[llvm] [VPlan] Unroll VPReplicateRecipe by VF. (PR #142433)

[via llvm-commits]

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@@ -495,9 +495,9 @@ Value *VPInstruction::generate(VPTransformState &State) {
   }
   case Instruction::ExtractElement: {
     assert(State.VF.isVector() && "Only extract elements from vectors");
-    Value *Vec = State.get(getOperand(0));
-    Value *Idx = State.get(getOperand(1), /*IsScalar=*/true);
-    return Builder.CreateExtractElement(Vec, Idx, Name);
+    unsigned IdxToExtract =
+        cast<ConstantInt>(getOperand(1)->getLiveInIRValue())->getZExtValue();
+    return State.get(getOperand(0), VPLane(IdxToExtract));
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ayalz wrote:

The fact that the second operand must be constant should be documented and verified (if modeled as a general operand rather than a "flag").

https://github.com/llvm/llvm-project/pull/142433