text: // Copyright 2006-2009 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
  //       with the distribution.
  //     * Neither the name of Google Inc. nor the names of its
  //       contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #ifndef V8_OBJECTS_H_
  #define V8_OBJECTS_H_
  
  #include "builtins.h"
  #include "code-stubs.h"
  #include "smart-pointer.h"
  #include "unicode-inl.h"
  #if V8_TARGET_ARCH_ARM
  #include "arm/constants-arm.h"
  #elif V8_TARGET_ARCH_MIPS
  #include "mips/constants-mips.h"
  #endif
  
  //
  // All object types in the V8 JavaScript are described in this file.
  //
  // Inheritance hierarchy:
  //   - Object
  //     - Smi          (immediate small integer)
  //     - Failure      (immediate for marking failed operation)
  //     - HeapObject   (superclass for everything allocated in the heap)
  //       - JSObject
  //         - JSArray
  //         - JSRegExp
  //         - JSFunction
  //         - GlobalObject
  //           - JSGlobalObject
  //           - JSBuiltinsObject
  //         - JSGlobalProxy
  //         - JSValue
  //       - Array
  //         - ByteArray
  //         - PixelArray
  //         - ExternalArray
  //           - ExternalByteArray
  //           - ExternalUnsignedByteArray
  //           - ExternalShortArray
  //           - ExternalUnsignedShortArray
  //           - ExternalIntArray
  //           - ExternalUnsignedIntArray
  //           - ExternalFloatArray
  //         - FixedArray
  //           - DescriptorArray
  //           - HashTable
  //             - Dictionary
  //             - SymbolTable
  //             - CompilationCacheTable
  //             - CodeCacheHashTable
  //             - MapCache
  //           - Context
  //           - GlobalContext
  //           - JSFunctionResultCache
  //       - String
  //         - SeqString
  //           - SeqAsciiString
  //           - SeqTwoByteString
  //         - ConsString
  //         - ExternalString
  //           - ExternalAsciiString
  //           - ExternalTwoByteString
  //       - HeapNumber
  //       - Code
  //       - Map
  //       - Oddball
  //       - Proxy
  //       - SharedFunctionInfo
  //       - Struct
  //         - AccessorInfo
  //         - AccessCheckInfo
  //         - InterceptorInfo
  //         - CallHandlerInfo
  //         - TemplateInfo
  //           - FunctionTemplateInfo
  //           - ObjectTemplateInfo
  //         - Script
  //         - SignatureInfo
  //         - TypeSwitchInfo
  //         - DebugInfo
  //         - BreakPointInfo
  //         - CodeCache
  //
  // Formats of Object*:
  //  Smi:        [31 bit signed int] 0
  //  HeapObject: [32 bit direct pointer] (4 byte aligned) | 01
  //  Failure:    [30 bit signed int] 11
  
  // Ecma-262 3rd 8.6.1
  enum PropertyAttributes {
    NONE              = v8::None,
    READ_ONLY         = v8::ReadOnly,
    DONT_ENUM         = v8::DontEnum,
    DONT_DELETE       = v8::DontDelete,
    ABSENT            = 16  // Used in runtime to indicate a property is absent.
    // ABSENT can never be stored in or returned from a descriptor's attributes
    // bitfield.  It is only used as a return value meaning the attributes of
    // a non-existent property.
  };
  
  namespace v8 {
  namespace internal {
  
  
  // PropertyDetails captures type and attributes for a property.
  // They are used both in property dictionaries and instance descriptors.
  class PropertyDetails BASE_EMBEDDED {
   public:
  
    PropertyDetails(PropertyAttributes attributes,
                    PropertyType type,
                    int index = 0) {
      ASSERT(TypeField::is_valid(type));
      ASSERT(AttributesField::is_valid(attributes));
      ASSERT(IndexField::is_valid(index));
  
      value_ = TypeField::encode(type)
          | AttributesField::encode(attributes)
          | IndexField::encode(index);
  
      ASSERT(type == this->type());
      ASSERT(attributes == this->attributes());
      ASSERT(index == this->index());
    }
  
    // Conversion for storing details as Object*.
    inline PropertyDetails(Smi* smi);
    inline Smi* AsSmi();
  
    PropertyType type() { return TypeField::decode(value_); }
  
    bool IsTransition() {
      PropertyType t = type();
      ASSERT(t != INTERCEPTOR);
      return t == MAP_TRANSITION || t == CONSTANT_TRANSITION;
    }
  
    bool IsProperty() {
      return type() < FIRST_PHANTOM_PROPERTY_TYPE;
    }
  
    PropertyAttributes attributes() { return AttributesField::decode(value_); }
  
    int index() { return IndexField::decode(value_); }
  
    inline PropertyDetails AsDeleted();
  
    static bool IsValidIndex(int index) { return IndexField::is_valid(index); }
  
    bool IsReadOnly() { return (attributes() & READ_ONLY) != 0; }
    bool IsDontDelete() { return (attributes() & DONT_DELETE) != 0; }
    bool IsDontEnum() { return (attributes() & DONT_ENUM) != 0; }
    bool IsDeleted() { return DeletedField::decode(value_) != 0;}
  
    // Bit fields in value_ (type, shift, size). Must be public so the
    // constants can be embedded in generated code.
    class TypeField:       public BitField<PropertyType,       0, 3> {};
    class AttributesField: public BitField<PropertyAttributes, 3, 3> {};
    class DeletedField:    public BitField<uint32_t,           6, 1> {};
    class IndexField:      public BitField<uint32_t,           7, 32-7> {};
  
    static const int kInitialIndex = 1;
   private:
    uint32_t value_;
  };
  
  
  // Setter that skips the write barrier if mode is SKIP_WRITE_BARRIER.
  enum WriteBarrierMode { SKIP_WRITE_BARRIER, UPDATE_WRITE_BARRIER };
  
  
  // PropertyNormalizationMode is used to specify whether to keep
  // inobject properties when normalizing properties of a JSObject.
  enum PropertyNormalizationMode {
    CLEAR_INOBJECT_PROPERTIES,
    KEEP_INOBJECT_PROPERTIES
  };
  
  
  // All Maps have a field instance_type containing a InstanceType.
  // It describes the type of the instances.
  //
  // As an example, a JavaScript object is a heap object and its map
  // instance_type is JS_OBJECT_TYPE.
  //
  // The names of the string instance types are intended to systematically
  // mirror their encoding in the instance_type field of the map.  The default
  // encoding is considered TWO_BYTE.  It is not mentioned in the name.  ASCII
  // encoding is mentioned explicitly in the name.  Likewise, the default
  // representation is considered sequential.  It is not mentioned in the
  // name.  The other representations (eg, CONS, EXTERNAL) are explicitly
  // mentioned.  Finally, the string is either a SYMBOL_TYPE (if it is a
  // symbol) or a STRING_TYPE (if it is not a symbol).
  //
  // NOTE: The following things are some that depend on the string types having
  // instance_types that are less than those of all other types:
  // HeapObject::Size, HeapObject::IterateBody, the typeof operator, and
  // Object::IsString.
  //
  // NOTE: Everything following JS_VALUE_TYPE is considered a
  // JSObject for GC purposes. The first four entries here have typeof
  // 'object', whereas JS_FUNCTION_TYPE has typeof 'function'.
  #define INSTANCE_TYPE_LIST_ALL(V)                                              \
    V(SYMBOL_TYPE)                                                               \
    V(ASCII_SYMBOL_TYPE)                                                         \
    V(CONS_SYMBOL_TYPE)                                                          \
    V(CONS_ASCII_SYMBOL_TYPE)                                                    \
    V(EXTERNAL_SYMBOL_TYPE)                                                      \
    V(EXTERNAL_ASCII_SYMBOL_TYPE)                                                \
    V(STRING_TYPE)                                                               \
    V(ASCII_STRING_TYPE)                                                         \
    V(CONS_STRING_TYPE)                                                          \
    V(CONS_ASCII_STRING_TYPE)                                                    \
    V(EXTERNAL_STRING_TYPE)                                                      \
    V(EXTERNAL_ASCII_STRING_TYPE)                                                \
    V(PRIVATE_EXTERNAL_ASCII_STRING_TYPE)                                        \
                                                                                 \
    V(MAP_TYPE)                                                                  \
    V(CODE_TYPE)                                                                 \
    V(JS_GLOBAL_PROPERTY_CELL_TYPE)                                              \
    V(ODDBALL_TYPE)                                                              \
                                                                                 \
    V(HEAP_NUMBER_TYPE)                                                          \
    V(PROXY_TYPE)                                                                \
    V(BYTE_ARRAY_TYPE)                                                           \
    V(PIXEL_ARRAY_TYPE)                                                          \
    /* Note: the order of these external array */                                \
    /* types is relied upon in */                                                \
    /* Object::IsExternalArray(). */                                             \
    V(EXTERNAL_BYTE_ARRAY_TYPE)                                                  \
    V(EXTERNAL_UNSIGNED_BYTE_ARRAY_TYPE)                                         \
    V(EXTERNAL_SHORT_ARRAY_TYPE)                                                 \
    V(EXTERNAL_UNSIGNED_SHORT_ARRAY_TYPE)                                        \
    V(EXTERNAL_INT_ARRAY_TYPE)                                                   \
    V(EXTERNAL_UNSIGNED_INT_ARRAY_TYPE)                                          \
    V(EXTERNAL_FLOAT_ARRAY_TYPE)                                                 \
    V(FILLER_TYPE)                                                               \
                                                                                 \
    V(FIXED_ARRAY_TYPE)                                                          \
    V(ACCESSOR_INFO_TYPE)                                                        \
    V(ACCESS_CHECK_INFO_TYPE)                                                    \
    V(INTERCEPTOR_INFO_TYPE)                                                     \
    V(SHARED_FUNCTION_INFO_TYPE)                                                 \
    V(CALL_HANDLER_INFO_TYPE)                                                    \
    V(FUNCTION_TEMPLATE_INFO_TYPE)                                               \
    V(OBJECT_TEMPLATE_INFO_TYPE)                                                 \
    V(SIGNATURE_INFO_TYPE)                                                       \
    V(TYPE_SWITCH_INFO_TYPE)                                                     \
    V(SCRIPT_TYPE)                                                               \
    V(CODE_CACHE_TYPE)                                                           \
                                                                                 \
    V(JS_VALUE_TYPE)                                                             \
    V(JS_OBJECT_TYPE)                                                            \
    V(JS_CONTEXT_EXTENSION_OBJECT_TYPE)                                          \
    V(JS_GLOBAL_OBJECT_TYPE)                                                     \
    V(JS_BUILTINS_OBJECT_TYPE)                                                   \
    V(JS_GLOBAL_PROXY_TYPE)                                                      \
    V(JS_ARRAY_TYPE)                                                             \
    V(JS_REGEXP_TYPE)                                                            \
                                                                                 \
    V(JS_FUNCTION_TYPE)                                                          \
  
