[llvm] [SimplifyCFG] Use hash map to continue hoisting the common instructions (PR #78615)

[via llvm-commits]

RouzbehPaktinat wrote:

> This PR is really pushing the bounds of what is appropriate to do in SimplifyCFG. The code has become quite hard to understand.
> 
> My primary concern with this implementation would be with non-determinism -- I don't think that your approach of only supporting hoisting for the first instruction with a given hash is viable (unless I am misunderstanding something).

I can fix non-deterministic  behavior and try to make code simpler so that it's easier to understand. Doing that along with addressing your other comments, will the code be in a good status to be merged?

https://github.com/llvm/llvm-project/pull/78615