0]; int b, c; };
                   struct X x;

                   void bad (void)
                   {
                     x.a[0] = 0;   // -Wzero-length-bounds
                     x.a[1] = 1;   // -Wzero-length-bounds
                     x.a[2] = 2;   // -Warray-bounds
                   }

           Option -Wzero-length-bounds is enabled by -Warray-bounds.

       -Wno-div-by-zero
           Do not warn about compile-time integer division by zero.  Floating-
           point division by zero is not warned about, as it can be a
           legitimate way of obtaining infinities and NaNs.

       -Wsystem-headers
           Print warning messages for constructs found in system header files.
           Warnings from system headers are normally suppressed, on the
           assumption that they usually do not indicate real problems and
           would only make the compiler output harder to read.  Using this
           command-line option tells GCC to emit warnings from system headers
           as if they occurred in user code.  However, note that using -Wall
           in conjunction with this option does not warn about unknown pragmas
           in system headers---for that, -Wunknown-pragmas must also be used.

       -Wtautological-compare
           Warn if a self-comparison always evaluates to true or false.  This
           warning detects various mistakes such as:

                   int i = 1;
                   ...
                   if (i > i) { ... }

           This warning also warns about bitwise comparisons that always
           evaluate to true or false, for instance:

                   if ((a & 16) == 10) { ... }

           will always be false.

           This warning is enabled by -Wall.

       -Wtrampolines
           Warn about trampolines generated for pointers to nested functions.
           A trampoline is a small piece of data or code that is created at
           run time on the stack when the address of a nested function is
           taken, and is used to call the nested function indirectly.  For
           some targets, it is made up of data only and thus requires no
           special treatment.  But, for most targets, it is made up of code
           and thus requires the stack to be made executable in order for the
           program to work properly.

       -Wfloat-equal
           Warn if floating-point values are used in equality comparisons.

           The idea behind this is that sometimes it is convenient (for the
           programmer) to consider floating-point values as approximations to
           infinitely precise real numbers.  If you are doing this, then you
           need to compute (by analyzing the code, or in some other way) the
           maximum or likely maximum error that the computation introduces,
           and allow for it when performing comparisons (and when producing
           output, but that's a different problem).  In particular, instead of
           testing for equality, you should check to see whether the two
           values have ranges that overlap; and this is done with the
           relational operators, so equality comparisons are probably
           mistaken.

       -Wtraditional (C and Objective-C only)
           Warn about certain constructs that behave differently in
           traditional and ISO C.  Also warn about ISO C constructs that have
           no traditional C equivalent, and/or problematic constructs that
           should be avoided.

           *   Macro parameters that appear within string literals in the
               macro body.  In traditional C macro replacement takes place
               within string literals, but in ISO C it does not.

           *   In traditional C, some preprocessor directives did not exist.
               Traditional preprocessors only considered a line to be a
               directive if the # appeared in column 1 on the line.  Therefore
               -Wtraditional warns about directives that traditional C
               understands but ignores because the # does not appear as the
               first character on the line.  It also suggests you hide
               directives like "#pragma" not understood by traditional C by
               indenting them.  Some traditional implementations do not
               recognize "#elif", so this option suggests avoiding it
               altogether.

           *   A function-like macro that appears without arguments.

           *   The unary plus operator.

           *   The U integer constant suffix, or the F or L floating-point
               constant suffixes.  (Traditional C does support the L suffix on
               integer constants.)  Note, these suffixes appear in macros
               defined in the system headers of most modern systems, e.g. the
               _MIN/_MAX macros in "<limits.h>".  Use of these macros in user
               code might normally lead to spurious warnings, however GCC's
               integrated preprocessor has enough context to avoid warning in
               these cases.

           *   A function declared external in one block and then used after
               the end of the block.

           *   A "switch" statement has an operand of type "long".

           *   A non-"static" function declaration follows a "static" one.
               This construct is not accepted by some traditional C compilers.

           *   The ISO type of an integer constant has a different width or
               signedness from its traditional type.  This warning is only
               issued if the base of the constant is ten.  I.e. hexadecimal or
               octal values, which typically represent bit patterns, are not
               warned about.

           *   Usage of ISO string concatenation is detected.

           *   Initialization of automatic aggregates.

           *   Identifier conflicts with labels.  Traditional C lacks a
               separate namespace for labels.

           *   Initialization of unions.  If the initializer is zero, the
               warning is omitted.  This is done under the assumption that the
               zero initializer in user code appears conditioned on e.g.
               "__STDC__" to avoid missing initializer warnings and relies on
               default initialization to zero in the traditional C case.

           *   Conversions by prototypes between fixed/floating-point values
               and vice versa.  The absence of these prototypes when compiling
               with traditional C causes serious problems.  This is a subset
               of the possible conversion warnings; for the full set use
               -Wtraditional-conversion.

           *   Use of ISO C style function definitions.  This warning
               intentionally is not issued for prototype declarations or
               variadic functions because these ISO C features appear in your
               code when using libiberty's traditional C compatibility macros,
               "PARAMS" and "VPARAMS".  This warning is also bypassed for
               nested functions because that feature is already a GCC
               extension and thus not relevant to traditional C compatibility.

       -Wtraditional-conversion (C and Objective-C only)
           Warn if a prototype causes a type conversion that is different from
           what would happen to the same argument in the absence of a
           prototype.  This includes conversions of fixed point to floating
           and vice versa, and conversions changing the width or signedness of
           a fixed-point argument except when the same as the default
           promotion.

       -Wdeclaration-after-statement (C and Objective-C only)
           Warn when a declaration is found after a statement in a block.
           This construct, known from C++, was introduced with ISO C99 and is
           by default allowed in GCC.  It is not supported by ISO C90.

       -Wshadow
           Warn whenever a local variable or type declaration shadows another
           variable, parameter, type, class member (in C++), or instance
           variable (in Objective-C) or whenever a built-in function is
           shadowed.  Note that in C++, the compiler warns if a local variable
           shadows an explicit typedef, but not if it shadows a
           struct/class/enum.  If this warning is enabled, it includes also
           all instances of local shadowing.  This means that
           -Wno-shadow=local and -Wno-shadow=compatible-local are ignored when
           -Wshadow is used.  Same as -Wshadow=global.

       -Wno-shadow-ivar (Objective-C only)
           Do not warn whenever a local variable shadows an instance variable
           in an Objective-C method.

       -Wshadow=global
           Warn for any shadowing.  Same as -Wshadow.

       -Wshadow=local
           Warn when a local variable shadows another local variable or
           parameter.

       -Wshadow=compatible-local
           Warn when a local variable shadows another local variable or
           parameter whose type is compatible with that of the shadowing
           variable.  In C++, type compatibility here means the type of the
           shadowing variable can be converted to that of the shadowed
           variable.  The creation of this flag (in addition to
           -Wshadow=local) is based on the idea that when a local variable
           shadows another one of incompatible type, it is most likely
           intentional, not a bug or typo, as shown in the following example:

                   for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
                   {
                     for (int i = 0; i < N; ++i)
                     {
                       ...
                     }
                     ...
                   }

           Since the two variable "i" in the example above have incompatible
           types, enabling only -Wshadow=compatible-local does not emit a
           warning.  Because their types are incompatible, if a programmer
           accidentally uses one in place of the other, type checking is
           expected to catch that and emit an error or warning.  Use of this
           flag instead of -Wshadow=local can possibly reduce the number of
           warnings triggered by intentional shadowing.  Note that this also
           means that shadowing "const char *i" by "char *i" does not emit a
           warning.

           This warning is also enabled by -Wshadow=local.

       -Wlarger-than=byte-size
           Warn whenever an object is defined whose size exceeds byte-size.
           -Wlarger-than=PTRDIFF_MAX is enabled by default.  Warnings
           controlled by the option can be disabled either by specifying byte-
           size of SIZE_MAX or more or by -Wno-larger-than.

       -Wno-larger-than
           Disable -Wlarger-than= warnings.  The option is equivalent to
           -Wlarger-than=SIZE_MAX or larger.

       -Wframe-larger-than=byte-size
           Warn if the size of a function frame exceeds byte-size.  The
           computation done to determine the stack frame size is approximate
           and not conservative.  The actual requirements may be somewhat
           greater than byte-size even if you do not get a warning.  In
           addition, any space allocated via "alloca", variable-length arrays,
           or related constructs is not included by the compiler when
           determining whether or not to issue a warning.
           -Wframe-larger-than=PTRDIFF_MAX is enabled by default.  Warnings
           controlled by the option can be disabled either by specifying byte-
           size of SIZE_MAX or more or by -Wno-frame-larger-than.

       -Wno-frame-larger-than
           Disable -Wframe-larger-than= warnings.  The option is equivalent to
           -Wframe-larger-than=SIZE_MAX or larger.

       -Wno-free-nonheap-object
           Do not warn when attempting to free an object that was not
           allocated on the heap.

       -Wstack-usage=byte-size
           Warn if the stack usage of a function might exceed byte-size.  The
           computation done to determine the stack usage is conservative.  Any
           space allocated via "alloca", variable-length arrays, or related
           constructs is included by the compiler when determining whether or
           not to issue a warning.

           The message is in keeping with the output of -fstack-usage.

           *   If the stack usage is fully static but exceeds the specified
               amount, it's:

                         warning: stack usage is 1120 bytes

           *   If the stack usage is (partly) dynamic but bounded, it's:

                         warning: stack usage might be 1648 bytes

           *   If the stack usage is (partly) dynamic and not bounded, it's:

                         warning: stack usage might be unbounded

           -Wstack-usage=PTRDIFF_MAX is enabled by default.  Warnings
           controlled by the option can be disabled either by specifying byte-
           size of SIZE_MAX or more or by -Wno-stack-usage.

       -Wno-stack-usage
           Disable -Wstack-usage= warnings.  The option is equivalent to
           -Wstack-usage=SIZE_MAX or larger.

       -Wunsafe-loop-optimizations
           Warn if the loop cannot be optimized because the compiler cannot
           assume anything on the bounds of the loop indices.  With
           -funsafe-loop-optimizations warn if the compiler makes such
           assumptions.

       -Wno-pedantic-ms-format (MinGW targets only)
           When used in combination with -Wformat and -pedantic without GNU
           extensions, this option disables the warnings about non-ISO
           "printf" / "scanf" format width specifiers "I32", "I64", and "I"
           used on Windows targets, which depend on the MS runtime.

       -Wpointer-arith
           Warn about anything that depends on the "size of" a function type
           or of "void".  GNU C assigns these types a size of 1, for
           convenience in calculations with "void *" pointers and pointers to
           functions.  In C++, warn also when an arithmetic operation involves
           "NULL".  This warning is also enabled by -Wpedantic.

       -Wno-pointer-compare
           Do not warn if a pointer is compared with a zero character
           constant.  This usually means that the pointer was meant to be
           dereferenced.  For example:

                   const char *p = foo ();
                   if (p == '\0')
                     return 42;

           Note that the code above is invalid in C++11.

           This warning is enabled by default.

       -Wtype-limits
           Warn if a comparison is always true or always false due to the
           limited range of the data type, but do not warn for constant
           expressions.  For example, warn if an unsigned variable is compared
           against zero with "<" or ">=".  This warning is also enabled by
           -Wextra.

       -Wabsolute-value (C and Objective-C only)
           Warn for calls to standard functions that compute the absolute
           value of an argument when a more appropriate standard function is
           available.  For example, calling "abs(3.14)" triggers the warning
           because the appropriate function to call to compute the absolute
           value of a double argument is "fabs".  The option also triggers
           warnings when the argument in a call to such a function has an
           unsigned type.  This warning can be suppressed with an explicit
           type cast and it is also enabled by -Wextra.

       -Wcomment
       -Wcomments
           Warn whenever a comment-start sequence /* appears in a /* comment,
           or whenever a backslash-newline appears in a // comment.  This
           warning is enabled by -Wall.

       -Wtrigraphs
           Warn if any trigraphs are encountered that might change the meaning
           of the program.  Trigraphs within comments are not warned about,
           except those that would form escaped newlines.

           This option is implied by -Wall.  If -Wall is not given, this
           option is still enabled unless trigraphs are enabled.  To get
           trigraph conversion without warnings, but get the other -Wall
           warnings, use -trigraphs -Wall -Wno-trigraphs.

       -Wundef
           Warn if an undefined identifier is evaluated in an "#if" directive.
           Such identifiers are replaced with zero.

       -Wexpansion-to-defined
           Warn whenever defined is encountered in the expansion of a macro
           (including the case where the macro is expanded by an #if
           directive).  Such usage is not portable.  This warning is also
           enabled by -Wpedantic and -Wextra.

       -Wunused-macros
           Warn about macros defined in the main file that are unused.  A
           macro is used if it is expanded or tested for existence at least
           once.  The preprocessor also warns if the macro has not been used
           at the time it is redefined or undefined.

           Built-in macros, macros defined on the command line, and macros
           defined in include files are not warned about.

           Note: If a macro is actually used, but only used in skipped
           conditional blocks, then the preprocessor reports it as unused.  To
           avoid the warning in such a case, you might improve the scope of
           the macro's definition by, for example, moving it into the first
           skipped block.  Alternatively, you could provide a dummy use with
           something like:

                   #if defined the_macro_causing_the_warning
                   #endif

       -Wno-endif-labels
           Do not warn whenever an "#else" or an "#endif" are followed by
           text.  This sometimes happens in older programs with code of the
           form

                   #if FOO
                   ...
                   #else FOO
                   ...
                   #endif FOO

           The second and third "FOO" should be in comments.  This warning is
           on by default.

       -Wbad-function-cast (C and Objective-C only)
           Warn when a function call is cast to a non-matching type.  For
           example, warn if a call to a function returning an integer type is
           cast to a pointer type.

       -Wc90-c99-compat (C and Objective-C only)
           Warn about features not present in ISO C90, but present in ISO C99.
           For instance, warn about use of variable length arrays, "long long"
           type, "bool" type, compound literals, designated initializers, and
           so on.  This option is independent of the standards mode.  Warnings
           are disabled in the expression that follows "__extension__".

       -Wc99-c11-compat (C and Objective-C only)
           Warn about features not present in ISO C99, but present in ISO C11.
           For instance, warn about use of anonymous structures and unions,
           "_Atomic" type qualifier, "_Thread_local" storage-class specifier,
           "_Alignas" specifier, "Alignof" operator, "_Generic" keyword, and
           so on.  This option is independent of the standards mode.  Warnings
           are disabled in the expression that follows "__extension__".

       -Wc11-c2x-compat (C and Objective-C only)
           Warn about features not present in ISO C11, but present in ISO C2X.
           For instance, warn about omitting the string in "_Static_assert",
           use of [[]] syntax for attributes, use of decimal floating-point
           types, and so on.  This option is independent of the standards
           mode.  Warnings are disabled in the expression that follows
           "__extension__".

       -Wc++-compat (C and Objective-C only)
           Warn about ISO C constructs that are outside of the common subset
           of ISO C and ISO C++, e.g. request for implicit conversion from
           "void *" to a pointer to non-"void" type.

       -Wc++11-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++
           1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are
           keywords in ISO C++ 2011.  This warning turns on -Wnarrowing and is
           enabled by -Wall.

       -Wc++14-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++
           2011 and ISO C++ 2014.  This warning is enabled by -Wall.

       -Wc++17-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++
           2014 and ISO C++ 2017.  This warning is enabled by -Wall.

       -Wc++20-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++
           2017 and ISO C++ 2020.  This warning is enabled by -Wall.

       -Wcast-qual
           Warn whenever a pointer is cast so as to remove a type qualifier
           from the target type.  For example, warn if a "const char *" is
           cast to an ordinary "char *".

           Also warn when making a cast that introduces a type qualifier in an
           unsafe way.  For example, casting "char **" to "const char **" is
           unsafe, as in this example:

                     /* p is char ** value.  */
                     const char **q = (const char **) p;
                     /* Assignment of readonly string to const char * is OK.  */
                     *q = "string";
                     /* Now char** pointer points to read-only memory.  */
                     **p = 'b';

       -Wcast-align
           Warn whenever a pointer is cast such that the required alignment of
           the target is increased.  For example, warn if a "char *" is cast
           to an "int *" on machines where integers can only be accessed at
           two- or four-byte boundaries.

       -Wcast-align=strict
           Warn whenever a pointer is cast such that the required alignment of
           the target is increased.  For example, warn if a "char *" is cast
           to an "int *" regardless of the target machine.

       -Wcast-function-type
           Warn when a function pointer is cast to an incompatible function
           pointer.  In a cast involving function types with a variable
           argument list only the types of initial arguments that are provided
           are considered.  Any parameter of pointer-type matches any other
           pointer-type.  Any benign differences in integral types are
           ignored, like "int" vs. "long" on ILP32 targets.  Likewise type
           qualifiers are ignored.  The function type "void (*) (void)" is
           special and matches everything, which can be used to suppress this
           warning.  In a cast involving pointer to member types this warning
           warns whenever the type cast is changing the pointer to member
           type.  This warning is enabled by -Wextra.

       -Wwrite-strings
           When compiling C, give string constants the type "const
           char[length]" so that copying the address of one into a non-"const"
           "char *" pointer produces a warning.  These warnings help you find
           at compile time code that can try to write into a string constant,
           but only if you have been very careful about using "const" in
           declarations and prototypes.  Otherwise, it is just a nuisance.
           This is why we did not make -Wall request these warnings.

           When compiling C++, warn about the deprecated conversion from
           string literals to "char *".  This warning is enabled by default
           for C++ programs.

       -Wclobbered
           Warn for variables that might be changed by "longjmp" or "vfork".
           This warning is also enabled by -Wextra.

       -Wconversion
           Warn for implicit conversions that may alter a value. This includes
           conversions between real and integer, like "abs (x)" when "x" is
           "double"; conversions between signed and unsigned, like "unsigned
           ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do
           not warn for explicit casts like "abs ((int) x)" and "ui =
           (unsigned) -1", or if the value is not changed by the conversion
           like in "abs (2.0)".  Warnings about conversions between signed and
           unsigned integers can be disabled by using -Wno-sign-conversion.

           For C++, also warn for confusing overload resolution for user-
           defined conversions; and conversions that never use a type
           conversion operator: conversions to "void", the same type, a base
           class or a reference to them. Warnings about conversions between
           signed and unsigned integers are disabled by default in C++ unless
           -Wsign-conversion is explicitly enabled.

           Warnings about conversion from arithmetic on a small type back to
           that type are only given with -Warith-conversion.

       -Wdangling-else
           Warn about constructions where there may be confusion to which "if"
           statement an "else" branch belongs.  Here is an example of such a
           case:

                   {
                     if (a)
                       if (b)
                         foo ();
                     else
                       bar ();
                   }

           In C/C++, every "else" branch belongs to the innermost possible
           "if" statement, which in this example is "if (b)".  This is often
           not what the programmer expected, as illustrated in the above
           example by indentation the programmer chose.  When there is the
           potential for this confusion, GCC issues a warning when this flag
           is specified.  To eliminate the warning, add explicit braces around
           the innermost "if" statement so there is no way the "else" can
           belong to the enclosing "if".  The resulting code looks like this:

                   {
                     if (a)
                       {
                         if (b)
                           foo ();
                         else
                           bar ();
                       }
                   }

           This warning is enabled by -Wparentheses.

       -Wdate-time
           Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are
           encountered as they might prevent bit-wise-identical reproducible
           compilations.

       -Wempty-body
           Warn if an empty body occurs in an "if", "else" or "do while"
           statement.  This warning is also enabled by -Wextra.

       -Wno-endif-labels
           Do not warn about stray tokens after "#else" and "#endif".

       -Wenum-compare
           Warn about a comparison between values of different enumerated
           types.  In C++ enumerated type mismatches in conditional
           expressions are also diagnosed and the warning is enabled by
           default.  In C this warning is enabled by -Wall.

       -Wenum-conversion (C, Objective-C only)
           Warn when a value of enumerated type is implicitly converted to a
           different enumerated type.  This warning is enabled by -Wextra.

       -Wjump-misses-init (C, Objective-C only)
           Warn if a "goto" statement or a "switch" statement jumps forward
           across the initialization of a variable, or jumps backward to a
           label after the variable has been initialized.  This only warns
           about variables that are initialized when they are declared.  This
           warning is only supported for C and Objective-C; in C++ this sort
           of branch is an error in any case.

           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled
           with the -Wno-jump-misses-init option.

       -Wsign-compare
           Warn when a comparison between signed and unsigned values could
           produce an incorrect result when the signed value is converted to
           unsigned.  In C++, this warning is also enabled by -Wall.  In C, it
           is also enabled by -Wextra.

       -Wsign-conversion
           Warn for implicit conversions that may change the sign of an
           integer value, like assigning a signed integer expression to an
           unsigned integer variable. An explicit cast silences the warning.
           In C, this option is enabled also by -Wconversion.

       -Wfloat-conversion
           Warn for implicit conversions that reduce the precision of a real
           value.  This includes conversions from real to integer, and from
           higher precision real to lower precision real values.  This option
           is also enabled by -Wconversion.

       -Wno-scalar-storage-order
           Do not warn on suspicious constructs involving reverse scalar
           storage order.

       -Wsizeof-pointer-div
           Warn for suspicious divisions of two sizeof expressions that divide
           the pointer size by the element size, which is the usual way to
           compute the array size but won't work out correctly with pointers.
           This warning warns e.g. about "sizeof (ptr) / sizeof (ptr[0])" if
           "ptr" is not an array, but a pointer.  This warning is enabled by
           -Wall.

       -Wsizeof-pointer-memaccess
           Warn for suspicious length parameters to certain string and memory
           built-in functions if the argument uses "sizeof".  This warning
           triggers for example for "memset (ptr, 0, sizeof (ptr));" if "ptr"
           is not an array, but a pointer, and suggests a possible fix, or
           about "memcpy (&foo, ptr, sizeof (&foo));".
           -Wsizeof-pointer-memaccess also warns about calls to bounded string
           copy functions like "strncat" or "strncpy" that specify as the
           bound a "sizeof" expression of the source array.  For example, in
           the following function the call to "strncat" specifies the size of
           the source string as the bound.  That is almost certainly a mistake
           and so the call is diagnosed.

                   void make_file (const char *name)
                   {
                     char path[PATH_MAX];
                     strncpy (path, name, sizeof path - 1);
                     strncat (path, ".text", sizeof ".text");
                     ...
                   }

           The -Wsizeof-pointer-memaccess option is enabled by -Wall.

       -Wno-sizeof-array-argument
           Do not warn when the "sizeof" operator is applied to a parameter
           that is declared as an array in a function definition.  This
           warning is enabled by default for C and C++ programs.

       -Wmemset-elt-size
           Warn for suspicious calls to the "memset" built-in function, if the
           first argument references an array, and the third argument is a
           number equal to the number of elements, but not equal to the size
           of the array in memory.  This indicates that the user has omitted a
           multiplication by the element size.  This warning is enabled by
           -Wall.

       -Wmemset-transposed-args
           Warn for suspicious calls to the "memset" built-in function where
           the second argument is not zero and the third argument is zero.
           For example, the call "memset (buf, sizeof buf, 0)" is diagnosed
           because "memset (buf, 0, sizeof buf)" was meant instead.  The
           diagnostic is only emitted if the third argument is a literal zero.
           Otherwise, if it is an expression that is folded to zero, or a cast
           of zero to some type, it is far less likely that the arguments have
           been mistakenly transposed and no warning is emitted.  This warning
           is enabled by -Wall.

       -Waddress
           Warn about suspicious uses of memory addresses. These include using
           the address of a function in a conditional expression, such as
           "void func(void); if (func)", and comparisons against the memory
           address of a string literal, such as "if (x == "abc")".  Such uses
           typically indicate a programmer error: the address of a function
           always evaluates to true, so their use in a conditional usually
           indicate that the programmer forgot the parentheses in a function
           call; and comparisons against string literals result in unspecified
           behavior and are not portable in C, so they usually indicate that
           the programmer intended to use "strcmp".  This warning is enabled
           by -Wall.

       -Wno-address-of-packed-member
           Do not warn when the address of packed member of struct or union is
           taken, which usually results in an unaligned pointer value.  This
           is enabled by default.

       -Wlogical-op
           Warn about suspicious uses of logical operators in expressions.
           This includes using logical operators in contexts where a bit-wise
           operator is likely to be expected.  Also warns when the operands of
           a logical operator are the same:

                   extern int a;
                   if (a < 0 && a < 0) { ... }

       -Wlogical-not-parentheses
           Warn about logical not used on the left hand side operand of a
           comparison.  This option does not warn if the right operand is
           considered to be a boolean expression.  Its purpose is to detect
           suspicious code like the following:

                   int a;
                   ...
                   if (!a > 1) { ... }

           It is possible to suppress the warning by wrapping the LHS into
           parentheses:

                   if ((!a) > 1) { ... }

           This warning is enabled by -Wall.

       -Waggregate-return
           Warn if any functions that return structures or unions are defined
           or called.  (In languages where you can return an array, this also
           elicits a warning.)

       -Wno-aggressive-loop-optimizations
           Warn if in a loop with constant number of iterations the compiler
           detects undefined behavior in some statement during one or more of
           the iterations.

       -Wno-attributes
           Do not warn if an unexpected "__attribute__" is used, such as
           unrecognized attributes, function attributes applied to variables,
           etc.  This does not stop errors for incorrect use of supported
           attributes.

       -Wno-builtin-declaration-mismatch
           Warn if a built-in function is declared with an incompatible
           signature or as a non-function, or when a built-in function
           declared with a type that does not include a prototype is called
           with arguments whose promoted types do not match those expected by
           the function.  When -Wextra is specified, also warn when a built-in
           function that takes arguments is declared without a prototype.  The
           -Wbuiltin-declaration-mismatch warning is enabled by default.  To
           avoid the warning include the appropriate header to bring the
           prototypes of built-in functions into scope.

           For example, the call to "memset" below is diagnosed by the warning
           because the function expects a value of type "size_t" as its
           argument but the type of 32 is "int".  With -Wextra, the
           declaration of the function is diagnosed as well.

                   extern void* memset ();
                   void f (void *d)
                   {
                     memset (d, '\0', 32);
                   }

       -Wno-builtin-macro-redefined
           Do not warn if certain built-in macros are redefined.  This
           suppresses warnings for redefinition of "__TIMESTAMP__",
           "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__".

       -Wstrict-prototypes (C and Objective-C only)
           Warn if a function is declared or defined without specifying the
           argument types.  (An old-style function definition is permitted
           without a warning if preceded by a declaration that specifies the
           argument types.)

       -Wold-style-declaration (C and Objective-C only)
           Warn for obsolescent usages, according to the C Standard, in a
           declaration. For example, warn if storage-class specifiers like
           "static" are not the first things in a declaration.  This warning
           is also enabled by -Wextra.

       -Wold-style-definition (C and Objective-C only)
           Warn if an old-style function definition is used.  A warning is
           given even if there is a previous prototype.  A definition using ()
           is not considered an old-style definition in C2X mode, because it
           is equivalent to (void) in that case, but is considered an old-
           style definition for older standards.

       -Wmissing-parameter-type (C and Objective-C only)
           A function parameter is declared without a type specifier in
           K&R-style functions:

                   void foo(bar) { }

           This warning is also enabled by -Wextra.

       -Wmissing-prototypes (C and Objective-C only)
           Warn if a global function is defined without a previous prototype
           declaration.  This warning is issued even if the definition itself
           provides a prototype.  Use this option to detect global functions
           that do not have a matching prototype declaration in a header file.
           This option is not valid for C++ because all function declarations
           provide prototypes and a non-matching declaration declares an
           overload rather than conflict with an earlier declaration.  Use
           -Wmissing-declarations to detect missing declarations in C++.

       -Wmissing-declarations
           Warn if a global function is defined without a previous
           declaration.  Do so even if the definition itself provides a
           prototype.  Use this option to detect global functions that are not
           declared in header files.  In C, no warnings are issued for
           functions with previous non-prototype declarations; use
           -Wmissing-prototypes to detect missing prototypes.  In C++, no
           warnings are issued for function templates, or for inline
           functions, or for functions in anonymous namespaces.

       -Wmissing-field-initializers
           Warn if a structure's initializer has some fields missing.  For
           example, the following code causes such a warning, because "x.h" is
           implicitly zero:

                   struct s { int f, g, h; };
                   struct s x = { 3, 4 };

           This option does not warn about designated initializers, so the
           following modification does not trigger a warning:

                   struct s { int f, g, h; };
                   struct s x = { .f = 3, .g = 4 };

           In C this option does not warn about the universal zero initializer
           { 0 }:

                   struct s { int f, g, h; };
                   struct s x = { 0 };

           Likewise, in C++ this option does not warn about the empty { }
           initializer, for example:

                   struct s { int f, g, h; };
                   s x = { };

           This warning is included in -Wextra.  To get other -Wextra warnings
           without this one, use -Wextra -Wno-missing-field-initializers.

       -Wno-multichar
           Do not warn if a multicharacter constant ('FOOF') is used.  Usually
           they indicate a typo in the user's code, as they have
           implementation-defined values, and should not be used in portable
           code.

       -Wnormalized=[none|id|nfc|nfkc]
           In ISO C and ISO C++, two identifiers are different if they are
           different sequences of characters.  However, sometimes when
           characters outside the basic ASCII character set are used, you can
           have two different character sequences that look the same.  To
           avoid confusion, the ISO 10646 standard sets out some normalization
           rules which when applied ensure that two sequences that look the
           same are turned into the same sequence.  GCC can warn you if you
           are using identifiers that have not been normalized; this option
           controls that warning.

           There are four levels of warning supported by GCC.  The default is
           -Wnormalized=nfc, which warns about any identifier that is not in
           the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
           form for most uses.  It is equivalent to -Wnormalized.

           Unfortunately, there are some characters allowed in identifiers by
           ISO C and ISO C++ that, when turned into NFC, are not allowed in
           identifiers.  That is, there's no way to use these symbols in
           portable ISO C or C++ and have all your identifiers in NFC.
           -Wnormalized=id suppresses the warning for these characters.  It is
           hoped that future versions of the standards involved will correct
           this, which is why this option is not the default.

           You can switch the warning off for all characters by writing
           -Wnormalized=none or -Wno-normalized.  You should only do this if
           you are using some other normalization scheme (like "D"), because
           otherwise you can easily create bugs that are literally impossible
           to see.

           Some characters in ISO 10646 have distinct meanings but look
           identical in some fonts or display methodologies, especially once
           formatting has been applied.  For instance "\u207F", "SUPERSCRIPT
           LATIN SMALL LETTER N", displays just like a regular "n" that has
           been placed in a superscript.  ISO 10646 defines the NFKC
           normalization scheme to convert all these into a standard form as
           well, and GCC warns if your code is not in NFKC if you use
           -Wnormalized=nfkc.  This warning is comparable to warning about
           every identifier that contains the letter O because it might be
           confused with the digit 0, and so is not the default, but may be
           useful as a local coding convention if the programming environment
           cannot be fixed to display these characters distinctly.

       -Wno-attribute-warning
           Do not warn about usage of functions declared with "warning"
           attribute.  By default, this warning is enabled.
           -Wno-attribute-warning can be used to disable the warning or
           -Wno-error=attribute-warning can be used to disable the error when
           compiled with -Werror flag.

       -Wno-deprecated
           Do not warn about usage of deprecated features.

       -Wno-deprecated-declarations
           Do not warn about uses of functions, variables, and types marked as
           deprecated by using the "deprecated" attribute.

       -Wno-overflow
           Do not warn about compile-time overflow in constant expressions.

       -Wno-odr
           Warn about One Definition Rule violations during link-time
           optimization.  Enabled by default.

       -Wopenmp-simd
           Warn if the vectorizer cost model overrides the OpenMP simd
           directive set by user.  The -fsimd-cost-model=unlimited option can
           be used to relax the cost model.

       -Woverride-init (C and Objective-C only)
           Warn if an initialized field without side effects is overridden
           when using designated initializers.

           This warning is included in -Wextra.  To get other -Wextra warnings
           without this one, use -Wextra -Wno-override-init.

       -Wno-override-init-side-effects (C and Objective-C only)
           Do not warn if an initialized field with side effects is overridden
           when using designated initializers.  This warning is enabled by
           default.

       -Wpacked
           Warn if a structure is given the packed attribute, but the packed
           attribute has no effect on the layout or size of the structure.
           Such structures may be mis-aligned for little benefit.  For
           instance, in this code, the variable "f.x" in "struct bar" is
           misaligned even though "struct bar" does not itself have the packed
           attribute:

                   struct foo {
                     int x;
                     char a, b, c, d;
                   } __attribute__((packed));
                   struct bar {
                     char z;
                     struct foo f;
                   };

       -Wnopacked-bitfield-compat
           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on
           bit-fields of type "char".  This was fixed in GCC 4.4 but the
           change can lead to differences in the structure layout.  GCC
           informs you when the offset of such a field has changed in GCC 4.4.
           For example there is no longer a 4-bit padding between field "a"
           and "b" in this structure:

                   struct foo
                   {
                     char a:4;
                     char b:8;
                   } __attribute__ ((packed));

           This warning is enabled by default.  Use
           -Wno-packed-bitfield-compat to disable this warning.

       -Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)
           Warn if a structure field with explicitly specified alignment in a
           packed struct or union is misaligned.  For example, a warning will
           be issued on "struct S", like, "warning: alignment 1 of 'struct S'
           is less than 8", in this code:

                   struct __attribute__ ((aligned (8))) S8 { char a[8]; };
                   struct __attribute__ ((packed)) S {
                     struct S8 s8;
                   };

           This warning is enabled by -Wall.

       -Wpadded
           Warn if padding is included in a structure, either to align an
           element of the structure or to align the whole structure.
           Sometimes when this happens it is possible to rearrange the fields
           of the structure to reduce the padding and so make the structure
           smaller.

       -Wredundant-decls
           Warn if anything is declared more than once in the same scope, even
           in cases where multiple declaration is valid and changes nothing.

       -Wrestrict
           Warn when an object referenced by a "restrict"-qualified parameter
           (or, in C++, a "__restrict"-qualified parameter) is aliased by
           another argument, or when copies between such objects overlap.  For
           example, the call to the "strcpy" function below attempts to
           truncate the string by replacing its initial characters with the
           last four.  However, because the call writes the terminating NUL
           into "a[4]", the copies overlap and the call is diagnosed.

                   void foo (void)
                   {
                     char a[] = "abcd1234";
                     strcpy (a, a + 4);
                     ...
                   }

           The -Wrestrict option detects some instances of simple overlap even
           without optimization but works best at -O2 and above.  It is
           included in -Wall.

       -Wnested-externs (C and Objective-C only)
           Warn if an "extern" declaration is encountered within a function.

       -Winline
           Warn if a function that is declared as inline cannot be inlined.
           Even with this option, the compiler does not warn about failures to
           inline functions declared in system headers.

           The compiler uses a variety of heuristics to determine whether or
           not to inline a function.  For example, the compiler takes into
           account the size of the function being inlined and the amount of
           inlining that has already been done in the current function.
           Therefore, seemingly insignificant changes in the source program
           can cause the warnings produced by -Winline to appear or disappear.

       -Wint-in-bool-context
           Warn for suspicious use of integer values where boolean values are
           expected, such as conditional expressions (?:) using non-boolean
           integer constants in boolean context, like "if (a <= b ? 2 : 3)".
           Or left shifting of signed integers in boolean context, like "for
           (a = 0; 1 << a; a++);".  Likewise for all kinds of multiplications
           regardless of the data type.  This warning is enabled by -Wall.

       -Wno-int-to-pointer-cast
           Suppress warnings from casts to pointer type of an integer of a
           different size. In C++, casting to a pointer type of smaller size
           is an error. Wint-to-pointer-cast is enabled by default.

       -Wno-pointer-to-int-cast (C and Objective-C only)
           Suppress warnings from casts from a pointer to an integer type of a
           different size.

       -Winvalid-pch
           Warn if a precompiled header is found in the search path but cannot
           be used.

       -Wlong-long
           Warn if "long long" type is used.  This is enabled by either
           -Wpedantic or -Wtraditional in ISO C90 and C++98 modes.  To inhibit
           the warning messages, use -Wno-long-long.

       -Wvariadic-macros
           Warn if variadic macros are used in ISO C90 mode, or if the GNU
           alternate syntax is used in ISO C99 mode.  This is enabled by
           either -Wpedantic or -Wtraditional.  To inhibit the warning
           messages, use -Wno-variadic-macros.

       -Wno-varargs
           Do not warn upon questionable usage of the macros used to handle
           variable arguments like "va_start".  These warnings are enabled by
           default.

       -Wvector-operation-performance
           Warn if vector operation is not implemented via SIMD capabilities
           of the architecture.  Mainly useful for the performance tuning.
           Vector operation can be implemented "piecewise", which means that
           the scalar operation is performed on every vector element; "in
           parallel", which means that the vector operation is implemented
           using scalars of wider type, which normally is more performance
           efficient; and "as a single scalar", which means that vector fits
           into a scalar type.

       -Wvla
           Warn if a variable-length array is used in the code.  -Wno-vla
           prevents the -Wpedantic warning of the variable-length array.

       -Wvla-larger-than=byte-size
           If this option is used, the compiler warns for declarations of
           variable-length arrays whose size is either unbounded, or bounded
           by an argument that allows the array size to exceed byte-size
           bytes.  This is similar to how -Walloca-larger-than=byte-size
           works, but with variable-length arrays.

           Note that GCC may optimize small variable-length arrays of a known
           value into plain arrays, so this warning may not get triggered for
           such arrays.

           -Wvla-larger-than=PTRDIFF_MAX is enabled by default but is
           typically only effective when -ftree-vrp is active (default for -O2
           and above).

           See also -Walloca-larger-than=byte-size.

       -Wno-vla-larger-than
           Disable -Wvla-larger-than= warnings.  The option is equivalent to
           -Wvla-larger-than=SIZE_MAX or larger.

       -Wvolatile-register-var
           Warn if a register variable is declared volatile.  The volatile
           modifier does not inhibit all optimizations that may eliminate
           reads and/or writes to register variables.  This warning is enabled
           by -Wall.

       -Wdisabled-optimization
           Warn if a requested optimization pass is disabled.  This warning
           does not generally indicate that there is anything wrong with your
           code; it merely indicates that GCC's optimizers are unable to
           handle the code effectively.  Often, the problem is that your code
           is too big or too complex; GCC refuses to optimize programs when
           the optimization itself is likely to take inordinate amounts of
           time.

       -Wpointer-sign (C and Objective-C only)
           Warn for pointer argument passing or assignment with different
           signedness.  This option is only supported for C and Objective-C.
           It is implied by -Wall and by -Wpedantic, which can be disabled
           with -Wno-pointer-sign.

       -Wstack-protector
           This option is only active when -fstack-protector is active.  It
           warns about functions that are not protected against stack
           smashing.

       -Woverlength-strings
           Warn about string constants that are longer than the "minimum
           maximum" length specified in the C standard.  Modern compilers
           generally allow string constants that are much longer than the
           standard's minimum limit, but very portable programs should avoid
           using longer strings.

           The limit applies after string constant concatenation, and does not
           count the trailing NUL.  In C90, the limit was 509 characters; in
           C99, it was raised to 4095.  C++98 does not specify a normative
           minimum maximum, so we do not diagnose overlength strings in C++.

           This option is implied by -Wpedantic, and can be disabled with
           -Wno-overlength-strings.

       -Wunsuffixed-float-constants (C and Objective-C only)
           Issue a warning for any floating constant that does not have a
           suffix.  When used together with -Wsystem-headers it warns about
           such constants in system header files.  This can be useful when
           preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma from
           the decimal floating-point extension to C99.

       -Wno-lto-type-mismatch
           During the link-time optimization, do not warn about type
           mismatches in global declarations from different compilation units.
           Requires -flto to be enabled.  Enabled by default.

       -Wno-designated-init (C and Objective-C only)
           Suppress warnings when a positional initializer is used to
           initialize a structure that has been marked with the
           "designated_init" attribute.

       -Wno-hsa
           Do not warn when HSAIL cannot be emitted for the compiled function
           or OpenMP construct.  These warnings are enabled by default.

   Options That Control Static Analysis
       -fanalyzer
           This option enables an static analysis of program flow which looks
           for "interesting" interprocedural paths through the code, and
           issues warnings for problems found on them.

           This analysis is much more expensive than other GCC warnings.

           Enabling this option effectively enables the following warnings:

           -Wanalyzer-double-fclose -Wanalyzer-double-free
           -Wanalyzer-exposure-through-output-file -Wanalyzer-file-leak
           -Wanalyzer-free-of-non-heap -Wanalyzer-malloc-leak
           -Wanalyzer-possible-null-argument
           -Wanalyzer-possible-null-dereference -Wanalyzer-null-argument
           -Wanalyzer-null-dereference -Wanalyzer-stale-setjmp-buffer
           -Wanalyzer-tainted-array-index
           -Wanalyzer-unsafe-call-within-signal-handler
           -Wanalyzer-use-after-free
           -Wanalyzer-use-of-pointer-in-stale-stack-frame

           This option is only available if GCC was configured with analyzer
           support enabled.

       -Wanalyzer-too-complex
           If -fanalyzer is enabled, the analyzer uses various heuristics to
           attempt to explore the control flow and data flow in the program,
           but these can be defeated by sufficiently complicated code.

           By default, the analysis silently stops if the code is too
           complicated for the analyzer to fully explore and it reaches an
           internal limit.  The -Wanalyzer-too-complex option warns if this
           occurs.

       -Wno-analyzer-double-fclose
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-double-fclose to disable it.

           This diagnostic warns for paths through the code in which a "FILE
           *" can have "fclose" called on it more than once.

       -Wno-analyzer-double-free
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-double-free to disable it.

           This diagnostic warns for paths through the code in which a pointer
           can have "free" called on it more than once.

       -Wno-analyzer-exposure-through-output-file
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-exposure-through-output-file to disable it.

           This diagnostic warns for paths through the code in which a
           security-sensitive value is written to an output file (such as
           writing a password to a log file).

       -Wno-analyzer-file-leak
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-file-leak to disable it.

           This diagnostic warns for paths through the code in which a
           "<stdio.h>" "FILE *" stream object is leaked.

       -Wno-analyzer-free-of-non-heap
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-free-of-non-heap to disable it.

           This diagnostic warns for paths through the code in which "free" is
           called on a non-heap pointer (e.g. an on-stack buffer, or a
           global).

       -Wno-analyzer-malloc-leak
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-malloc-leak to disable it.

           This diagnostic warns for paths through the code in which a pointer
           allocated via "malloc" is leaked.

       -Wno-analyzer-possible-null-argument
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-possible-null-argument to disable it.

           This diagnostic warns for paths through the code in which a
           possibly-NULL value is passed to a function argument marked with
           "__attribute__((nonnull))" as requiring a non-NULL value.

       -Wno-analyzer-possible-null-dereference
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-possible-null-dereference to disable it.

           This diagnostic warns for paths through the code in which a
           possibly-NULL value is dereferenced.

       -Wno-analyzer-null-argument
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-null-argument to disable it.

           This diagnostic warns for paths through the code in which a value
           known to be NULL is passed to a function argument marked with
           "__attribute__((nonnull))" as requiring a non-NULL value.

       -Wno-analyzer-null-dereference
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-null-dereference to disable it.

           This diagnostic warns for paths through the code in which a value
           known to be NULL is dereferenced.

       -Wno-analyzer-stale-setjmp-buffer
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-stale-setjmp-buffer to disable it.

           This diagnostic warns for paths through the code in which "longjmp"
           is called to rewind to a "jmp_buf" relating to a "setjmp" call in a
           function that has returned.

           When "setjmp" is called on a "jmp_buf" to record a rewind location,
           it records the stack frame.  The stack frame becomes invalid when
           the function containing the "setjmp" call returns.  Attempting to
           rewind to it via "longjmp" would reference a stack frame that no
           longer exists, and likely lead to a crash (or worse).

       -Wno-analyzer-tainted-array-index
           This warning requires both -fanalyzer and -fanalyzer-checker=taint
           to enable it; use -Wno-analyzer-tainted-array-index to disable it.

           This diagnostic warns for paths through the code in which a value
           that could be under an attacker's control is used as the index of
           an array access without being sanitized.

       -Wno-analyzer-unsafe-call-within-signal-handler
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-unsafe-call-within-signal-handler to disable it.

           This diagnostic warns for paths through the code in which a
           function known to be async-signal-unsafe (such as "fprintf") is
           called from a signal handler.

       -Wno-analyzer-use-after-free
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-use-after-free to disable it.

           This diagnostic warns for paths through the code in which a pointer
           is used after "free" is called on it.

       -Wno-analyzer-use-of-pointer-in-stale-stack-frame
           This warning requires -fanalyzer, which enables it; use
           -Wno-analyzer-use-of-pointer-in-stale-stack-frame to disable it.

           This diagnostic warns for paths through the code in which a pointer
           is dereferenced that points to a variable in a stale stack frame.

       Pertinent parameters for controlling the exploration are: --param
       analyzer-bb-explosion-factor=value, --param
       analyzer-max-enodes-per-program-point=value, --param
       analyzer-max-recursion-depth=value, and --param
       analyzer-min-snodes-for-call-summary=value.

       The following options control the analyzer.

       -fanalyzer-call-summaries
           Simplify interprocedural analysis by computing the effect of
           certain calls, rather than exploring all paths through the function
           from callsite to each possible return.

           If enabled, call summaries are only used for functions with more
           than one call site, and that are sufficiently complicated (as per
           --param analyzer-min-snodes-for-call-summary=value).

       -fanalyzer-checker=name
           Restrict the analyzer to run just the named checker, and enable it.

           Some checkers are disabled by default (even with -fanalyzer), such
           as the "taint" checker that implements
           -Wanalyzer-tainted-array-index, and this option is required to
           enable them.

       -fanalyzer-fine-grained
           This option is intended for analyzer developers.

           Internally the analyzer builds an "exploded graph" that combines
           control flow graphs with data flow information.

           By default, an edge in this graph can contain the effects of a run
           of multiple statements within a basic block.  With
           -fanalyzer-fine-grained, each statement gets its own edge.

       -fanalyzer-show-duplicate-count
           This option is intended for analyzer developers: if multiple
           diagnostics have been detected as being duplicates of each other,
           it emits a note when reporting the best diagnostic, giving the
           number of additional diagnostics that were suppressed by the
           deduplication logic.

       -fno-analyzer-state-merge
           This option is intended for analyzer developers.

           By default the analyzer attempts to simplify analysis by merging
           sufficiently similar states at each program point as it builds its
           "exploded graph".  With -fno-analyzer-state-merge this merging can
           be suppressed, for debugging state-handling issues.

       -fno-analyzer-state-purge
           This option is intended for analyzer developers.

           By default the analyzer attempts to simplify analysis by purging
           aspects of state at a program point that appear to no longer be
           relevant e.g. the values of locals that aren't accessed later in
           the function and which aren't relevant to leak analysis.

           With -fno-analyzer-state-purge this purging of state can be
           suppressed, for debugging state-handling issues.

       -fanalyzer-transitivity
           This option enables transitivity of constraints within the
           analyzer.

       -fanalyzer-verbose-edges
           This option is intended for analyzer developers.  It enables more
           verbose, lower-level detail in the descriptions of control flow
           within diagnostic paths.

       -fanalyzer-verbose-state-changes
           This option is intended for analyzer developers.  It enables more
           verbose, lower-level detail in the descriptions of events relating
           to state machines within diagnostic paths.

       -fanalyzer-verbosity=level
           This option controls the complexity of the control flow paths that
           are emitted for analyzer diagnostics.

           The level can be one of:

           0   At this level, interprocedural call and return events are
               displayed, along with the most pertinent state-change events
               relating to a diagnostic.  For example, for a double-"free"
               diagnostic, both calls to "free" will be shown.

           1   As per the previous level, but also show events for the entry
               to each function.

           2   As per the previous level, but also show events relating to
               control flow that are significant to triggering the issue (e.g.
               "true path taken" at a conditional).

               This level is the default.

           3   As per the previous level, but show all control flow events,
               not just significant ones.

           4   This level is intended for analyzer developers; it adds various
               other events intended for debugging the analyzer.

       -fdump-analyzer
           Dump internal details about what the analyzer is doing to
           file.analyzer.txt.  This option is overridden by
           -fdump-analyzer-stderr.

       -fdump-analyzer-stderr
           Dump internal details about what the analyzer is doing to stderr.
           This option overrides -fdump-analyzer.

       -fdump-analyzer-callgraph
           Dump a representation of the call graph suitable for viewing with
           GraphViz to file.callgraph.dot.

       -fdump-analyzer-exploded-graph
           Dump a representation of the "exploded graph" suitable for viewing
           with GraphViz to file.eg.dot.  Nodes are color-coded based on
           state-machine states to emphasize state changes.

       -fdump-analyzer-exploded-nodes
           Emit diagnostics showing where nodes in the "exploded graph" are in
           relation to the program source.

       -fdump-analyzer-exploded-nodes-2
           Dump a textual representation of the "exploded graph" to
           file.eg.txt.

       -fdump-analyzer-exploded-nodes-3
           Dump a textual representation of the "exploded graph" to one dump
           file per node, to file.eg-id.txt.  This is typically a large number
           of dump files.

       -fdump-analyzer-state-purge
           As per -fdump-analyzer-supergraph, dump a representation of the
           "supergraph" suitable for viewing with GraphViz, but annotate the
           graph with information on what state will be purged at each node.
           The graph is written to file.state-purge.dot.

       -fdump-analyzer-supergraph
           Dump representations of the "supergraph" suitable for viewing with
           GraphViz to file.supergraph.dot and to file.supergraph-eg.dot.
           These show all of the control flow graphs in the program, with
           interprocedural edges for calls and returns.  The second dump
           contains annotations showing nodes in the "exploded graph" and
           diagnostics associated with them.

   Options for Debugging Your Program
       To tell GCC to emit extra information for use by a debugger, in almost
       all cases you need only to add -g to your other options.

       GCC allows you to use -g with -O.  The shortcuts taken by optimized
       code may occasionally be surprising: some variables you declared may
       not exist at all; flow of control may briefly move where you did not
       expect it; some statements may not be executed because they compute
       constant results or their values are already at hand; some statements
       may execute in different places because they have been moved out of
       loops.  Nevertheless it is possible to debug optimized output.  This
       makes it reasonable to use the optimizer for programs that might have
       bugs.

       If you are not using some other optimization option, consider using -Og
       with -g.  With no -O option at all, some compiler passes that collect
       information useful for debugging do not run at all, so that -Og may
       result in a better debugging experience.

       -g  Produce debugging information in the operating system's native
           format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
           debugging information.

           On most systems that use stabs format, -g enables use of extra
           debugging information that only GDB can use; this extra information
           makes debugging work better in GDB but probably makes other
           debuggers crash or refuse to read the program.  If you want to
           control for certain whether to generate the extra information, use
           -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).

       -ggdb
           Produce debugging information for use by GDB.  This means to use
           the most expressive format available (DWARF, stabs, or the native
           format if neither of those are supported), including GDB extensions
           if at all possible.

       -gdwarf
       -gdwarf-version
           Produce debugging information in DWARF format (if that is
           supported).  The value of version may be either 2, 3, 4 or 5; the
           default version for most targets is 4.  DWARF Version 5 is only
           experimental.

           Note that with DWARF Version 2, some ports require and always use
           some non-conflicting DWARF 3 extensions in the unwind tables.

