[PATCH] D133853: [AST] Add msvc-specific C++11 attributes

[S. B. Tam via Phabricator via cfe-commits]

cpplearner added a comment.

In D133853#3808674 <https://reviews.llvm.org/D133853#3808674>, @aaron.ballman wrote:

> Now I'm wondering why the attribute exists at all. If it's functionally equivalent to `constexpr` as a keyword, what are the use cases for the attribute?

It appears that `[[msvc::constexpr]]` does not make a function `constexpr`, but if `[[msvc::constexpr]]` is used in a function definition //and// in a call to that function, then the annotated function call can be evaluated during constant evaluation: https://godbolt.org/z/3MPTsz6Yn

Apparently this is used to implement constexpr `std::construct_at`, which needs to call placement `operator new`, but the latter is not `constexpr`.


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https://reviews.llvm.org/D133853