  #ifdef ENABLE_DEBUGGER_SUPPORT
  #define INSTANCE_TYPE_LIST_DEBUGGER(V)                                         \
    V(DEBUG_INFO_TYPE)                                                           \
    V(BREAK_POINT_INFO_TYPE)
  #else
  #define INSTANCE_TYPE_LIST_DEBUGGER(V)
  #endif
  
  #define INSTANCE_TYPE_LIST(V)                                                  \
    INSTANCE_TYPE_LIST_ALL(V)                                                    \
    INSTANCE_TYPE_LIST_DEBUGGER(V)
  
  
  // Since string types are not consecutive, this macro is used to
  // iterate over them.
  #define STRING_TYPE_LIST(V)                                                    \
    V(SYMBOL_TYPE,                                                               \
      SeqTwoByteString::kAlignedSize,                                            \
      symbol,                                                                    \
      Symbol)                                                                    \
    V(ASCII_SYMBOL_TYPE,                                                         \
      SeqAsciiString::kAlignedSize,                                              \
      ascii_symbol,                                                              \
      AsciiSymbol)                                                               \
    V(CONS_SYMBOL_TYPE,                                                          \
      ConsString::kSize,                                                         \
      cons_symbol,                                                               \
      ConsSymbol)                                                                \
    V(CONS_ASCII_SYMBOL_TYPE,                                                    \
      ConsString::kSize,                                                         \
      cons_ascii_symbol,                                                         \
      ConsAsciiSymbol)                                                           \
    V(EXTERNAL_SYMBOL_TYPE,                                                      \
      ExternalTwoByteString::kSize,                                              \
      external_symbol,                                                           \
      ExternalSymbol)                                                            \
    V(EXTERNAL_ASCII_SYMBOL_TYPE,                                                \
      ExternalAsciiString::kSize,                                                \
      external_ascii_symbol,                                                     \
      ExternalAsciiSymbol)                                                       \
    V(STRING_TYPE,                                                               \
      SeqTwoByteString::kAlignedSize,                                            \
      string,                                                                    \
      String)                                                                    \
    V(ASCII_STRING_TYPE,                                                         \
      SeqAsciiString::kAlignedSize,                                              \
      ascii_string,                                                              \
      AsciiString)                                                               \
    V(CONS_STRING_TYPE,                                                          \
      ConsString::kSize,                                                         \
      cons_string,                                                               \
      ConsString)                                                                \
    V(CONS_ASCII_STRING_TYPE,                                                    \
      ConsString::kSize,                                                         \
      cons_ascii_string,                                                         \
      ConsAsciiString)                                                           \
    V(EXTERNAL_STRING_TYPE,                                                      \
      ExternalTwoByteString::kSize,                                              \
      external_string,                                                           \
      ExternalString)                                                            \
    V(EXTERNAL_ASCII_STRING_TYPE,                                                \
      ExternalAsciiString::kSize,                                                \
      external_ascii_string,                                                     \
      ExternalAsciiString)                                                       \
  
  // A struct is a simple object a set of object-valued fields.  Including an
  // object type in this causes the compiler to generate most of the boilerplate
  // code for the class including allocation and garbage collection routines,
  // casts and predicates.  All you need to define is the class, methods and
  // object verification routines.  Easy, no?
  //
  // Note that for subtle reasons related to the ordering or numerical values of
  // type tags, elements in this list have to be added to the INSTANCE_TYPE_LIST
  // manually.
  #define STRUCT_LIST_ALL(V)                                                     \
    V(ACCESSOR_INFO, AccessorInfo, accessor_info)                                \
    V(ACCESS_CHECK_INFO, AccessCheckInfo, access_check_info)                     \
    V(INTERCEPTOR_INFO, InterceptorInfo, interceptor_info)                       \
    V(CALL_HANDLER_INFO, CallHandlerInfo, call_handler_info)                     \
    V(FUNCTION_TEMPLATE_INFO, FunctionTemplateInfo, function_template_info)      \
    V(OBJECT_TEMPLATE_INFO, ObjectTemplateInfo, object_template_info)            \
    V(SIGNATURE_INFO, SignatureInfo, signature_info)                             \
    V(TYPE_SWITCH_INFO, TypeSwitchInfo, type_switch_info)                        \
    V(SCRIPT, Script, script)                                                    \
    V(CODE_CACHE, CodeCache, code_cache)
  
  #ifdef ENABLE_DEBUGGER_SUPPORT
  #define STRUCT_LIST_DEBUGGER(V)                                                \
    V(DEBUG_INFO, DebugInfo, debug_info)                                         \
    V(BREAK_POINT_INFO, BreakPointInfo, break_point_info)
  #else
  #define STRUCT_LIST_DEBUGGER(V)
  #endif
  
  #define STRUCT_LIST(V)                                                         \
    STRUCT_LIST_ALL(V)                                                           \
    STRUCT_LIST_DEBUGGER(V)
  
  // We use the full 8 bits of the instance_type field to encode heap object
  // instance types.  The high-order bit (bit 7) is set if the object is not a
  // string, and cleared if it is a string.
  const uint32_t kIsNotStringMask = 0x80;
  const uint32_t kStringTag = 0x0;
  const uint32_t kNotStringTag = 0x80;
  
  // Bit 6 indicates that the object is a symbol (if set) or not (if cleared).
  // There are not enough types that the non-string types (with bit 7 set) can
  // have bit 6 set too.
  const uint32_t kIsSymbolMask = 0x40;
  const uint32_t kNotSymbolTag = 0x0;
  const uint32_t kSymbolTag = 0x40;
  
  // If bit 7 is clear then bit 2 indicates whether the string consists of
  // two-byte characters or one-byte characters.
  const uint32_t kStringEncodingMask = 0x4;
  const uint32_t kTwoByteStringTag = 0x0;
  const uint32_t kAsciiStringTag = 0x4;
  
  // If bit 7 is clear, the low-order 2 bits indicate the representation
  // of the string.
  const uint32_t kStringRepresentationMask = 0x03;
  enum StringRepresentationTag {
    kSeqStringTag = 0x0,
    kConsStringTag = 0x1,
    kExternalStringTag = 0x3
  };
  
  
  // A ConsString with an empty string as the right side is a candidate
  // for being shortcut by the garbage collector unless it is a
  // symbol. It's not common to have non-flat symbols, so we do not
  // shortcut them thereby avoiding turning symbols into strings. See
  // heap.cc and mark-compact.cc.
  const uint32_t kShortcutTypeMask =
      kIsNotStringMask |
      kIsSymbolMask |
      kStringRepresentationMask;
  const uint32_t kShortcutTypeTag = kConsStringTag;
  
  
  enum InstanceType {
    // String types.
    SYMBOL_TYPE = kSymbolTag | kSeqStringTag,
    ASCII_SYMBOL_TYPE = kAsciiStringTag | kSymbolTag | kSeqStringTag,
    CONS_SYMBOL_TYPE = kSymbolTag | kConsStringTag,
    CONS_ASCII_SYMBOL_TYPE = kAsciiStringTag | kSymbolTag | kConsStringTag,
    EXTERNAL_SYMBOL_TYPE = kSymbolTag | kExternalStringTag,
    EXTERNAL_ASCII_SYMBOL_TYPE =
        kAsciiStringTag | kSymbolTag | kExternalStringTag,
    STRING_TYPE = kSeqStringTag,
    ASCII_STRING_TYPE = kAsciiStringTag | kSeqStringTag,
    CONS_STRING_TYPE = kConsStringTag,
    CONS_ASCII_STRING_TYPE = kAsciiStringTag | kConsStringTag,
    EXTERNAL_STRING_TYPE = kExternalStringTag,
    EXTERNAL_ASCII_STRING_TYPE = kAsciiStringTag | kExternalStringTag,
    PRIVATE_EXTERNAL_ASCII_STRING_TYPE = EXTERNAL_ASCII_STRING_TYPE,
  
    // Objects allocated in their own spaces (never in new space).
    MAP_TYPE = kNotStringTag,  // FIRST_NONSTRING_TYPE
    CODE_TYPE,
    ODDBALL_TYPE,
    JS_GLOBAL_PROPERTY_CELL_TYPE,
  
    // "Data", objects that cannot contain non-map-word pointers to heap
    // objects.
    HEAP_NUMBER_TYPE,
    PROXY_TYPE,
    BYTE_ARRAY_TYPE,
    PIXEL_ARRAY_TYPE,
    EXTERNAL_BYTE_ARRAY_TYPE,  // FIRST_EXTERNAL_ARRAY_TYPE
    EXTERNAL_UNSIGNED_BYTE_ARRAY_TYPE,
    EXTERNAL_SHORT_ARRAY_TYPE,
    EXTERNAL_UNSIGNED_SHORT_ARRAY_TYPE,
    EXTERNAL_INT_ARRAY_TYPE,
    EXTERNAL_UNSIGNED_INT_ARRAY_TYPE,
    EXTERNAL_FLOAT_ARRAY_TYPE,  // LAST_EXTERNAL_ARRAY_TYPE
    FILLER_TYPE,  // LAST_DATA_TYPE
  
    // Structs.
    ACCESSOR_INFO_TYPE,
    ACCESS_CHECK_INFO_TYPE,
    INTERCEPTOR_INFO_TYPE,
    CALL_HANDLER_INFO_TYPE,
    FUNCTION_TEMPLATE_INFO_TYPE,
    OBJECT_TEMPLATE_INFO_TYPE,
    SIGNATURE_INFO_TYPE,
    TYPE_SWITCH_INFO_TYPE,
    SCRIPT_TYPE,
    CODE_CACHE_TYPE,
  #ifdef ENABLE_DEBUGGER_SUPPORT
    DEBUG_INFO_TYPE,
    BREAK_POINT_INFO_TYPE,
  #endif
  
