zig cc: integration with -m flags #4912
Description
Extracted from #4784.
As you can see there are quite a few -m flags that control CPU features:
flagpd1("m16"),
flagpd1("m32"),
flagpd1("m3dnow"),
flagpd1("m3dnowa"),
flagpd1("m64"),
flagpd1("m80387"),
flagpd1("mabi=ieeelongdouble"),
flagpd1("mabicalls"),
flagpd1("madx"),
flagpd1("maes"),
sepd1("main-file-name"),
flagpd1("malign-double"),
flagpd1("maltivec"),
flagpd1("marm"),
flagpd1("masm-verbose"),
flagpd1("massembler-fatal-warnings"),
flagpd1("massembler-no-warn"),
flagpd1("matomics"),
flagpd1("mavx"),
flagpd1("mavx2"),
flagpd1("mavx512bf16"),
flagpd1("mavx512bitalg"),
flagpd1("mavx512bw"),
flagpd1("mavx512cd"),
flagpd1("mavx512dq"),
flagpd1("mavx512er"),
flagpd1("mavx512f"),
flagpd1("mavx512ifma"),
flagpd1("mavx512pf"),
flagpd1("mavx512vbmi"),
flagpd1("mavx512vbmi2"),
flagpd1("mavx512vl"),
flagpd1("mavx512vnni"),
flagpd1("mavx512vp2intersect"),
flagpd1("mavx512vpopcntdq"),
flagpd1("fmax-identifier-length"),
flagpd1("fno-max-identifier-length"),
flagpd1("mbackchain"),
flagpd1("mbig-endian"),
flagpd1("mbmi"),
flagpd1("mbmi2"),
flagpd1("mbranch-likely"),
flagpd1("mbranch-target-enforce"),
flagpd1("mbranches-within-32B-boundaries"),
flagpd1("mbulk-memory"),
flagpd1("mcheck-zero-division"),
flagpd1("mcldemote"),
flagpd1("mclflushopt"),
flagpd1("mclwb"),
flagpd1("mclzero"),
flagpd1("mcmodel=medany"),
flagpd1("mcmodel=medlow"),
flagpd1("mcmpb"),
flagpd1("mcmse"),
sepd1("mcode-model"),
flagpd1("mcode-object-v3"),
flagpd1("mconstant-cfstrings"),
flagpd1("mconstructor-aliases"),
flagpd1("mcpu=?"),
flagpd1("mcrbits"),
flagpd1("mcrc"),
flagpd1("mcumode"),
flagpd1("mcx16"),
sepd1("mdebug-pass"),
flagpd1("mdirect-move"),
flagpd1("mdisable-tail-calls"),
flagpd1("mdouble-float"),
flagpd1("mdsp"),
flagpd1("mdspr2"),
sepd1("meabi"),
flagpd1("membedded-data"),
flagpd1("menable-no-infs"),
flagpd1("menable-no-nans"),
flagpd1("menable-unsafe-fp-math"),
flagpd1("menqcmd"),
flagpd1("fmerge-constants"),
flagpd1("fno-merge-constants"),
flagpd1("mexception-handling"),
flagpd1("mexecute-only"),
flagpd1("mextern-sdata"),
flagpd1("mf16c"),
flagpd1("mfancy-math-387"),
flagpd1("mfentry"),
flagpd1("mfix-and-continue"),
flagpd1("mfix-cortex-a53-835769"),
flagpd1("mfloat128"),
sepd1("mfloat-abi"),
flagpd1("mfma"),
flagpd1("mfma4"),
flagpd1("mfp32"),
flagpd1("mfp64"),
sepd1("mfpmath"),
flagpd1("mfprnd"),
flagpd1("mfpxx"),
flagpd1("mfsgsbase"),
flagpd1("mfxsr"),
flagpd1("mgeneral-regs-only"),
flagpd1("mgfni"),
flagpd1("mginv"),
flagpd1("mglibc"),
flagpd1("mglobal-merge"),
flagpd1("mgpopt"),
flagpd1("mhard-float"),
flagpd1("mhvx"),
flagpd1("mhtm"),
flagpd1("miamcu"),
flagpd1("mieee-fp"),
flagpd1("mieee-rnd-near"),
flagpd1("migrate"),
flagpd1("no-finalize-removal"),
flagpd1("no-ns-alloc-error"),
flagpd1("mimplicit-float"),
flagpd1("mincremental-linker-compatible"),
flagpd1("minline-all-stringops"),
flagpd1("minvariant-function-descriptors"),
flagpd1("minvpcid"),
flagpd1("mips1"),
flagpd1("mips16"),
flagpd1("mips2"),
flagpd1("mips3"),
flagpd1("mips32"),
flagpd1("mips32r2"),
flagpd1("mips32r3"),
flagpd1("mips32r5"),
flagpd1("mips32r6"),
flagpd1("mips4"),
flagpd1("mips5"),
flagpd1("mips64"),
flagpd1("mips64r2"),
