[X86][SSE] Add support for combining scalar_to_vector(extract_vector_elt) into a target shuffle.

Correctly flagging upper elements as undef.

llvm-svn: 294020

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index a7a141050d9..f4b81063bcc 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -5729,6 +5729,20 @@ static bool getFauxShuffleMask(SDValue N, SmallVectorImpl<int> &Mask,
     Ops.push_back(IsAndN ? N1 : N0);
     return true;
   }
+  case ISD::SCALAR_TO_VECTOR: {
+    // Match against a scalar_to_vector of an extract from a similar vector.
+    SDValue N0 = N.getOperand(0);
+    if (N0.getOpcode() != ISD::EXTRACT_VECTOR_ELT ||
+        N0.getOperand(0).getValueType() != VT ||
+        !isa<ConstantSDNode>(N0.getOperand(1)) ||
+        NumElts <= N0.getConstantOperandVal(1) ||
+        !N->isOnlyUserOf(N0.getNode()))
+      return false;
+    Ops.push_back(N0.getOperand(0));
+    Mask.push_back(N0.getConstantOperandVal(1));
+    Mask.append(NumElts - 1, SM_SentinelUndef);
+    return true;
+  }
   case X86ISD::PINSRB:
   case X86ISD::PINSRW: {
     SDValue InVec = N.getOperand(0);