Index: lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2418,6 +2418,7 @@
 /// If A has one use, and M is inverted, we can convert it into:
 ///    |  D  |
 ///   ((x ^ y) & ~M) ^ x
+/// If the M is constant, we want to unfold it to (x & M) | (y & ~M)
 static Instruction *visitMaskedMerge(BinaryOperator &I,
                                      InstCombiner::BuilderTy &Builder) {
   Value *B, *X, *D;
@@ -2436,6 +2437,15 @@
     return BinaryOperator::CreateXor(NewA, X);
   }
 
+  Constant *C;
+  if (D->hasOneUse() && match(M, m_Constant(C))) {
+    // Unfold.
+    Value *LHS = Builder.CreateAnd(X, C);
+    Value *iC = Builder.CreateNot(C);
+    Value *RHS = Builder.CreateAnd(B, iC);
+    return BinaryOperator::CreateOr(LHS, RHS);
+  }
+
   return nullptr;
 }
 
Index: test/Transforms/InstCombine/unfold-masked-merge-with-const-mask-scalar.ll
===================================================================
--- test/Transforms/InstCombine/unfold-masked-merge-with-const-mask-scalar.ll
+++ test/Transforms/InstCombine/unfold-masked-merge-with-const-mask-scalar.ll
@@ -8,9 +8,9 @@
 
 define i4 @scalar0 (i4 %x, i4 %y) {
 ; CHECK-LABEL: @scalar0(
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], 1
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[N1]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[X:%.*]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[Y:%.*]], -2
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %n0 = xor i4 %x, %y
@@ -21,9 +21,9 @@
 
 define i4 @scalar1 (i4 %x, i4 %y) {
 ; CHECK-LABEL: @scalar1(
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[N1]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[X:%.*]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[Y:%.*]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %n0 = xor i4 %x, %y
@@ -140,9 +140,9 @@
 
 define i4 @c_1_0_0 (i4 %x, i4 %y) {
 ; CHECK-LABEL: @c_1_0_0(
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[N1]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[X:%.*]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[Y:%.*]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %n0 = xor i4 %y, %x ; swapped order
@@ -153,9 +153,9 @@
 
 define i4 @c_0_1_0 (i4 %x, i4 %y) {
 ; CHECK-LABEL: @c_0_1_0(
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[N1]], [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[Y:%.*]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[X:%.*]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %n0 = xor i4 %x, %y
@@ -168,9 +168,9 @@
 ; CHECK-LABEL: @c_0_0_1(
 ; CHECK-NEXT:    [[X:%.*]] = call i4 @gen4()
 ; CHECK-NEXT:    [[Y:%.*]] = call i4 @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[X]], [[Y]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[Y]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[X]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[Y]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %x  = call i4 @gen4()
@@ -183,9 +183,9 @@
 
 define i4 @c_1_1_0 (i4 %x, i4 %y) {
 ; CHECK-LABEL: @c_1_1_0(
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[N1]], [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[Y:%.*]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[X:%.*]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %n0 = xor i4 %y, %x ; swapped order
@@ -197,9 +197,9 @@
 define i4 @c_1_0_1 (i4 %x) {
 ; CHECK-LABEL: @c_1_0_1(
 ; CHECK-NEXT:    [[Y:%.*]] = call i4 @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[Y]], [[X:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[Y]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[X:%.*]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[Y]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %y  = call i4 @gen4()
@@ -212,9 +212,9 @@
 define i4 @c_0_1_1 (i4 %y) {
 ; CHECK-LABEL: @c_0_1_1(
 ; CHECK-NEXT:    [[X:%.*]] = call i4 @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[X]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[X]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[Y:%.*]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[X]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %x  = call i4 @gen4()
@@ -228,9 +228,9 @@
 ; CHECK-LABEL: @c_1_1_1(
 ; CHECK-NEXT:    [[X:%.*]] = call i4 @gen4()
 ; CHECK-NEXT:    [[Y:%.*]] = call i4 @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor i4 [[Y]], [[X]]
-; CHECK-NEXT:    [[N1:%.*]] = and i4 [[N0]], -2
-; CHECK-NEXT:    [[R:%.*]] = xor i4 [[X]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i4 [[Y]], -2
+; CHECK-NEXT:    [[TMP2:%.*]] = and i4 [[X]], 1
+; CHECK-NEXT:    [[R:%.*]] = or i4 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i4 [[R]]
 ;
   %x  = call i4 @gen4()
Index: test/Transforms/InstCombine/unfold-masked-merge-with-const-mask-vector.ll
===================================================================
--- test/Transforms/InstCombine/unfold-masked-merge-with-const-mask-vector.ll
+++ test/Transforms/InstCombine/unfold-masked-merge-with-const-mask-vector.ll
@@ -8,9 +8,9 @@
 
