Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -18174,6 +18174,7 @@
   SDValue LHS = N->getOperand(0);
   SDValue RHS = N->getOperand(1);
   SDValue Ops[] = {LHS, RHS};
+  EVT VT = N->getValueType(0);
 
   // See if we can constant fold the vector operation.
   if (SDValue Fold = DAG.FoldConstantVectorArithmetic(
@@ -18191,7 +18192,6 @@
     ShuffleVectorSDNode *SVN1 = cast<ShuffleVectorSDNode>(RHS);
 
     if (SVN0->getMask().equals(SVN1->getMask())) {
-      EVT VT = N->getValueType(0);
       SDValue UndefVector = LHS.getOperand(1);
       SDValue NewBinOp = DAG.getNode(N->getOpcode(), SDLoc(N), VT,
                                      LHS.getOperand(0), RHS.getOperand(0),
@@ -18202,6 +18202,26 @@
     }
   }
 
+  // VBinOp (ins undef, X, Z), (ins undef, Y, Z) --> ins VecC, (VBinOp X, Y), Z
+  if (LHS.getOpcode() == ISD::INSERT_SUBVECTOR && LHS.getOperand(0).isUndef() &&
+      RHS.getOpcode() == ISD::INSERT_SUBVECTOR && RHS.getOperand(0).isUndef() &&
+      LHS.getOperand(2) == RHS.getOperand(2) &&
+      (LHS.hasOneUse() || RHS.hasOneUse())) {
+    SDValue X = LHS.getOperand(1);
+    SDValue Y = RHS.getOperand(1);
+    SDValue Z = LHS.getOperand(2);
+    EVT NarrowVT = X.getValueType();
+    if (NarrowVT == Y.getValueType() &&
+        TLI.isOperationLegalOrCustomOrPromote(N->getOpcode(), NarrowVT)) {
+      // (binop undef, undef) may not return undef, so compute that result.
+      SDLoc DL(N);
+      SDValue VecC = DAG.getNode(N->getOpcode(), DL, VT, DAG.getUNDEF(VT),
+                                 DAG.getUNDEF(VT));
+      SDValue NarrowBO = DAG.getNode(N->getOpcode(), DL, NarrowVT, X, Y);
+      return DAG.getNode(ISD::INSERT_SUBVECTOR, DL, VT, VecC, NarrowBO, Z);
+    }
+  }
+
   return SDValue();
 }
 
Index: test/CodeGen/X86/avx512-hadd-hsub.ll
===================================================================
--- test/CodeGen/X86/avx512-hadd-hsub.ll
+++ test/CodeGen/X86/avx512-hadd-hsub.ll
@@ -111,14 +111,14 @@
 ; KNL:       # %bb.0:
 ; KNL-NEXT:    vshufps {{.*#+}} ymm2 = ymm0[0,2],ymm1[0,2],ymm0[4,6],ymm1[4,6]
 ; KNL-NEXT:    vshufps {{.*#+}} ymm0 = ymm0[1,3],ymm1[1,3],ymm0[5,7],ymm1[5,7]
-; KNL-NEXT:    vpaddd %zmm0, %zmm2, %zmm0
+; KNL-NEXT:    vpaddd %ymm0, %ymm2, %ymm0
 ; KNL-NEXT:    retq
 ;
 ; SKX-LABEL: hadd_16_3:
 ; SKX:       # %bb.0:
 ; SKX-NEXT:    vshufps {{.*#+}} ymm2 = ymm0[0,2],ymm1[0,2],ymm0[4,6],ymm1[4,6]
 ; SKX-NEXT:    vshufps {{.*#+}} ymm0 = ymm0[1,3],ymm1[1,3],ymm0[5,7],ymm1[5,7]
-; SKX-NEXT:    vpaddd %zmm0, %zmm2, %zmm0
+; SKX-NEXT:    vpaddd %ymm0, %ymm2, %ymm0
 ; SKX-NEXT:    retq
   %x226 = shufflevector <16 x i32> %x225, <16 x i32> %x227, <16 x i32> <i32 0, i32 2, i32 16, i32 18
 , i32 4, i32 6, i32 20, i32 22, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -134,14 +134,14 @@
 ; KNL:       # %bb.0:
 ; KNL-NEXT:    vshufps {{.*#+}} ymm2 = ymm0[0,2],ymm1[0,2],ymm0[4,6],ymm1[4,6]
 ; KNL-NEXT:    vshufps {{.*#+}} ymm0 = ymm0[1,3],ymm1[1,3],ymm0[5,7],ymm1[5,7]
-; KNL-NEXT:    vaddps %zmm0, %zmm2, %zmm0
+; KNL-NEXT:    vaddps %ymm0, %ymm2, %ymm0
 ; KNL-NEXT:    retq
 ;
