[llvm] [SimplifyCFG] Add optimization for switches of powers of two (PR #70977)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Shouldn't this transform be part of SwitchToLookupTable()? I'm not sure it makes sense to do this independently, if we can't form a lookup table.

https://github.com/llvm/llvm-project/pull/70977