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

[Sam Tebbs via llvm-commits]

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@@ -327,6 +327,37 @@ 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));
+  Value *PhiVal = State.get(getOperand(1));
+  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"));
+
+  State.set(this, V);
+  State.addMetadata(V, dyn_cast_or_null<Instruction>(getUnderlyingValue()));
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SamTebbs33 wrote:

I'm actually not sure. I think this was modeled after how other execute functions do it, such as that for `VPWidenSelectRecipe` which also uses the underlying value and doesn't check for null.

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