 ; SKX-LABEL: fhadd_16_3:
 ; SKX:       # %bb.0:
 ; SKX-NEXT:    vshufps {{.*#+}} ymm2 = ymm0[0,2],ymm1[0,2],ymm0[4,6],ymm1[4,6]
 ; SKX-NEXT:    vshufps {{.*#+}} ymm0 = ymm0[1,3],ymm1[1,3],ymm0[5,7],ymm1[5,7]
-; SKX-NEXT:    vaddps %zmm0, %zmm2, %zmm0
+; SKX-NEXT:    vaddps %ymm0, %ymm2, %ymm0
 ; SKX-NEXT:    retq
   %x226 = shufflevector <16 x float> %x225, <16 x float> %x227, <16 x i32> <i32 0, i32 2, i32 16, i32 18
 , i32 4, i32 6, i32 20, i32 22, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -156,14 +156,14 @@
 ; KNL:       # %bb.0:
 ; KNL-NEXT:    vunpcklpd {{.*#+}} ymm2 = ymm0[0],ymm1[0],ymm0[2],ymm1[2]
 ; KNL-NEXT:    vunpckhpd {{.*#+}} ymm0 = ymm0[1],ymm1[1],ymm0[3],ymm1[3]
-; KNL-NEXT:    vaddpd %zmm0, %zmm2, %zmm0
+; KNL-NEXT:    vaddpd %ymm0, %ymm2, %ymm0
 ; KNL-NEXT:    retq
 ;
 ; SKX-LABEL: fhadd_16_4:
 ; SKX:       # %bb.0:
 ; SKX-NEXT:    vunpcklpd {{.*#+}} ymm2 = ymm0[0],ymm1[0],ymm0[2],ymm1[2]
 ; SKX-NEXT:    vunpckhpd {{.*#+}} ymm0 = ymm0[1],ymm1[1],ymm0[3],ymm1[3]
-; SKX-NEXT:    vaddpd %zmm0, %zmm2, %zmm0
+; SKX-NEXT:    vaddpd %ymm0, %ymm2, %ymm0
 ; SKX-NEXT:    retq
   %x226 = shufflevector <8 x double> %x225, <8 x double> %x227, <8 x i32> <i32 0, i32 8, i32 2, i32 10, i32 undef, i32 undef, i32 undef, i32 undef>
   %x228 = shufflevector <8 x double> %x225, <8 x double> %x227, <8 x i32> <i32 1, i32 9, i32 3, i32 11, i32 undef ,i32 undef, i32 undef, i32 undef>
Index: test/CodeGen/X86/scalarize-fp.ll
===================================================================
--- test/CodeGen/X86/scalarize-fp.ll
+++ test/CodeGen/X86/scalarize-fp.ll
@@ -198,9 +198,8 @@
 ;
 ; AVX-LABEL: fadd_op1_constant_v4f64:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vaddpd %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vaddpd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %v = insertelement <4 x double> undef, double %x, i32 0
   %b = fadd <4 x double> %v, <double 42.0, double undef, double undef, double undef>
@@ -219,7 +218,7 @@
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vaddpd %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vaddpd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %x = load double, double* %p
   %v = insertelement <4 x double> undef, double %x, i32 0
@@ -237,9 +236,8 @@
 ;
 ; AVX-LABEL: fsub_op0_constant_v4f64:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vsubpd %ymm0, %ymm1, %ymm0
+; AVX-NEXT:    vsubpd %xmm0, %xmm1, %xmm0
 ; AVX-NEXT:    retq
   %v = insertelement <4 x double> undef, double %x, i32 0
   %b = fsub <4 x double> <double 42.0, double undef, double undef, double undef>, %v
@@ -258,7 +256,7 @@
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vsubpd %ymm0, %ymm1, %ymm0
+; AVX-NEXT:    vsubpd %xmm0, %xmm1, %xmm0
 ; AVX-NEXT:    retq
   %x = load double, double* %p
   %v = insertelement <4 x double> undef, double %x, i32 0
@@ -275,9 +273,8 @@
 ;
 ; AVX-LABEL: fmul_op1_constant_v4f64:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vmulpd %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vmulpd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %v = insertelement <4 x double> undef, double %x, i32 0
