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

[via llvm-commits]

amehsan wrote:

> TBH I don't know why `GVNHoist` is disabled by default :( https://godbolt.org/z/ETGzxK1Wq

IIRC that is because of functional issues in GVNHoist

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