man gcc

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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 stage 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 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.

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  -no-canonical-prefixes -pipe  -pass-exit-codes
           -x language  -v  -###  --help[=class[,...]]  --target-help
           --version -wrapper @file -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 -aux-info filename
           -fallow-parameterless-variadic-functions -fno-asm  -fno-builtin
           -fno-builtin-function -fhosted  -ffreestanding -fopenacc -fopenmp
           -fopenmp-simd -fms-extensions -fplan9-extensions -trigraphs
           -traditional -traditional-cpp -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  -fcheck-new
           -fconstexpr-depth=n  -ffriend-injection -fno-elide-constructors
           -fno-enforce-eh-specs -ffor-scope  -fno-for-scope
           -fno-gnu-keywords -fno-implicit-templates
           -fno-implicit-inline-templates -fno-implement-inlines
           -fms-extensions -fno-nonansi-builtins  -fnothrow-opt
           -fno-operator-names -fno-optional-diags  -fpermissive
           -fno-pretty-templates -frepo  -fno-rtti -fsized-deallocation
           -fstats  -ftemplate-backtrace-limit=n -ftemplate-depth=n
           -fno-threadsafe-statics  -fuse-cxa-atexit -fno-weak  -nostdinc++
           -fvisibility-inlines-hidden -fvtable-verify=[std|preinit|none]
           -fvtv-counts -fvtv-debug -fvisibility-ms-compat
           -fext-numeric-literals -Wabi=n  -Wabi-tag  -Wconversion-null
           -Wctor-dtor-privacy -Wdelete-non-virtual-dtor -Wliteral-suffix
           -Wnarrowing -Wnoexcept -Wnon-virtual-dtor  -Wreorder -Weffc++
           -Wstrict-null-sentinel -Wno-non-template-friend  -Wold-style-cast
           -Woverloaded-virtual  -Wno-pmf-conversions -Wsign-promo

       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-protocol  -Wselector -Wstrict-selector-match
           -Wundeclared-selector

       Language Independent Options
           -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
           -fdiagnostics-color=[auto|never|always]
           -fno-diagnostics-show-option -fno-diagnostics-show-caret

       Warning Options
           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors -w
           -Wextra  -Wall  -Waddress  -Waggregate-return
           -Waggressive-loop-optimizations -Warray-bounds -Warray-bounds=n
           -Wbool-compare -Wno-attributes -Wno-builtin-macro-redefined
           -Wc90-c99-compat -Wc99-c11-compat -Wc++-compat -Wc++11-compat
           -Wc++14-compat -Wcast-align  -Wcast-qual -Wchar-subscripts
           -Wclobbered  -Wcomment -Wconditionally-supported -Wconversion
           -Wcoverage-mismatch -Wdate-time -Wdelete-incomplete -Wno-cpp
           -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init
           -Wdisabled-optimization -Wno-discarded-qualifiers
           -Wno-discarded-array-qualifiers -Wno-div-by-zero -Wdouble-promotion
           -Wempty-body  -Wenum-compare -Wno-endif-labels -Werror  -Werror=*
           -Wfatal-errors  -Wfloat-equal  -Wformat  -Wformat=2
           -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral
           -Wformat-security  -Wformat-signedness  -Wformat-y2k
           -Wframe-larger-than=len -Wno-free-nonheap-object -Wjump-misses-init
           -Wignored-qualifiers  -Wincompatible-pointer-types -Wimplicit
           -Wimplicit-function-declaration  -Wimplicit-int -Winit-self
           -Winline  -Wno-int-conversion -Wno-int-to-pointer-cast
           -Wno-invalid-offsetof -Winvalid-pch -Wlarger-than=len
           -Wunsafe-loop-optimizations -Wlogical-op -Wlogical-not-parentheses
           -Wlong-long -Wmain -Wmaybe-uninitialized -Wmemset-transposed-args
           -Wmissing-braces -Wmissing-field-initializers
           -Wmissing-include-dirs -Wno-multichar  -Wnonnull
           -Wnormalized=[none|id|nfc|nfkc]
            -Wodr  -Wno-overflow  -Wopenmp-simd -Woverlength-strings  -Wpacked
           -Wpacked-bitfield-compat  -Wpadded -Wparentheses
           -Wpedantic-ms-format -Wno-pedantic-ms-format -Wpointer-arith
           -Wno-pointer-to-int-cast -Wredundant-decls  -Wno-return-local-addr
           -Wreturn-type  -Wsequence-point  -Wshadow  -Wno-shadow-ivar
           -Wshift-count-negative -Wshift-count-overflow -Wsign-compare
           -Wsign-conversion -Wfloat-conversion -Wsizeof-pointer-memaccess
           -Wsizeof-array-argument -Wstack-protector -Wstack-usage=len
           -Wstrict-aliasing -Wstrict-aliasing=n  -Wstrict-overflow
           -Wstrict-overflow=n
           -Wsuggest-attribute=[pure|const|noreturn|format]
           -Wsuggest-final-types  -Wsuggest-final-methods  -Wsuggest-override
           -Wmissing-format-attribute -Wswitch  -Wswitch-default
           -Wswitch-enum -Wswitch-bool -Wsync-nand -Wsystem-headers
           -Wtrampolines  -Wtrigraphs  -Wtype-limits  -Wundef -Wuninitialized
           -Wunknown-pragmas  -Wno-pragmas -Wunsuffixed-float-constants
           -Wunused  -Wunused-function -Wunused-label  -Wunused-local-typedefs
           -Wunused-parameter -Wno-unused-result -Wunused-value
           -Wunused-variable -Wunused-but-set-parameter
           -Wunused-but-set-variable -Wuseless-cast -Wvariadic-macros
           -Wvector-operation-performance -Wvla -Wvolatile-register-var
           -Wwrite-strings -Wzero-as-null-pointer-constant

