[llvm] [SimplifyCFG] Simplify switch instruction that has duplicate arms (PR #114262)

[via llvm-commits]

goldsteinn wrote:

As a general feedback, I think the current implementation is a bit too constrained for my liking, in that it will make it difficult to extend to generally handle equal basic blocks with more than just one branch without entirely rewriting.

I would be more in favor of implementing this by hashing the BBs and arbitrarily de-duplicating equal BBs.

https://github.com/llvm/llvm-project/pull/114262