[PATCH] D66364: Diagnose use of _Thread_local as an extension when appropriate

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

`_Thread_local` is a reserved identifier; we generally don't produce extension warnings for uses of reserved identifiers. (Eg, there's no warning for `_Atomic` in C++ or `_Bool` in C89, and no warning for uses of `__type_traits` or `__builtins`.)

But I note that we *do* warn for some of these already (eg, `_Generic`, `_Static_assert`, `_Alignas`, and `_Alignof` get a warning). We should choose a rule and apply it consistently.

What's the motivation for warning on this? Maybe that can inform whether these warnings are useful in general.


Repository:
  rC Clang

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  https://reviews.llvm.org/D66364/new/

https://reviews.llvm.org/D66364