       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
           -dletters  -dumpspecs  -dumpmachine  -dumpversion -fsanitize=style
           -fsanitize-recover -fsanitize-recover=style
           -fasan-shadow-offset=number -fsanitize-undefined-trap-on-error
           -fcheck-pointer-bounds -fchkp-check-incomplete-type
           -fchkp-first-field-has-own-bounds -fchkp-narrow-bounds
           -fchkp-narrow-to-innermost-array -fchkp-optimize
           -fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions
           -fchkp-use-static-bounds -fchkp-use-static-const-bounds
           -fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read
           -fchkp-check-read -fchkp-check-write -fchkp-store-bounds
           -fchkp-instrument-calls -fchkp-instrument-marked-only
           -fchkp-use-wrappers -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-noaddr -fdump-unnumbered
           -fdump-unnumbered-links -fdump-translation-unit[-n]
           -fdump-class-hierarchy[-n] -fdump-ipa-all -fdump-ipa-cgraph
           -fdump-ipa-inline -fdump-passes -fdump-statistics -fdump-tree-all
           -fdump-tree-original[-n] -fdump-tree-optimized[-n] -fdump-tree-cfg
           -fdump-tree-alias -fdump-tree-ch -fdump-tree-ssa[-n]
           -fdump-tree-pre[-n] -fdump-tree-ccp[-n] -fdump-tree-dce[-n]
           -fdump-tree-gimple[-raw] -fdump-tree-dom[-n] -fdump-tree-dse[-n]
           -fdump-tree-phiprop[-n] -fdump-tree-phiopt[-n]
           -fdump-tree-forwprop[-n] -fdump-tree-copyrename[-n] -fdump-tree-nrv
           -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra[-n]
           -fdump-tree-forwprop[-n] -fdump-tree-fre[-n]
           -fdump-tree-vtable-verify -fdump-tree-vrp[-n]
           -fdump-tree-storeccp[-n] -fdump-final-insns=file
           -fcompare-debug[=opts]  -fcompare-debug-second
           -feliminate-dwarf2-dups -fno-eliminate-unused-debug-types
           -feliminate-unused-debug-symbols -femit-class-debug-always
           -fenable-kind-pass -fenable-kind-pass=range-list
           -fdebug-types-section -fmem-report-wpa -fmem-report
           -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs
           -fopt-info -fopt-info-options[=file] -frandom-seed=string
           -fsched-verbose=n -fsel-sched-verbose -fsel-sched-dump-cfg
           -fsel-sched-pipelining-verbose -fstack-usage  -ftest-coverage
           -ftime-report -fvar-tracking -fvar-tracking-assignments
           -fvar-tracking-assignments-toggle -g  -glevel  -gtoggle  -gcoff
           -gdwarf-version -ggdb  -grecord-gcc-switches
           -gno-record-gcc-switches -gstabs  -gstabs+  -gstrict-dwarf
           -gno-strict-dwarf -gvms  -gxcoff  -gxcoff+ -gz[=type]
           -fno-merge-debug-strings -fno-dwarf2-cfi-asm
           -fdebug-prefix-map=old=new -femit-struct-debug-baseonly
           -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-
           list] -p  -pg  -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]

       Optimization Options
           -faggressive-loop-optimizations -falign-functions[=n]
           -falign-jumps[=n] -falign-labels[=n] -falign-loops[=n]
           -fassociative-math -fauto-profile -fauto-profile[=path]
           -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize
           -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves
           -fcheck-data-deps -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
           -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-cp-alignment
           -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf
           -fira-algorithm=algorithm -fira-region=region -fira-hoist-pressure
           -fira-loop-pressure -fno-ira-share-save-slots
           -fno-ira-share-spill-slots -fira-verbose=n
           -fisolate-erroneous-paths-dereference
           -fisolate-erroneous-paths-attribute -fivopts
           -fkeep-inline-functions -fkeep-static-consts -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
           -flto-report -flto-report-wpa -fmerge-all-constants
           -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves
           -fmove-loop-invariants -fno-branch-count-reg -fno-defer-pop
           -fno-function-cse -fno-guess-branch-probability -fno-inline
           -fno-math-errno -fno-peephole -fno-peephole2 -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-report -fprofile-correction -fprofile-dir=path
           -fprofile-generate -fprofile-generate=path -fprofile-use
           -fprofile-use=path -fprofile-values -fprofile-reorder-functions
           -freciprocal-math -free -frename-registers -freorder-blocks
           -freorder-blocks-and-partition -freorder-functions
           -frerun-cse-after-loop -freschedule-modulo-scheduled-loops
           -frounding-math -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 -fsignaling-nans
           -fsingle-precision-constant -fsplit-ivs-in-unroller
           -fsplit-wide-types -fssa-phiopt -fstack-protector
           -fstack-protector-all -fstack-protector-strong
           -fstack-protector-explicit -fstdarg-opt -fstrict-aliasing
           -fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp
           -ftree-builtin-call-dce -ftree-ccp -ftree-ch
           -ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop
           -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse
           -ftree-forwprop -ftree-fre -ftree-loop-if-convert
           -ftree-loop-if-convert-stores -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-sink
           -ftree-slsr -ftree-sra -ftree-switch-conversion -ftree-tail-merge
           -ftree-ter -ftree-vectorize -ftree-vrp -funit-at-a-time
           -funroll-all-loops -funroll-loops -funsafe-loop-optimizations
           -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

