Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -27153,13 +27153,18 @@
       }
       if (Match) {
         unsigned SrcSize = std::max(128u, NumDstElts * MaskEltSize);
-        SrcVT = MVT::getVectorVT(MaskVT.getScalarType(), SrcSize / MaskEltSize);
-        if (SrcVT != MaskVT)
+        MVT ScalarTy = MaskVT.isInteger() ? MaskVT.getScalarType() :
+                                            MVT::getIntegerVT(MaskEltSize);
+        SrcVT = MVT::getVectorVT(ScalarTy, SrcSize / MaskEltSize);
+
+        if (SrcVT.getSizeInBits() != MaskVT.getSizeInBits()) {
           V1 = extractSubVector(V1, 0, DAG, DL, SrcSize);
+          Shuffle = unsigned(X86ISD::VZEXT);
+        } else
+          Shuffle = unsigned(ISD::ZERO_EXTEND_VECTOR_INREG);
+
         DstVT = MVT::getIntegerVT(Scale * MaskEltSize);
         DstVT = MVT::getVectorVT(DstVT, NumDstElts);
-        Shuffle = SrcVT != MaskVT ? unsigned(X86ISD::VZEXT)
-                                  : unsigned(ISD::ZERO_EXTEND_VECTOR_INREG);
         return true;
       }
     }
Index: test/CodeGen/X86/vector-shuffle-combining-avx2.ll
===================================================================
--- test/CodeGen/X86/vector-shuffle-combining-avx2.ll
+++ test/CodeGen/X86/vector-shuffle-combining-avx2.ll
@@ -897,3 +897,65 @@
   %3 = shufflevector <32 x i8> %2, <32 x i8> undef, <32 x i32> <i32 0, i32 1, i32 1, i32 2, i32 3, i32 4, i32 4, i32 5, i32 6, i32 7, i32 7, i32 8, i32 9, i32 10, i32 10, i32 11, i32 16, i32 17, i32 17, i32 18, i32 19, i32 20, i32 20, i32 21, i32 22, i32 23, i32 23, i32 24, i32 25, i32 26, i32 26, i32 27>
   ret <32 x i8> %3
 }
+
+define internal fastcc <8 x float> @PR34577(<8 x float> %inp0, <8 x float> %inp1, <8 x float> %inp2) #0 {
+; X32-AVX2-LABEL: PR34577:
+; X32-AVX2:       # BB#0: # %entry
+; X32-AVX2-NEXT:    vpxor %xmm2, %xmm2, %xmm2
+; X32-AVX2-NEXT:    vpmovzxdq {{.*#+}} ymm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero
+; X32-AVX2-NEXT:    vpblendd {{.*#+}} ymm0 = ymm2[0,1,2,3],ymm0[4,5,6,7]
+; X32-AVX2-NEXT:    vmovaps {{.*#+}} ymm2 = <u,u,7,2,u,u,3,2>
+; X32-AVX2-NEXT:    vpermps %ymm1, %ymm2, %ymm1
+; X32-AVX2-NEXT:    vblendpd {{.*#+}} ymm0 = ymm0[0],ymm1[1],ymm0[2],ymm1[3]
+; X32-AVX2-NEXT:    retl
+;
+; X32-AVX512-LABEL: PR34577:
+; X32-AVX512:       # BB#0: # %entry
+; X32-AVX512-NEXT:    vmovaps {{.*#+}} ymm3 = <1,u,u,u,2,u,5,0>
+; X32-AVX512-NEXT:    vpermps %ymm0, %ymm3, %ymm0
+; X32-AVX512-NEXT:    vmovaps {{.*#+}} ymm3 = <u,2,3,5,u,5,u,u>
+; X32-AVX512-NEXT:    vpermps %ymm2, %ymm3, %ymm2
