[llvm] [llvm][opt][Transforms] Preserve AMDGPU atomic metadata (PR #140314)

[Alex Voicu via llvm-commits]

AlexVlx wrote:

> I wonder whether it would make sense to have a fallback behavior that allows preserving metadata if it is exactly the same on both instructions, even if it's unknown.
> 
> Do we have any metadata where preserving it in case of exact equality would be invalid?

@nikic not that I am aware of, but I'm also not an MD wizard (as evidenced by the `::intersect` misuse). Intuitively, it seems as if it's an impossibility for things to work independently, but break merged. We could try to do this, and hope that test coverage is adequate?

https://github.com/llvm/llvm-project/pull/140314