[llvm] [CodeGen] Disallow mixing of ignorable uses in MachineCSE (PR #193522)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

isIgnorableUse is a poorly conceived API. It's not actually ignorable, it requires the knowledge of the CFG context to determine. 

https://github.com/llvm/llvm-project/pull/193522