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

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gonzalobg wrote:

Thanks, that clarifies it for me.

It seems like `clear_padding` is used to solve two different problems: 
- Implement `valueRepresentationEquals`: the goal of this function is to compare the non-padding bytes of an object.
  * How is this implemented today without `clear_padding`? (Do we just compare the padding bytes and fail more often?)
  * This sounds like it would benefit from being its own intrinsic to perform a byte-wise comparison of objects value representation (or to extract padding byte offsets, etc.). 
- performance tuning: increase the probability of CAS succeeding by keeping padding bytes zeroed in memory.

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