[libcxx-commits] [clang] [libcxx] [clang] Add builtin to clear padding bytes (prework for P0528R3) (PR #75371)

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gonzalobg wrote:

How would we use this intrinsic to implement a compare and exchange loop for `atomic_ref`? 

For the compare to succeed, the values of the padding bytes of the `expected` value passed in would need to match the values of that padding bytes in memory, which may not be zero.

https://github.com/llvm/llvm-project/pull/75371