[llvm] [AMDGPU] Improve selection of ballot.i64 intrinsic in wave32 mode in SelectionDAG. (PR #71556)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Right, but InstCombine is a bit late.

I'm confused, InstCombine can't be too late, it runs many times after all IR producers. There's no practical path between the sanitizer passes and the backend where it won't run 

https://github.com/llvm/llvm-project/pull/71556