1 files changed, 9 insertions, 4 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 7a22caf9c8b..10cce7813dc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8064,10 +8064,15 @@ static SDValue tryToFoldExtendOfConstant(SDNode *N, const TargetLowering &TLI,
   unsigned NumElts = VT.getVectorNumElements();
   SDLoc DL(N);
 
-  for (unsigned i=0; i != NumElts; ++i) {
-    SDValue Op = N0->getOperand(i);
-    if (Op->isUndef()) {
-      Elts.push_back(DAG.getUNDEF(SVT));
+  // For zero-extensions, UNDEF elements still guarantee to have the upper
+  // bits set to zero.
+  bool IsZext =
+      Opcode == ISD::ZERO_EXTEND || Opcode == ISD::ZERO_EXTEND_VECTOR_INREG;
+
+  for (unsigned i = 0; i != NumElts; ++i) {
+    SDValue Op = N0.getOperand(i);
+    if (Op.isUndef()) {
+      Elts.push_back(IsZext ? DAG.getConstant(0, DL, SVT) : DAG.getUNDEF(SVT));
       continue;
     }