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

[via llvm-commits]

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@@ -608,6 +608,32 @@ Value *VPInstruction::generate(VPTransformState &State) {
     return Builder.CreateVectorSplat(
         State.VF, State.get(getOperand(0), /*IsScalar*/ true), "broadcast");
   }
+  case VPInstruction::BuildStructVector: {
+    // For struct types, we need to build a new 'wide' struct type, where each
+    // element is widened, i.e. we crate a struct of vectors .
+    auto *StructTy =
+        cast<StructType>(State.TypeAnalysis.inferScalarType(getOperand(0)));
+    Value *Res = PoisonValue::get(toVectorizedTy(StructTy, State.VF));
+    for (const auto &[Idx, Op] : enumerate(operands())) {
+      for (unsigned I = 0; I != StructTy->getNumElements(); I++) {
+        Value *ScalarValue = Builder.CreateExtractValue(State.get(Op, true), I);
+        Value *VectorValue = Builder.CreateExtractValue(Res, I);
+        VectorValue =
+            Builder.CreateInsertElement(VectorValue, ScalarValue, Idx);
+        Res = Builder.CreateInsertValue(Res, VectorValue, I);
+      }
+    }
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ayalz wrote:

Would be good to clarify that `Idx` represents an enumeration of vector elements while `I` represents an enumeration of struct fields. Admittedly `StructTy->getNumElements()` may also cause confusion. How about `LaneIndex` and `FieldIndex`?

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