[llvm] [LV] Teach LoopVectorizationLegality about struct vector calls (PR #119221)

[Benjamin Maxwell via llvm-commits]

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@@ -943,11 +955,24 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
       if (CI && !VFDatabase::getMappings(*CI).empty())
         VecCallVariantsFound = true;
 
+      auto canWidenInstruction = [this](Instruction const &Inst) {
+        Type *InstTy = Inst.getType();
+        if (isa<CallInst>(Inst) && isa<StructType>(InstTy) &&
+            canWidenCallReturnType(InstTy)) {
+          StructVecCallFound = true;
+          // For now, we can only widen struct values returned from calls where
+          // all users are extractvalue instructions.
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MacDue wrote:

Rephased the comment (and added a TODO around the flag, which would help clarify too). 

https://github.com/llvm/llvm-project/pull/119221