flagpd1("mips64r3"),
flagpd1("mips64r5"),
flagpd1("mips64r6"),
flagpd1("misel"),
flagpd1("mkernel"),
flagpd1("mldc1-sdc1"),
sepd1("mlimit-float-precision"),
sepd1("mlink-bitcode-file"),
sepd1("mlink-builtin-bitcode"),
sepd1("mlink-cuda-bitcode"),
flagpd1("mlittle-endian"),
sepd1("mllvm"),
flagpd1("mlocal-sdata"),
flagpd1("mlong-calls"),
flagpd1("mlong-double-128"),
flagpd1("mlong-double-64"),
flagpd1("mlong-double-80"),
flagpd1("mlongcall"),
flagpd1("mlwp"),
flagpd1("mlzcnt"),
flagpd1("mmadd4"),
flagpd1("mmemops"),
flagpd1("mmfcrf"),
flagpd1("mmfocrf"),
flagpd1("mmicromips"),
flagpd1("mmmx"),
flagpd1("mmovbe"),
flagpd1("mmovdir64b"),
flagpd1("mmovdiri"),
flagpd1("mmpx"),
flagpd1("mms-bitfields"),
flagpd1("mmsa"),
flagpd1("mmt"),
flagpd1("mmultivalue"),
flagpd1("mmutable-globals"),
flagpd1("mmwaitx"),
flagpd1("mno-3dnow"),
flagpd1("mno-3dnowa"),
flagpd1("mno-80387"),
flagpd1("mno-abicalls"),
flagpd1("mno-adx"),
flagpd1("mno-aes"),
flagpd1("mno-altivec"),
flagpd1("mno-atomics"),
flagpd1("mno-avx"),
flagpd1("mno-avx2"),
flagpd1("mno-avx512bf16"),
flagpd1("mno-avx512bitalg"),
flagpd1("mno-avx512bw"),
flagpd1("mno-avx512cd"),
flagpd1("mno-avx512dq"),
flagpd1("mno-avx512er"),
flagpd1("mno-avx512f"),
flagpd1("mno-avx512ifma"),
flagpd1("mno-avx512pf"),
flagpd1("mno-avx512vbmi"),
flagpd1("mno-avx512vbmi2"),
flagpd1("mno-avx512vl"),
flagpd1("mno-avx512vnni"),
flagpd1("mno-avx512vp2intersect"),
flagpd1("mno-avx512vpopcntdq"),
flagpd1("mno-backchain"),
flagpd1("mno-bmi"),
flagpd1("mno-bmi2"),
flagpd1("mno-branch-likely"),
flagpd1("mno-bulk-memory"),
flagpd1("mno-check-zero-division"),
flagpd1("mno-cldemote"),
flagpd1("mno-clflushopt"),
flagpd1("mno-clwb"),
flagpd1("mno-clzero"),
flagpd1("mno-cmpb"),
flagpd1("mno-code-object-v3"),
flagpd1("mno-constant-cfstrings"),
flagpd1("mno-crbits"),
flagpd1("mno-crc"),
flagpd1("mno-cumode"),
flagpd1("mno-cx16"),
flagpd1("mno-dsp"),
flagpd1("mno-dspr2"),
flagpd1("mno-embedded-data"),
flagpd1("mno-enqcmd"),
flagpd1("mno-exception-handling"),
flagpd1("mnoexecstack"),
flagpd1("mno-execute-only"),
flagpd1("mno-extern-sdata"),
flagpd1("mno-f16c"),
flagpd1("mno-fix-cortex-a53-835769"),
flagpd1("mno-float128"),
flagpd1("mno-fma"),
flagpd1("mno-fma4"),
flagpd1("mno-fprnd"),
flagpd1("mno-fsgsbase"),
flagpd1("mno-fxsr"),
flagpd1("mno-gfni"),
flagpd1("mno-ginv"),
flagpd1("mno-global-merge"),
flagpd1("mno-gpopt"),
flagpd1("mno-hvx"),
flagpd1("mno-htm"),
flagpd1("mno-iamcu"),
flagpd1("mno-implicit-float"),
flagpd1("mno-incremental-linker-compatible"),
flagpd1("mno-inline-all-stringops"),
flagpd1("mno-invariant-function-descriptors"),
flagpd1("mno-invpcid"),
flagpd1("mno-isel"),
flagpd1("mno-ldc1-sdc1"),
flagpd1("mno-local-sdata"),
flagpd1("mno-long-calls"),
flagpd1("mno-longcall"),
flagpd1("mno-lwp"),
flagpd1("mno-lzcnt"),
flagpd1("mno-madd4"),
flagpd1("mno-memops"),
flagpd1("mno-mfcrf"),
flagpd1("mno-mfocrf"),
flagpd1("mno-micromips"),
flagpd1("mno-mips16"),
flagpd1("mno-mmx"),
flagpd1("mno-movbe"),
flagpd1("mno-movdir64b"),
flagpd1("mno-movdiri"),
flagpd1("mno-movt"),
flagpd1("mno-mpx"),
flagpd1("mno-ms-bitfields"),
flagpd1("mno-msa"),
flagpd1("mno-mt"),
flagpd1("mno-multivalue"),
flagpd1("mno-mutable-globals"),
