Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -54,6 +54,36 @@
   return Builder.CreateSelect(Builder.CreateICmp(Pred, A, B), A, B);
 }
 
+/// Fold
+///   %A = icmp eq/ne i8 %x, 0
+///   %B = op i8 %x, %z
+///   %C = select i1 %A, i8 %B, i8 %y
+/// To
+///   %C = select i1 %A, i8 %z, i8 %y
+/// OP: binop with an identity constant
+/// TODO: support for non-commutative and FP opcodes
+static Instruction *foldSelectBinOpIdentity(SelectInst &Sel) {
+
+  Value *Cond = Sel.getCondition();
+  Value *X, *Z;
+  Constant *C;
+  CmpInst::Predicate Pred;
+  if (!match(Cond, m_ICmp(Pred, m_Value(X), m_Constant(C))) ||
+      !ICmpInst::isEquality(Pred))
+    return nullptr;
+
+  bool IsEq = Pred == ICmpInst::ICMP_EQ;
+  auto *BO =
+      dyn_cast<BinaryOperator>(IsEq ? Sel.getTrueValue() : Sel.getFalseValue());
+  // TODO: support for undefs
+  if (BO && match(BO, m_c_BinOp(m_Specific(X), m_Value(Z))) &&
+      ConstantExpr::getBinOpIdentity(BO->getOpcode(), X->getType()) == C) {
+    Sel.setOperand(IsEq ? 1 : 2, Z);
+    return &Sel;
+  }
+  return nullptr;
+}
+
 /// This folds:
 ///  select (icmp eq (and X, C1)), TC, FC
 ///    iff C1 is a power 2 and the difference between TC and FC is a power-of-2.
@@ -1961,5 +1991,8 @@
   if (Instruction *Select = foldSelectCmpXchg(SI))
     return Select;
 
+  if (Instruction *Select = foldSelectBinOpIdentity(SI))
+    return Select;
+
   return nullptr;
 }
Index: llvm/trunk/test/Transforms/InstCombine/select-binop-icmp.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/select-binop-icmp.ll
+++ llvm/trunk/test/Transforms/InstCombine/select-binop-icmp.ll
@@ -6,8 +6,7 @@
 define i32 @select_xor_icmp(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_xor_icmp(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[B:%.*]] = xor i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, 0
@@ -19,8 +18,7 @@
 define i32 @select_xor_icmp2(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_xor_icmp2(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[B:%.*]] = xor i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp ne i32 %x, 0
@@ -32,8 +30,7 @@
 define i32 @select_xor_icmp_meta(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_xor_icmp_meta(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[B:%.*]] = xor i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]], !prof !0
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]], !prof !0
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, 0
@@ -45,8 +42,7 @@
 define i32 @select_mul_icmp(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_mul_icmp(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 1
-; CHECK-NEXT:    [[B:%.*]] = mul i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, 1
@@ -58,8 +54,7 @@
 define i32 @select_add_icmp(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_add_icmp(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[B:%.*]] = add i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, 0
@@ -71,8 +66,7 @@
 define i32 @select_or_icmp(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_or_icmp(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[B:%.*]] = or i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, 0