+; X32-AVX512-NEXT:    vblendps {{.*#+}} ymm0 = ymm0[0],ymm2[1,2,3],ymm0[4],ymm2[5],ymm0[6,7]
+; X32-AVX512-NEXT:    vxorps %xmm2, %xmm2, %xmm2
+; X32-AVX512-NEXT:    movb $86, %al
+; X32-AVX512-NEXT:    kmovw %eax, %k1
+; X32-AVX512-NEXT:    vblendmps %zmm0, %zmm2, %zmm0 {%k1}
+; X32-AVX512-NEXT:    vblendpd {{.*#+}} ymm0 = ymm2[0,1],ymm0[2,3]
+; X32-AVX512-NEXT:    vmovaps {{.*#+}} ymm2 = <u,u,7,2,u,u,3,2>
+; X32-AVX512-NEXT:    vpermps %ymm1, %ymm2, %ymm1
+; X32-AVX512-NEXT:    vblendpd {{.*#+}} ymm0 = ymm0[0],ymm1[1],ymm0[2],ymm1[3]
+; X32-AVX512-NEXT:    retl
+;
+; X64-AVX2-LABEL: PR34577:
+; X64-AVX2:       # BB#0: # %entry
+; X64-AVX2-NEXT:    vpxor %xmm2, %xmm2, %xmm2
+; X64-AVX2-NEXT:    vpmovzxdq {{.*#+}} ymm0 = xmm0[0],zero,xmm0[1],zero,xmm0[2],zero,xmm0[3],zero
+; X64-AVX2-NEXT:    vpblendd {{.*#+}} ymm0 = ymm2[0,1,2,3],ymm0[4,5,6,7]
+; X64-AVX2-NEXT:    vmovaps {{.*#+}} ymm2 = <u,u,7,2,u,u,3,2>
+; X64-AVX2-NEXT:    vpermps %ymm1, %ymm2, %ymm1
+; X64-AVX2-NEXT:    vblendpd {{.*#+}} ymm0 = ymm0[0],ymm1[1],ymm0[2],ymm1[3]
+; X64-AVX2-NEXT:    retq
+;
+; X64-AVX512-LABEL: PR34577:
+; X64-AVX512:       # BB#0: # %entry
+; X64-AVX512-NEXT:    vmovaps {{.*#+}} ymm3 = <1,u,u,u,2,u,5,0>
+; X64-AVX512-NEXT:    vpermps %ymm0, %ymm3, %ymm0
+; X64-AVX512-NEXT:    vmovaps {{.*#+}} ymm3 = <u,2,3,5,u,5,u,u>
+; X64-AVX512-NEXT:    vpermps %ymm2, %ymm3, %ymm2
+; X64-AVX512-NEXT:    vblendps {{.*#+}} ymm0 = ymm0[0],ymm2[1,2,3],ymm0[4],ymm2[5],ymm0[6,7]
+; X64-AVX512-NEXT:    vxorps %xmm2, %xmm2, %xmm2
+; X64-AVX512-NEXT:    movb $86, %al
+; X64-AVX512-NEXT:    kmovw %eax, %k1
+; X64-AVX512-NEXT:    vblendmps %zmm0, %zmm2, %zmm0 {%k1}
+; X64-AVX512-NEXT:    vblendpd {{.*#+}} ymm0 = ymm2[0,1],ymm0[2,3]
+; X64-AVX512-NEXT:    vmovaps {{.*#+}} ymm2 = <u,u,7,2,u,u,3,2>
+; X64-AVX512-NEXT:    vpermps %ymm1, %ymm2, %ymm1
+; X64-AVX512-NEXT:    vblendpd {{.*#+}} ymm0 = ymm0[0],ymm1[1],ymm0[2],ymm1[3]
+; X64-AVX512-NEXT:    retq
+entry:
+  %shuf0 = shufflevector <8 x float> %inp0, <8 x float> %inp2, <8 x i32> <i32 1, i32 10, i32 11, i32 13, i32 2, i32 13, i32 5, i32 0>
+  %sel = select <8 x i1> <i1 false, i1 true, i1 true, i1 false, i1 true, i1 false, i1 true, i1 false>, <8 x float> %shuf0, <8 x float> zeroinitializer
+  %shuf1 = shufflevector <8 x float> zeroinitializer, <8 x float> %sel, <8 x i32> <i32 6, i32 11, i32 6, i32 15, i32 12, i32 11, i32 1, i32 3>
+  %shuf2 = shufflevector <8 x float> %inp1, <8 x float> %shuf1, <8 x i32> <i32 15, i32 10, i32 7, i32 2, i32 12, i32 undef, i32 3, i32 2>
+  ret <8 x float> %shuf2
+}