           Version 4 may require GDB 7.0 and -fvar-tracking-assignments for
           maximum benefit.

           GCC no longer supports DWARF Version 1, which is substantially
           different than Version 2 and later.  For historical reasons, some
           other DWARF-related options such as -fno-dwarf2-cfi-asm) retain a
           reference to DWARF Version 2 in their names, but apply to all
           currently-supported versions of DWARF.

       -gstabs
           Produce debugging information in stabs format (if that is
           supported), without GDB extensions.  This is the format used by DBX
           on most BSD systems.  On MIPS, Alpha and System V Release 4 systems
           this option produces stabs debugging output that is not understood
           by DBX. On System V Release 4 systems this option requires the GNU
           assembler.

       -gstabs+
           Produce debugging information in stabs format (if that is
           supported), using GNU extensions understood only by the GNU
           debugger (GDB).  The use of these extensions is likely to make
           other debuggers crash or refuse to read the program.

       -gxcoff
           Produce debugging information in XCOFF format (if that is
           supported).  This is the format used by the DBX debugger on IBM
           RS/6000 systems.

       -gxcoff+
           Produce debugging information in XCOFF format (if that is
           supported), using GNU extensions understood only by the GNU
           debugger (GDB).  The use of these extensions is likely to make
           other debuggers crash or refuse to read the program, and may cause
           assemblers other than the GNU assembler (GAS) to fail with an
           error.

       -gvms
           Produce debugging information in Alpha/VMS debug format (if that is
           supported).  This is the format used by DEBUG on Alpha/VMS systems.

       -glevel
       -ggdblevel
       -gstabslevel
       -gxcofflevel
       -gvmslevel
           Request debugging information and also use level to specify how
           much information.  The default level is 2.

           Level 0 produces no debug information at all.  Thus, -g0 negates
           -g.

           Level 1 produces minimal information, enough for making backtraces
           in parts of the program that you don't plan to debug.  This
           includes descriptions of functions and external variables, and line
           number tables, but no information about local variables.

           Level 3 includes extra information, such as all the macro
           definitions present in the program.  Some debuggers support macro
           expansion when you use -g3.

           If you use multiple -g options, with or without level numbers, the
           last such option is the one that is effective.

           -gdwarf does not accept a concatenated debug level, to avoid
           confusion with -gdwarf-level.  Instead use an additional -glevel
           option to change the debug level for DWARF.

       -fno-eliminate-unused-debug-symbols
           By default, no debug information is produced for symbols that are
           not actually used. Use this option if you want debug information
           for all symbols.

       -femit-class-debug-always
           Instead of emitting debugging information for a C++ class in only
           one object file, emit it in all object files using the class.  This
           option should be used only with debuggers that are unable to handle
           the way GCC normally emits debugging information for classes
           because using this option increases the size of debugging
           information by as much as a factor of two.

       -fno-merge-debug-strings
           Direct the linker to not merge together strings in the debugging
           information that are identical in different object files.  Merging
           is not supported by all assemblers or linkers.  Merging decreases
           the size of the debug information in the output file at the cost of
           increasing link processing time.  Merging is enabled by default.

       -fdebug-prefix-map=old=new
           When compiling files residing in directory old, record debugging
           information describing them as if the files resided in directory
           new instead.  This can be used to replace a build-time path with an
           install-time path in the debug info.  It can also be used to change
           an absolute path to a relative path by using . for new.  This can
           give more reproducible builds, which are location independent, but
           may require an extra command to tell GDB where to find the source
           files. See also -ffile-prefix-map.

       -fvar-tracking
           Run variable tracking pass.  It computes where variables are stored
           at each position in code.  Better debugging information is then
           generated (if the debugging information format supports this
           information).

           It is enabled by default when compiling with optimization (-Os, -O,
           -O2, ...), debugging information (-g) and the debug info format
           supports it.

       -fvar-tracking-assignments
           Annotate assignments to user variables early in the compilation and
           attempt to carry the annotations over throughout the compilation
           all the way to the end, in an attempt to improve debug information
           while optimizing.  Use of -gdwarf-4 is recommended along with it.

           It can be enabled even if var-tracking is disabled, in which case
           annotations are created and maintained, but discarded at the end.
           By default, this flag is enabled together with -fvar-tracking,
           except when selective scheduling is enabled.

       -gsplit-dwarf
           Separate as much DWARF debugging information as possible into a
           separate output file with the extension .dwo.  This option allows
           the build system to avoid linking files with debug information.  To
           be useful, this option requires a debugger capable of reading .dwo
           files.

       -gdescribe-dies
           Add description attributes to some DWARF DIEs that have no name
           attribute, such as artificial variables, external references and
           call site parameter DIEs.

       -gpubnames
           Generate DWARF ".debug_pubnames" and ".debug_pubtypes" sections.

       -ggnu-pubnames
           Generate ".debug_pubnames" and ".debug_pubtypes" sections in a
           format suitable for conversion into a GDB index.  This option is
           only useful with a linker that can produce GDB index version 7.

       -fdebug-types-section
           When using DWARF Version 4 or higher, type DIEs can be put into
           their own ".debug_types" section instead of making them part of the
           ".debug_info" section.  It is more efficient to put them in a
           separate comdat section since the linker can then remove
           duplicates.  But not all DWARF consumers support ".debug_types"
           sections yet and on some objects ".debug_types" produces larger
           instead of smaller debugging information.

       -grecord-gcc-switches
       -gno-record-gcc-switches
           This switch causes the command-line options used to invoke the
           compiler that may affect code generation to be appended to the
           DW_AT_producer attribute in DWARF debugging information.  The
           options are concatenated with spaces separating them from each
           other and from the compiler version.  It is enabled by default.
           See also -frecord-gcc-switches for another way of storing compiler
           options into the object file.

       -gstrict-dwarf
           Disallow using extensions of later DWARF standard version than
           selected with -gdwarf-version.  On most targets using non-
           conflicting DWARF extensions from later standard versions is
           allowed.

       -gno-strict-dwarf
           Allow using extensions of later DWARF standard version than
           selected with -gdwarf-version.

       -gas-loc-support
           Inform the compiler that the assembler supports ".loc" directives.
           It may then use them for the assembler to generate DWARF2+ line
           number tables.

           This is generally desirable, because assembler-generated line-
           number tables are a lot more compact than those the compiler can
           generate itself.

           This option will be enabled by default if, at GCC configure time,
           the assembler was found to support such directives.

       -gno-as-loc-support
           Force GCC to generate DWARF2+ line number tables internally, if
           DWARF2+ line number tables are to be generated.

       -gas-locview-support
           Inform the compiler that the assembler supports "view" assignment
           and reset assertion checking in ".loc" directives.

           This option will be enabled by default if, at GCC configure time,
           the assembler was found to support them.

       -gno-as-locview-support
           Force GCC to assign view numbers internally, if
           -gvariable-location-views are explicitly requested.

       -gcolumn-info
       -gno-column-info
           Emit location column information into DWARF debugging information,
           rather than just file and line.  This option is enabled by default.

       -gstatement-frontiers
       -gno-statement-frontiers
           This option causes GCC to create markers in the internal
           representation at the beginning of statements, and to keep them
           roughly in place throughout compilation, using them to guide the
           output of "is_stmt" markers in the line number table.  This is
           enabled by default when compiling with optimization (-Os, -O, -O2,
           ...), and outputting DWARF 2 debug information at the normal level.

       -gvariable-location-views
       -gvariable-location-views=incompat5
       -gno-variable-location-views
           Augment variable location lists with progressive view numbers
           implied from the line number table.  This enables debug information
           consumers to inspect state at certain points of the program, even
           if no instructions associated with the corresponding source
           locations are present at that point.  If the assembler lacks
           support for view numbers in line number tables, this will cause the
           compiler to emit the line number table, which generally makes them
           somewhat less compact.  The augmented line number tables and
           location lists are fully backward-compatible, so they can be
           consumed by debug information consumers that are not aware of these
           augmentations, but they won't derive any benefit from them either.

           This is enabled by default when outputting DWARF 2 debug
           information at the normal level, as long as there is assembler
           support, -fvar-tracking-assignments is enabled and -gstrict-dwarf
           is not.  When assembler support is not available, this may still be
           enabled, but it will force GCC to output internal line number
           tables, and if -ginternal-reset-location-views is not enabled, that
           will most certainly lead to silently mismatching location views.

           There is a proposed representation for view numbers that is not
           backward compatible with the location list format introduced in
           DWARF 5, that can be enabled with
           -gvariable-location-views=incompat5.  This option may be removed in
           the future, is only provided as a reference implementation of the
           proposed representation.  Debug information consumers are not
           expected to support this extended format, and they would be
           rendered unable to decode location lists using it.

       -ginternal-reset-location-views
       -gno-internal-reset-location-views
           Attempt to determine location views that can be omitted from
           location view lists.  This requires the compiler to have very
           accurate insn length estimates, which isn't always the case, and it
           may cause incorrect view lists to be generated silently when using
           an assembler that does not support location view lists.  The GNU
           assembler will flag any such error as a "view number mismatch".
           This is only enabled on ports that define a reliable estimation
           function.

       -ginline-points
       -gno-inline-points
           Generate extended debug information for inlined functions.
           Location view tracking markers are inserted at inlined entry
           points, so that address and view numbers can be computed and output
           in debug information.  This can be enabled independently of
           location views, in which case the view numbers won't be output, but
           it can only be enabled along with statement frontiers, and it is
           only enabled by default if location views are enabled.

       -gz[=type]
           Produce compressed debug sections in DWARF format, if that is
           supported.  If type is not given, the default type depends on the
           capabilities of the assembler and linker used.  type may be one of
           none (don't compress debug sections), zlib (use zlib compression in
           ELF gABI format), or zlib-gnu (use zlib compression in traditional
           GNU format).  If the linker doesn't support writing compressed
           debug sections, the option is rejected.  Otherwise, if the
           assembler does not support them, -gz is silently ignored when
           producing object files.

       -femit-struct-debug-baseonly
           Emit debug information for struct-like types only when the base
           name of the compilation source file matches the base name of file
           in which the struct is defined.

           This option substantially reduces the size of debugging
           information, but at significant potential loss in type information
           to the debugger.  See -femit-struct-debug-reduced for a less
           aggressive option.  See -femit-struct-debug-detailed for more
           detailed control.

           This option works only with DWARF debug output.

       -femit-struct-debug-reduced
           Emit debug information for struct-like types only when the base
           name of the compilation source file matches the base name of file
           in which the type is defined, unless the struct is a template or
           defined in a system header.

           This option significantly reduces the size of debugging
           information, with some potential loss in type information to the
           debugger.  See -femit-struct-debug-baseonly for a more aggressive
           option.  See -femit-struct-debug-detailed for more detailed
           control.

           This option works only with DWARF debug output.

       -femit-struct-debug-detailed[=spec-list]
           Specify the struct-like types for which the compiler generates
           debug information.  The intent is to reduce duplicate struct debug
           information between different object files within the same program.

           This option is a detailed version of -femit-struct-debug-reduced
           and -femit-struct-debug-baseonly, which serves for most needs.

           A specification has the
           syntax[dir:|ind:][ord:|gen:](any|sys|base|none)

           The optional first word limits the specification to structs that
           are used directly (dir:) or used indirectly (ind:).  A struct type
           is used directly when it is the type of a variable, member.
           Indirect uses arise through pointers to structs.  That is, when use
           of an incomplete struct is valid, the use is indirect.  An example
           is struct one direct; struct two * indirect;.

           The optional second word limits the specification to ordinary
           structs (ord:) or generic structs (gen:).  Generic structs are a
           bit complicated to explain.  For C++, these are non-explicit
           specializations of template classes, or non-template classes within
           the above.  Other programming languages have generics, but
           -femit-struct-debug-detailed does not yet implement them.

           The third word specifies the source files for those structs for
           which the compiler should emit debug information.  The values none
           and any have the normal meaning.  The value base means that the
           base of name of the file in which the type declaration appears must
           match the base of the name of the main compilation file.  In
           practice, this means that when compiling foo.c, debug information
           is generated for types declared in that file and foo.h, but not
           other header files.  The value sys means those types satisfying
           base or declared in system or compiler headers.

           You may need to experiment to determine the best settings for your
           application.

           The default is -femit-struct-debug-detailed=all.

           This option works only with DWARF debug output.

       -fno-dwarf2-cfi-asm
           Emit DWARF unwind info as compiler generated ".eh_frame" section
           instead of using GAS ".cfi_*" directives.

       -fno-eliminate-unused-debug-types
           Normally, when producing DWARF output, GCC avoids producing debug
           symbol output for types that are nowhere used in the source file
           being compiled.  Sometimes it is useful to have GCC emit debugging
           information for all types declared in a compilation unit,
           regardless of whether or not they are actually used in that
           compilation unit, for example if, in the debugger, you want to cast
           a value to a type that is not actually used in your program (but is
           declared).  More often, however, this results in a significant
           amount of wasted space.

   Options That Control Optimization
       These options control various sorts of optimizations.

       Without any optimization option, the compiler's goal is to reduce the
       cost of compilation and to make debugging produce the expected results.
       Statements are independent: if you stop the program with a breakpoint
       between statements, you can then assign a new value to any variable or
       change the program counter to any other statement in the function and
       get exactly the results you expect from the source code.

       Turning on optimization flags makes the compiler attempt to improve the
       performance and/or code size at the expense of compilation time and
       possibly the ability to debug the program.

       The compiler performs optimization based on the knowledge it has of the
       program.  Compiling multiple files at once to a single output file mode
       allows the compiler to use information gained from all of the files
       when compiling each of them.

       Not all optimizations are controlled directly by a flag.  Only
       optimizations that have a flag are listed in this section.

       Most optimizations are completely disabled at -O0 or if an -O level is
       not set on the command line, even if individual optimization flags are
       specified.  Similarly, -Og suppresses many optimization passes.

       Depending on the target and how GCC was configured, a slightly
       different set of optimizations may be enabled at each -O level than
       those listed here.  You can invoke GCC with -Q --help=optimizers to
       find out the exact set of optimizations that are enabled at each level.

       -O
       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a
           lot more memory for a large function.

           With -O, the compiler tries to reduce code size and execution time,
           without performing any optimizations that take a great deal of
           compilation time.

           -O turns on the following optimization flags:

           -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments
           -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch
           -fdse -fforward-propagate -fguess-branch-probability
           -fif-conversion -fif-conversion2 -finline-functions-called-once
           -fipa-profile -fipa-pure-const -fipa-reference
           -fipa-reference-addressable -fmerge-constants
           -fmove-loop-invariants -fomit-frame-pointer -freorder-blocks
           -fshrink-wrap -fshrink-wrap-separate -fsplit-wide-types
           -fssa-backprop -fssa-phiopt -ftree-bit-ccp -ftree-ccp -ftree-ch
           -ftree-coalesce-vars -ftree-copy-prop -ftree-dce
           -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre
           -ftree-phiprop -ftree-pta -ftree-scev-cprop -ftree-sink -ftree-slsr
           -ftree-sra -ftree-ter -funit-at-a-time

       -O2 Optimize even more.  GCC performs nearly all supported
           optimizations that do not involve a space-speed tradeoff.  As
           compared to -O, this option increases both compilation time and the
           performance of the generated code.

           -O2 turns on all optimization flags specified by -O.  It also turns
           on the following optimization flags:

           -falign-functions  -falign-jumps -falign-labels  -falign-loops
           -fcaller-saves -fcode-hoisting -fcrossjumping -fcse-follow-jumps
           -fcse-skip-blocks -fdelete-null-pointer-checks -fdevirtualize
           -fdevirtualize-speculatively -fexpensive-optimizations
           -ffinite-loops -fgcse  -fgcse-lm -fhoist-adjacent-loads
           -finline-functions -finline-small-functions -findirect-inlining
           -fipa-bit-cp  -fipa-cp  -fipa-icf -fipa-ra  -fipa-sra  -fipa-vrp
           -fisolate-erroneous-paths-dereference -flra-remat
           -foptimize-sibling-calls -foptimize-strlen -fpartial-inlining
           -fpeephole2 -freorder-blocks-algorithm=stc
           -freorder-blocks-and-partition  -freorder-functions
           -frerun-cse-after-loop -fschedule-insns  -fschedule-insns2
           -fsched-interblock  -fsched-spec -fstore-merging -fstrict-aliasing
           -fthread-jumps -ftree-builtin-call-dce -ftree-pre
           -ftree-switch-conversion  -ftree-tail-merge -ftree-vrp

           Please note the warning under -fgcse about invoking -O2 on programs
           that use computed gotos.

       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
           and also turns on the following optimization flags:

           -fgcse-after-reload -fipa-cp-clone -floop-interchange
           -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning
           -fsplit-loops -fsplit-paths -ftree-loop-distribution
           -ftree-loop-vectorize -ftree-partial-pre -ftree-slp-vectorize
           -funswitch-loops -fvect-cost-model -fvect-cost-model=dynamic
           -fversion-loops-for-strides

       -O0 Reduce compilation time and make debugging produce the expected
           results.  This is the default.

       -Os Optimize for size.  -Os enables all -O2 optimizations except those
           that often increase code size:

           -falign-functions  -falign-jumps -falign-labels  -falign-loops
           -fprefetch-loop-arrays  -freorder-blocks-algorithm=stc

           It also enables -finline-functions, causes the compiler to tune for
           code size rather than execution speed, and performs further
           optimizations designed to reduce code size.

       -Ofast
           Disregard strict standards compliance.  -Ofast enables all -O3
           optimizations.  It also enables optimizations that are not valid
           for all standard-compliant programs.  It turns on -ffast-math,
           -fallow-store-data-races and the Fortran-specific -fstack-arrays,
           unless -fmax-stack-var-size is specified, and -fno-protect-parens.

       -Og Optimize debugging experience.  -Og should be the optimization
           level of choice for the standard edit-compile-debug cycle, offering
           a reasonable level of optimization while maintaining fast
           compilation and a good debugging experience.  It is a better choice
           than -O0 for producing debuggable code because some compiler passes
           that collect debug information are disabled at -O0.

           Like -O0, -Og completely disables a number of optimization passes
           so that individual options controlling them have no effect.
           Otherwise -Og enables all -O1 optimization flags except for those
           that may interfere with debugging:

           -fbranch-count-reg  -fdelayed-branch -fdse  -fif-conversion
           -fif-conversion2 -finline-functions-called-once
           -fmove-loop-invariants  -fssa-phiopt -ftree-bit-ccp  -ftree-dse
           -ftree-pta  -ftree-sra

       If you use multiple -O options, with or without level numbers, the last
       such option is the one that is effective.

       Options of the form -fflag specify machine-independent flags.  Most
       flags have both positive and negative forms; the negative form of -ffoo
       is -fno-foo.  In the table below, only one of the forms is listed---the
       one you typically use.  You can figure out the other form by either
       removing no- or adding it.

       The following options control specific optimizations.  They are either
       activated by -O options or are related to ones that are.  You can use
       the following flags in the rare cases when "fine-tuning" of
       optimizations to be performed is desired.

       -fno-defer-pop
           For machines that must pop arguments after a function call, always
           pop the arguments as soon as each function returns.  At levels -O1
           and higher, -fdefer-pop is the default; this allows the compiler to
           let arguments accumulate on the stack for several function calls
           and pop them all at once.

       -fforward-propagate
           Perform a forward propagation pass on RTL.  The pass tries to
           combine two instructions and checks if the result can be
           simplified.  If loop unrolling is active, two passes are performed
           and the second is scheduled after loop unrolling.

           This option is enabled by default at optimization levels -O, -O2,
           -O3, -Os.

       -ffp-contract=style
           -ffp-contract=off disables floating-point expression contraction.
           -ffp-contract=fast enables floating-point expression contraction
           such as forming of fused multiply-add operations if the target has
           native support for them.  -ffp-contract=on enables floating-point
           expression contraction if allowed by the language standard.  This
           is currently not implemented and treated equal to
           -ffp-contract=off.

           The default is -ffp-contract=fast.

       -fomit-frame-pointer
           Omit the frame pointer in functions that don't need one.  This
           avoids the instructions to save, set up and restore the frame
           pointer; on many targets it also makes an extra register available.

           On some targets this flag has no effect because the standard
           calling sequence always uses a frame pointer, so it cannot be
           omitted.

           Note that -fno-omit-frame-pointer doesn't guarantee the frame
           pointer is used in all functions.  Several targets always omit the
           frame pointer in leaf functions.

           Enabled by default at -O and higher.

       -foptimize-sibling-calls
           Optimize sibling and tail recursive calls.

           Enabled at levels -O2, -O3, -Os.

       -foptimize-strlen
           Optimize various standard C string functions (e.g. "strlen",
           "strchr" or "strcpy") and their "_FORTIFY_SOURCE" counterparts into
           faster alternatives.

           Enabled at levels -O2, -O3.

       -fno-inline
           Do not expand any functions inline apart from those marked with the
           "always_inline" attribute.  This is the default when not
           optimizing.

           Single functions can be exempted from inlining by marking them with
           the "noinline" attribute.

       -finline-small-functions
           Integrate functions into their callers when their body is smaller
           than expected function call code (so overall size of program gets
           smaller).  The compiler heuristically decides which functions are
           simple enough to be worth integrating in this way.  This inlining
           applies to all functions, even those not declared inline.

           Enabled at levels -O2, -O3, -Os.

       -findirect-inlining
           Inline also indirect calls that are discovered to be known at
           compile time thanks to previous inlining.  This option has any
           effect only when inlining itself is turned on by the
           -finline-functions or -finline-small-functions options.

           Enabled at levels -O2, -O3, -Os.

       -finline-functions
           Consider all functions for inlining, even if they are not declared
           inline.  The compiler heuristically decides which functions are
           worth integrating in this way.

           If all calls to a given function are integrated, and the function
           is declared "static", then the function is normally not output as
           assembler code in its own right.

           Enabled at levels -O2, -O3, -Os.  Also enabled by -fprofile-use and
           -fauto-profile.

       -finline-functions-called-once
           Consider all "static" functions called once for inlining into their
           caller even if they are not marked "inline".  If a call to a given
           function is integrated, then the function is not output as
           assembler code in its own right.

           Enabled at levels -O1, -O2, -O3 and -Os, but not -Og.

       -fearly-inlining
           Inline functions marked by "always_inline" and functions whose body
           seems smaller than the function call overhead early before doing
           -fprofile-generate instrumentation and real inlining pass.  Doing
           so makes profiling significantly cheaper and usually inlining
           faster on programs having large chains of nested wrapper functions.

           Enabled by default.

       -fipa-sra
           Perform interprocedural scalar replacement of aggregates, removal
           of unused parameters and replacement of parameters passed by
           reference by parameters passed by value.

           Enabled at levels -O2, -O3 and -Os.

       -finline-limit=n
           By default, GCC limits the size of functions that can be inlined.
           This flag allows coarse control of this limit.  n is the size of
           functions that can be inlined in number of pseudo instructions.

           Inlining is actually controlled by a number of parameters, which
           may be specified individually by using --param name=value.  The
           -finline-limit=n option sets some of these parameters as follows:

           max-inline-insns-single
               is set to n/2.

           max-inline-insns-auto
               is set to n/2.

           See below for a documentation of the individual parameters
           controlling inlining and for the defaults of these parameters.

           Note: there may be no value to -finline-limit that results in
           default behavior.

           Note: pseudo instruction represents, in this particular context, an
           abstract measurement of function's size.  In no way does it
           represent a count of assembly instructions and as such its exact
           meaning might change from one release to an another.

       -fno-keep-inline-dllexport
           This is a more fine-grained version of -fkeep-inline-functions,
           which applies only to functions that are declared using the
           "dllexport" attribute or declspec.

       -fkeep-inline-functions
           In C, emit "static" functions that are declared "inline" into the
           object file, even if the function has been inlined into all of its
           callers.  This switch does not affect functions using the "extern
           inline" extension in GNU C90.  In C++, emit any and all inline
           functions into the object file.

       -fkeep-static-functions
           Emit "static" functions into the object file, even if the function
           is never used.

       -fkeep-static-consts
           Emit variables declared "static const" when optimization isn't
           turned on, even if the variables aren't referenced.

           GCC enables this option by default.  If you want to force the
           compiler to check if a variable is referenced, regardless of
           whether or not optimization is turned on, use the
           -fno-keep-static-consts option.

       -fmerge-constants
           Attempt to merge identical constants (string constants and
           floating-point constants) across compilation units.

           This option is the default for optimized compilation if the
           assembler and linker support it.  Use -fno-merge-constants to
           inhibit this behavior.

           Enabled at levels -O, -O2, -O3, -Os.

       -fmerge-all-constants
           Attempt to merge identical constants and identical variables.

           This option implies -fmerge-constants.  In addition to
           -fmerge-constants this considers e.g. even constant initialized
           arrays or initialized constant variables with integral or floating-
           point types.  Languages like C or C++ require each variable,
           including multiple instances of the same variable in recursive
           calls, to have distinct locations, so using this option results in
           non-conforming behavior.

       -fmodulo-sched
           Perform swing modulo scheduling immediately before the first
           scheduling pass.  This pass looks at innermost loops and reorders
           their instructions by overlapping different iterations.

       -fmodulo-sched-allow-regmoves
           Perform more aggressive SMS-based modulo scheduling with register
           moves allowed.  By setting this flag certain anti-dependences edges
           are deleted, which triggers the generation of reg-moves based on
           the life-range analysis.  This option is effective only with
           -fmodulo-sched enabled.

       -fno-branch-count-reg
           Disable the optimization pass that scans for opportunities to use
           "decrement and branch" instructions on a count register instead of
           instruction sequences that decrement a register, compare it against
           zero, and then branch based upon the result.  This option is only
           meaningful on architectures that support such instructions, which
           include x86, PowerPC, IA-64 and S/390.  Note that the
           -fno-branch-count-reg option doesn't remove the decrement and
           branch instructions from the generated instruction stream
           introduced by other optimization passes.

           The default is -fbranch-count-reg at -O1 and higher, except for
           -Og.

       -fno-function-cse
           Do not put function addresses in registers; make each instruction
           that calls a constant function contain the function's address
           explicitly.

           This option results in less efficient code, but some strange hacks
           that alter the assembler output may be confused by the
           optimizations performed when this option is not used.

           The default is -ffunction-cse

       -fno-zero-initialized-in-bss
           If the target supports a BSS section, GCC by default puts variables
           that are initialized to zero into BSS.  This can save space in the
           resulting code.

           This option turns off this behavior because some programs
           explicitly rely on variables going to the data section---e.g., so
           that the resulting executable can find the beginning of that
           section and/or make assumptions based on that.

           The default is -fzero-initialized-in-bss.

       -fthread-jumps
           Perform optimizations that check to see if a jump branches to a
           location where another comparison subsumed by the first is found.
           If so, the first branch is redirected to either the destination of
           the second branch or a point immediately following it, depending on
           whether the condition is known to be true or false.

           Enabled at levels -O2, -O3, -Os.

       -fsplit-wide-types
           When using a type that occupies multiple registers, such as "long
           long" on a 32-bit system, split the registers apart and allocate
           them independently.  This normally generates better code for those
           types, but may make debugging more difficult.

           Enabled at levels -O, -O2, -O3, -Os.

       -fsplit-wide-types-early
           Fully split wide types early, instead of very late.  This option
           has no effect unless -fsplit-wide-types is turned on.

           This is the default on some targets.

       -fcse-follow-jumps
           In common subexpression elimination (CSE), scan through jump
           instructions when the target of the jump is not reached by any
           other path.  For example, when CSE encounters an "if" statement
           with an "else" clause, CSE follows the jump when the condition
           tested is false.

           Enabled at levels -O2, -O3, -Os.

       -fcse-skip-blocks
           This is similar to -fcse-follow-jumps, but causes CSE to follow
           jumps that conditionally skip over blocks.  When CSE encounters a
           simple "if" statement with no else clause, -fcse-skip-blocks causes
           CSE to follow the jump around the body of the "if".

           Enabled at levels -O2, -O3, -Os.

       -frerun-cse-after-loop
           Re-run common subexpression elimination after loop optimizations
           are performed.

           Enabled at levels -O2, -O3, -Os.

       -fgcse
           Perform a global common subexpression elimination pass.  This pass
           also performs global constant and copy propagation.

           Note: When compiling a program using computed gotos, a GCC
           extension, you may get better run-time performance if you disable
           the global common subexpression elimination pass by adding
           -fno-gcse to the command line.

           Enabled at levels -O2, -O3, -Os.

       -fgcse-lm
           When -fgcse-lm is enabled, global common subexpression elimination
           attempts to move loads that are only killed by stores into
           themselves.  This allows a loop containing a load/store sequence to
           be changed to a load outside the loop, and a copy/store within the
           loop.

           Enabled by default when -fgcse is enabled.

       -fgcse-sm
           When -fgcse-sm is enabled, a store motion pass is run after global
           common subexpression elimination.  This pass attempts to move
           stores out of loops.  When used in conjunction with -fgcse-lm,
           loops containing a load/store sequence can be changed to a load
           before the loop and a store after the loop.

           Not enabled at any optimization level.

       -fgcse-las
           When -fgcse-las is enabled, the global common subexpression
           elimination pass eliminates redundant loads that come after stores
           to the same memory location (both partial and full redundancies).

           Not enabled at any optimization level.

       -fgcse-after-reload
           When -fgcse-after-reload is enabled, a redundant load elimination
           pass is performed after reload.  The purpose of this pass is to
           clean up redundant spilling.

           Enabled by -fprofile-use and -fauto-profile.

       -faggressive-loop-optimizations
           This option tells the loop optimizer to use language constraints to
           derive bounds for the number of iterations of a loop.  This assumes
           that loop code does not invoke undefined behavior by for example
           causing signed integer overflows or out-of-bound array accesses.
           The bounds for the number of iterations of a loop are used to guide
           loop unrolling and peeling and loop exit test optimizations.  This
           option is enabled by default.

       -funconstrained-commons
           This option tells the compiler that variables declared in common
           blocks (e.g. Fortran) may later be overridden with longer trailing
           arrays. This prevents certain optimizations that depend on knowing
           the array bounds.

       -fcrossjumping
           Perform cross-jumping transformation.  This transformation unifies
           equivalent code and saves code size.  The resulting code may or may
           not perform better than without cross-jumping.

           Enabled at levels -O2, -O3, -Os.

       -fauto-inc-dec
           Combine increments or decrements of addresses with memory accesses.
           This pass is always skipped on architectures that do not have
           instructions to support this.  Enabled by default at -O and higher
           on architectures that support this.

       -fdce
           Perform dead code elimination (DCE) on RTL. Enabled by default at
           -O and higher.

       -fdse
           Perform dead store elimination (DSE) on RTL. Enabled by default at
           -O and higher.

       -fif-conversion
           Attempt to transform conditional jumps into branch-less
           equivalents.  This includes use of conditional moves, min, max, set
           flags and abs instructions, and some tricks doable by standard
           arithmetics.  The use of conditional execution on chips where it is
           available is controlled by -fif-conversion2.

           Enabled at levels -O, -O2, -O3, -Os, but not with -Og.

       -fif-conversion2
           Use conditional execution (where available) to transform
           conditional jumps into branch-less equivalents.

           Enabled at levels -O, -O2, -O3, -Os, but not with -Og.

       -fdeclone-ctor-dtor
           The C++ ABI requires multiple entry points for constructors and
           destructors: one for a base subobject, one for a complete object,
           and one for a virtual destructor that calls operator delete
           afterwards.  For a hierarchy with virtual bases, the base and
           complete variants are clones, which means two copies of the
           function.  With this option, the base and complete variants are
           changed to be thunks that call a common implementation.

           Enabled by -Os.

       -fdelete-null-pointer-checks
           Assume that programs cannot safely dereference null pointers, and
           that no code or data element resides at address zero.  This option
           enables simple constant folding optimizations at all optimization
           levels.  In addition, other optimization passes in GCC use this
           flag to control global dataflow analyses that eliminate useless
           checks for null pointers; these assume that a memory access to
           address zero always results in a trap, so that if a pointer is
           checked after it has already been dereferenced, it cannot be null.

           Note however that in some environments this assumption is not true.
           Use -fno-delete-null-pointer-checks to disable this optimization
           for programs that depend on that behavior.

           This option is enabled by default on most targets.  On Nios II ELF,
           it defaults to off.  On AVR, CR16, and MSP430, this option is
           completely disabled.

           Passes that use the dataflow information are enabled independently
           at different optimization levels.

       -fdevirtualize
           Attempt to convert calls to virtual functions to direct calls.
           This is done both within a procedure and interprocedurally as part
           of indirect inlining (-findirect-inlining) and interprocedural
           constant propagation (-fipa-cp).  Enabled at levels -O2, -O3, -Os.

       -fdevirtualize-speculatively
           Attempt to convert calls to virtual functions to speculative direct
           calls.  Based on the analysis of the type inheritance graph,
           determine for a given call the set of likely targets. If the set is
           small, preferably of size 1, change the call into a conditional
           deciding between direct and indirect calls.  The speculative calls
           enable more optimizations, such as inlining.  When they seem
           useless after further optimization, they are converted back into
           original form.

       -fdevirtualize-at-ltrans
           Stream extra information needed for aggressive devirtualization
           when running the link-time optimizer in local transformation mode.
           This option enables more devirtualization but significantly
           increases the size of streamed data. For this reason it is disabled
           by default.

       -fexpensive-optimizations
           Perform a number of minor optimizations that are relatively
           expensive.

           Enabled at levels -O2, -O3, -Os.

       -free
           Attempt to remove redundant extension instructions.  This is
           especially helpful for the x86-64 architecture, which implicitly
           zero-extends in 64-bit registers after writing to their lower
           32-bit half.

           Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os.

       -fno-lifetime-dse
           In C++ the value of an object is only affected by changes within
           its lifetime: when the constructor begins, the object has an
           indeterminate value, and any changes during the lifetime of the
           object are dead when the object is destroyed.  Normally dead store
           elimination will take advantage of this; if your code relies on the
           value of the object storage persisting beyond the lifetime of the
           object, you can use this flag to disable this optimization.  To
           preserve stores before the constructor starts (e.g. because your
           operator new clears the object storage) but still treat the object
           as dead after the destructor, you can use -flifetime-dse=1.  The
           default behavior can be explicitly selected with -flifetime-dse=2.
           -flifetime-dse=0 is equivalent to -fno-lifetime-dse.

       -flive-range-shrinkage
           Attempt to decrease register pressure through register live range
           shrinkage.  This is helpful for fast processors with small or
           moderate size register sets.

       -fira-algorithm=algorithm
           Use the specified coloring algorithm for the integrated register
           allocator.  The algorithm argument can be priority, which specifies
           Chow's priority coloring, or CB, which specifies Chaitin-Briggs
           coloring.  Chaitin-Briggs coloring is not implemented for all
           architectures, but for those targets that do support it, it is the
           default because it generates better code.

       -fira-region=region
           Use specified regions for the integrated register allocator.  The
           region argument should be one of the following:

           all Use all loops as register allocation regions.  This can give
               the best results for machines with a small and/or irregular
               register set.

           mixed
               Use all loops except for loops with small register pressure as
               the regions.  This value usually gives the best results in most
               cases and for most architectures, and is enabled by default
               when compiling with optimization for speed (-O, -O2, ...).

           one Use all functions as a single region.  This typically results
               in the smallest code size, and is enabled by default for -Os or
               -O0.

       -fira-hoist-pressure
           Use IRA to evaluate register pressure in the code hoisting pass for
           decisions to hoist expressions.  This option usually results in
           smaller code, but it can slow the compiler down.

           This option is enabled at level -Os for all targets.

       -fira-loop-pressure
           Use IRA to evaluate register pressure in loops for decisions to
           move loop invariants.  This option usually results in generation of
           faster and smaller code on machines with large register files (>=
           32 registers), but it can slow the compiler down.

           This option is enabled at level -O3 for some targets.

       -fno-ira-share-save-slots
           Disable sharing of stack slots used for saving call-used hard
           registers living through a call.  Each hard register gets a
           separate stack slot, and as a result function stack frames are
           larger.

       -fno-ira-share-spill-slots
           Disable sharing of stack slots allocated for pseudo-registers.
           Each pseudo-register that does not get a hard register gets a
           separate stack slot, and as a result function stack frames are
           larger.

       -flra-remat
           Enable CFG-sensitive rematerialization in LRA.  Instead of loading
           values of spilled pseudos, LRA tries to rematerialize (recalculate)
           values if it is profitable.

           Enabled at levels -O2, -O3, -Os.

       -fdelayed-branch
           If supported for the target machine, attempt to reorder
           instructions to exploit instruction slots available after delayed
           branch instructions.

           Enabled at levels -O, -O2, -O3, -Os, but not at -Og.

       -fschedule-insns
           If supported for the target machine, attempt to reorder
           instructions to eliminate execution stalls due to required data
           being unavailable.  This helps machines that have slow floating
           point or memory load instructions by allowing other instructions to
           be issued until the result of the load or floating-point
           instruction is required.

           Enabled at levels -O2, -O3.

       -fschedule-insns2
           Similar to -fschedule-insns, but requests an additional pass of
           instruction scheduling after register allocation has been done.
           This is especially useful on machines with a relatively small
           number of registers and where memory load instructions take more
           than one cycle.

           Enabled at levels -O2, -O3, -Os.

       -fno-sched-interblock
           Disable instruction scheduling across basic blocks, which is
           normally enabled when scheduling before register allocation, i.e.
           with -fschedule-insns or at -O2 or higher.

       -fno-sched-spec
           Disable speculative motion of non-load instructions, which is
           normally enabled when scheduling before register allocation, i.e.
           with -fschedule-insns or at -O2 or higher.

       -fsched-pressure
           Enable register pressure sensitive insn scheduling before register
           allocation.  This only makes sense when scheduling before register
           allocation is enabled, i.e. with -fschedule-insns or at -O2 or
           higher.  Usage of this option can improve the generated code and
           decrease its size by preventing register pressure increase above
           the number of available hard registers and subsequent spills in
           register allocation.

       -fsched-spec-load
           Allow speculative motion of some load instructions.  This only
           makes sense when scheduling before register allocation, i.e. with
           -fschedule-insns or at -O2 or higher.

       -fsched-spec-load-dangerous
           Allow speculative motion of more load instructions.  This only
           makes sense when scheduling before register allocation, i.e. with
           -fschedule-insns or at -O2 or higher.

       -fsched-stalled-insns
       -fsched-stalled-insns=n
           Define how many insns (if any) can be moved prematurely from the
           queue of stalled insns into the ready list during the second
           scheduling pass.  -fno-sched-stalled-insns means that no insns are
           moved prematurely, -fsched-stalled-insns=0 means there is no limit
           on how many queued insns can be moved prematurely.
           -fsched-stalled-insns without a value is equivalent to
           -fsched-stalled-insns=1.

       -fsched-stalled-insns-dep
       -fsched-stalled-insns-dep=n
           Define how many insn groups (cycles) are examined for a dependency
           on a stalled insn that is a candidate for premature removal from
           the queue of stalled insns.  This has an effect only during the
           second scheduling pass, and only if -fsched-stalled-insns is used.
           -fno-sched-stalled-insns-dep is equivalent to
           -fsched-stalled-insns-dep=0.  -fsched-stalled-insns-dep without a
           value is equivalent to -fsched-stalled-insns-dep=1.

       -fsched2-use-superblocks
           When scheduling after register allocation, use superblock
           scheduling.  This allows motion across basic block boundaries,
           resulting in faster schedules.  This option is experimental, as not
           all machine descriptions used by GCC model the CPU closely enough
           to avoid unreliable results from the algorithm.

           This only makes sense when scheduling after register allocation,
           i.e. with -fschedule-insns2 or at -O2 or higher.

       -fsched-group-heuristic
           Enable the group heuristic in the scheduler.  This heuristic favors
           the instruction that belongs to a schedule group.  This is enabled
           by default when scheduling is enabled, i.e. with -fschedule-insns
           or -fschedule-insns2 or at -O2 or higher.

       -fsched-critical-path-heuristic
           Enable the critical-path heuristic in the scheduler.  This
           heuristic favors instructions on the critical path.  This is
           enabled by default when scheduling is enabled, i.e. with
           -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -fsched-spec-insn-heuristic
           Enable the speculative instruction heuristic in the scheduler.
           This heuristic favors speculative instructions with greater
           dependency weakness.  This is enabled by default when scheduling is
           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
           or higher.

       -fsched-rank-heuristic
           Enable the rank heuristic in the scheduler.  This heuristic favors
           the instruction belonging to a basic block with greater size or
           frequency.  This is enabled by default when scheduling is enabled,
           i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or
           higher.

       -fsched-last-insn-heuristic
           Enable the last-instruction heuristic in the scheduler.  This
           heuristic favors the instruction that is less dependent on the last
           instruction scheduled.  This is enabled by default when scheduling
           is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at
           -O2 or higher.

       -fsched-dep-count-heuristic
           Enable the dependent-count heuristic in the scheduler.  This
           heuristic favors the instruction that has more instructions
           depending on it.  This is enabled by default when scheduling is
           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
           or higher.

       -freschedule-modulo-scheduled-loops
           Modulo scheduling is performed before traditional scheduling.  If a
           loop is modulo scheduled, later scheduling passes may change its
           schedule.  Use this option to control that behavior.

       -fselective-scheduling
           Schedule instructions using selective scheduling algorithm.
           Selective scheduling runs instead of the first scheduler pass.

       -fselective-scheduling2
           Schedule instructions using selective scheduling algorithm.
           Selective scheduling runs instead of the second scheduler pass.

       -fsel-sched-pipelining
           Enable software pipelining of innermost loops during selective
           scheduling.  This option has no effect unless one of
           -fselective-scheduling or -fselective-scheduling2 is turned on.

       -fsel-sched-pipelining-outer-loops
           When pipelining loops during selective scheduling, also pipeline
           outer loops.  This option has no effect unless
           -fsel-sched-pipelining is turned on.

       -fsemantic-interposition
           Some object formats, like ELF, allow interposing of symbols by the
           dynamic linker.  This means that for symbols exported from the DSO,
           the compiler cannot perform interprocedural propagation, inlining
           and other optimizations in anticipation that the function or
           variable in question may change. While this feature is useful, for
           example, to rewrite memory allocation functions by a debugging
           implementation, it is expensive in the terms of code quality.  With
           -fno-semantic-interposition the compiler assumes that if
           interposition happens for functions the overwriting function will
           have precisely the same semantics (and side effects).  Similarly if
           interposition happens for variables, the constructor of the
           variable will be the same. The flag has no effect for functions
           explicitly declared inline (where it is never allowed for
           interposition to change semantics) and for symbols explicitly
           declared weak.

       -fshrink-wrap
           Emit function prologues only before parts of the function that need
           it, rather than at the top of the function.  This flag is enabled
           by default at -O and higher.

       -fshrink-wrap-separate
           Shrink-wrap separate parts of the prologue and epilogue separately,
           so that those parts are only executed when needed.  This option is
           on by default, but has no effect unless -fshrink-wrap is also
           turned on and the target supports this.

       -fcaller-saves
           Enable allocation of values to registers that are clobbered by
           function calls, by emitting extra instructions to save and restore
           the registers around such calls.  Such allocation is done only when
           it seems to result in better code.

           This option is always enabled by default on certain machines,
           usually those which have no call-preserved registers to use
           instead.

           Enabled at levels -O2, -O3, -Os.

       -fcombine-stack-adjustments
           Tracks stack adjustments (pushes and pops) and stack memory
           references and then tries to find ways to combine them.

           Enabled by default at -O1 and higher.

       -fipa-ra
           Use caller save registers for allocation if those registers are not
           used by any called function.  In that case it is not necessary to
           save and restore them around calls.  This is only possible if
           called functions are part of same compilation unit as current
           function and they are compiled before it.

           Enabled at levels -O2, -O3, -Os, however the option is disabled if
           generated code will be instrumented for profiling (-p, or -pg) or
           if callee's register usage cannot be known exactly (this happens on
           targets that do not expose prologues and epilogues in RTL).

       -fconserve-stack
           Attempt to minimize stack usage.  The compiler attempts to use less
           stack space, even if that makes the program slower.  This option
           implies setting the large-stack-frame parameter to 100 and the
           large-stack-frame-growth parameter to 400.

       -ftree-reassoc
           Perform reassociation on trees.  This flag is enabled by default at
           -O and higher.

       -fcode-hoisting
           Perform code hoisting.  Code hoisting tries to move the evaluation
           of expressions executed on all paths to the function exit as early
           as possible.  This is especially useful as a code size
           optimization, but it often helps for code speed as well.  This flag
           is enabled by default at -O2 and higher.

       -ftree-pre
           Perform partial redundancy elimination (PRE) on trees.  This flag
           is enabled by default at -O2 and -O3.

       -ftree-partial-pre
           Make partial redundancy elimination (PRE) more aggressive.  This
           flag is enabled by default at -O3.

       -ftree-forwprop
           Perform forward propagation on trees.  This flag is enabled by
           default at -O and higher.

       -ftree-fre
           Perform full redundancy elimination (FRE) on trees.  The difference
           between FRE and PRE is that FRE only considers expressions that are
           computed on all paths leading to the redundant computation.  This
           analysis is faster than PRE, though it exposes fewer redundancies.
           This flag is enabled by default at -O and higher.

       -ftree-phiprop
           Perform hoisting of loads from conditional pointers on trees.  This
           pass is enabled by default at -O and higher.

       -fhoist-adjacent-loads
           Speculatively hoist loads from both branches of an if-then-else if
           the loads are from adjacent locations in the same structure and the
           target architecture has a conditional move instruction.  This flag
           is enabled by default at -O2 and higher.

       -ftree-copy-prop
           Perform copy propagation on trees.  This pass eliminates
           unnecessary copy operations.  This flag is enabled by default at -O
           and higher.

       -fipa-pure-const
           Discover which functions are pure or constant.  Enabled by default
           at -O and higher.

       -fipa-reference
           Discover which static variables do not escape the compilation unit.
           Enabled by default at -O and higher.

       -fipa-reference-addressable
           Discover read-only, write-only and non-addressable static
           variables.  Enabled by default at -O and higher.

       -fipa-stack-alignment
           Reduce stack alignment on call sites if possible.  Enabled by
           default.

       -fipa-pta
           Perform interprocedural pointer analysis and interprocedural
           modification and reference analysis.  This option can cause
           excessive memory and compile-time usage on large compilation units.
           It is not enabled by default at any optimization level.

       -fipa-profile
           Perform interprocedural profile propagation.  The functions called
           only from cold functions are marked as cold. Also functions
           executed once (such as "cold", "noreturn", static constructors or
           destructors) are identified. Cold functions and loop less parts of
           functions executed once are then optimized for size.  Enabled by
           default at -O and higher.

       -fipa-cp
           Perform interprocedural constant propagation.  This optimization
           analyzes the program to determine when values passed to functions
           are constants and then optimizes accordingly.  This optimization
           can substantially increase performance if the application has
           constants passed to functions.  This flag is enabled by default at
           -O2, -Os and -O3.  It is also enabled by -fprofile-use and
           -fauto-profile.

       -fipa-cp-clone
           Perform function cloning to make interprocedural constant
           propagation stronger.  When enabled, interprocedural constant
           propagation performs function cloning when externally visible
           function can be called with constant arguments.  Because this
           optimization can create multiple copies of functions, it may
           significantly increase code size (see --param
           ipa-cp-unit-growth=value).  This flag is enabled by default at -O3.
           It is also enabled by -fprofile-use and -fauto-profile.

       -fipa-bit-cp
           When enabled, perform interprocedural bitwise constant propagation.
           This flag is enabled by default at -O2 and by -fprofile-use and
           -fauto-profile.  It requires that -fipa-cp is enabled.

       -fipa-vrp
           When enabled, perform interprocedural propagation of value ranges.
           This flag is enabled by default at -O2. It requires that -fipa-cp
           is enabled.

       -fipa-icf
           Perform Identical Code Folding for functions and read-only
           variables.  The optimization reduces code size and may disturb
           unwind stacks by replacing a function by equivalent one with a
           different name. The optimization works more effectively with link-
           time optimization enabled.

           Although the behavior is similar to the Gold Linker's ICF
           optimization, GCC ICF works on different levels and thus the
           optimizations are not same - there are equivalences that are found
           only by GCC and equivalences found only by Gold.

           This flag is enabled by default at -O2 and -Os.

       -flive-patching=level
           Control GCC's optimizations to produce output suitable for live-
           patching.

           If the compiler's optimization uses a function's body or
           information extracted from its body to optimize/change another
           function, the latter is called an impacted function of the former.
           If a function is patched, its impacted functions should be patched
           too.

           The impacted functions are determined by the compiler's
           interprocedural optimizations.  For example, a caller is impacted
           when inlining a function into its caller, cloning a function and
           changing its caller to call this new clone, or extracting a
           function's pureness/constness information to optimize its direct or
           indirect callers, etc.

           Usually, the more IPA optimizations enabled, the larger the number
           of impacted functions for each function.  In order to control the
           number of impacted functions and more easily compute the list of
           impacted function, IPA optimizations can be partially enabled at
           two different levels.

           The level argument should be one of the following:

           inline-clone
               Only enable inlining and cloning optimizations, which includes
               inlining, cloning, interprocedural scalar replacement of
               aggregates and partial inlining.  As a result, when patching a
               function, all its callers and its clones' callers are impacted,
               therefore need to be patched as well.

               -flive-patching=inline-clone disables the following
               optimization flags: -fwhole-program  -fipa-pta  -fipa-reference
               -fipa-ra -fipa-icf  -fipa-icf-functions  -fipa-icf-variables
               -fipa-bit-cp  -fipa-vrp  -fipa-pure-const
               -fipa-reference-addressable -fipa-stack-alignment

           inline-only-static
               Only enable inlining of static functions.  As a result, when
               patching a static function, all its callers are impacted and so
               need to be patched as well.

               In addition to all the flags that -flive-patching=inline-clone
               disables, -flive-patching=inline-only-static disables the
               following additional optimization flags: -fipa-cp-clone
               -fipa-sra  -fpartial-inlining  -fipa-cp

           When -flive-patching is specified without any value, the default
           value is inline-clone.

           This flag is disabled by default.

           Note that -flive-patching is not supported with link-time
           optimization (-flto).

       -fisolate-erroneous-paths-dereference
           Detect paths that trigger erroneous or undefined behavior due to
           dereferencing a null pointer.  Isolate those paths from the main
           control flow and turn the statement with erroneous or undefined
           behavior into a trap.  This flag is enabled by default at -O2 and
           higher and depends on -fdelete-null-pointer-checks also being
           enabled.

       -fisolate-erroneous-paths-attribute
           Detect paths that trigger erroneous or undefined behavior due to a
           null value being used in a way forbidden by a "returns_nonnull" or
           "nonnull" attribute.  Isolate those paths from the main control
           flow and turn the statement with erroneous or undefined behavior
           into a trap.  This is not currently enabled, but may be enabled by
           -O2 in the future.

       -ftree-sink
           Perform forward store motion on trees.  This flag is enabled by
           default at -O and higher.

       -ftree-bit-ccp
           Perform sparse conditional bit constant propagation on trees and
           propagate pointer alignment information.  This pass only operates
           on local scalar variables and is enabled by default at -O1 and
           higher, except for -Og.  It requires that -ftree-ccp is enabled.

       -ftree-ccp
           Perform sparse conditional constant propagation (CCP) on trees.
           This pass only operates on local scalar variables and is enabled by
           default at -O and higher.

