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

[Benjamin Maxwell via llvm-commits]

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@@ -335,10 +335,10 @@ Value *VPTransformState::get(VPValue *Def, bool NeedsScalar) {
   } else {
     // Initialize packing with insertelements to start from undef.
     assert(!VF.isScalable() && "VF is assumed to be non scalable.");
-    Value *Undef = PoisonValue::get(VectorType::get(LastInst->getType(), VF));
+    Value *Undef = PoisonValue::get(toVectorizedTy(LastInst->getType(), VF));
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MacDue wrote:

I don't think spilling those out would make sense. Within this patch, all of these changes are needed for the core functionality to work (switching the call does change behavior). If I landed these as an NFC, it makes it less obvious that these are required changes for the struct vectorization.  

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