[llvm] [LoopInterchange] Reject inner-latch lcssa PHI feeding the exit condition (PR #202863)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj commented:

As far as I understand (and based on my local testing), the root cause of the issue is that  `MoveInstructions` in `LoopInterchangeTransform::transform` doesn't handle PHIs properly. If PHIs were moved appropriately, we wouldn't need to bail out early, and more loop-interchange opportunities could be enabled. I'm not sure whether it's worth the effort, so I don't object to the current approach, but if we decide to go this way, could you please add assert in `MoveInstructions` to clarify that it doesn't support PHIs?

https://github.com/llvm/llvm-project/pull/202863