       -fssa-backprop
           Propagate information about uses of a value up the definition chain
           in order to simplify the definitions.  For example, this pass
           strips sign operations if the sign of a value never matters.  The
           flag is enabled by default at -O and higher.

       -fssa-phiopt
           Perform pattern matching on SSA PHI nodes to optimize conditional
           code.  This pass is enabled by default at -O1 and higher, except
           for -Og.

       -ftree-switch-conversion
           Perform conversion of simple initializations in a switch to
           initializations from a scalar array.  This flag is enabled by
           default at -O2 and higher.

       -ftree-tail-merge
           Look for identical code sequences.  When found, replace one with a
           jump to the other.  This optimization is known as tail merging or
           cross jumping.  This flag is enabled by default at -O2 and higher.
           The compilation time in this pass can be limited using max-tail-
           merge-comparisons parameter and max-tail-merge-iterations
           parameter.

       -ftree-dce
           Perform dead code elimination (DCE) on trees.  This flag is enabled
           by default at -O and higher.

       -ftree-builtin-call-dce
           Perform conditional dead code elimination (DCE) for calls to built-
           in functions that may set "errno" but are otherwise free of side
           effects.  This flag is enabled by default at -O2 and higher if -Os
           is not also specified.

       -ffinite-loops
           Assume that a loop with an exit will eventually take the exit and
           not loop indefinitely.  This allows the compiler to remove loops
           that otherwise have no side-effects, not considering eventual
           endless looping as such.

           This option is enabled by default at -O2 for C++ with -std=c++11 or
           higher.

       -ftree-dominator-opts
           Perform a variety of simple scalar cleanups (constant/copy
           propagation, redundancy elimination, range propagation and
           expression simplification) based on a dominator tree traversal.
           This also performs jump threading (to reduce jumps to jumps). This
           flag is enabled by default at -O and higher.

       -ftree-dse
           Perform dead store elimination (DSE) on trees.  A dead store is a
           store into a memory location that is later overwritten by another
           store without any intervening loads.  In this case the earlier
           store can be deleted.  This flag is enabled by default at -O and
           higher.

       -ftree-ch
           Perform loop header copying on trees.  This is beneficial since it
           increases effectiveness of code motion optimizations.  It also
           saves one jump.  This flag is enabled by default at -O and higher.
           It is not enabled for -Os, since it usually increases code size.

       -ftree-loop-optimize
           Perform loop optimizations on trees.  This flag is enabled by
           default at -O and higher.

       -ftree-loop-linear
       -floop-strip-mine
       -floop-block
           Perform loop nest optimizations.  Same as -floop-nest-optimize.  To
           use this code transformation, GCC has to be configured with
           --with-isl to enable the Graphite loop transformation
           infrastructure.

       -fgraphite-identity
           Enable the identity transformation for graphite.  For every SCoP we
           generate the polyhedral representation and transform it back to
           gimple.  Using -fgraphite-identity we can check the costs or
           benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some
           minimal optimizations are also performed by the code generator isl,
           like index splitting and dead code elimination in loops.

       -floop-nest-optimize
           Enable the isl based loop nest optimizer.  This is a generic loop
           nest optimizer based on the Pluto optimization algorithms.  It
           calculates a loop structure optimized for data-locality and
           parallelism.  This option is experimental.

       -floop-parallelize-all
           Use the Graphite data dependence analysis to identify loops that
           can be parallelized.  Parallelize all the loops that can be
           analyzed to not contain loop carried dependences without checking
           that it is profitable to parallelize the loops.

       -ftree-coalesce-vars
           While transforming the program out of the SSA representation,
           attempt to reduce copying by coalescing versions of different user-
           defined variables, instead of just compiler temporaries.  This may
           severely limit the ability to debug an optimized program compiled
           with -fno-var-tracking-assignments.  In the negated form, this flag
           prevents SSA coalescing of user variables.  This option is enabled
           by default if optimization is enabled, and it does very little
           otherwise.

       -ftree-loop-if-convert
           Attempt to transform conditional jumps in the innermost loops to
           branch-less equivalents.  The intent is to remove control-flow from
           the innermost loops in order to improve the ability of the
           vectorization pass to handle these loops.  This is enabled by
           default if vectorization is enabled.

       -ftree-loop-distribution
           Perform loop distribution.  This flag can improve cache performance
           on big loop bodies and allow further loop optimizations, like
           parallelization or vectorization, to take place.  For example, the
           loop

                   DO I = 1, N
                     A(I) = B(I) + C
                     D(I) = E(I) * F
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = B(I) + C
                   ENDDO
                   DO I = 1, N
                      D(I) = E(I) * F
                   ENDDO

           This flag is enabled by default at -O3.  It is also enabled by
           -fprofile-use and -fauto-profile.

       -ftree-loop-distribute-patterns
           Perform loop distribution of patterns that can be code generated
           with calls to a library.  This flag is enabled by default at -O2
           and higher, and by -fprofile-use and -fauto-profile.

           This pass distributes the initialization loops and generates a call
           to memset zero.  For example, the loop

                   DO I = 1, N
                     A(I) = 0
                     B(I) = A(I) + I
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = 0
                   ENDDO
                   DO I = 1, N
                      B(I) = A(I) + I
                   ENDDO

           and the initialization loop is transformed into a call to memset
           zero.  This flag is enabled by default at -O3.  It is also enabled
           by -fprofile-use and -fauto-profile.

       -floop-interchange
           Perform loop interchange outside of graphite.  This flag can
           improve cache performance on loop nest and allow further loop
           optimizations, like vectorization, to take place.  For example, the
           loop

                   for (int i = 0; i < N; i++)
                     for (int j = 0; j < N; j++)
                       for (int k = 0; k < N; k++)
                         c[i][j] = c[i][j] + a[i][k]*b[k][j];

           is transformed to

                   for (int i = 0; i < N; i++)
                     for (int k = 0; k < N; k++)
                       for (int j = 0; j < N; j++)
                         c[i][j] = c[i][j] + a[i][k]*b[k][j];

           This flag is enabled by default at -O3.  It is also enabled by
           -fprofile-use and -fauto-profile.

       -floop-unroll-and-jam
           Apply unroll and jam transformations on feasible loops.  In a loop
           nest this unrolls the outer loop by some factor and fuses the
           resulting multiple inner loops.  This flag is enabled by default at
           -O3.  It is also enabled by -fprofile-use and -fauto-profile.

       -ftree-loop-im
           Perform loop invariant motion on trees.  This pass moves only
           invariants that are hard to handle at RTL level (function calls,
           operations that expand to nontrivial sequences of insns).  With
           -funswitch-loops it also moves operands of conditions that are
           invariant out of the loop, so that we can use just trivial
           invariantness analysis in loop unswitching.  The pass also includes
           store motion.

       -ftree-loop-ivcanon
           Create a canonical counter for number of iterations in loops for
           which determining number of iterations requires complicated
           analysis.  Later optimizations then may determine the number
           easily.  Useful especially in connection with unrolling.

       -ftree-scev-cprop
           Perform final value replacement.  If a variable is modified in a
           loop in such a way that its value when exiting the loop can be
           determined using only its initial value and the number of loop
           iterations, replace uses of the final value by such a computation,
           provided it is sufficiently cheap.  This reduces data dependencies
           and may allow further simplifications.  Enabled by default at -O
           and higher.

       -fivopts
           Perform induction variable optimizations (strength reduction,
           induction variable merging and induction variable elimination) on
           trees.

       -ftree-parallelize-loops=n
           Parallelize loops, i.e., split their iteration space to run in n
           threads.  This is only possible for loops whose iterations are
           independent and can be arbitrarily reordered.  The optimization is
           only profitable on multiprocessor machines, for loops that are CPU-
           intensive, rather than constrained e.g. by memory bandwidth.  This
           option implies -pthread, and thus is only supported on targets that
           have support for -pthread.

       -ftree-pta
           Perform function-local points-to analysis on trees.  This flag is
           enabled by default at -O1 and higher, except for -Og.

       -ftree-sra
           Perform scalar replacement of aggregates.  This pass replaces
           structure references with scalars to prevent committing structures
           to memory too early.  This flag is enabled by default at -O1 and
           higher, except for -Og.

       -fstore-merging
           Perform merging of narrow stores to consecutive memory addresses.
           This pass merges contiguous stores of immediate values narrower
           than a word into fewer wider stores to reduce the number of
           instructions.  This is enabled by default at -O2 and higher as well
           as -Os.

       -ftree-ter
           Perform temporary expression replacement during the SSA->normal
           phase.  Single use/single def temporaries are replaced at their use
           location with their defining expression.  This results in non-
           GIMPLE code, but gives the expanders much more complex trees to
           work on resulting in better RTL generation.  This is enabled by
           default at -O and higher.

       -ftree-slsr
           Perform straight-line strength reduction on trees.  This recognizes
           related expressions involving multiplications and replaces them by
           less expensive calculations when possible.  This is enabled by
           default at -O and higher.

       -ftree-vectorize
           Perform vectorization on trees. This flag enables
           -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly
           specified.

       -ftree-loop-vectorize
           Perform loop vectorization on trees. This flag is enabled by
           default at -O3 and by -ftree-vectorize, -fprofile-use, and
           -fauto-profile.

       -ftree-slp-vectorize
           Perform basic block vectorization on trees. This flag is enabled by
           default at -O3 and by -ftree-vectorize, -fprofile-use, and
           -fauto-profile.

       -fvect-cost-model=model
           Alter the cost model used for vectorization.  The model argument
           should be one of unlimited, dynamic or cheap.  With the unlimited
           model the vectorized code-path is assumed to be profitable while
           with the dynamic model a runtime check guards the vectorized code-
           path to enable it only for iteration counts that will likely
           execute faster than when executing the original scalar loop.  The
           cheap model disables vectorization of loops where doing so would be
           cost prohibitive for example due to required runtime checks for
           data dependence or alignment but otherwise is equal to the dynamic
           model.  The default cost model depends on other optimization flags
           and is either dynamic or cheap.

       -fsimd-cost-model=model
           Alter the cost model used for vectorization of loops marked with
           the OpenMP simd directive.  The model argument should be one of
           unlimited, dynamic, cheap.  All values of model have the same
           meaning as described in -fvect-cost-model and by default a cost
           model defined with -fvect-cost-model is used.

       -ftree-vrp
           Perform Value Range Propagation on trees.  This is similar to the
           constant propagation pass, but instead of values, ranges of values
           are propagated.  This allows the optimizers to remove unnecessary
           range checks like array bound checks and null pointer checks.  This
           is enabled by default at -O2 and higher.  Null pointer check
           elimination is only done if -fdelete-null-pointer-checks is
           enabled.

       -fsplit-paths
           Split paths leading to loop backedges.  This can improve dead code
           elimination and common subexpression elimination.  This is enabled
           by default at -O3 and above.

       -fsplit-ivs-in-unroller
           Enables expression of values of induction variables in later
           iterations of the unrolled loop using the value in the first
           iteration.  This breaks long dependency chains, thus improving
           efficiency of the scheduling passes.

           A combination of -fweb and CSE is often sufficient to obtain the
           same effect.  However, that is not reliable in cases where the loop
           body is more complicated than a single basic block.  It also does
           not work at all on some architectures due to restrictions in the
           CSE pass.

           This optimization is enabled by default.

       -fvariable-expansion-in-unroller
           With this option, the compiler creates multiple copies of some
           local variables when unrolling a loop, which can result in superior
           code.

           This optimization is enabled by default for PowerPC targets, but
           disabled by default otherwise.

       -fpartial-inlining
           Inline parts of functions.  This option has any effect only when
           inlining itself is turned on by the -finline-functions or
           -finline-small-functions options.

           Enabled at levels -O2, -O3, -Os.

       -fpredictive-commoning
           Perform predictive commoning optimization, i.e., reusing
           computations (especially memory loads and stores) performed in
           previous iterations of loops.

           This option is enabled at level -O3.  It is also enabled by
           -fprofile-use and -fauto-profile.

       -fprefetch-loop-arrays
           If supported by the target machine, generate instructions to
           prefetch memory to improve the performance of loops that access
           large arrays.

           This option may generate better or worse code; results are highly
           dependent on the structure of loops within the source code.

           Disabled at level -Os.

       -fno-printf-return-value
           Do not substitute constants for known return value of formatted
           output functions such as "sprintf", "snprintf", "vsprintf", and
           "vsnprintf" (but not "printf" of "fprintf").  This transformation
           allows GCC to optimize or even eliminate branches based on the
           known return value of these functions called with arguments that
           are either constant, or whose values are known to be in a range
           that makes determining the exact return value possible.  For
           example, when -fprintf-return-value is in effect, both the branch
           and the body of the "if" statement (but not the call to "snprint")
           can be optimized away when "i" is a 32-bit or smaller integer
           because the return value is guaranteed to be at most 8.

                   char buf[9];
                   if (snprintf (buf, "%08x", i) >= sizeof buf)
                     ...

           The -fprintf-return-value option relies on other optimizations and
           yields best results with -O2 and above.  It works in tandem with
           the -Wformat-overflow and -Wformat-truncation options.  The
           -fprintf-return-value option is enabled by default.

       -fno-peephole
       -fno-peephole2
           Disable any machine-specific peephole optimizations.  The
           difference between -fno-peephole and -fno-peephole2 is in how they
           are implemented in the compiler; some targets use one, some use the
           other, a few use both.

           -fpeephole is enabled by default.  -fpeephole2 enabled at levels
           -O2, -O3, -Os.

       -fno-guess-branch-probability
           Do not guess branch probabilities using heuristics.

           GCC uses heuristics to guess branch probabilities if they are not
           provided by profiling feedback (-fprofile-arcs).  These heuristics
           are based on the control flow graph.  If some branch probabilities
           are specified by "__builtin_expect", then the heuristics are used
           to guess branch probabilities for the rest of the control flow
           graph, taking the "__builtin_expect" info into account.  The
           interactions between the heuristics and "__builtin_expect" can be
           complex, and in some cases, it may be useful to disable the
           heuristics so that the effects of "__builtin_expect" are easier to
           understand.

           It is also possible to specify expected probability of the
           expression with "__builtin_expect_with_probability" built-in
           function.

           The default is -fguess-branch-probability at levels -O, -O2, -O3,
           -Os.

       -freorder-blocks
           Reorder basic blocks in the compiled function in order to reduce
           number of taken branches and improve code locality.

           Enabled at levels -O, -O2, -O3, -Os.

       -freorder-blocks-algorithm=algorithm
           Use the specified algorithm for basic block reordering.  The
           algorithm argument can be simple, which does not increase code size
           (except sometimes due to secondary effects like alignment), or stc,
           the "software trace cache" algorithm, which tries to put all often
           executed code together, minimizing the number of branches executed
           by making extra copies of code.

           The default is simple at levels -O, -Os, and stc at levels -O2,
           -O3.

       -freorder-blocks-and-partition
           In addition to reordering basic blocks in the compiled function, in
           order to reduce number of taken branches, partitions hot and cold
           basic blocks into separate sections of the assembly and .o files,
           to improve paging and cache locality performance.

           This optimization is automatically turned off in the presence of
           exception handling or unwind tables (on targets using
           setjump/longjump or target specific scheme), for linkonce sections,
           for functions with a user-defined section attribute and on any
           architecture that does not support named sections.  When
           -fsplit-stack is used this option is not enabled by default (to
           avoid linker errors), but may be enabled explicitly (if using a
           working linker).

           Enabled for x86 at levels -O2, -O3, -Os.

       -freorder-functions
           Reorder functions in the object file in order to improve code
           locality.  This is implemented by using special subsections
           ".text.hot" for most frequently executed functions and
           ".text.unlikely" for unlikely executed functions.  Reordering is
           done by the linker so object file format must support named
           sections and linker must place them in a reasonable way.

           This option isn't effective unless you either provide profile
           feedback (see -fprofile-arcs for details) or manually annotate
           functions with "hot" or "cold" attributes.

           Enabled at levels -O2, -O3, -Os.

       -fstrict-aliasing
           Allow the compiler to assume the strictest aliasing rules
           applicable to the language being compiled.  For C (and C++), this
           activates optimizations based on the type of expressions.  In
           particular, an object of one type is assumed never to reside at the
           same address as an object of a different type, unless the types are
           almost the same.  For example, an "unsigned int" can alias an
           "int", but not a "void*" or a "double".  A character type may alias
           any other type.

           Pay special attention to code like this:

                   union a_union {
                     int i;
                     double d;
                   };

                   int f() {
                     union a_union t;
                     t.d = 3.0;
                     return t.i;
                   }

           The practice of reading from a different union member than the one
           most recently written to (called "type-punning") is common.  Even
           with -fstrict-aliasing, type-punning is allowed, provided the
           memory is accessed through the union type.  So, the code above
           works as expected.    However, this code might not:

                   int f() {
                     union a_union t;
                     int* ip;
                     t.d = 3.0;
                     ip = &t.i;
                     return *ip;
                   }

           Similarly, access by taking the address, casting the resulting
           pointer and dereferencing the result has undefined behavior, even
           if the cast uses a union type, e.g.:

                   int f() {
                     double d = 3.0;
                     return ((union a_union *) &d)->i;
                   }

           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.

       -falign-functions
       -falign-functions=n
       -falign-functions=n:m
       -falign-functions=n:m:n2
       -falign-functions=n:m:n2:m2
           Align the start of functions to the next power-of-two greater than
           or equal to n, skipping up to m-1 bytes.  This ensures that at
           least the first m bytes of the function can be fetched by the CPU
           without crossing an n-byte alignment boundary.

           If m is not specified, it defaults to n.

           Examples: -falign-functions=32 aligns functions to the next 32-byte
           boundary, -falign-functions=24 aligns to the next 32-byte boundary
           only if this can be done by skipping 23 bytes or less,
           -falign-functions=32:7 aligns to the next 32-byte boundary only if
           this can be done by skipping 6 bytes or less.

           The second pair of n2:m2 values allows you to specify a secondary
           alignment: -falign-functions=64:7:32:3 aligns to the next 64-byte
           boundary if this can be done by skipping 6 bytes or less, otherwise
           aligns to the next 32-byte boundary if this can be done by skipping
           2 bytes or less.  If m2 is not specified, it defaults to n2.

           Some assemblers only support this flag when n is a power of two; in
           that case, it is rounded up.

           -fno-align-functions and -falign-functions=1 are equivalent and
           mean that functions are not aligned.

           If n is not specified or is zero, use a machine-dependent default.
           The maximum allowed n option value is 65536.

           Enabled at levels -O2, -O3.

       -flimit-function-alignment
           If this option is enabled, the compiler tries to avoid
           unnecessarily overaligning functions. It attempts to instruct the
           assembler to align by the amount specified by -falign-functions,
           but not to skip more bytes than the size of the function.

       -falign-labels
       -falign-labels=n
       -falign-labels=n:m
       -falign-labels=n:m:n2
       -falign-labels=n:m:n2:m2
           Align all branch targets to a power-of-two boundary.

           Parameters of this option are analogous to the -falign-functions
           option.  -fno-align-labels and -falign-labels=1 are equivalent and
           mean that labels are not aligned.

           If -falign-loops or -falign-jumps are applicable and are greater
           than this value, then their values are used instead.

           If n is not specified or is zero, use a machine-dependent default
           which is very likely to be 1, meaning no alignment.  The maximum
           allowed n option value is 65536.

           Enabled at levels -O2, -O3.

       -falign-loops
       -falign-loops=n
       -falign-loops=n:m
       -falign-loops=n:m:n2
       -falign-loops=n:m:n2:m2
           Align loops to a power-of-two boundary.  If the loops are executed
           many times, this makes up for any execution of the dummy padding
           instructions.

           If -falign-labels is greater than this value, then its value is
           used instead.

           Parameters of this option are analogous to the -falign-functions
           option.  -fno-align-loops and -falign-loops=1 are equivalent and
           mean that loops are not aligned.  The maximum allowed n option
           value is 65536.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -falign-jumps
       -falign-jumps=n
       -falign-jumps=n:m
       -falign-jumps=n:m:n2
       -falign-jumps=n:m:n2:m2
           Align branch targets to a power-of-two boundary, for branch targets
           where the targets can only be reached by jumping.  In this case, no
           dummy operations need be executed.

           If -falign-labels is greater than this value, then its value is
           used instead.

           Parameters of this option are analogous to the -falign-functions
           option.  -fno-align-jumps and -falign-jumps=1 are equivalent and
           mean that loops are not aligned.

           If n is not specified or is zero, use a machine-dependent default.
           The maximum allowed n option value is 65536.

           Enabled at levels -O2, -O3.

       -fno-allocation-dce
           Do not remove unused C++ allocations in dead code elimination.

       -fallow-store-data-races
           Allow the compiler to introduce new data races on stores.

           Enabled at level -Ofast.

       -funit-at-a-time
           This option is left for compatibility reasons. -funit-at-a-time has
           no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder
           and -fno-section-anchors.

           Enabled by default.

       -fno-toplevel-reorder
           Do not reorder top-level functions, variables, and "asm"
           statements.  Output them in the same order that they appear in the
           input file.  When this option is used, unreferenced static
           variables are not removed.  This option is intended to support
           existing code that relies on a particular ordering.  For new code,
           it is better to use attributes when possible.

           -ftoplevel-reorder is the default at -O1 and higher, and also at
           -O0 if -fsection-anchors is explicitly requested.  Additionally
           -fno-toplevel-reorder implies -fno-section-anchors.

       -fweb
           Constructs webs as commonly used for register allocation purposes
           and assign each web individual pseudo register.  This allows the
           register allocation pass to operate on pseudos directly, but also
           strengthens several other optimization passes, such as CSE, loop
           optimizer and trivial dead code remover.  It can, however, make
           debugging impossible, since variables no longer stay in a "home
           register".

           Enabled by default with -funroll-loops.

       -fwhole-program
           Assume that the current compilation unit represents the whole
           program being compiled.  All public functions and variables with
           the exception of "main" and those merged by attribute
           "externally_visible" become static functions and in effect are
           optimized more aggressively by interprocedural optimizers.

           This option should not be used in combination with -flto.  Instead
           relying on a linker plugin should provide safer and more precise
           information.

       -flto[=n]
           This option runs the standard link-time optimizer.  When invoked
           with source code, it generates GIMPLE (one of GCC's internal
           representations) and writes it to special ELF sections in the
           object file.  When the object files are linked together, all the
           function bodies are read from these ELF sections and instantiated
           as if they had been part of the same translation unit.

           To use the link-time optimizer, -flto and optimization options
           should be specified at compile time and during the final link.  It
           is recommended that you compile all the files participating in the
           same link with the same options and also specify those options at
           link time.  For example:

                   gcc -c -O2 -flto foo.c
                   gcc -c -O2 -flto bar.c
                   gcc -o myprog -flto -O2 foo.o bar.o

           The first two invocations to GCC save a bytecode representation of
           GIMPLE into special ELF sections inside foo.o and bar.o.  The final
           invocation reads the GIMPLE bytecode from foo.o and bar.o, merges
           the two files into a single internal image, and compiles the result
           as usual.  Since both foo.o and bar.o are merged into a single
           image, this causes all the interprocedural analyses and
           optimizations in GCC to work across the two files as if they were a
           single one.  This means, for example, that the inliner is able to
           inline functions in bar.o into functions in foo.o and vice-versa.

           Another (simpler) way to enable link-time optimization is:

                   gcc -o myprog -flto -O2 foo.c bar.c

           The above generates bytecode for foo.c and bar.c, merges them
           together into a single GIMPLE representation and optimizes them as
           usual to produce myprog.

           The important thing to keep in mind is that to enable link-time
           optimizations you need to use the GCC driver to perform the link
           step.  GCC automatically performs link-time optimization if any of
           the objects involved were compiled with the -flto command-line
           option.  You can always override the automatic decision to do link-
           time optimization by passing -fno-lto to the link command.

           To make whole program optimization effective, it is necessary to
           make certain whole program assumptions.  The compiler needs to know
           what functions and variables can be accessed by libraries and
           runtime outside of the link-time optimized unit.  When supported by
           the linker, the linker plugin (see -fuse-linker-plugin) passes
           information to the compiler about used and externally visible
           symbols.  When the linker plugin is not available, -fwhole-program
           should be used to allow the compiler to make these assumptions,
           which leads to more aggressive optimization decisions.

           When a file is compiled with -flto without -fuse-linker-plugin, the
           generated object file is larger than a regular object file because
           it contains GIMPLE bytecodes and the usual final code (see
           -ffat-lto-objects.  This means that object files with LTO
           information can be linked as normal object files; if -fno-lto is
           passed to the linker, no interprocedural optimizations are applied.
           Note that when -fno-fat-lto-objects is enabled the compile stage is
           faster but you cannot perform a regular, non-LTO link on them.

           When producing the final binary, GCC only applies link-time
           optimizations to those files that contain bytecode.  Therefore, you
           can mix and match object files and libraries with GIMPLE bytecodes
           and final object code.  GCC automatically selects which files to
           optimize in LTO mode and which files to link without further
           processing.

           Generally, options specified at link time override those specified
           at compile time, although in some cases GCC attempts to infer link-
           time options from the settings used to compile the input files.

           If you do not specify an optimization level option -O at link time,
           then GCC uses the highest optimization level used when compiling
           the object files.  Note that it is generally ineffective to specify
           an optimization level option only at link time and not at compile
           time, for two reasons.  First, compiling without optimization
           suppresses compiler passes that gather information needed for
           effective optimization at link time.  Second, some early
           optimization passes can be performed only at compile time and not
           at link time.

           There are some code generation flags preserved by GCC when
           generating bytecodes, as they need to be used during the final
           link.  Currently, the following options and their settings are
           taken from the first object file that explicitly specifies them:
           -fPIC, -fpic, -fpie, -fcommon, -fexceptions, -fnon-call-exceptions,
           -fgnu-tm and all the -m target flags.

           Certain ABI-changing flags are required to match in all compilation
           units, and trying to override this at link time with a conflicting
           value is ignored.  This includes options such as
           -freg-struct-return and -fpcc-struct-return.

           Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv,
           -fno-trapv or -fno-strict-aliasing are passed through to the link
           stage and merged conservatively for conflicting translation units.
           Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take
           precedence; and for example -ffp-contract=off takes precedence over
           -ffp-contract=fast.  You can override them at link time.

           Diagnostic options such as -Wstringop-overflow are passed through
           to the link stage and their setting matches that of the compile-
           step at function granularity.  Note that this matters only for
           diagnostics emitted during optimization.  Note that code transforms
           such as inlining can lead to warnings being enabled or disabled for
           regions if code not consistent with the setting at compile time.

           When you need to pass options to the assembler via -Wa or
           -Xassembler make sure to either compile such translation units with
           -fno-lto or consistently use the same assembler options on all
           translation units.  You can alternatively also specify assembler
           options at LTO link time.

           To enable debug info generation you need to supply -g at compile
           time.  If any of the input files at link time were built with debug
           info generation enabled the link will enable debug info generation
           as well.  Any elaborate debug info settings like the dwarf level
           -gdwarf-5 need to be explicitly repeated at the linker command line
           and mixing different settings in different translation units is
           discouraged.

           If LTO encounters objects with C linkage declared with incompatible
           types in separate translation units to be linked together
           (undefined behavior according to ISO C99 6.2.7), a non-fatal
           diagnostic may be issued.  The behavior is still undefined at run
           time.  Similar diagnostics may be raised for other languages.

           Another feature of LTO is that it is possible to apply
           interprocedural optimizations on files written in different
           languages:

                   gcc -c -flto foo.c
                   g++ -c -flto bar.cc
                   gfortran -c -flto baz.f90
                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran

           Notice that the final link is done with g++ to get the C++ runtime
           libraries and -lgfortran is added to get the Fortran runtime
           libraries.  In general, when mixing languages in LTO mode, you
           should use the same link command options as when mixing languages
           in a regular (non-LTO) compilation.

           If object files containing GIMPLE bytecode are stored in a library
           archive, say libfoo.a, it is possible to extract and use them in an
           LTO link if you are using a linker with plugin support.  To create
           static libraries suitable for LTO, use gcc-ar and gcc-ranlib
           instead of ar and ranlib; to show the symbols of object files with
           GIMPLE bytecode, use gcc-nm.  Those commands require that ar,
           ranlib and nm have been compiled with plugin support.  At link
           time, use the flag -fuse-linker-plugin to ensure that the library
           participates in the LTO optimization process:

                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo

           With the linker plugin enabled, the linker extracts the needed
           GIMPLE files from libfoo.a and passes them on to the running GCC to
           make them part of the aggregated GIMPLE image to be optimized.

           If you are not using a linker with plugin support and/or do not
           enable the linker plugin, then the objects inside libfoo.a are
           extracted and linked as usual, but they do not participate in the
           LTO optimization process.  In order to make a static library
           suitable for both LTO optimization and usual linkage, compile its
           object files with -flto -ffat-lto-objects.

           Link-time optimizations do not require the presence of the whole
           program to operate.  If the program does not require any symbols to
           be exported, it is possible to combine -flto and -fwhole-program to
           allow the interprocedural optimizers to use more aggressive
           assumptions which may lead to improved optimization opportunities.
           Use of -fwhole-program is not needed when linker plugin is active
           (see -fuse-linker-plugin).

           The current implementation of LTO makes no attempt to generate
           bytecode that is portable between different types of hosts.  The
           bytecode files are versioned and there is a strict version check,
           so bytecode files generated in one version of GCC do not work with
           an older or newer version of GCC.

           Link-time optimization does not work well with generation of
           debugging information on systems other than those using a
           combination of ELF and DWARF.

           If you specify the optional n, the optimization and code generation
           done at link time is executed in parallel using n parallel jobs by
           utilizing an installed make program.  The environment variable MAKE
           may be used to override the program used.

           You can also specify -flto=jobserver to use GNU make's job server
           mode to determine the number of parallel jobs. This is useful when
           the Makefile calling GCC is already executing in parallel.  You
           must prepend a + to the command recipe in the parent Makefile for
           this to work.  This option likely only works if MAKE is GNU make.
           Even without the option value, GCC tries to automatically detect a
           running GNU make's job server.

           Use -flto=auto to use GNU make's job server, if available, or
           otherwise fall back to autodetection of the number of CPU threads
           present in your system.

       -flto-partition=alg
           Specify the partitioning algorithm used by the link-time optimizer.
           The value is either 1to1 to specify a partitioning mirroring the
           original source files or balanced to specify partitioning into
           equally sized chunks (whenever possible) or max to create new
           partition for every symbol where possible.  Specifying none as an
           algorithm disables partitioning and streaming completely.  The
           default value is balanced. While 1to1 can be used as an workaround
           for various code ordering issues, the max partitioning is intended
           for internal testing only.  The value one specifies that exactly
           one partition should be used while the value none bypasses
           partitioning and executes the link-time optimization step directly
           from the WPA phase.

       -flto-compression-level=n
           This option specifies the level of compression used for
           intermediate language written to LTO object files, and is only
           meaningful in conjunction with LTO mode (-flto).  Valid values are
           0 (no compression) to 9 (maximum compression).  Values outside this
           range are clamped to either 0 or 9.  If the option is not given, a
           default balanced compression setting is used.

       -fuse-linker-plugin
           Enables the use of a linker plugin during link-time optimization.
           This option relies on plugin support in the linker, which is
           available in gold or in GNU ld 2.21 or newer.

           This option enables the extraction of object files with GIMPLE
           bytecode out of library archives. This improves the quality of
           optimization by exposing more code to the link-time optimizer.
           This information specifies what symbols can be accessed externally
           (by non-LTO object or during dynamic linking).  Resulting code
           quality improvements on binaries (and shared libraries that use
           hidden visibility) are similar to -fwhole-program.  See -flto for a
           description of the effect of this flag and how to use it.

           This option is enabled by default when LTO support in GCC is
           enabled and GCC was configured for use with a linker supporting
           plugins (GNU ld 2.21 or newer or gold).

       -ffat-lto-objects
           Fat LTO objects are object files that contain both the intermediate
           language and the object code. This makes them usable for both LTO
           linking and normal linking. This option is effective only when
           compiling with -flto and is ignored at link time.

           -fno-fat-lto-objects improves compilation time over plain LTO, but
           requires the complete toolchain to be aware of LTO. It requires a
           linker with linker plugin support for basic functionality.
           Additionally, nm, ar and ranlib need to support linker plugins to
           allow a full-featured build environment (capable of building static
           libraries etc).  GCC provides the gcc-ar, gcc-nm, gcc-ranlib
           wrappers to pass the right options to these tools. With non fat LTO
           makefiles need to be modified to use them.

           Note that modern binutils provide plugin auto-load mechanism.
           Installing the linker plugin into $libdir/bfd-plugins has the same
           effect as usage of the command wrappers (gcc-ar, gcc-nm and gcc-
           ranlib).

           The default is -fno-fat-lto-objects on targets with linker plugin
           support.

       -fcompare-elim
           After register allocation and post-register allocation instruction
           splitting, identify arithmetic instructions that compute processor
           flags similar to a comparison operation based on that arithmetic.
           If possible, eliminate the explicit comparison operation.

           This pass only applies to certain targets that cannot explicitly
           represent the comparison operation before register allocation is
           complete.

           Enabled at levels -O, -O2, -O3, -Os.

       -fcprop-registers
           After register allocation and post-register allocation instruction
           splitting, perform a copy-propagation pass to try to reduce
           scheduling dependencies and occasionally eliminate the copy.

           Enabled at levels -O, -O2, -O3, -Os.

       -fprofile-correction
           Profiles collected using an instrumented binary for multi-threaded
           programs may be inconsistent due to missed counter updates. When
           this option is specified, GCC uses heuristics to correct or smooth
           out such inconsistencies. By default, GCC emits an error message
           when an inconsistent profile is detected.

           This option is enabled by -fauto-profile.

       -fprofile-partial-training
           With "-fprofile-use" all portions of programs not executed during
           train run are optimized agressively for size rather than speed.  In
           some cases it is not practical to train all possible hot paths in
           the program. (For example, program may contain functions specific
           for a given hardware and trianing may not cover all hardware
           configurations program is run on.)  With
           "-fprofile-partial-training" profile feedback will be ignored for
           all functions not executed during the train run leading them to be
           optimized as if they were compiled without profile feedback. This
           leads to better performance when train run is not representative
           but also leads to significantly bigger code.

       -fprofile-use
       -fprofile-use=path
           Enable profile feedback-directed optimizations, and the following
           optimizations, many of which are generally profitable only with
           profile feedback available:

           -fbranch-probabilities  -fprofile-values -funroll-loops
           -fpeel-loops  -ftracer  -fvpt -finline-functions  -fipa-cp
           -fipa-cp-clone  -fipa-bit-cp -fpredictive-commoning  -fsplit-loops
           -funswitch-loops -fgcse-after-reload  -ftree-loop-vectorize
           -ftree-slp-vectorize -fvect-cost-model=dynamic
           -ftree-loop-distribute-patterns -fprofile-reorder-functions

           Before you can use this option, you must first generate profiling
           information.

           By default, GCC emits an error message if the feedback profiles do
           not match the source code.  This error can be turned into a warning
           by using -Wno-error=coverage-mismatch.  Note this may result in
           poorly optimized code.  Additionally, by default, GCC also emits a
           warning message if the feedback profiles do not exist (see
           -Wmissing-profile).

           If path is specified, GCC looks at the path to find the profile
           feedback data files. See -fprofile-dir.

       -fauto-profile
       -fauto-profile=path
           Enable sampling-based feedback-directed optimizations, and the
           following optimizations, many of which are generally profitable
           only with profile feedback available:

           -fbranch-probabilities  -fprofile-values -funroll-loops
           -fpeel-loops  -ftracer  -fvpt -finline-functions  -fipa-cp
           -fipa-cp-clone  -fipa-bit-cp -fpredictive-commoning  -fsplit-loops
           -funswitch-loops -fgcse-after-reload  -ftree-loop-vectorize
           -ftree-slp-vectorize -fvect-cost-model=dynamic
           -ftree-loop-distribute-patterns -fprofile-correction

           path is the name of a file containing AutoFDO profile information.
           If omitted, it defaults to fbdata.afdo in the current directory.

           Producing an AutoFDO profile data file requires running your
           program with the perf utility on a supported GNU/Linux target
           system.  For more information, see <https://perf.wiki.kernel.org/>.

           E.g.

                   perf record -e br_inst_retired:near_taken -b -o perf.data \
                       -- your_program

           Then use the create_gcov tool to convert the raw profile data to a
           format that can be used by GCC.  You must also supply the
           unstripped binary for your program to this tool.  See
           <https://github.com/google/autofdo>.

           E.g.

                   create_gcov --binary=your_program.unstripped --profile=perf.data \
                       --gcov=profile.afdo

       The following options control compiler behavior regarding floating-
       point arithmetic.  These options trade off between speed and
       correctness.  All must be specifically enabled.

       -ffloat-store
           Do not store floating-point variables in registers, and inhibit
           other options that might change whether a floating-point value is
           taken from a register or memory.

           This option prevents undesirable excess precision on machines such
           as the 68000 where the floating registers (of the 68881) keep more
           precision than a "double" is supposed to have.  Similarly for the
           x86 architecture.  For most programs, the excess precision does
           only good, but a few programs rely on the precise definition of
           IEEE floating point.  Use -ffloat-store for such programs, after
           modifying them to store all pertinent intermediate computations
           into variables.

       -fexcess-precision=style
           This option allows further control over excess precision on
           machines where floating-point operations occur in a format with
           more precision or range than the IEEE standard and interchange
           floating-point types.  By default, -fexcess-precision=fast is in
           effect; this means that operations may be carried out in a wider
           precision than the types specified in the source if that would
           result in faster code, and it is unpredictable when rounding to the
           types specified in the source code takes place.  When compiling C,
           if -fexcess-precision=standard is specified then excess precision
           follows the rules specified in ISO C99; in particular, both casts
           and assignments cause values to be rounded to their semantic types
           (whereas -ffloat-store only affects assignments).  This option is
           enabled by default for C if a strict conformance option such as
           -std=c99 is used.  -ffast-math enables -fexcess-precision=fast by
           default regardless of whether a strict conformance option is used.

           -fexcess-precision=standard is not implemented for languages other
           than C.  On the x86, it has no effect if -mfpmath=sse or
           -mfpmath=sse+387 is specified; in the former case, IEEE semantics
           apply without excess precision, and in the latter, rounding is
           unpredictable.

       -ffast-math
           Sets the options -fno-math-errno, -funsafe-math-optimizations,
           -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans,
           -fcx-limited-range and -fexcess-precision=fast.

           This option causes the preprocessor macro "__FAST_MATH__" to be
           defined.

           This option is not turned on by any -O option besides -Ofast since
           it can result in incorrect output for programs that depend on an
           exact implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.

       -fno-math-errno
           Do not set "errno" after calling math functions that are executed
           with a single instruction, e.g., "sqrt".  A program that relies on
           IEEE exceptions for math error handling may want to use this flag
           for speed while maintaining IEEE arithmetic compatibility.

           This option is not turned on by any -O option since it can result
           in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.

           The default is -fmath-errno.

           On Darwin systems, the math library never sets "errno".  There is
           therefore no reason for the compiler to consider the possibility
           that it might, and -fno-math-errno is the default.

       -funsafe-math-optimizations
           Allow optimizations for floating-point arithmetic that (a) assume
           that arguments and results are valid and (b) may violate IEEE or
           ANSI standards.  When used at link time, it may include libraries
           or startup files that change the default FPU control word or other
           similar optimizations.

           This option is not turned on by any -O option since it can result
           in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.  Enables
           -fno-signed-zeros, -fno-trapping-math, -fassociative-math and
           -freciprocal-math.

           The default is -fno-unsafe-math-optimizations.

       -fassociative-math
           Allow re-association of operands in series of floating-point
           operations.  This violates the ISO C and C++ language standard by
           possibly changing computation result.  NOTE: re-ordering may change
           the sign of zero as well as ignore NaNs and inhibit or create
           underflow or overflow (and thus cannot be used on code that relies
           on rounding behavior like "(x + 2**52) - 2**52".  May also reorder
           floating-point comparisons and thus may not be used when ordered
           comparisons are required.  This option requires that both
           -fno-signed-zeros and -fno-trapping-math be in effect.  Moreover,
           it doesn't make much sense with -frounding-math. For Fortran the
           option is automatically enabled when both -fno-signed-zeros and
           -fno-trapping-math are in effect.

           The default is -fno-associative-math.

       -freciprocal-math
           Allow the reciprocal of a value to be used instead of dividing by
           the value if this enables optimizations.  For example "x / y" can
           be replaced with "x * (1/y)", which is useful if "(1/y)" is subject
           to common subexpression elimination.  Note that this loses
           precision and increases the number of flops operating on the value.

           The default is -fno-reciprocal-math.

       -ffinite-math-only
           Allow optimizations for floating-point arithmetic that assume that
           arguments and results are not NaNs or +-Infs.

           This option is not turned on by any -O option since it can result
           in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.

           The default is -fno-finite-math-only.

       -fno-signed-zeros
           Allow optimizations for floating-point arithmetic that ignore the
           signedness of zero.  IEEE arithmetic specifies the behavior of
           distinct +0.0 and -0.0 values, which then prohibits simplification
           of expressions such as x+0.0 or 0.0*x (even with
           -ffinite-math-only).  This option implies that the sign of a zero
           result isn't significant.

           The default is -fsigned-zeros.

       -fno-trapping-math
           Compile code assuming that floating-point operations cannot
           generate user-visible traps.  These traps include division by zero,
           overflow, underflow, inexact result and invalid operation.  This
           option requires that -fno-signaling-nans be in effect.  Setting
           this option may allow faster code if one relies on "non-stop" IEEE
           arithmetic, for example.

           This option should never be turned on by any -O option since it can
           result in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions.

           The default is -ftrapping-math.

       -frounding-math
           Disable transformations and optimizations that assume default
           floating-point rounding behavior.  This is round-to-zero for all
           floating point to integer conversions, and round-to-nearest for all
           other arithmetic truncations.  This option should be specified for
           programs that change the FP rounding mode dynamically, or that may
           be executed with a non-default rounding mode.  This option disables
           constant folding of floating-point expressions at compile time
           (which may be affected by rounding mode) and arithmetic
           transformations that are unsafe in the presence of sign-dependent
           rounding modes.

           The default is -fno-rounding-math.

           This option is experimental and does not currently guarantee to
           disable all GCC optimizations that are affected by rounding mode.
           Future versions of GCC may provide finer control of this setting
           using C99's "FENV_ACCESS" pragma.  This command-line option will be
           used to specify the default state for "FENV_ACCESS".

       -fsignaling-nans
           Compile code assuming that IEEE signaling NaNs may generate user-
           visible traps during floating-point operations.  Setting this
           option disables optimizations that may change the number of
           exceptions visible with signaling NaNs.  This option implies
           -ftrapping-math.

           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be
           defined.

           The default is -fno-signaling-nans.

           This option is experimental and does not currently guarantee to
           disable all GCC optimizations that affect signaling NaN behavior.

       -fno-fp-int-builtin-inexact
           Do not allow the built-in functions "ceil", "floor", "round" and
           "trunc", and their "float" and "long double" variants, to generate
           code that raises the "inexact" floating-point exception for
           noninteger arguments.  ISO C99 and C11 allow these functions to
           raise the "inexact" exception, but ISO/IEC TS 18661-1:2014, the C
           bindings to IEEE 754-2008, as integrated into ISO C2X, does not
           allow these functions to do so.

           The default is -ffp-int-builtin-inexact, allowing the exception to
           be raised, unless C2X or a later C standard is selected.  This
           option does nothing unless -ftrapping-math is in effect.

           Even if -fno-fp-int-builtin-inexact is used, if the functions
           generate a call to a library function then the "inexact" exception
           may be raised if the library implementation does not follow TS
           18661.

       -fsingle-precision-constant
           Treat floating-point constants as single precision instead of
           implicitly converting them to double-precision constants.

       -fcx-limited-range
           When enabled, this option states that a range reduction step is not
           needed when performing complex division.  Also, there is no
           checking whether the result of a complex multiplication or division
           is "NaN + I*NaN", with an attempt to rescue the situation in that
           case.  The default is -fno-cx-limited-range, but is enabled by
           -ffast-math.

           This option controls the default setting of the ISO C99
           "CX_LIMITED_RANGE" pragma.  Nevertheless, the option applies to all
           languages.

       -fcx-fortran-rules
           Complex multiplication and division follow Fortran rules.  Range
           reduction is done as part of complex division, but there is no
           checking whether the result of a complex multiplication or division
           is "NaN + I*NaN", with an attempt to rescue the situation in that
           case.

           The default is -fno-cx-fortran-rules.

       The following options control optimizations that may improve
       performance, but are not enabled by any -O options.  This section
       includes experimental options that may produce broken code.

       -fbranch-probabilities
           After running a program compiled with -fprofile-arcs, you can
           compile it a second time using -fbranch-probabilities, to improve
           optimizations based on the number of times each branch was taken.
           When a program compiled with -fprofile-arcs exits, it saves arc
           execution counts to a file called sourcename.gcda for each source
           file.  The information in this data file is very dependent on the
           structure of the generated code, so you must use the same source
           code and the same optimization options for both compilations.

           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each
           JUMP_INSN and CALL_INSN.  These can be used to improve
           optimization.  Currently, they are only used in one place: in
           reorg.c, instead of guessing which path a branch is most likely to
           take, the REG_BR_PROB values are used to exactly determine which
           path is taken more often.

           Enabled by -fprofile-use and -fauto-profile.

       -fprofile-values
           If combined with -fprofile-arcs, it adds code so that some data
           about values of expressions in the program is gathered.

           With -fbranch-probabilities, it reads back the data gathered from
           profiling values of expressions for usage in optimizations.

           Enabled by -fprofile-generate, -fprofile-use, and -fauto-profile.

       -fprofile-reorder-functions
           Function reordering based on profile instrumentation collects first
           time of execution of a function and orders these functions in
           ascending order.

           Enabled with -fprofile-use.

       -fvpt
           If combined with -fprofile-arcs, this option instructs the compiler
           to add code to gather information about values of expressions.

           With -fbranch-probabilities, it reads back the data gathered and
           actually performs the optimizations based on them.  Currently the
           optimizations include specialization of division operations using
           the knowledge about the value of the denominator.

           Enabled with -fprofile-use and -fauto-profile.

       -frename-registers
           Attempt to avoid false dependencies in scheduled code by making use
           of registers left over after register allocation.  This
           optimization most benefits processors with lots of registers.
           Depending on the debug information format adopted by the target,
           however, it can make debugging impossible, since variables no
           longer stay in a "home register".

           Enabled by default with -funroll-loops.

       -fschedule-fusion
           Performs a target dependent pass over the instruction stream to
           schedule instructions of same type together because target machine
           can execute them more efficiently if they are adjacent to each
           other in the instruction flow.

           Enabled at levels -O2, -O3, -Os.

       -ftracer
           Perform tail duplication to enlarge superblock size.  This
           transformation simplifies the control flow of the function allowing
           other optimizations to do a better job.

           Enabled by -fprofile-use and -fauto-profile.

       -funroll-loops
           Unroll loops whose number of iterations can be determined at
           compile time or upon entry to the loop.  -funroll-loops implies
           -frerun-cse-after-loop, -fweb and -frename-registers.  It also
           turns on complete loop peeling (i.e. complete removal of loops with
           a small constant number of iterations).  This option makes code
           larger, and may or may not make it run faster.

           Enabled by -fprofile-use and -fauto-profile.

       -funroll-all-loops
           Unroll all loops, even if their number of iterations is uncertain
           when the loop is entered.  This usually makes programs run more
           slowly.  -funroll-all-loops implies the same options as
           -funroll-loops.

       -fpeel-loops
           Peels loops for which there is enough information that they do not
           roll much (from profile feedback or static analysis).  It also
           turns on complete loop peeling (i.e. complete removal of loops with
           small constant number of iterations).

           Enabled by -O3, -fprofile-use, and -fauto-profile.

       -fmove-loop-invariants
           Enables the loop invariant motion pass in the RTL loop optimizer.
           Enabled at level -O1 and higher, except for -Og.

       -fsplit-loops
           Split a loop into two if it contains a condition that's always true
           for one side of the iteration space and false for the other.

           Enabled by -fprofile-use and -fauto-profile.

       -funswitch-loops
           Move branches with loop invariant conditions out of the loop, with
           duplicates of the loop on both branches (modified according to
           result of the condition).

           Enabled by -fprofile-use and -fauto-profile.

       -fversion-loops-for-strides
           If a loop iterates over an array with a variable stride, create
           another version of the loop that assumes the stride is always one.
           For example:

                   for (int i = 0; i < n; ++i)
                     x[i * stride] = ...;

           becomes:

                   if (stride == 1)
                     for (int i = 0; i < n; ++i)
                       x[i] = ...;
                   else
                     for (int i = 0; i < n; ++i)
                       x[i * stride] = ...;

           This is particularly useful for assumed-shape arrays in Fortran
           where (for example) it allows better vectorization assuming
           contiguous accesses.  This flag is enabled by default at -O3.  It
           is also enabled by -fprofile-use and -fauto-profile.

       -ffunction-sections
       -fdata-sections
           Place each function or data item into its own section in the output
           file if the target supports arbitrary sections.  The name of the
           function or the name of the data item determines the section's name
           in the output file.

           Use these options on systems where the linker can perform
           optimizations to improve locality of reference in the instruction
           space.  Most systems using the ELF object format have linkers with
           such optimizations.  On AIX, the linker rearranges sections
           (CSECTs) based on the call graph.  The performance impact varies.

           Together with a linker garbage collection (linker --gc-sections
           option) these options may lead to smaller statically-linked
           executables (after stripping).

           On ELF/DWARF systems these options do not degenerate the quality of
           the debug information.  There could be issues with other object
           files/debug info formats.

           Only use these options when there are significant benefits from
           doing so.  When you specify these options, the assembler and linker
           create larger object and executable files and are also slower.
           These options affect code generation.  They prevent optimizations
           by the compiler and assembler using relative locations inside a
           translation unit since the locations are unknown until link time.
           An example of such an optimization is relaxing calls to short call
           instructions.

       -fstdarg-opt
           Optimize the prologue of variadic argument functions with respect
           to usage of those arguments.

       -fsection-anchors
           Try to reduce the number of symbolic address calculations by using
           shared "anchor" symbols to address nearby objects.  This
           transformation can help to reduce the number of GOT entries and GOT
           accesses on some targets.

           For example, the implementation of the following function "foo":

                   static int a, b, c;
                   int foo (void) { return a + b + c; }

           usually calculates the addresses of all three variables, but if you
           compile it with -fsection-anchors, it accesses the variables from a
           common anchor point instead.  The effect is similar to the
           following pseudocode (which isn't valid C):

                   int foo (void)
                   {
                     register int *xr = &x;
                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
                   }

           Not all targets support this option.

       --param name=value
           In some places, GCC uses various constants to control the amount of
           optimization that is done.  For example, GCC does not inline
           functions that contain more than a certain number of instructions.
           You can control some of these constants on the command line using
           the --param option.

           The names of specific parameters, and the meaning of the values,
           are tied to the internals of the compiler, and are subject to
           change without notice in future releases.

           In order to get minimal, maximal and default value of a parameter,
           one can use --help=param -Q options.