    FIXED_ARRAY_TYPE,
    SHARED_FUNCTION_INFO_TYPE,
  
    JS_VALUE_TYPE,  // FIRST_JS_OBJECT_TYPE
    JS_OBJECT_TYPE,
    JS_CONTEXT_EXTENSION_OBJECT_TYPE,
    JS_GLOBAL_OBJECT_TYPE,
    JS_BUILTINS_OBJECT_TYPE,
    JS_GLOBAL_PROXY_TYPE,
    JS_ARRAY_TYPE,
    JS_REGEXP_TYPE,  // LAST_JS_OBJECT_TYPE
  
    JS_FUNCTION_TYPE,
  
    // Pseudo-types
    FIRST_TYPE = 0x0,
    LAST_TYPE = JS_FUNCTION_TYPE,
    INVALID_TYPE = FIRST_TYPE - 1,
    FIRST_NONSTRING_TYPE = MAP_TYPE,
    // Boundaries for testing for an external array.
    FIRST_EXTERNAL_ARRAY_TYPE = EXTERNAL_BYTE_ARRAY_TYPE,
    LAST_EXTERNAL_ARRAY_TYPE = EXTERNAL_FLOAT_ARRAY_TYPE,
    // Boundary for promotion to old data space/old pointer space.
    LAST_DATA_TYPE = FILLER_TYPE,
    // Boundaries for testing the type is a JavaScript "object".  Note that
    // function objects are not counted as objects, even though they are
    // implemented as such; only values whose typeof is "object" are included.
    FIRST_JS_OBJECT_TYPE = JS_VALUE_TYPE,
    LAST_JS_OBJECT_TYPE = JS_REGEXP_TYPE
  };
  
  
  enum CompareResult {
    LESS      = -1,
    EQUAL     =  0,
    GREATER   =  1,
  
    NOT_EQUAL = GREATER
  };
  
  
  #define DECL_BOOLEAN_ACCESSORS(name)   \
    inline bool name();                  \
    inline void set_##name(bool value);  \
  
  
  #define DECL_ACCESSORS(name, type)                                      \
    inline type* name();                                                  \
    inline void set_##name(type* value,                                   \
                           WriteBarrierMode mode = UPDATE_WRITE_BARRIER); \
  
  
  class StringStream;
  class ObjectVisitor;
  
  struct ValueInfo : public Malloced {
    ValueInfo() : type(FIRST_TYPE), ptr(NULL), str(NULL), number(0) { }
    InstanceType type;
    Object* ptr;
    const char* str;
    double number;
  };
  
  
  // A template-ized version of the IsXXX functions.
  template <class C> static inline bool Is(Object* obj);
  
  
  // Object is the abstract superclass for all classes in the
  // object hierarchy.
  // Object does not use any virtual functions to avoid the
  // allocation of the C++ vtable.
  // Since Smi and Failure are subclasses of Object no
  // data members can be present in Object.
  class Object BASE_EMBEDDED {
   public:
    // Type testing.
    inline bool IsSmi();
    inline bool IsHeapObject();
    inline bool IsHeapNumber();
    inline bool IsString();
    inline bool IsSymbol();
    // See objects-inl.h for more details
    inline bool IsSeqString();
    inline bool IsExternalString();
    inline bool IsExternalTwoByteString();
    inline bool IsExternalAsciiString();
    inline bool IsSeqTwoByteString();
    inline bool IsSeqAsciiString();
    inline bool IsConsString();
  
    inline bool IsNumber();
    inline bool IsByteArray();
    inline bool IsPixelArray();
    inline bool IsExternalArray();
    inline bool IsExternalByteArray();
    inline bool IsExternalUnsignedByteArray();
    inline bool IsExternalShortArray();
    inline bool IsExternalUnsignedShortArray();
    inline bool IsExternalIntArray();
    inline bool IsExternalUnsignedIntArray();
    inline bool IsExternalFloatArray();
    inline bool IsFailure();
    inline bool IsRetryAfterGC();
    inline bool IsOutOfMemoryFailure();
    inline bool IsException();
    inline bool IsJSObject();
    inline bool IsJSContextExtensionObject();
    inline bool IsMap();
    inline bool IsFixedArray();
    inline bool IsDescriptorArray();
    inline bool IsContext();
    inline bool IsCatchContext();
    inline bool IsGlobalContext();
    inline bool IsJSFunction();
    inline bool IsCode();
    inline bool IsOddball();
    inline bool IsSharedFunctionInfo();
    inline bool IsJSValue();
    inline bool IsStringWrapper();
    inline bool IsProxy();
    inline bool IsBoolean();
    inline bool IsJSArray();
    inline bool IsJSRegExp();
    inline bool IsHashTable();
    inline bool IsDictionary();
    inline bool IsSymbolTable();
    inline bool IsCompilationCacheTable();
    inline bool IsCodeCacheHashTable();
    inline bool IsMapCache();
    inline bool IsPrimitive();
    inline bool IsGlobalObject();
    inline bool IsJSGlobalObject();
    inline bool IsJSBuiltinsObject();
    inline bool IsJSGlobalProxy();
    inline bool IsUndetectableObject();
    inline bool IsAccessCheckNeeded();
    inline bool IsJSGlobalPropertyCell();
  
    // Returns true if this object is an instance of the specified
    // function template.
    inline bool IsInstanceOf(FunctionTemplateInfo* type);
  
    inline bool IsStruct();
  #define DECLARE_STRUCT_PREDICATE(NAME, Name, name) inline bool Is##Name();
    STRUCT_LIST(DECLARE_STRUCT_PREDICATE)
  #undef DECLARE_STRUCT_PREDICATE
  
    // Oddball testing.
    INLINE(bool IsUndefined());
    INLINE(bool IsTheHole());
    INLINE(bool IsNull());
    INLINE(bool IsTrue());
    INLINE(bool IsFalse());
  
    // Extract the number.
    inline double Number();
  
    inline bool HasSpecificClassOf(String* name);
  
    Object* ToObject();             // ECMA-262 9.9.
    Object* ToBoolean();            // ECMA-262 9.2.
  
    // Convert to a JSObject if needed.
    // global_context is used when creating wrapper object.
    Object* ToObject(Context* global_context);
  
    // Converts this to a Smi if possible.
    // Failure is returned otherwise.
    inline Object* ToSmi();
  
    void Lookup(String* name, LookupResult* result);
  
    // Property access.
    inline Object* GetProperty(String* key);
    inline Object* GetProperty(String* key, PropertyAttributes* attributes);
    Object* GetPropertyWithReceiver(Object* receiver,
                                    String* key,
                                    PropertyAttributes* attributes);
    Object* GetProperty(Object* receiver,
                        LookupResult* result,
                        String* key,
                        PropertyAttributes* attributes);
    Object* GetPropertyWithCallback(Object* receiver,
                                    Object* structure,
                                    String* name,
                                    Object* holder);
    Object* GetPropertyWithDefinedGetter(Object* receiver,
                                         JSFunction* getter);
  
    inline Object* GetElement(uint32_t index);
    Object* GetElementWithReceiver(Object* receiver, uint32_t index);
  
    // Return the object's prototype (might be Heap::null_value()).
    Object* GetPrototype();
  
    // Returns true if this is a JSValue containing a string and the index is
    // < the length of the string.  Used to implement [] on strings.
    inline bool IsStringObjectWithCharacterAt(uint32_t index);
  
  #ifdef DEBUG
    // Prints this object with details.
    void Print();
    void PrintLn();
    // Verifies the object.
    void Verify();
  
    // Verify a pointer is a valid object pointer.
    static void VerifyPointer(Object* p);
  #endif
  
    // Prints this object without details.
    void ShortPrint();
  
    // Prints this object without details to a message accumulator.
    void ShortPrint(StringStream* accumulator);
  
    // Casting: This cast is only needed to satisfy macros in objects-inl.h.
    static Object* cast(Object* value) { return value; }
  
    // Layout description.
    static const int kHeaderSize = 0;  // Object does not take up any space.
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Object);
  };
  
  
  // Smi represents integer Numbers that can be stored in 31 bits.
  // Smis are immediate which means they are NOT allocated in the heap.
  // The this pointer has the following format: [31 bit signed int] 0
  // For long smis it has the following format:
  //     [32 bit signed int] [31 bits zero padding] 0
  // Smi stands for small integer.
  class Smi: public Object {
   public:
    // Returns the integer value.
    inline int value();
  
    // Convert a value to a Smi object.
    static inline Smi* FromInt(int value);
  
    static inline Smi* FromIntptr(intptr_t value);
  
    // Returns whether value can be represented in a Smi.
    static inline bool IsValid(intptr_t value);
  
    // Casting.
    static inline Smi* cast(Object* object);
  
    // Dispatched behavior.
    void SmiPrint();
    void SmiPrint(StringStream* accumulator);
  #ifdef DEBUG
    void SmiVerify();
  #endif
  
    static const int kMinValue = (-1 << (kSmiValueSize - 1));
    static const int kMaxValue = -(kMinValue + 1);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Smi);
  };
  
  
  // Failure is used for reporting out of memory situations and
  // propagating exceptions through the runtime system.  Failure objects
  // are transient and cannot occur as part of the object graph.
  //
  // Failures are a single word, encoded as follows:
  // +-------------------------+---+--+--+
  // |...rrrrrrrrrrrrrrrrrrrrrr|sss|tt|11|
  // +-------------------------+---+--+--+
  //                          7 6 4 32 10
  //
  //
  // The low two bits, 0-1, are the failure tag, 11.  The next two bits,
  // 2-3, are a failure type tag 'tt' with possible values:
  //   00 RETRY_AFTER_GC
  //   01 EXCEPTION
  //   10 INTERNAL_ERROR
  //   11 OUT_OF_MEMORY_EXCEPTION
  //
  // The next three bits, 4-6, are an allocation space tag 'sss'.  The
  // allocation space tag is 000 for all failure types except
  // RETRY_AFTER_GC.  For RETRY_AFTER_GC, the possible values are the
  // allocation spaces (the encoding is found in globals.h).
  //
  // The remaining bits is the size of the allocation request in units
  // of the pointer size, and is zeroed except for RETRY_AFTER_GC
  // failures.  The 25 bits (on a 32 bit platform) gives a representable
  // range of 2^27 bytes (128MB).
  
