Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5380,11 +5380,11 @@
   auto matchAndXor = [&X, &Y, &M](SDValue And, unsigned XorIdx, SDValue Other) {
     if (And.getOpcode() != ISD::AND || !And.hasOneUse())
       return false;
-    if (And.getOperand(XorIdx).getOpcode() != ISD::XOR ||
-        !And.getOperand(XorIdx).hasOneUse())
+    SDValue Xor = And.getOperand(XorIdx);
+    if (Xor.getOpcode() != ISD::XOR || !Xor.hasOneUse())
       return false;
-    SDValue Xor0 = And.getOperand(XorIdx).getOperand(0);
-    SDValue Xor1 = And.getOperand(XorIdx).getOperand(1);
+    SDValue Xor0 = Xor.getOperand(0);
+    SDValue Xor1 = Xor.getOperand(1);
     if (Other == Xor0)
       std::swap(Xor0, Xor1);
     if (Other != Xor1)
@@ -5395,6 +5395,11 @@
     return true;
   };
 
+  // Don't do anything if the second operand of xor is a constant.
+  // It can only be a second operand because of canonicalization.
+  if (isa<ConstantSDNode>(N->getOperand(1).getNode()))
+    return SDValue();
+
   SDValue A = N->getOperand(0);
   SDValue B = N->getOperand(1);
   if (!matchAndXor(A, 0, B) && !matchAndXor(A, 1, B) && !matchAndXor(B, 0, A) &&
Index: test/CodeGen/AArch64/unfold-masked-merge-scalar-variablemask.ll
===================================================================
--- test/CodeGen/AArch64/unfold-masked-merge-scalar-variablemask.ll
+++ test/CodeGen/AArch64/unfold-masked-merge-scalar-variablemask.ll
@@ -347,8 +347,8 @@
 define i32 @in_constant_varx_mone(i32 %x, i32 %y, i32 %mask) {
 ; CHECK-LABEL: in_constant_varx_mone:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    and w8, w0, w2
-; CHECK-NEXT:    orn w0, w8, w2
+; CHECK-NEXT:    bic w8, w2, w0
+; CHECK-NEXT:    mvn w0, w8
 ; CHECK-NEXT:    ret
   %n0 = xor i32 %x, -1 ; %x
   %n1 = and i32 %n0, %mask
@@ -370,8 +370,9 @@
 define i32 @in_constant_varx_mone_invmask(i32 %x, i32 %y, i32 %mask) {
 ; CHECK-LABEL: in_constant_varx_mone_invmask:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    bic w8, w0, w2
-; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mvn w8, w0
+; CHECK-NEXT:    bic w8, w8, w2
+; CHECK-NEXT:    mvn w0, w8
 ; CHECK-NEXT:    ret
   %notmask = xor i32 %mask, -1
   %n0 = xor i32 %x, -1 ; %x
@@ -397,9 +398,9 @@
 ; CHECK-LABEL: in_constant_varx_42:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    mov w8, #42
-; CHECK-NEXT:    bic w8, w8, w2
-; CHECK-NEXT:    and w9, w0, w2
-; CHECK-NEXT:    orr w0, w9, w8
+; CHECK-NEXT:    eor w9, w0, w8
+; CHECK-NEXT:    and w9, w9, w2
+; CHECK-NEXT:    eor w0, w9, w8
 ; CHECK-NEXT:    ret
   %n0 = xor i32 %x, 42 ; %x
   %n1 = and i32 %n0, %mask
@@ -424,9 +425,9 @@
 ; CHECK-LABEL: in_constant_varx_42_invmask:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    mov w8, #42
-; CHECK-NEXT:    and w8, w2, w8
-; CHECK-NEXT:    bic w9, w0, w2
-; CHECK-NEXT:    orr w0, w9, w8
+; CHECK-NEXT:    eor w9, w0, w8
+; CHECK-NEXT:    bic w9, w9, w2
+; CHECK-NEXT:    eor w0, w9, w8
 ; CHECK-NEXT:    ret
   %notmask = xor i32 %mask, -1
   %n0 = xor i32 %x, 42 ; %x
Index: test/CodeGen/X86/unfold-masked-merge-scalar-variablemask.ll
===================================================================
--- test/CodeGen/X86/unfold-masked-merge-scalar-variablemask.ll
+++ test/CodeGen/X86/unfold-masked-merge-scalar-variablemask.ll
@@ -570,10 +570,8 @@
 ;
 ; CHECK-BMI-LABEL: in_constant_varx_mone:
 ; CHECK-BMI:       # %bb.0:
-; CHECK-BMI-NEXT:    andl %edx, %edi
-; CHECK-BMI-NEXT:    notl %edx
-; CHECK-BMI-NEXT:    orl %edi, %edx
-; CHECK-BMI-NEXT:    movl %edx, %eax
+; CHECK-BMI-NEXT:    andnl %edx, %edi, %eax
+; CHECK-BMI-NEXT:    notl %eax
 ; CHECK-BMI-NEXT:    retq
   %n0 = xor i32 %x, -1 ; %x
   %n1 = and i32 %n0, %mask
@@ -612,8 +610,9 @@
 ;
 ; CHECK-BMI-LABEL: in_constant_varx_mone_invmask:
 ; CHECK-BMI:       # %bb.0:
-; CHECK-BMI-NEXT:    andnl %edi, %edx, %eax
-; CHECK-BMI-NEXT:    orl %edx, %eax
+; CHECK-BMI-NEXT:    notl %edx
+; CHECK-BMI-NEXT:    andnl %edx, %edi, %eax
+; CHECK-BMI-NEXT:    notl %eax
 ; CHECK-BMI-NEXT:    retq
   %notmask = xor i32 %mask, -1
   %n0 = xor i32 %x, -1 ; %x
@@ -656,11 +655,10 @@
 ;
 ; CHECK-BMI-LABEL: in_constant_varx_42:
 ; CHECK-BMI:       # %bb.0:
+; CHECK-BMI-NEXT:    xorl $42, %edi
 ; CHECK-BMI-NEXT:    andl %edx, %edi
-; CHECK-BMI-NEXT:    notl %edx
-; CHECK-BMI-NEXT:    andl $42, %edx
-; CHECK-BMI-NEXT:    orl %edi, %edx
-; CHECK-BMI-NEXT:    movl %edx, %eax
+; CHECK-BMI-NEXT:    xorl $42, %edi
+; CHECK-BMI-NEXT:    movl %edi, %eax
 ; CHECK-BMI-NEXT:    retq
   %n0 = xor i32 %x, 42 ; %x
   %n1 = and i32 %n0, %mask
@@ -702,9 +700,9 @@
 ;
 ; CHECK-BMI-LABEL: in_constant_varx_42_invmask:
 ; CHECK-BMI:       # %bb.0:
+; CHECK-BMI-NEXT:    xorl $42, %edi
 ; CHECK-BMI-NEXT:    andnl %edi, %edx, %eax
-; CHECK-BMI-NEXT:    andl $42, %edx
-; CHECK-BMI-NEXT:    orl %edx, %eax
+; CHECK-BMI-NEXT:    xorl $42, %eax
 ; CHECK-BMI-NEXT:    retq
   %notmask = xor i32 %mask, -1
   %n0 = xor i32 %x, 42 ; %x