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

[Jon Chesterfield via llvm-commits]

JonChesterfield wrote:

The early exits need to be much earlier. Check the commandline flag before mutating the module, not partway through. Likewise check at least one function has this attribute before changing anything.

I see there are analysis passes running as well. Ideally running those wouldn't break anything but in reality paranoia is the way forward here.

Please check the command line flag and for the presence of the attribute before mutating the IR. A module scope flag sounds great, much better than checking individual functions, but again check it before changing the IR.

The purpose here is to have the pass do literally nothing when the sanitizer is disabled. Ideally it wouldn't even be constructed.

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