[llvm] [AMDGPU][DAGCombiner][GlobalISel] Prevent FMA contraction when multiply cannot be eliminated (PR #169735)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

This is really big and hard to review all the impacts. Can you do this one instance at a time?

https://github.com/llvm/llvm-project/pull/169735