  // Failure type tag info.
  const int kFailureTypeTagSize = 2;
  const int kFailureTypeTagMask = (1 << kFailureTypeTagSize) - 1;
  
  class Failure: public Object {
   public:
    // RuntimeStubs assumes EXCEPTION = 1 in the compiler-generated code.
    enum Type {
      RETRY_AFTER_GC = 0,
      EXCEPTION = 1,       // Returning this marker tells the real exception
                           // is in Top::pending_exception.
      INTERNAL_ERROR = 2,
      OUT_OF_MEMORY_EXCEPTION = 3
    };
  
    inline Type type() const;
  
    // Returns the space that needs to be collected for RetryAfterGC failures.
    inline AllocationSpace allocation_space() const;
  
    // Returns the number of bytes requested (up to the representable maximum)
    // for RetryAfterGC failures.
    inline int requested() const;
  
    inline bool IsInternalError() const;
    inline bool IsOutOfMemoryException() const;
  
    static Failure* RetryAfterGC(int requested_bytes, AllocationSpace space);
    static inline Failure* RetryAfterGC(int requested_bytes);  // NEW_SPACE
    static inline Failure* Exception();
    static inline Failure* InternalError();
    static inline Failure* OutOfMemoryException();
    // Casting.
    static inline Failure* cast(Object* object);
  
    // Dispatched behavior.
    void FailurePrint();
    void FailurePrint(StringStream* accumulator);
  #ifdef DEBUG
    void FailureVerify();
  #endif
  
   private:
    inline intptr_t value() const;
    static inline Failure* Construct(Type type, intptr_t value = 0);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(Failure);
  };
  
  
  // Heap objects typically have a map pointer in their first word.  However,
  // during GC other data (eg, mark bits, forwarding addresses) is sometimes
  // encoded in the first word.  The class MapWord is an abstraction of the
  // value in a heap object's first word.
  class MapWord BASE_EMBEDDED {
   public:
    // Normal state: the map word contains a map pointer.
  
    // Create a map word from a map pointer.
    static inline MapWord FromMap(Map* map);
  
    // View this map word as a map pointer.
    inline Map* ToMap();
  
  
    // Scavenge collection: the map word of live objects in the from space
    // contains a forwarding address (a heap object pointer in the to space).
  
    // True if this map word is a forwarding address for a scavenge
    // collection.  Only valid during a scavenge collection (specifically,
    // when all map words are heap object pointers, ie. not during a full GC).
    inline bool IsForwardingAddress();
  
    // Create a map word from a forwarding address.
    static inline MapWord FromForwardingAddress(HeapObject* object);
  
    // View this map word as a forwarding address.
    inline HeapObject* ToForwardingAddress();
  
    // Marking phase of full collection: the map word of live objects is
    // marked, and may be marked as overflowed (eg, the object is live, its
    // children have not been visited, and it does not fit in the marking
    // stack).
  
    // True if this map word's mark bit is set.
    inline bool IsMarked();
  
    // Return this map word but with its mark bit set.
    inline void SetMark();
  
    // Return this map word but with its mark bit cleared.
    inline void ClearMark();
  
    // True if this map word's overflow bit is set.
    inline bool IsOverflowed();
  
    // Return this map word but with its overflow bit set.
    inline void SetOverflow();
  
    // Return this map word but with its overflow bit cleared.
    inline void ClearOverflow();
  
  
    // Compacting phase of a full compacting collection: the map word of live
    // objects contains an encoding of the original map address along with the
    // forwarding address (represented as an offset from the first live object
    // in the same page as the (old) object address).
  
    // Create a map word from a map address and a forwarding address offset.
    static inline MapWord EncodeAddress(Address map_address, int offset);
  
    // Return the map address encoded in this map word.
    inline Address DecodeMapAddress(MapSpace* map_space);
  
    // Return the forwarding offset encoded in this map word.
    inline int DecodeOffset();
  
  
    // During serialization: the map word is used to hold an encoded
    // address, and possibly a mark bit (set and cleared with SetMark
    // and ClearMark).
  
    // Create a map word from an encoded address.
    static inline MapWord FromEncodedAddress(Address address);
  
    inline Address ToEncodedAddress();
  
    // Bits used by the marking phase of the garbage collector.
    //
    // The first word of a heap object is normally a map pointer. The last two
    // bits are tagged as '01' (kHeapObjectTag). We reuse the last two bits to
    // mark an object as live and/or overflowed:
    //   last bit = 0, marked as alive
    //   second bit = 1, overflowed
    // An object is only marked as overflowed when it is marked as live while
    // the marking stack is overflowed.
    static const int kMarkingBit = 0;  // marking bit
    static const int kMarkingMask = (1 << kMarkingBit);  // marking mask
    static const int kOverflowBit = 1;  // overflow bit
    static const int kOverflowMask = (1 << kOverflowBit);  // overflow mask
  
    // Forwarding pointers and map pointer encoding. On 32 bit all the bits are
    // used.
    // +-----------------+------------------+-----------------+
    // |forwarding offset|page offset of map|page index of map|
    // +-----------------+------------------+-----------------+
    //          ^                 ^                  ^
    //          |                 |                  |
    //          |                 |          kMapPageIndexBits
    //          |         kMapPageOffsetBits
    // kForwardingOffsetBits
    static const int kMapPageOffsetBits = kPageSizeBits - kMapAlignmentBits;
    static const int kForwardingOffsetBits = kPageSizeBits - kObjectAlignmentBits;
  #ifdef V8_HOST_ARCH_64_BIT
    static const int kMapPageIndexBits = 16;
  #else
    // Use all the 32-bits to encode on a 32-bit platform.
    static const int kMapPageIndexBits =
        32 - (kMapPageOffsetBits + kForwardingOffsetBits);
  #endif
  
    static const int kMapPageIndexShift = 0;
    static const int kMapPageOffsetShift =
        kMapPageIndexShift + kMapPageIndexBits;
    static const int kForwardingOffsetShift =
        kMapPageOffsetShift + kMapPageOffsetBits;
  
    // Bit masks covering the different parts the encoding.
    static const uintptr_t kMapPageIndexMask =
        (1 << kMapPageOffsetShift) - 1;
    static const uintptr_t kMapPageOffsetMask =
        ((1 << kForwardingOffsetShift) - 1) & ~kMapPageIndexMask;
    static const uintptr_t kForwardingOffsetMask =
        ~(kMapPageIndexMask | kMapPageOffsetMask);
  
   private:
    // HeapObject calls the private constructor and directly reads the value.
    friend class HeapObject;
  
    explicit MapWord(uintptr_t value) : value_(value) {}
  
    uintptr_t value_;
  };
  
  
  // HeapObject is the superclass for all classes describing heap allocated
  // objects.
  class HeapObject: public Object {
   public:
    // [map]: Contains a map which contains the object's reflective
    // information.
    inline Map* map();
    inline void set_map(Map* value);
  
    // During garbage collection, the map word of a heap object does not
    // necessarily contain a map pointer.
    inline MapWord map_word();
    inline void set_map_word(MapWord map_word);
  
    // Converts an address to a HeapObject pointer.
    static inline HeapObject* FromAddress(Address address);
  
    // Returns the address of this HeapObject.
    inline Address address();
  
    // Iterates over pointers contained in the object (including the Map)
    void Iterate(ObjectVisitor* v);
  
    // Iterates over all pointers contained in the object except the
    // first map pointer.  The object type is given in the first
    // parameter. This function does not access the map pointer in the
    // object, and so is safe to call while the map pointer is modified.
    void IterateBody(InstanceType type, int object_size, ObjectVisitor* v);
  
    // This method only applies to struct objects.  Iterates over all the fields
    // of this struct.
    void IterateStructBody(int object_size, ObjectVisitor* v);
  
    // Returns the heap object's size in bytes
    inline int Size();
  
    // Given a heap object's map pointer, returns the heap size in bytes
    // Useful when the map pointer field is used for other purposes.
    // GC internal.
    inline int SizeFromMap(Map* map);
  
    // Support for the marking heap objects during the marking phase of GC.
    // True if the object is marked live.
    inline bool IsMarked();
  
    // Mutate this object's map pointer to indicate that the object is live.
    inline void SetMark();
  
    // Mutate this object's map pointer to remove the indication that the
    // object is live (ie, partially restore the map pointer).
    inline void ClearMark();
  
    // True if this object is marked as overflowed.  Overflowed objects have
    // been reached and marked during marking of the heap, but their children
    // have not necessarily been marked and they have not been pushed on the
    // marking stack.
    inline bool IsOverflowed();
  
    // Mutate this object's map pointer to indicate that the object is
    // overflowed.
    inline void SetOverflow();
  
    // Mutate this object's map pointer to remove the indication that the
    // object is overflowed (ie, partially restore the map pointer).
    inline void ClearOverflow();
  
    // Returns the field at offset in obj, as a read/write Object* reference.
    // Does no checking, and is safe to use during GC, while maps are invalid.
    // Does not update remembered sets, so should only be assigned to
    // during marking GC.
    static inline Object** RawField(HeapObject* obj, int offset);
  
    // Casting.
    static inline HeapObject* cast(Object* obj);
  
    // Return the write barrier mode for this. Callers of this function
    // must be able to present a reference to an AssertNoAllocation
    // object as a sign that they are not going to use this function
    // from code that allocates and thus invalidates the returned write
    // barrier mode.
    inline WriteBarrierMode GetWriteBarrierMode(const AssertNoAllocation&);
  
    // Dispatched behavior.
    void HeapObjectShortPrint(StringStream* accumulator);
  #ifdef DEBUG
    void HeapObjectPrint();
    void HeapObjectVerify();
    inline void VerifyObjectField(int offset);
  
    void PrintHeader(const char* id);
  
    // Verify a pointer is a valid HeapObject pointer that points to object
    // areas in the heap.
    static void VerifyHeapPointer(Object* p);
  #endif
  
    // Layout description.
    // First field in a heap object is map.
    static const int kMapOffset = Object::kHeaderSize;
    static const int kHeaderSize = kMapOffset + kPointerSize;
  
