Fix `atomic_ref::is_lock_free()` on x64

microsoft / STL

MSVC's implementation of the C++ Standard Library.

Other

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Closed StephanTLavavej closed 1 day ago

StephanTLavavej commented 1 week ago

Fixes #4728.

For !_ATOMIC_HAS_DCAS:

If we're is_always_lock_free (power of two, at most 1 pointer), return true.
Otherwise, we have to be _Is_potentially_lock_free (power of two, at most 2 pointers) and have cmpxchg16b.

StephanTLavavej commented 3 days ago

I'm speculatively mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.