           In each case, the value is an integer.  The following choices of
           name are recognized for all targets:

           predictable-branch-outcome
               When branch is predicted to be taken with probability lower
               than this threshold (in percent), then it is considered well
               predictable.

           max-rtl-if-conversion-insns
               RTL if-conversion tries to remove conditional branches around a
               block and replace them with conditionally executed
               instructions.  This parameter gives the maximum number of
               instructions in a block which should be considered for if-
               conversion.  The compiler will also use other heuristics to
               decide whether if-conversion is likely to be profitable.

           max-rtl-if-conversion-predictable-cost
           max-rtl-if-conversion-unpredictable-cost
               RTL if-conversion will try to remove conditional branches
               around a block and replace them with conditionally executed
               instructions.  These parameters give the maximum permissible
               cost for the sequence that would be generated by if-conversion
               depending on whether the branch is statically determined to be
               predictable or not.  The units for this parameter are the same
               as those for the GCC internal seq_cost metric.  The compiler
               will try to provide a reasonable default for this parameter
               using the BRANCH_COST target macro.

           max-crossjump-edges
               The maximum number of incoming edges to consider for cross-
               jumping.  The algorithm used by -fcrossjumping is O(N^2) in the
               number of edges incoming to each block.  Increasing values mean
               more aggressive optimization, making the compilation time
               increase with probably small improvement in executable size.

           min-crossjump-insns
               The minimum number of instructions that must be matched at the
               end of two blocks before cross-jumping is performed on them.
               This value is ignored in the case where all instructions in the
               block being cross-jumped from are matched.

           max-grow-copy-bb-insns
               The maximum code size expansion factor when copying basic
               blocks instead of jumping.  The expansion is relative to a jump
               instruction.

           max-goto-duplication-insns
               The maximum number of instructions to duplicate to a block that
               jumps to a computed goto.  To avoid O(N^2) behavior in a number
               of passes, GCC factors computed gotos early in the compilation
               process, and unfactors them as late as possible.  Only computed
               jumps at the end of a basic blocks with no more than max-goto-
               duplication-insns are unfactored.

           max-delay-slot-insn-search
               The maximum number of instructions to consider when looking for
               an instruction to fill a delay slot.  If more than this
               arbitrary number of instructions are searched, the time savings
               from filling the delay slot are minimal, so stop searching.
               Increasing values mean more aggressive optimization, making the
               compilation time increase with probably small improvement in
               execution time.

           max-delay-slot-live-search
               When trying to fill delay slots, the maximum number of
               instructions to consider when searching for a block with valid
               live register information.  Increasing this arbitrarily chosen
               value means more aggressive optimization, increasing the
               compilation time.  This parameter should be removed when the
               delay slot code is rewritten to maintain the control-flow
               graph.

           max-gcse-memory
               The approximate maximum amount of memory that can be allocated
               in order to perform the global common subexpression elimination
               optimization.  If more memory than specified is required, the
               optimization is not done.

           max-gcse-insertion-ratio
               If the ratio of expression insertions to deletions is larger
               than this value for any expression, then RTL PRE inserts or
               removes the expression and thus leaves partially redundant
               computations in the instruction stream.

           max-pending-list-length
               The maximum number of pending dependencies scheduling allows
               before flushing the current state and starting over.  Large
               functions with few branches or calls can create excessively
               large lists which needlessly consume memory and resources.

           max-modulo-backtrack-attempts
               The maximum number of backtrack attempts the scheduler should
               make when modulo scheduling a loop.  Larger values can
               exponentially increase compilation time.

           max-inline-insns-single
               Several parameters control the tree inliner used in GCC.  This
               number sets the maximum number of instructions (counted in
               GCC's internal representation) in a single function that the
               tree inliner considers for inlining.  This only affects
               functions declared inline and methods implemented in a class
               declaration (C++).

           max-inline-insns-auto
               When you use -finline-functions (included in -O3), a lot of
               functions that would otherwise not be considered for inlining
               by the compiler are investigated.  To those functions, a
               different (more restrictive) limit compared to functions
               declared inline can be applied (--param max-inline-insns-auto).

           max-inline-insns-small
               This is bound applied to calls which are considered relevant
               with -finline-small-functions.

           max-inline-insns-size
               This is bound applied to calls which are optimized for size.
               Small growth may be desirable to anticipate optimization
               oppurtunities exposed by inlining.

           uninlined-function-insns
               Number of instructions accounted by inliner for function
               overhead such as function prologue and epilogue.

           uninlined-function-time
               Extra time accounted by inliner for function overhead such as
               time needed to execute function prologue and epilogue

           inline-heuristics-hint-percent
               The scale (in percents) applied to inline-insns-single,
               inline-insns-single-O2, inline-insns-auto when inline
               heuristics hints that inlining is very profitable (will enable
               later optimizations).

           uninlined-thunk-insns
           uninlined-thunk-time
               Same as --param uninlined-function-insns and --param uninlined-
               function-time but applied to function thunks

           inline-min-speedup
               When estimated performance improvement of caller + callee
               runtime exceeds this threshold (in percent), the function can
               be inlined regardless of the limit on --param max-inline-insns-
               single and --param max-inline-insns-auto.

           large-function-insns
               The limit specifying really large functions.  For functions
               larger than this limit after inlining, inlining is constrained
               by --param large-function-growth.  This parameter is useful
               primarily to avoid extreme compilation time caused by non-
               linear algorithms used by the back end.

           large-function-growth
               Specifies maximal growth of large function caused by inlining
               in percents.  For example, parameter value 100 limits large
               function growth to 2.0 times the original size.

           large-unit-insns
               The limit specifying large translation unit.  Growth caused by
               inlining of units larger than this limit is limited by --param
               inline-unit-growth.  For small units this might be too tight.
               For example, consider a unit consisting of function A that is
               inline and B that just calls A three times.  If B is small
               relative to A, the growth of unit is 300\% and yet such
               inlining is very sane.  For very large units consisting of
               small inlineable functions, however, the overall unit growth
               limit is needed to avoid exponential explosion of code size.
               Thus for smaller units, the size is increased to --param large-
               unit-insns before applying --param inline-unit-growth.

           inline-unit-growth
               Specifies maximal overall growth of the compilation unit caused
               by inlining.  For example, parameter value 20 limits unit
               growth to 1.2 times the original size. Cold functions (either
               marked cold via an attribute or by profile feedback) are not
               accounted into the unit size.

           ipa-cp-unit-growth
               Specifies maximal overall growth of the compilation unit caused
               by interprocedural constant propagation.  For example,
               parameter value 10 limits unit growth to 1.1 times the original
               size.

           large-stack-frame
               The limit specifying large stack frames.  While inlining the
               algorithm is trying to not grow past this limit too much.

           large-stack-frame-growth
               Specifies maximal growth of large stack frames caused by
               inlining in percents.  For example, parameter value 1000 limits
               large stack frame growth to 11 times the original size.

           max-inline-insns-recursive
           max-inline-insns-recursive-auto
               Specifies the maximum number of instructions an out-of-line
               copy of a self-recursive inline function can grow into by
               performing recursive inlining.

               --param max-inline-insns-recursive applies to functions
               declared inline.  For functions not declared inline, recursive
               inlining happens only when -finline-functions (included in -O3)
               is enabled; --param max-inline-insns-recursive-auto applies
               instead.

           max-inline-recursive-depth
           max-inline-recursive-depth-auto
               Specifies the maximum recursion depth used for recursive
               inlining.

               --param max-inline-recursive-depth applies to functions
               declared inline.  For functions not declared inline, recursive
               inlining happens only when -finline-functions (included in -O3)
               is enabled; --param max-inline-recursive-depth-auto applies
               instead.

           min-inline-recursive-probability
               Recursive inlining is profitable only for function having deep
               recursion in average and can hurt for function having little
               recursion depth by increasing the prologue size or complexity
               of function body to other optimizers.

               When profile feedback is available (see -fprofile-generate) the
               actual recursion depth can be guessed from the probability that
               function recurses via a given call expression.  This parameter
               limits inlining only to call expressions whose probability
               exceeds the given threshold (in percents).

           early-inlining-insns
               Specify growth that the early inliner can make.  In effect it
               increases the amount of inlining for code having a large
               abstraction penalty.

           max-early-inliner-iterations
               Limit of iterations of the early inliner.  This basically
               bounds the number of nested indirect calls the early inliner
               can resolve.  Deeper chains are still handled by late inlining.

           comdat-sharing-probability
               Probability (in percent) that C++ inline function with comdat
               visibility are shared across multiple compilation units.

           profile-func-internal-id
               A parameter to control whether to use function internal id in
               profile database lookup. If the value is 0, the compiler uses
               an id that is based on function assembler name and filename,
               which makes old profile data more tolerant to source changes
               such as function reordering etc.

           min-vect-loop-bound
               The minimum number of iterations under which loops are not
               vectorized when -ftree-vectorize is used.  The number of
               iterations after vectorization needs to be greater than the
               value specified by this option to allow vectorization.

           gcse-cost-distance-ratio
               Scaling factor in calculation of maximum distance an expression
               can be moved by GCSE optimizations.  This is currently
               supported only in the code hoisting pass.  The bigger the
               ratio, the more aggressive code hoisting is with simple
               expressions, i.e., the expressions that have cost less than
               gcse-unrestricted-cost.  Specifying 0 disables hoisting of
               simple expressions.

           gcse-unrestricted-cost
               Cost, roughly measured as the cost of a single typical machine
               instruction, at which GCSE optimizations do not constrain the
               distance an expression can travel.  This is currently supported
               only in the code hoisting pass.  The lesser the cost, the more
               aggressive code hoisting is.  Specifying 0 allows all
               expressions to travel unrestricted distances.

           max-hoist-depth
               The depth of search in the dominator tree for expressions to
               hoist.  This is used to avoid quadratic behavior in hoisting
               algorithm.  The value of 0 does not limit on the search, but
               may slow down compilation of huge functions.

           max-tail-merge-comparisons
               The maximum amount of similar bbs to compare a bb with.  This
               is used to avoid quadratic behavior in tree tail merging.

           max-tail-merge-iterations
               The maximum amount of iterations of the pass over the function.
               This is used to limit compilation time in tree tail merging.

           store-merging-allow-unaligned
               Allow the store merging pass to introduce unaligned stores if
               it is legal to do so.

           max-stores-to-merge
               The maximum number of stores to attempt to merge into wider
               stores in the store merging pass.

           max-unrolled-insns
               The maximum number of instructions that a loop may have to be
               unrolled.  If a loop is unrolled, this parameter also
               determines how many times the loop code is unrolled.

           max-average-unrolled-insns
               The maximum number of instructions biased by probabilities of
               their execution that a loop may have to be unrolled.  If a loop
               is unrolled, this parameter also determines how many times the
               loop code is unrolled.

           max-unroll-times
               The maximum number of unrollings of a single loop.

           max-peeled-insns
               The maximum number of instructions that a loop may have to be
               peeled.  If a loop is peeled, this parameter also determines
               how many times the loop code is peeled.

           max-peel-times
               The maximum number of peelings of a single loop.

           max-peel-branches
               The maximum number of branches on the hot path through the
               peeled sequence.

           max-completely-peeled-insns
               The maximum number of insns of a completely peeled loop.

           max-completely-peel-times
               The maximum number of iterations of a loop to be suitable for
               complete peeling.

           max-completely-peel-loop-nest-depth
               The maximum depth of a loop nest suitable for complete peeling.

           max-unswitch-insns
               The maximum number of insns of an unswitched loop.

           max-unswitch-level
               The maximum number of branches unswitched in a single loop.

           lim-expensive
               The minimum cost of an expensive expression in the loop
               invariant motion.

           min-loop-cond-split-prob
               When FDO profile information is available, min-loop-cond-split-
               prob specifies minimum threshold for probability of semi-
               invariant condition statement to trigger loop split.

           iv-consider-all-candidates-bound
               Bound on number of candidates for induction variables, below
               which all candidates are considered for each use in induction
               variable optimizations.  If there are more candidates than
               this, only the most relevant ones are considered to avoid
               quadratic time complexity.

           iv-max-considered-uses
               The induction variable optimizations give up on loops that
               contain more induction variable uses.

           iv-always-prune-cand-set-bound
               If the number of candidates in the set is smaller than this
               value, always try to remove unnecessary ivs from the set when
               adding a new one.

           avg-loop-niter
               Average number of iterations of a loop.

           dse-max-object-size
               Maximum size (in bytes) of objects tracked bytewise by dead
               store elimination.  Larger values may result in larger
               compilation times.

           dse-max-alias-queries-per-store
               Maximum number of queries into the alias oracle per store.
               Larger values result in larger compilation times and may result
               in more removed dead stores.

           scev-max-expr-size
               Bound on size of expressions used in the scalar evolutions
               analyzer.  Large expressions slow the analyzer.

           scev-max-expr-complexity
               Bound on the complexity of the expressions in the scalar
               evolutions analyzer.  Complex expressions slow the analyzer.

           max-tree-if-conversion-phi-args
               Maximum number of arguments in a PHI supported by TREE if
               conversion unless the loop is marked with simd pragma.

           vect-max-version-for-alignment-checks
               The maximum number of run-time checks that can be performed
               when doing loop versioning for alignment in the vectorizer.

           vect-max-version-for-alias-checks
               The maximum number of run-time checks that can be performed
               when doing loop versioning for alias in the vectorizer.

           vect-max-peeling-for-alignment
               The maximum number of loop peels to enhance access alignment
               for vectorizer. Value -1 means no limit.

           max-iterations-to-track
               The maximum number of iterations of a loop the brute-force
               algorithm for analysis of the number of iterations of the loop
               tries to evaluate.

           hot-bb-count-fraction
               The denominator n of fraction 1/n of the maximal execution
               count of a basic block in the entire program that a basic block
               needs to at least have in order to be considered hot.  The
               default is 10000, which means that a basic block is considered
               hot if its execution count is greater than 1/10000 of the
               maximal execution count.  0 means that it is never considered
               hot.  Used in non-LTO mode.

           hot-bb-count-ws-permille
               The number of most executed permilles, ranging from 0 to 1000,
               of the profiled execution of the entire program to which the
               execution count of a basic block must be part of in order to be
               considered hot.  The default is 990, which means that a basic
               block is considered hot if its execution count contributes to
               the upper 990 permilles, or 99.0%, of the profiled execution of
               the entire program.  0 means that it is never considered hot.
               Used in LTO mode.

           hot-bb-frequency-fraction
               The denominator n of fraction 1/n of the execution frequency of
               the entry block of a function that a basic block of this
               function needs to at least have in order to be considered hot.
               The default is 1000, which means that a basic block is
               considered hot in a function if it is executed more frequently
               than 1/1000 of the frequency of the entry block of the
               function.  0 means that it is never considered hot.

           unlikely-bb-count-fraction
               The denominator n of fraction 1/n of the number of profiled
               runs of the entire program below which the execution count of a
               basic block must be in order for the basic block to be
               considered unlikely executed.  The default is 20, which means
               that a basic block is considered unlikely executed if it is
               executed in fewer than 1/20, or 5%, of the runs of the program.
               0 means that it is always considered unlikely executed.

           max-predicted-iterations
               The maximum number of loop iterations we predict statically.
               This is useful in cases where a function contains a single loop
               with known bound and another loop with unknown bound.  The
               known number of iterations is predicted correctly, while the
               unknown number of iterations average to roughly 10.  This means
               that the loop without bounds appears artificially cold relative
               to the other one.

           builtin-expect-probability
               Control the probability of the expression having the specified
               value. This parameter takes a percentage (i.e. 0 ... 100) as
               input.

           builtin-string-cmp-inline-length
               The maximum length of a constant string for a builtin string
               cmp call eligible for inlining.

           align-threshold
               Select fraction of the maximal frequency of executions of a
               basic block in a function to align the basic block.

           align-loop-iterations
               A loop expected to iterate at least the selected number of
               iterations is aligned.

           tracer-dynamic-coverage
           tracer-dynamic-coverage-feedback
               This value is used to limit superblock formation once the given
               percentage of executed instructions is covered.  This limits
               unnecessary code size expansion.

               The tracer-dynamic-coverage-feedback parameter is used only
               when profile feedback is available.  The real profiles (as
               opposed to statically estimated ones) are much less balanced
               allowing the threshold to be larger value.

           tracer-max-code-growth
               Stop tail duplication once code growth has reached given
               percentage.  This is a rather artificial limit, as most of the
               duplicates are eliminated later in cross jumping, so it may be
               set to much higher values than is the desired code growth.

           tracer-min-branch-ratio
               Stop reverse growth when the reverse probability of best edge
               is less than this threshold (in percent).

           tracer-min-branch-probability
           tracer-min-branch-probability-feedback
               Stop forward growth if the best edge has probability lower than
               this threshold.

               Similarly to tracer-dynamic-coverage two parameters are
               provided.  tracer-min-branch-probability-feedback is used for
               compilation with profile feedback and tracer-min-branch-
               probability compilation without.  The value for compilation
               with profile feedback needs to be more conservative (higher) in
               order to make tracer effective.

           stack-clash-protection-guard-size
               Specify the size of the operating system provided stack guard
               as 2 raised to num bytes.  Higher values may reduce the number
               of explicit probes, but a value larger than the operating
               system provided guard will leave code vulnerable to stack clash
               style attacks.

           stack-clash-protection-probe-interval
               Stack clash protection involves probing stack space as it is
               allocated.  This param controls the maximum distance between
               probes into the stack as 2 raised to num bytes.  Higher values
               may reduce the number of explicit probes, but a value larger
               than the operating system provided guard will leave code
               vulnerable to stack clash style attacks.

           max-cse-path-length
               The maximum number of basic blocks on path that CSE considers.

           max-cse-insns
               The maximum number of instructions CSE processes before
               flushing.

           ggc-min-expand
               GCC uses a garbage collector to manage its own memory
               allocation.  This parameter specifies the minimum percentage by
               which the garbage collector's heap should be allowed to expand
               between collections.  Tuning this may improve compilation
               speed; it has no effect on code generation.

               The default is 30% + 70% * (RAM/1GB) with an upper bound of
               100% when RAM >= 1GB.  If "getrlimit" is available, the notion
               of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or
               "RLIMIT_AS".  If GCC is not able to calculate RAM on a
               particular platform, the lower bound of 30% is used.  Setting
               this parameter and ggc-min-heapsize to zero causes a full
               collection to occur at every opportunity.  This is extremely
               slow, but can be useful for debugging.

           ggc-min-heapsize
               Minimum size of the garbage collector's heap before it begins
               bothering to collect garbage.  The first collection occurs
               after the heap expands by ggc-min-expand% beyond ggc-min-
               heapsize.  Again, tuning this may improve compilation speed,
               and has no effect on code generation.

               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
               that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
               exceeded, but with a lower bound of 4096 (four megabytes) and
               an upper bound of 131072 (128 megabytes).  If GCC is not able
               to calculate RAM on a particular platform, the lower bound is
               used.  Setting this parameter very large effectively disables
               garbage collection.  Setting this parameter and ggc-min-expand
               to zero causes a full collection to occur at every opportunity.

           max-reload-search-insns
               The maximum number of instruction reload should look backward
               for equivalent register.  Increasing values mean more
               aggressive optimization, making the compilation time increase
               with probably slightly better performance.

           max-cselib-memory-locations
               The maximum number of memory locations cselib should take into
               account.  Increasing values mean more aggressive optimization,
               making the compilation time increase with probably slightly
               better performance.

           max-sched-ready-insns
               The maximum number of instructions ready to be issued the
               scheduler should consider at any given time during the first
               scheduling pass.  Increasing values mean more thorough
               searches, making the compilation time increase with probably
               little benefit.

           max-sched-region-blocks
               The maximum number of blocks in a region to be considered for
               interblock scheduling.

           max-pipeline-region-blocks
               The maximum number of blocks in a region to be considered for
               pipelining in the selective scheduler.

           max-sched-region-insns
               The maximum number of insns in a region to be considered for
               interblock scheduling.

           max-pipeline-region-insns
               The maximum number of insns in a region to be considered for
               pipelining in the selective scheduler.

           min-spec-prob
               The minimum probability (in percents) of reaching a source
               block for interblock speculative scheduling.

           max-sched-extend-regions-iters
               The maximum number of iterations through CFG to extend regions.
               A value of 0 disables region extensions.

           max-sched-insn-conflict-delay
               The maximum conflict delay for an insn to be considered for
               speculative motion.

           sched-spec-prob-cutoff
               The minimal probability of speculation success (in percents),
               so that speculative insns are scheduled.

           sched-state-edge-prob-cutoff
               The minimum probability an edge must have for the scheduler to
               save its state across it.

           sched-mem-true-dep-cost
               Minimal distance (in CPU cycles) between store and load
               targeting same memory locations.

           selsched-max-lookahead
               The maximum size of the lookahead window of selective
               scheduling.  It is a depth of search for available
               instructions.

           selsched-max-sched-times
               The maximum number of times that an instruction is scheduled
               during selective scheduling.  This is the limit on the number
               of iterations through which the instruction may be pipelined.

           selsched-insns-to-rename
               The maximum number of best instructions in the ready list that
               are considered for renaming in the selective scheduler.

           sms-min-sc
               The minimum value of stage count that swing modulo scheduler
               generates.

           max-last-value-rtl
               The maximum size measured as number of RTLs that can be
               recorded in an expression in combiner for a pseudo register as
               last known value of that register.

           max-combine-insns
               The maximum number of instructions the RTL combiner tries to
               combine.

           integer-share-limit
               Small integer constants can use a shared data structure,
               reducing the compiler's memory usage and increasing its speed.
               This sets the maximum value of a shared integer constant.

           ssp-buffer-size
               The minimum size of buffers (i.e. arrays) that receive stack
               smashing protection when -fstack-protection is used.

           min-size-for-stack-sharing
               The minimum size of variables taking part in stack slot sharing
               when not optimizing.

           max-jump-thread-duplication-stmts
               Maximum number of statements allowed in a block that needs to
               be duplicated when threading jumps.

           max-fields-for-field-sensitive
               Maximum number of fields in a structure treated in a field
               sensitive manner during pointer analysis.

           prefetch-latency
               Estimate on average number of instructions that are executed
               before prefetch finishes.  The distance prefetched ahead is
               proportional to this constant.  Increasing this number may also
               lead to less streams being prefetched (see simultaneous-
               prefetches).

           simultaneous-prefetches
               Maximum number of prefetches that can run at the same time.

           l1-cache-line-size
               The size of cache line in L1 data cache, in bytes.

           l1-cache-size
               The size of L1 data cache, in kilobytes.

           l2-cache-size
               The size of L2 data cache, in kilobytes.

           prefetch-dynamic-strides
               Whether the loop array prefetch pass should issue software
               prefetch hints for strides that are non-constant.  In some
               cases this may be beneficial, though the fact the stride is
               non-constant may make it hard to predict when there is clear
               benefit to issuing these hints.

               Set to 1 if the prefetch hints should be issued for non-
               constant strides.  Set to 0 if prefetch hints should be issued
               only for strides that are known to be constant and below
               prefetch-minimum-stride.

           prefetch-minimum-stride
               Minimum constant stride, in bytes, to start using prefetch
               hints for.  If the stride is less than this threshold, prefetch
               hints will not be issued.

               This setting is useful for processors that have hardware
               prefetchers, in which case there may be conflicts between the
               hardware prefetchers and the software prefetchers.  If the
               hardware prefetchers have a maximum stride they can handle, it
               should be used here to improve the use of software prefetchers.

               A value of -1 means we don't have a threshold and therefore
               prefetch hints can be issued for any constant stride.

               This setting is only useful for strides that are known and
               constant.

           loop-interchange-max-num-stmts
               The maximum number of stmts in a loop to be interchanged.

           loop-interchange-stride-ratio
               The minimum ratio between stride of two loops for interchange
               to be profitable.

           min-insn-to-prefetch-ratio
               The minimum ratio between the number of instructions and the
               number of prefetches to enable prefetching in a loop.

           prefetch-min-insn-to-mem-ratio
               The minimum ratio between the number of instructions and the
               number of memory references to enable prefetching in a loop.

           use-canonical-types
               Whether the compiler should use the "canonical" type system.
               Should always be 1, which uses a more efficient internal
               mechanism for comparing types in C++ and Objective-C++.
               However, if bugs in the canonical type system are causing
               compilation failures, set this value to 0 to disable canonical
               types.

           switch-conversion-max-branch-ratio
               Switch initialization conversion refuses to create arrays that
               are bigger than switch-conversion-max-branch-ratio times the
               number of branches in the switch.

           max-partial-antic-length
               Maximum length of the partial antic set computed during the
               tree partial redundancy elimination optimization (-ftree-pre)
               when optimizing at -O3 and above.  For some sorts of source
               code the enhanced partial redundancy elimination optimization
               can run away, consuming all of the memory available on the host
               machine.  This parameter sets a limit on the length of the sets
               that are computed, which prevents the runaway behavior.
               Setting a value of 0 for this parameter allows an unlimited set
               length.

           rpo-vn-max-loop-depth
               Maximum loop depth that is value-numbered optimistically.  When
               the limit hits the innermost rpo-vn-max-loop-depth loops and
               the outermost loop in the loop nest are value-numbered
               optimistically and the remaining ones not.

           sccvn-max-alias-queries-per-access
               Maximum number of alias-oracle queries we perform when looking
               for redundancies for loads and stores.  If this limit is hit
               the search is aborted and the load or store is not considered
               redundant.  The number of queries is algorithmically limited to
               the number of stores on all paths from the load to the function
               entry.

           ira-max-loops-num
               IRA uses regional register allocation by default.  If a
               function contains more loops than the number given by this
               parameter, only at most the given number of the most
               frequently-executed loops form regions for regional register
               allocation.

           ira-max-conflict-table-size
               Although IRA uses a sophisticated algorithm to compress the
               conflict table, the table can still require excessive amounts
               of memory for huge functions.  If the conflict table for a
               function could be more than the size in MB given by this
               parameter, the register allocator instead uses a faster,
               simpler, and lower-quality algorithm that does not require
               building a pseudo-register conflict table.

           ira-loop-reserved-regs
               IRA can be used to evaluate more accurate register pressure in
               loops for decisions to move loop invariants (see -O3).  The
               number of available registers reserved for some other purposes
               is given by this parameter.  Default of the parameter is the
               best found from numerous experiments.

           lra-inheritance-ebb-probability-cutoff
               LRA tries to reuse values reloaded in registers in subsequent
               insns.  This optimization is called inheritance.  EBB is used
               as a region to do this optimization.  The parameter defines a
               minimal fall-through edge probability in percentage used to add
               BB to inheritance EBB in LRA.  The default value was chosen
               from numerous runs of SPEC2000 on x86-64.

           loop-invariant-max-bbs-in-loop
               Loop invariant motion can be very expensive, both in
               compilation time and in amount of needed compile-time memory,
               with very large loops.  Loops with more basic blocks than this
               parameter won't have loop invariant motion optimization
               performed on them.

           loop-max-datarefs-for-datadeps
               Building data dependencies is expensive for very large loops.
               This parameter limits the number of data references in loops
               that are considered for data dependence analysis.  These large
               loops are no handled by the optimizations using loop data
               dependencies.

           max-vartrack-size
               Sets a maximum number of hash table slots to use during
               variable tracking dataflow analysis of any function.  If this
               limit is exceeded with variable tracking at assignments
               enabled, analysis for that function is retried without it,
               after removing all debug insns from the function.  If the limit
               is exceeded even without debug insns, var tracking analysis is
               completely disabled for the function.  Setting the parameter to
               zero makes it unlimited.

           max-vartrack-expr-depth
               Sets a maximum number of recursion levels when attempting to
               map variable names or debug temporaries to value expressions.
               This trades compilation time for more complete debug
               information.  If this is set too low, value expressions that
               are available and could be represented in debug information may
               end up not being used; setting this higher may enable the
               compiler to find more complex debug expressions, but compile
               time and memory use may grow.

           max-debug-marker-count
               Sets a threshold on the number of debug markers (e.g. begin
               stmt markers) to avoid complexity explosion at inlining or
               expanding to RTL. If a function has more such gimple stmts than
               the set limit, such stmts will be dropped from the inlined copy
               of a function, and from its RTL expansion.

           min-nondebug-insn-uid
               Use uids starting at this parameter for nondebug insns.  The
               range below the parameter is reserved exclusively for debug
               insns created by -fvar-tracking-assignments, but debug insns
               may get (non-overlapping) uids above it if the reserved range
               is exhausted.

           ipa-sra-ptr-growth-factor
               IPA-SRA replaces a pointer to an aggregate with one or more new
               parameters only when their cumulative size is less or equal to
               ipa-sra-ptr-growth-factor times the size of the original
               pointer parameter.

           ipa-sra-max-replacements
               Maximum pieces of an aggregate that IPA-SRA tracks.  As a
               consequence, it is also the maximum number of replacements of a
               formal parameter.

           sra-max-scalarization-size-Ospeed
           sra-max-scalarization-size-Osize
               The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA)
               aim to replace scalar parts of aggregates with uses of
               independent scalar variables.  These parameters control the
               maximum size, in storage units, of aggregate which is
               considered for replacement when compiling for speed (sra-max-
               scalarization-size-Ospeed) or size (sra-max-scalarization-size-
               Osize) respectively.

           sra-max-propagations
               The maximum number of artificial accesses that Scalar
               Replacement of Aggregates (SRA) will track, per one local
               variable, in order to facilitate copy propagation.

           tm-max-aggregate-size
               When making copies of thread-local variables in a transaction,
               this parameter specifies the size in bytes after which
               variables are saved with the logging functions as opposed to
               save/restore code sequence pairs.  This option only applies
               when using -fgnu-tm.

           graphite-max-nb-scop-params
               To avoid exponential effects in the Graphite loop transforms,
               the number of parameters in a Static Control Part (SCoP) is
               bounded.  A value of zero can be used to lift the bound.  A
               variable whose value is unknown at compilation time and defined
               outside a SCoP is a parameter of the SCoP.

           loop-block-tile-size
               Loop blocking or strip mining transforms, enabled with
               -floop-block or -floop-strip-mine, strip mine each loop in the
               loop nest by a given number of iterations.  The strip length
               can be changed using the loop-block-tile-size parameter.

           ipa-cp-value-list-size
               IPA-CP attempts to track all possible values and types passed
               to a function's parameter in order to propagate them and
               perform devirtualization.  ipa-cp-value-list-size is the
               maximum number of values and types it stores per one formal
               parameter of a function.

           ipa-cp-eval-threshold
               IPA-CP calculates its own score of cloning profitability
               heuristics and performs those cloning opportunities with scores
               that exceed ipa-cp-eval-threshold.

           ipa-cp-max-recursive-depth
               Maximum depth of recursive cloning for self-recursive function.

           ipa-cp-min-recursive-probability
               Recursive cloning only when the probability of call being
               executed exceeds the parameter.

           ipa-cp-recursion-penalty
               Percentage penalty the recursive functions will receive when
               they are evaluated for cloning.

           ipa-cp-single-call-penalty
               Percentage penalty functions containing a single call to
               another function will receive when they are evaluated for
               cloning.

           ipa-max-agg-items
               IPA-CP is also capable to propagate a number of scalar values
               passed in an aggregate. ipa-max-agg-items controls the maximum
               number of such values per one parameter.

           ipa-cp-loop-hint-bonus
               When IPA-CP determines that a cloning candidate would make the
               number of iterations of a loop known, it adds a bonus of ipa-
               cp-loop-hint-bonus to the profitability score of the candidate.

           ipa-max-aa-steps
               During its analysis of function bodies, IPA-CP employs alias
               analysis in order to track values pointed to by function
               parameters.  In order not spend too much time analyzing huge
               functions, it gives up and consider all memory clobbered after
               examining ipa-max-aa-steps statements modifying memory.

           ipa-max-switch-predicate-bounds
               Maximal number of boundary endpoints of case ranges of switch
               statement.  For switch exceeding this limit, IPA-CP will not
               construct cloning cost predicate, which is used to estimate
               cloning benefit, for default case of the switch statement.

           ipa-max-param-expr-ops
               IPA-CP will analyze conditional statement that references some
               function parameter to estimate benefit for cloning upon certain
               constant value.  But if number of operations in a parameter
               expression exceeds ipa-max-param-expr-ops, the expression is
               treated as complicated one, and is not handled by IPA analysis.

           lto-partitions
               Specify desired number of partitions produced during WHOPR
               compilation.  The number of partitions should exceed the number
               of CPUs used for compilation.

           lto-min-partition
               Size of minimal partition for WHOPR (in estimated
               instructions).  This prevents expenses of splitting very small
               programs into too many partitions.

           lto-max-partition
               Size of max partition for WHOPR (in estimated instructions).
               to provide an upper bound for individual size of partition.
               Meant to be used only with balanced partitioning.

           lto-max-streaming-parallelism
               Maximal number of parallel processes used for LTO streaming.

           cxx-max-namespaces-for-diagnostic-help
               The maximum number of namespaces to consult for suggestions
               when C++ name lookup fails for an identifier.

           sink-frequency-threshold
               The maximum relative execution frequency (in percents) of the
               target block relative to a statement's original block to allow
               statement sinking of a statement.  Larger numbers result in
               more aggressive statement sinking.  A small positive adjustment
               is applied for statements with memory operands as those are
               even more profitable so sink.

           max-stores-to-sink
               The maximum number of conditional store pairs that can be sunk.
               Set to 0 if either vectorization (-ftree-vectorize) or if-
               conversion (-ftree-loop-if-convert) is disabled.

           case-values-threshold
               The smallest number of different values for which it is best to
               use a jump-table instead of a tree of conditional branches.  If
               the value is 0, use the default for the machine.

           jump-table-max-growth-ratio-for-size
               The maximum code size growth ratio when expanding into a jump
               table (in percent).  The parameter is used when optimizing for
               size.

           jump-table-max-growth-ratio-for-speed
               The maximum code size growth ratio when expanding into a jump
               table (in percent).  The parameter is used when optimizing for
               speed.

           tree-reassoc-width
               Set the maximum number of instructions executed in parallel in
               reassociated tree. This parameter overrides target dependent
               heuristics used by default if has non zero value.

           sched-pressure-algorithm
               Choose between the two available implementations of
               -fsched-pressure.  Algorithm 1 is the original implementation
               and is the more likely to prevent instructions from being
               reordered.  Algorithm 2 was designed to be a compromise between
               the relatively conservative approach taken by algorithm 1 and
               the rather aggressive approach taken by the default scheduler.
               It relies more heavily on having a regular register file and
               accurate register pressure classes.  See haifa-sched.c in the
               GCC sources for more details.

               The default choice depends on the target.

           max-slsr-cand-scan
               Set the maximum number of existing candidates that are
               considered when seeking a basis for a new straight-line
               strength reduction candidate.

           asan-globals
               Enable buffer overflow detection for global objects.  This kind
               of protection is enabled by default if you are using
               -fsanitize=address option.  To disable global objects
               protection use --param asan-globals=0.

           asan-stack
               Enable buffer overflow detection for stack objects.  This kind
               of protection is enabled by default when using
               -fsanitize=address.  To disable stack protection use --param
               asan-stack=0 option.

           asan-instrument-reads
               Enable buffer overflow detection for memory reads.  This kind
               of protection is enabled by default when using
               -fsanitize=address.  To disable memory reads protection use
               --param asan-instrument-reads=0.

           asan-instrument-writes
               Enable buffer overflow detection for memory writes.  This kind
               of protection is enabled by default when using
               -fsanitize=address.  To disable memory writes protection use
               --param asan-instrument-writes=0 option.

           asan-memintrin
               Enable detection for built-in functions.  This kind of
               protection is enabled by default when using -fsanitize=address.
               To disable built-in functions protection use --param
               asan-memintrin=0.

           asan-use-after-return
               Enable detection of use-after-return.  This kind of protection
               is enabled by default when using the -fsanitize=address option.
               To disable it use --param asan-use-after-return=0.

               Note: By default the check is disabled at run time.  To enable
               it, add "detect_stack_use_after_return=1" to the environment
               variable ASAN_OPTIONS.

           asan-instrumentation-with-call-threshold
               If number of memory accesses in function being instrumented is
               greater or equal to this number, use callbacks instead of
               inline checks.  E.g. to disable inline code use --param
               asan-instrumentation-with-call-threshold=0.

           use-after-scope-direct-emission-threshold
               If the size of a local variable in bytes is smaller or equal to
               this number, directly poison (or unpoison) shadow memory
               instead of using run-time callbacks.

           max-fsm-thread-path-insns
               Maximum number of instructions to copy when duplicating blocks
               on a finite state automaton jump thread path.

           max-fsm-thread-length
               Maximum number of basic blocks on a finite state automaton jump
               thread path.

           max-fsm-thread-paths
               Maximum number of new jump thread paths to create for a finite
               state automaton.

           parloops-chunk-size
               Chunk size of omp schedule for loops parallelized by parloops.

           parloops-schedule
               Schedule type of omp schedule for loops parallelized by
               parloops (static, dynamic, guided, auto, runtime).

           parloops-min-per-thread
               The minimum number of iterations per thread of an innermost
               parallelized loop for which the parallelized variant is
               preferred over the single threaded one.  Note that for a
               parallelized loop nest the minimum number of iterations of the
               outermost loop per thread is two.

           max-ssa-name-query-depth
               Maximum depth of recursion when querying properties of SSA
               names in things like fold routines.  One level of recursion
               corresponds to following a use-def chain.

           hsa-gen-debug-stores
               Enable emission of special debug stores within HSA kernels
               which are then read and reported by libgomp plugin.  Generation
               of these stores is disabled by default, use --param
               hsa-gen-debug-stores=1 to enable it.

           max-speculative-devirt-maydefs
               The maximum number of may-defs we analyze when looking for a
               must-def specifying the dynamic type of an object that invokes
               a virtual call we may be able to devirtualize speculatively.

           max-vrp-switch-assertions
               The maximum number of assertions to add along the default edge
               of a switch statement during VRP.

           unroll-jam-min-percent
               The minimum percentage of memory references that must be
               optimized away for the unroll-and-jam transformation to be
               considered profitable.

           unroll-jam-max-unroll
               The maximum number of times the outer loop should be unrolled
               by the unroll-and-jam transformation.

           max-rtl-if-conversion-unpredictable-cost
               Maximum permissible cost for the sequence that would be
               generated by the RTL if-conversion pass for a branch that is
               considered unpredictable.

           max-variable-expansions-in-unroller
               If -fvariable-expansion-in-unroller is used, the maximum number
               of times that an individual variable will be expanded during
               loop unrolling.

           tracer-min-branch-probability-feedback
               Stop forward growth if the probability of best edge is less
               than this threshold (in percent). Used when profile feedback is
               available.

           partial-inlining-entry-probability
               Maximum probability of the entry BB of split region (in percent
               relative to entry BB of the function) to make partial inlining
               happen.

           max-tracked-strlens
               Maximum number of strings for which strlen optimization pass
               will track string lengths.

           gcse-after-reload-partial-fraction
               The threshold ratio for performing partial redundancy
               elimination after reload.

           gcse-after-reload-critical-fraction
               The threshold ratio of critical edges execution count that
               permit performing redundancy elimination after reload.

           max-loop-header-insns
               The maximum number of insns in loop header duplicated by the
               copy loop headers pass.

           vect-epilogues-nomask
               Enable loop epilogue vectorization using smaller vector size.

           slp-max-insns-in-bb
               Maximum number of instructions in basic block to be considered
               for SLP vectorization.

           avoid-fma-max-bits
               Maximum number of bits for which we avoid creating FMAs.

           sms-loop-average-count-threshold
               A threshold on the average loop count considered by the swing
               modulo scheduler.

           sms-dfa-history
               The number of cycles the swing modulo scheduler considers when
               checking conflicts using DFA.

           max-inline-insns-recursive-auto
               The maximum number of instructions non-inline function can grow
               to via recursive inlining.

           graphite-allow-codegen-errors
               Whether codegen errors should be ICEs when -fchecking.

           sms-max-ii-factor
               A factor for tuning the upper bound that swing modulo scheduler
               uses for scheduling a loop.

           lra-max-considered-reload-pseudos
               The max number of reload pseudos which are considered during
               spilling a non-reload pseudo.

           max-pow-sqrt-depth
               Maximum depth of sqrt chains to use when synthesizing
               exponentiation by a real constant.

           max-dse-active-local-stores
               Maximum number of active local stores in RTL dead store
               elimination.

           asan-instrument-allocas
               Enable asan allocas/VLAs protection.

           max-iterations-computation-cost
               Bound on the cost of an expression to compute the number of
               iterations.

           max-isl-operations
               Maximum number of isl operations, 0 means unlimited.

           graphite-max-arrays-per-scop
               Maximum number of arrays per scop.

           max-vartrack-reverse-op-size
               Max. size of loc list for which reverse ops should be added.

           tracer-dynamic-coverage-feedback
               The percentage of function, weighted by execution frequency,
               that must be covered by trace formation.  Used when profile
               feedback is available.

           max-inline-recursive-depth-auto
               The maximum depth of recursive inlining for non-inline
               functions.

           fsm-scale-path-stmts
               Scale factor to apply to the number of statements in a
               threading path when comparing to the number of (scaled) blocks.

           fsm-maximum-phi-arguments
               Maximum number of arguments a PHI may have before the FSM
               threader will not try to thread through its block.

           uninit-control-dep-attempts
               Maximum number of nested calls to search for control
               dependencies during uninitialized variable analysis.

           sra-max-scalarization-size-Osize
               Maximum size, in storage units, of an aggregate which should be
               considered for scalarization when compiling for size.

           fsm-scale-path-blocks
               Scale factor to apply to the number of blocks in a threading
               path when comparing to the number of (scaled) statements.

           sched-autopref-queue-depth
               Hardware autoprefetcher scheduler model control flag.  Number
               of lookahead cycles the model looks into; at ' ' only enable
               instruction sorting heuristic.

           loop-versioning-max-inner-insns
               The maximum number of instructions that an inner loop can have
               before the loop versioning pass considers it too big to copy.

           loop-versioning-max-outer-insns
               The maximum number of instructions that an outer loop can have
               before the loop versioning pass considers it too big to copy,
               discounting any instructions in inner loops that directly
               benefit from versioning.

           ssa-name-def-chain-limit
               The maximum number of SSA_NAME assignments to follow in
               determining a property of a variable such as its value.  This
               limits the number of iterations or recursive calls GCC performs
               when optimizing certain statements or when determining their
               validity prior to issuing diagnostics.

           store-merging-max-size
               Maximum size of a single store merging region in bytes.

           hash-table-verification-limit
               The number of elements for which hash table verification is
               done for each searched element.

           max-find-base-term-values
               Maximum number of VALUEs handled during a single find_base_term
               call.

           analyzer-max-enodes-per-program-point
               The maximum number of exploded nodes per program point within
               the analyzer, before terminating analysis of that point.

           analyzer-min-snodes-for-call-summary
               The minimum number of supernodes within a function for the
               analyzer to consider summarizing its effects at call sites.

           analyzer-max-recursion-depth
               The maximum number of times a callsite can appear in a call
               stack within the analyzer, before terminating analysis of a
               call that would recurse deeper.

           gimple-fe-computed-hot-bb-threshold
               The number of executions of a basic block which is considered
               hot.  The parameter is used only in GIMPLE FE.

           analyzer-bb-explosion-factor
               The maximum number of 'after supernode' exploded nodes within
               the analyzer per supernode, before terminating analysis.

           The following choices of name are available on AArch64 targets:

           aarch64-sve-compare-costs
               When vectorizing for SVE, consider using "unpacked" vectors for
               smaller elements and use the cost model to pick the cheapest
               approach.  Also use the cost model to choose between SVE and
               Advanced SIMD vectorization.

               Using unpacked vectors includes storing smaller elements in
               larger containers and accessing elements with extending loads
               and truncating stores.

           aarch64-float-recp-precision
               The number of Newton iterations for calculating the reciprocal
               for float type.  The precision of division is proportional to
               this param when division approximation is enabled.  The default
               value is 1.

           aarch64-double-recp-precision
               The number of Newton iterations for calculating the reciprocal
               for double type.  The precision of division is propotional to
               this param when division approximation is enabled.  The default
               value is 2.

           aarch64-autovec-preference
               Force an ISA selection strategy for auto-vectorization.
               Accepts values from 0 to 4, inclusive.

               0   Use the default heuristics.

               1   Use only Advanced SIMD for auto-vectorization.

               2   Use only SVE for auto-vectorization.

               3   Use both Advanced SIMD and SVE.  Prefer Advanced SIMD when
                   the costs are deemed equal.

               4   Use both Advanced SIMD and SVE.  Prefer SVE when the costs
                   are deemed equal.

               The default value is 0.

   Program Instrumentation Options
       GCC supports a number of command-line options that control adding run-
       time instrumentation to the code it normally generates.  For example,
       one purpose of instrumentation is collect profiling statistics for use
       in finding program hot spots, code coverage analysis, or profile-guided
       optimizations.  Another class of program instrumentation is adding run-
       time checking to detect programming errors like invalid pointer
       dereferences or out-of-bounds array accesses, as well as deliberately
       hostile attacks such as stack smashing or C++ vtable hijacking.  There
       is also a general hook which can be used to implement other forms of
       tracing or function-level instrumentation for debug or program analysis
       purposes.

       -p
       -pg Generate extra code to write profile information suitable for the
           analysis program prof (for -p) or gprof (for -pg).  You must use
           this option when compiling the source files you want data about,
           and you must also use it when linking.

           You can use the function attribute "no_instrument_function" to
           suppress profiling of individual functions when compiling with
           these options.

       -fprofile-arcs
           Add code so that program flow arcs are instrumented.  During
           execution the program records how many times each branch and call
           is executed and how many times it is taken or returns.  On targets
           that support constructors with priority support, profiling properly
           handles constructors, destructors and C++ constructors (and
           destructors) of classes which are used as a type of a global
           variable.

           When the compiled program exits it saves this data to a file called
           auxname.gcda for each source file.  The data may be used for
           profile-directed optimizations (-fbranch-probabilities), or for
           test coverage analysis (-ftest-coverage).  Each object file's
           auxname is generated from the name of the output file, if
           explicitly specified and it is not the final executable, otherwise
           it is the basename of the source file.  In both cases any suffix is
           removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda
           for output file specified as -o dir/foo.o).

       --coverage
           This option is used to compile and link code instrumented for
           coverage analysis.  The option is a synonym for -fprofile-arcs
           -ftest-coverage (when compiling) and -lgcov (when linking).  See
           the documentation for those options for more details.

           *   Compile the source files with -fprofile-arcs plus optimization
               and code generation options.  For test coverage analysis, use
               the additional -ftest-coverage option.  You do not need to
               profile every source file in a program.

           *   Compile the source files additionally with -fprofile-abs-path
               to create absolute path names in the .gcno files.  This allows
               gcov to find the correct sources in projects where compilations
               occur with different working directories.

           *   Link your object files with -lgcov or -fprofile-arcs (the
               latter implies the former).

           *   Run the program on a representative workload to generate the
               arc profile information.  This may be repeated any number of
               times.  You can run concurrent instances of your program, and
               provided that the file system supports locking, the data files
               will be correctly updated.  Unless a strict ISO C dialect
               option is in effect, "fork" calls are detected and correctly
               handled without double counting.

           *   For profile-directed optimizations, compile the source files
               again with the same optimization and code generation options
               plus -fbranch-probabilities.

           *   For test coverage analysis, use gcov to produce human readable
               information from the .gcno and .gcda files.  Refer to the gcov
               documentation for further information.

           With -fprofile-arcs, for each function of your program GCC creates
           a program flow graph, then finds a spanning tree for the graph.
           Only arcs that are not on the spanning tree have to be
           instrumented: the compiler adds code to count the number of times
           that these arcs are executed.  When an arc is the only exit or only
           entrance to a block, the instrumentation code can be added to the
           block; otherwise, a new basic block must be created to hold the
           instrumentation code.

       -ftest-coverage
           Produce a notes file that the gcov code-coverage utility can use to
           show program coverage.  Each source file's note file is called
           auxname.gcno.  Refer to the -fprofile-arcs option above for a
           description of auxname and instructions on how to generate test
           coverage data.  Coverage data matches the source files more closely
           if you do not optimize.

       -fprofile-abs-path
           Automatically convert relative source file names to absolute path
           names in the .gcno files.  This allows gcov to find the correct
           sources in projects where compilations occur with different working
           directories.

       -fprofile-dir=path
           Set the directory to search for the profile data files in to path.
           This option affects only the profile data generated by
           -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by
           -fprofile-use and -fbranch-probabilities and its related options.
           Both absolute and relative paths can be used.  By default, GCC uses
           the current directory as path, thus the profile data file appears
           in the same directory as the object file.  In order to prevent the
           file name clashing, if the object file name is not an absolute
           path, we mangle the absolute path of the sourcename.gcda file and
           use it as the file name of a .gcda file.  See similar option
           -fprofile-note.

           When an executable is run in a massive parallel environment, it is
           recommended to save profile to different folders.  That can be done
           with variables in path that are exported during run-time:

           %p  process ID.

           %q{VAR}
               value of environment variable VAR

       -fprofile-generate
       -fprofile-generate=path
           Enable options usually used for instrumenting application to
           produce profile useful for later recompilation with profile
           feedback based optimization.  You must use -fprofile-generate both
           when compiling and when linking your program.

           The following options are enabled: -fprofile-arcs,
           -fprofile-values, -finline-functions, and -fipa-bit-cp.

           If path is specified, GCC looks at the path to find the profile
           feedback data files. See -fprofile-dir.

           To optimize the program based on the collected profile information,
           use -fprofile-use.

       -fprofile-note=path
           If path is specified, GCC saves .gcno file into path location.  If
           you combine the option with multiple source files, the .gcno file
           will be overwritten.

       -fprofile-prefix-path=path
           This option can be used in combination with
           profile-generate=profile_dir and profile-use=profile_dir to inform
           GCC where is the base directory of built source tree.  By default
           profile_dir will contain files with mangled absolute paths of all
           object files in the built project.  This is not desirable when
           directory used to build the instrumented binary differs from the
           directory used to build the binary optimized with profile feedback
           because the profile data will not be found during the optimized
           build.  In such setups -fprofile-prefix-path=path with path
           pointing to the base directory of the build can be used to strip
           the irrelevant part of the path and keep all file names relative to
           the main build directory.

       -fprofile-update=method
           Alter the update method for an application instrumented for profile
           feedback based optimization.  The method argument should be one of
           single, atomic or prefer-atomic.  The first one is useful for
           single-threaded applications, while the second one prevents profile
           corruption by emitting thread-safe code.

           Warning: When an application does not properly join all threads (or
           creates an detached thread), a profile file can be still corrupted.

           Using prefer-atomic would be transformed either to atomic, when
           supported by a target, or to single otherwise.  The GCC driver
           automatically selects prefer-atomic when -pthread is present in the
           command line.

       -fprofile-filter-files=regex
           Instrument only functions from files where names match any regular
           expression (separated by a semi-colon).

           For example, -fprofile-filter-files=main.c;module.*.c will
           instrument only main.c and all C files starting with 'module'.

       -fprofile-exclude-files=regex
           Instrument only functions from files where names do not match all
           the regular expressions (separated by a semi-colon).

           For example, -fprofile-exclude-files=/usr/* will prevent
           instrumentation of all files that are located in /usr/ folder.

       -fprofile-reproducible=[multithreaded|parallel-runs|serial]
           Control level of reproducibility of profile gathered by
           "-fprofile-generate".  This makes it possible to rebuild program
           with same outcome which is useful, for example, for distribution
           packages.

