[PATCH] D136036: [Clang] Add __has_builtin_constexpr support

[Evgeny Shulgin via Phabricator via cfe-commits]

Izaron added a comment.

A builtin is considered "constexpr" if it has `E` in its attributes in `Builtins.def`.

The list of constexpr builtins is consistent, the code in `ExprConstant.cpp` (where the actual constant evaluation of builtins is being done) guards it.
If builtin is not marked with `E`, it surely won't be evaluated, and vice versa - if builtin is marked but there is no code for evaluating it, there is a `llvm_unreachable`.

This macro will be needed because we are making constexpr `<cmath>` and `<cstdlib>`. We will conditionally make the functions constexpr until all supported compilers have full support.

We had a discussion where we found out that we need `__has_builtin_constexpr`: https://discourse.llvm.org/t/how-do-we-plan-to-make-constexpr-cmath-and-cstdlib/65930 Please read it if you wonder why we need it =) Thank you for your attention!


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D136036/new/

https://reviews.llvm.org/D136036