Remove the obsolete OverwriteMode optimization.

src/ic/ic-state.h

Index: src/ic/ic-state.h
diff --git a/src/ic/ic-state.h b/src/ic/ic-state.h
index 72fc865c68d1ebe221f37829f5e457bf7c12cd84..b5f58ed211a1800ede1b7c6022409cfa04669797 100644
--- a/src/ic/ic-state.h
+++ b/src/ic/ic-state.h
@@ -54,16 +54,12 @@ class CallICState FINAL BASE_EMBEDDED {
 std::ostream& operator<<(std::ostream& os, const CallICState& s);
 
 
-// Mode to overwrite BinaryExpression values.
-enum OverwriteMode { NO_OVERWRITE, OVERWRITE_LEFT, OVERWRITE_RIGHT };
-
 class BinaryOpICState FINAL BASE_EMBEDDED {
  public:
   BinaryOpICState(Isolate* isolate, ExtraICState extra_ic_state);
 
-  BinaryOpICState(Isolate* isolate, Token::Value op, OverwriteMode mode)
+  BinaryOpICState(Isolate* isolate, Token::Value op)
       : op_(op),
-        mode_(mode),
         left_kind_(NONE),
         right_kind_(NONE),
         result_kind_(NONE),
@@ -91,14 +87,6 @@ class BinaryOpICState FINAL BASE_EMBEDDED {
                                   void (*Generate)(Isolate*,
                                                    const BinaryOpICState&));
 
-  bool CanReuseDoubleBox() const {
-    return (result_kind_ > SMI && result_kind_ <= NUMBER) &&
-           ((mode_ == OVERWRITE_LEFT && left_kind_ > SMI &&
-             left_kind_ <= NUMBER) ||
-            (mode_ == OVERWRITE_RIGHT && right_kind_ > SMI &&
-             right_kind_ <= NUMBER));
-  }
-
   // Returns true if the IC _could_ create allocation mementos.
   bool CouldCreateAllocationMementos() const {
     if (left_kind_ == STRING || right_kind_ == STRING) {
@@ -127,7 +115,6 @@ class BinaryOpICState FINAL BASE_EMBEDDED {
   static const int LAST_TOKEN = Token::MOD;
 
   Token::Value op() const { return op_; }
-  OverwriteMode mode() const { return mode_; }
   Maybe<int> fixed_right_arg() const { return fixed_right_arg_; }
 
   Type* GetLeftType(Zone* zone) const { return KindToType(left_kind_, zone); }
@@ -154,17 +141,15 @@ class BinaryOpICState FINAL BASE_EMBEDDED {
   // We truncate the last bit of the token.
   STATIC_ASSERT(LAST_TOKEN - FIRST_TOKEN < (1 << 4));
   class OpField : public BitField<int, 0, 4> {};
-  class OverwriteModeField : public BitField<OverwriteMode, 4, 2> {};
-  class ResultKindField : public BitField<Kind, 6, 3> {};
-  class LeftKindField : public BitField<Kind, 9, 3> {};
+  class ResultKindField : public BitField<Kind, 4, 3> {};
+  class LeftKindField : public BitField<Kind, 7, 3> {};
   // When fixed right arg is set, we don't need to store the right kind.
   // Thus the two fields can overlap.
-  class HasFixedRightArgField : public BitField<bool, 12, 1> {};
-  class FixedRightArgValueField : public BitField<int, 13, 4> {};
-  class RightKindField : public BitField<Kind, 13, 3> {};
+  class HasFixedRightArgField : public BitField<bool, 10, 1> {};
+  class FixedRightArgValueField : public BitField<int, 11, 4> {};
+  class RightKindField : public BitField<Kind, 11, 3> {};
 
   Token::Value op_;
-  OverwriteMode mode_;
   Kind left_kind_;
   Kind right_kind_;
   Kind result_kind_;