           With -fprofile-reproducible=serial the profile gathered by
           -fprofile-generate is reproducible provided the trained program
           behaves the same at each invocation of the train run, it is not
           multi-threaded and profile data streaming is always done in the
           same order.  Note that profile streaming happens at the end of
           program run but also before "fork" function is invoked.

           Note that it is quite common that execution counts of some part of
           programs depends, for example, on length of temporary file names or
           memory space randomization (that may affect hash-table collision
           rate).  Such non-reproducible part of programs may be annotated by
           "no_instrument_function" function attribute. "gcov-dump" with -l
           can be used to dump gathered data and verify that they are indeed
           reproducible.

           With -fprofile-reproducible=parallel-runs collected profile stays
           reproducible regardless the order of streaming of the data into
           gcda files.  This setting makes it possible to run multiple
           instances of instrumented program in parallel (such as with "make
           -j"). This reduces quality of gathered data, in particular of
           indirect call profiling.

       -fsanitize=address
           Enable AddressSanitizer, a fast memory error detector.  Memory
           access instructions are instrumented to detect out-of-bounds and
           use-after-free bugs.  The option enables
           -fsanitize-address-use-after-scope.  See
           <https://github.com/google/sanitizers/wiki/AddressSanitizer> for
           more details.  The run-time behavior can be influenced using the
           ASAN_OPTIONS environment variable.  When set to "help=1", the
           available options are shown at startup of the instrumented program.
           See
           <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags>
           for a list of supported options.  The option cannot be combined
           with -fsanitize=thread.

       -fsanitize=kernel-address
           Enable AddressSanitizer for Linux kernel.  See
           <https://github.com/google/kasan/wiki> for more details.

       -fsanitize=pointer-compare
           Instrument comparison operation (<, <=, >, >=) with pointer
           operands.  The option must be combined with either
           -fsanitize=kernel-address or -fsanitize=address The option cannot
           be combined with -fsanitize=thread.  Note: By default the check is
           disabled at run time.  To enable it, add
           "detect_invalid_pointer_pairs=2" to the environment variable
           ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects
           invalid operation only when both pointers are non-null.

       -fsanitize=pointer-subtract
           Instrument subtraction with pointer operands.  The option must be
           combined with either -fsanitize=kernel-address or
           -fsanitize=address The option cannot be combined with
           -fsanitize=thread.  Note: By default the check is disabled at run
           time.  To enable it, add "detect_invalid_pointer_pairs=2" to the
           environment variable ASAN_OPTIONS. Using
           "detect_invalid_pointer_pairs=1" detects invalid operation only
           when both pointers are non-null.

       -fsanitize=thread
           Enable ThreadSanitizer, a fast data race detector.  Memory access
           instructions are instrumented to detect data race bugs.  See
           <https://github.com/google/sanitizers/wiki#threadsanitizer> for
           more details. The run-time behavior can be influenced using the
           TSAN_OPTIONS environment variable; see
           <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags>
           for a list of supported options.  The option cannot be combined
           with -fsanitize=address, -fsanitize=leak.

           Note that sanitized atomic builtins cannot throw exceptions when
           operating on invalid memory addresses with non-call exceptions
           (-fnon-call-exceptions).

       -fsanitize=leak
           Enable LeakSanitizer, a memory leak detector.  This option only
           matters for linking of executables and the executable is linked
           against a library that overrides "malloc" and other allocator
           functions.  See
           <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer>
           for more details.  The run-time behavior can be influenced using
           the LSAN_OPTIONS environment variable.  The option cannot be
           combined with -fsanitize=thread.

       -fsanitize=undefined
           Enable UndefinedBehaviorSanitizer, a fast undefined behavior
           detector.  Various computations are instrumented to detect
           undefined behavior at runtime.  Current suboptions are:

           -fsanitize=shift
               This option enables checking that the result of a shift
               operation is not undefined.  Note that what exactly is
               considered undefined differs slightly between C and C++, as
               well as between ISO C90 and C99, etc.  This option has two
               suboptions, -fsanitize=shift-base and
               -fsanitize=shift-exponent.

           -fsanitize=shift-exponent
               This option enables checking that the second argument of a
               shift operation is not negative and is smaller than the
               precision of the promoted first argument.

           -fsanitize=shift-base
               If the second argument of a shift operation is within range,
               check that the result of a shift operation is not undefined.
               Note that what exactly is considered undefined differs slightly
               between C and C++, as well as between ISO C90 and C99, etc.

           -fsanitize=integer-divide-by-zero
               Detect integer division by zero as well as "INT_MIN / -1"
               division.

           -fsanitize=unreachable
               With this option, the compiler turns the
               "__builtin_unreachable" call into a diagnostics message call
               instead.  When reaching the "__builtin_unreachable" call, the
               behavior is undefined.

           -fsanitize=vla-bound
               This option instructs the compiler to check that the size of a
               variable length array is positive.

           -fsanitize=null
               This option enables pointer checking.  Particularly, the
               application built with this option turned on will issue an
               error message when it tries to dereference a NULL pointer, or
               if a reference (possibly an rvalue reference) is bound to a
               NULL pointer, or if a method is invoked on an object pointed by
               a NULL pointer.

           -fsanitize=return
               This option enables return statement checking.  Programs built
               with this option turned on will issue an error message when the
               end of a non-void function is reached without actually
               returning a value.  This option works in C++ only.

           -fsanitize=signed-integer-overflow
               This option enables signed integer overflow checking.  We check
               that the result of "+", "*", and both unary and binary "-" does
               not overflow in the signed arithmetics.  Note, integer
               promotion rules must be taken into account.  That is, the
               following is not an overflow:

                       signed char a = SCHAR_MAX;
                       a++;

           -fsanitize=bounds
               This option enables instrumentation of array bounds.  Various
               out of bounds accesses are detected.  Flexible array members,
               flexible array member-like arrays, and initializers of
               variables with static storage are not instrumented.

           -fsanitize=bounds-strict
               This option enables strict instrumentation of array bounds.
               Most out of bounds accesses are detected, including flexible
               array members and flexible array member-like arrays.
               Initializers of variables with static storage are not
               instrumented.

           -fsanitize=alignment
               This option enables checking of alignment of pointers when they
               are dereferenced, or when a reference is bound to
               insufficiently aligned target, or when a method or constructor
               is invoked on insufficiently aligned object.

           -fsanitize=object-size
               This option enables instrumentation of memory references using
               the "__builtin_object_size" function.  Various out of bounds
               pointer accesses are detected.

           -fsanitize=float-divide-by-zero
               Detect floating-point division by zero.  Unlike other similar
               options, -fsanitize=float-divide-by-zero is not enabled by
               -fsanitize=undefined, since floating-point division by zero can
               be a legitimate way of obtaining infinities and NaNs.

           -fsanitize=float-cast-overflow
               This option enables floating-point type to integer conversion
               checking.  We check that the result of the conversion does not
               overflow.  Unlike other similar options,
               -fsanitize=float-cast-overflow is not enabled by
               -fsanitize=undefined.  This option does not work well with
               "FE_INVALID" exceptions enabled.

           -fsanitize=nonnull-attribute
               This option enables instrumentation of calls, checking whether
               null values are not passed to arguments marked as requiring a
               non-null value by the "nonnull" function attribute.

           -fsanitize=returns-nonnull-attribute
               This option enables instrumentation of return statements in
               functions marked with "returns_nonnull" function attribute, to
               detect returning of null values from such functions.

           -fsanitize=bool
               This option enables instrumentation of loads from bool.  If a
               value other than 0/1 is loaded, a run-time error is issued.

           -fsanitize=enum
               This option enables instrumentation of loads from an enum type.
               If a value outside the range of values for the enum type is
               loaded, a run-time error is issued.

           -fsanitize=vptr
               This option enables instrumentation of C++ member function
               calls, member accesses and some conversions between pointers to
               base and derived classes, to verify the referenced object has
               the correct dynamic type.

           -fsanitize=pointer-overflow
               This option enables instrumentation of pointer arithmetics.  If
               the pointer arithmetics overflows, a run-time error is issued.

           -fsanitize=builtin
               This option enables instrumentation of arguments to selected
               builtin functions.  If an invalid value is passed to such
               arguments, a run-time error is issued.  E.g. passing 0 as the
               argument to "__builtin_ctz" or "__builtin_clz" invokes
               undefined behavior and is diagnosed by this option.

           While -ftrapv causes traps for signed overflows to be emitted,
           -fsanitize=undefined gives a diagnostic message.  This currently
           works only for the C family of languages.

       -fno-sanitize=all
           This option disables all previously enabled sanitizers.
           -fsanitize=all is not allowed, as some sanitizers cannot be used
           together.

       -fasan-shadow-offset=number
           This option forces GCC to use custom shadow offset in
           AddressSanitizer checks.  It is useful for experimenting with
           different shadow memory layouts in Kernel AddressSanitizer.

       -fsanitize-sections=s1,s2,...
           Sanitize global variables in selected user-defined sections.  si
           may contain wildcards.

       -fsanitize-recover[=opts]
           -fsanitize-recover= controls error recovery mode for sanitizers
           mentioned in comma-separated list of opts.  Enabling this option
           for a sanitizer component causes it to attempt to continue running
           the program as if no error happened.  This means multiple runtime
           errors can be reported in a single program run, and the exit code
           of the program may indicate success even when errors have been
           reported.  The -fno-sanitize-recover= option can be used to alter
           this behavior: only the first detected error is reported and
           program then exits with a non-zero exit code.

           Currently this feature only works for -fsanitize=undefined (and its
           suboptions except for -fsanitize=unreachable and
           -fsanitize=return), -fsanitize=float-cast-overflow,
           -fsanitize=float-divide-by-zero, -fsanitize=bounds-strict,
           -fsanitize=kernel-address and -fsanitize=address.  For these
           sanitizers error recovery is turned on by default, except
           -fsanitize=address, for which this feature is experimental.
           -fsanitize-recover=all and -fno-sanitize-recover=all is also
           accepted, the former enables recovery for all sanitizers that
           support it, the latter disables recovery for all sanitizers that
           support it.

           Even if a recovery mode is turned on the compiler side, it needs to
           be also enabled on the runtime library side, otherwise the failures
           are still fatal.  The runtime library defaults to "halt_on_error=0"
           for ThreadSanitizer and UndefinedBehaviorSanitizer, while default
           value for AddressSanitizer is "halt_on_error=1". This can be
           overridden through setting the "halt_on_error" flag in the
           corresponding environment variable.

           Syntax without an explicit opts parameter is deprecated.  It is
           equivalent to specifying an opts list of:

                   undefined,float-cast-overflow,float-divide-by-zero,bounds-strict

       -fsanitize-address-use-after-scope
           Enable sanitization of local variables to detect use-after-scope
           bugs.  The option sets -fstack-reuse to none.

       -fsanitize-undefined-trap-on-error
           The -fsanitize-undefined-trap-on-error option instructs the
           compiler to report undefined behavior using "__builtin_trap" rather
           than a "libubsan" library routine.  The advantage of this is that
           the "libubsan" library is not needed and is not linked in, so this
           is usable even in freestanding environments.

       -fsanitize-coverage=trace-pc
           Enable coverage-guided fuzzing code instrumentation.  Inserts a
           call to "__sanitizer_cov_trace_pc" into every basic block.

       -fsanitize-coverage=trace-cmp
           Enable dataflow guided fuzzing code instrumentation.  Inserts a
           call to "__sanitizer_cov_trace_cmp1", "__sanitizer_cov_trace_cmp2",
           "__sanitizer_cov_trace_cmp4" or "__sanitizer_cov_trace_cmp8" for
           integral comparison with both operands variable or
           "__sanitizer_cov_trace_const_cmp1",
           "__sanitizer_cov_trace_const_cmp2",
           "__sanitizer_cov_trace_const_cmp4" or
           "__sanitizer_cov_trace_const_cmp8" for integral comparison with one
           operand constant, "__sanitizer_cov_trace_cmpf" or
           "__sanitizer_cov_trace_cmpd" for float or double comparisons and
           "__sanitizer_cov_trace_switch" for switch statements.

       -fcf-protection=[full|branch|return|none|check]
           Enable code instrumentation of control-flow transfers to increase
           program security by checking that target addresses of control-flow
           transfer instructions (such as indirect function call, function
           return, indirect jump) are valid.  This prevents diverting the flow
           of control to an unexpected target.  This is intended to protect
           against such threats as Return-oriented Programming (ROP), and
           similarly call/jmp-oriented programming (COP/JOP).

           The value "branch" tells the compiler to implement checking of
           validity of control-flow transfer at the point of indirect branch
           instructions, i.e. call/jmp instructions.  The value "return"
           implements checking of validity at the point of returning from a
           function.  The value "full" is an alias for specifying both
           "branch" and "return". The value "none" turns off instrumentation.

           The value "check" is used for the final link with link-time
           optimization (LTO).  An error is issued if LTO object files are
           compiled with different -fcf-protection values.  The value "check"
           is ignored at the compile time.

           The macro "__CET__" is defined when -fcf-protection is used.  The
           first bit of "__CET__" is set to 1 for the value "branch" and the
           second bit of "__CET__" is set to 1 for the "return".

           You can also use the "nocf_check" attribute to identify which
           functions and calls should be skipped from instrumentation.

           Currently the x86 GNU/Linux target provides an implementation based
           on Intel Control-flow Enforcement Technology (CET).

       -fstack-protector
           Emit extra code to check for buffer overflows, such as stack
           smashing attacks.  This is done by adding a guard variable to
           functions with vulnerable objects.  This includes functions that
           call "alloca", and functions with buffers larger than or equal to 8
           bytes.  The guards are initialized when a function is entered and
           then checked when the function exits.  If a guard check fails, an
           error message is printed and the program exits.  Only variables
           that are actually allocated on the stack are considered, optimized
           away variables or variables allocated in registers don't count.

       -fstack-protector-all
           Like -fstack-protector except that all functions are protected.

       -fstack-protector-strong
           Like -fstack-protector but includes additional functions to be
           protected --- those that have local array definitions, or have
           references to local frame addresses.  Only variables that are
           actually allocated on the stack are considered, optimized away
           variables or variables allocated in registers don't count.

       -fstack-protector-explicit
           Like -fstack-protector but only protects those functions which have
           the "stack_protect" attribute.

       -fstack-check
           Generate code to verify that you do not go beyond the boundary of
           the stack.  You should specify this flag if you are running in an
           environment with multiple threads, but you only rarely need to
           specify it in a single-threaded environment since stack overflow is
           automatically detected on nearly all systems if there is only one
           stack.

           Note that this switch does not actually cause checking to be done;
           the operating system or the language runtime must do that.  The
           switch causes generation of code to ensure that they see the stack
           being extended.

           You can additionally specify a string parameter: no means no
           checking, generic means force the use of old-style checking,
           specific means use the best checking method and is equivalent to
           bare -fstack-check.

           Old-style checking is a generic mechanism that requires no specific
           target support in the compiler but comes with the following
           drawbacks:

           1.  Modified allocation strategy for large objects: they are always
               allocated dynamically if their size exceeds a fixed threshold.
               Note this may change the semantics of some code.

           2.  Fixed limit on the size of the static frame of functions: when
               it is topped by a particular function, stack checking is not
               reliable and a warning is issued by the compiler.

           3.  Inefficiency: because of both the modified allocation strategy
               and the generic implementation, code performance is hampered.

           Note that old-style stack checking is also the fallback method for
           specific if no target support has been added in the compiler.

           -fstack-check= is designed for Ada's needs to detect infinite
           recursion and stack overflows.  specific is an excellent choice
           when compiling Ada code.  It is not generally sufficient to protect
           against stack-clash attacks.  To protect against those you want
           -fstack-clash-protection.

       -fstack-clash-protection
           Generate code to prevent stack clash style attacks.  When this
           option is enabled, the compiler will only allocate one page of
           stack space at a time and each page is accessed immediately after
           allocation.  Thus, it prevents allocations from jumping over any
           stack guard page provided by the operating system.

           Most targets do not fully support stack clash protection.  However,
           on those targets -fstack-clash-protection will protect dynamic
           stack allocations.  -fstack-clash-protection may also provide
           limited protection for static stack allocations if the target
           supports -fstack-check=specific.

       -fstack-limit-register=reg
       -fstack-limit-symbol=sym
       -fno-stack-limit
           Generate code to ensure that the stack does not grow beyond a
           certain value, either the value of a register or the address of a
           symbol.  If a larger stack is required, a signal is raised at run
           time.  For most targets, the signal is raised before the stack
           overruns the boundary, so it is possible to catch the signal
           without taking special precautions.

           For instance, if the stack starts at absolute address 0x80000000
           and grows downwards, you can use the flags
           -fstack-limit-symbol=__stack_limit and
           -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of
           128KB.  Note that this may only work with the GNU linker.

           You can locally override stack limit checking by using the
           "no_stack_limit" function attribute.

       -fsplit-stack
           Generate code to automatically split the stack before it overflows.
           The resulting program has a discontiguous stack which can only
           overflow if the program is unable to allocate any more memory.
           This is most useful when running threaded programs, as it is no
           longer necessary to calculate a good stack size to use for each
           thread.  This is currently only implemented for the x86 targets
           running GNU/Linux.

           When code compiled with -fsplit-stack calls code compiled without
           -fsplit-stack, there may not be much stack space available for the
           latter code to run.  If compiling all code, including library code,
           with -fsplit-stack is not an option, then the linker can fix up
           these calls so that the code compiled without -fsplit-stack always
           has a large stack.  Support for this is implemented in the gold
           linker in GNU binutils release 2.21 and later.

       -fvtable-verify=[std|preinit|none]
           This option is only available when compiling C++ code.  It turns on
           (or off, if using -fvtable-verify=none) the security feature that
           verifies at run time, for every virtual call, that the vtable
           pointer through which the call is made is valid for the type of the
           object, and has not been corrupted or overwritten.  If an invalid
           vtable pointer is detected at run time, an error is reported and
           execution of the program is immediately halted.

           This option causes run-time data structures to be built at program
           startup, which are used for verifying the vtable pointers.  The
           options std and preinit control the timing of when these data
           structures are built.  In both cases the data structures are built
           before execution reaches "main".  Using -fvtable-verify=std causes
           the data structures to be built after shared libraries have been
           loaded and initialized.  -fvtable-verify=preinit causes them to be
           built before shared libraries have been loaded and initialized.

           If this option appears multiple times in the command line with
           different values specified, none takes highest priority over both
           std and preinit; preinit takes priority over std.

       -fvtv-debug
           When used in conjunction with -fvtable-verify=std or
           -fvtable-verify=preinit, causes debug versions of the runtime
           functions for the vtable verification feature to be called.  This
           flag also causes the compiler to log information about which vtable
           pointers it finds for each class.  This information is written to a
           file named vtv_set_ptr_data.log in the directory named by the
           environment variable VTV_LOGS_DIR if that is defined or the current
           working directory otherwise.

           Note:  This feature appends data to the log file. If you want a
           fresh log file, be sure to delete any existing one.

       -fvtv-counts
           This is a debugging flag.  When used in conjunction with
           -fvtable-verify=std or -fvtable-verify=preinit, this causes the
           compiler to keep track of the total number of virtual calls it
           encounters and the number of verifications it inserts.  It also
           counts the number of calls to certain run-time library functions
           that it inserts and logs this information for each compilation
           unit.  The compiler writes this information to a file named
           vtv_count_data.log in the directory named by the environment
           variable VTV_LOGS_DIR if that is defined or the current working
           directory otherwise.  It also counts the size of the vtable pointer
           sets for each class, and writes this information to
           vtv_class_set_sizes.log in the same directory.

           Note:  This feature appends data to the log files.  To get fresh
           log files, be sure to delete any existing ones.

       -finstrument-functions
           Generate instrumentation calls for entry and exit to functions.
           Just after function entry and just before function exit, the
           following profiling functions are called with the address of the
           current function and its call site.  (On some platforms,
           "__builtin_return_address" does not work beyond the current
           function, so the call site information may not be available to the
           profiling functions otherwise.)

                   void __cyg_profile_func_enter (void *this_fn,
                                                  void *call_site);
                   void __cyg_profile_func_exit  (void *this_fn,
                                                  void *call_site);

           The first argument is the address of the start of the current
           function, which may be looked up exactly in the symbol table.

           This instrumentation is also done for functions expanded inline in
           other functions.  The profiling calls indicate where, conceptually,
           the inline function is entered and exited.  This means that
           addressable versions of such functions must be available.  If all
           your uses of a function are expanded inline, this may mean an
           additional expansion of code size.  If you use "extern inline" in
           your C code, an addressable version of such functions must be
           provided.  (This is normally the case anyway, but if you get lucky
           and the optimizer always expands the functions inline, you might
           have gotten away without providing static copies.)

           A function may be given the attribute "no_instrument_function", in
           which case this instrumentation is not done.  This can be used, for
           example, for the profiling functions listed above, high-priority
           interrupt routines, and any functions from which the profiling
           functions cannot safely be called (perhaps signal handlers, if the
           profiling routines generate output or allocate memory).

       -finstrument-functions-exclude-file-list=file,file,...
           Set the list of functions that are excluded from instrumentation
           (see the description of -finstrument-functions).  If the file that
           contains a function definition matches with one of file, then that
           function is not instrumented.  The match is done on substrings: if
           the file parameter is a substring of the file name, it is
           considered to be a match.

           For example:

                   -finstrument-functions-exclude-file-list=/bits/stl,include/sys

           excludes any inline function defined in files whose pathnames
           contain /bits/stl or include/sys.

           If, for some reason, you want to include letter , in one of sym,
           write ,. For example,
           -finstrument-functions-exclude-file-list=',,tmp' (note the single
           quote surrounding the option).

       -finstrument-functions-exclude-function-list=sym,sym,...
           This is similar to -finstrument-functions-exclude-file-list, but
           this option sets the list of function names to be excluded from
           instrumentation.  The function name to be matched is its user-
           visible name, such as "vector<int> blah(const vector<int> &)", not
           the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE").  The
           match is done on substrings: if the sym parameter is a substring of
           the function name, it is considered to be a match.  For C99 and C++
           extended identifiers, the function name must be given in UTF-8, not
           using universal character names.

       -fpatchable-function-entry=N[,M]
           Generate N NOPs right at the beginning of each function, with the
           function entry point before the Mth NOP. If M is omitted, it
           defaults to 0 so the function entry points to the address just at
           the first NOP. The NOP instructions reserve extra space which can
           be used to patch in any desired instrumentation at run time,
           provided that the code segment is writable.  The amount of space is
           controllable indirectly via the number of NOPs; the NOP instruction
           used corresponds to the instruction emitted by the internal GCC
           back-end interface "gen_nop".  This behavior is target-specific and
           may also depend on the architecture variant and/or other
           compilation options.

           For run-time identification, the starting addresses of these areas,
           which correspond to their respective function entries minus M, are
           additionally collected in the "__patchable_function_entries"
           section of the resulting binary.

           Note that the value of "__attribute__ ((patchable_function_entry
           (N,M)))" takes precedence over command-line option
           -fpatchable-function-entry=N,M.  This can be used to increase the
           area size or to remove it completely on a single function.  If
           "N=0", no pad location is recorded.

           The NOP instructions are inserted at---and maybe before, depending
           on M---the function entry address, even before the prologue.

   Options Controlling the Preprocessor
       These options control the C preprocessor, which is run on each C source
       file before actual compilation.

       If you use the -E option, nothing is done except preprocessing.  Some
       of these options make sense only together with -E because they cause
       the preprocessor output to be unsuitable for actual compilation.

       In addition to the options listed here, there are a number of options
       to control search paths for include files documented in Directory
       Options.  Options to control preprocessor diagnostics are listed in
       Warning Options.

       -D name
           Predefine name as a macro, with definition 1.

       -D name=definition
           The contents of definition are tokenized and processed as if they
           appeared during translation phase three in a #define directive.  In
           particular, the definition is truncated by embedded newline
           characters.

           If you are invoking the preprocessor from a shell or shell-like
           program you may need to use the shell's quoting syntax to protect
           characters such as spaces that have a meaning in the shell syntax.

           If you wish to define a function-like macro on the command line,
           write its argument list with surrounding parentheses before the
           equals sign (if any).  Parentheses are meaningful to most shells,
           so you should quote the option.  With sh and csh,
           -D'name(args...)=definition' works.

           -D and -U options are processed in the order they are given on the
           command line.  All -imacros file and -include file options are
           processed after all -D and -U options.

       -U name
           Cancel any previous definition of name, either built in or provided
           with a -D option.

       -include file
           Process file as if "#include "file"" appeared as the first line of
           the primary source file.  However, the first directory searched for
           file is the preprocessor's working directory instead of the
           directory containing the main source file.  If not found there, it
           is searched for in the remainder of the "#include "..."" search
           chain as normal.

           If multiple -include options are given, the files are included in
           the order they appear on the command line.

       -imacros file
           Exactly like -include, except that any output produced by scanning
           file is thrown away.  Macros it defines remain defined.  This
           allows you to acquire all the macros from a header without also
           processing its declarations.

           All files specified by -imacros are processed before all files
           specified by -include.

       -undef
           Do not predefine any system-specific or GCC-specific macros.  The
           standard predefined macros remain defined.

       -pthread
           Define additional macros required for using the POSIX threads
           library.  You should use this option consistently for both
           compilation and linking.  This option is supported on GNU/Linux
           targets, most other Unix derivatives, and also on x86 Cygwin and
           MinGW targets.

       -M  Instead of outputting the result of preprocessing, output a rule
           suitable for make describing the dependencies of the main source
           file.  The preprocessor outputs one make rule containing the object
           file name for that source file, a colon, and the names of all the
           included files, including those coming from -include or -imacros
           command-line options.

           Unless specified explicitly (with -MT or -MQ), the object file name
           consists of the name of the source file with any suffix replaced
           with object file suffix and with any leading directory parts
           removed.  If there are many included files then the rule is split
           into several lines using \-newline.  The rule has no commands.

           This option does not suppress the preprocessor's debug output, such
           as -dM.  To avoid mixing such debug output with the dependency
           rules you should explicitly specify the dependency output file with
           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
           Debug output is still sent to the regular output stream as normal.

           Passing -M to the driver implies -E, and suppresses warnings with
           an implicit -w.

       -MM Like -M but do not mention header files that are found in system
           header directories, nor header files that are included, directly or
           indirectly, from such a header.

           This implies that the choice of angle brackets or double quotes in
           an #include directive does not in itself determine whether that
           header appears in -MM dependency output.

       -MF file
           When used with -M or -MM, specifies a file to write the
           dependencies to.  If no -MF switch is given the preprocessor sends
           the rules to the same place it would send preprocessed output.

           When used with the driver options -MD or -MMD, -MF overrides the
           default dependency output file.

           If file is -, then the dependencies are written to stdout.

       -MG In conjunction with an option such as -M requesting dependency
           generation, -MG assumes missing header files are generated files
           and adds them to the dependency list without raising an error.  The
           dependency filename is taken directly from the "#include" directive
           without prepending any path.  -MG also suppresses preprocessed
           output, as a missing header file renders this useless.

           This feature is used in automatic updating of makefiles.

       -MP This option instructs CPP to add a phony target for each dependency
           other than the main file, causing each to depend on nothing.  These
           dummy rules work around errors make gives if you remove header
           files without updating the Makefile to match.

           This is typical output:

                   test.o: test.c test.h

                   test.h:

       -MT target
           Change the target of the rule emitted by dependency generation.  By
           default CPP takes the name of the main input file, deletes any
           directory components and any file suffix such as .c, and appends
           the platform's usual object suffix.  The result is the target.

           An -MT option sets the target to be exactly the string you specify.
           If you want multiple targets, you can specify them as a single
           argument to -MT, or use multiple -MT options.

           For example, -MT '$(objpfx)foo.o' might give

                   $(objpfx)foo.o: foo.c

       -MQ target
           Same as -MT, but it quotes any characters which are special to
           Make.  -MQ '$(objpfx)foo.o' gives

                   $$(objpfx)foo.o: foo.c

           The default target is automatically quoted, as if it were given
           with -MQ.

       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
           The driver determines file based on whether an -o option is given.
           If it is, the driver uses its argument but with a suffix of .d,
           otherwise it takes the name of the input file, removes any
           directory components and suffix, and applies a .d suffix.

           If -MD is used in conjunction with -E, any -o switch is understood
           to specify the dependency output file, but if used without -E, each
           -o is understood to specify a target object file.

           Since -E is not implied, -MD can be used to generate a dependency
           output file as a side effect of the compilation process.

       -MMD
           Like -MD except mention only user header files, not system header
           files.

       -fpreprocessed
           Indicate to the preprocessor that the input file has already been
           preprocessed.  This suppresses things like macro expansion,
           trigraph conversion, escaped newline splicing, and processing of
           most directives.  The preprocessor still recognizes and removes
           comments, so that you can pass a file preprocessed with -C to the
           compiler without problems.  In this mode the integrated
           preprocessor is little more than a tokenizer for the front ends.

           -fpreprocessed is implicit if the input file has one of the
           extensions .i, .ii or .mi.  These are the extensions that GCC uses
           for preprocessed files created by -save-temps.

       -cxx-isystem dir
           Search dir for C++ header files, after all directories specified by
           -I but before the standard system directories.  Mark it as a system
           directory, so that it gets the same special treatment as is applied
           to the standard system directories.

       -fdirectives-only
           When preprocessing, handle directives, but do not expand macros.

           The option's behavior depends on the -E and -fpreprocessed options.

           With -E, preprocessing is limited to the handling of directives
           such as "#define", "#ifdef", and "#error".  Other preprocessor
           operations, such as macro expansion and trigraph conversion are not
           performed.  In addition, the -dD option is implicitly enabled.

           With -fpreprocessed, predefinition of command line and most builtin
           macros is disabled.  Macros such as "__LINE__", which are
           contextually dependent, are handled normally.  This enables
           compilation of files previously preprocessed with "-E
           -fdirectives-only".

           With both -E and -fpreprocessed, the rules for -fpreprocessed take
           precedence.  This enables full preprocessing of files previously
           preprocessed with "-E -fdirectives-only".

       -iremap src:dst
           Replace the prefix src in __FILE__ with dst at expansion time.
           This option can be specified more than once.  Processing stops at
           the first match.

       -fdollars-in-identifiers
           Accept $ in identifiers.

       -fextended-identifiers
           Accept universal character names and extended characters in
           identifiers.  This option is enabled by default for C99 (and later
           C standard versions) and C++.

       -fno-canonical-system-headers
           When preprocessing, do not shorten system header paths with
           canonicalization.

       -fmax-include-depth=depth
           Set the maximum depth of the nested #include. The default is 200.

       -ftabstop=width
           Set the distance between tab stops.  This helps the preprocessor
           report correct column numbers in warnings or errors, even if tabs
           appear on the line.  If the value is less than 1 or greater than
           100, the option is ignored.  The default is 8.

       -ftrack-macro-expansion[=level]
           Track locations of tokens across macro expansions. This allows the
           compiler to emit diagnostic about the current macro expansion stack
           when a compilation error occurs in a macro expansion. Using this
           option makes the preprocessor and the compiler consume more memory.
           The level parameter can be used to choose the level of precision of
           token location tracking thus decreasing the memory consumption if
           necessary. Value 0 of level de-activates this option. Value 1
           tracks tokens locations in a degraded mode for the sake of minimal
           memory overhead. In this mode all tokens resulting from the
           expansion of an argument of a function-like macro have the same
           location. Value 2 tracks tokens locations completely. This value is
           the most memory hungry.  When this option is given no argument, the
           default parameter value is 2.

           Note that "-ftrack-macro-expansion=2" is activated by default.

       -fmacro-prefix-map=old=new
           When preprocessing files residing in directory old, expand the
           "__FILE__" and "__BASE_FILE__" macros as if the files resided in
           directory new instead.  This can be used to change an absolute path
           to a relative path by using . for new which can result in more
           reproducible builds that are location independent.  This option
           also affects "__builtin_FILE()" during compilation.  See also
           -ffile-prefix-map.

       -fexec-charset=charset
           Set the execution character set, used for string and character
           constants.  The default is UTF-8.  charset can be any encoding
           supported by the system's "iconv" library routine.

       -fwide-exec-charset=charset
           Set the wide execution character set, used for wide string and
           character constants.  The default is UTF-32 or UTF-16, whichever
           corresponds to the width of "wchar_t".  As with -fexec-charset,
           charset can be any encoding supported by the system's "iconv"
           library routine; however, you will have problems with encodings
           that do not fit exactly in "wchar_t".

       -finput-charset=charset
           Set the input character set, used for translation from the
           character set of the input file to the source character set used by
           GCC.  If the locale does not specify, or GCC cannot get this
           information from the locale, the default is UTF-8.  This can be
           overridden by either the locale or this command-line option.
           Currently the command-line option takes precedence if there's a
           conflict.  charset can be any encoding supported by the system's
           "iconv" library routine.

       -fpch-deps
           When using precompiled headers, this flag causes the dependency-
           output flags to also list the files from the precompiled header's
           dependencies.  If not specified, only the precompiled header are
           listed and not the files that were used to create it, because those
           files are not consulted when a precompiled header is used.

       -fpch-preprocess
           This option allows use of a precompiled header together with -E.
           It inserts a special "#pragma", "#pragma GCC pch_preprocess
           "filename"" in the output to mark the place where the precompiled
           header was found, and its filename.  When -fpreprocessed is in use,
           GCC recognizes this "#pragma" and loads the PCH.

           This option is off by default, because the resulting preprocessed
           output is only really suitable as input to GCC.  It is switched on
           by -save-temps.

           You should not write this "#pragma" in your own code, but it is
           safe to edit the filename if the PCH file is available in a
           different location.  The filename may be absolute or it may be
           relative to GCC's current directory.

       -fworking-directory
           Enable generation of linemarkers in the preprocessor output that
           let the compiler know the current working directory at the time of
           preprocessing.  When this option is enabled, the preprocessor
           emits, after the initial linemarker, a second linemarker with the
           current working directory followed by two slashes.  GCC uses this
           directory, when it's present in the preprocessed input, as the
           directory emitted as the current working directory in some
           debugging information formats.  This option is implicitly enabled
           if debugging information is enabled, but this can be inhibited with
           the negated form -fno-working-directory.  If the -P flag is present
           in the command line, this option has no effect, since no "#line"
           directives are emitted whatsoever.

       -A predicate=answer
           Make an assertion with the predicate predicate and answer answer.
           This form is preferred to the older form -A predicate(answer),
           which is still supported, because it does not use shell special
           characters.

       -A -predicate=answer
           Cancel an assertion with the predicate predicate and answer answer.

       -C  Do not discard comments.  All comments are passed through to the
           output file, except for comments in processed directives, which are
           deleted along with the directive.

           You should be prepared for side effects when using -C; it causes
           the preprocessor to treat comments as tokens in their own right.
           For example, comments appearing at the start of what would be a
           directive line have the effect of turning that line into an
           ordinary source line, since the first token on the line is no
           longer a #.

       -CC Do not discard comments, including during macro expansion.  This is
           like -C, except that comments contained within macros are also
           passed through to the output file where the macro is expanded.

           In addition to the side effects of the -C option, the -CC option
           causes all C++-style comments inside a macro to be converted to
           C-style comments.  This is to prevent later use of that macro from
           inadvertently commenting out the remainder of the source line.

           The -CC option is generally used to support lint comments.

       -P  Inhibit generation of linemarkers in the output from the
           preprocessor.  This might be useful when running the preprocessor
           on something that is not C code, and will be sent to a program
           which might be confused by the linemarkers.

       -traditional
       -traditional-cpp
           Try to imitate the behavior of pre-standard C preprocessors, as
           opposed to ISO C preprocessors.  See the GNU CPP manual for
           details.

           Note that GCC does not otherwise attempt to emulate a pre-standard
           C compiler, and these options are only supported with the -E
           switch, or when invoking CPP explicitly.

       -trigraphs
           Support ISO C trigraphs.  These are three-character sequences, all
           starting with ??, that are defined by ISO C to stand for single
           characters.  For example, ??/ stands for \, so '??/n' is a
           character constant for a newline.

           The nine trigraphs and their replacements are

                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
                   Replacement:      [    ]    {    }    #    \    ^    |    ~

           By default, GCC ignores trigraphs, but in standard-conforming modes
           it converts them.  See the -std and -ansi options.

       -remap
           Enable special code to work around file systems which only permit
           very short file names, such as MS-DOS.

       -H  Print the name of each header file used, in addition to other
           normal activities.  Each name is indented to show how deep in the
           #include stack it is.  Precompiled header files are also printed,
           even if they are found to be invalid; an invalid precompiled header
           file is printed with ...x and a valid one with ...! .

       -dletters
           Says to make debugging dumps during compilation as specified by
           letters.  The flags documented here are those relevant to the
           preprocessor.  Other letters are interpreted by the compiler
           proper, or reserved for future versions of GCC, and so are silently
           ignored.  If you specify letters whose behavior conflicts, the
           result is undefined.

           -dM Instead of the normal output, generate a list of #define
               directives for all the macros defined during the execution of
               the preprocessor, including predefined macros.  This gives you
               a way of finding out what is predefined in your version of the
               preprocessor.  Assuming you have no file foo.h, the command

                       touch foo.h; cpp -dM foo.h

               shows all the predefined macros.

               If you use -dM without the -E option, -dM is interpreted as a
               synonym for -fdump-rtl-mach.

           -dD Like -dM except in two respects: it does not include the
               predefined macros, and it outputs both the #define directives
               and the result of preprocessing.  Both kinds of output go to
               the standard output file.

           -dN Like -dD, but emit only the macro names, not their expansions.

           -dI Output #include directives in addition to the result of
               preprocessing.

           -dU Like -dD except that only macros that are expanded, or whose
               definedness is tested in preprocessor directives, are output;
               the output is delayed until the use or test of the macro; and
               #undef directives are also output for macros tested but
               undefined at the time.

       -fdebug-cpp
           This option is only useful for debugging GCC.  When used from CPP
           or with -E, it dumps debugging information about location maps.
           Every token in the output is preceded by the dump of the map its
           location belongs to.

           When used from GCC without -E, this option has no effect.

       -Wp,option
           You can use -Wp,option to bypass the compiler driver and pass
           option directly through to the preprocessor.  If option contains
           commas, it is split into multiple options at the commas.  However,
           many options are modified, translated or interpreted by the
           compiler driver before being passed to the preprocessor, and -Wp
           forcibly bypasses this phase.  The preprocessor's direct interface
           is undocumented and subject to change, so whenever possible you
           should avoid using -Wp and let the driver handle the options
           instead.

       -Xpreprocessor option
           Pass option as an option to the preprocessor.  You can use this to
           supply system-specific preprocessor options that GCC does not
           recognize.

           If you want to pass an option that takes an argument, you must use
           -Xpreprocessor twice, once for the option and once for the
           argument.

       -no-integrated-cpp
           Perform preprocessing as a separate pass before compilation.  By
           default, GCC performs preprocessing as an integrated part of input
           tokenization and parsing.  If this option is provided, the
           appropriate language front end (cc1, cc1plus, or cc1obj for C, C++,
           and Objective-C, respectively) is instead invoked twice, once for
           preprocessing only and once for actual compilation of the
           preprocessed input.  This option may be useful in conjunction with
           the -B or -wrapper options to specify an alternate preprocessor or
           perform additional processing of the program source between normal
           preprocessing and compilation.

   Passing Options to the Assembler
       You can pass options to the assembler.

       -Wa,option
           Pass option as an option to the assembler.  If option contains
           commas, it is split into multiple options at the commas.

       -Xassembler option
           Pass option as an option to the assembler.  You can use this to
           supply system-specific assembler options that GCC does not
           recognize.

           If you want to pass an option that takes an argument, you must use
           -Xassembler twice, once for the option and once for the argument.

   Options for Linking
       These options come into play when the compiler links object files into
       an executable output file.  They are meaningless if the compiler is not
       doing a link step.

       object-file-name
           A file name that does not end in a special recognized suffix is
           considered to name an object file or library.  (Object files are
           distinguished from libraries by the linker according to the file
           contents.)  If linking is done, these object files are used as
           input to the linker.

       -c
       -S
       -E  If any of these options is used, then the linker is not run, and
           object file names should not be used as arguments.

       -flinker-output=type
           This option controls code generation of the link-time optimizer.
           By default the linker output is automatically determined by the
           linker plugin.  For debugging the compiler and if incremental
           linking with a non-LTO object file is desired, it may be useful to
           control the type manually.

           If type is exec, code generation produces a static binary. In this
           case -fpic and -fpie are both disabled.

           If type is dyn, code generation produces a shared library.  In this
           case -fpic or -fPIC is preserved, but not enabled automatically.
           This allows to build shared libraries without position-independent
           code on architectures where this is possible, i.e. on x86.

           If type is pie, code generation produces an -fpie executable. This
           results in similar optimizations as exec except that -fpie is not
           disabled if specified at compilation time.

           If type is rel, the compiler assumes that incremental linking is
           done.  The sections containing intermediate code for link-time
           optimization are merged, pre-optimized, and output to the resulting
           object file. In addition, if -ffat-lto-objects is specified, binary
           code is produced for future non-LTO linking. The object file
           produced by incremental linking is smaller than a static library
           produced from the same object files.  At link time the result of
           incremental linking also loads faster than a static library
           assuming that the majority of objects in the library are used.

           Finally nolto-rel configures the compiler for incremental linking
           where code generation is forced, a final binary is produced, and
           the intermediate code for later link-time optimization is stripped.
           When multiple object files are linked together the resulting code
           is better optimized than with link-time optimizations disabled (for
           example, cross-module inlining happens), but most of benefits of
           whole program optimizations are lost.

           During the incremental link (by -r) the linker plugin defaults to
           rel. With current interfaces to GNU Binutils it is however not
           possible to incrementally link LTO objects and non-LTO objects into
           a single mixed object file.  If any of object files in incremental
           link cannot be used for link-time optimization, the linker plugin
           issues a warning and uses nolto-rel. To maintain whole program
           optimization, it is recommended to link such objects into static
           library instead. Alternatively it is possible to use H.J. Lu's
           binutils with support for mixed objects.

       -fuse-ld=bfd
           Use the bfd linker instead of the default linker.

       -fuse-ld=gold
           Use the gold linker instead of the default linker.

       -fuse-ld=lld
           Use the LLVM lld linker instead of the default linker.

       -llibrary
       -l library
           Search the library named library when linking.  (The second
           alternative with the library as a separate argument is only for
           POSIX compliance and is not recommended.)

           The -l option is passed directly to the linker by GCC.  Refer to
           your linker documentation for exact details.  The general
           description below applies to the GNU linker.

           The linker searches a standard list of directories for the library.
           The directories searched include several standard system
           directories plus any that you specify with -L.

           Static libraries are archives of object files, and have file names
           like liblibrary.a.  Some targets also support shared libraries,
           which typically have names like liblibrary.so.  If both static and
           shared libraries are found, the linker gives preference to linking
           with the shared library unless the -static option is used.

           It makes a difference where in the command you write this option;
           the linker searches and processes libraries and object files in the
           order they are specified.  Thus, foo.o -lz bar.o searches library z
           after file foo.o but before bar.o.  If bar.o refers to functions in
           z, those functions may not be loaded.

       -lobjc
           You need this special case of the -l option in order to link an
           Objective-C or Objective-C++ program.

       -nostartfiles
           Do not use the standard system startup files when linking.  The
           standard system libraries are used normally, unless -nostdlib,
           -nolibc, or -nodefaultlibs is used.

       -nodefaultlibs
           Do not use the standard system libraries when linking.  Only the
           libraries you specify are passed to the linker, and options
           specifying linkage of the system libraries, such as -static-libgcc
           or -shared-libgcc, are ignored.  The standard startup files are
           used normally, unless -nostartfiles is used.

           The compiler may generate calls to "memcmp", "memset", "memcpy" and
           "memmove".  These entries are usually resolved by entries in libc.
           These entry points should be supplied through some other mechanism
           when this option is specified.

       -nolibc
           Do not use the C library or system libraries tightly coupled with
           it when linking.  Still link with the startup files, libgcc or
           toolchain provided language support libraries such as libgnat,
           libgfortran or libstdc++ unless options preventing their inclusion
           are used as well.  This typically removes -lc from the link command
           line, as well as system libraries that normally go with it and
           become meaningless when absence of a C library is assumed, for
           example -lpthread or -lm in some configurations.  This is intended
           for bare-board targets when there is indeed no C library available.

       -nostdlib
           Do not use the standard system startup files or libraries when
           linking.  No startup files and only the libraries you specify are
           passed to the linker, and options specifying linkage of the system
           libraries, such as -static-libgcc or -shared-libgcc, are ignored.

           The compiler may generate calls to "memcmp", "memset", "memcpy" and
           "memmove".  These entries are usually resolved by entries in libc.
           These entry points should be supplied through some other mechanism
           when this option is specified.

           One of the standard libraries bypassed by -nostdlib and
           -nodefaultlibs is libgcc.a, a library of internal subroutines which
           GCC uses to overcome shortcomings of particular machines, or
           special needs for some languages.

           In most cases, you need libgcc.a even when you want to avoid other
           standard libraries.  In other words, when you specify -nostdlib or
           -nodefaultlibs you should usually specify -lgcc as well.  This
           ensures that you have no unresolved references to internal GCC
           library subroutines.  (An example of such an internal subroutine is
           "__main", used to ensure C++ constructors are called.)

       -e entry
       --entry=entry
           Specify that the program entry point is entry.  The argument is
           interpreted by the linker; the GNU linker accepts either a symbol
           name or an address.

       -pie
           Produce a dynamically linked position independent executable on
           targets that support it.  For predictable results, you must also
           specify the same set of options used for compilation (-fpie, -fPIE,
           or model suboptions) when you specify this linker option.

       -no-pie
           Don't produce a dynamically linked position independent executable.

       -static-pie
           Produce a static position independent executable on targets that
           support it.  A static position independent executable is similar to
           a static executable, but can be loaded at any address without a
           dynamic linker.  For predictable results, you must also specify the
           same set of options used for compilation (-fpie, -fPIE, or model
           suboptions) when you specify this linker option.

       -pthread
           Link with the POSIX threads library.  This option is supported on
           GNU/Linux targets, most other Unix derivatives, and also on x86
           Cygwin and MinGW targets.  On some targets this option also sets
           flags for the preprocessor, so it should be used consistently for
           both compilation and linking.

       -r  Produce a relocatable object as output.  This is also known as
           partial linking.

       -rdynamic
           Pass the flag -export-dynamic to the ELF linker, on targets that
           support it. This instructs the linker to add all symbols, not only
           used ones, to the dynamic symbol table. This option is needed for
           some uses of "dlopen" or to allow obtaining backtraces from within
           a program.

       -s  Remove all symbol table and relocation information from the
           executable.

       -static
           On systems that support dynamic linking, this overrides -pie and
           prevents linking with the shared libraries.  On other systems, this
           option has no effect.

       -shared
           Produce a shared object which can then be linked with other objects
           to form an executable.  Not all systems support this option.  For
           predictable results, you must also specify the same set of options
           used for compilation (-fpic, -fPIC, or model suboptions) when you
           specify this linker option.[1]

       -shared-libgcc
       -static-libgcc
           On systems that provide libgcc as a shared library, these options
           force the use of either the shared or static version, respectively.
           If no shared version of libgcc was built when the compiler was
           configured, these options have no effect.

           There are several situations in which an application should use the
           shared libgcc instead of the static version.  The most common of
           these is when the application wishes to throw and catch exceptions
           across different shared libraries.  In that case, each of the
           libraries as well as the application itself should use the shared
           libgcc.

           Therefore, the G++ driver automatically adds -shared-libgcc
           whenever you build a shared library or a main executable, because
           C++ programs typically use exceptions, so this is the right thing
           to do.

           If, instead, you use the GCC driver to create shared libraries, you
           may find that they are not always linked with the shared libgcc.
           If GCC finds, at its configuration time, that you have a non-GNU
           linker or a GNU linker that does not support option --eh-frame-hdr,
           it links the shared version of libgcc into shared libraries by
           default.  Otherwise, it takes advantage of the linker and optimizes
           away the linking with the shared version of libgcc, linking with
           the static version of libgcc by default.  This allows exceptions to
           propagate through such shared libraries, without incurring
           relocation costs at library load time.

           However, if a library or main executable is supposed to throw or
           catch exceptions, you must link it using the G++ driver, or using
           the option -shared-libgcc, such that it is linked with the shared
           libgcc.

       -static-libasan
           When the -fsanitize=address option is used to link a program, the
           GCC driver automatically links against libasan.  If libasan is
           available as a shared library, and the -static option is not used,
           then this links against the shared version of libasan.  The
           -static-libasan option directs the GCC driver to link libasan
           statically, without necessarily linking other libraries statically.

       -static-libtsan
           When the -fsanitize=thread option is used to link a program, the
           GCC driver automatically links against libtsan.  If libtsan is
           available as a shared library, and the -static option is not used,
           then this links against the shared version of libtsan.  The
           -static-libtsan option directs the GCC driver to link libtsan
           statically, without necessarily linking other libraries statically.

       -static-liblsan
           When the -fsanitize=leak option is used to link a program, the GCC
           driver automatically links against liblsan.  If liblsan is
           available as a shared library, and the -static option is not used,
           then this links against the shared version of liblsan.  The
           -static-liblsan option directs the GCC driver to link liblsan
           statically, without necessarily linking other libraries statically.

       -static-libubsan
           When the -fsanitize=undefined option is used to link a program, the
           GCC driver automatically links against libubsan.  If libubsan is
           available as a shared library, and the -static option is not used,
           then this links against the shared version of libubsan.  The
           -static-libubsan option directs the GCC driver to link libubsan
           statically, without necessarily linking other libraries statically.

       -static-libstdc++
           When the g++ program is used to link a C++ program, it normally
           automatically links against libstdc++.  If libstdc++ is available
           as a shared library, and the -static option is not used, then this
           links against the shared version of libstdc++.  That is normally
           fine.  However, it is sometimes useful to freeze the version of
           libstdc++ used by the program without going all the way to a fully
           static link.  The -static-libstdc++ option directs the g++ driver
           to link libstdc++ statically, without necessarily linking other
           libraries statically.

       -symbolic
           Bind references to global symbols when building a shared object.
           Warn about any unresolved references (unless overridden by the link
           editor option -Xlinker -z -Xlinker defs).  Only a few systems
           support this option.

       -T script
           Use script as the linker script.  This option is supported by most
           systems using the GNU linker.  On some targets, such as bare-board
           targets without an operating system, the -T option may be required
           when linking to avoid references to undefined symbols.

       -Xlinker option
           Pass option as an option to the linker.  You can use this to supply
           system-specific linker options that GCC does not recognize.

           If you want to pass an option that takes a separate argument, you
           must use -Xlinker twice, once for the option and once for the
           argument.  For example, to pass -assert definitions, you must write
           -Xlinker -assert -Xlinker definitions.  It does not work to write
           -Xlinker "-assert definitions", because this passes the entire
           string as a single argument, which is not what the linker expects.

           When using the GNU linker, it is usually more convenient to pass
           arguments to linker options using the option=value syntax than as
           separate arguments.  For example, you can specify -Xlinker
           -Map=output.map rather than -Xlinker -Map -Xlinker output.map.
           Other linkers may not support this syntax for command-line options.

       -Wl,option
           Pass option as an option to the linker.  If option contains commas,
           it is split into multiple options at the commas.  You can use this
           syntax to pass an argument to the option.  For example,
           -Wl,-Map,output.map passes -Map output.map to the linker.  When
           using the GNU linker, you can also get the same effect with
           -Wl,-Map=output.map.