       Preprocessor Options
           -Aquestion=answer -A-question[=answer] -C  -dD  -dI  -dM  -dN
           -Dmacro[=defn]  -E  -H -idirafter dir -include file  -imacros file
           -iprefix file  -iwithprefix dir -iwithprefixbefore dir  -isystem
           dir -imultilib dir -isysroot dir -M  -MM  -MF  -MG  -MP  -MQ  -MT
           -nostdinc -P  -fdebug-cpp -ftrack-macro-expansion
           -fworking-directory -remap -trigraphs  -undef  -Umacro -Wp,option
           -Xpreprocessor option -no-integrated-cpp

       Assembler Option
           -Wa,option  -Xassembler option

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

       Directory Options
           -Bprefix -Idir -iplugindir=dir -iquotedir -Ldir -specs=file -I-
           --sysroot=dir --no-sysroot-suffix

       Machine Dependent Options
           AArch64 Options -mabi=name  -mbig-endian  -mlittle-endian
           -mgeneral-regs-only -mcmodel=tiny  -mcmodel=small  -mcmodel=large
           -mstrict-align -momit-leaf-frame-pointer
           -mno-omit-leaf-frame-pointer -mtls-dialect=desc
           -mtls-dialect=traditional -mfix-cortex-a53-835769
           -mno-fix-cortex-a53-835769 -mfix-cortex-a53-843419
           -mno-fix-cortex-a53-843419 -march=name  -mcpu=name  -mtune=name

           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

           ARC Options -mbarrel-shifter -mcpu=cpu -mA6 -mARC600 -mA7 -mARC700
           -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr -mea -mno-mpy
           -mmul32x16 -mmul64 -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 -mepilogue-cfi -mlong-calls
           -mmedium-calls -msdata -mucb-mcount -mvolatile-cache -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 -mno-millicode -mmixed-code -mq-class
           -mRcq -mRcw -msize-level=level -mtune=cpu -mmultcost=num
           -munalign-prob-threshold=probability

           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-float
           -mno-apcs-float -mapcs-reentrant  -mno-apcs-reentrant
           -msched-prolog  -mno-sched-prolog -mlittle-endian  -mbig-endian
           -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 -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

           AVR Options -mmcu=mcu -maccumulate-args -mbranch-cost=cost
           -mcall-prologues -mint8 -mn_flash=size -mno-interrupts -mrelax
           -mrmw -mstrict-X -mtiny-stack -nodevicelib -Waddr-space-convert

           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

           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

           FR30 Options -msmall-model -mno-lsim

           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 -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 -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

           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

           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 -mmicromips
           -mno-micromips -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 -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-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 -mfp-exceptions -mno-fp-exceptions
           -mvr4130-align -mno-vr4130-align -msynci -mno-synci
           -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address

           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 -mhwmult= -minrt

           NDS32 Options -mbig-endian -mlittle-endian -mreduced-regs
           -mfull-regs -mcmov -mno-cmov -mperf-ext -mno-perf-ext -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 -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

           Nvidia PTX Options -m32 -m64 -mmainkernel

           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45
           -m10 -mbcopy  -mbcopy-builtin  -mint32  -mno-int16 -mint16
           -mno-int32  -mfloat32  -mno-float64 -mfloat64  -mno-float32
           -mabshi  -mno-abshi -mbranch-expensive  -mbranch-cheap -munix-asm
           -mdec-asm

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

           PowerPC Options See RS/6000 and PowerPC Options.

           RL78 Options -msim -mmul=none -mmul=g13 -mmul=rl78 -m64bit-doubles
           -m32bit-doubles

           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
           -mmfpgpr -mno-mfpgpr -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
           -msingle-float -mdouble-float -msimple-fpu -mstring  -mno-string
           -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  -maltivec -mswdiv
           -msingle-pic-base -mprioritize-restricted-insns=priority
           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
           -mcall-sysv  -mcall-netbsd -maix-struct-return
           -msvr4-struct-return -mabi=abi-type -msecure-plt -mbss-plt
           -mblock-move-inline-limit=num -misel -mno-isel -misel=yes
           -misel=no -mspe -mno-spe -mspe=yes  -mspe=no -mpaired
           -mgen-cell-microcode -mwarn-cell-microcode -mvrsave -mno-vrsave
           -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mfloat-gprs=yes
           -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double -mprototype
           -mno-prototype -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
           -msdata=opt  -mvxworks  -G num  -pthread -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
           -mdirect-move -mno-direct-move -mquad-memory -mno-quad-memory
           -mquad-memory-atomic -mno-quad-memory-atomic -mcompat-align-parm
           -mno-compat-align-parm -mupper-regs-df -mno-upper-regs-df
           -mupper-regs-sf -mno-upper-regs-sf -mupper-regs -mno-upper-regs

