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

[Graham Hunter via llvm-commits]

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@@ -327,6 +327,38 @@ InstructionCost VPSingleDefRecipe::computeCost(ElementCount VF,
   return UI ? Ctx.getLegacyCost(UI, VF) : 0;
 }
 
+void VPPartialReductionRecipe::execute(VPTransformState &State) {
+  State.setDebugLocFrom(getDebugLoc());
+  auto &Builder = State.Builder;
+
+  assert(Opcode == Instruction::Add && "Unhandled partial reduction opcode");
+
+  Value *BinOpVal = State.get(getOperand(0), 0);
+  Value *PhiVal = State.get(getOperand(1), 0);
+  assert(PhiVal && BinOpVal && "Phi and Mul must be set");
+
+  Type *RetTy = PhiVal->getType();
+
+  CallInst *V = Builder.CreateIntrinsic(
+      RetTy, Intrinsic::experimental_vector_partial_reduce_add,
+      {PhiVal, BinOpVal}, nullptr, Twine("partial.reduce"));
+
+  // Use this vector value for all users of the original instruction.
+  State.set(this, V, 0);
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huntergr-arm wrote:

3rd operand can be removed here for the same reason, we're not setting scalar values.

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