    STATIC_CHECK(kMapOffset == Internals::kHeapObjectMapOffset);
  
   protected:
    // helpers for calling an ObjectVisitor to iterate over pointers in the
    // half-open range [start, end) specified as integer offsets
    inline void IteratePointers(ObjectVisitor* v, int start, int end);
    // as above, for the single element at "offset"
    inline void IteratePointer(ObjectVisitor* v, int offset);
  
    // Computes the object size from the map.
    // Should only be used from SizeFromMap.
    int SlowSizeFromMap(Map* map);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(HeapObject);
  };
  
  
  // The HeapNumber class describes heap allocated numbers that cannot be
  // represented in a Smi (small integer)
  class HeapNumber: public HeapObject {
   public:
    // [value]: number value.
    inline double value();
    inline void set_value(double value);
  
    // Casting.
    static inline HeapNumber* cast(Object* obj);
  
    // Dispatched behavior.
    Object* HeapNumberToBoolean();
    void HeapNumberPrint();
    void HeapNumberPrint(StringStream* accumulator);
  #ifdef DEBUG
    void HeapNumberVerify();
  #endif
  
    inline int get_exponent();
    inline int get_sign();
  
    // Layout description.
    static const int kValueOffset = HeapObject::kHeaderSize;
    // IEEE doubles are two 32 bit words.  The first is just mantissa, the second
    // is a mixture of sign, exponent and mantissa.  Our current platforms are all
    // little endian apart from non-EABI arm which is little endian with big
    // endian floating point word ordering!
  #if !defined(V8_HOST_ARCH_ARM) || defined(USE_ARM_EABI)
    static const int kMantissaOffset = kValueOffset;
    static const int kExponentOffset = kValueOffset + 4;
  #else
    static const int kMantissaOffset = kValueOffset + 4;
    static const int kExponentOffset = kValueOffset;
  # define BIG_ENDIAN_FLOATING_POINT 1
  #endif
    static const int kSize = kValueOffset + kDoubleSize;
    static const uint32_t kSignMask = 0x80000000u;
    static const uint32_t kExponentMask = 0x7ff00000u;
    static const uint32_t kMantissaMask = 0xfffffu;
    static const int kExponentBias = 1023;
    static const int kExponentShift = 20;
    static const int kMantissaBitsInTopWord = 20;
    static const int kNonMantissaBitsInTopWord = 12;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(HeapNumber);
  };
  
  
  // The JSObject describes real heap allocated JavaScript objects with
  // properties.
  // Note that the map of JSObject changes during execution to enable inline
  // caching.
  class JSObject: public HeapObject {
   public:
    enum DeleteMode { NORMAL_DELETION, FORCE_DELETION };
    enum ElementsKind {
      FAST_ELEMENTS,
      DICTIONARY_ELEMENTS,
      PIXEL_ELEMENTS,
      EXTERNAL_BYTE_ELEMENTS,
      EXTERNAL_UNSIGNED_BYTE_ELEMENTS,
      EXTERNAL_SHORT_ELEMENTS,
      EXTERNAL_UNSIGNED_SHORT_ELEMENTS,
      EXTERNAL_INT_ELEMENTS,
      EXTERNAL_UNSIGNED_INT_ELEMENTS,
      EXTERNAL_FLOAT_ELEMENTS
    };
  
    // [properties]: Backing storage for properties.
    // properties is a FixedArray in the fast case, and a Dictionary in the
    // slow case.
    DECL_ACCESSORS(properties, FixedArray)  // Get and set fast properties.
    inline void initialize_properties();
    inline bool HasFastProperties();
    inline StringDictionary* property_dictionary();  // Gets slow properties.
  
    // [elements]: The elements (properties with names that are integers).
    // elements is a FixedArray in the fast case, and a Dictionary in the slow
    // case or a PixelArray in a special case.
    DECL_ACCESSORS(elements, Array)  // Get and set fast elements.
    inline void initialize_elements();
    inline ElementsKind GetElementsKind();
    inline bool HasFastElements();
    inline bool HasDictionaryElements();
    inline bool HasPixelElements();
    inline bool HasExternalArrayElements();
    inline bool HasExternalByteElements();
    inline bool HasExternalUnsignedByteElements();
    inline bool HasExternalShortElements();
    inline bool HasExternalUnsignedShortElements();
    inline bool HasExternalIntElements();
    inline bool HasExternalUnsignedIntElements();
    inline bool HasExternalFloatElements();
    inline bool AllowsSetElementsLength();
    inline NumberDictionary* element_dictionary();  // Gets slow elements.
  
    // Collects elements starting at index 0.
    // Undefined values are placed after non-undefined values.
    // Returns the number of non-undefined values.
    Object* PrepareElementsForSort(uint32_t limit);
    // As PrepareElementsForSort, but only on objects where elements is
    // a dictionary, and it will stay a dictionary.
    Object* PrepareSlowElementsForSort(uint32_t limit);
  
    Object* SetProperty(String* key,
                        Object* value,
                        PropertyAttributes attributes);
    Object* SetProperty(LookupResult* result,
                        String* key,
                        Object* value,
                        PropertyAttributes attributes);
    Object* SetPropertyWithFailedAccessCheck(LookupResult* result,
                                             String* name,
                                             Object* value);
    Object* SetPropertyWithCallback(Object* structure,
                                    String* name,
                                    Object* value,
                                    JSObject* holder);
    Object* SetPropertyWithDefinedSetter(JSFunction* setter,
                                         Object* value);
    Object* SetPropertyWithInterceptor(String* name,
                                       Object* value,
                                       PropertyAttributes attributes);
    Object* SetPropertyPostInterceptor(String* name,
                                       Object* value,
                                       PropertyAttributes attributes);
    Object* IgnoreAttributesAndSetLocalProperty(String* key,
                                                Object* value,
                                                PropertyAttributes attributes);
  
    // Retrieve a value in a normalized object given a lookup result.
    // Handles the special representation of JS global objects.
    Object* GetNormalizedProperty(LookupResult* result);
  
    // Sets the property value in a normalized object given a lookup result.
    // Handles the special representation of JS global objects.
    Object* SetNormalizedProperty(LookupResult* result, Object* value);
  
    // Sets the property value in a normalized object given (key, value, details).
    // Handles the special representation of JS global objects.
    Object* SetNormalizedProperty(String* name,
                                  Object* value,
                                  PropertyDetails details);
  
    // Deletes the named property in a normalized object.
    Object* DeleteNormalizedProperty(String* name, DeleteMode mode);
  
    // Returns the class name ([[Class]] property in the specification).
    String* class_name();
  
    // Returns the constructor name (the name (possibly, inferred name) of the
    // function that was used to instantiate the object).
    String* constructor_name();
  
    // Retrieve interceptors.
    InterceptorInfo* GetNamedInterceptor();
    InterceptorInfo* GetIndexedInterceptor();
  
    inline PropertyAttributes GetPropertyAttribute(String* name);
    PropertyAttributes GetPropertyAttributeWithReceiver(JSObject* receiver,
                                                        String* name);
    PropertyAttributes GetLocalPropertyAttribute(String* name);
  
    Object* DefineAccessor(String* name, bool is_getter, JSFunction* fun,
                           PropertyAttributes attributes);
    Object* LookupAccessor(String* name, bool is_getter);
  
    // Used from Object::GetProperty().
    Object* GetPropertyWithFailedAccessCheck(Object* receiver,
                                             LookupResult* result,
                                             String* name,
                                             PropertyAttributes* attributes);
    Object* GetPropertyWithInterceptor(JSObject* receiver,
                                       String* name,
                                       PropertyAttributes* attributes);
    Object* GetPropertyPostInterceptor(JSObject* receiver,
                                       String* name,
                                       PropertyAttributes* attributes);
    Object* GetLocalPropertyPostInterceptor(JSObject* receiver,
                                            String* name,
                                            PropertyAttributes* attributes);
  
    // Returns true if this is an instance of an api function and has
    // been modified since it was created.  May give false positives.
    bool IsDirty();
  
    bool HasProperty(String* name) {
      return GetPropertyAttribute(name) != ABSENT;
    }
  
    // Can cause a GC if it hits an interceptor.
    bool HasLocalProperty(String* name) {
      return GetLocalPropertyAttribute(name) != ABSENT;
    }
  
    // If the receiver is a JSGlobalProxy this method will return its prototype,
    // otherwise the result is the receiver itself.
    inline Object* BypassGlobalProxy();
  
    // Accessors for hidden properties object.
    //
    // Hidden properties are not local properties of the object itself.
    // Instead they are stored on an auxiliary JSObject stored as a local
    // property with a special name Heap::hidden_symbol(). But if the
    // receiver is a JSGlobalProxy then the auxiliary object is a property
    // of its prototype.
    //
    // Has/Get/SetHiddenPropertiesObject methods don't allow the holder to be
    // a JSGlobalProxy. Use BypassGlobalProxy method above to get to the real
    // holder.
    //
    // These accessors do not touch interceptors or accessors.
    inline bool HasHiddenPropertiesObject();
    inline Object* GetHiddenPropertiesObject();
    inline Object* SetHiddenPropertiesObject(Object* hidden_obj);
  
    Object* DeleteProperty(String* name, DeleteMode mode);
    Object* DeleteElement(uint32_t index, DeleteMode mode);
  
    // Tests for the fast common case for property enumeration.
    bool IsSimpleEnum();
  
    // Do we want to keep the elements in fast case when increasing the
    // capacity?
    bool ShouldConvertToSlowElements(int new_capacity);
    // Returns true if the backing storage for the slow-case elements of
    // this object takes up nearly as much space as a fast-case backing
    // storage would.  In that case the JSObject should have fast
    // elements.
    bool ShouldConvertToFastElements();
  
    // Return the object's prototype (might be Heap::null_value()).
    inline Object* GetPrototype();
  
    // Set the object's prototype (only JSObject and null are allowed).
    Object* SetPrototype(Object* value, bool skip_hidden_prototypes);
  
    // Tells whether the index'th element is present.
    inline bool HasElement(uint32_t index);
    bool HasElementWithReceiver(JSObject* receiver, uint32_t index);
    bool HasLocalElement(uint32_t index);
  
    bool HasElementWithInterceptor(JSObject* receiver, uint32_t index);
    bool HasElementPostInterceptor(JSObject* receiver, uint32_t index);
  