           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 -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
           -mtpf-trace -mno-tpf-trace  -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 -m5-64media
           -m5-64media-nofpu -m5-32media  -m5-32media-nofpu -m5-compact
           -m5-compact-nofpu -mb  -ml  -mdalign  -mrelax -mbigtable -mfmovd
           -mhitachi -mrenesas -mno-renesas -mnomacsave -mieee -mno-ieee
           -mbitops  -misize  -minline-ic_invalidate -mpadstruct -mspace
           -mprefergot  -musermode -multcost=number -mdiv=strategy
           -mdivsi3_libfunc=name -mfixed-range=register-range
           -mindexed-addressing -mgettrcost=number -mpt-fixed
           -maccumulate-outgoing-args -minvalid-symbols -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 -pthread

           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 -munaligned-doubles
           -mno-unaligned-doubles -muser-mode  -mno-user-mode -mv8plus
           -mno-v8plus  -mvis  -mno-vis -mvis2  -mno-vis2  -mvis3  -mno-vis3
           -mcbcond -mno-cbcond -mfmaf  -mno-fmaf  -mpopc  -mno-popc
           -mfix-at697f -mfix-ut699

           SPU Options -mwarn-reloc -merror-reloc -msafe-dma -munsafe-dma
           -mbranch-hints -msmall-mem -mlarge-mem -mstdmain
           -mfixed-range=register-range -mea32 -mea64
           -maddress-space-conversion -mno-address-space-conversion
           -mcache-size=cache-size -matomic-updates -mno-atomic-updates

           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  -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 -mmmx  -msse  -msse2 -msse3 -mssse3 -msse4.1
           -msse4.2 -msse4 -mavx -mavx2 -mavx512f -mavx512pf -mavx512er
           -mavx512cd -msha -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma
           -mprefetchwt1 -mclflushopt -mxsavec -mxsaves -msse4a -m3dnow
           -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt -mbmi2 -mfxsr
           -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mmwaitx -mthreads
           -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 -mlarge-data-threshold=num -msse2avx -mfentry -mrecord-mcount
           -mnop-mcount -m8bit-idiv -mavx256-split-unaligned-load
           -mavx256-split-unaligned-store -malign-data=type
           -mstack-protector-guard=guard -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 -mtarget-align
           -mno-target-align -mlongcalls  -mno-longcalls

           zSeries Options See S/390 and zSeries Options.

       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  -finstrument-functions
           -finstrument-functions-exclude-function-list=sym,sym,...
           -finstrument-functions-exclude-file-list=file,file,...  -fno-common
           -fno-ident -fpcc-struct-return  -fpic  -fPIC -fpie -fPIE
           -fno-jump-tables -frecord-gcc-switches -freg-struct-return
           -fshort-enums -fshort-double  -fshort-wchar -fverbose-asm
           -fpack-struct[=n]  -fstack-check -fstack-limit-register=reg
           -fstack-limit-symbol=sym -fno-stack-limit -fsplit-stack
           -fleading-underscore  -ftls-model=model -fstack-reuse=reuse_level
           -ftrapv  -fwrapv  -fbounds-check
           -fvisibility=[default|internal|hidden|protected]
           -fstrict-volatile-bitfields -fsync-libcalls

   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.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
                   f77  f77-cpp-input f95  f95-cpp-input
                   go
                   java

       -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).

       -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.

       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.

       -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.

       --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.

           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 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

       -no-canonical-prefixes
           Do not expand any symbolic links, resolve references to /../ or
           /./, or make the path absolute when generating a relative prefix.

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

       -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 ....

       -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.

           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.  This is the default for C code.  The
               name gnu1x is deprecated.

           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.  This is the default for C++ code.

           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.  The name gnu++1y is deprecated.

           c++1z
               The next revision of the ISO C++ standard, tentatively planned
               for 2017.  Support is highly experimental, and will almost
               certainly change in incompatible ways in future releases.

           gnu++1z
               GNU dialect of -std=c++1z.  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.

       -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))

       -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 v2.0 <http://www.openacc.org/>.  This option
           implies -pthread, and thus is only supported on targets that have
           support for -pthread.

           Note that this is an experimental feature, incomplete, and subject
           to change in future versions of GCC.  See
           <https://gcc.gnu.org/wiki/OpenACC> for more information.

       -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 v4.0 <http://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.

       -fcilkplus
           Enable the usage of Cilk Plus language extension features for
           C/C++.  When the option -fcilkplus is specified, enable the usage
           of the Cilk Plus Language extension features for C/C++.  The
           present implementation follows ABI version 1.2.  This is an
           experimental feature that is only partially complete, and whose
           interface may change in future versions of GCC as the official
           specification changes.  Currently, all features but "_Cilk_for"
           have been implemented.

       -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 but 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++.

       -trigraphs
           Support ISO C trigraphs.  The -ansi option (and -std options for
           strict ISO C conformance) implies -trigraphs.

