[llvm] [AMDGPU] Waterfall loop codegen improvement in SIInstrInfo (PR #192415)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> it might not be safe to insert exec-changing instructions like v_cmpx in the middle of a basic block.

It is not safe, these should have isTerminator set to be safe 

https://github.com/llvm/llvm-project/pull/192415