Adding fast path for generalizing maps.

src/property-details.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 81 matching lines @@
 
   static Representation None() { return Representation(kNone); }
   static Representation Tagged() { return Representation(kTagged); }
   static Representation Smi() { return Representation(kSmi); }
   static Representation Integer32() { return Representation(kInteger32); }
   static Representation Double() { return Representation(kDouble); }
   static Representation External() { return Representation(kExternal); }
 
   static Representation FromKind(Kind kind) { return Representation(kind); }
 
-  bool Equals(const Representation& other) {
+  bool Equals(const Representation& other) const {
     return kind_ == other.kind_;
   }
 
-  bool is_more_general_than(const Representation& other) {
+  bool is_more_general_than(const Representation& other) const {
     ASSERT(kind_ != kExternal);
     ASSERT(other.kind_ != kExternal);
     return kind_ > other.kind_;
   }
 
+  bool fits_into(const Representation& other) const {
+    return other.is_more_general_than(*this) || other.Equals(*this);
+  }
+
   Representation generalize(Representation other) {
     if (is_more_general_than(other)) {
       return *this;
     } else {
       return other;
     }
   }
 
   Kind kind() const { return static_cast<Kind>(kind_); }
   bool IsNone() const { return kind_ == kNone; }
@@ skipping 115 matching lines @@
     value_ = RepresentationField::update(
         value, EncodeRepresentation(representation));
   }
 
   uint32_t value_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROPERTY_DETAILS_H_