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

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

I don't understand this transform; the load/store forwarding optimization already happens in this example and this folds to an empty function: https://godbolt.org/z/xqhc77q8c

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