[llvm] [StructurizeCFG] Hoist and simplify zero-cost incoming else phi values (PR #139605)

[via llvm-commits]

https://github.com/ruiling approved this pull request.

Thanks for making this! Frankly speaking, I am not quite sure whether this would cause register pressure increase in some case. But I think this mostly looks reasonable to me. Just some small nits.

https://github.com/llvm/llvm-project/pull/139605