[turbofan] Support for combining branches with <Operation>WithOverflow.

src/compiler/instruction-selector-impl.h

Index: src/compiler/instruction-selector-impl.h
diff --git a/src/compiler/instruction-selector-impl.h b/src/compiler/instruction-selector-impl.h
index 31031d8410aa5029287fea421feae98bd1d672a0..5b1dfac4aba399c9e010f69208e3899a458a27e8 100644
--- a/src/compiler/instruction-selector-impl.h
+++ b/src/compiler/instruction-selector-impl.h
@@ -48,6 +48,7 @@ class OperandGenerator {
   }
 
   InstructionOperand* DefineAsConstant(Node* node) {
+    selector()->MarkAsDefined(node);
     sequence()->AddConstant(node->id(), ToConstant(node));
     return ConstantOperand::Create(node->id(), zone());
   }
@@ -179,12 +180,16 @@ class OperandGenerator {
     ASSERT_NOT_NULL(node);
     ASSERT_NOT_NULL(operand);
     operand->set_virtual_register(node->id());
+    selector()->MarkAsDefined(node);
     return operand;
   }
 
   UnallocatedOperand* Use(Node* node, UnallocatedOperand* operand) {
-    selector_->MarkAsUsed(node);
-    return Define(node, operand);
+    ASSERT_NOT_NULL(node);
+    ASSERT_NOT_NULL(operand);
+    operand->set_virtual_register(node->id());
+    selector()->MarkAsUsed(node);
+    return operand;
   }
 
   UnallocatedOperand* ToUnallocatedOperand(LinkageLocation location) {
@@ -215,6 +220,8 @@ class OperandGenerator {
 // instruction and the branch or set it should be combined with.
 class FlagsContinuation V8_FINAL {
  public:
+  FlagsContinuation() : mode_(kFlags_none) {}
+
   // Creates a new flags continuation from the given condition and true/false
   // blocks.
   FlagsContinuation(FlagsCondition condition, BasicBlock* true_block,
@@ -236,7 +243,10 @@ class FlagsContinuation V8_FINAL {
   bool IsNone() const { return mode_ == kFlags_none; }
   bool IsBranch() const { return mode_ == kFlags_branch; }
   bool IsSet() const { return mode_ == kFlags_set; }
-  FlagsCondition condition() const { return condition_; }
+  FlagsCondition condition() const {
+    ASSERT(!IsNone());
+    return condition_;
+  }
   Node* result() const {
     ASSERT(IsSet());
     return result_;
@@ -250,9 +260,13 @@ class FlagsContinuation V8_FINAL {
     return false_block_;
   }
 
-  void Negate() { condition_ = static_cast<FlagsCondition>(condition_ ^ 1); }
+  void Negate() {
+    ASSERT(!IsNone());
+    condition_ = static_cast<FlagsCondition>(condition_ ^ 1);
+  }
 
   void Commute() {
+    ASSERT(!IsNone());
     switch (condition_) {
       case kEqual:
       case kNotEqual:
@@ -312,8 +326,11 @@ class FlagsContinuation V8_FINAL {
 
   // Encodes this flags continuation into the given opcode.
   InstructionCode Encode(InstructionCode opcode) {
-    return opcode | FlagsModeField::encode(mode_) |
-           FlagsConditionField::encode(condition_);
+    opcode |= FlagsModeField::encode(mode_);
+    if (mode_ != kFlags_none) {
+      opcode |= FlagsConditionField::encode(condition_);
+    }
+    return opcode;
   }
 
  private: