[llvm] AMDGPU: share LDS budget logic and add experimental LDS buffering pass (PR #166388)

[Yaxun Liu via llvm-commits]

yxsamliu wrote:

@shiltian Re: supported pattern

The one-use pair appears after SROA splits a partly updated object. An access through another pointer may alias, so existing passes cannot remove the pair. I added a test showing this flow. I kept this patch focused on the pattern seen in rocRand. I will study other useful patterns further and follow up separately.

https://github.com/llvm/llvm-project/pull/166388