yaxunl marked an inline comment as done.
yaxunl added inline comments.
================
Comment at: clang/docs/LanguageExtensions.rst:275
+ // On amdgcn target
+ #if __has_target_feature("s-memtime-inst")
+ x = __builtin_amdgcn_s_memtime();
----------------
tra wrote:
> Do you have a better example? This particular case could've been handled by
> existing `__has_builtin()`.
>
> While I could see usefulness of checking features (e.g. for CUDA/NVPTX it
> could be used to chose inline assembly supported only by newer PTX versions,
> but even then that choice could be made using existing methods, even if they
> are not always direct (e.g. by using CUDA_VERSION as a proxy for "new enough
> PTX version").
>
`__has_builtin` returns 1 as long as the builtin is known to clang, even if the
builtin is not supported by the target CPU. This is because the required target
feature for a builtin is in ASTContext, whereas `__has_builtin` is evaluated in
preprocessor, where the information is not known.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D125555/new/
https://reviews.llvm.org/D125555
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