[llvm] [AMDGPU] Teach SIPreEmitPeephole pass to preserve MachineLoopInfo (PR #178868)

[Dark Steve via llvm-commits]

https://github.com/PrasoonMishra commented:

@arsenm @cdevadas I was thinking about how to preserve loop info when a branch is removed. The issue is we'd need to check if blocks are still reachable within the loop, handle cascading removals, and detect if the loop gets destroyed entirely; essentially a BFS from the header. Will this solution be acceptable? This feels like we're almost recomputing loop info anyway. What do you think?

https://github.com/llvm/llvm-project/pull/178868