[llvm] [SimplifyCFG] Simplify conditional branches on const icmp eq's (PR #73334)

[via llvm-commits]

yonillasky wrote:

I've sort of managed to implement the CR suggestion.
I'm intercepting only the BB removals inside `simplifyFunctionCFGImpl`, not the 5 use cases of DeleteDeadBlock inside the SimplifyCFG modules. It seems to be sufficient for the use case I am interested in.
Will run and fix UTs as necessary. It should have a smaller effect now, since it only fixes the problem if SimplifyCFG was the one to introduce it.


https://github.com/llvm/llvm-project/pull/73334