[libcxx-commits] [libcxx] [libc++] Improve performance of std::atomic_flag on Windows (PR #163524)

[Alex Guteniev via libcxx-commits]

AlexGuteniev wrote:

I observe that just substituting `WaitOnAddress` where other platforms used FUTEX will work, but that does not take advantage of multiple sizes supported by `WaitOnAddress`.

`WaitOnAddress` can wait on 1, 2, 4, or 8 bytes in both x86-64 and 32-bit x86, so can implement most `atomic<T>::wait` operations directly.

Though taking advantage of varying sizes seems complicated, so maybe not worth doing.

https://github.com/llvm/llvm-project/pull/163524