       -u symbol
           Pretend the symbol symbol is undefined, to force linking of library
           modules to define it.  You can use -u multiple times with different
           symbols to force loading of additional library modules.

       -z keyword
           -z is passed directly on to the linker along with the keyword
           keyword. See the section in the documentation of your linker for
           permitted values and their meanings.

   Options for Directory Search
       These options specify directories to search for header files, for
       libraries and for parts of the compiler:

       -I dir
       -iquote dir
       -isystem dir
       -idirafter dir
           Add the directory dir to the list of directories to be searched for
           header files during preprocessing.  If dir begins with = or
           $SYSROOT, then the = or $SYSROOT is replaced by the sysroot prefix;
           see --sysroot and -isysroot.

           Directories specified with -iquote apply only to the quote form of
           the directive, "#include "file"".  Directories specified with -I,
           -isystem, or -idirafter apply to lookup for both the
           "#include "file"" and "#include <file>" directives.

           You can specify any number or combination of these options on the
           command line to search for header files in several directories.
           The lookup order is as follows:

           1.  For the quote form of the include directive, the directory of
               the current file is searched first.

           2.  For the quote form of the include directive, the directories
               specified by -iquote options are searched in left-to-right
               order, as they appear on the command line.

           3.  Directories specified with -I options are scanned in left-to-
               right order.

           4.  Directories specified with -isystem options are scanned in
               left-to-right order.

           5.  Standard system directories are scanned.

           6.  Directories specified with -idirafter options are scanned in
               left-to-right order.

           You can use -I to override a system header file, substituting your
           own version, since these directories are searched before the
           standard system header file directories.  However, you should not
           use this option to add directories that contain vendor-supplied
           system header files; use -isystem for that.

           The -isystem and -idirafter options also mark the directory as a
           system directory, so that it gets the same special treatment that
           is applied to the standard system directories.

           If a standard system include directory, or a directory specified
           with -isystem, is also specified with -I, the -I option is ignored.
           The directory is still searched but as a system directory at its
           normal position in the system include chain.  This is to ensure
           that GCC's procedure to fix buggy system headers and the ordering
           for the "#include_next" directive are not inadvertently changed.
           If you really need to change the search order for system
           directories, use the -nostdinc and/or -isystem options.

       -I- Split the include path.  This option has been deprecated.  Please
           use -iquote instead for -I directories before the -I- and remove
           the -I- option.

           Any directories specified with -I options before -I- are searched
           only for headers requested with "#include "file""; they are not
           searched for "#include <file>".  If additional directories are
           specified with -I options after the -I-, those directories are
           searched for all #include directives.

           In addition, -I- inhibits the use of the directory of the current
           file directory as the first search directory for "#include "file"".
           There is no way to override this effect of -I-.

       -iprefix prefix
           Specify prefix as the prefix for subsequent -iwithprefix options.
           If the prefix represents a directory, you should include the final
           /.

       -iwithprefix dir
       -iwithprefixbefore dir
           Append dir to the prefix specified previously with -iprefix, and
           add the resulting directory to the include search path.
           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
           puts it where -idirafter would.

       -isysroot dir
           This option is like the --sysroot option, but applies only to
           header files (except for Darwin targets, where it applies to both
           header files and libraries).  See the --sysroot option for more
           information.

       -imultilib dir
           Use dir as a subdirectory of the directory containing target-
           specific C++ headers.

       -nostdinc
           Do not search the standard system directories for header files.
           Only the directories explicitly specified with -I, -iquote,
           -isystem, and/or -idirafter options (and the directory of the
           current file, if appropriate) are searched.

       -nostdinc++
           Do not search for header files in the C++-specific standard
           directories, but do still search the other standard directories.
           (This option is used when building the C++ library.)

       -iplugindir=dir
           Set the directory to search for plugins that are passed by
           -fplugin=name instead of -fplugin=path/name.so.  This option is not
           meant to be used by the user, but only passed by the driver.

       -Ldir
           Add directory dir to the list of directories to be searched for -l.

       -Bprefix
           This option specifies where to find the executables, libraries,
           include files, and data files of the compiler itself.

           The compiler driver program runs one or more of the subprograms
           cpp, cc1, as and ld.  It tries prefix as a prefix for each program
           it tries to run, both with and without machine/version/ for the
           corresponding target machine and compiler version.

           For each subprogram to be run, the compiler driver first tries the
           -B prefix, if any.  If that name is not found, or if -B is not
           specified, the driver tries two standard prefixes, /usr/lib/gcc/
           and /usr/local/lib/gcc/.  If neither of those results in a file
           name that is found, the unmodified program name is searched for
           using the directories specified in your PATH environment variable.

           The compiler checks to see if the path provided by -B refers to a
           directory, and if necessary it adds a directory separator character
           at the end of the path.

           -B prefixes that effectively specify directory names also apply to
           libraries in the linker, because the compiler translates these
           options into -L options for the linker.  They also apply to include
           files in the preprocessor, because the compiler translates these
           options into -isystem options for the preprocessor.  In this case,
           the compiler appends include to the prefix.

           The runtime support file libgcc.a can also be searched for using
           the -B prefix, if needed.  If it is not found there, the two
           standard prefixes above are tried, and that is all.  The file is
           left out of the link if it is not found by those means.

           Another way to specify a prefix much like the -B prefix is to use
           the environment variable GCC_EXEC_PREFIX.

           As a special kludge, if the path provided by -B is [dir/]stageN/,
           where N is a number in the range 0 to 9, then it is replaced by
           [dir/]include.  This is to help with boot-strapping the compiler.

       -no-canonical-prefixes
           Do not expand any symbolic links, resolve references to /../ or
           /./, or make the path absolute when generating a relative prefix.

       --sysroot=dir
           Use dir as the logical root directory for headers and libraries.
           For example, if the compiler normally searches for headers in
           /usr/include and libraries in /usr/lib, it instead searches
           dir/usr/include and dir/usr/lib.

           If you use both this option and the -isysroot option, then the
           --sysroot option applies to libraries, but the -isysroot option
           applies to header files.

           The GNU linker (beginning with version 2.16) has the necessary
           support for this option.  If your linker does not support this
           option, the header file aspect of --sysroot still works, but the
           library aspect does not.

       --no-sysroot-suffix
           For some targets, a suffix is added to the root directory specified
           with --sysroot, depending on the other options used, so that
           headers may for example be found in dir/suffix/usr/include instead
           of dir/usr/include.  This option disables the addition of such a
           suffix.

   Options for Code Generation Conventions
       These machine-independent options control the interface conventions
       used in code generation.

       Most of them have both positive and negative forms; the negative form
       of -ffoo is -fno-foo.  In the table below, only one of the forms is
       listed---the one that is not the default.  You can figure out the other
       form by either removing no- or adding it.

       -fstack-reuse=reuse-level
           This option controls stack space reuse for user declared local/auto
           variables and compiler generated temporaries.  reuse_level can be
           all, named_vars, or none. all enables stack reuse for all local
           variables and temporaries, named_vars enables the reuse only for
           user defined local variables with names, and none disables stack
           reuse completely. The default value is all. The option is needed
           when the program extends the lifetime of a scoped local variable or
           a compiler generated temporary beyond the end point defined by the
           language.  When a lifetime of a variable ends, and if the variable
           lives in memory, the optimizing compiler has the freedom to reuse
           its stack space with other temporaries or scoped local variables
           whose live range does not overlap with it. Legacy code extending
           local lifetime is likely to break with the stack reuse
           optimization.

           For example,

                      int *p;
                      {
                        int local1;

                        p = &local1;
                        local1 = 10;
                        ....
                      }
                      {
                         int local2;
                         local2 = 20;
                         ...
                      }

                      if (*p == 10)  // out of scope use of local1
                        {

                        }

           Another example:

                      struct A
                      {
                          A(int k) : i(k), j(k) { }
                          int i;
                          int j;
                      };

                      A *ap;

                      void foo(const A& ar)
                      {
                         ap = &ar;
                      }

                      void bar()
                      {
                         foo(A(10)); // temp object's lifetime ends when foo returns

                         {
                           A a(20);
                           ....
                         }
                         ap->i+= 10;  // ap references out of scope temp whose space
                                      // is reused with a. What is the value of ap->i?
                      }

           The lifetime of a compiler generated temporary is well defined by
           the C++ standard. When a lifetime of a temporary ends, and if the
           temporary lives in memory, the optimizing compiler has the freedom
           to reuse its stack space with other temporaries or scoped local
           variables whose live range does not overlap with it. However some
           of the legacy code relies on the behavior of older compilers in
           which temporaries' stack space is not reused, the aggressive stack
           reuse can lead to runtime errors. This option is used to control
           the temporary stack reuse optimization.

       -ftrapv
           This option generates traps for signed overflow on addition,
           subtraction, multiplication operations.  The options -ftrapv and
           -fwrapv override each other, so using -ftrapv -fwrapv on the
           command-line results in -fwrapv being effective.  Note that only
           active options override, so using -ftrapv -fwrapv -fno-wrapv on the
           command-line results in -ftrapv being effective.

       -fwrapv
           This option instructs the compiler to assume that signed arithmetic
           overflow of addition, subtraction and multiplication wraps around
           using twos-complement representation.  This flag enables some
           optimizations and disables others.  The options -ftrapv and -fwrapv
           override each other, so using -ftrapv -fwrapv on the command-line
           results in -fwrapv being effective.  Note that only active options
           override, so using -ftrapv -fwrapv -fno-wrapv on the command-line
           results in -ftrapv being effective.

       -fwrapv-pointer
           This option instructs the compiler to assume that pointer
           arithmetic overflow on addition and subtraction wraps around using
           twos-complement representation.  This flag disables some
           optimizations which assume pointer overflow is invalid.

       -fstrict-overflow
           This option implies -fno-wrapv -fno-wrapv-pointer and when negated
           implies -fwrapv -fwrapv-pointer.

       -fexceptions
           Enable exception handling.  Generates extra code needed to
           propagate exceptions.  For some targets, this implies GCC generates
           frame unwind information for all functions, which can produce
           significant data size overhead, although it does not affect
           execution.  If you do not specify this option, GCC enables it by
           default for languages like C++ that normally require exception
           handling, and disables it for languages like C that do not normally
           require it.  However, you may need to enable this option when
           compiling C code that needs to interoperate properly with exception
           handlers written in C++.  You may also wish to disable this option
           if you are compiling older C++ programs that don't use exception
           handling.

       -fnon-call-exceptions
           Generate code that allows trapping instructions to throw
           exceptions.  Note that this requires platform-specific runtime
           support that does not exist everywhere.  Moreover, it only allows
           trapping instructions to throw exceptions, i.e. memory references
           or floating-point instructions.  It does not allow exceptions to be
           thrown from arbitrary signal handlers such as "SIGALRM".

       -fdelete-dead-exceptions
           Consider that instructions that may throw exceptions but don't
           otherwise contribute to the execution of the program can be
           optimized away.  This option is enabled by default for the Ada
           front end, as permitted by the Ada language specification.
           Optimization passes that cause dead exceptions to be removed are
           enabled independently at different optimization levels.

       -funwind-tables
           Similar to -fexceptions, except that it just generates any needed
           static data, but does not affect the generated code in any other
           way.  You normally do not need to enable this option; instead, a
           language processor that needs this handling enables it on your
           behalf.

       -fasynchronous-unwind-tables
           Generate unwind table in DWARF format, if supported by target
           machine.  The table is exact at each instruction boundary, so it
           can be used for stack unwinding from asynchronous events (such as
           debugger or garbage collector).

       -fno-gnu-unique
           On systems with recent GNU assembler and C library, the C++
           compiler uses the "STB_GNU_UNIQUE" binding to make sure that
           definitions of template static data members and static local
           variables in inline functions are unique even in the presence of
           "RTLD_LOCAL"; this is necessary to avoid problems with a library
           used by two different "RTLD_LOCAL" plugins depending on a
           definition in one of them and therefore disagreeing with the other
           one about the binding of the symbol.  But this causes "dlclose" to
           be ignored for affected DSOs; if your program relies on
           reinitialization of a DSO via "dlclose" and "dlopen", you can use
           -fno-gnu-unique.

       -fpcc-struct-return
           Return "short" "struct" and "union" values in memory like longer
           ones, rather than in registers.  This convention is less efficient,
           but it has the advantage of allowing intercallability between GCC-
           compiled files and files compiled with other compilers,
           particularly the Portable C Compiler (pcc).

           The precise convention for returning structures in memory depends
           on the target configuration macros.

           Short structures and unions are those whose size and alignment
           match that of some integer type.

           Warning: code compiled with the -fpcc-struct-return switch is not
           binary compatible with code compiled with the -freg-struct-return
           switch.  Use it to conform to a non-default application binary
           interface.

       -freg-struct-return
           Return "struct" and "union" values in registers when possible.
           This is more efficient for small structures than
           -fpcc-struct-return.

           If you specify neither -fpcc-struct-return nor -freg-struct-return,
           GCC defaults to whichever convention is standard for the target.
           If there is no standard convention, GCC defaults to
           -fpcc-struct-return, except on targets where GCC is the principal
           compiler.  In those cases, we can choose the standard, and we chose
           the more efficient register return alternative.

           Warning: code compiled with the -freg-struct-return switch is not
           binary compatible with code compiled with the -fpcc-struct-return
           switch.  Use it to conform to a non-default application binary
           interface.

       -fshort-enums
           Allocate to an "enum" type only as many bytes as it needs for the
           declared range of possible values.  Specifically, the "enum" type
           is equivalent to the smallest integer type that has enough room.

           Warning: the -fshort-enums switch causes GCC to generate code that
           is not binary compatible with code generated without that switch.
           Use it to conform to a non-default application binary interface.

       -fshort-wchar
           Override the underlying type for "wchar_t" to be "short unsigned
           int" instead of the default for the target.  This option is useful
           for building programs to run under WINE.

           Warning: the -fshort-wchar switch causes GCC to generate code that
           is not binary compatible with code generated without that switch.
           Use it to conform to a non-default application binary interface.

       -fcommon
           In C code, this option controls the placement of global variables
           defined without an initializer, known as tentative definitions in
           the C standard.  Tentative definitions are distinct from
           declarations of a variable with the "extern" keyword, which do not
           allocate storage.

           The default is -fno-common, which specifies that the compiler
           places uninitialized global variables in the BSS section of the
           object file.  This inhibits the merging of tentative definitions by
           the linker so you get a multiple-definition error if the same
           variable is accidentally defined in more than one compilation unit.

           The -fcommon places uninitialized global variables in a common
           block.  This allows the linker to resolve all tentative definitions
           of the same variable in different compilation units to the same
           object, or to a non-tentative definition.  This behavior is
           inconsistent with C++, and on many targets implies a speed and code
           size penalty on global variable references.  It is mainly useful to
           enable legacy code to link without errors.

       -fno-ident
           Ignore the "#ident" directive.

       -finhibit-size-directive
           Don't output a ".size" assembler directive, or anything else that
           would cause trouble if the function is split in the middle, and the
           two halves are placed at locations far apart in memory.  This
           option is used when compiling crtstuff.c; you should not need to
           use it for anything else.

       -fverbose-asm
           Put extra commentary information in the generated assembly code to
           make it more readable.  This option is generally only of use to
           those who actually need to read the generated assembly code
           (perhaps while debugging the compiler itself).

           -fno-verbose-asm, the default, causes the extra information to be
           omitted and is useful when comparing two assembler files.

           The added comments include:

           *   information on the compiler version and command-line options,

           *   the source code lines associated with the assembly
               instructions, in the form FILENAME:LINENUMBER:CONTENT OF LINE,

           *   hints on which high-level expressions correspond to the various
               assembly instruction operands.

           For example, given this C source file:

                   int test (int n)
                   {
                     int i;
                     int total = 0;

                     for (i = 0; i < n; i++)
                       total += i * i;

                     return total;
                   }

           compiling to (x86_64) assembly via -S and emitting the result
           direct to stdout via -o -

                   gcc -S test.c -fverbose-asm -Os -o -

           gives output similar to this:

                           .file   "test.c"
                   # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
                     [...snip...]
                   # options passed:
                     [...snip...]

                           .text
                           .globl  test
                           .type   test, @function
                   test:
                   .LFB0:
                           .cfi_startproc
                   # test.c:4:   int total = 0;
                           xorl    %eax, %eax      # <retval>
                   # test.c:6:   for (i = 0; i < n; i++)
                           xorl    %edx, %edx      # i
                   .L2:
                   # test.c:6:   for (i = 0; i < n; i++)
                           cmpl    %edi, %edx      # n, i
                           jge     .L5     #,
                   # test.c:7:     total += i * i;
                           movl    %edx, %ecx      # i, tmp92
                           imull   %edx, %ecx      # i, tmp92
                   # test.c:6:   for (i = 0; i < n; i++)
                           incl    %edx    # i
                   # test.c:7:     total += i * i;
                           addl    %ecx, %eax      # tmp92, <retval>
                           jmp     .L2     #
                   .L5:
                   # test.c:10: }
                           ret
                           .cfi_endproc
                   .LFE0:
                           .size   test, .-test
                           .ident  "GCC: (GNU) 7.0.0 20160809 (experimental)"
                           .section        .note.GNU-stack,"",@progbits

           The comments are intended for humans rather than machines and hence
           the precise format of the comments is subject to change.

       -frecord-gcc-switches
           This switch causes the command line used to invoke the compiler to
           be recorded into the object file that is being created.  This
           switch is only implemented on some targets and the exact format of
           the recording is target and binary file format dependent, but it
           usually takes the form of a section containing ASCII text.  This
           switch is related to the -fverbose-asm switch, but that switch only
           records information in the assembler output file as comments, so it
           never reaches the object file.  See also -grecord-gcc-switches for
           another way of storing compiler options into the object file.

       -fpic
           Generate position-independent code (PIC) suitable for use in a
           shared library, if supported for the target machine.  Such code
           accesses all constant addresses through a global offset table
           (GOT).  The dynamic loader resolves the GOT entries when the
           program starts (the dynamic loader is not part of GCC; it is part
           of the operating system).  If the GOT size for the linked
           executable exceeds a machine-specific maximum size, you get an
           error message from the linker indicating that -fpic does not work;
           in that case, recompile with -fPIC instead.  (These maximums are 8k
           on the SPARC, 28k on AArch64 and 32k on the m68k and RS/6000.  The
           x86 has no such limit.)

           Position-independent code requires special support, and therefore
           works only on certain machines.  For the x86, GCC supports PIC for
           System V but not for the Sun 386i.  Code generated for the IBM
           RS/6000 is always position-independent.

           When this flag is set, the macros "__pic__" and "__PIC__" are
           defined to 1.

       -fPIC
           If supported for the target machine, emit position-independent
           code, suitable for dynamic linking and avoiding any limit on the
           size of the global offset table.  This option makes a difference on
           AArch64, m68k, PowerPC and SPARC.

           Position-independent code requires special support, and therefore
           works only on certain machines.

           When this flag is set, the macros "__pic__" and "__PIC__" are
           defined to 2.

       -fpie
       -fPIE
           These options are similar to -fpic and -fPIC, but the generated
           position-independent code can be only linked into executables.
           Usually these options are used to compile code that will be linked
           using the -pie GCC option.

           -fpie and -fPIE both define the macros "__pie__" and "__PIE__".
           The macros have the value 1 for -fpie and 2 for -fPIE.

       -fno-plt
           Do not use the PLT for external function calls in position-
           independent code.  Instead, load the callee address at call sites
           from the GOT and branch to it.  This leads to more efficient code
           by eliminating PLT stubs and exposing GOT loads to optimizations.
           On architectures such as 32-bit x86 where PLT stubs expect the GOT
           pointer in a specific register, this gives more register allocation
           freedom to the compiler.  Lazy binding requires use of the PLT;
           with -fno-plt all external symbols are resolved at load time.

           Alternatively, the function attribute "noplt" can be used to avoid
           calls through the PLT for specific external functions.

           In position-dependent code, a few targets also convert calls to
           functions that are marked to not use the PLT to use the GOT
           instead.

       -fno-jump-tables
           Do not use jump tables for switch statements even where it would be
           more efficient than other code generation strategies.  This option
           is of use in conjunction with -fpic or -fPIC for building code that
           forms part of a dynamic linker and cannot reference the address of
           a jump table.  On some targets, jump tables do not require a GOT
           and this option is not needed.

       -ffixed-reg
           Treat the register named reg as a fixed register; generated code
           should never refer to it (except perhaps as a stack pointer, frame
           pointer or in some other fixed role).

           reg must be the name of a register.  The register names accepted
           are machine-specific and are defined in the "REGISTER_NAMES" macro
           in the machine description macro file.

           This flag does not have a negative form, because it specifies a
           three-way choice.

       -fcall-used-reg
           Treat the register named reg as an allocable register that is
           clobbered by function calls.  It may be allocated for temporaries
           or variables that do not live across a call.  Functions compiled
           this way do not save and restore the register reg.

           It is an error to use this flag with the frame pointer or stack
           pointer.  Use of this flag for other registers that have fixed
           pervasive roles in the machine's execution model produces
           disastrous results.

           This flag does not have a negative form, because it specifies a
           three-way choice.

       -fcall-saved-reg
           Treat the register named reg as an allocable register saved by
           functions.  It may be allocated even for temporaries or variables
           that live across a call.  Functions compiled this way save and
           restore the register reg if they use it.

           It is an error to use this flag with the frame pointer or stack
           pointer.  Use of this flag for other registers that have fixed
           pervasive roles in the machine's execution model produces
           disastrous results.

           A different sort of disaster results from the use of this flag for
           a register in which function values may be returned.

           This flag does not have a negative form, because it specifies a
           three-way choice.

       -fpack-struct[=n]
           Without a value specified, pack all structure members together
           without holes.  When a value is specified (which must be a small
           power of two), pack structure members according to this value,
           representing the maximum alignment (that is, objects with default
           alignment requirements larger than this are output potentially
           unaligned at the next fitting location.

           Warning: the -fpack-struct switch causes GCC to generate code that
           is not binary compatible with code generated without that switch.
           Additionally, it makes the code suboptimal.  Use it to conform to a
           non-default application binary interface.

       -fleading-underscore
           This option and its counterpart, -fno-leading-underscore, forcibly
           change the way C symbols are represented in the object file.  One
           use is to help link with legacy assembly code.

           Warning: the -fleading-underscore switch causes GCC to generate
           code that is not binary compatible with code generated without that
           switch.  Use it to conform to a non-default application binary
           interface.  Not all targets provide complete support for this
           switch.

       -ftls-model=model
           Alter the thread-local storage model to be used.  The model
           argument should be one of global-dynamic, local-dynamic, initial-
           exec or local-exec.  Note that the choice is subject to
           optimization: the compiler may use a more efficient model for
           symbols not visible outside of the translation unit, or if -fpic is
           not given on the command line.

           The default without -fpic is initial-exec; with -fpic the default
           is global-dynamic.

       -ftrampolines
           For targets that normally need trampolines for nested functions,
           always generate them instead of using descriptors.  Otherwise, for
           targets that do not need them, like for example HP-PA or IA-64, do
           nothing.

           A trampoline is a small piece of code that is created at run time
           on the stack when the address of a nested function is taken, and is
           used to call the nested function indirectly.  Therefore, it
           requires the stack to be made executable in order for the program
           to work properly.

           -fno-trampolines is enabled by default on a language by language
           basis to let the compiler avoid generating them, if it computes
           that this is safe, and replace them with descriptors.  Descriptors
           are made up of data only, but the generated code must be prepared
           to deal with them.  As of this writing, -fno-trampolines is enabled
           by default only for Ada.

           Moreover, code compiled with -ftrampolines and code compiled with
           -fno-trampolines are not binary compatible if nested functions are
           present.  This option must therefore be used on a program-wide
           basis and be manipulated with extreme care.

       -fvisibility=[default|internal|hidden|protected]
           Set the default ELF image symbol visibility to the specified
           option---all symbols are marked with this unless overridden within
           the code.  Using this feature can very substantially improve
           linking and load times of shared object libraries, produce more
           optimized code, provide near-perfect API export and prevent symbol
           clashes.  It is strongly recommended that you use this in any
           shared objects you distribute.

           Despite the nomenclature, default always means public; i.e.,
           available to be linked against from outside the shared object.
           protected and internal are pretty useless in real-world usage so
           the only other commonly used option is hidden.  The default if
           -fvisibility isn't specified is default, i.e., make every symbol
           public.

           A good explanation of the benefits offered by ensuring ELF symbols
           have the correct visibility is given by "How To Write Shared
           Libraries" by Ulrich Drepper (which can be found at
           <https://www.akkadia.org/drepper/>)---however a superior solution
           made possible by this option to marking things hidden when the
           default is public is to make the default hidden and mark things
           public.  This is the norm with DLLs on Windows and with
           -fvisibility=hidden and "__attribute__ ((visibility("default")))"
           instead of "__declspec(dllexport)" you get almost identical
           semantics with identical syntax.  This is a great boon to those
           working with cross-platform projects.

           For those adding visibility support to existing code, you may find
           "#pragma GCC visibility" of use.  This works by you enclosing the
           declarations you wish to set visibility for with (for example)
           "#pragma GCC visibility push(hidden)" and "#pragma GCC visibility
           pop".  Bear in mind that symbol visibility should be viewed as part
           of the API interface contract and thus all new code should always
           specify visibility when it is not the default; i.e., declarations
           only for use within the local DSO should always be marked
           explicitly as hidden as so to avoid PLT indirection
           overheads---making this abundantly clear also aids readability and
           self-documentation of the code.  Note that due to ISO C++
           specification requirements, "operator new" and "operator delete"
           must always be of default visibility.

           Be aware that headers from outside your project, in particular
           system headers and headers from any other library you use, may not
           be expecting to be compiled with visibility other than the default.
           You may need to explicitly say "#pragma GCC visibility
           push(default)" before including any such headers.

           "extern" declarations are not affected by -fvisibility, so a lot of
           code can be recompiled with -fvisibility=hidden with no
           modifications.  However, this means that calls to "extern"
           functions with no explicit visibility use the PLT, so it is more
           effective to use "__attribute ((visibility))" and/or "#pragma GCC
           visibility" to tell the compiler which "extern" declarations should
           be treated as hidden.

           Note that -fvisibility does affect C++ vague linkage entities. This
           means that, for instance, an exception class that is be thrown
           between DSOs must be explicitly marked with default visibility so
           that the type_info nodes are unified between the DSOs.

           An overview of these techniques, their benefits and how to use them
           is at <http://gcc.gnu.org/wiki/Visibility>.

       -fstrict-volatile-bitfields
           This option should be used if accesses to volatile bit-fields (or
           other structure fields, although the compiler usually honors those
           types anyway) should use a single access of the width of the
           field's type, aligned to a natural alignment if possible.  For
           example, targets with memory-mapped peripheral registers might
           require all such accesses to be 16 bits wide; with this flag you
           can declare all peripheral bit-fields as "unsigned short" (assuming
           short is 16 bits on these targets) to force GCC to use 16-bit
           accesses instead of, perhaps, a more efficient 32-bit access.

           If this option is disabled, the compiler uses the most efficient
           instruction.  In the previous example, that might be a 32-bit load
           instruction, even though that accesses bytes that do not contain
           any portion of the bit-field, or memory-mapped registers unrelated
           to the one being updated.

           In some cases, such as when the "packed" attribute is applied to a
           structure field, it may not be possible to access the field with a
           single read or write that is correctly aligned for the target
           machine.  In this case GCC falls back to generating multiple
           accesses rather than code that will fault or truncate the result at
           run time.

           Note:  Due to restrictions of the C/C++11 memory model, write
           accesses are not allowed to touch non bit-field members.  It is
           therefore recommended to define all bits of the field's type as
           bit-field members.

           The default value of this option is determined by the application
           binary interface for the target processor.

       -fsync-libcalls
           This option controls whether any out-of-line instance of the
           "__sync" family of functions may be used to implement the C++11
           "__atomic" family of functions.

           The default value of this option is enabled, thus the only useful
           form of the option is -fno-sync-libcalls.  This option is used in
           the implementation of the libatomic runtime library.

   GCC Developer Options
       This section describes command-line options that are primarily of
       interest to GCC developers, including options to support compiler
       testing and investigation of compiler bugs and compile-time performance
       problems.  This includes options that produce debug dumps at various
       points in the compilation; that print statistics such as memory use and
       execution time; and that print information about GCC's configuration,
       such as where it searches for libraries.  You should rarely need to use
       any of these options for ordinary compilation and linking tasks.

       Many developer options that cause GCC to dump output to a file take an
       optional =filename suffix. You can specify stdout or - to dump to
       standard output, and stderr for standard error.

       If =filename is omitted, a default dump file name is constructed by
       concatenating the base dump file name, a pass number, phase letter, and
       pass name.  The base dump file name is the name of output file produced
       by the compiler if explicitly specified and not an executable;
       otherwise it is the source file name.  The pass number is determined by
       the order passes are registered with the compiler's pass manager.  This
       is generally the same as the order of execution, but passes registered
       by plugins, target-specific passes, or passes that are otherwise
       registered late are numbered higher than the pass named final, even if
       they are executed earlier.  The phase letter is one of i (inter-
       procedural analysis), l (language-specific), r (RTL), or t (tree).  The
       files are created in the directory of the output file.

       -fcallgraph-info
       -fcallgraph-info=MARKERS
           Makes the compiler output callgraph information for the program, on
           a per-object-file basis.  The information is generated in the
           common VCG format.  It can be decorated with additional, per-node
           and/or per-edge information, if a list of comma-separated markers
           is additionally specified.  When the "su" marker is specified, the
           callgraph is decorated with stack usage information; it is
           equivalent to -fstack-usage.  When the "da" marker is specified,
           the callgraph is decorated with information about dynamically
           allocated objects.

           When compiling with -flto, no callgraph information is output along
           with the object file.  At LTO link time, -fcallgraph-info may
           generate multiple callgraph information files next to intermediate
           LTO output files.

       -dletters
       -fdump-rtl-pass
       -fdump-rtl-pass=filename
           Says to make debugging dumps during compilation at times specified
           by letters.  This is used for debugging the RTL-based passes of the
           compiler.

           Some -dletters switches have different meaning when -E is used for
           preprocessing.

           Debug dumps can be enabled with a -fdump-rtl switch or some -d
           option letters.  Here are the possible letters for use in pass and
           letters, and their meanings:

           -fdump-rtl-alignments
               Dump after branch alignments have been computed.

           -fdump-rtl-asmcons
               Dump after fixing rtl statements that have unsatisfied in/out
               constraints.

           -fdump-rtl-auto_inc_dec
               Dump after auto-inc-dec discovery.  This pass is only run on
               architectures that have auto inc or auto dec instructions.

           -fdump-rtl-barriers
               Dump after cleaning up the barrier instructions.

           -fdump-rtl-bbpart
               Dump after partitioning hot and cold basic blocks.

           -fdump-rtl-bbro
               Dump after block reordering.

           -fdump-rtl-btl1
           -fdump-rtl-btl2
               -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the
               two branch target load optimization passes.

           -fdump-rtl-bypass
               Dump after jump bypassing and control flow optimizations.

           -fdump-rtl-combine
               Dump after the RTL instruction combination pass.

           -fdump-rtl-compgotos
               Dump after duplicating the computed gotos.

           -fdump-rtl-ce1
           -fdump-rtl-ce2
           -fdump-rtl-ce3
               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable
               dumping after the three if conversion passes.

           -fdump-rtl-cprop_hardreg
               Dump after hard register copy propagation.

           -fdump-rtl-csa
               Dump after combining stack adjustments.

           -fdump-rtl-cse1
           -fdump-rtl-cse2
               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the
               two common subexpression elimination passes.

           -fdump-rtl-dce
               Dump after the standalone dead code elimination passes.

           -fdump-rtl-dbr
               Dump after delayed branch scheduling.

           -fdump-rtl-dce1
           -fdump-rtl-dce2
               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the
               two dead store elimination passes.

           -fdump-rtl-eh
               Dump after finalization of EH handling code.

           -fdump-rtl-eh_ranges
               Dump after conversion of EH handling range regions.

           -fdump-rtl-expand
               Dump after RTL generation.

           -fdump-rtl-fwprop1
           -fdump-rtl-fwprop2
               -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after
               the two forward propagation passes.

           -fdump-rtl-gcse1
           -fdump-rtl-gcse2
               -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after
               global common subexpression elimination.

           -fdump-rtl-init-regs
               Dump after the initialization of the registers.

           -fdump-rtl-initvals
               Dump after the computation of the initial value sets.

           -fdump-rtl-into_cfglayout
               Dump after converting to cfglayout mode.

           -fdump-rtl-ira
               Dump after iterated register allocation.

           -fdump-rtl-jump
               Dump after the second jump optimization.

           -fdump-rtl-loop2
               -fdump-rtl-loop2 enables dumping after the rtl loop
               optimization passes.

           -fdump-rtl-mach
               Dump after performing the machine dependent reorganization
               pass, if that pass exists.

           -fdump-rtl-mode_sw
               Dump after removing redundant mode switches.

           -fdump-rtl-rnreg
               Dump after register renumbering.

           -fdump-rtl-outof_cfglayout
               Dump after converting from cfglayout mode.

           -fdump-rtl-peephole2
               Dump after the peephole pass.

           -fdump-rtl-postreload
               Dump after post-reload optimizations.

           -fdump-rtl-pro_and_epilogue
               Dump after generating the function prologues and epilogues.

           -fdump-rtl-sched1
           -fdump-rtl-sched2
               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after
               the basic block scheduling passes.

           -fdump-rtl-ree
               Dump after sign/zero extension elimination.

           -fdump-rtl-seqabstr
               Dump after common sequence discovery.

           -fdump-rtl-shorten
               Dump after shortening branches.

           -fdump-rtl-sibling
               Dump after sibling call optimizations.

           -fdump-rtl-split1
           -fdump-rtl-split2
           -fdump-rtl-split3
           -fdump-rtl-split4
           -fdump-rtl-split5
               These options enable dumping after five rounds of instruction
               splitting.

           -fdump-rtl-sms
               Dump after modulo scheduling.  This pass is only run on some
               architectures.

           -fdump-rtl-stack
               Dump after conversion from GCC's "flat register file" registers
               to the x87's stack-like registers.  This pass is only run on
               x86 variants.

           -fdump-rtl-subreg1
           -fdump-rtl-subreg2
               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after
               the two subreg expansion passes.

           -fdump-rtl-unshare
               Dump after all rtl has been unshared.

           -fdump-rtl-vartrack
               Dump after variable tracking.

           -fdump-rtl-vregs
               Dump after converting virtual registers to hard registers.

           -fdump-rtl-web
               Dump after live range splitting.

           -fdump-rtl-regclass
           -fdump-rtl-subregs_of_mode_init
           -fdump-rtl-subregs_of_mode_finish
           -fdump-rtl-dfinit
           -fdump-rtl-dfinish
               These dumps are defined but always produce empty files.

           -da
           -fdump-rtl-all
               Produce all the dumps listed above.

           -dA Annotate the assembler output with miscellaneous debugging
               information.

           -dD Dump all macro definitions, at the end of preprocessing, in
               addition to normal output.

           -dH Produce a core dump whenever an error occurs.

           -dp Annotate the assembler output with a comment indicating which
               pattern and alternative is used.  The length and cost of each
               instruction are also printed.

           -dP Dump the RTL in the assembler output as a comment before each
               instruction.  Also turns on -dp annotation.

           -dx Just generate RTL for a function instead of compiling it.
               Usually used with -fdump-rtl-expand.

       -fdump-debug
           Dump debugging information generated during the debug generation
           phase.

       -fdump-earlydebug
           Dump debugging information generated during the early debug
           generation phase.

       -fdump-noaddr
           When doing debugging dumps, suppress address output.  This makes it
           more feasible to use diff on debugging dumps for compiler
           invocations with different compiler binaries and/or different text
           / bss / data / heap / stack / dso start locations.

       -freport-bug
           Collect and dump debug information into a temporary file if an
           internal compiler error (ICE) occurs.

       -fdump-unnumbered
           When doing debugging dumps, suppress instruction numbers and
           address output.  This makes it more feasible to use diff on
           debugging dumps for compiler invocations with different options, in
           particular with and without -g.

       -fdump-unnumbered-links
           When doing debugging dumps (see -d option above), suppress
           instruction numbers for the links to the previous and next
           instructions in a sequence.

       -fdump-ipa-switch
       -fdump-ipa-switch-options
           Control the dumping at various stages of inter-procedural analysis
           language tree to a file.  The file name is generated by appending a
           switch specific suffix to the source file name, and the file is
           created in the same directory as the output file.  The following
           dumps are possible:

           all Enables all inter-procedural analysis dumps.

           cgraph
               Dumps information about call-graph optimization, unused
               function removal, and inlining decisions.

           inline
               Dump after function inlining.

           Additionally, the options -optimized, -missed, -note, and -all can
           be provided, with the same meaning as for -fopt-info, defaulting to
           -optimized.

           For example, -fdump-ipa-inline-optimized-missed will emit
           information on callsites that were inlined, along with callsites
           that were not inlined.

           By default, the dump will contain messages about successful
           optimizations (equivalent to -optimized) together with low-level
           details about the analysis.

       -fdump-lang-all
       -fdump-lang-switch
       -fdump-lang-switch-options
       -fdump-lang-switch-options=filename
           Control the dumping of language-specific information.  The options
           and filename portions behave as described in the -fdump-tree
           option.  The following switch values are accepted:

           all Enable all language-specific dumps.

           class
               Dump class hierarchy information.  Virtual table information is
               emitted unless 'slim' is specified.  This option is applicable
               to C++ only.

           raw Dump the raw internal tree data.  This option is applicable to
               C++ only.

       -fdump-passes
           Print on stderr the list of optimization passes that are turned on
           and off by the current command-line options.

       -fdump-statistics-option
           Enable and control dumping of pass statistics in a separate file.
           The file name is generated by appending a suffix ending in
           .statistics to the source file name, and the file is created in the
           same directory as the output file.  If the -option form is used,
           -stats causes counters to be summed over the whole compilation unit
           while -details dumps every event as the passes generate them.  The
           default with no option is to sum counters for each function
           compiled.

       -fdump-tree-all
       -fdump-tree-switch
       -fdump-tree-switch-options
       -fdump-tree-switch-options=filename
           Control the dumping at various stages of processing the
           intermediate language tree to a file.  If the -options form is
           used, options is a list of - separated options which control the
           details of the dump.  Not all options are applicable to all dumps;
           those that are not meaningful are ignored.  The following options
           are available

           address
               Print the address of each node.  Usually this is not meaningful
               as it changes according to the environment and source file.
               Its primary use is for tying up a dump file with a debug
               environment.

           asmname
               If "DECL_ASSEMBLER_NAME" has been set for a given decl, use
               that in the dump instead of "DECL_NAME".  Its primary use is
               ease of use working backward from mangled names in the assembly
               file.

           slim
               When dumping front-end intermediate representations, inhibit
               dumping of members of a scope or body of a function merely
               because that scope has been reached.  Only dump such items when
               they are directly reachable by some other path.

               When dumping pretty-printed trees, this option inhibits dumping
               the bodies of control structures.

               When dumping RTL, print the RTL in slim (condensed) form
               instead of the default LISP-like representation.

           raw Print a raw representation of the tree.  By default, trees are
               pretty-printed into a C-like representation.

           details
               Enable more detailed dumps (not honored by every dump option).
               Also include information from the optimization passes.

           stats
               Enable dumping various statistics about the pass (not honored
               by every dump option).

           blocks
               Enable showing basic block boundaries (disabled in raw dumps).

           graph
               For each of the other indicated dump files (-fdump-rtl-pass),
               dump a representation of the control flow graph suitable for
               viewing with GraphViz to file.passid.pass.dot.  Each function
               in the file is pretty-printed as a subgraph, so that GraphViz
               can render them all in a single plot.

               This option currently only works for RTL dumps, and the RTL is
               always dumped in slim form.

           vops
               Enable showing virtual operands for every statement.

           lineno
               Enable showing line numbers for statements.

           uid Enable showing the unique ID ("DECL_UID") for each variable.

           verbose
               Enable showing the tree dump for each statement.

           eh  Enable showing the EH region number holding each statement.

           scev
               Enable showing scalar evolution analysis details.

           optimized
               Enable showing optimization information (only available in
               certain passes).

           missed
               Enable showing missed optimization information (only available
               in certain passes).

           note
               Enable other detailed optimization information (only available
               in certain passes).

           all Turn on all options, except raw, slim, verbose and lineno.

           optall
               Turn on all optimization options, i.e., optimized, missed, and
               note.

           To determine what tree dumps are available or find the dump for a
           pass of interest follow the steps below.

           1.  Invoke GCC with -fdump-passes and in the stderr output look for
               a code that corresponds to the pass you are interested in.  For
               example, the codes "tree-evrp", "tree-vrp1", and "tree-vrp2"
               correspond to the three Value Range Propagation passes.  The
               number at the end distinguishes distinct invocations of the
               same pass.

           2.  To enable the creation of the dump file, append the pass code
               to the -fdump- option prefix and invoke GCC with it.  For
               example, to enable the dump from the Early Value Range
               Propagation pass, invoke GCC with the -fdump-tree-evrp option.
               Optionally, you may specify the name of the dump file.  If you
               don't specify one, GCC creates as described below.

           3.  Find the pass dump in a file whose name is composed of three
               components separated by a period: the name of the source file
               GCC was invoked to compile, a numeric suffix indicating the
               pass number followed by the letter t for tree passes (and the
               letter r for RTL passes), and finally the pass code.  For
               example, the Early VRP pass dump might be in a file named
               myfile.c.038t.evrp in the current working directory.  Note that
               the numeric codes are not stable and may change from one
               version of GCC to another.

       -fopt-info
       -fopt-info-options
       -fopt-info-options=filename
           Controls optimization dumps from various optimization passes. If
           the -options form is used, options is a list of - separated option
           keywords to select the dump details and optimizations.

           The options can be divided into three groups:

           1.  options describing what kinds of messages should be emitted,

           2.  options describing the verbosity of the dump, and

           3.  options describing which optimizations should be included.

           The options from each group can be freely mixed as they are non-
           overlapping. However, in case of any conflicts, the later options
           override the earlier options on the command line.

           The following options control which kinds of messages should be
           emitted:

           optimized
               Print information when an optimization is successfully applied.
               It is up to a pass to decide which information is relevant. For
               example, the vectorizer passes print the source location of
               loops which are successfully vectorized.

           missed
               Print information about missed optimizations. Individual passes
               control which information to include in the output.

           note
               Print verbose information about optimizations, such as certain
               transformations, more detailed messages about decisions etc.

           all Print detailed optimization information. This includes
               optimized, missed, and note.

           The following option controls the dump verbosity:

           internals
               By default, only "high-level" messages are emitted. This option
               enables additional, more detailed, messages, which are likely
               to only be of interest to GCC developers.

           One or more of the following option keywords can be used to
           describe a group of optimizations:

           ipa Enable dumps from all interprocedural optimizations.

           loop
               Enable dumps from all loop optimizations.

           inline
               Enable dumps from all inlining optimizations.

           omp Enable dumps from all OMP (Offloading and Multi Processing)
               optimizations.

           vec Enable dumps from all vectorization optimizations.

           optall
               Enable dumps from all optimizations. This is a superset of the
               optimization groups listed above.

           If options is omitted, it defaults to optimized-optall, which means
           to dump messages about successful optimizations from all the
           passes, omitting messages that are treated as "internals".

           If the filename is provided, then the dumps from all the applicable
           optimizations are concatenated into the filename.  Otherwise the
           dump is output onto stderr. Though multiple -fopt-info options are
           accepted, only one of them can include a filename. If other
           filenames are provided then all but the first such option are
           ignored.

           Note that the output filename is overwritten in case of multiple
           translation units. If a combined output from multiple translation
           units is desired, stderr should be used instead.

           In the following example, the optimization info is output to
           stderr:

                   gcc -O3 -fopt-info

           This example:

                   gcc -O3 -fopt-info-missed=missed.all

           outputs missed optimization report from all the passes into
           missed.all, and this one:

                   gcc -O2 -ftree-vectorize -fopt-info-vec-missed

           prints information about missed optimization opportunities from
           vectorization passes on stderr.  Note that -fopt-info-vec-missed is
           equivalent to -fopt-info-missed-vec.  The order of the optimization
           group names and message types listed after -fopt-info does not
           matter.

           As another example,

                   gcc -O3 -fopt-info-inline-optimized-missed=inline.txt

           outputs information about missed optimizations as well as optimized
           locations from all the inlining passes into inline.txt.

           Finally, consider:

                   gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt

           Here the two output filenames vec.miss and loop.opt are in conflict
           since only one output file is allowed. In this case, only the first
           option takes effect and the subsequent options are ignored. Thus
           only vec.miss is produced which contains dumps from the vectorizer
           about missed opportunities.

       -fsave-optimization-record
           Write a SRCFILE.opt-record.json.gz file detailing what
           optimizations were performed, for those optimizations that support
           -fopt-info.

           This option is experimental and the format of the data within the
           compressed JSON file is subject to change.

           It is roughly equivalent to a machine-readable version of
           -fopt-info-all, as a collection of messages with source file, line
           number and column number, with the following additional data for
           each message:

           *   the execution count of the code being optimized, along with
               metadata about whether this was from actual profile data, or
               just an estimate, allowing consumers to prioritize messages by
               code hotness,

           *   the function name of the code being optimized, where
               applicable,

           *   the "inlining chain" for the code being optimized, so that when
               a function is inlined into several different places (which
               might themselves be inlined), the reader can distinguish
               between the copies,

           *   objects identifying those parts of the message that refer to
               expressions, statements or symbol-table nodes, which of these
               categories they are, and, when available, their source code
               location,

           *   the GCC pass that emitted the message, and

           *   the location in GCC's own code from which the message was
               emitted

           Additionally, some messages are logically nested within other
           messages, reflecting implementation details of the optimization
           passes.

       -fsched-verbose=n
           On targets that use instruction scheduling, this option controls
           the amount of debugging output the scheduler prints to the dump
           files.

           For n greater than zero, -fsched-verbose outputs the same
           information as -fdump-rtl-sched1 and -fdump-rtl-sched2.  For n
           greater than one, it also output basic block probabilities,
           detailed ready list information and unit/insn info.  For n greater
           than two, it includes RTL at abort point, control-flow and regions
           info.  And for n over four, -fsched-verbose also includes
           dependence info.

       -fenable-kind-pass
       -fdisable-kind-pass=range-list
           This is a set of options that are used to explicitly disable/enable
           optimization passes.  These options are intended for use for
           debugging GCC. Compiler users should use regular options for
           enabling/disabling passes instead.

           -fdisable-ipa-pass
               Disable IPA pass pass. pass is the pass name.  If the same pass
               is statically invoked in the compiler multiple times, the pass
               name should be appended with a sequential number starting from
               1.

           -fdisable-rtl-pass
           -fdisable-rtl-pass=range-list
               Disable RTL pass pass.  pass is the pass name.  If the same
               pass is statically invoked in the compiler multiple times, the
               pass name should be appended with a sequential number starting
               from 1.  range-list is a comma-separated list of function
               ranges or assembler names.  Each range is a number pair
               separated by a colon.  The range is inclusive in both ends.  If
               the range is trivial, the number pair can be simplified as a
               single number.  If the function's call graph node's uid falls
               within one of the specified ranges, the pass is disabled for
               that function.  The uid is shown in the function header of a
               dump file, and the pass names can be dumped by using option
               -fdump-passes.

           -fdisable-tree-pass
           -fdisable-tree-pass=range-list
               Disable tree pass pass.  See -fdisable-rtl for the description
               of option arguments.

           -fenable-ipa-pass
               Enable IPA pass pass.  pass is the pass name.  If the same pass
               is statically invoked in the compiler multiple times, the pass
               name should be appended with a sequential number starting from
               1.

           -fenable-rtl-pass
           -fenable-rtl-pass=range-list
               Enable RTL pass pass.  See -fdisable-rtl for option argument
               description and examples.

           -fenable-tree-pass
           -fenable-tree-pass=range-list
               Enable tree pass pass.  See -fdisable-rtl for the description
               of option arguments.

           Here are some examples showing uses of these options.

                   # disable ccp1 for all functions
                      -fdisable-tree-ccp1
                   # disable complete unroll for function whose cgraph node uid is 1
                      -fenable-tree-cunroll=1
                   # disable gcse2 for functions at the following ranges [1,1],
                   # [300,400], and [400,1000]
                   # disable gcse2 for functions foo and foo2
                      -fdisable-rtl-gcse2=foo,foo2
                   # disable early inlining
                      -fdisable-tree-einline
                   # disable ipa inlining
                      -fdisable-ipa-inline
                   # enable tree full unroll
                      -fenable-tree-unroll

       -fchecking
       -fchecking=n
           Enable internal consistency checking.  The default depends on the
           compiler configuration.  -fchecking=2 enables further internal
           consistency checking that might affect code generation.

       -frandom-seed=string
           This option provides a seed that GCC uses in place of random
           numbers in generating certain symbol names that have to be
           different in every compiled file.  It is also used to place unique
           stamps in coverage data files and the object files that produce
           them.  You can use the -frandom-seed option to produce reproducibly
           identical object files.

           The string can either be a number (decimal, octal or hex) or an
           arbitrary string (in which case it's converted to a number by
           computing CRC32).

           The string should be different for every file you compile.

       -save-temps
       -save-temps=cwd
           Store the usual "temporary" intermediate files permanently; place
           them in the current directory and name them based on the source
           file.  Thus, compiling foo.c with -c -save-temps produces files
           foo.i and foo.s, as well as foo.o.  This creates a preprocessed
           foo.i output file even though the compiler now normally uses an
           integrated preprocessor.

           When used in combination with the -x command-line option,
           -save-temps is sensible enough to avoid over writing an input
           source file with the same extension as an intermediate file.  The
           corresponding intermediate file may be obtained by renaming the
           source file before using -save-temps.

           If you invoke GCC in parallel, compiling several different source
           files that share a common base name in different subdirectories or
           the same source file compiled for multiple output destinations, it
           is likely that the different parallel compilers will interfere with
           each other, and overwrite the temporary files.  For instance:

                   gcc -save-temps -o outdir1/foo.o indir1/foo.c&
                   gcc -save-temps -o outdir2/foo.o indir2/foo.c&

           may result in foo.i and foo.o being written to simultaneously by
           both compilers.

       -save-temps=obj
           Store the usual "temporary" intermediate files permanently.  If the
           -o option is used, the temporary files are based on the object
           file.  If the -o option is not used, the -save-temps=obj switch
           behaves like -save-temps.

           For example:

                   gcc -save-temps=obj -c foo.c
                   gcc -save-temps=obj -c bar.c -o dir/xbar.o
                   gcc -save-temps=obj foobar.c -o dir2/yfoobar

           creates foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i,
           dir2/yfoobar.s, and dir2/yfoobar.o.

       -time[=file]
           Report the CPU time taken by each subprocess in the compilation
           sequence.  For C source files, this is the compiler proper and
           assembler (plus the linker if linking is done).

           Without the specification of an output file, the output looks like
           this:

                   # cc1 0.12 0.01
                   # as 0.00 0.01

           The first number on each line is the "user time", that is time
           spent executing the program itself.  The second number is "system
           time", time spent executing operating system routines on behalf of
           the program.  Both numbers are in seconds.

