[PATCH] D125555: [clang] Add __has_target_feature

[Yaxun Liu via Phabricator via cfe-commits]

yaxunl marked an inline comment as done.
yaxunl added inline comments.


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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.


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  https://reviews.llvm.org/D125555/new/

https://reviews.llvm.org/D125555