[PATCH] D25403: [CUDA] Mark __libcpp_{isnan, isinf, isfinite} as constexpr.

[Hal Finkel via cfe-commits]

hfinkel added a comment.

In https://reviews.llvm.org/D25403#580444, @jlebar wrote:

> //Let "CE" mean "constexpr-evaluatable". //
>
> libc++ attempts to be backwards-compatible with old versions of clang, right?


Yea, we'd need to ifdef the test for older versions of Clang. I've just summarized my overall proposal in a previous comment.

> Old versions of clang are going to fail, since the builtin will not be CE.  Is the idea to write a test that checks that, if `__builtin_isfinite` is CE, then `__libcpp_isfinite` is also CE?  AIUI you can only test CE-ness by detecting a compile failure failure.
> 
> So is the idea that we would have a shell script that tries to compile a file, checking for CE-ness of the builtins, and,  if and only if that succeeds, then checks for CE-ness of __libcpp_isfinite?




https://reviews.llvm.org/D25403