           With the specification of an output file, the output is appended to
           the named file, and it looks like this:

                   0.12 0.01 cc1 <options>
                   0.00 0.01 as <options>

           The "user time" and the "system time" are moved before the program
           name, and the options passed to the program are displayed, so that
           one can later tell what file was being compiled, and with which
           options.

       -fdump-final-insns[=file]
           Dump the final internal representation (RTL) to file.  If the
           optional argument is omitted (or if file is "."), the name of the
           dump file is determined by appending ".gkd" to the compilation
           output file name.

       -fcompare-debug[=opts]
           If no error occurs during compilation, run the compiler a second
           time, adding opts and -fcompare-debug-second to the arguments
           passed to the second compilation.  Dump the final internal
           representation in both compilations, and print an error if they
           differ.

           If the equal sign is omitted, the default -gtoggle is used.

           The environment variable GCC_COMPARE_DEBUG, if defined, non-empty
           and nonzero, implicitly enables -fcompare-debug.  If
           GCC_COMPARE_DEBUG is defined to a string starting with a dash, then
           it is used for opts, otherwise the default -gtoggle is used.

           -fcompare-debug=, with the equal sign but without opts, is
           equivalent to -fno-compare-debug, which disables the dumping of the
           final representation and the second compilation, preventing even
           GCC_COMPARE_DEBUG from taking effect.

           To verify full coverage during -fcompare-debug testing, set
           GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC
           rejects as an invalid option in any actual compilation (rather than
           preprocessing, assembly or linking).  To get just a warning,
           setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden
           will do.

       -fcompare-debug-second
           This option is implicitly passed to the compiler for the second
           compilation requested by -fcompare-debug, along with options to
           silence warnings, and omitting other options that would cause the
           compiler to produce output to files or to standard output as a side
           effect.  Dump files and preserved temporary files are renamed so as
           to contain the ".gk" additional extension during the second
           compilation, to avoid overwriting those generated by the first.

           When this option is passed to the compiler driver, it causes the
           first compilation to be skipped, which makes it useful for little
           other than debugging the compiler proper.

       -gtoggle
           Turn off generation of debug info, if leaving out this option
           generates it, or turn it on at level 2 otherwise.  The position of
           this argument in the command line does not matter; it takes effect
           after all other options are processed, and it does so only once, no
           matter how many times it is given.  This is mainly intended to be
           used with -fcompare-debug.

       -fvar-tracking-assignments-toggle
           Toggle -fvar-tracking-assignments, in the same way that -gtoggle
           toggles -g.

       -Q  Makes the compiler print out each function name as it is compiled,
           and print some statistics about each pass when it finishes.

       -ftime-report
           Makes the compiler print some statistics about the time consumed by
           each pass when it finishes.

       -ftime-report-details
           Record the time consumed by infrastructure parts separately for
           each pass.

       -fira-verbose=n
           Control the verbosity of the dump file for the integrated register
           allocator.  The default value is 5.  If the value n is greater or
           equal to 10, the dump output is sent to stderr using the same
           format as n minus 10.

       -flto-report
           Prints a report with internal details on the workings of the link-
           time optimizer.  The contents of this report vary from version to
           version.  It is meant to be useful to GCC developers when
           processing object files in LTO mode (via -flto).

           Disabled by default.

       -flto-report-wpa
           Like -flto-report, but only print for the WPA phase of link-time
           optimization.

       -fmem-report
           Makes the compiler print some statistics about permanent memory
           allocation when it finishes.

       -fmem-report-wpa
           Makes the compiler print some statistics about permanent memory
           allocation for the WPA phase only.

       -fpre-ipa-mem-report
       -fpost-ipa-mem-report
           Makes the compiler print some statistics about permanent memory
           allocation before or after interprocedural optimization.

       -fprofile-report
           Makes the compiler print some statistics about consistency of the
           (estimated) profile and effect of individual passes.

       -fstack-usage
           Makes the compiler output stack usage information for the program,
           on a per-function basis.  The filename for the dump is made by
           appending .su to the auxname.  auxname is generated from the name
           of the output file, if explicitly specified and it is not an
           executable, otherwise it is the basename of the source file.  An
           entry is made up of three fields:

           *   The name of the function.

           *   A number of bytes.

           *   One or more qualifiers: "static", "dynamic", "bounded".

           The qualifier "static" means that the function manipulates the
           stack statically: a fixed number of bytes are allocated for the
           frame on function entry and released on function exit; no stack
           adjustments are otherwise made in the function.  The second field
           is this fixed number of bytes.

           The qualifier "dynamic" means that the function manipulates the
           stack dynamically: in addition to the static allocation described
           above, stack adjustments are made in the body of the function, for
           example to push/pop arguments around function calls.  If the
           qualifier "bounded" is also present, the amount of these
           adjustments is bounded at compile time and the second field is an
           upper bound of the total amount of stack used by the function.  If
           it is not present, the amount of these adjustments is not bounded
           at compile time and the second field only represents the bounded
           part.

       -fstats
           Emit statistics about front-end processing at the end of the
           compilation.  This option is supported only by the C++ front end,
           and the information is generally only useful to the G++ development
           team.

       -fdbg-cnt-list
           Print the name and the counter upper bound for all debug counters.

       -fdbg-cnt=counter-value-list
           Set the internal debug counter lower and upper bound.  counter-
           value-list is a comma-separated list of
           name:lower_bound1-upper_bound1 [:lower_bound2-upper_bound2...]
           tuples which sets the name of the counter and list of closed
           intervals.  The lower_bound is optional and is zero initialized if
           not set.  For example, with -fdbg-cnt=dce:2-4:10-11,tail_call:10,
           "dbg_cnt(dce)" returns true only for second, third, fourth, tenth
           and eleventh invocation.  For "dbg_cnt(tail_call)" true is returned
           for first 10 invocations.

       -print-file-name=library
           Print the full absolute name of the library file library that would
           be used when linking---and don't do anything else.  With this
           option, GCC does not compile or link anything; it just prints the
           file name.

       -print-multi-directory
           Print the directory name corresponding to the multilib selected by
           any other switches present in the command line.  This directory is
           supposed to exist in GCC_EXEC_PREFIX.

       -print-multi-lib
           Print the mapping from multilib directory names to compiler
           switches that enable them.  The directory name is separated from
           the switches by ;, and each switch starts with an @ instead of the
           -, without spaces between multiple switches.  This is supposed to
           ease shell processing.

       -print-multi-os-directory
           Print the path to OS libraries for the selected multilib, relative
           to some lib subdirectory.  If OS libraries are present in the lib
           subdirectory and no multilibs are used, this is usually just ., if
           OS libraries are present in libsuffix sibling directories this
           prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
           present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
           or ev6.

       -print-multiarch
           Print the path to OS libraries for the selected multiarch, relative
           to some lib subdirectory.

       -print-prog-name=program
           Like -print-file-name, but searches for a program such as cpp.

       -print-libgcc-file-name
           Same as -print-file-name=libgcc.a.

           This is useful when you use -nostdlib or -nodefaultlibs but you do
           want to link with libgcc.a.  You can do:

                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`

       -print-search-dirs
           Print the name of the configured installation directory and a list
           of program and library directories gcc searches---and don't do
           anything else.

           This is useful when gcc prints the error message installation
           problem, cannot exec cpp0: No such file or directory.  To resolve
           this you either need to put cpp0 and the other compiler components
           where gcc expects to find them, or you can set the environment
           variable GCC_EXEC_PREFIX to the directory where you installed them.
           Don't forget the trailing /.

       -print-sysroot
           Print the target sysroot directory that is used during compilation.
           This is the target sysroot specified either at configure time or
           using the --sysroot option, possibly with an extra suffix that
           depends on compilation options.  If no target sysroot is specified,
           the option prints nothing.

       -print-sysroot-headers-suffix
           Print the suffix added to the target sysroot when searching for
           headers, or give an error if the compiler is not configured with
           such a suffix---and don't do anything else.

       -dumpmachine
           Print the compiler's target machine (for example,
           i686-pc-linux-gnu)---and don't do anything else.

       -dumpversion
           Print the compiler version (for example, 3.0, 6.3.0 or 7)---and
           don't do anything else.  This is the compiler version used in
           filesystem paths and specs. Depending on how the compiler has been
           configured it can be just a single number (major version), two
           numbers separated by a dot (major and minor version) or three
           numbers separated by dots (major, minor and patchlevel version).

       -dumpfullversion
           Print the full compiler version---and don't do anything else. The
           output is always three numbers separated by dots, major, minor and
           patchlevel version.

       -dumpspecs
           Print the compiler's built-in specs---and don't do anything else.
           (This is used when GCC itself is being built.)

   Machine-Dependent Options
       Each target machine supported by GCC can have its own options---for
       example, to allow you to compile for a particular processor variant or
       ABI, or to control optimizations specific to that machine.  By
       convention, the names of machine-specific options start with -m.

       Some configurations of the compiler also support additional target-
       specific options, usually for compatibility with other compilers on the
       same platform.

       AArch64 Options

       These options are defined for AArch64 implementations:

       -mabi=name
           Generate code for the specified data model.  Permissible values are
           ilp32 for SysV-like data model where int, long int and pointers are
           32 bits, and lp64 for SysV-like data model where int is 32 bits,
           but long int and pointers are 64 bits.

           The default depends on the specific target configuration.  Note
           that the LP64 and ILP32 ABIs are not link-compatible; you must
           compile your entire program with the same ABI, and link with a
           compatible set of libraries.

       -mbig-endian
           Generate big-endian code.  This is the default when GCC is
           configured for an aarch64_be-*-* target.

       -mgeneral-regs-only
           Generate code which uses only the general-purpose registers.  This
           will prevent the compiler from using floating-point and Advanced
           SIMD registers but will not impose any restrictions on the
           assembler.

       -mlittle-endian
           Generate little-endian code.  This is the default when GCC is
           configured for an aarch64-*-* but not an aarch64_be-*-* target.

       -mcmodel=tiny
           Generate code for the tiny code model.  The program and its
           statically defined symbols must be within 1MB of each other.
           Programs can be statically or dynamically linked.

       -mcmodel=small
           Generate code for the small code model.  The program and its
           statically defined symbols must be within 4GB of each other.
           Programs can be statically or dynamically linked.  This is the
           default code model.

       -mcmodel=large
           Generate code for the large code model.  This makes no assumptions
           about addresses and sizes of sections.  Programs can be statically
           linked only.  The -mcmodel=large option is incompatible with
           -mabi=ilp32, -fpic and -fPIC.

       -mstrict-align
       -mno-strict-align
           Avoid or allow generating memory accesses that may not be aligned
           on a natural object boundary as described in the architecture
           specification.

       -momit-leaf-frame-pointer
       -mno-omit-leaf-frame-pointer
           Omit or keep the frame pointer in leaf functions.  The former
           behavior is the default.

       -mstack-protector-guard=guard
       -mstack-protector-guard-reg=reg
       -mstack-protector-guard-offset=offset
           Generate stack protection code using canary at guard.  Supported
           locations are global for a global canary or sysreg for a canary in
           an appropriate system register.

           With the latter choice the options -mstack-protector-guard-reg=reg
           and -mstack-protector-guard-offset=offset furthermore specify which
           system register to use as base register for reading the canary, and
           from what offset from that base register. There is no default
           register or offset as this is entirely for use within the Linux
           kernel.

       -mstack-protector-guard=guard
       -mstack-protector-guard-reg=reg
       -mstack-protector-guard-offset=offset
           Generate stack protection code using canary at guard.  Supported
           locations are global for a global canary or sysreg for a canary in
           an appropriate system register.

           With the latter choice the options -mstack-protector-guard-reg=reg
           and -mstack-protector-guard-offset=offset furthermore specify which
           system register to use as base register for reading the canary, and
           from what offset from that base register. There is no default
           register or offset as this is entirely for use within the Linux
           kernel.

       -mtls-dialect=desc
           Use TLS descriptors as the thread-local storage mechanism for
           dynamic accesses of TLS variables.  This is the default.

       -mtls-dialect=traditional
           Use traditional TLS as the thread-local storage mechanism for
           dynamic accesses of TLS variables.

       -mtls-size=size
           Specify bit size of immediate TLS offsets.  Valid values are 12,
           24, 32, 48.  This option requires binutils 2.26 or newer.

       -mfix-cortex-a53-835769
       -mno-fix-cortex-a53-835769
           Enable or disable the workaround for the ARM Cortex-A53 erratum
           number 835769.  This involves inserting a NOP instruction between
           memory instructions and 64-bit integer multiply-accumulate
           instructions.

       -mfix-cortex-a53-843419
       -mno-fix-cortex-a53-843419
           Enable or disable the workaround for the ARM Cortex-A53 erratum
           number 843419.  This erratum workaround is made at link time and
           this will only pass the corresponding flag to the linker.

       -mlow-precision-recip-sqrt
       -mno-low-precision-recip-sqrt
           Enable or disable the reciprocal square root approximation.  This
           option only has an effect if -ffast-math or
           -funsafe-math-optimizations is used as well.  Enabling this reduces
           precision of reciprocal square root results to about 16 bits for
           single precision and to 32 bits for double precision.

       -mlow-precision-sqrt
       -mno-low-precision-sqrt
           Enable or disable the square root approximation.  This option only
           has an effect if -ffast-math or -funsafe-math-optimizations is used
           as well.  Enabling this reduces precision of square root results to
           about 16 bits for single precision and to 32 bits for double
           precision.  If enabled, it implies -mlow-precision-recip-sqrt.

       -mlow-precision-div
       -mno-low-precision-div
           Enable or disable the division approximation.  This option only has
           an effect if -ffast-math or -funsafe-math-optimizations is used as
           well.  Enabling this reduces precision of division results to about
           16 bits for single precision and to 32 bits for double precision.

       -mtrack-speculation
       -mno-track-speculation
           Enable or disable generation of additional code to track
           speculative execution through conditional branches.  The tracking
           state can then be used by the compiler when expanding calls to
           "__builtin_speculation_safe_copy" to permit a more efficient code
           sequence to be generated.

       -moutline-atomics
       -mno-outline-atomics
           Enable or disable calls to out-of-line helpers to implement atomic
           operations.  These helpers will, at runtime, determine if the LSE
           instructions from ARMv8.1-A can be used; if not, they will use the
           load/store-exclusive instructions that are present in the base
           ARMv8.0 ISA.

           This option is only applicable when compiling for the base ARMv8.0
           instruction set.  If using a later revision, e.g. -march=armv8.1-a
           or -march=armv8-a+lse, the ARMv8.1-Atomics instructions will be
           used directly.  The same applies when using -mcpu= when the
           selected cpu supports the lse feature.  This option is on by
           default.

       -march=name
           Specify the name of the target architecture and, optionally, one or
           more feature modifiers.  This option has the form
           -march=arch{+[no]feature}*.

           The table below summarizes the permissible values for arch and the
           features that they enable by default:

           arch value : Architecture : Includes by default
           armv8-a : Armv8-A : +fp, +simd
           armv8.1-a : Armv8.1-A : armv8-a, +crc, +lse, +rdma
           armv8.2-a : Armv8.2-A : armv8.1-a
           armv8.3-a : Armv8.3-A : armv8.2-a
           armv8.4-a : Armv8.4-A : armv8.3-a, +fp16fml, +dotprod
           armv8.5-a : Armv8.5-A : armv8.4-a, +sb, +ssbs, +predres
           armv8.6-a : Armv8.6-A : armv8.5-a, +bf16, +i8mm

           The value native is available on native AArch64 GNU/Linux and
           causes the compiler to pick the architecture of the host system.
           This option has no effect if the compiler is unable to recognize
           the architecture of the host system,

           The permissible values for feature are listed in the sub-section on
           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
           Where conflicting feature modifiers are specified, the right-most
           feature is used.

           GCC uses name to determine what kind of instructions it can emit
           when generating assembly code.  If -march is specified without
           either of -mtune or -mcpu also being specified, the code is tuned
           to perform well across a range of target processors implementing
           the target architecture.

       -mtune=name
           Specify the name of the target processor for which GCC should tune
           the performance of the code.  Permissible values for this option
           are: generic, cortex-a35, cortex-a53, cortex-a55, cortex-a57,
           cortex-a72, cortex-a73, cortex-a75, cortex-a76, cortex-a76ae,
           cortex-a77, cortex-a65, cortex-a65ae, cortex-a34, ares, exynos-m1,
           emag, falkor, neoverse-e1, neoverse-n1, neoverse-n2, neoverse-v1,
           qdf24xx, saphira, phecda, xgene1, vulcan, octeontx, octeontx81,
           octeontx83, octeontx2, octeontx2t98, octeontx2t96 octeontx2t93,
           octeontx2f95, octeontx2f95n, octeontx2f95mm, a64fx, thunderx,
           thunderxt88, thunderxt88p1, thunderxt81, tsv110, thunderxt83,
           thunderx2t99, thunderx3t110, zeus, cortex-a57.cortex-a53,
           cortex-a72.cortex-a53, cortex-a73.cortex-a35,
           cortex-a73.cortex-a53, cortex-a75.cortex-a55, cortex-a76.cortex-a55
           native.

           The values cortex-a57.cortex-a53, cortex-a72.cortex-a53,
           cortex-a73.cortex-a35, cortex-a73.cortex-a53,
           cortex-a75.cortex-a55, cortex-a76.cortex-a55 specify that GCC
           should tune for a big.LITTLE system.

           Additionally on native AArch64 GNU/Linux systems the value native
           tunes performance to the host system.  This option has no effect if
           the compiler is unable to recognize the processor of the host
           system.

           Where none of -mtune=, -mcpu= or -march= are specified, the code is
           tuned to perform well across a range of target processors.

           This option cannot be suffixed by feature modifiers.

       -mcpu=name
           Specify the name of the target processor, optionally suffixed by
           one or more feature modifiers.  This option has the form
           -mcpu=cpu{+[no]feature}*, where the permissible values for cpu are
           the same as those available for -mtune.  The permissible values for
           feature are documented in the sub-section on
           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.
           Where conflicting feature modifiers are specified, the right-most
           feature is used.

           GCC uses name to determine what kind of instructions it can emit
           when generating assembly code (as if by -march) and to determine
           the target processor for which to tune for performance (as if by
           -mtune).  Where this option is used in conjunction with -march or
           -mtune, those options take precedence over the appropriate part of
           this option.

       -moverride=string
           Override tuning decisions made by the back-end in response to a
           -mtune= switch.  The syntax, semantics, and accepted values for
           string in this option are not guaranteed to be consistent across
           releases.

           This option is only intended to be useful when developing GCC.

       -mverbose-cost-dump
           Enable verbose cost model dumping in the debug dump files.  This
           option is provided for use in debugging the compiler.

       -mpc-relative-literal-loads
       -mno-pc-relative-literal-loads
           Enable or disable PC-relative literal loads.  With this option
           literal pools are accessed using a single instruction and emitted
           after each function.  This limits the maximum size of functions to
           1MB.  This is enabled by default for -mcmodel=tiny.

       -msign-return-address=scope
           Select the function scope on which return address signing will be
           applied.  Permissible values are none, which disables return
           address signing, non-leaf, which enables pointer signing for
           functions which are not leaf functions, and all, which enables
           pointer signing for all functions.  The default value is none. This
           option has been deprecated by -mbranch-protection.

       -mbranch-protection=none|standard|pac-ret[+leaf+b-key]|bti
           Select the branch protection features to use.  none is the default
           and turns off all types of branch protection.  standard turns on
           all types of branch protection features.  If a feature has
           additional tuning options, then standard sets it to its standard
           level.  pac-ret[+leaf] turns on return address signing to its
           standard level: signing functions that save the return address to
           memory (non-leaf functions will practically always do this) using
           the a-key.  The optional argument leaf can be used to extend the
           signing to include leaf functions.  The optional argument b-key can
           be used to sign the functions with the B-key instead of the A-key.
           bti turns on branch target identification mechanism.

       -mharden-sls=opts
           Enable compiler hardening against straight line speculation (SLS).
           opts is a comma-separated list of the following options:

           retbr
           blr

           In addition, -mharden-sls=all enables all SLS hardening while
           -mharden-sls=none disables all SLS hardening.

       -msve-vector-bits=bits
           Specify the number of bits in an SVE vector register.  This option
           only has an effect when SVE is enabled.

           GCC supports two forms of SVE code generation: "vector-length
           agnostic" output that works with any size of vector register and
           "vector-length specific" output that allows GCC to make assumptions
           about the vector length when it is useful for optimization reasons.
           The possible values of bits are: scalable, 128, 256, 512, 1024 and
           2048.  Specifying scalable selects vector-length agnostic output.
           At present -msve-vector-bits=128 also generates vector-length
           agnostic output for big-endian targets.  All other values generate
           vector-length specific code.  The behavior of these values may
           change in future releases and no value except scalable should be
           relied on for producing code that is portable across different
           hardware SVE vector lengths.

           The default is -msve-vector-bits=scalable, which produces vector-
           length agnostic code.

       -march and -mcpu Feature Modifiers

       Feature modifiers used with -march and -mcpu can be any of the
       following and their inverses nofeature:

       crc Enable CRC extension.  This is on by default for -march=armv8.1-a.

       crypto
           Enable Crypto extension.  This also enables Advanced SIMD and
           floating-point instructions.

       fp  Enable floating-point instructions.  This is on by default for all
           possible values for options -march and -mcpu.

       simd
           Enable Advanced SIMD instructions.  This also enables floating-
           point instructions.  This is on by default for all possible values
           for options -march and -mcpu.

       sve Enable Scalable Vector Extension instructions.  This also enables
           Advanced SIMD and floating-point instructions.

       lse Enable Large System Extension instructions.  This is on by default
           for -march=armv8.1-a.

       rdma
           Enable Round Double Multiply Accumulate instructions.  This is on
           by default for -march=armv8.1-a.

       fp16
           Enable FP16 extension.  This also enables floating-point
           instructions.

       fp16fml
           Enable FP16 fmla extension.  This also enables FP16 extensions and
           floating-point instructions. This option is enabled by default for
           -march=armv8.4-a. Use of this option with architectures prior to
           Armv8.2-A is not supported.

       rcpc
           Enable the RcPc extension.  This does not change code generation
           from GCC, but is passed on to the assembler, enabling inline asm
           statements to use instructions from the RcPc extension.

       dotprod
           Enable the Dot Product extension.  This also enables Advanced SIMD
           instructions.

       aes Enable the Armv8-a aes and pmull crypto extension.  This also
           enables Advanced SIMD instructions.

       sha2
           Enable the Armv8-a sha2 crypto extension.  This also enables
           Advanced SIMD instructions.

       sha3
           Enable the sha512 and sha3 crypto extension.  This also enables
           Advanced SIMD instructions. Use of this option with architectures
           prior to Armv8.2-A is not supported.

       sm4 Enable the sm3 and sm4 crypto extension.  This also enables
           Advanced SIMD instructions.  Use of this option with architectures
           prior to Armv8.2-A is not supported.

       profile
           Enable the Statistical Profiling extension.  This option is only to
           enable the extension at the assembler level and does not affect
           code generation.

       rng Enable the Armv8.5-a Random Number instructions.  This option is
           only to enable the extension at the assembler level and does not
           affect code generation.

       memtag
           Enable the Armv8.5-a Memory Tagging Extensions.  Use of this option
           with architectures prior to Armv8.5-A is not supported.

       sb  Enable the Armv8-a Speculation Barrier instruction.  This option is
           only to enable the extension at the assembler level and does not
           affect code generation.  This option is enabled by default for
           -march=armv8.5-a.

       ssbs
           Enable the Armv8-a Speculative Store Bypass Safe instruction.  This
           option is only to enable the extension at the assembler level and
           does not affect code generation.  This option is enabled by default
           for -march=armv8.5-a.

       predres
           Enable the Armv8-a Execution and Data Prediction Restriction
           instructions.  This option is only to enable the extension at the
           assembler level and does not affect code generation.  This option
           is enabled by default for -march=armv8.5-a.

       sve2
           Enable the Armv8-a Scalable Vector Extension 2.  This also enables
           SVE instructions.

       sve2-bitperm
           Enable SVE2 bitperm instructions.  This also enables SVE2
           instructions.

       sve2-sm4
           Enable SVE2 sm4 instructions.  This also enables SVE2 instructions.

       sve2-aes
           Enable SVE2 aes instructions.  This also enables SVE2 instructions.

       sve2-sha3
           Enable SVE2 sha3 instructions.  This also enables SVE2
           instructions.

       tme Enable the Transactional Memory Extension.

       i8mm
           Enable 8-bit Integer Matrix Multiply instructions.  This also
           enables Advanced SIMD and floating-point instructions.  This option
           is enabled by default for -march=armv8.6-a.  Use of this option
           with architectures prior to Armv8.2-A is not supported.

       f32mm
           Enable 32-bit Floating point Matrix Multiply instructions.  This
           also enables SVE instructions.  Use of this option with
           architectures prior to Armv8.2-A is not supported.

       f64mm
           Enable 64-bit Floating point Matrix Multiply instructions.  This
           also enables SVE instructions.  Use of this option with
           architectures prior to Armv8.2-A is not supported.

       bf16
           Enable brain half-precision floating-point instructions.  This also
           enables Advanced SIMD and floating-point instructions.  This option
           is enabled by default for -march=armv8.6-a.  Use of this option
           with architectures prior to Armv8.2-A is not supported.

       Feature crypto implies aes, sha2, and simd, which implies fp.
       Conversely, nofp implies nosimd, which implies nocrypto, noaes and
       nosha2.

       Adapteva Epiphany Options

       These -m options are defined for Adapteva Epiphany:

       -mhalf-reg-file
           Don't allocate any register in the range "r32"..."r63".  That
           allows code to run on hardware variants that lack these registers.

       -mprefer-short-insn-regs
           Preferentially allocate registers that allow short instruction
           generation.  This can result in increased instruction count, so
           this may either reduce or increase overall code size.

       -mbranch-cost=num
           Set the cost of branches to roughly num "simple" instructions.
           This cost is only a heuristic and is not guaranteed to produce
           consistent results across releases.

       -mcmove
           Enable the generation of conditional moves.

       -mnops=num
           Emit num NOPs before every other generated instruction.

       -mno-soft-cmpsf
           For single-precision floating-point comparisons, emit an "fsub"
           instruction and test the flags.  This is faster than a software
           comparison, but can get incorrect results in the presence of NaNs,
           or when two different small numbers are compared such that their
           difference is calculated as zero.  The default is -msoft-cmpsf,
           which uses slower, but IEEE-compliant, software comparisons.

       -mstack-offset=num
           Set the offset between the top of the stack and the stack pointer.
           E.g., a value of 8 means that the eight bytes in the range
           "sp+0...sp+7" can be used by leaf functions without stack
           allocation.  Values other than 8 or 16 are untested and unlikely to
           work.  Note also that this option changes the ABI; compiling a
           program with a different stack offset than the libraries have been
           compiled with generally does not work.  This option can be useful
           if you want to evaluate if a different stack offset would give you
           better code, but to actually use a different stack offset to build
           working programs, it is recommended to configure the toolchain with
           the appropriate --with-stack-offset=num option.

       -mno-round-nearest
           Make the scheduler assume that the rounding mode has been set to
           truncating.  The default is -mround-nearest.

       -mlong-calls
           If not otherwise specified by an attribute, assume all calls might
           be beyond the offset range of the "b" / "bl" instructions, and
           therefore load the function address into a register before
           performing a (otherwise direct) call.  This is the default.

       -mshort-calls
           If not otherwise specified by an attribute, assume all direct calls
           are in the range of the "b" / "bl" instructions, so use these
           instructions for direct calls.  The default is -mlong-calls.

       -msmall16
           Assume addresses can be loaded as 16-bit unsigned values.  This
           does not apply to function addresses for which -mlong-calls
           semantics are in effect.

       -mfp-mode=mode
           Set the prevailing mode of the floating-point unit.  This
           determines the floating-point mode that is provided and expected at
           function call and return time.  Making this mode match the mode you
           predominantly need at function start can make your programs smaller
           and faster by avoiding unnecessary mode switches.

           mode can be set to one the following values:

           caller
               Any mode at function entry is valid, and retained or restored
               when the function returns, and when it calls other functions.
               This mode is useful for compiling libraries or other
               compilation units you might want to incorporate into different
               programs with different prevailing FPU modes, and the
               convenience of being able to use a single object file outweighs
               the size and speed overhead for any extra mode switching that
               might be needed, compared with what would be needed with a more
               specific choice of prevailing FPU mode.

           truncate
               This is the mode used for floating-point calculations with
               truncating (i.e. round towards zero) rounding mode.  That
               includes conversion from floating point to integer.

           round-nearest
               This is the mode used for floating-point calculations with
               round-to-nearest-or-even rounding mode.

           int This is the mode used to perform integer calculations in the
               FPU, e.g.  integer multiply, or integer multiply-and-
               accumulate.

           The default is -mfp-mode=caller

       -mno-split-lohi
       -mno-postinc
       -mno-postmodify
           Code generation tweaks that disable, respectively, splitting of
           32-bit loads, generation of post-increment addresses, and
           generation of post-modify addresses.  The defaults are msplit-lohi,
           -mpost-inc, and -mpost-modify.

       -mnovect-double
           Change the preferred SIMD mode to SImode.  The default is
           -mvect-double, which uses DImode as preferred SIMD mode.

       -max-vect-align=num
           The maximum alignment for SIMD vector mode types.  num may be 4 or
           8.  The default is 8.  Note that this is an ABI change, even though
           many library function interfaces are unaffected if they don't use
           SIMD vector modes in places that affect size and/or alignment of
           relevant types.

       -msplit-vecmove-early
           Split vector moves into single word moves before reload.  In theory
           this can give better register allocation, but so far the reverse
           seems to be generally the case.

       -m1reg-reg
           Specify a register to hold the constant -1, which makes loading
           small negative constants and certain bitmasks faster.  Allowable
           values for reg are r43 and r63, which specify use of that register
           as a fixed register, and none, which means that no register is used
           for this purpose.  The default is -m1reg-none.

       AMD GCN Options

       These options are defined specifically for the AMD GCN port.

       -march=gpu
       -mtune=gpu
           Set architecture type or tuning for gpu. Supported values for gpu
           are

           fiji
               Compile for GCN3 Fiji devices (gfx803).

           gfx900
               Compile for GCN5 Vega 10 devices (gfx900).

           gfx906
               Compile for GCN5 Vega 20 devices (gfx906).

       -mstack-size=bytes
           Specify how many bytes of stack space will be requested for each
           GPU thread (wave-front).  Beware that there may be many threads and
           limited memory available.  The size of the stack allocation may
           also have an impact on run-time performance.  The default is 32KB
           when using OpenACC or OpenMP, and 1MB otherwise.

       ARC Options

       The following options control the architecture variant for which code
       is being compiled:

       -mbarrel-shifter
           Generate instructions supported by barrel shifter.  This is the
           default unless -mcpu=ARC601 or -mcpu=ARCEM is in effect.

       -mjli-always
           Force to call a function using jli_s instruction.  This option is
           valid only for ARCv2 architecture.

       -mcpu=cpu
           Set architecture type, register usage, and instruction scheduling
           parameters for cpu.  There are also shortcut alias options
           available for backward compatibility and convenience.  Supported
           values for cpu are

           arc600
               Compile for ARC600.  Aliases: -mA6, -mARC600.

           arc601
               Compile for ARC601.  Alias: -mARC601.

           arc700
               Compile for ARC700.  Aliases: -mA7, -mARC700.  This is the
               default when configured with --with-cpu=arc700.

           arcem
               Compile for ARC EM.

           archs
               Compile for ARC HS.

           em  Compile for ARC EM CPU with no hardware extensions.

           em4 Compile for ARC EM4 CPU.

           em4_dmips
               Compile for ARC EM4 DMIPS CPU.

           em4_fpus
               Compile for ARC EM4 DMIPS CPU with the single-precision
               floating-point extension.

           em4_fpuda
               Compile for ARC EM4 DMIPS CPU with single-precision floating-
               point and double assist instructions.

           hs  Compile for ARC HS CPU with no hardware extensions except the
               atomic instructions.

           hs34
               Compile for ARC HS34 CPU.

           hs38
               Compile for ARC HS38 CPU.

           hs38_linux
               Compile for ARC HS38 CPU with all hardware extensions on.

           arc600_norm
               Compile for ARC 600 CPU with "norm" instructions enabled.

           arc600_mul32x16
               Compile for ARC 600 CPU with "norm" and 32x16-bit multiply
               instructions enabled.

           arc600_mul64
               Compile for ARC 600 CPU with "norm" and "mul64"-family
               instructions enabled.

           arc601_norm
               Compile for ARC 601 CPU with "norm" instructions enabled.

           arc601_mul32x16
               Compile for ARC 601 CPU with "norm" and 32x16-bit multiply
               instructions enabled.

           arc601_mul64
               Compile for ARC 601 CPU with "norm" and "mul64"-family
               instructions enabled.

           nps400
               Compile for ARC 700 on NPS400 chip.

           em_mini
               Compile for ARC EM minimalist configuration featuring reduced
               register set.

       -mdpfp
       -mdpfp-compact
           Generate double-precision FPX instructions, tuned for the compact
           implementation.

       -mdpfp-fast
           Generate double-precision FPX instructions, tuned for the fast
           implementation.

       -mno-dpfp-lrsr
           Disable "lr" and "sr" instructions from using FPX extension aux
           registers.

       -mea
           Generate extended arithmetic instructions.  Currently only "divaw",
           "adds", "subs", and "sat16" are supported.  Only valid for
           -mcpu=ARC700.

       -mno-mpy
           Do not generate "mpy"-family instructions for ARC700.  This option
           is deprecated.

       -mmul32x16
           Generate 32x16-bit multiply and multiply-accumulate instructions.

       -mmul64
           Generate "mul64" and "mulu64" instructions.  Only valid for
           -mcpu=ARC600.

       -mnorm
           Generate "norm" instructions.  This is the default if -mcpu=ARC700
           is in effect.

       -mspfp
       -mspfp-compact
           Generate single-precision FPX instructions, tuned for the compact
           implementation.

       -mspfp-fast
           Generate single-precision FPX instructions, tuned for the fast
           implementation.

       -msimd
           Enable generation of ARC SIMD instructions via target-specific
           builtins.  Only valid for -mcpu=ARC700.

       -msoft-float
           This option ignored; it is provided for compatibility purposes
           only.  Software floating-point code is emitted by default, and this
           default can overridden by FPX options; -mspfp, -mspfp-compact, or
           -mspfp-fast for single precision, and -mdpfp, -mdpfp-compact, or
           -mdpfp-fast for double precision.

       -mswap
           Generate "swap" instructions.

       -matomic
           This enables use of the locked load/store conditional extension to
           implement atomic memory built-in functions.  Not available for ARC
           6xx or ARC EM cores.

       -mdiv-rem
           Enable "div" and "rem" instructions for ARCv2 cores.

       -mcode-density
           Enable code density instructions for ARC EM. This option is on by
           default for ARC HS.

       -mll64
           Enable double load/store operations for ARC HS cores.

       -mtp-regno=regno
           Specify thread pointer register number.

       -mmpy-option=multo
           Compile ARCv2 code with a multiplier design option.  You can
           specify the option using either a string or numeric value for
           multo.  wlh1 is the default value.  The recognized values are:

           0
           none
               No multiplier available.

           1
           w   16x16 multiplier, fully pipelined.  The following instructions
               are enabled: "mpyw" and "mpyuw".

           2
           wlh1
               32x32 multiplier, fully pipelined (1 stage).  The following
               instructions are additionally enabled: "mpy", "mpyu", "mpym",
               "mpymu", and "mpy_s".

           3
           wlh2
               32x32 multiplier, fully pipelined (2 stages).  The following
               instructions are additionally enabled: "mpy", "mpyu", "mpym",
               "mpymu", and "mpy_s".

           4
           wlh3
               Two 16x16 multipliers, blocking, sequential.  The following
               instructions are additionally enabled: "mpy", "mpyu", "mpym",
               "mpymu", and "mpy_s".

           5
           wlh4
               One 16x16 multiplier, blocking, sequential.  The following
               instructions are additionally enabled: "mpy", "mpyu", "mpym",
               "mpymu", and "mpy_s".

           6
           wlh5
               One 32x4 multiplier, blocking, sequential.  The following
               instructions are additionally enabled: "mpy", "mpyu", "mpym",
               "mpymu", and "mpy_s".

           7
           plus_dmpy
               ARC HS SIMD support.

           8
           plus_macd
               ARC HS SIMD support.

           9
           plus_qmacw
               ARC HS SIMD support.

           This option is only available for ARCv2 cores.

       -mfpu=fpu
           Enables support for specific floating-point hardware extensions for
           ARCv2 cores.  Supported values for fpu are:

           fpus
               Enables support for single-precision floating-point hardware
               extensions.

           fpud
               Enables support for double-precision floating-point hardware
               extensions.  The single-precision floating-point extension is
               also enabled.  Not available for ARC EM.

           fpuda
               Enables support for double-precision floating-point hardware
               extensions using double-precision assist instructions.  The
               single-precision floating-point extension is also enabled.
               This option is only available for ARC EM.

           fpuda_div
               Enables support for double-precision floating-point hardware
               extensions using double-precision assist instructions.  The
               single-precision floating-point, square-root, and divide
               extensions are also enabled.  This option is only available for
               ARC EM.

           fpuda_fma
               Enables support for double-precision floating-point hardware
               extensions using double-precision assist instructions.  The
               single-precision floating-point and fused multiply and add
               hardware extensions are also enabled.  This option is only
               available for ARC EM.

           fpuda_all
               Enables support for double-precision floating-point hardware
               extensions using double-precision assist instructions.  All
               single-precision floating-point hardware extensions are also
               enabled.  This option is only available for ARC EM.

           fpus_div
               Enables support for single-precision floating-point, square-
               root and divide hardware extensions.

           fpud_div
               Enables support for double-precision floating-point, square-
               root and divide hardware extensions.  This option includes
               option fpus_div. Not available for ARC EM.

           fpus_fma
               Enables support for single-precision floating-point and fused
               multiply and add hardware extensions.

           fpud_fma
               Enables support for double-precision floating-point and fused
               multiply and add hardware extensions.  This option includes
               option fpus_fma.  Not available for ARC EM.

           fpus_all
               Enables support for all single-precision floating-point
               hardware extensions.

           fpud_all
               Enables support for all single- and double-precision floating-
               point hardware extensions.  Not available for ARC EM.

       -mirq-ctrl-saved=register-range, blink, lp_count
           Specifies general-purposes registers that the processor
           automatically saves/restores on interrupt entry and exit.
           register-range is specified as two registers separated by a dash.
           The register range always starts with "r0", the upper limit is "fp"
           register.  blink and lp_count are optional.  This option is only
           valid for ARC EM and ARC HS cores.

       -mrgf-banked-regs=number
           Specifies the number of registers replicated in second register
           bank on entry to fast interrupt.  Fast interrupts are interrupts
           with the highest priority level P0.  These interrupts save only PC
           and STATUS32 registers to avoid memory transactions during
           interrupt entry and exit sequences.  Use this option when you are
           using fast interrupts in an ARC V2 family processor.  Permitted
           values are 4, 8, 16, and 32.

       -mlpc-width=width
           Specify the width of the "lp_count" register.  Valid values for
           width are 8, 16, 20, 24, 28 and 32 bits.  The default width is
           fixed to 32 bits.  If the width is less than 32, the compiler does
           not attempt to transform loops in your program to use the zero-
           delay loop mechanism unless it is known that the "lp_count"
           register can hold the required loop-counter value.  Depending on
           the width specified, the compiler and run-time library might
           continue to use the loop mechanism for various needs.  This option
           defines macro "__ARC_LPC_WIDTH__" with the value of width.

       -mrf16
           This option instructs the compiler to generate code for a 16-entry
           register file.  This option defines the "__ARC_RF16__" preprocessor
           macro.

       -mbranch-index
           Enable use of "bi" or "bih" instructions to implement jump tables.

       The following options are passed through to the assembler, and also
       define preprocessor macro symbols.

       -mdsp-packa
           Passed down to the assembler to enable the DSP Pack A extensions.
           Also sets the preprocessor symbol "__Xdsp_packa".  This option is
           deprecated.

       -mdvbf
           Passed down to the assembler to enable the dual Viterbi butterfly
           extension.  Also sets the preprocessor symbol "__Xdvbf".  This
           option is deprecated.

       -mlock
           Passed down to the assembler to enable the locked load/store
           conditional extension.  Also sets the preprocessor symbol
           "__Xlock".

       -mmac-d16
           Passed down to the assembler.  Also sets the preprocessor symbol
           "__Xxmac_d16".  This option is deprecated.

       -mmac-24
           Passed down to the assembler.  Also sets the preprocessor symbol
           "__Xxmac_24".  This option is deprecated.

       -mrtsc
           Passed down to the assembler to enable the 64-bit time-stamp
           counter extension instruction.  Also sets the preprocessor symbol
           "__Xrtsc".  This option is deprecated.

       -mswape
           Passed down to the assembler to enable the swap byte ordering
           extension instruction.  Also sets the preprocessor symbol
           "__Xswape".

       -mtelephony
           Passed down to the assembler to enable dual- and single-operand
           instructions for telephony.  Also sets the preprocessor symbol
           "__Xtelephony".  This option is deprecated.

       -mxy
           Passed down to the assembler to enable the XY memory extension.
           Also sets the preprocessor symbol "__Xxy".

       The following options control how the assembly code is annotated:

       -misize
           Annotate assembler instructions with estimated addresses.

       -mannotate-align
           Explain what alignment considerations lead to the decision to make
           an instruction short or long.

       The following options are passed through to the linker:

       -marclinux
           Passed through to the linker, to specify use of the "arclinux"
           emulation.  This option is enabled by default in tool chains built
           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
           profiling is not requested.

       -marclinux_prof
           Passed through to the linker, to specify use of the "arclinux_prof"
           emulation.  This option is enabled by default in tool chains built
           for "arc-linux-uclibc" and "arceb-linux-uclibc" targets when
           profiling is requested.

       The following options control the semantics of generated code:

       -mlong-calls
           Generate calls as register indirect calls, thus providing access to
           the full 32-bit address range.

       -mmedium-calls
           Don't use less than 25-bit addressing range for calls, which is the
           offset available for an unconditional branch-and-link instruction.
           Conditional execution of function calls is suppressed, to allow use
           of the 25-bit range, rather than the 21-bit range with conditional
           branch-and-link.  This is the default for tool chains built for
           "arc-linux-uclibc" and "arceb-linux-uclibc" targets.

       -G num
           Put definitions of externally-visible data in a small data section
           if that data is no bigger than num bytes.  The default value of num
           is 4 for any ARC configuration, or 8 when we have double load/store
           operations.

       -mno-sdata
           Do not generate sdata references.  This is the default for tool
           chains built for "arc-linux-uclibc" and "arceb-linux-uclibc"
           targets.

       -mvolatile-cache
           Use ordinarily cached memory accesses for volatile references.
           This is the default.

       -mno-volatile-cache
           Enable cache bypass for volatile references.

       The following options fine tune code generation:

       -malign-call
           Do alignment optimizations for call instructions.

       -mauto-modify-reg
           Enable the use of pre/post modify with register displacement.

       -mbbit-peephole
           Enable bbit peephole2.

       -mno-brcc
           This option disables a target-specific pass in arc_reorg to
           generate compare-and-branch ("brcc") instructions.  It has no
           effect on generation of these instructions driven by the combiner
           pass.

       -mcase-vector-pcrel
           Use PC-relative switch case tables to enable case table shortening.
           This is the default for -Os.

       -mcompact-casesi
           Enable compact "casesi" pattern.  This is the default for -Os, and
           only available for ARCv1 cores.  This option is deprecated.

       -mno-cond-exec
           Disable the ARCompact-specific pass to generate conditional
           execution instructions.

           Due to delay slot scheduling and interactions between operand
           numbers, literal sizes, instruction lengths, and the support for
           conditional execution, the target-independent pass to generate
           conditional execution is often lacking, so the ARC port has kept a
           special pass around that tries to find more conditional execution
           generation opportunities after register allocation, branch
           shortening, and delay slot scheduling have been done.  This pass
           generally, but not always, improves performance and code size, at
           the cost of extra compilation time, which is why there is an option
           to switch it off.  If you have a problem with call instructions
           exceeding their allowable offset range because they are
           conditionalized, you should consider using -mmedium-calls instead.

       -mearly-cbranchsi
           Enable pre-reload use of the "cbranchsi" pattern.

       -mexpand-adddi
           Expand "adddi3" and "subdi3" at RTL generation time into "add.f",
           "adc" etc.  This option is deprecated.

       -mindexed-loads
           Enable the use of indexed loads.  This can be problematic because
           some optimizers then assume that indexed stores exist, which is not
           the case.

       -mlra
           Enable Local Register Allocation.  This is still experimental for
           ARC, so by default the compiler uses standard reload (i.e.
           -mno-lra).

       -mlra-priority-none
           Don't indicate any priority for target registers.

       -mlra-priority-compact
           Indicate target register priority for r0..r3 / r12..r15.

       -mlra-priority-noncompact
           Reduce target register priority for r0..r3 / r12..r15.

       -mmillicode
           When optimizing for size (using -Os), prologues and epilogues that
           have to save or restore a large number of registers are often
           shortened by using call to a special function in libgcc; this is
           referred to as a millicode call.  As these calls can pose
           performance issues, and/or cause linking issues when linking in a
           nonstandard way, this option is provided to turn on or off
           millicode call generation.

       -mcode-density-frame
           This option enable the compiler to emit "enter" and "leave"
           instructions.  These instructions are only valid for CPUs with
           code-density feature.

       -mmixed-code
           Tweak register allocation to help 16-bit instruction generation.
           This generally has the effect of decreasing the average instruction
           size while increasing the instruction count.

       -mq-class
           Ths option is deprecated.  Enable q instruction alternatives.  This
           is the default for -Os.

       -mRcq
           Enable Rcq constraint handling.  Most short code generation depends
           on this.  This is the default.

       -mRcw
           Enable Rcw constraint handling.  Most ccfsm condexec mostly depends
           on this.  This is the default.

       -msize-level=level
           Fine-tune size optimization with regards to instruction lengths and
           alignment.  The recognized values for level are:

           0   No size optimization.  This level is deprecated and treated
               like 1.

           1   Short instructions are used opportunistically.

           2   In addition, alignment of loops and of code after barriers are
               dropped.

           3   In addition, optional data alignment is dropped, and the option
               Os is enabled.

           This defaults to 3 when -Os is in effect.  Otherwise, the behavior
           when this is not set is equivalent to level 1.

       -mtune=cpu
           Set instruction scheduling parameters for cpu, overriding any
           implied by -mcpu=.

           Supported values for cpu are

           ARC600
               Tune for ARC600 CPU.

           ARC601
               Tune for ARC601 CPU.

           ARC700
               Tune for ARC700 CPU with standard multiplier block.

           ARC700-xmac
               Tune for ARC700 CPU with XMAC block.

           ARC725D
               Tune for ARC725D CPU.

           ARC750D
               Tune for ARC750D CPU.

       -mmultcost=num
           Cost to assume for a multiply instruction, with 4 being equal to a
           normal instruction.

       -munalign-prob-threshold=probability
           Set probability threshold for unaligning branches.  When tuning for
           ARC700 and optimizing for speed, branches without filled delay slot
           are preferably emitted unaligned and long, unless profiling
           indicates that the probability for the branch to be taken is below
           probability.  The default is (REG_BR_PROB_BASE/2), i.e. 5000.

       The following options are maintained for backward compatibility, but
       are now deprecated and will be removed in a future release:

       -margonaut
           Obsolete FPX.

       -mbig-endian
       -EB Compile code for big-endian targets.  Use of these options is now
           deprecated.  Big-endian code is supported by configuring GCC to
           build "arceb-elf32" and "arceb-linux-uclibc" targets, for which big
           endian is the default.

       -mlittle-endian
       -EL Compile code for little-endian targets.  Use of these options is
           now deprecated.  Little-endian code is supported by configuring GCC
           to build "arc-elf32" and "arc-linux-uclibc" targets, for which
           little endian is the default.

       -mbarrel_shifter
           Replaced by -mbarrel-shifter.

       -mdpfp_compact
           Replaced by -mdpfp-compact.

       -mdpfp_fast
           Replaced by -mdpfp-fast.

       -mdsp_packa
           Replaced by -mdsp-packa.

       -mEA
           Replaced by -mea.

       -mmac_24
           Replaced by -mmac-24.

       -mmac_d16
           Replaced by -mmac-d16.

       -mspfp_compact
           Replaced by -mspfp-compact.

       -mspfp_fast
           Replaced by -mspfp-fast.

       -mtune=cpu
           Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced
           by ARC600, ARC601, ARC700 and ARC700-xmac respectively.

       -multcost=num
           Replaced by -mmultcost.

       ARM Options

       These -m options are defined for the ARM port:

       -mabi=name
           Generate code for the specified ABI.  Permissible values are: apcs-
           gnu, atpcs, aapcs, aapcs-linux and iwmmxt.

       -mapcs-frame
           Generate a stack frame that is compliant with the ARM Procedure
           Call Standard for all functions, even if this is not strictly
           necessary for correct execution of the code.  Specifying
           -fomit-frame-pointer with this option causes the stack frames not
           to be generated for leaf functions.  The default is
           -mno-apcs-frame.  This option is deprecated.

       -mapcs
           This is a synonym for -mapcs-frame and is deprecated.

       -mthumb-interwork
           Generate code that supports calling between the ARM and Thumb
           instruction sets.  Without this option, on pre-v5 architectures,
           the two instruction sets cannot be reliably used inside one
           program.  The default is -mno-thumb-interwork, since slightly
           larger code is generated when -mthumb-interwork is specified.  In
           AAPCS configurations this option is meaningless.

       -mno-sched-prolog
           Prevent the reordering of instructions in the function prologue, or
           the merging of those instruction with the instructions in the
           function's body.  This means that all functions start with a
           recognizable set of instructions (or in fact one of a choice from a
           small set of different function prologues), and this information
           can be used to locate the start of functions inside an executable
           piece of code.  The default is -msched-prolog.

       -mfloat-abi=name
           Specifies which floating-point ABI to use.  Permissible values are:
           soft, softfp and hard.

           Specifying soft causes GCC to generate output containing library
           calls for floating-point operations.  softfp allows the generation
           of code using hardware floating-point instructions, but still uses
           the soft-float calling conventions.  hard allows generation of
           floating-point instructions and uses FPU-specific calling
           conventions.

           The default depends on the specific target configuration.  Note
           that the hard-float and soft-float ABIs are not link-compatible;
           you must compile your entire program with the same ABI, and link
           with a compatible set of libraries.

       -mgeneral-regs-only
           Generate code which uses only the general-purpose registers.  This
           will prevent the compiler from using floating-point and Advanced
           SIMD registers but will not impose any restrictions on the
           assembler.

       -mlittle-endian
           Generate code for a processor running in little-endian mode.  This
           is the default for all standard configurations.

       -mbig-endian
           Generate code for a processor running in big-endian mode; the
           default is to compile code for a little-endian processor.

       -mbe8
       -mbe32
           When linking a big-endian image select between BE8 and BE32
           formats.  The option has no effect for little-endian images and is
           ignored.  The default is dependent on the selected target
           architecture.  For ARMv6 and later architectures the default is
           BE8, for older architectures the default is BE32.  BE32 format has
           been deprecated by ARM.

