[clang] [llvm] [IR] Allow integer vector atomicrmw (PR #190716)

[Yonah Goldberg via cfe-commits]

YonahGoldberg wrote:

> If `elementwise` is not specified, and if the vector is smaller than the native size supported by the backend, and the backends don't override them, then AtomicExpand should just expand these with a cmpxchg loop. Otherwise, we don't have builtins for these, so the backend should just fail.

Sounds good, I think this matches my current implementation.

> If `elementwise` is specified, we can fragment the atomic into smaller atomics, like we do for FP vectors.

Well elementwise expansion will be left to a my other PR, but I think the elementwise expansion shouldn't be the default. We should by default treat elementwise atomics as normal atomics.



https://github.com/llvm/llvm-project/pull/190716