[llvm] [LV] Add initial support for vectorizing literal struct return values (PR #109833)

[Matt Arsenault via llvm-commits]

================
@@ -5452,10 +5453,13 @@ InstructionCost LoopVectorizationCostModel::computePredInstDiscount(
     // and phi nodes.
     TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput;
     if (isScalarWithPredication(I, VF) && !I->getType()->isVoidTy()) {
-      ScalarCost += TTI.getScalarizationOverhead(
-          cast<VectorType>(ToVectorTy(I->getType(), VF)),
-          APInt::getAllOnes(VF.getFixedValue()), /*Insert*/ true,
-          /*Extract*/ false, CostKind);
+      Type *WideTy = ToWideTy(I->getType(), VF);
+      for (Type *VectorTy : getContainedTypes(WideTy)) {
+        ScalarCost += TTI.getScalarizationOverhead(
+            cast<VectorType>(VectorTy), APInt::getAllOnes(VF.getFixedValue()),
+            /*Insert*/ true,
+            /*Extract*/ false, CostKind);
----------------
arsenm wrote:

```suggestion
            /*Insert=*/ true,
            /*Extract=*/ false, CostKind);
```

https://github.com/llvm/llvm-project/pull/109833