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

[Florian Hahn via llvm-commits]

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@@ -2408,23 +2414,32 @@ class VPInterleaveRecipe : public VPRecipeBase {
   Instruction *getInsertPos() const { return IG->getInsertPos(); }
 };
 
-/// A recipe to represent inloop reduction operations, performing a reduction on
-/// a vector operand into a scalar value, and adding the result to a chain.
-/// The Operands are {ChainOp, VecOp, [Condition]}.
+/// A recipe to represent inloop, ordered or partial reduction operations. It
+/// performs a reduction on a vector operand into a scalar (vector in the case
+/// of a partial reduction) value, and adds the result to a chain. The Operands
+/// are {ChainOp, VecOp, [Condition]}.
 class VPReductionRecipe : public VPRecipeWithIRFlags {
   /// The recurrence kind for the reduction in question.
   RecurKind RdxKind;
   bool IsOrdered;
   /// Whether the reduction is conditional.
   bool IsConditional = false;
+  /// The scaling factor, relative to the VF, that this recipe's output is
+  /// divided by.
+  /// For outer-loop reductions this is equal to 1.
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fhahn wrote:

I still need to take a closer look to see how everything fits together, but I am not sure if it is a good idea to make the existing VPReductionRecipe even more complicated.

The main motivation is to use VPMulAccumulateReductionRecipe for partial reductions?

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