[llvm] [LoopInterchange] Check all inner-exit LCSSA PHIs (PR #200860)

[Ryotaro Kasuga via llvm-commits]

================
@@ -1371,8 +1371,10 @@ areInnerLoopExitPHIsSupported(Loop *OuterL, Loop *InnerL,
     // from the loop latch.
     if (PHI.getNumIncomingValues() > 1)
       return false;
+    // The reduction LCSSA PHI's store user is rewritten by reduction2Memory();
+    // skip its user-check but keep validating the remaining LCSSA PHIs.
----------------
kasuga-fj wrote:

```suggestion
    // The reduction LCSSA PHI's store user is rewritten by reduction2Memory();
    // skip its user-check but keep validating the remaining PHIs.
```

I'm not confident, but the remaining PHIs aren't necessarily LCSSA PHIs?

https://github.com/llvm/llvm-project/pull/200860