   %b = fmul <4 x double> %v, <double 42.0, double undef, double undef, double undef>
@@ -296,7 +293,7 @@
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vmulpd %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vmulpd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %x = load double, double* %p
   %v = insertelement <4 x double> undef, double %x, i32 0
@@ -313,9 +310,8 @@
 ;
 ; AVX-LABEL: fdiv_op1_constant_v4f64:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vdivpd %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vdivpd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %v = insertelement <4 x double> undef, double %x, i32 0
   %b = fdiv <4 x double> %v, <double 42.0, double undef, double undef, double undef>
@@ -334,7 +330,7 @@
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vdivpd %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vdivpd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %x = load double, double* %p
   %v = insertelement <4 x double> undef, double %x, i32 0
@@ -352,9 +348,8 @@
 ;
 ; AVX-LABEL: fdiv_op0_constant_v4f64:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vdivpd %ymm0, %ymm1, %ymm0
+; AVX-NEXT:    vdivpd %xmm0, %xmm1, %xmm0
 ; AVX-NEXT:    retq
   %v = insertelement <4 x double> undef, double %x, i32 0
   %b = fdiv <4 x double> <double 42.0, double undef, double undef, double undef>, %v
@@ -373,7 +368,7 @@
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vdivpd %ymm0, %ymm1, %ymm0
+; AVX-NEXT:    vdivpd %xmm0, %xmm1, %xmm0
 ; AVX-NEXT:    retq
   %x = load double, double* %p
   %v = insertelement <4 x double> undef, double %x, i32 0
Index: test/CodeGen/X86/vector-partial-undef.ll
===================================================================
--- test/CodeGen/X86/vector-partial-undef.ll
+++ test/CodeGen/X86/vector-partial-undef.ll
@@ -13,9 +13,7 @@
 ;
 ; AVX-LABEL: xor_insert_insert:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    # kill: def $xmm1 killed $xmm1 def $ymm1
-; AVX-NEXT:    # kill: def $xmm0 killed $xmm0 def $ymm0
-; AVX-NEXT:    vxorps %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vxorps %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %xw = shufflevector <2 x i64> %x, <2 x i64> undef, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
   %yw = shufflevector <2 x i64> %y, <2 x i64> undef, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
@@ -32,9 +30,9 @@
 ;
 ; AVX-LABEL: xor_insert_insert_high_half:
 ; AVX:       # %bb.0:
-; AVX-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
-; AVX-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm1
-; AVX-NEXT:    vxorps %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vxorps %xmm1, %xmm0, %xmm0
+; AVX-NEXT:    vxorps %xmm1, %xmm1, %xmm1
+; AVX-NEXT:    vinsertf128 $1, %xmm0, %ymm1, %ymm0
 ; AVX-NEXT:    retq
   %xw = shufflevector <2 x i64> %x, <2 x i64> undef, <4 x i32> <i32 undef, i32 undef, i32 0, i32 1>
   %yw = shufflevector <2 x i64> %y, <2 x i64> undef, <4 x i32> <i32 undef, i32 undef, i32 0, i32 1>