       -march=name[+extension...]
           This specifies the name of the target ARM architecture.  GCC uses
           this name to determine what kind of instructions it can emit when
           generating assembly code.  This option can be used in conjunction
           with or instead of the -mcpu= option.

           Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j,
           armv6k, armv6kz, armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve,
           armv8-a, armv8.1-a, armv8.2-a, armv8.3-a, armv8.4-a, armv8.5-a,
           armv8.6-a, armv7-r, armv8-r, armv6-m, armv6s-m, armv7-m, armv7e-m,
           armv8-m.base, armv8-m.main, armv8.1-m.main, iwmmxt and iwmmxt2.

           Additionally, the following architectures, which lack support for
           the Thumb execution state, are recognized but support is
           deprecated: armv4.

           Many of the architectures support extensions.  These can be added
           by appending +extension to the architecture name.  Extension
           options are processed in order and capabilities accumulate.  An
           extension will also enable any necessary base extensions upon which
           it depends.  For example, the +crypto extension will always enable
           the +simd extension.  The exception to the additive construction is
           for extensions that are prefixed with +no...: these extensions
           disable the specified option and any other extensions that may
           depend on the presence of that extension.

           For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to
           writing -march=armv7-a+vfpv4 since the +simd option is entirely
           disabled by the +nofp option that follows it.

           Most extension names are generically named, but have an effect that
           is dependent upon the architecture to which it is applied.  For
           example, the +simd option can be applied to both armv7-a and
           armv8-a architectures, but will enable the original ARMv7-A
           Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant
           for armv8-a.

           The table below lists the supported extensions for each
           architecture.  Architectures not mentioned do not support any
           extensions.

           armv5te
           armv6
           armv6j
           armv6k
           armv6kz
           armv6t2
           armv6z
           armv6zk
               +fp The VFPv2 floating-point instructions.  The extension
                   +vfpv2 can be used as an alias for this extension.

               +nofp
                   Disable the floating-point instructions.

           armv7
               The common subset of the ARMv7-A, ARMv7-R and ARMv7-M
               architectures.

               +fp The VFPv3 floating-point instructions, with 16 double-
                   precision registers.  The extension +vfpv3-d16 can be used
                   as an alias for this extension.  Note that floating-point
                   is not supported by the base ARMv7-M architecture, but is
                   compatible with both the ARMv7-A and ARMv7-R architectures.

               +nofp
                   Disable the floating-point instructions.

           armv7-a
               +mp The multiprocessing extension.

               +sec
                   The security extension.

               +fp The VFPv3 floating-point instructions, with 16 double-
                   precision registers.  The extension +vfpv3-d16 can be used
                   as an alias for this extension.

               +simd
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
                   instructions.  The extensions +neon and +neon-vfpv3 can be
                   used as aliases for this extension.

               +vfpv3
                   The VFPv3 floating-point instructions, with 32 double-
                   precision registers.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions, with 16 double-
                   precision registers and the half-precision floating-point
                   conversion operations.

               +vfpv3-fp16
                   The VFPv3 floating-point instructions, with 32 double-
                   precision registers and the half-precision floating-point
                   conversion operations.

               +vfpv4-d16
                   The VFPv4 floating-point instructions, with 16 double-
                   precision registers.

               +vfpv4
                   The VFPv4 floating-point instructions, with 32 double-
                   precision registers.

               +neon-fp16
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
                   instructions, with the half-precision floating-point
                   conversion operations.

               +neon-vfpv4
                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
                   instructions.

               +nosimd
                   Disable the Advanced SIMD instructions (does not disable
                   floating point).

               +nofp
                   Disable the floating-point and Advanced SIMD instructions.

           armv7ve
               The extended version of the ARMv7-A architecture with support
               for virtualization.

               +fp The VFPv4 floating-point instructions, with 16 double-
                   precision registers.  The extension +vfpv4-d16 can be used
                   as an alias for this extension.

               +simd
                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point
                   instructions.  The extension +neon-vfpv4 can be used as an
                   alias for this extension.

               +vfpv3-d16
                   The VFPv3 floating-point instructions, with 16 double-
                   precision registers.

               +vfpv3
                   The VFPv3 floating-point instructions, with 32 double-
                   precision registers.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions, with 16 double-
                   precision registers and the half-precision floating-point
                   conversion operations.

               +vfpv3-fp16
                   The VFPv3 floating-point instructions, with 32 double-
                   precision registers and the half-precision floating-point
                   conversion operations.

               +vfpv4-d16
                   The VFPv4 floating-point instructions, with 16 double-
                   precision registers.

               +vfpv4
                   The VFPv4 floating-point instructions, with 32 double-
                   precision registers.

               +neon
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
                   instructions.  The extension +neon-vfpv3 can be used as an
                   alias for this extension.

               +neon-fp16
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point
                   instructions, with the half-precision floating-point
                   conversion operations.

               +nosimd
                   Disable the Advanced SIMD instructions (does not disable
                   floating point).

               +nofp
                   Disable the floating-point and Advanced SIMD instructions.

           armv8-a
               +crc
                   The Cyclic Redundancy Check (CRC) instructions.

               +simd
                   The ARMv8-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic
                   instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

           armv8.1-a
               +simd
                   The ARMv8.1-A Advanced SIMD and floating-point
                   instructions.

               +crypto
                   The cryptographic instructions.  This also enables the
                   Advanced SIMD and floating-point instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic
                   instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

           armv8.2-a
           armv8.3-a
               +fp16
                   The half-precision floating-point data processing
                   instructions.  This also enables the Advanced SIMD and
                   floating-point instructions.

               +fp16fml
                   The half-precision floating-point fmla extension.  This
                   also enables the half-precision floating-point extension
                   and Advanced SIMD and floating-point instructions.

               +simd
                   The ARMv8.1-A Advanced SIMD and floating-point
                   instructions.

               +crypto
                   The cryptographic instructions.  This also enables the
                   Advanced SIMD and floating-point instructions.

               +dotprod
                   Enable the Dot Product extension.  This also enables
                   Advanced SIMD instructions.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic
                   instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also
                   enables Advanced SIMD and floating-point instructions.

               +bf16
                   Brain half-precision floating-point instructions.  This
                   also enables Advanced SIMD and floating-point instructions.

           armv8.4-a
               +fp16
                   The half-precision floating-point data processing
                   instructions.  This also enables the Advanced SIMD and
                   floating-point instructions as well as the Dot Product
                   extension and the half-precision floating-point fmla
                   extension.

               +simd
                   The ARMv8.3-A Advanced SIMD and floating-point instructions
                   as well as the Dot Product extension.

               +crypto
                   The cryptographic instructions.  This also enables the
                   Advanced SIMD and floating-point instructions as well as
                   the Dot Product extension.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic
                   instructions.

               +sb Speculation Barrier Instruction.

               +predres
                   Execution and Data Prediction Restriction Instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also
                   enables Advanced SIMD and floating-point instructions.

               +bf16
                   Brain half-precision floating-point instructions.  This
                   also enables Advanced SIMD and floating-point instructions.

           armv8.5-a
               +fp16
                   The half-precision floating-point data processing
                   instructions.  This also enables the Advanced SIMD and
                   floating-point instructions as well as the Dot Product
                   extension and the half-precision floating-point fmla
                   extension.

               +simd
                   The ARMv8.3-A Advanced SIMD and floating-point instructions
                   as well as the Dot Product extension.

               +crypto
                   The cryptographic instructions.  This also enables the
                   Advanced SIMD and floating-point instructions as well as
                   the Dot Product extension.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic
                   instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also
                   enables Advanced SIMD and floating-point instructions.

               +bf16
                   Brain half-precision floating-point instructions.  This
                   also enables Advanced SIMD and floating-point instructions.

           armv8.6-a
               +fp16
                   The half-precision floating-point data processing
                   instructions.  This also enables the Advanced SIMD and
                   floating-point instructions as well as the Dot Product
                   extension and the half-precision floating-point fmla
                   extension.

               +simd
                   The ARMv8.3-A Advanced SIMD and floating-point instructions
                   as well as the Dot Product extension.

               +crypto
                   The cryptographic instructions.  This also enables the
                   Advanced SIMD and floating-point instructions as well as
                   the Dot Product extension.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic
                   instructions.

               +i8mm
                   8-bit Integer Matrix Multiply instructions.  This also
                   enables Advanced SIMD and floating-point instructions.

               +bf16
                   Brain half-precision floating-point instructions.  This
                   also enables Advanced SIMD and floating-point instructions.

           armv7-r
               +fp.sp
                   The single-precision VFPv3 floating-point instructions.
                   The extension +vfpv3xd can be used as an alias for this
                   extension.

               +fp The VFPv3 floating-point instructions with 16 double-
                   precision registers.  The extension +vfpv3-d16 can be used
                   as an alias for this extension.

               +vfpv3xd-d16-fp16
                   The single-precision VFPv3 floating-point instructions with
                   16 double-precision registers and the half-precision
                   floating-point conversion operations.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions with 16 double-
                   precision registers and the half-precision floating-point
                   conversion operations.

               +nofp
                   Disable the floating-point extension.

               +idiv
                   The ARM-state integer division instructions.

               +noidiv
                   Disable the ARM-state integer division extension.

           armv7e-m
               +fp The single-precision VFPv4 floating-point instructions.

               +fpv5
                   The single-precision FPv5 floating-point instructions.

               +fp.dp
                   The single- and double-precision FPv5 floating-point
                   instructions.

               +nofp
                   Disable the floating-point extensions.

           armv8.1-m.main
               +dsp
                   The DSP instructions.

               +mve
                   The M-Profile Vector Extension (MVE) integer instructions.

               +mve.fp
                   The M-Profile Vector Extension (MVE) integer and single
                   precision floating-point instructions.

               +fp The single-precision floating-point instructions.

               +fp.dp
                   The single- and double-precision floating-point
                   instructions.

               +nofp
                   Disable the floating-point extension.

               +cdecp0, +cdecp1, ... , +cdecp7
                   Enable the Custom Datapath Extension (CDE) on selected
                   coprocessors according to the numbers given in the options
                   in the range 0 to 7.

           armv8-m.main
               +dsp
                   The DSP instructions.

               +nodsp
                   Disable the DSP extension.

               +fp The single-precision floating-point instructions.

               +fp.dp
                   The single- and double-precision floating-point
                   instructions.

               +nofp
                   Disable the floating-point extension.

               +cdecp0, +cdecp1, ... , +cdecp7
                   Enable the Custom Datapath Extension (CDE) on selected
                   coprocessors according to the numbers given in the options
                   in the range 0 to 7.

           armv8-r
               +crc
                   The Cyclic Redundancy Check (CRC) instructions.

               +fp.sp
                   The single-precision FPv5 floating-point instructions.

               +simd
                   The ARMv8-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic
                   instructions.

           -march=native causes the compiler to auto-detect the architecture
           of the build computer.  At present, this feature is only supported
           on GNU/Linux, and not all architectures are recognized.  If the
           auto-detect is unsuccessful the option has no effect.

       -mtune=name
           This option specifies the name of the target ARM processor for
           which GCC should tune the performance of the code.  For some ARM
           implementations better performance can be obtained by using this
           option.  Permissible names are: arm7tdmi, arm7tdmi-s, arm710t,
           arm720t, arm740t, strongarm, strongarm110, strongarm1100,
           0strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t,
           arm922t, arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t,
           arm9tdmi, arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e,
           arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp,
           arm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s,
           generic-armv7-a, cortex-a5, cortex-a7, cortex-a8, cortex-a9,
           cortex-a12, cortex-a15, cortex-a17, cortex-a32, cortex-a35,
           cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73,
           cortex-a75, cortex-a76, cortex-a76ae, cortex-a77, ares, cortex-r4,
           cortex-r4f, cortex-r5, cortex-r7, cortex-r8, cortex-r52, cortex-m0,
           cortex-m0plus, cortex-m1, cortex-m3, cortex-m4, cortex-m7,
           cortex-m23, cortex-m33, cortex-m35p, cortex-m55,
           cortex-m1.small-multiply, cortex-m0.small-multiply,
           cortex-m0plus.small-multiply, exynos-m1, marvell-pj4, neoverse-n1,
           neoverse-n2, neoverse-v1, xscale, iwmmxt, iwmmxt2, ep9312, fa526,
           fa626, fa606te, fa626te, fmp626, fa726te, xgene1.

           Additionally, this option can specify that GCC should tune the
           performance of the code for a big.LITTLE system.  Permissible names
           are: cortex-a15.cortex-a7, cortex-a17.cortex-a7,
           cortex-a57.cortex-a53, cortex-a72.cortex-a53,
           cortex-a72.cortex-a35, cortex-a73.cortex-a53,
           cortex-a75.cortex-a55, cortex-a76.cortex-a55.

           -mtune=generic-arch specifies that GCC should tune the performance
           for a blend of processors within architecture arch.  The aim is to
           generate code that run well on the current most popular processors,
           balancing between optimizations that benefit some CPUs in the
           range, and avoiding performance pitfalls of other CPUs.  The
           effects of this option may change in future GCC versions as CPU
           models come and go.

           -mtune permits the same extension options as -mcpu, but the
           extension options do not affect the tuning of the generated code.

           -mtune=native causes the compiler to auto-detect the CPU of the
           build computer.  At present, this feature is only supported on
           GNU/Linux, and not all architectures are recognized.  If the auto-
           detect is unsuccessful the option has no effect.

       -mcpu=name[+extension...]
           This specifies the name of the target ARM processor.  GCC uses this
           name to derive the name of the target ARM architecture (as if
           specified by -march) and the ARM processor type for which to tune
           for performance (as if specified by -mtune).  Where this option is
           used in conjunction with -march or -mtune, those options take
           precedence over the appropriate part of this option.

           Many of the supported CPUs implement optional architectural
           extensions.  Where this is so the architectural extensions are
           normally enabled by default.  If implementations that lack the
           extension exist, then the extension syntax can be used to disable
           those extensions that have been omitted.  For floating-point and
           Advanced SIMD (Neon) instructions, the settings of the options
           -mfloat-abi and -mfpu must also be considered: floating-point and
           Advanced SIMD instructions will only be used if -mfloat-abi is not
           set to soft; and any setting of -mfpu other than auto will override
           the available floating-point and SIMD extension instructions.

           For example, cortex-a9 can be found in three major configurations:
           integer only, with just a floating-point unit or with floating-
           point and Advanced SIMD.  The default is to enable all the
           instructions, but the extensions +nosimd and +nofp can be used to
           disable just the SIMD or both the SIMD and floating-point
           instructions respectively.

           Permissible names for this option are the same as those for -mtune.

           The following extension options are common to the listed CPUs:

           +nodsp
               Disable the DSP instructions on cortex-m33, cortex-m35p.

           +nofp
               Disables the floating-point instructions on arm9e, arm946e-s,
               arm966e-s, arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s,
               arm1026ej-s, cortex-r5, cortex-r7, cortex-r8, cortex-m4,
               cortex-m7, cortex-m33 and cortex-m35p.  Disables the floating-
               point and SIMD instructions on generic-armv7-a, cortex-a5,
               cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15,
               cortex-a17, cortex-a15.cortex-a7, cortex-a17.cortex-a7,
               cortex-a32, cortex-a35, cortex-a53 and cortex-a55.

           +nofp.dp
               Disables the double-precision component of the floating-point
               instructions on cortex-r5, cortex-r7, cortex-r8, cortex-r52 and
               cortex-m7.

           +nosimd
               Disables the SIMD (but not floating-point) instructions on
               generic-armv7-a, cortex-a5, cortex-a7 and cortex-a9.

           +crypto
               Enables the cryptographic instructions on cortex-a32,
               cortex-a35, cortex-a53, cortex-a55, cortex-a57, cortex-a72,
               cortex-a73, cortex-a75, exynos-m1, xgene1,
               cortex-a57.cortex-a53, cortex-a72.cortex-a53,
               cortex-a73.cortex-a35, cortex-a73.cortex-a53 and
               cortex-a75.cortex-a55.

           Additionally the generic-armv7-a pseudo target defaults to VFPv3
           with 16 double-precision registers.  It supports the following
           extension options: mp, sec, vfpv3-d16, vfpv3, vfpv3-d16-fp16,
           vfpv3-fp16, vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16,
           neon-vfpv4.  The meanings are the same as for the extensions to
           -march=armv7-a.

           -mcpu=generic-arch is also permissible, and is equivalent to
           -march=arch -mtune=generic-arch.  See -mtune for more information.

           -mcpu=native causes the compiler to auto-detect the CPU of the
           build computer.  At present, this feature is only supported on
           GNU/Linux, and not all architectures are recognized.  If the auto-
           detect is unsuccessful the option has no effect.

       -mfpu=name
           This specifies what floating-point hardware (or hardware emulation)
           is available on the target.  Permissible names are: auto, vfpv2,
           vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
           vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16,
           neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3
           and vfp is an alias for vfpv2.

           The setting auto is the default and is special.  It causes the
           compiler to select the floating-point and Advanced SIMD
           instructions based on the settings of -mcpu and -march.

           If the selected floating-point hardware includes the NEON extension
           (e.g. -mfpu=neon), note that floating-point operations are not
           generated by GCC's auto-vectorization pass unless
           -funsafe-math-optimizations is also specified.  This is because
           NEON hardware does not fully implement the IEEE 754 standard for
           floating-point arithmetic (in particular denormal values are
           treated as zero), so the use of NEON instructions may lead to a
           loss of precision.

           You can also set the fpu name at function level by using the
           "target("fpu=")" function attributes or pragmas.

       -mfp16-format=name
           Specify the format of the "__fp16" half-precision floating-point
           type.  Permissible names are none, ieee, and alternative; the
           default is none, in which case the "__fp16" type is not defined.

       -mstructure-size-boundary=n
           The sizes of all structures and unions are rounded up to a multiple
           of the number of bits set by this option.  Permissible values are
           8, 32 and 64.  The default value varies for different toolchains.
           For the COFF targeted toolchain the default value is 8.  A value of
           64 is only allowed if the underlying ABI supports it.

           Specifying a larger number can produce faster, more efficient code,
           but can also increase the size of the program.  Different values
           are potentially incompatible.  Code compiled with one value cannot
           necessarily expect to work with code or libraries compiled with
           another value, if they exchange information using structures or
           unions.

           This option is deprecated.

       -mabort-on-noreturn
           Generate a call to the function "abort" at the end of a "noreturn"
           function.  It is executed if the function tries to return.

       -mlong-calls
       -mno-long-calls
           Tells the compiler to perform function calls by first loading the
           address of the function into a register and then performing a
           subroutine call on this register.  This switch is needed if the
           target function lies outside of the 64-megabyte addressing range of
           the offset-based version of subroutine call instruction.

           Even if this switch is enabled, not all function calls are turned
           into long calls.  The heuristic is that static functions, functions
           that have the "short_call" attribute, functions that are inside the
           scope of a "#pragma no_long_calls" directive, and functions whose
           definitions have already been compiled within the current
           compilation unit are not turned into long calls.  The exceptions to
           this rule are that weak function definitions, functions with the
           "long_call" attribute or the "section" attribute, and functions
           that are within the scope of a "#pragma long_calls" directive are
           always turned into long calls.

           This feature is not enabled by default.  Specifying -mno-long-calls
           restores the default behavior, as does placing the function calls
           within the scope of a "#pragma long_calls_off" directive.  Note
           these switches have no effect on how the compiler generates code to
           handle function calls via function pointers.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather
           than loading it in the prologue for each function.  The runtime
           system is responsible for initializing this register with an
           appropriate value before execution begins.

       -mpic-register=reg
           Specify the register to be used for PIC addressing.  For standard
           PIC base case, the default is any suitable register determined by
           compiler.  For single PIC base case, the default is R9 if target is
           EABI based or stack-checking is enabled, otherwise the default is
           R10.

       -mpic-data-is-text-relative
           Assume that the displacement between the text and data segments is
           fixed at static link time.  This permits using PC-relative
           addressing operations to access data known to be in the data
           segment.  For non-VxWorks RTP targets, this option is enabled by
           default.  When disabled on such targets, it will enable
           -msingle-pic-base by default.

       -mpoke-function-name
           Write the name of each function into the text section, directly
           preceding the function prologue.  The generated code is similar to
           this:

                        t0
                            .ascii "arm_poke_function_name", 0
                            .align
                        t1
                            .word 0xff000000 + (t1 - t0)
                        arm_poke_function_name
                            mov     ip, sp
                            stmfd   sp!, {fp, ip, lr, pc}
                            sub     fp, ip, #4

           When performing a stack backtrace, code can inspect the value of
           "pc" stored at "fp + 0".  If the trace function then looks at
           location "pc - 12" and the top 8 bits are set, then we know that
           there is a function name embedded immediately preceding this
           location and has length "((pc[-3]) & 0xff000000)".

       -mthumb
       -marm
           Select between generating code that executes in ARM and Thumb
           states.  The default for most configurations is to generate code
           that executes in ARM state, but the default can be changed by
           configuring GCC with the --with-mode=state configure option.

           You can also override the ARM and Thumb mode for each function by
           using the "target("thumb")" and "target("arm")" function attributes
           or pragmas.

       -mflip-thumb
           Switch ARM/Thumb modes on alternating functions.  This option is
           provided for regression testing of mixed Thumb/ARM code generation,
           and is not intended for ordinary use in compiling code.

       -mtpcs-frame
           Generate a stack frame that is compliant with the Thumb Procedure
           Call Standard for all non-leaf functions.  (A leaf function is one
           that does not call any other functions.)  The default is
           -mno-tpcs-frame.

       -mtpcs-leaf-frame
           Generate a stack frame that is compliant with the Thumb Procedure
           Call Standard for all leaf functions.  (A leaf function is one that
           does not call any other functions.)  The default is
           -mno-apcs-leaf-frame.

       -mcallee-super-interworking
           Gives all externally visible functions in the file being compiled
           an ARM instruction set header which switches to Thumb mode before
           executing the rest of the function.  This allows these functions to
           be called from non-interworking code.  This option is not valid in
           AAPCS configurations because interworking is enabled by default.

       -mcaller-super-interworking
           Allows calls via function pointers (including virtual functions) to
           execute correctly regardless of whether the target code has been
           compiled for interworking or not.  There is a small overhead in the
           cost of executing a function pointer if this option is enabled.
           This option is not valid in AAPCS configurations because
           interworking is enabled by default.

       -mtp=name
           Specify the access model for the thread local storage pointer.  The
           valid models are soft, which generates calls to "__aeabi_read_tp",
           cp15, which fetches the thread pointer from "cp15" directly
           (supported in the arm6k architecture), and auto, which uses the
           best available method for the selected processor.  The default
           setting is auto.

       -mtls-dialect=dialect
           Specify the dialect to use for accessing thread local storage.  Two
           dialects are supported---gnu and gnu2.  The gnu dialect selects the
           original GNU scheme for supporting local and global dynamic TLS
           models.  The gnu2 dialect selects the GNU descriptor scheme, which
           provides better performance for shared libraries.  The GNU
           descriptor scheme is compatible with the original scheme, but does
           require new assembler, linker and library support.  Initial and
           local exec TLS models are unaffected by this option and always use
           the original scheme.

       -mword-relocations
           Only generate absolute relocations on word-sized values (i.e.
           R_ARM_ABS32).  This is enabled by default on targets (uClinux,
           SymbianOS) where the runtime loader imposes this restriction, and
           when -fpic or -fPIC is specified. This option conflicts with
           -mslow-flash-data.

       -mfix-cortex-m3-ldrd
           Some Cortex-M3 cores can cause data corruption when "ldrd"
           instructions with overlapping destination and base registers are
           used.  This option avoids generating these instructions.  This
           option is enabled by default when -mcpu=cortex-m3 is specified.

       -munaligned-access
       -mno-unaligned-access
           Enables (or disables) reading and writing of 16- and 32- bit values
           from addresses that are not 16- or 32- bit aligned.  By default
           unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
           ARMv8-M Baseline architectures, and enabled for all other
           architectures.  If unaligned access is not enabled then words in
           packed data structures are accessed a byte at a time.

           The ARM attribute "Tag_CPU_unaligned_access" is set in the
           generated object file to either true or false, depending upon the
           setting of this option.  If unaligned access is enabled then the
           preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined.

       -mneon-for-64bits
           This option is deprecated and has no effect.

       -mslow-flash-data
           Assume loading data from flash is slower than fetching instruction.
           Therefore literal load is minimized for better performance.  This
           option is only supported when compiling for ARMv7 M-profile and off
           by default. It conflicts with -mword-relocations.

       -masm-syntax-unified
           Assume inline assembler is using unified asm syntax.  The default
           is currently off which implies divided syntax.  This option has no
           impact on Thumb2. However, this may change in future releases of
           GCC. Divided syntax should be considered deprecated.

       -mrestrict-it
           Restricts generation of IT blocks to conform to the rules of
           ARMv8-A.  IT blocks can only contain a single 16-bit instruction
           from a select set of instructions. This option is on by default for
           ARMv8-A Thumb mode.

       -mprint-tune-info
           Print CPU tuning information as comment in assembler file.  This is
           an option used only for regression testing of the compiler and not
           intended for ordinary use in compiling code.  This option is
           disabled by default.

       -mverbose-cost-dump
           Enable verbose cost model dumping in the debug dump files.  This
           option is provided for use in debugging the compiler.

       -mpure-code
           Do not allow constant data to be placed in code sections.
           Additionally, when compiling for ELF object format give all text
           sections the ELF processor-specific section attribute
           "SHF_ARM_PURECODE".  This option is only available when generating
           non-pic code for M-profile targets.

       -mcmse
           Generate secure code as per the "ARMv8-M Security Extensions:
           Requirements on Development Tools Engineering Specification", which
           can be found on
           <https://developer.arm.com/documentation/ecm0359818/latest/>.

       -mfdpic
       -mno-fdpic
           Select the FDPIC ABI, which uses 64-bit function descriptors to
           represent pointers to functions.  When the compiler is configured
           for "arm-*-uclinuxfdpiceabi" targets, this option is on by default
           and implies -fPIE if none of the PIC/PIE-related options is
           provided.  On other targets, it only enables the FDPIC-specific
           code generation features, and the user should explicitly provide
           the PIC/PIE-related options as needed.

           Note that static linking is not supported because it would still
           involve the dynamic linker when the program self-relocates.  If
           such behavior is acceptable, use -static and -Wl,-dynamic-linker
           options.

           The opposite -mno-fdpic option is useful (and required) to build
           the Linux kernel using the same ("arm-*-uclinuxfdpiceabi")
           toolchain as the one used to build the userland programs.

       AVR Options

       These options are defined for AVR implementations:

       -mmcu=mcu
           Specify Atmel AVR instruction set architectures (ISA) or MCU type.

           The default for this option is avr2.

           GCC supports the following AVR devices and ISAs:

           "avr2"
               "Classic" devices with up to 8 KiB of program memory.  mcu =
               "attiny22", "attiny26", "at90s2313", "at90s2323", "at90s2333",
               "at90s2343", "at90s4414", "at90s4433", "at90s4434",
               "at90c8534", "at90s8515", "at90s8535".

           "avr25"
               "Classic" devices with up to 8 KiB of program memory and with
               the "MOVW" instruction.  mcu = "attiny13", "attiny13a",
               "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a",
               "attiny2313", "attiny2313a", "attiny43u", "attiny44",
               "attiny44a", "attiny45", "attiny48", "attiny441", "attiny461",
               "attiny461a", "attiny4313", "attiny84", "attiny84a",
               "attiny85", "attiny87", "attiny88", "attiny828", "attiny841",
               "attiny861", "attiny861a", "ata5272", "ata6616c", "at86rf401".

           "avr3"
               "Classic" devices with 16 KiB up to 64 KiB of program memory.
               mcu = "at76c711", "at43usb355".

           "avr31"
               "Classic" devices with 128 KiB of program memory.  mcu =
               "atmega103", "at43usb320".

           "avr35"
               "Classic" devices with 16 KiB up to 64 KiB of program memory
               and with the "MOVW" instruction.  mcu = "attiny167",
               "attiny1634", "atmega8u2", "atmega16u2", "atmega32u2",
               "ata5505", "ata6617c", "ata664251", "at90usb82", "at90usb162".

           "avr4"
               "Enhanced" devices with up to 8 KiB of program memory.  mcu =
               "atmega48", "atmega48a", "atmega48p", "atmega48pa",
               "atmega48pb", "atmega8", "atmega8a", "atmega8hva", "atmega88",
               "atmega88a", "atmega88p", "atmega88pa", "atmega88pb",
               "atmega8515", "atmega8535", "ata6285", "ata6286", "ata6289",
               "ata6612c", "at90pwm1", "at90pwm2", "at90pwm2b", "at90pwm3",
               "at90pwm3b", "at90pwm81".

           "avr5"
               "Enhanced" devices with 16 KiB up to 64 KiB of program memory.
               mcu = "atmega16", "atmega16a", "atmega16hva", "atmega16hva2",
               "atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4",
               "atmega161", "atmega162", "atmega163", "atmega164a",
               "atmega164p", "atmega164pa", "atmega165", "atmega165a",
               "atmega165p", "atmega165pa", "atmega168", "atmega168a",
               "atmega168p", "atmega168pa", "atmega168pb", "atmega169",
               "atmega169a", "atmega169p", "atmega169pa", "atmega32",
               "atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb",
               "atmega32m1", "atmega32u4", "atmega32u6", "atmega323",
               "atmega324a", "atmega324p", "atmega324pa", "atmega325",
               "atmega325a", "atmega325p", "atmega325pa", "atmega328",
               "atmega328p", "atmega328pb", "atmega329", "atmega329a",
               "atmega329p", "atmega329pa", "atmega3250", "atmega3250a",
               "atmega3250p", "atmega3250pa", "atmega3290", "atmega3290a",
               "atmega3290p", "atmega3290pa", "atmega406", "atmega64",
               "atmega64a", "atmega64c1", "atmega64hve", "atmega64hve2",
               "atmega64m1", "atmega64rfr2", "atmega640", "atmega644",
               "atmega644a", "atmega644p", "atmega644pa", "atmega644rfr2",
               "atmega645", "atmega645a", "atmega645p", "atmega649",
               "atmega649a", "atmega649p", "atmega6450", "atmega6450a",
               "atmega6450p", "atmega6490", "atmega6490a", "atmega6490p",
               "ata5795", "ata5790", "ata5790n", "ata5791", "ata6613c",
               "ata6614q", "ata5782", "ata5831", "ata8210", "ata8510",
               "ata5702m322", "at90pwm161", "at90pwm216", "at90pwm316",
               "at90can32", "at90can64", "at90scr100", "at90usb646",
               "at90usb647", "at94k", "m3000".

           "avr51"
               "Enhanced" devices with 128 KiB of program memory.  mcu =
               "atmega128", "atmega128a", "atmega128rfa1", "atmega128rfr2",
               "atmega1280", "atmega1281", "atmega1284", "atmega1284p",
               "atmega1284rfr2", "at90can128", "at90usb1286", "at90usb1287".

           "avr6"
               "Enhanced" devices with 3-byte PC, i.e. with more than 128 KiB
               of program memory.  mcu = "atmega256rfr2", "atmega2560",
               "atmega2561", "atmega2564rfr2".

           "avrxmega2"
               "XMEGA" devices with more than 8 KiB and up to 64 KiB of
               program memory.  mcu = "atxmega8e5", "atxmega16a4",
               "atxmega16a4u", "atxmega16c4", "atxmega16d4", "atxmega16e5",
               "atxmega32a4", "atxmega32a4u", "atxmega32c3", "atxmega32c4",
               "atxmega32d3", "atxmega32d4", "atxmega32e5".

           "avrxmega3"
               "XMEGA" devices with up to 64 KiB of combined program memory
               and RAM, and with program memory visible in the RAM address
               space.  mcu = "attiny202", "attiny204", "attiny212",
               "attiny214", "attiny402", "attiny404", "attiny406",
               "attiny412", "attiny414", "attiny416", "attiny417",
               "attiny804", "attiny806", "attiny807", "attiny814",
               "attiny816", "attiny817", "attiny1604", "attiny1606",
               "attiny1607", "attiny1614", "attiny1616", "attiny1617",
               "attiny3214", "attiny3216", "attiny3217", "atmega808",
               "atmega809", "atmega1608", "atmega1609", "atmega3208",
               "atmega3209", "atmega4808", "atmega4809".

           "avrxmega4"
               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
               program memory.  mcu = "atxmega64a3", "atxmega64a3u",
               "atxmega64a4u", "atxmega64b1", "atxmega64b3", "atxmega64c3",
               "atxmega64d3", "atxmega64d4".

           "avrxmega5"
               "XMEGA" devices with more than 64 KiB and up to 128 KiB of
               program memory and more than 64 KiB of RAM. mcu =
               "atxmega64a1", "atxmega64a1u".

           "avrxmega6"
               "XMEGA" devices with more than 128 KiB of program memory.  mcu
               = "atxmega128a3", "atxmega128a3u", "atxmega128b1",
               "atxmega128b3", "atxmega128c3", "atxmega128d3", "atxmega128d4",
               "atxmega192a3", "atxmega192a3u", "atxmega192c3",
               "atxmega192d3", "atxmega256a3", "atxmega256a3b",
               "atxmega256a3bu", "atxmega256a3u", "atxmega256c3",
               "atxmega256d3", "atxmega384c3", "atxmega384d3".

           "avrxmega7"
               "XMEGA" devices with more than 128 KiB of program memory and
               more than 64 KiB of RAM. mcu = "atxmega128a1", "atxmega128a1u",
               "atxmega128a4u".

           "avrtiny"
               "TINY" Tiny core devices with 512 B up to 4 KiB of program
               memory.  mcu = "attiny4", "attiny5", "attiny9", "attiny10",
               "attiny20", "attiny40".

           "avr1"
               This ISA is implemented by the minimal AVR core and supported
               for assembler only.  mcu = "attiny11", "attiny12", "attiny15",
               "attiny28", "at90s1200".

       -mabsdata
           Assume that all data in static storage can be accessed by LDS / STS
           instructions.  This option has only an effect on reduced Tiny
           devices like ATtiny40.  See also the "absdata" AVR Variable
           Attributes,variable attribute.

       -maccumulate-args
           Accumulate outgoing function arguments and acquire/release the
           needed stack space for outgoing function arguments once in function
           prologue/epilogue.  Without this option, outgoing arguments are
           pushed before calling a function and popped afterwards.

           Popping the arguments after the function call can be expensive on
           AVR so that accumulating the stack space might lead to smaller
           executables because arguments need not be removed from the stack
           after such a function call.

           This option can lead to reduced code size for functions that
           perform several calls to functions that get their arguments on the
           stack like calls to printf-like functions.

       -mbranch-cost=cost
           Set the branch costs for conditional branch instructions to cost.
           Reasonable values for cost are small, non-negative integers. The
           default branch cost is 0.

       -mcall-prologues
           Functions prologues/epilogues are expanded as calls to appropriate
           subroutines.  Code size is smaller.

       -mdouble=bits
       -mlong-double=bits
           Set the size (in bits) of the "double" or "long double" type,
           respectively.  Possible values for bits are 32 and 64.  Whether or
           not a specific value for bits is allowed depends on the
           "--with-double=" and "--with-long-double=" configure options
           ("https://gcc.gnu.org/install/configure.html#avr"), and the same
           applies for the default values of the options.

       -mgas-isr-prologues
           Interrupt service routines (ISRs) may use the "__gcc_isr" pseudo
           instruction supported by GNU Binutils.  If this option is on, the
           feature can still be disabled for individual ISRs by means of the
           AVR Function Attributes,,"no_gccisr" function attribute.  This
           feature is activated per default if optimization is on (but not
           with -Og, @pxref{Optimize Options}), and if GNU Binutils support
           PR21683 ("https://sourceware.org/PR21683").

       -mint8
           Assume "int" to be 8-bit integer.  This affects the sizes of all
           types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes,
           and "long long" is 4 bytes.  Please note that this option does not
           conform to the C standards, but it results in smaller code size.

       -mmain-is-OS_task
           Do not save registers in "main".  The effect is the same like
           attaching attribute AVR Function Attributes,,"OS_task" to "main".
           It is activated per default if optimization is on.

       -mn-flash=num
           Assume that the flash memory has a size of num times 64 KiB.

       -mno-interrupts
           Generated code is not compatible with hardware interrupts.  Code
           size is smaller.

       -mrelax
           Try to replace "CALL" resp. "JMP" instruction by the shorter
           "RCALL" resp. "RJMP" instruction if applicable.  Setting -mrelax
           just adds the --mlink-relax option to the assembler's command line
           and the --relax option to the linker's command line.

           Jump relaxing is performed by the linker because jump offsets are
           not known before code is located. Therefore, the assembler code
           generated by the compiler is the same, but the instructions in the
           executable may differ from instructions in the assembler code.

           Relaxing must be turned on if linker stubs are needed, see the
           section on "EIND" and linker stubs below.

       -mrmw
           Assume that the device supports the Read-Modify-Write instructions
           "XCH", "LAC", "LAS" and "LAT".

       -mshort-calls
           Assume that "RJMP" and "RCALL" can target the whole program memory.

           This option is used internally for multilib selection.  It is not
           an optimization option, and you don't need to set it by hand.

       -msp8
           Treat the stack pointer register as an 8-bit register, i.e. assume
           the high byte of the stack pointer is zero.  In general, you don't
           need to set this option by hand.

           This option is used internally by the compiler to select and build
           multilibs for architectures "avr2" and "avr25".  These
           architectures mix devices with and without "SPH".  For any setting
           other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or
           removes this option from the compiler proper's command line,
           because the compiler then knows if the device or architecture has
           an 8-bit stack pointer and thus no "SPH" register or not.

       -mstrict-X
           Use address register "X" in a way proposed by the hardware.  This
           means that "X" is only used in indirect, post-increment or pre-
           decrement addressing.

           Without this option, the "X" register may be used in the same way
           as "Y" or "Z" which then is emulated by additional instructions.
           For example, loading a value with "X+const" addressing with a small
           non-negative "const < 64" to a register Rn is performed as

                   adiw r26, const   ; X += const
                   ld   <Rn>, X        ; <Rn> = *X
                   sbiw r26, const   ; X -= const

       -mtiny-stack
           Only change the lower 8 bits of the stack pointer.

       -mfract-convert-truncate
           Allow to use truncation instead of rounding towards zero for
           fractional fixed-point types.

       -nodevicelib
           Don't link against AVR-LibC's device specific library "lib<mcu>.a".

       -nodevicespecs
           Don't add -specs=device-specs/specs-mcu to the compiler driver's
           command line.  The user takes responsibility for supplying the sub-
           processes like compiler proper, assembler and linker with
           appropriate command line options.  This means that the user has to
           supply her private device specs file by means of -specs=path-to-
           specs-file.  There is no more need for option -mmcu=mcu.

           This option can also serve as a replacement for the older way of
           specifying custom device-specs files that needed -B some-path to
           point to a directory which contains a folder named "device-specs"
           which contains a specs file named "specs-mcu", where mcu was
           specified by -mmcu=mcu.

       -Waddr-space-convert
           Warn about conversions between address spaces in the case where the
           resulting address space is not contained in the incoming address
           space.

       -Wmisspelled-isr
           Warn if the ISR is misspelled, i.e. without __vector prefix.
           Enabled by default.

       "EIND" and Devices with More Than 128 Ki Bytes of Flash

       Pointers in the implementation are 16 bits wide.  The address of a
       function or label is represented as word address so that indirect jumps
       and calls can target any code address in the range of 64 Ki words.

       In order to facilitate indirect jump on devices with more than 128 Ki
       bytes of program memory space, there is a special function register
       called "EIND" that serves as most significant part of the target
       address when "EICALL" or "EIJMP" instructions are used.

       Indirect jumps and calls on these devices are handled as follows by the
       compiler and are subject to some limitations:

       *   The compiler never sets "EIND".

       *   The compiler uses "EIND" implicitly in "EICALL"/"EIJMP"
           instructions or might read "EIND" directly in order to emulate an
           indirect call/jump by means of a "RET" instruction.

       *   The compiler assumes that "EIND" never changes during the startup
           code or during the application. In particular, "EIND" is not
           saved/restored in function or interrupt service routine
           prologue/epilogue.

       *   For indirect calls to functions and computed goto, the linker
           generates stubs. Stubs are jump pads sometimes also called
           trampolines. Thus, the indirect call/jump jumps to such a stub.
           The stub contains a direct jump to the desired address.

       *   Linker relaxation must be turned on so that the linker generates
           the stubs correctly in all situations. See the compiler option
           -mrelax and the linker option --relax.  There are corner cases
           where the linker is supposed to generate stubs but aborts without
           relaxation and without a helpful error message.

       *   The default linker script is arranged for code with "EIND = 0".  If
           code is supposed to work for a setup with "EIND != 0", a custom
           linker script has to be used in order to place the sections whose
           name start with ".trampolines" into the segment where "EIND" points
           to.

       *   The startup code from libgcc never sets "EIND".  Notice that
           startup code is a blend of code from libgcc and AVR-LibC.  For the
           impact of AVR-LibC on "EIND", see the AVR-LibC user manual
           ("http://nongnu.org/avr-libc/user-manual/").

       *   It is legitimate for user-specific startup code to set up "EIND"
           early, for example by means of initialization code located in
           section ".init3". Such code runs prior to general startup code that
           initializes RAM and calls constructors, but after the bit of
           startup code from AVR-LibC that sets "EIND" to the segment where
           the vector table is located.

                   #include <avr/io.h>

                   static void
                   __attribute__((section(".init3"),naked,used,no_instrument_function))
                   init3_set_eind (void)
                   {
                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
                   }

           The "__trampolines_start" symbol is defined in the linker script.

       *   Stubs are generated automatically by the linker if the following
           two conditions are met:

           -<The address of a label is taken by means of the "gs" modifier>
               (short for generate stubs) like so:

                       LDI r24, lo8(gs(<func>))
                       LDI r25, hi8(gs(<func>))

           -<The final location of that label is in a code segment>
               outside the segment where the stubs are located.

       *   The compiler emits such "gs" modifiers for code labels in the
           following situations:

           -<Taking address of a function or code label.>
           -<Computed goto.>
           -<If prologue-save function is used, see -mcall-prologues>
               command-line option.

           -<Switch/case dispatch tables. If you do not want such dispatch>
               tables you can specify the -fno-jump-tables command-line
               option.

           -<C and C++ constructors/destructors called during
           startup/shutdown.>
           -<If the tools hit a "gs()" modifier explained above.>
       *   Jumping to non-symbolic addresses like so is not supported:

                   int main (void)
                   {
                       /* Call function at word address 0x2 */
                       return ((int(*)(void)) 0x2)();
                   }

           Instead, a stub has to be set up, i.e. the function has to be
           called through a symbol ("func_4" in the example):

                   int main (void)
                   {
                       extern int func_4 (void);

                       /* Call function at byte address 0x4 */
                       return func_4();
                   }

           and the application be linked with -Wl,--defsym,func_4=0x4.
           Alternatively, "func_4" can be defined in the linker script.

       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function
       Registers

       Some AVR devices support memories larger than the 64 KiB range that can
       be accessed with 16-bit pointers.  To access memory locations outside
       this 64 KiB range, the content of a "RAMP" register is used as high
       part of the address: The "X", "Y", "Z" address register is concatenated
       with the "RAMPX", "RAMPY", "RAMPZ" special function register,
       respectively, to get a wide address. Similarly, "RAMPD" is used
       together with direct addressing.

       *   The startup code initializes the "RAMP" special function registers
           with zero.

       *   If a AVR Named Address Spaces,named address space other than
           generic or "__flash" is used, then "RAMPZ" is set as needed before
           the operation.

       *   If the device supports RAM larger than 64 KiB and the compiler
           needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is
           reset to zero after the operation.

       *   If the device comes with a specific "RAMP" register, the ISR
           prologue/epilogue saves/restores that SFR and initializes it with
           zero in case the ISR code might (implicitly) use it.

       *   RAM larger than 64 KiB is not supported by GCC for AVR targets.  If
           you use inline assembler to read from locations outside the 16-bit
           address range and change one of the "RAMP" registers, you must
           reset it to zero after the access.

       AVR Built-in Macros

       GCC defines several built-in macros so that the user code can test for
       the presence or absence of features.  Almost any of the following
       built-in macros are deduced from device capabilities and thus triggered
       by the -mmcu= command-line option.

       For even more AVR-specific built-in macros see AVR Named Address Spaces
       and AVR Built-in Functions.

       "__AVR_ARCH__"
           Build-in macro that resolves to a decimal number that identifies
           the architecture and depends on the -mmcu=mcu option.  Possible
           values are:

           2, 25, 3, 31, 35, 4, 5, 51, 6

           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5",
           "avr51", "avr6",

           respectively and

           100, 102, 103, 104, 105, 106, 107

           for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4",
           "avrxmega5", "avrxmega6", "avrxmega7", respectively.  If mcu
           specifies a device, this built-in macro is set accordingly. For
           example, with -mmcu=atmega8 the macro is defined to 4.

       "__AVR_Device__"
           Setting -mmcu=device defines this built-in macro which reflects the
           device's name. For example, -mmcu=atmega8 defines the built-in
           macro "__AVR_ATmega8__", -mmcu=attiny261a defines
           "__AVR_ATtiny261A__", etc.

           The built-in macros' names follow the scheme "__AVR_Device__" where
           Device is the device name as from the AVR user manual. The
           difference between Device in the built-in macro and device in
           -mmcu=device is that the latter is always lowercase.

           If device is not a device but only a core architecture like avr51,
           this macro is not defined.

       "__AVR_DEVICE_NAME__"
           Setting -mmcu=device defines this built-in macro to the device's
           name. For example, with -mmcu=atmega8 the macro is defined to
           "atmega8".

           If device is not a device but only a core architecture like avr51,
           this macro is not defined.

       "__AVR_XMEGA__"
           The device / architecture belongs to the XMEGA family of devices.

       "__AVR_HAVE_ELPM__"
           The device has the "ELPM" instruction.

       "__AVR_HAVE_ELPMX__"
           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.

       "__AVR_HAVE_MOVW__"
           The device has the "MOVW" instruction to perform 16-bit register-
           register moves.

       "__AVR_HAVE_LPMX__"
           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.

       "__AVR_HAVE_MUL__"
           The device has a hardware multiplier.

       "__AVR_HAVE_JMP_CALL__"
           The device has the "JMP" and "CALL" instructions.  This is the case
           for devices with more than 8 KiB of program memory.

       "__AVR_HAVE_EIJMP_EICALL__"
       "__AVR_3_BYTE_PC__"
           The device has the "EIJMP" and "EICALL" instructions.  This is the
           case for devices with more than 128 KiB of program memory.  This
           also means that the program counter (PC) is 3 bytes wide.

       "__AVR_2_BYTE_PC__"
           The program counter (PC) is 2 bytes wide. This is the case for
           devices with up to 128 KiB of program memory.

       "__AVR_HAVE_8BIT_SP__"
       "__AVR_HAVE_16BIT_SP__"
           The stack pointer (SP) register is treated as 8-bit respectively
           16-bit register by the compiler.  The definition of these macros is
           affected by -mtiny-stack.

       "__AVR_HAVE_SPH__"
       "__AVR_SP8__"
           The device has the SPH (high part of stack pointer) special
           function register or has an 8-bit stack pointer, respectively.  The
           definition of these macros is affected by -mmcu= and in the cases
           of -mmcu=avr2 and -mmcu=avr25 also by -msp8.

       "__AVR_HAVE_RAMPD__"
       "__AVR_HAVE_RAMPX__"
       "__AVR_HAVE_RAMPY__"
       "__AVR_HAVE_RAMPZ__"
           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special
           function register, respectively.

       "__NO_INTERRUPTS__"
           This macro reflects the -mno-interrupts command-line option.

       "__AVR_ERRATA_SKIP__"
       "__AVR_ERRATA_SKIP_JMP_CALL__"
           Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
           instructions because of a hardware erratum.  Skip instructions are
           "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".  The second macro is
           only defined if "__AVR_HAVE_JMP_CALL__" is also set.

       "__AVR_ISA_RMW__"
           The device has Read-Modify-Write instructions (XCH, LAC, LAS and
           LAT).

       "__AVR_SFR_OFFSET__=offset"
           Instructions that can address I/O special function registers
           directly like "IN", "OUT", "SBI", etc. may use a different address
           as if addressed by an instruction to access RAM like "LD" or "STS".
           This offset depends on the device architecture and has to be
           subtracted from the RAM address in order to get the respective I/O
           address.

       "__AVR_SHORT_CALLS__"
           The -mshort-calls command line option is set.

       "__AVR_PM_BASE_ADDRESS__=addr"
           Some devices support reading from flash memory by means of "LD*"
           instructions.  The flash memory is seen in the data address space
           at an offset of "__AVR_PM_BASE_ADDRESS__".  If this macro is not
           defined, this feature is not available.  If defined, the address
           space is linear and there is no need to put ".rodata" into RAM.
           This is handled by the default linker description file, and is
           currently available for "avrtiny" and "avrxmega3".  Even more
           convenient, there is no need to use address spaces like "__flash"
           or features like attribute "progmem" and "pgm_read_*".

       "__WITH_AVRLIBC__"
           The compiler is configured to be used together with AVR-Libc.  See
           the --with-avrlibc configure option.

       "__HAVE_DOUBLE_MULTILIB__"
           Defined if -mdouble= acts as a multilib option.

       "__HAVE_DOUBLE32__"
       "__HAVE_DOUBLE64__"
           Defined if the compiler supports 32-bit double resp. 64-bit double.
           The actual layout is specified by option -mdouble=.

       "__DEFAULT_DOUBLE__"
           The size in bits of "double" if -mdouble= is not set.  To test the
           layout of "double" in a program, use the built-in macro
           "__SIZEOF_DOUBLE__".

       "__HAVE_LONG_DOUBLE32__"
       "__HAVE_LONG_DOUBLE64__"
       "__HAVE_LONG_DOUBLE_MULTILIB__"
       "__DEFAULT_LONG_DOUBLE__"
           Same as above, but for "long double" instead of "double".

       "__WITH_DOUBLE_COMPARISON__"
           Reflects the "--with-double-comparison={tristate|bool|libf7}"
           configure option ("https://gcc.gnu.org/install/configure.html#avr")
           and is defined to 2 or 3.

       "__WITH_LIBF7_LIBGCC__"
       "__WITH_LIBF7_MATH__"
       "__WITH_LIBF7_MATH_SYMBOLS__"
           Reflects the "--with-libf7={libgcc|math|math-symbols}"
           configure option
           ("https://gcc.gnu.org/install/configure.html#avr").

       Blackfin Options

       -mcpu=cpu[-sirevision]
           Specifies the name of the target Blackfin processor.  Currently,
           cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
           bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
           bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
           bf547m, bf548m, bf549m, bf561, bf592.

           The optional sirevision specifies the silicon revision of the
           target Blackfin processor.  Any workarounds available for the
           targeted silicon revision are enabled.  If sirevision is none, no
           workarounds are enabled.  If sirevision is any, all workarounds for
           the targeted processor are enabled.  The "__SILICON_REVISION__"
           macro is defined to two hexadecimal digits representing the major
           and minor numbers in the silicon revision.  If sirevision is none,
           the "__SILICON_REVISION__" is not defined.  If sirevision is any,
           the "__SILICON_REVISION__" is defined to be 0xffff.  If this
           optional sirevision is not used, GCC assumes the latest known
           silicon r