[llvm] [LoopInterchange] Also look at lcssa phis in outer loop latch block (PR #160889)

[Ryotaro Kasuga via llvm-commits]

================
@@ -1872,6 +1873,50 @@ static void moveLCSSAPhis(BasicBlock *InnerExit, BasicBlock *InnerHeader,
   InnerLatch->replacePhiUsesWith(InnerLatch, OuterLatch);
 }
 
+// This deals with a corner case when a LCSSA phi node appears in a non-exit
----------------
kasuga-fj wrote:

This comment seems to only explain the problem, but not how to address it. It may be better to describe what this function performs.

https://github.com/llvm/llvm-project/pull/160889