[DAGCombine] combineShuffleOfScalars - handle non-zero SCALAR_TO_VECTOR indices (PR41097)

rL356292 reduces the size of scalar_to_vector if we know the upper bits are undef - which means that shuffles may find they are suddenly referencing scalar_to_vector elements other than zero - so make sure we handle this as undef.

llvm-svn: 356327

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index f6363e271a1..98eb1a1bfe7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17596,8 +17596,8 @@ static SDValue combineShuffleOfScalars(ShuffleVectorSDNode *SVN,
       if (S.getOpcode() == ISD::BUILD_VECTOR) {
         Op = S.getOperand(Idx);
       } else if (S.getOpcode() == ISD::SCALAR_TO_VECTOR) {
-        assert(Idx == 0 && "Unexpected SCALAR_TO_VECTOR operand index.");
-        Op = S.getOperand(0);
+        SDValue Op0 = S.getOperand(0);
+        Op = Idx == 0 ? Op0 : DAG.getUNDEF(Op0.getValueType());
       } else {
         // Operand can't be combined - bail out.
         return SDValue();