diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2793,16 +2793,26 @@
 /// the opcode and bypass the mask operation.
 static SDValue foldAddSubMasked1(bool IsAdd, SDValue N0, SDValue N1,
                                  SelectionDAG &DAG, const SDLoc &DL) {
+  if (N1.getOpcode() == ISD::ZERO_EXTEND)
+    N1 = N1.getOperand(0);
+
   if (N1.getOpcode() != ISD::AND || !isOneOrOneSplat(N1->getOperand(1)))
     return SDValue();
 
   EVT VT = N0.getValueType();
-  if (DAG.ComputeNumSignBits(N1.getOperand(0)) != VT.getScalarSizeInBits())
+  SDValue N10 = N1.getOperand(0);
+  if (N10.getValueType() != VT && N10.getOpcode() == ISD::TRUNCATE)
+    N10 = N10.getOperand(0);
+
+  if (N10.getValueType() != VT)
+    return SDValue();
+
+  if (DAG.ComputeNumSignBits(N10) != VT.getScalarSizeInBits())
     return SDValue();
 
   // add N0, (and (AssertSext X, i1), 1) --> sub N0, X
   // sub N0, (and (AssertSext X, i1), 1) --> add N0, X
-  return DAG.getNode(IsAdd ? ISD::SUB : ISD::ADD, DL, VT, N0, N1.getOperand(0));
+  return DAG.getNode(IsAdd ? ISD::SUB : ISD::ADD, DL, VT, N0, N10);
 }
 
 /// Helper for doing combines based on N0 and N1 being added to each other.
diff --git a/llvm/test/CodeGen/X86/known-signbits-vector.ll b/llvm/test/CodeGen/X86/known-signbits-vector.ll
--- a/llvm/test/CodeGen/X86/known-signbits-vector.ll
+++ b/llvm/test/CodeGen/X86/known-signbits-vector.ll
@@ -679,8 +679,6 @@
 ; X64:       # %bb.0:
 ; X64-NEXT:    vcmpeqsd %xmm1, %xmm0, %xmm0
 ; X64-NEXT:    vmovq %xmm0, %rax
-; X64-NEXT:    andl $1, %eax
-; X64-NEXT:    negq %rax
 ; X64-NEXT:    retq
   %3 = fcmp oeq double %0, %1
   %4 = sext i1 %3 to i64