Index: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3693,7 +3693,7 @@
     }
     return ComputeNumSignBits(Src, Depth + 1);
   }
-  case ISD::CONCAT_VECTORS:
+  case ISD::CONCAT_VECTORS: {
     // Determine the minimum number of sign bits across all demanded
     // elts of the input vectors. Early out if the result is already 1.
     Tmp = std::numeric_limits<unsigned>::max();
@@ -3711,6 +3711,40 @@
     assert(Tmp <= VTBits && "Failed to determine minimum sign bits");
     return Tmp;
   }
+  case ISD::INSERT_SUBVECTOR: {
+    // If we know the element index, demand any elements from the subvector and
+    // the remainder from the src its inserted into, otherwise demand them all.
+    SDValue Src = Op.getOperand(0);
+    SDValue Sub = Op.getOperand(1);
+    auto *SubIdx = dyn_cast<ConstantSDNode>(Op.getOperand(2));
+    unsigned NumSubElts = Sub.getValueType().getVectorNumElements();
+    if (SubIdx && SubIdx->getAPIntValue().ule(NumElts - NumSubElts)) {
+      Tmp = std::numeric_limits<unsigned>::max();
+      uint64_t Idx = SubIdx->getZExtValue();
+      APInt DemandedSubElts = DemandedElts.extractBits(NumSubElts, Idx);
+      if (!!DemandedSubElts) {
+        Tmp = ComputeNumSignBits(Sub, DemandedSubElts, Depth + 1);
+        if (Tmp == 1) return 1; // early-out
+      }
+      APInt SubMask = APInt::getBitsSet(NumElts, Idx, Idx + NumSubElts);
+      APInt DemandedSrcElts = DemandedElts & ~SubMask;
+      if (!!DemandedSrcElts) {
+        Tmp2 = ComputeNumSignBits(Src, DemandedSrcElts, Depth + 1);
+        Tmp = std::min(Tmp, Tmp2);
+      }
+      assert(Tmp <= VTBits && "Failed to determine minimum sign bits");
+      return Tmp;
+    }
+
+    // Not able to determine the index so just assume worst case.
+    Tmp = ComputeNumSignBits(Sub, Depth + 1);
+    if (Tmp == 1) return 1; // early-out
+    Tmp2 = ComputeNumSignBits(Src, Depth + 1);
+    Tmp = std::min(Tmp, Tmp2);
+    assert(Tmp <= VTBits && "Failed to determine minimum sign bits");
+    return Tmp;
+  }
+  }
 
   // If we are looking at the loaded value of the SDNode.
   if (Op.getResNo() == 0) {
Index: llvm/trunk/test/CodeGen/X86/known-signbits-vector.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/known-signbits-vector.ll
+++ llvm/trunk/test/CodeGen/X86/known-signbits-vector.ll
@@ -394,20 +394,11 @@
 ; X32-LABEL: cross_bb_signbits_insert_subvec:
 ; X32:       # %bb.0:
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-NEXT:    vextractf128 $1, %ymm0, %xmm3
-; X32-NEXT:    vpxor %xmm2, %xmm2, %xmm2
-; X32-NEXT:    vpcmpeqb %xmm2, %xmm3, %xmm3
-; X32-NEXT:    vpcmpeqb %xmm2, %xmm0, %xmm0
-; X32-NEXT:    vinsertf128 $1, %xmm3, %ymm0, %ymm0
-; X32-NEXT:    vextractf128 $1, %ymm0, %xmm3
-; X32-NEXT:    vpsllw $7, %xmm3, %xmm3
-; X32-NEXT:    vmovdqa {{.*#+}} xmm4 = [128,128,128,128,128,128,128,128,128,128,128,128,128,128,128,128]
-; X32-NEXT:    vpand %xmm4, %xmm3, %xmm3
-; X32-NEXT:    vpcmpgtb %xmm3, %xmm2, %xmm3
-; X32-NEXT:    vpsllw $7, %xmm0, %xmm0
-; X32-NEXT:    vpand %xmm4, %xmm0, %xmm0
-; X32-NEXT:    vpcmpgtb %xmm0, %xmm2, %xmm0
-; X32-NEXT:    vinsertf128 $1, %xmm3, %ymm0, %ymm0
+; X32-NEXT:    vextractf128 $1, %ymm0, %xmm2
+; X32-NEXT:    vpxor %xmm3, %xmm3, %xmm3
+; X32-NEXT:    vpcmpeqb %xmm3, %xmm2, %xmm2
+; X32-NEXT:    vpcmpeqb %xmm3, %xmm0, %xmm0
+; X32-NEXT:    vinsertf128 $1, %xmm2, %ymm0, %ymm0
 ; X32-NEXT:    vandnps %ymm1, %ymm0, %ymm1
 ; X32-NEXT:    vandps {{\.LCPI.*}}, %ymm0, %ymm0
 ; X32-NEXT:    vorps %ymm1, %ymm0, %ymm0
@@ -417,20 +408,11 @@
 ;
 ; X64-LABEL: cross_bb_signbits_insert_subvec:
 ; X64:       # %bb.0:
-; X64-NEXT:    vextractf128 $1, %ymm0, %xmm3
-; X64-NEXT:    vpxor %xmm2, %xmm2, %xmm2
-; X64-NEXT:    vpcmpeqb %xmm2, %xmm3, %xmm3
-; X64-NEXT:    vpcmpeqb %xmm2, %xmm0, %xmm0
-; X64-NEXT:    vinsertf128 $1, %xmm3, %ymm0, %ymm0
-; X64-NEXT:    vextractf128 $1, %ymm0, %xmm3
-; X64-NEXT:    vpsllw $7, %xmm3, %xmm3
-; X64-NEXT:    vmovdqa {{.*#+}} xmm4 = [128,128,128,128,128,128,128,128,128,128,128,128,128,128,128,128]
-; X64-NEXT:    vpand %xmm4, %xmm3, %xmm3
-; X64-NEXT:    vpcmpgtb %xmm3, %xmm2, %xmm3
-; X64-NEXT:    vpsllw $7, %xmm0, %xmm0
-; X64-NEXT:    vpand %xmm4, %xmm0, %xmm0
-; X64-NEXT:    vpcmpgtb %xmm0, %xmm2, %xmm0
-; X64-NEXT:    vinsertf128 $1, %xmm3, %ymm0, %ymm0
+; X64-NEXT:    vextractf128 $1, %ymm0, %xmm2
+; X64-NEXT:    vpxor %xmm3, %xmm3, %xmm3
+; X64-NEXT:    vpcmpeqb %xmm3, %xmm2, %xmm2
+; X64-NEXT:    vpcmpeqb %xmm3, %xmm0, %xmm0
+; X64-NEXT:    vinsertf128 $1, %xmm2, %ymm0, %ymm0
 ; X64-NEXT:    vandnps %ymm1, %ymm0, %ymm1
 ; X64-NEXT:    vandps {{.*}}(%rip), %ymm0, %ymm0
 ; X64-NEXT:    vorps %ymm1, %ymm0, %ymm0