       -traditional
       -traditional-cpp
           Formerly, these options caused GCC to attempt to emulate a pre-
           standard C compiler.  They are now only supported with the -E
           switch.  The preprocessor continues to support a pre-standard mode.
           See the GNU CPP manual for details.

       -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.

   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 -frepo -O -c firstClass.C

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

       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".

           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 2.  If another
           ABI version is explicitly selected, this defaults to 0.

           The compatibility version is also set by -Wabi=n.

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

       -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).

       -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.

       -fdeduce-init-list
           Enable deduction of a template type parameter as
           "std::initializer_list" from a brace-enclosed initializer list,
           i.e.

                   template <class T> auto forward(T t) -> decltype (realfn (t))
                   {
                     return realfn (t);
                   }

                   void f()
                   {
                     forward({1,2}); // call forward<std::initializer_list<int>>
                   }

           This deduction was implemented as a possible extension to the
           originally proposed semantics for the C++11 standard, but was not
           part of the final standard, so it is disabled by default.  This
           option is deprecated, and may be removed in a future version of
           G++.

       -ffriend-injection
           Inject friend functions into the enclosing namespace, so that they
           are visible outside the scope of the class in which they are
           declared.  Friend functions were documented to work this way in the
           old Annotated C++ Reference Manual.  However, in ISO C++ a friend
           function that is not declared in an enclosing scope can only be
           found using argument dependent lookup.  GCC defaults to the
           standard behavior.

           This option is for compatibility, and may be removed in a future
           release of G++.

       -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.

       -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.

       -ffor-scope
       -fno-for-scope
           If -ffor-scope is specified, the scope of variables declared in a
           for-init-statement is limited to the "for" loop itself, as
           specified by the C++ standard.  If -fno-for-scope is specified, the
           scope of variables declared in a for-init-statement extends to the
           end of the enclosing scope, as was the case in old versions of G++,
           and other (traditional) implementations of C++.

           If neither flag is given, the default is to follow the standard,
           but to allow and give a warning for old-style code that would
           otherwise be invalid, or have different behavior.

       -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.  -ansi implies -fno-gnu-keywords.

       -fno-implicit-templates
           Never emit code for non-inline templates that are instantiated
           implicitly (i.e. by use); only emit code for explicit
           instantiations.

       -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.

       -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.

       -frepo
           Enable automatic template instantiation at link time.  This option
           also implies -fno-implicit-templates.

       -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.

       -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.

       -fstats
           Emit statistics about front-end processing at the end of the
           compilation.  This information is generally only useful to the G++
           development team.

       -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.

       -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.

       -fvtable-verify=[std|preinit|none]
           Turn 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.

       -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++.

       -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 optimization, warning, and code generation options
       have meanings only for C++ programs:

       -Wabi (C, Objective-C, C++ and Objective-C++ only)
           When an explicit -fabi-version=n option is used, causes G++ to warn
           when it generates code that is probably not compatible with the
           vendor-neutral C++ ABI.  Since G++ now defaults to -fabi-version=0,
           -Wabi has no effect unless either an older ABI version is selected
           (with -fabi-version=n) or an older compatibility version is
           selected (with -Wabi=n or -fabi-compat-version=n).

           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.

           -Wabi can also be used with an explicit version number to warn
           about compatibility with a particular -fabi-version level, e.g.
           -Wabi=2 to warn about changes relative to -fabi-version=2.
           Specifying a version number also sets -fabi-compat-version=n.

           The 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.

           It also warns 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.  For example:

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

               "union U" is always passed in memory.

       -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.

       -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.

       -Wliteral-suffix (C++ and Objective-C++ only)
           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 warning is enabled by default.

       -Wnarrowing (C++ and Objective-C++ only)
           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.

           With -std=c++11, -Wno-narrowing suppresses the diagnostic required
           by the standard.  Note that this does not affect the meaning of
           well-formed code; narrowing conversions are still considered ill-
           formed in SFINAE context.

       -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.

       -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.

       -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.

       -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,
           ...).

       The following -W... options are not affected by -Wall.

       -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-templatized friend functions are declared
           within a template.  Since the advent of explicit template
           specification support in G++, if the name of the friend is an
           unqualified-id (i.e., friend foo(int)), the C++ language
           specification demands that the friend declare or define an
           ordinary, nontemplate function.  (Section 14.5.3).  Before G++
           implemented explicit specification, unqualified-ids could be
           interpreted as a particular specialization of a templatized
           function.  Because this non-conforming behavior is no longer the
           default behavior for G++, -Wnon-template-friend allows the compiler
           to check existing code for potential trouble spots and is on by
           default.  This new compiler behavior can be turned off with
           -Wno-non-template-friend, which keeps the conformant compiler code
           but disables the helpful warning.

       -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.

   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++ and Java.  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 ld(1) not to statically link in
           the resulting object file, and allow dyld(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-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.

       -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 means to use color only when the standard error is
           a terminal.  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:caret=01;32:locus=01:quote=01

           where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan,
           01;32 is bold green and 01 is bold. 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.

           "caret="
               SGR substring for caret line.

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

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

       -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.

   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.

       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.

