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

[Florian Hahn via llvm-commits]

================
@@ -8741,6 +8853,23 @@ 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];
+  if (isa<VPReductionPHIRecipe>(BinOp->getDefiningRecipe()))
+    std::swap(BinOp, Phi);
+
----------------
fhahn wrote:

```suggestion
  assert(isa<VPReductionPHIRecipe>(Phi) & "...");
```

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