[llvm-branch-commits] [IVUsers] Look through loop-external single-value phi nodes (PR #191684)

[Aiden Grossman via llvm-branch-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/191684

If we are in LCSSA form, variables that are live out of the loop are
obscured through phi-nodes. We want to look through as we would if we
are not in LCSSA (e.g., instcombine ran in between). This prevents
regressions when updating LSR to preserve LCSSA.