    Object* SetFastElement(uint32_t index, Object* value);
  
    // Set the index'th array element.
    // A Failure object is returned if GC is needed.
    Object* SetElement(uint32_t index, Object* value);
  
    // Returns the index'th element.
    // The undefined object if index is out of bounds.
    Object* GetElementWithReceiver(JSObject* receiver, uint32_t index);
  
    void SetFastElements(FixedArray* elements);
    Object* SetSlowElements(Object* length);
  
    // Lookup interceptors are used for handling properties controlled by host
    // objects.
    inline bool HasNamedInterceptor();
    inline bool HasIndexedInterceptor();
  
    // Support functions for v8 api (needed for correct interceptor behavior).
    bool HasRealNamedProperty(String* key);
    bool HasRealElementProperty(uint32_t index);
    bool HasRealNamedCallbackProperty(String* key);
  
    // Initializes the array to a certain length
    Object* SetElementsLength(Object* length);
  
    // Get the header size for a JSObject.  Used to compute the index of
    // internal fields as well as the number of internal fields.
    inline int GetHeaderSize();
  
    inline int GetInternalFieldCount();
    inline Object* GetInternalField(int index);
    inline void SetInternalField(int index, Object* value);
  
    // Lookup a property.  If found, the result is valid and has
    // detailed information.
    void LocalLookup(String* name, LookupResult* result);
    void Lookup(String* name, LookupResult* result);
  
    // The following lookup functions skip interceptors.
    void LocalLookupRealNamedProperty(String* name, LookupResult* result);
    void LookupRealNamedProperty(String* name, LookupResult* result);
    void LookupRealNamedPropertyInPrototypes(String* name, LookupResult* result);
    void LookupCallbackSetterInPrototypes(String* name, LookupResult* result);
    Object* LookupCallbackSetterInPrototypes(uint32_t index);
    void LookupCallback(String* name, LookupResult* result);
  
    // Returns the number of properties on this object filtering out properties
    // with the specified attributes (ignoring interceptors).
    int NumberOfLocalProperties(PropertyAttributes filter);
    // Returns the number of enumerable properties (ignoring interceptors).
    int NumberOfEnumProperties();
    // Fill in details for properties into storage starting at the specified
    // index.
    void GetLocalPropertyNames(FixedArray* storage, int index);
  
    // Returns the number of properties on this object filtering out properties
    // with the specified attributes (ignoring interceptors).
    int NumberOfLocalElements(PropertyAttributes filter);
    // Returns the number of enumerable elements (ignoring interceptors).
    int NumberOfEnumElements();
    // Returns the number of elements on this object filtering out elements
    // with the specified attributes (ignoring interceptors).
    int GetLocalElementKeys(FixedArray* storage, PropertyAttributes filter);
    // Count and fill in the enumerable elements into storage.
    // (storage->length() == NumberOfEnumElements()).
    // If storage is NULL, will count the elements without adding
    // them to any storage.
    // Returns the number of enumerable elements.
    int GetEnumElementKeys(FixedArray* storage);
  
    // Add a property to a fast-case object using a map transition to
    // new_map.
    Object* AddFastPropertyUsingMap(Map* new_map,
                                    String* name,
                                    Object* value);
  
    // Add a constant function property to a fast-case object.
    // This leaves a CONSTANT_TRANSITION in the old map, and
    // if it is called on a second object with this map, a
    // normal property is added instead, with a map transition.
    // This avoids the creation of many maps with the same constant
    // function, all orphaned.
    Object* AddConstantFunctionProperty(String* name,
                                        JSFunction* function,
                                        PropertyAttributes attributes);
  
    Object* ReplaceSlowProperty(String* name,
                                Object* value,
                                PropertyAttributes attributes);
  
    // Converts a descriptor of any other type to a real field,
    // backed by the properties array.  Descriptors of visible
    // types, such as CONSTANT_FUNCTION, keep their enumeration order.
    // Converts the descriptor on the original object's map to a
    // map transition, and the the new field is on the object's new map.
    Object* ConvertDescriptorToFieldAndMapTransition(
        String* name,
        Object* new_value,
        PropertyAttributes attributes);
  
    // Converts a descriptor of any other type to a real field,
    // backed by the properties array.  Descriptors of visible
    // types, such as CONSTANT_FUNCTION, keep their enumeration order.
    Object* ConvertDescriptorToField(String* name,
                                     Object* new_value,
                                     PropertyAttributes attributes);
  
    // Add a property to a fast-case object.
    Object* AddFastProperty(String* name,
                            Object* value,
                            PropertyAttributes attributes);
  
    // Add a property to a slow-case object.
    Object* AddSlowProperty(String* name,
                            Object* value,
                            PropertyAttributes attributes);
  
    // Add a property to an object.
    Object* AddProperty(String* name,
                        Object* value,
                        PropertyAttributes attributes);
  
    // Convert the object to use the canonical dictionary
    // representation. If the object is expected to have additional properties
    // added this number can be indicated to have the backing store allocated to
    // an initial capacity for holding these properties.
    Object* NormalizeProperties(PropertyNormalizationMode mode,
                                int expected_additional_properties);
    Object* NormalizeElements();
  
    // Transform slow named properties to fast variants.
    // Returns failure if allocation failed.
    Object* TransformToFastProperties(int unused_property_fields);
  
    // Access fast-case object properties at index.
    inline Object* FastPropertyAt(int index);
    inline Object* FastPropertyAtPut(int index, Object* value);
  
    // Access to in object properties.
    inline Object* InObjectPropertyAt(int index);
    inline Object* InObjectPropertyAtPut(int index,
                                         Object* value,
                                         WriteBarrierMode mode
                                         = UPDATE_WRITE_BARRIER);
  
    // initializes the body after properties slot, properties slot is
    // initialized by set_properties
    // Note: this call does not update write barrier, it is caller's
    // reponsibility to ensure that *v* can be collected without WB here.
    inline void InitializeBody(int object_size);
  
    // Check whether this object references another object
    bool ReferencesObject(Object* obj);
  
    // Casting.
    static inline JSObject* cast(Object* obj);
  
    // Dispatched behavior.
    void JSObjectIterateBody(int object_size, ObjectVisitor* v);
    void JSObjectShortPrint(StringStream* accumulator);
  #ifdef DEBUG
    void JSObjectPrint();
    void JSObjectVerify();
    void PrintProperties();
    void PrintElements();
  
    // Structure for collecting spill information about JSObjects.
    class SpillInformation {
     public:
      void Clear();
      void Print();
      int number_of_objects_;
      int number_of_objects_with_fast_properties_;
      int number_of_objects_with_fast_elements_;
      int number_of_fast_used_fields_;
      int number_of_fast_unused_fields_;
      int number_of_slow_used_properties_;
      int number_of_slow_unused_properties_;
      int number_of_fast_used_elements_;
      int number_of_fast_unused_elements_;
      int number_of_slow_used_elements_;
      int number_of_slow_unused_elements_;
    };
  
    void IncrementSpillStatistics(SpillInformation* info);
  #endif
    Object* SlowReverseLookup(Object* value);
  
    // Maximal number of elements (numbered 0 .. kMaxElementCount - 1).
    // Also maximal value of JSArray's length property.
    static const uint32_t kMaxElementCount = 0xffffffffu;
  
    static const uint32_t kMaxGap = 1024;
    static const int kMaxFastElementsLength = 5000;
    static const int kInitialMaxFastElementArray = 100000;
    static const int kMaxFastProperties = 8;
    static const int kMaxInstanceSize = 255 * kPointerSize;
    // When extending the backing storage for property values, we increase
    // its size by more than the 1 entry necessary, so sequentially adding fields
    // to the same object requires fewer allocations and copies.
    static const int kFieldsAdded = 3;
  
    // Layout description.
    static const int kPropertiesOffset = HeapObject::kHeaderSize;
    static const int kElementsOffset = kPropertiesOffset + kPointerSize;
    static const int kHeaderSize = kElementsOffset + kPointerSize;
  
    STATIC_CHECK(kHeaderSize == Internals::kJSObjectHeaderSize);
  
    Object* GetElementWithInterceptor(JSObject* receiver, uint32_t index);
  
   private:
    Object* SetElementWithInterceptor(uint32_t index, Object* value);
    Object* SetElementWithoutInterceptor(uint32_t index, Object* value);
  
    Object* GetElementPostInterceptor(JSObject* receiver, uint32_t index);
  
    Object* DeletePropertyPostInterceptor(String* name, DeleteMode mode);
    Object* DeletePropertyWithInterceptor(String* name);
  
    Object* DeleteElementPostInterceptor(uint32_t index, DeleteMode mode);
    Object* DeleteElementWithInterceptor(uint32_t index);
  
    PropertyAttributes GetPropertyAttributePostInterceptor(JSObject* receiver,
                                                           String* name,
                                                           bool continue_search);
    PropertyAttributes GetPropertyAttributeWithInterceptor(JSObject* receiver,
                                                           String* name,
                                                           bool continue_search);
    PropertyAttributes GetPropertyAttributeWithFailedAccessCheck(
        Object* receiver,
        LookupResult* result,
        String* name,
        bool continue_search);
    PropertyAttributes GetPropertyAttribute(JSObject* receiver,
                                            LookupResult* result,
                                            String* name,
                                            bool continue_search);
  
    // Returns true if most of the elements backing storage is used.
    bool HasDenseElements();
  
    Object* DefineGetterSetter(String* name, PropertyAttributes attributes);
  
    void LookupInDescriptor(String* name, LookupResult* result);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSObject);
  };
  
  
  // Abstract super class arrays. It provides length behavior.
  class Array: public HeapObject {
   public:
    // [length]: length of the array.
    inline int length();
    inline void set_length(int value);
  
    // Convert an object to an array index.
    // Returns true if the conversion succeeded.
    static inline bool IndexFromObject(Object* object, uint32_t* index);
  
    // Layout descriptor.
    static const int kLengthOffset = HeapObject::kHeaderSize;
  
   protected:
    // No code should use the Array class directly, only its subclasses.
    // Use the kHeaderSize of the appropriate subclass, which may be aligned.
    static const int kHeaderSize = kLengthOffset + kIntSize;
    static const int kAlignedSize = POINTER_SIZE_ALIGN(kHeaderSize);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Array);
  };
  