flagpd1("mno-mwaitx"),
flagpd1("mno-neg-immediates"),
flagpd1("mno-nontrapping-fptoint"),
flagpd1("mno-nvj"),
flagpd1("mno-nvs"),
flagpd1("mno-odd-spreg"),
flagpd1("mno-omit-leaf-frame-pointer"),
flagpd1("mno-outline"),
flagpd1("mno-packed-stack"),
flagpd1("mno-packets"),
flagpd1("mno-pascal-strings"),
flagpd1("mno-pclmul"),
flagpd1("mno-pconfig"),
flagpd1("mno-pie-copy-relocations"),
flagpd1("mno-pku"),
flagpd1("mno-popcnt"),
flagpd1("mno-popcntd"),
flagpd1("mno-power8-vector"),
flagpd1("mno-power9-vector"),
flagpd1("mno-prefetchwt1"),
flagpd1("mno-prfchw"),
flagpd1("mno-ptwrite"),
flagpd1("mno-pure-code"),
flagpd1("mno-qpx"),
flagpd1("mno-rdpid"),
flagpd1("mno-rdrnd"),
flagpd1("mno-rdseed"),
flagpd1("mno-red-zone"),
flagpd1("mno-reference-types"),
flagpd1("mno-relax"),
flagpd1("mno-relax-all"),
flagpd1("mno-relax-pic-calls"),
flagpd1("mno-restrict-it"),
flagpd1("mno-retpoline"),
flagpd1("mno-retpoline-external-thunk"),
flagpd1("mno-rtd"),
flagpd1("mno-rtm"),
flagpd1("mno-sahf"),
flagpd1("mno-save-restore"),
flagpd1("mno-sgx"),
flagpd1("mno-sha"),
flagpd1("mno-shstk"),
flagpd1("mno-sign-ext"),
flagpd1("mno-simd128"),
flagpd1("mno-soft-float"),
flagpd1("mno-spe"),
flagpd1("mno-speculative-load-hardening"),
flagpd1("mno-sram-ecc"),
flagpd1("mno-sse"),
flagpd1("mno-sse2"),
flagpd1("mno-sse3"),
flagpd1("mno-sse4"),
flagpd1("mno-sse4.1"),
flagpd1("mno-sse4.2"),
flagpd1("mno-sse4a"),
flagpd1("mno-ssse3"),
flagpd1("mno-stack-arg-probe"),
flagpd1("mno-stackrealign"),
flagpd1("mno-tail-call"),
flagpd1("mno-tbm"),
flagpd1("mno-thumb"),
flagpd1("mno-tls-direct-seg-refs"),
flagpd1("mno-unaligned-access"),
flagpd1("mno-unimplemented-simd128"),
flagpd1("mno-vaes"),
flagpd1("mno-virt"),
flagpd1("mno-vpclmulqdq"),
flagpd1("mno-vsx"),
flagpd1("mno-vx"),
flagpd1("mno-vzeroupper"),
flagpd1("mno-waitpkg"),
flagpd1("mno-warn-nonportable-cfstrings"),
flagpd1("mno-wavefrontsize64"),
flagpd1("mno-wbnoinvd"),
flagpd1("mno-x87"),
flagpd1("mno-xgot"),
flagpd1("mno-xnack"),
flagpd1("mno-xop"),
flagpd1("mno-xsave"),
flagpd1("mno-xsavec"),
flagpd1("mno-xsaveopt"),
flagpd1("mno-xsaves"),
flagpd1("mno-zero-initialized-in-bss"),
flagpd1("mno-zvector"),
flagpd1("mnocrc"),
flagpd1("mno-direct-move"),
flagpd1("mnontrapping-fptoint"),
flagpd1("mnop-mcount"),
flagpd1("mno-crypto"),Currently the way these work is they will be forwarded to clang without zig being aware of them. The forwarding happens after zig specifies the CPU features flags, so I believe there is not currently a correctness problem here. However, zig does have CPU features awareness, and when these flags are specified, zig's idea of what CPU features are enabled can be incorrect (even though it ends up passing correct flags to clang). I can't think of this causing an actual problem, but it's an "invariant" that is violated, which could have unforeseen consequences in the future. For example, one thing is that these flags will cause false negatives in the cache (zig could have cached something but did not).
Hopefully there is someway to solve these in bulk; although if maintaining a manual mapping of these flags to CPU features is what is required, it would still be workable.