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

[Graham Hunter via llvm-commits]

================
@@ -8671,6 +8754,24 @@ VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
   return tryToWiden(Instr, Operands, VPBB);
 }
 
+VPRecipeBase *
+VPRecipeBuilder::tryToCreatePartialReduction(Instruction *Reduction,
+                                             ArrayRef<VPValue *> Operands) {
+  assert(Operands.size() == 2 &&
+         "Unexpected number of operands for partial reduction");
+
+  VPValue *BinOp = Operands[0];
+  VPValue *Phi = Operands[1];
+  VPRecipeBase *BinOpRecipe = BinOp->getDefiningRecipe();
+  if (isa<VPReductionPHIRecipe>(BinOpRecipe))
----------------
huntergr-arm wrote:

nit: can remove a single use local
```suggestion
  if (isa<VPReductionPHIRecipe>(BinOp->getDefiningRecipe()))
```

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