[llvm] StructurizeCFG: Optimize phi insertion during ssa reconstruction (PR #101301)

[Sameer Sahasrabuddhe via llvm-commits]

https://github.com/ssahasra commented:

EquivalenceClasses is interesting. It will be good if that further simplifies the code here!

Also, if the order in which the PHIs are visited can potentially have some noticeable effect on the output, please do put that in a comment somewhere.

https://github.com/llvm/llvm-project/pull/101301