 define <2 x i4> @splat (<2 x i4> %x, <2 x i4> %y) {
 ; CHECK-LABEL: @splat(
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[N1]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[X:%.*]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[Y:%.*]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %n0 = xor <2 x i4> %x, %y
@@ -21,9 +21,9 @@
 
 define <3 x i4> @splat_undef (<3 x i4> %x, <3 x i4> %y) {
 ; CHECK-LABEL: @splat_undef(
-; CHECK-NEXT:    [[N0:%.*]] = xor <3 x i4> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <3 x i4> [[N0]], <i4 -2, i4 undef, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <3 x i4> [[N1]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <3 x i4> [[X:%.*]], <i4 -2, i4 undef, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <3 x i4> [[Y:%.*]], <i4 1, i4 undef, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <3 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <3 x i4> [[R]]
 ;
   %n0 = xor <3 x i4> %x, %y
@@ -34,9 +34,9 @@
 
 define <2 x i4> @nonsplat (<2 x i4> %x, <2 x i4> %y) {
 ; CHECK-LABEL: @nonsplat(
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 1>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[N1]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[X:%.*]], <i4 -2, i4 1>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[Y:%.*]], <i4 1, i4 -2>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %n0 = xor <2 x i4> %x, %y
@@ -153,9 +153,9 @@
 
 define <2 x i4> @c_1_0_0 (<2 x i4> %x, <2 x i4> %y) {
 ; CHECK-LABEL: @c_1_0_0(
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[N1]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[X:%.*]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[Y:%.*]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %n0 = xor <2 x i4> %y, %x ; swapped order
@@ -166,9 +166,9 @@
 
 define <2 x i4> @c_0_1_0 (<2 x i4> %x, <2 x i4> %y) {
 ; CHECK-LABEL: @c_0_1_0(
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[N1]], [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[Y:%.*]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[X:%.*]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %n0 = xor <2 x i4> %x, %y
@@ -181,9 +181,9 @@
 ; CHECK-LABEL: @c_0_0_1(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i4> @gen4()
 ; CHECK-NEXT:    [[Y:%.*]] = call <2 x i4> @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[X]], [[Y]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[Y]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[X]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[Y]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %x  = call <2 x i4> @gen4()
@@ -196,9 +196,9 @@
 
 define <2 x i4> @c_1_1_0 (<2 x i4> %x, <2 x i4> %y) {
 ; CHECK-LABEL: @c_1_1_0(
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[N1]], [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[Y:%.*]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[X:%.*]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %n0 = xor <2 x i4> %y, %x ; swapped order
@@ -210,9 +210,9 @@
 define <2 x i4> @c_1_0_1 (<2 x i4> %x) {
 ; CHECK-LABEL: @c_1_0_1(
 ; CHECK-NEXT:    [[Y:%.*]] = call <2 x i4> @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[Y]], [[X:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[Y]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[X:%.*]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[Y]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %y  = call <2 x i4> @gen4()
@@ -225,9 +225,9 @@
 define <2 x i4> @c_0_1_1 (<2 x i4> %y) {
 ; CHECK-LABEL: @c_0_1_1(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i4> @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[X]], [[Y:%.*]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[X]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[Y:%.*]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[X]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %x  = call <2 x i4> @gen4()
@@ -241,9 +241,9 @@
 ; CHECK-LABEL: @c_1_1_1(
 ; CHECK-NEXT:    [[X:%.*]] = call <2 x i4> @gen4()
 ; CHECK-NEXT:    [[Y:%.*]] = call <2 x i4> @gen4()
-; CHECK-NEXT:    [[N0:%.*]] = xor <2 x i4> [[Y]], [[X]]
-; CHECK-NEXT:    [[N1:%.*]] = and <2 x i4> [[N0]], <i4 -2, i4 -2>
-; CHECK-NEXT:    [[R:%.*]] = xor <2 x i4> [[X]], [[N1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i4> [[Y]], <i4 -2, i4 -2>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i4> [[X]], <i4 1, i4 1>
+; CHECK-NEXT:    [[R:%.*]] = or <2 x i4> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <2 x i4> [[R]]
 ;
   %x  = call <2 x i4> @gen4()