       -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 __.  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) -Wc++11-compat
           -Wc++14-compat -Wchar-subscripts -Wenum-compare (in C/ObjC; this is
           on by default in C++) -Wimplicit-int (C and Objective-C only)
           -Wimplicit-function-declaration (C and Objective-C only) -Wcomment
           -Wformat -Wmain (only for C/ObjC and unless -ffreestanding)
           -Wmaybe-uninitialized -Wmissing-braces (only for C/ObjC) -Wnonnull
           -Wopenmp-simd -Wparentheses -Wpointer-sign -Wreorder -Wreturn-type
           -Wsequence-point -Wsign-compare (only in C++) -Wstrict-aliasing
           -Wstrict-overflow=1 -Wswitch -Wtrigraphs -Wuninitialized
           -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value
           -Wunused-variable -Wvolatile-register-var

           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 -Wempty-body -Wignored-qualifiers
           -Wmissing-field-initializers -Wmissing-parameter-type (C only)
           -Wold-style-declaration (C only) -Woverride-init -Wsign-compare
           -Wtype-limits -Wuninitialized -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 a derived class's
               copy constructor.

       -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.

       -Wcomment
           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.

       -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-gen 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".

       -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.

           -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.

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

           -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.

               NOTE: In Ubuntu 8.10 and later versions this option is enabled
               by default for C, C++, ObjC, ObjC++.  To disable, use
               -Wno-format-security, or disable all format warnings with
               -Wformat=0.  To make format security warnings fatal, specify
               -Werror=format-security.

           -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.

       -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++.

       -Wimplicit-int (C and Objective-C only)
           Warn when a declaration does not specify a type.  This warning is
           enabled by -Wall.

       -Wimplicit-function-declaration (C and Objective-C only)
           Give a warning whenever a function is used before being declared.
           In C99 mode (-std=c99 or -std=gnu99), this warning is enabled by
           default and it is made into an error by -pedantic-errors. This
           warning is also enabled by -Wall.

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

       -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.

       -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.

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

                   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.

       -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 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 ();
                       }
                   }

           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.

           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 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), and about a "return" statement with an expression in a
           function whose return type is "void".

           For C++, a function without return type always produces a
           diagnostic message, even when -Wno-return-type is specified.  The
           only exceptions are "main" and functions defined in system headers.

           This warning is enabled by -Wall.

       -Wshift-count-negative
           Warn if shift count is negative. This warning is enabled by
           default.

       -Wshift-count-overflow
           Warn if shift count >= width of type. This warning is enabled by
           default.

       -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.

       -Wswitch-bool
           Warn whenever a "switch" statement has an index of 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.

       -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.

       -Wtrigraphs
           Warn if any trigraphs are encountered that might change the meaning
           of the program (trigraphs within comments are not warned about).
           This warning is enabled by -Wall.

       -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 variable or non-constant static variable is
           unused aside from its declaration.  This warning is enabled by
           -Wall.

           To suppress this warning use the "unused" attribute.

       -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 or if a variable may be clobbered by a "setjmp" call.
           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 or clobbered
           elements of structure, union or array variables as well as for
           variables that are uninitialized or clobbered 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 depends 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.

       -Wmaybe-uninitialized
           For an automatic 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 made optional
           because GCC is not smart enough to see all the reasons why the code
           might be 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".  These warnings as well are
           possible only in optimizing compilation.

           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.

       -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 -fstrict-overflow is active.  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,  with -fstrict-overflow, 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 -fstrict-overflow is in effect, 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.

       -Wsuggest-attribute=[pure|const|noreturn|format]
           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
               Warn about functions that might be candidates for attributes
               "pure", "const" or "noreturn".  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-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.

       -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.

       -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.

       -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.

       -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.

       -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.

       -Wundef
           Warn if an undefined identifier is evaluated in an "#if" directive.

       -Wno-endif-labels
           Do not warn whenever an "#else" or an "#endif" are followed by
           text.

       -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.

       -Wno-shadow-ivar (Objective-C only)
           Do not warn whenever a local variable shadows an instance variable
           in an Objective-C method.

       -Wlarger-than=len
           Warn whenever an object of larger than len bytes is defined.

       -Wframe-larger-than=len
           Warn if the size of a function frame is larger than len bytes.  The
           computation done to determine the stack frame size is approximate
           and not conservative.  The actual requirements may be somewhat
           greater than len 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.

       -Wno-free-nonheap-object
           Do not warn when attempting to free an object that was not
           allocated on the heap.

       -Wstack-usage=len
           Warn if the stack usage of a function might be larger than len
           bytes.  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

       -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.

       -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.

       -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__".

       -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.

       -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.

       -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.

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

       -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.

       -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.

       -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.

       -Wdate-time
           Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are
           encountered as they might prevent bit-wise-identical reproducible
           compilations.

       -Wdelete-incomplete (C++ and Objective-C++ only)
           Warn when deleting a pointer to incomplete type, which may cause
           undefined behavior at runtime.  This warning is enabled by default.

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

       -Wempty-body
           Warn if an empty body occurs in an "if", "else" or "do while"
           statement.  This warning is also enabled by -Wextra.

       -Wenum-compare
           Warn about a comparison between values of different enumerated
           types.  In C++ enumeral mismatches in conditional expressions are
           also diagnosed and the warning is enabled by default.  In C this
           warning is enabled by -Wall.

       -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.  This warning is also enabled by -Wextra; to get the
           other warnings of -Wextra without this warning, use -Wextra
           -Wno-sign-compare.

       -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.

       -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.