@@ -84,8 +78,7 @@
 define i32 @select_and_icmp(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_and_icmp(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], -1
-; CHECK-NEXT:    [[B:%.*]] = and i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, -1
@@ -97,8 +90,7 @@
 define <2 x i8> @select_xor_icmp_vec(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
 ; CHECK-LABEL: @select_xor_icmp_vec(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq <2 x i8> [[X:%.*]], zeroinitializer
-; CHECK-NEXT:    [[B:%.*]] = xor <2 x i8> [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select <2 x i1> [[A]], <2 x i8> [[B]], <2 x i8> [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select <2 x i1> [[A]], <2 x i8> [[Z:%.*]], <2 x i8> [[Y:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[C]]
 ;
   %A = icmp eq <2 x i8>  %x, <i8 0, i8 0>
@@ -111,8 +103,7 @@
 ; CHECK-LABEL: @select_xor_icmp_vec_use(
 ; CHECK-NEXT:    [[A:%.*]] = icmp ne <2 x i8> [[X:%.*]], zeroinitializer
 ; CHECK-NEXT:    call void @use(<2 x i1> [[A]])
-; CHECK-NEXT:    [[B:%.*]] = xor <2 x i8> [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select <2 x i1> [[A]], <2 x i8> [[Y:%.*]], <2 x i8> [[B]]
+; CHECK-NEXT:    [[C:%.*]] = select <2 x i1> [[A]], <2 x i8> [[Y:%.*]], <2 x i8> [[Z:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[C]]
 ;
   %A = icmp ne <2 x i8>  %x, <i8 0, i8 0>
@@ -125,8 +116,7 @@
 define i32 @select_xor_inv_icmp(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_xor_inv_icmp(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[B:%.*]] = xor i32 [[Z:%.*]], [[X]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp eq i32 %x, 0
@@ -138,8 +128,7 @@
 define i32 @select_xor_inv_icmp2(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @select_xor_inv_icmp2(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[B:%.*]] = xor i32 [[X]], [[Z:%.*]]
-; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[B]], i32 [[Y:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = select i1 [[A]], i32 [[Z:%.*]], i32 [[Y:%.*]]
 ; CHECK-NEXT:    ret i32 [[C]]
 ;
   %A = icmp ne i32 %x, 0
@@ -240,6 +229,7 @@
   ret <2 x i8>  %C
 }
 
+; TODO: support for undefs, check for an identity constant does not handle them yet
 define <2 x i8> @select_xor_icmp_vec_bad_2(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
 ; CHECK-LABEL: @select_xor_icmp_vec_bad_2(
 ; CHECK-NEXT:    [[A:%.*]] = icmp eq <2 x i8> [[X:%.*]], <i8 0, i8 undef>
Index: llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll
===================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll
+++ llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll
@@ -5,15 +5,15 @@
 define void @test_simple(i32* %p, i32 %a, i32 %b) {
 ; CHECK-LABEL: @test_simple(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = icmp ne i32 [[A:%.*]], 0
+; CHECK-NEXT:    [[X1:%.*]] = icmp ne i32 [[A:%.*]], 0
 ; CHECK-NEXT:    [[X2:%.*]] = icmp eq i32 [[B:%.*]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = xor i1 [[X2]], true
-; CHECK-NEXT:    [[TMP2:%.*]] = or i1 [[TMP0]], [[TMP1]]
