[llvm] [Transforms] Speed up SSAUpdater::FindExistingPHI (PR #100281)

[David Li via llvm-commits]

https://github.com/david-xl commented:

is it better to use RAII idiom for this (using a dtor of a block scoped object to do the cleanup)? A matching status can be be set to false at the start of the for loop and set to true at the end of the loop.

https://github.com/llvm/llvm-project/pull/100281