       -Wsizeof-pointer-memaccess
           Warn for suspicious length parameters to certain string and memory
           built-in functions if the argument uses "sizeof".  This warning
           warns e.g.  about "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));".  This warning is enabled by
           -Wall.

       -Wsizeof-array-argument
           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-transposed-args
           Warn for suspicious calls to the "memset" built-in function, if the
           second argument is not zero and the third argument is zero.  This
           warns e.g.@ about "memset (buf, sizeof buf, 0)" where most probably
           "memset (buf, 0, sizeof buf)" was meant instead.  The diagnostics
           is only emitted if the third argument is literal zero.  If it is
           some expression that is folded to zero, a cast of zero to some
           type, etc., it is far less likely that the user has mistakenly
           exchanged the arguments 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.

       -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.

       -Wlogical-not-parentheses
           Warn about logical not used on the left hand side operand of a
           comparison.  This option does not warn if the RHS operand is of a
           boolean type.  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-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.

       -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 either 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-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.  Requires -flto-odr-type-merging to be enabled.
           Enabled by default.

       -Wopenmp-simd
           Warn if the vectorizer cost model overrides the OpenMP or the Cilk
           Plus 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.

       -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;
                   };

       -Wpacked-bitfield-compat
           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on
           bit-fields of type "char".  This has been 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.

       -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.

       -Wnested-externs (C and Objective-C only)
           Warn if an "extern" declaration is encountered within a function.

       -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.

       -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.

       -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.

       -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 can't
           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.

       -Wvarargs
           Warn upon questionable usage of the macros used to handle variable
           arguments like "va_start".  This is default.  To inhibit the
           warning messages, use -Wno-varargs.

       -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.

       -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.

       -Wvla
           Warn if variable length array is used in the code.  -Wno-vla
           prevents the -Wpedantic warning of the variable length array.

       -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-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.

   Options for Debugging Your Program or GCC
       GCC has various special options that are used for debugging either your
       program or GCC:

       -g  Produce debugging information in the operating system's native
           format (stabs, COFF, XCOFF, or DWARF 2).  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).

           GCC allows you to use -g with -O.  The shortcuts taken by optimized
           code may occasionally produce surprising results: 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 proves possible to debug optimized output.  This
           makes it reasonable to use the optimizer for programs that might
           have bugs.

           The following options are useful when GCC is generated with the
           capability for more than one debugging format.

       -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.

       -ggdb
           Produce debugging information for use by GDB.  This means to use
           the most expressive format available (DWARF 2, stabs, or the native
           format if neither of those are supported), including GDB extensions
           if at all possible.

       -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.

       -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 or SDB.  On System V Release 4 systems this option requires
           the GNU assembler.

       -feliminate-unused-debug-symbols
           Produce debugging information in stabs format (if that is
           supported), for only symbols that are actually used.

       -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.

       -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 sections 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.

       -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.

       -gcoff
           Produce debugging information in COFF format (if that is
           supported).  This is the format used by SDB on most System V
           systems prior to System V Release 4.

       -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.

       -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.

       -grecord-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.  See also
           -frecord-gcc-switches for another way of storing compiler options
           into the object file.  This is the default.

       -gno-record-gcc-switches
           Disallow appending command-line options to the DW_AT_producer
           attribute in DWARF debugging information.

       -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.

       -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.

       -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
       -gcofflevel
       -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.

           -gdwarf-2 does not accept a concatenated debug level, because GCC
           used to support an option -gdwarf that meant to generate debug
           information in version 1 of the DWARF format (which is very
           different from version 2), and it would have been too confusing.
           That debug format is long obsolete, but the option cannot be
           changed now.  Instead use an additional -glevel option to change
           the debug level for DWARF.

       -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.

       -fsanitize=address
           Enable AddressSanitizer, a fast memory error detector.  Memory
           access instructions are instrumented to detect out-of-bounds and
           use-after-free bugs.  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 instrumended program.
           See
           <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags>
           for a list of supported options.

       -fsanitize=kernel-address
           Enable AddressSanitizer for Linux kernel.  See
           <https://github.com/google/kasan/wiki> for more details.

       -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.

       -fsanitize=leak
           Enable LeakSanitizer, a memory leak detector.  This option only
           matters for linking of executables and if neither
           -fsanitize=address nor -fsanitize=thread is used.  In that case 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.

       -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.

           -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=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.

           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-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 and -fsanitize=kernel-address.  For
           these sanitizers error recovery is turned on by default.
           -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.

           Syntax without explicit opts parameter is deprecated.  It is
           equivalent to

                   -fsanitize-recover=undefined,float-cast-overflow,float-divide-by-zero

           Similarly -fno-sanitize-recover is equivalent to

                   -fno-sanitize-recover=undefined,float-cast-overflow,float-divide-by-zero

       -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.

       -fcheck-pointer-bounds
           Enable Pointer Bounds Checker instrumentation.  Each memory
           reference is instrumented with checks of the pointer used for
           memory access against bounds associated with that pointer.