  
  // FixedArray describes fixed sized arrays where element
  // type is Object*.
  
  class FixedArray: public Array {
   public:
  
    // Setter and getter for elements.
    inline Object* get(int index);
    // Setter that uses write barrier.
    inline void set(int index, Object* value);
  
    // Setter that doesn't need write barrier).
    inline void set(int index, Smi* value);
    // Setter with explicit barrier mode.
    inline void set(int index, Object* value, WriteBarrierMode mode);
  
    // Setters for frequently used oddballs located in old space.
    inline void set_undefined(int index);
    inline void set_null(int index);
    inline void set_the_hole(int index);
  
    // Gives access to raw memory which stores the array's data.
    inline Object** data_start();
  
    // Copy operations.
    inline Object* Copy();
    Object* CopySize(int new_length);
  
    // Add the elements of a JSArray to this FixedArray.
    Object* AddKeysFromJSArray(JSArray* array);
  
    // Compute the union of this and other.
    Object* UnionOfKeys(FixedArray* other);
  
    // Copy a sub array from the receiver to dest.
    void CopyTo(int pos, FixedArray* dest, int dest_pos, int len);
  
    // Garbage collection support.
    static int SizeFor(int length) { return kHeaderSize + length * kPointerSize; }
  
    // Code Generation support.
    static int OffsetOfElementAt(int index) { return SizeFor(index); }
  
    // Casting.
    static inline FixedArray* cast(Object* obj);
  
    static const int kHeaderSize = Array::kAlignedSize;
  
    // Maximal allowed size, in bytes, of a single FixedArray.
    // Prevents overflowing size computations, as well as extreme memory
    // consumption.
    static const int kMaxSize = 512 * MB;
    // Maximally allowed length of a FixedArray.
    static const int kMaxLength = (kMaxSize - kHeaderSize) / kPointerSize;
  
    // Dispatched behavior.
    int FixedArraySize() { return SizeFor(length()); }
    void FixedArrayIterateBody(ObjectVisitor* v);
  #ifdef DEBUG
    void FixedArrayPrint();
    void FixedArrayVerify();
    // Checks if two FixedArrays have identical contents.
    bool IsEqualTo(FixedArray* other);
  #endif
  
    // Swap two elements in a pair of arrays.  If this array and the
    // numbers array are the same object, the elements are only swapped
    // once.
    void SwapPairs(FixedArray* numbers, int i, int j);
  
    // Sort prefix of this array and the numbers array as pairs wrt. the
    // numbers.  If the numbers array and the this array are the same
    // object, the prefix of this array is sorted.
    void SortPairs(FixedArray* numbers, uint32_t len);
  
   protected:
    // Set operation on FixedArray without using write barriers. Can
    // only be used for storing old space objects or smis.
    static inline void fast_set(FixedArray* array, int index, Object* value);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(FixedArray);
  };
  
  
  // DescriptorArrays are fixed arrays used to hold instance descriptors.
  // The format of the these objects is:
  //   [0]: point to a fixed array with (value, detail) pairs.
  //   [1]: next enumeration index (Smi), or pointer to small fixed array:
  //          [0]: next enumeration index (Smi)
  //          [1]: pointer to fixed array with enum cache
  //   [2]: first key
  //   [length() - 1]: last key
  //
  class DescriptorArray: public FixedArray {
   public:
    // Is this the singleton empty_descriptor_array?
    inline bool IsEmpty();
  
    // Returns the number of descriptors in the array.
    int number_of_descriptors() {
      return IsEmpty() ? 0 : length() - kFirstIndex;
    }
  
    int NextEnumerationIndex() {
      if (IsEmpty()) return PropertyDetails::kInitialIndex;
      Object* obj = get(kEnumerationIndexIndex);
      if (obj->IsSmi()) {
        return Smi::cast(obj)->value();
      } else {
        Object* index = FixedArray::cast(obj)->get(kEnumCacheBridgeEnumIndex);
        return Smi::cast(index)->value();
      }
    }
  
    // Set next enumeration index and flush any enum cache.
    void SetNextEnumerationIndex(int value) {
      if (!IsEmpty()) {
        fast_set(this, kEnumerationIndexIndex, Smi::FromInt(value));
      }
    }
    bool HasEnumCache() {
      return !IsEmpty() && !get(kEnumerationIndexIndex)->IsSmi();
    }
  
    Object* GetEnumCache() {
      ASSERT(HasEnumCache());
      FixedArray* bridge = FixedArray::cast(get(kEnumerationIndexIndex));
      return bridge->get(kEnumCacheBridgeCacheIndex);
    }
  
    // Initialize or change the enum cache,
    // using the supplied storage for the small "bridge".
    void SetEnumCache(FixedArray* bridge_storage, FixedArray* new_cache);
  
    // Accessors for fetching instance descriptor at descriptor number.
    inline String* GetKey(int descriptor_number);
    inline Object* GetValue(int descriptor_number);
    inline Smi* GetDetails(int descriptor_number);
    inline PropertyType GetType(int descriptor_number);
    inline int GetFieldIndex(int descriptor_number);
    inline JSFunction* GetConstantFunction(int descriptor_number);
    inline Object* GetCallbacksObject(int descriptor_number);
    inline AccessorDescriptor* GetCallbacks(int descriptor_number);
    inline bool IsProperty(int descriptor_number);
    inline bool IsTransition(int descriptor_number);
    inline bool IsNullDescriptor(int descriptor_number);
    inline bool IsDontEnum(int descriptor_number);
  
    // Accessor for complete descriptor.
    inline void Get(int descriptor_number, Descriptor* desc);
    inline void Set(int descriptor_number, Descriptor* desc);
  
    // Transfer complete descriptor from another descriptor array to
    // this one.
    inline void CopyFrom(int index, DescriptorArray* src, int src_index);
  
    // Copy the descriptor array, insert a new descriptor and optionally
    // remove map transitions.  If the descriptor is already present, it is
    // replaced.  If a replaced descriptor is a real property (not a transition
    // or null), its enumeration index is kept as is.
    // If adding a real property, map transitions must be removed.  If adding
    // a transition, they must not be removed.  All null descriptors are removed.
    Object* CopyInsert(Descriptor* descriptor, TransitionFlag transition_flag);
  
    // Remove all transitions.  Return  a copy of the array with all transitions
    // removed, or a Failure object if the new array could not be allocated.
    Object* RemoveTransitions();
  
    // Sort the instance descriptors by the hash codes of their keys.
    void Sort();
  
    // Search the instance descriptors for given name.
    inline int Search(String* name);
  
    // Tells whether the name is present int the array.
    bool Contains(String* name) { return kNotFound != Search(name); }
  
    // Perform a binary search in the instance descriptors represented
    // by this fixed array.  low and high are descriptor indices.  If there
    // are three instance descriptors in this array it should be called
    // with low=0 and high=2.
    int BinarySearch(String* name, int low, int high);
  
    // Perform a linear search in the instance descriptors represented
    // by this fixed array.  len is the number of descriptor indices that are
    // valid.  Does not require the descriptors to be sorted.
    int LinearSearch(String* name, int len);
  
    // Allocates a DescriptorArray, but returns the singleton
    // empty descriptor array object if number_of_descriptors is 0.
    static Object* Allocate(int number_of_descriptors);
  
    // Casting.
    static inline DescriptorArray* cast(Object* obj);
  
    // Constant for denoting key was not found.
    static const int kNotFound = -1;
  
    static const int kContentArrayIndex = 0;
    static const int kEnumerationIndexIndex = 1;
    static const int kFirstIndex = 2;
  
    // The length of the "bridge" to the enum cache.
    static const int kEnumCacheBridgeLength = 2;
    static const int kEnumCacheBridgeEnumIndex = 0;
    static const int kEnumCacheBridgeCacheIndex = 1;
  
    // Layout description.
    static const int kContentArrayOffset = FixedArray::kHeaderSize;
    static const int kEnumerationIndexOffset = kContentArrayOffset + kPointerSize;
    static const int kFirstOffset = kEnumerationIndexOffset + kPointerSize;
  
    // Layout description for the bridge array.
    static const int kEnumCacheBridgeEnumOffset = FixedArray::kHeaderSize;
    static const int kEnumCacheBridgeCacheOffset =
      kEnumCacheBridgeEnumOffset + kPointerSize;
  
  #ifdef DEBUG
    // Print all the descriptors.
    void PrintDescriptors();
  
    // Is the descriptor array sorted and without duplicates?
    bool IsSortedNoDuplicates();
  
    // Are two DescriptorArrays equal?
    bool IsEqualTo(DescriptorArray* other);
  #endif
  
    // The maximum number of descriptors we want in a descriptor array (should
    // fit in a page).
    static const int kMaxNumberOfDescriptors = 1024 + 512;
  
   private:
    // Conversion from descriptor number to array indices.
    static int ToKeyIndex(int descriptor_number) {
      return descriptor_number+kFirstIndex;
    }
  
    static int ToDetailsIndex(int descriptor_number) {
      return (descriptor_number << 1) + 1;
    }
  
    static int ToValueIndex(int descriptor_number) {
      return descriptor_number << 1;
    }
  
    bool is_null_descriptor(int descriptor_number) {
      return PropertyDetails(GetDetails(descriptor_number)).type() ==
          NULL_DESCRIPTOR;
    }
    // Swap operation on FixedArray without using write barriers.
    static inline void fast_swap(FixedArray* array, int first, int second);
  
    // Swap descriptor first and second.
    inline void Swap(int first, int second);
  
    FixedArray* GetContentArray() {
      return FixedArray::cast(get(kContentArrayIndex));
    }
    DISALLOW_IMPLICIT_CONSTRUCTORS(DescriptorArray);
  };
  
