Index: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
@@ -30628,6 +30628,9 @@
     // Byte blends are only available in AVX2
     if (VT == MVT::v32i8 && !Subtarget.hasAVX2())
       return SDValue();
+    // There are no 512-bit blend instructions that use sign bits.
+    if (VT.is512BitVector())
+      return SDValue();
 
     assert(BitWidth >= 8 && BitWidth <= 64 && "Invalid mask size");
     APInt DemandedMask(APInt::getSignMask(BitWidth));
Index: llvm/trunk/test/CodeGen/X86/pr34139.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/pr34139.ll
+++ llvm/trunk/test/CodeGen/X86/pr34139.ll
@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -mcpu=knl | FileCheck %s
+
+define void @f_f(<16 x double>* %ptr) {
+; CHECK-LABEL: f_f:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    vpcmpeqd %xmm0, %xmm0, %xmm0
+; CHECK-NEXT:    vmovdqa %xmm0, (%rax)
+; CHECK-NEXT:    vpternlogd $255, %zmm0, %zmm0, %zmm0
+; CHECK-NEXT:    vmovapd (%rdi), %zmm1
+; CHECK-NEXT:    vmovapd 64(%rdi), %zmm2
+; CHECK-NEXT:    vptestmq %zmm0, %zmm0, %k1
+; CHECK-NEXT:    vmovapd %zmm0, %zmm1 {%k1}
+; CHECK-NEXT:    vmovapd %zmm0, %zmm2 {%k1}
+; CHECK-NEXT:    vmovapd %zmm2, 64(%rdi)
+; CHECK-NEXT:    vmovapd %zmm1, (%rdi)
+  store <16 x i8> <i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1>, <16 x i8>* undef
+  %load_mask8.i.i.i = load <16 x i8>, <16 x i8>* undef
+  %v.i.i.i.i = load <16 x double>, <16 x double>* %ptr
+  %mask_vec_i1.i.i.i51.i.i = icmp ne <16 x i8> %load_mask8.i.i.i, zeroinitializer
+  %v1.i.i.i.i = select <16 x i1> %mask_vec_i1.i.i.i51.i.i, <16 x double> undef, <16 x double> %v.i.i.i.i
+  store <16 x double> %v1.i.i.i.i, <16 x double>* %ptr
+  unreachable
+}