[llvm] [LV] Use VPReductionRecipe for partial reductions (PR #144908)

[Matthew Devereau via llvm-commits]

================
@@ -8278,11 +8279,15 @@ VPRecipeBase *VPRecipeBuilder::tryToCreateWidenRecipe(VPSingleDefRecipe *R,
              Phi->getIncomingValueForBlock(OrigLoop->getLoopPreheader()));
 
       // If the PHI is used by a partial reduction, set the scale factor.
-      unsigned ScaleFactor =
-          getScalingForReduction(RdxDesc.getLoopExitInstr()).value_or(1);
-      PhiRecipe = new VPReductionPHIRecipe(
-          Phi, RdxDesc, *StartV, CM.isInLoopReduction(Phi),
-          CM.useOrderedReductions(RdxDesc), ScaleFactor);
+      bool UseInLoopReduction = CM.isInLoopReduction(Phi);
+      bool UseOrderedReductions = CM.useOrderedReductions(RdxDesc);
+      auto ScaleFactor =
+          (UseOrderedReductions || UseInLoopReduction)
+              ? 0
+              : getScalingForReduction(RdxDesc.getLoopExitInstr()).value_or(1);
+      PhiRecipe = new VPReductionPHIRecipe(Phi, RdxDesc, *StartV,
+                                           CM.isInLoopReduction(Phi),
----------------
MDevereau wrote:

```suggestion
                                           UseInLoopReduction
```

https://github.com/llvm/llvm-project/pull/144908