[llvm] [AMDGPU] Introduce "amdgpu-sw-lower-lds" pass to lower LDS accesses. (PR #87265)

[Jon Chesterfield via llvm-commits]

https://github.com/JonChesterfield approved this pull request.

OK, the check to only run the pass if the module is tagged with nosanitize_address covers my concerns. If that gets renamed or the semantics around its introduction change in the future this pass can update to match.

I'm hitting the green mark here to unblock progress for the sanitizer project. I think they're going to need runtime tests to get the bugs out of this and that's going to go smoother with the pass in trunk than it would with the only copy in rocm. I don't think lit tests are going to suffice in practice.

My objections raised in March about the approach and the existence of this pass at all also remain in place but iteration should continue. Hopefully in the future this pass will be deleted in favour of a simpler mechanism.

https://github.com/llvm/llvm-project/pull/87265