[llvm] [SimplifyCFG] Transform switch to select when common bits uniquely identify one case (PR #145233)

[Gábor Spaits via llvm-commits]

spaits wrote:

Gentle ping @antoniofrighetto @dtcxzyw @nikic .
Sorry for pinging you. Could you please provide some input?
Do you think I am addressing the issue in the correct way? (Is it appropiate to solve it in SimplifyCFG or a later InstCombine would be better?)

https://github.com/llvm/llvm-project/pull/145233