[llvm] [LoopFusion] Fix sink instructions (PR #147501)

[Ryotaro Kasuga via llvm-commits]

================
@@ -1176,9 +1176,31 @@ struct LoopFuser {
     return true;
   }
 
+  void fixPHINodes(SmallVector<Instruction *, 4> &SafeToSink,
+                   const FusionCandidate &FC0,
+                   const FusionCandidate &FC1) const {
+    // Iterate over SafeToSink instructions and update PHI nodes
+    // to take values from the latch block of FC0 if they are taking
+    // from the latch block of FC1.
+    for (Instruction *Inst : SafeToSink) {
+      LLVM_DEBUG(dbgs() << "UPDATING: Instruction: " << *Inst << "\n");
+      // Continue if the instruction is not a PHI node.
+      if (!isa<PHINode>(Inst))
+        continue;
+      PHINode *Phi = dyn_cast<PHINode>(Inst);
+      LLVM_DEBUG(dbgs() << "UPDATING: PHI node: " << *Phi << "\n");
----------------
kasuga-fj wrote:

If `Inst` is a PHI node, the following messages will be printed, which seem redundant to me.

```
UPDATING: Instruction: phi ...
UPDATING: PHI node: phi ...
```

If it is not a PHI node, the following message will be displayed, but it is not actually updated.

```
UPDATING: Instruction: ...
```

https://github.com/llvm/llvm-project/pull/147501