           Currently there is only an implementation for Intel MPX available,
           thus x86 target and -mmpx are required to enable this feature.
           MPX-based instrumentation requires a runtime library to enable MPX
           in hardware and handle bounds violation signals.  By default when
           -fcheck-pointer-bounds and -mmpx options are used to link a
           program, the GCC driver links against the libmpx runtime library
           and libmpxwrappers library.  It also passes '-z bndplt' to a linker
           in case it supports this option (which is checked on libmpx
           configuration).  Note that old versions of linker may ignore
           option.  Gold linker doesn't support '-z bndplt' option.  With no
           '-z bndplt' support in linker all calls to dynamic libraries lose
           passed bounds reducing overall protection level.  It's highly
           recommended to use linker with '-z bndplt' support.  In case such
           linker is not available it is adviced to always use
           -static-libmpxwrappers for better protection level or use -static
           to completely avoid external calls to dynamic libraries.  MPX-based
           instrumentation may be used for debugging and also may be included
           in production code to increase program security.  Depending on
           usage, you may have different requirements for the runtime library.
           The current version of the MPX runtime library is more oriented for
           use as a debugging tool.  MPX runtime library usage implies
           -lpthread.  See also -static-libmpx.  The runtime library  behavior
           can be influenced using various CHKP_RT_* environment variables.
           See
           <https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler>
           for more details.

           Generated instrumentation may be controlled by various -fchkp-*
           options and by the "bnd_variable_size" structure field attribute
           and "bnd_legacy", and "bnd_instrument" function attributes.  GCC
           also provides a number of built-in functions for controlling the
           Pointer Bounds Checker.

       -fchkp-check-incomplete-type
           Generate pointer bounds checks for variables with incomplete type.
           Enabled by default.

       -fchkp-narrow-bounds
           Controls bounds used by Pointer Bounds Checker for pointers to
           object fields.  If narrowing is enabled then field bounds are used.
           Otherwise object bounds are used.  See also
           -fchkp-narrow-to-innermost-array and
           -fchkp-first-field-has-own-bounds.  Enabled by default.

       -fchkp-first-field-has-own-bounds
           Forces Pointer Bounds Checker to use narrowed bounds for the
           address of the first field in the structure.  By default a pointer
           to the first field has the same bounds as a pointer to the whole
           structure.

       -fchkp-narrow-to-innermost-array
           Forces Pointer Bounds Checker to use bounds of the innermost arrays
           in case of nested static array access.  By default this option is
           disabled and bounds of the outermost array are used.

       -fchkp-optimize
           Enables Pointer Bounds Checker optimizations.  Enabled by default
           at optimization levels -O, -O2, -O3.

       -fchkp-use-fast-string-functions
           Enables use of *_nobnd versions of string functions (not copying
           bounds) by Pointer Bounds Checker.  Disabled by default.

       -fchkp-use-nochk-string-functions
           Enables use of *_nochk versions of string functions (not checking
           bounds) by Pointer Bounds Checker.  Disabled by default.

       -fchkp-use-static-bounds
           Allow Pointer Bounds Checker to generate static bounds holding
           bounds of static variables.  Enabled by default.

       -fchkp-use-static-const-bounds
           Use statically-initialized bounds for constant bounds instead of
           generating them each time they are required.  By default enabled
           when -fchkp-use-static-bounds is enabled.

       -fchkp-treat-zero-dynamic-size-as-infinite
           With this option, objects with incomplete type whose dynamically-
           obtained size is zero are treated as having infinite size instead
           by Pointer Bounds Checker.  This option may be helpful if a program
           is linked with a library missing size information for some symbols.
           Disabled by default.

       -fchkp-check-read
           Instructs Pointer Bounds Checker to generate checks for all read
           accesses to memory.  Enabled by default.

       -fchkp-check-write
           Instructs Pointer Bounds Checker to generate checks for all write
           accesses to memory.  Enabled by default.

       -fchkp-store-bounds
           Instructs Pointer Bounds Checker to generate bounds stores for
           pointer writes.  Enabled by default.

       -fchkp-instrument-calls
           Instructs Pointer Bounds Checker to pass pointer bounds to calls.
           Enabled by default.

       -fchkp-instrument-marked-only
           Instructs Pointer Bounds Checker to instrument only functions
           marked with the "bnd_instrument" attribute.  Disabled by default.

       -fchkp-use-wrappers
           Allows Pointer Bounds Checker to replace calls to built-in
           functions with calls to wrapper functions.  When
           -fchkp-use-wrappers is used to link a program, the GCC driver
           automatically links against libmpxwrappers.  See also
           -static-libmpxwrappers.  Enabled by default.

       -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 side-
           effect compiler outputs to files or to the standard output.  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.

       -feliminate-dwarf2-dups
           Compress DWARF 2 debugging information by eliminating duplicated
           information about each symbol.  This option only makes sense when
           generating DWARF 2 debugging information with -gdwarf-2.

       -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 2.

       -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 2.

       -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 2.

       -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 in directory old, record debugging information
           describing them as in new instead.

       -fno-dwarf2-cfi-asm
           Emit DWARF 2 unwind info as compiler generated ".eh_frame" section
           instead of using GAS ".cfi_*" directives.

       -p  Generate extra code to write profile information suitable for the
           analysis program prof.  You must use this option when compiling the
           source files you want data about, and you must also use it when
           linking.

       -pg Generate extra code to write profile information suitable for the
           analysis program gprof.  You must use this option when compiling
           the source files you want data about, and you must also use it when
           linking.

       -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.

       -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.

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