[llvm] [LV] Vectorize conditional scalar assignments (PR #158088)

[Mel Chen via llvm-commits]

================
@@ -1118,7 +1143,11 @@ bool RecurrenceDescriptor::isReductionPHI(PHINode *Phi, Loop *TheLoop,
                       << "\n");
     return true;
   }
-
+  if (AddReductionVar(Phi, RecurKind::FindLast, TheLoop, FMF, RedDes, DB, AC,
+                      DT, SE)) {
+    LLVM_DEBUG(dbgs() << "Found a FindLast reduction PHI." << *Phi << "\n");
+    return true;
+  }
----------------
Mel-Chen wrote:

We can remove 
```
  if (AddReductionVar(Phi, RecurKind::FindLastIVSMax, TheLoop, FMF, RedDes, DB,
                      AC, DT, SE)) {
    LLVM_DEBUG(dbgs() << "Found a FindLastIV reduction PHI." << *Phi << "\n");
    return true;
  }
  if (AddReductionVar(Phi, RecurKind::FindFirstIVSMin, TheLoop, FMF, RedDes, DB,
                      AC, DT, SE)) {
    LLVM_DEBUG(dbgs() << "Found a FindFirstIV reduction PHI." << *Phi << "\n");
    return true;
  }
```
and replace them with this code.

https://github.com/llvm/llvm-project/pull/158088