[PATCH] D151590: [Driver] Add ClangFlags::TargetSpecific to simplify err_drv_unsupported_opt_for_target processing

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

@jansvoboda11

For ELF operating systems (that traditionally use GCC), I think unsupported `-m*` options as errors are very desired as that's the GCC behavior and some configure system will prefer it.

I think x86 `-m*` options are the most possible options to be misused.

  % clang -c --target=aarch64-unknown-linux-gnu -msse4.2 a.c    # warning instead of error, not ideal
  clang: warning: argument unused during compilation: '-msse4.2' [-Wunused-command-line-argument]
  % aarch64-linux-gnu-gcc -msse4.2 a.c
  aarch64-linux-gnu-gcc: error: unrecognized command-line option ‘-msse4.2’

For macOS universal binary builds (`-arch`), I wonder whether we want to refine the current behavior:

  % clang -fdriver-only -c --target=x86_64-apple-darwin -arch arm64 -arch x86_64 -mavx512vl a.c   # no warning
  % clang -fdriver-only -c --target=x86_64-apple-darwin -arch arm64 -mavx512vl a.c   # no -arch x86_64
  clang: warning: argument unused during compilation: '-mavx512vl' [-Wunused-command-line-argument]     # or an error if we make mavx512vl TargetSpecific

The `-arch arm64 -mavx512vl ` situation isn't very common. Though not-carefully-written CMake may make the mistakes: `llvm/lib/Support/BLAKE3/CMakeLists.txt` (fixed by f231829304d15dca0dad8bafe35c4277904db602 <https://reviews.llvm.org/rGf231829304d15dca0dad8bafe35c4277904db602>) and in-tree misuse:  tsan (https://github.com/llvm/llvm-project/issues/63270).
(I think the two use sites are unusual.)


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https://reviews.llvm.org/D151590