[llvm] [VPlan] Add ReductionStartVector VPInstruction. (PR #142290)

[Mel Chen via llvm-commits]

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@@ -89,6 +89,8 @@ Type *VPTypeAnalysis::inferScalarTypeForRecipe(const VPInstruction *R) {
                inferScalarType(R->getOperand(1)) &&
            "different types inferred for different operands");
     return IntegerType::get(Ctx, 1);
+  case VPInstruction::ReductionStartVector:
+    return inferScalarType(R->getOperand(0));
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Mel-Chen wrote:

Would it make sense to move `case VPInstruction::ReductionStartVector:` below `case Instruction::Freeze:` so they can share the same return `inferScalarType(R->getOperand(0))` statement?

https://github.com/llvm/llvm-project/pull/142290