1 files changed, 12 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index f7fe3e8add4..80f1afe310f 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -35750,6 +35750,18 @@ static SDValue combineInsertSubvector(SDNode *N, SelectionDAG &DAG,
         return DAG.getNode(ISD::INSERT_SUBVECTOR, dl, OpVT,
                            getZeroVector(OpVT, Subtarget, DAG, dl), SubVec2,
                            Vec.getOperand(2));
+
+      // If we are inserting into both halves of the vector, the starting
+      // vector should be undef. If it isn't, make it so. Only do this if the
+      // the early insert has no other uses.
+      // TODO: Should this be a generic DAG combine?
+      if (!Vec.getOperand(0).isUndef() && Vec.hasOneUse()) {
+        Vec = DAG.getNode(ISD::INSERT_SUBVECTOR, dl, OpVT, DAG.getUNDEF(OpVT),
+                          SubVec2, Vec.getOperand(2));
+        DCI.AddToWorklist(Vec.getNode());
+        return DAG.getNode(ISD::INSERT_SUBVECTOR, dl, OpVT, Vec, SubVec, Idx);
+
+      }
     }
   }