Explicitly handle ConstantAggregateZero

Author: npanchen

llvm/lib/Analysis/ConstantFolding.cpp

@@ -3998,20 +3998,28 @@ ConstantFoldStructCall(StringRef Name, Intrinsic::ID IntrinsicID,
     if (!Vec)
       return nullptr;
 
-    unsigned NumElements =
-        cast<VectorType>(Vec->getType())->getElementCount().getKnownMinValue() /
-        2;
+    auto VecTy = cast<VectorType>(Vec->getType());
+    unsigned NumElements = VecTy->getElementCount().getKnownMinValue() / 2;
+
     SmallVector<Constant *, 4> Res0(NumElements), Res1(NumElements);
-    for (unsigned I = 0; I < NumElements; ++I) {
-      Constant *Elt0 = Vec->getAggregateElement(2 * I);
-      Constant *Elt1 = Vec->getAggregateElement(2 * I + 1);
-      if (!Elt0 || !Elt1)
-        return nullptr;
-      Res0[I] = Elt0;
-      Res1[I] = Elt1;
+    if (isa<ConstantAggregateZero>(Vec)) {
+      auto *HalfVecTy = VectorType::getHalfElementsVectorType(VecTy);
+      return ConstantStruct::get(StTy, ConstantAggregateZero::get(HalfVecTy),
+                                 ConstantAggregateZero::get(HalfVecTy));
     }
-    return ConstantStruct::get(StTy, ConstantVector::get(Res0),
-                               ConstantVector::get(Res1));
+    if (isa<FixedVectorType>(Vec->getType())) {
+      for (unsigned I = 0; I < NumElements; ++I) {
+        Constant *Elt0 = Vec->getAggregateElement(2 * I);
+        Constant *Elt1 = Vec->getAggregateElement(2 * I + 1);
+        if (!Elt0 || !Elt1)
+          return nullptr;
+        Res0[I] = Elt0;
+        Res1[I] = Elt1;
+      }
+      return ConstantStruct::get(StTy, ConstantVector::get(Res0),
+                                 ConstantVector::get(Res1));
+    }
+    return nullptr;
   }
   default:
     // TODO: Constant folding of vector intrinsics that fall through here does