[llvm] AtomicExpand: Preserve metadata when expanding partword RMW (PR #89769)

[Philip Reames via llvm-commits]

preames wrote:

Is it legal to preserve aliasing metadata?  What if we had a narrow rmw widened to a larger type where only the additional bits accessed aliased an unrelated access?  

https://github.com/llvm/llvm-project/pull/89769