[llvm] [LoopVectorizer] Add support for partial reductions (PR #92418)

[Florian Hahn via llvm-commits]

================
@@ -8687,9 +8794,14 @@ VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
           Legal->getReductionVars().find(Phi)->second;
       assert(RdxDesc.getRecurrenceStartValue() ==
              Phi->getIncomingValueForBlock(OrigLoop->getLoopPreheader()));
-      PhiRecipe = new VPReductionPHIRecipe(Phi, RdxDesc, *StartV,
-                                           CM.isInLoopReduction(Phi),
-                                           CM.useOrderedReductions(RdxDesc));
+
+      // If the PHI is used by a partial reduction, set the scale factor
----------------
fhahn wrote:

nit
```suggestion
      // If the PHI is used by a partial reduction, set the scale factor.
```

https://github.com/llvm/llvm-project/pull/92418