diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 0179cf181cf..3cbd6d046bc 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9836,8 +9836,35 @@ SDValue DAGCombiner::visitCONCAT_VECTORS(SDNode *N) {
     return N->getOperand(0);
 
   // Check if all of the operands are undefs.
+  EVT VT = N->getValueType(0);
   if (ISD::allOperandsUndef(N))
-    return DAG.getUNDEF(N->getValueType(0));
+    return DAG.getUNDEF(VT);
+
+  // Optimize concat_vectors where one of the vectors is undef.
+  if (N->getNumOperands() == 2 &&
+      N->getOperand(1)->getOpcode() == ISD::UNDEF) {
+    SDValue In = N->getOperand(0);
+    assert(In->getValueType(0).isVector() && "Must concat vectors");
+
+    // Transform: concat_vectors(scalar, undef) -> scalar_to_vector(sclr).
+    if (In->getOpcode() == ISD::BITCAST &&
+        !In->getOperand(0)->getValueType(0).isVector()) {
+      SDValue Scalar = In->getOperand(0);
+      EVT SclTy = Scalar->getValueType(0);
+
+      if (!SclTy.isFloatingPoint() && !SclTy.isInteger())
+        return SDValue();
+
+      EVT NVT = EVT::getVectorVT(*DAG.getContext(), SclTy,
+                                 VT.getSizeInBits() / SclTy.getSizeInBits());
+      if (!TLI.isTypeLegal(NVT) || !TLI.isTypeLegal(Scalar.getValueType()))
+        return SDValue();
+
+      SDLoc dl = SDLoc(N);
+      SDValue Res = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, NVT, Scalar);
+      return DAG.getNode(ISD::BITCAST, dl, VT, Res);
+    }
+  }
 
   // Type legalization of vectors and DAG canonicalization of SHUFFLE_VECTOR
   // nodes often generate nop CONCAT_VECTOR nodes.
diff --git a/lib/Target/AArch64/AArch64InstrNEON.td b/lib/Target/AArch64/AArch64InstrNEON.td
index 9efbb0d34fe..10dde19318e 100644
--- a/lib/Target/AArch64/AArch64InstrNEON.td
+++ b/lib/Target/AArch64/AArch64InstrNEON.td
@@ -5130,6 +5130,10 @@ def : Pat<(v1f64 (scalar_to_vector (f64 FPR64:$Rn))),
 def : Pat<(v1f64 (scalar_to_vector (f64 FPR64:$src))),
           (FMOVdd $src)>;
 
+def : Pat<(v2f64 (scalar_to_vector (f64 FPR64:$src))),
+          (INSERT_SUBREG (v2f64 (IMPLICIT_DEF)),
+                         (f64 FPR64:$src), sub_64)>;
+
 class NeonI_DUP_Elt<bit Q, string asmop, string rdlane,  string rnlane,
                     RegisterOperand ResVPR, ValueType ResTy,
                     ValueType OpTy, Operand OpImm>
@@ -5300,4 +5304,4 @@ def : Pat<(v1i64 (extract_subvector (v2i64 VPR128:$Rn), (i64 0))),
 def : Pat<(v2f32 (extract_subvector (v4f32 VPR128:$Rn), (i64 0))),
           (v2f32 (EXTRACT_SUBREG VPR128:$Rn, sub_64))>;
 def : Pat<(v1f64 (extract_subvector (v2f64 VPR128:$Rn), (i64 0))),
-          (v1f64 (EXTRACT_SUBREG VPR128:$Rn, sub_64))>;
\ No newline at end of file
+          (v1f64 (EXTRACT_SUBREG VPR128:$Rn, sub_64))>;
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 31ff797960e..0d7818943c8 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -1500,7 +1500,6 @@ void X86TargetLowering::resetOperationActions() {
   }
 
   // We have target-specific dag combine patterns for the following nodes:
-  setTargetDAGCombine(ISD::CONCAT_VECTORS);
   setTargetDAGCombine(ISD::VECTOR_SHUFFLE);
   setTargetDAGCombine(ISD::EXTRACT_VECTOR_ELT);
   setTargetDAGCombine(ISD::VSELECT);
@@ -16155,50 +16154,6 @@ static SDValue PerformShuffleCombine256(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
-static SDValue PerformConcatCombine(SDNode *N, SelectionDAG &DAG,
-                                    TargetLowering::DAGCombinerInfo &DCI,
-                                    const X86Subtarget *Subtarget) {
-  // Creating a v8i16 from a v4i16 argument and an undef runs into trouble in
-  // type legalization and ends up spilling to the stack. Avoid that by
-  // creating a vector first and bitcasting the result rather than
-  // bitcasting the source then creating the vector. Similar problems with
-  // v8i8.
-
-  // No point in doing this after legalize, so early exit for that.
-  if (!DCI.isBeforeLegalize())
-    return SDValue();
-
-  EVT VT = N->getValueType(0);
-  SDValue Op0 = N->getOperand(0);
-  SDValue Op1 = N->getOperand(1);
-  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-  if (VT.getSizeInBits() == 128 && N->getNumOperands() == 2 &&
-      Op1->getOpcode() == ISD::UNDEF &&
-      Op0->getOpcode() == ISD::BITCAST &&
-      !TLI.isTypeLegal(Op0->getValueType(0)) &&
-      TLI.isTypeLegal(Op0->getOperand(0)->getValueType(0))) {
-    if (Op0->getOperand(0)->getValueType(0).isVector())
-      return SDValue();
-    SDValue Scalar = Op0->getOperand(0);
-    // Any legal type here will be a simple value type.
-    MVT SVT = Scalar->getValueType(0).getSimpleVT();
-    // As a special case, bail out on MMX values.
-    if (SVT == MVT::x86mmx)
-      return SDValue();
-    EVT NVT = MVT::getVectorVT(SVT, 2);
-    // If the result vector type isn't legal, this transform won't really
-    // help, so bail on that, too.
-    if (!TLI.isTypeLegal(NVT))
-      return SDValue();
-    SDLoc dl = SDLoc(N);
-    SDValue Res = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, NVT, Scalar);
-    Res = DAG.getNode(ISD::BITCAST, dl, VT, Res);
-    return Res;
-  }
-
-  return SDValue();
-}
-
 /// PerformShuffleCombine - Performs several different shuffle combines.
 static SDValue PerformShuffleCombine(SDNode *N, SelectionDAG &DAG,
                                      TargetLowering::DAGCombinerInfo &DCI,
@@ -19077,7 +19032,6 @@ SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
   case X86ISD::VPERMILP:
   case X86ISD::VPERM2X128:
   case ISD::VECTOR_SHUFFLE: return PerformShuffleCombine(N, DAG, DCI,Subtarget);
-  case ISD::CONCAT_VECTORS: return PerformConcatCombine(N, DAG, DCI, Subtarget);
   case ISD::FMA:            return PerformFMACombine(N, DAG, Subtarget);
   }