-; CHECK-NEXT:    br i1 [[TMP2]], label [[TMP3:%.*]], label [[TMP4:%.*]]
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X2]], true
+; CHECK-NEXT:    [[TMP1:%.*]] = or i1 [[X1]], [[TMP0]]
+; CHECK-NEXT:    br i1 [[TMP1]], label [[TMP2:%.*]], label [[TMP3:%.*]]
 ; CHECK:         [[NOT_X2:%.*]] = xor i1 [[X2]], true
-; CHECK-NEXT:    [[DOT:%.*]] = zext i1 [[NOT_X2]] to i32
-; CHECK-NEXT:    store i32 [[DOT]], i32* [[P:%.*]], align 4
-; CHECK-NEXT:    br label [[TMP4]]
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = zext i1 [[NOT_X2]] to i32
+; CHECK-NEXT:    store i32 [[SPEC_SELECT]], i32* [[P:%.*]], align 4
+; CHECK-NEXT:    br label [[TMP3]]
 ; CHECK:         ret void
 ;
 entry:
@@ -44,8 +44,8 @@
 ; CHECK-NEXT:    [[X2:%.*]] = icmp eq i32 [[B:%.*]], 0
 ; CHECK-NEXT:    [[TMP0:%.*]] = or i1 [[X1]], [[X2]]
 ; CHECK-NEXT:    br i1 [[TMP0]], label [[TMP1:%.*]], label [[TMP2:%.*]]
-; CHECK:         [[DOT:%.*]] = zext i1 [[X2]] to i32
-; CHECK-NEXT:    store i32 [[DOT]], i32* [[P:%.*]], align 4
+; CHECK:         [[SPEC_SELECT:%.*]] = zext i1 [[X2]] to i32
+; CHECK-NEXT:    store i32 [[SPEC_SELECT]], i32* [[P:%.*]], align 4
 ; CHECK-NEXT:    br label [[TMP2]]
 ; CHECK:         ret void
 ;
@@ -76,16 +76,16 @@
 ; CHECK-NEXT:    [[TMP0:%.*]] = or i32 [[B:%.*]], [[A:%.*]]
 ; CHECK-NEXT:    [[X4:%.*]] = icmp eq i32 [[D:%.*]], 0
 ; CHECK-NEXT:    [[TMP1:%.*]] = or i32 [[TMP0]], [[C:%.*]]
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i32 [[TMP1]], 0
-; CHECK-NEXT:    [[TMP2:%.*]] = xor i1 [[X4]], true
-; CHECK-NEXT:    [[TMP4:%.*]] = or i1 [[TMP3]], [[TMP2]]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i32 [[TMP1]], 0
+; CHECK-NEXT:    [[TMP3:%.*]] = xor i1 [[X4]], true
+; CHECK-NEXT:    [[TMP4:%.*]] = or i1 [[TMP2]], [[TMP3]]
 ; CHECK-NEXT:    br i1 [[TMP4]], label [[TMP5:%.*]], label [[TMP6:%.*]]
 ; CHECK:         [[X3:%.*]] = icmp eq i32 [[C]], 0
-; CHECK-NEXT:    [[NOT_X2:%.*]] = icmp ne i32 [[B]], 0
-; CHECK-NEXT:    [[DOT:%.*]] = zext i1 [[NOT_X2]] to i32
-; CHECK-NEXT:    [[DOT_:%.*]] = select i1 [[X3]], i32 [[DOT]], i32 2
-; CHECK-NEXT:    [[DOT__:%.*]] = select i1 [[X4]], i32 [[DOT_]], i32 3
-; CHECK-NEXT:    store i32 [[DOT__]], i32* [[P:%.*]], align 4
+; CHECK-NEXT:    [[X2:%.*]] = icmp ne i32 [[B]], 0
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = zext i1 [[X2]] to i32
+; CHECK-NEXT:    [[SPEC_SELECT1:%.*]] = select i1 [[X3]], i32 [[SPEC_SELECT]], i32 2
+; CHECK-NEXT:    [[SPEC_SELECT2:%.*]] = select i1 [[X4]], i32 [[SPEC_SELECT1]], i32 3
+; CHECK-NEXT:    store i32 [[SPEC_SELECT2]], i32* [[P:%.*]], align 4
 ; CHECK-NEXT:    br label [[TMP6]]
 ; CHECK:         ret void
 ;
@@ -265,8 +265,7 @@
 ; CHECK-LABEL: @test_diamond_simple(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[X1:%.*]] = icmp eq i32 [[A:%.*]], 0
-; CHECK-NEXT:    [[Z1:%.*]] = add i32 [[A]], [[B:%.*]]
-; CHECK-NEXT:    [[Z2:%.*]] = select i1 [[X1]], i32 [[Z1]], i32 0
+; CHECK-NEXT:    [[Z2:%.*]] = select i1 [[X1]], i32 [[B:%.*]], i32 0
 ; CHECK-NEXT:    [[X2:%.*]] = icmp eq i32 [[B]], 0
 ; CHECK-NEXT:    [[Z3:%.*]] = sub i32 [[Z2]], [[B]]
 ; CHECK-NEXT:    [[Z4:%.*]] = select i1 [[X2]], i32 [[Z3]], i32 3