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

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

I've fixed the crashes, but still seeing some regressions in compile time. I'm also just about out of ideas for improvements to the code in this patch. I would greatly appreciate any insights from the reviewers on where I can look to improve.

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