  
  // HashTable is a subclass of FixedArray that implements a hash table
  // that uses open addressing and quadratic probing.
  //
  // In order for the quadratic probing to work, elements that have not
  // yet been used and elements that have been deleted are
  // distinguished.  Probing continues when deleted elements are
  // encountered and stops when unused elements are encountered.
  //
  // - Elements with key == undefined have not been used yet.
  // - Elements with key == null have been deleted.
  //
  // The hash table class is parameterized with a Shape and a Key.
  // Shape must be a class with the following interface:
  //   class ExampleShape {
  //    public:
  //      // Tells whether key matches other.
  //     static bool IsMatch(Key key, Object* other);
  //     // Returns the hash value for key.
  //     static uint32_t Hash(Key key);
  //     // Returns the hash value for object.
  //     static uint32_t HashForObject(Key key, Object* object);
  //     // Convert key to an object.
  //     static inline Object* AsObject(Key key);
  //     // The prefix size indicates number of elements in the beginning
  //     // of the backing storage.
  //     static const int kPrefixSize = ..;
  //     // The Element size indicates number of elements per entry.
  //     static const int kEntrySize = ..;
  //   };
  // The prefix size indicates an amount of memory in the
  // beginning of the backing storage that can be used for non-element
  // information by subclasses.
  
  template<typename Shape, typename Key>
  class HashTable: public FixedArray {
   public:
    // Returns the number of elements in the hash table.
    int NumberOfElements() {
      return Smi::cast(get(kNumberOfElementsIndex))->value();
    }
  
    // Returns the number of deleted elements in the hash table.
    int NumberOfDeletedElements() {
      return Smi::cast(get(kNumberOfDeletedElementsIndex))->value();
    }
  
    // Returns the capacity of the hash table.
    int Capacity() {
      return Smi::cast(get(kCapacityIndex))->value();
    }
  
    // ElementAdded should be called whenever an element is added to a
    // hash table.
    void ElementAdded() { SetNumberOfElements(NumberOfElements() + 1); }
  
    // ElementRemoved should be called whenever an element is removed from
    // a hash table.
    void ElementRemoved() {
      SetNumberOfElements(NumberOfElements() - 1);
      SetNumberOfDeletedElements(NumberOfDeletedElements() + 1);
    }
    void ElementsRemoved(int n) {
      SetNumberOfElements(NumberOfElements() - n);
      SetNumberOfDeletedElements(NumberOfDeletedElements() + n);
    }
  
    // Returns a new HashTable object. Might return Failure.
    static Object* Allocate(int at_least_space_for,
                            PretenureFlag pretenure = NOT_TENURED);
  
    // Returns the key at entry.
    Object* KeyAt(int entry) { return get(EntryToIndex(entry)); }
  
    // Tells whether k is a real key.  Null and undefined are not allowed
    // as keys and can be used to indicate missing or deleted elements.
    bool IsKey(Object* k) {
      return !k->IsNull() && !k->IsUndefined();
    }
  
    // Garbage collection support.
    void IteratePrefix(ObjectVisitor* visitor);
    void IterateElements(ObjectVisitor* visitor);
  
    // Casting.
    static inline HashTable* cast(Object* obj);
  
    // Compute the probe offset (quadratic probing).
    INLINE(static uint32_t GetProbeOffset(uint32_t n)) {
      return (n + n * n) >> 1;
    }
  
    static const int kNumberOfElementsIndex = 0;
    static const int kNumberOfDeletedElementsIndex = 1;
    static const int kCapacityIndex = 2;
    static const int kPrefixStartIndex = 3;
    static const int kElementsStartIndex =
        kPrefixStartIndex + Shape::kPrefixSize;
    static const int kEntrySize = Shape::kEntrySize;
    static const int kElementsStartOffset =
        kHeaderSize + kElementsStartIndex * kPointerSize;
    static const int kCapacityOffset =
        kHeaderSize + kCapacityIndex * kPointerSize;
  
    // Constant used for denoting a absent entry.
    static const int kNotFound = -1;
  
    // Maximal capacity of HashTable. Based on maximal length of underlying
    // FixedArray. Staying below kMaxCapacity also ensures that EntryToIndex
    // cannot overflow.
    static const int kMaxCapacity =
        (FixedArray::kMaxLength - kElementsStartOffset) / kEntrySize;
  
    // Find entry for key otherwise return -1.
    int FindEntry(Key key);
  
   protected:
  
    // Find the entry at which to insert element with the given key that
    // has the given hash value.
    uint32_t FindInsertionEntry(uint32_t hash);
  
    // Returns the index for an entry (of the key)
    static inline int EntryToIndex(int entry) {
      return (entry * kEntrySize) + kElementsStartIndex;
    }
  
    // Update the number of elements in the hash table.
    void SetNumberOfElements(int nof) {
      fast_set(this, kNumberOfElementsIndex, Smi::FromInt(nof));
    }
  
    // Update the number of deleted elements in the hash table.
    void SetNumberOfDeletedElements(int nod) {
      fast_set(this, kNumberOfDeletedElementsIndex, Smi::FromInt(nod));
    }
  
    // Sets the capacity of the hash table.
    void SetCapacity(int capacity) {
      // To scale a computed hash code to fit within the hash table, we
      // use bit-wise AND with a mask, so the capacity must be positive
      // and non-zero.
      ASSERT(capacity > 0);
      ASSERT(capacity <= kMaxCapacity);
      fast_set(this, kCapacityIndex, Smi::FromInt(capacity));
    }
  
  
    // Returns probe entry.
    static uint32_t GetProbe(uint32_t hash, uint32_t number, uint32_t size) {
      ASSERT(IsPowerOf2(size));
      return (hash + GetProbeOffset(number)) & (size - 1);
    }
  
    static uint32_t FirstProbe(uint32_t hash, uint32_t size) {
      return hash & (size - 1);
    }
  
    static uint32_t NextProbe(uint32_t last, uint32_t number, uint32_t size) {
      return (last + number) & (size - 1);
    }
  
    // Ensure enough space for n additional elements.
    Object* EnsureCapacity(int n, Key key);
  };
  
  
  
  // HashTableKey is an abstract superclass for virtual key behavior.
  class HashTableKey {
   public:
    // Returns whether the other object matches this key.
    virtual bool IsMatch(Object* other) = 0;
    // Returns the hash value for this key.
    virtual uint32_t Hash() = 0;
    // Returns the hash value for object.
    virtual uint32_t HashForObject(Object* key) = 0;
    // Returns the key object for storing into the hash table.
    // If allocations fails a failure object is returned.
    virtual Object* AsObject() = 0;
    // Required.
    virtual ~HashTableKey() {}
  };
  
  class SymbolTableShape {
   public:
    static bool IsMatch(HashTableKey* key, Object* value) {
      return key->IsMatch(value);
    }
    static uint32_t Hash(HashTableKey* key) {
      return key->Hash();
    }
    static uint32_t HashForObject(HashTableKey* key, Object* object) {
      return key->HashForObject(object);
    }
    static Object* AsObject(HashTableKey* key) {
      return key->AsObject();
    }
  
    static const int kPrefixSize = 0;
    static const int kEntrySize = 1;
  };
  
  // SymbolTable.
  //
  // No special elements in the prefix and the element size is 1
  // because only the symbol itself (the key) needs to be stored.
  class SymbolTable: public HashTable<SymbolTableShape, HashTableKey*> {
   public:
    // Find symbol in the symbol table.  If it is not there yet, it is
    // added.  The return value is the symbol table which might have
    // been enlarged.  If the return value is not a failure, the symbol
    // pointer *s is set to the symbol found.
    Object* LookupSymbol(Vector<const char> str, Object** s);
    Object* LookupString(String* key, Object** s);
  
    // Looks up a symbol that is equal to the given string and returns
    // true if it is found, assigning the symbol to the given output
    // parameter.
    bool LookupSymbolIfExists(String* str, String** symbol);
    bool LookupTwoCharsSymbolIfExists(uint32_t c1, uint32_t c2, String** symbol);
  
    // Casting.
    static inline SymbolTable* cast(Object* obj);
  
   private:
    Object* LookupKey(HashTableKey* key, Object** s);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(SymbolTable);
  };
  
  
  class MapCacheShape {
   public:
    static bool IsMatch(HashTableKey* key, Object* value) {
      return key->IsMatch(value);
    }
    static uint32_t Hash(HashTableKey* key) {
      return key->Hash();
    }
  
    static uint32_t HashForObject(HashTableKey* key, Object* object) {
      return key->HashForObject(object);
    }
  
    static Object* AsObject(HashTableKey* key) {
      return key->AsObject();
    }
  
    static const int kPrefixSize = 0;
    static const int kEntrySize = 2;
  };
  
  
  // MapCache.
  //
  // Maps keys that are a fixed array of symbols to a map.
  // Used for canonicalize maps for object literals.
  class MapCache: public HashTable<MapCacheShape, HashTableKey*> {
   public:
    // Find cached value for a string key, otherwise return null.
    Object* Lookup(FixedArray* key);
    Object* Put(FixedArray* key, Map* value);
    static inline MapCache* cast(Object* obj);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(MapCache);
  };
  
  
  template <typename Shape, typename Key>
  class Dictionary: public HashTable<Shape, Key> {
   public:
  
    static inline Dictionary<Shape, Key>* cast(Object* obj) {
      return reinterpret_cast<Dictionary<Shape, Key>*>(obj);
    }
  
    // Returns the value at entry.
    Object* ValueAt(int entry) {
      return this->get(HashTable<Shape, Key>::EntryToIndex(entry)+1);
    }
  
    // Set the value for entry.
    void ValueAtPut(int entry, Object* value) {
      this->set(HashTable<Shape, Key>::EntryToIndex(entry)+1, value);
    }
  
    // Returns the property details for the property at entry.
    PropertyDetails DetailsAt(int entry) {
      ASSERT(entry >= 0);  // Not found is -1, which is not caught by get().
      return PropertyDetails(
          Smi::cast(this->get(HashTable<Shape, Key>::EntryToIndex(entry) + 2)));
    }
  
    // Set the details for entry.
    void DetailsAtPut(int entry, PropertyDetails value) {
      this->set(HashTable<Shape, Key>::EntryToIndex(entry) + 2, value.AsSmi());
    }
  
    // Sorting support
    void CopyValuesTo(FixedArray* elements);
  
    // Delete a property from the dictionary.
    Object* DeleteProperty(int entry, JSObject::DeleteMode mode);
  
    // Returns the number of elements in the dictionary filtering out properties
    // with the specified attributes.
    int NumberOfElementsFilterAttributes(PropertyAttributes filter);
  
    // Returns the number of enumerable elements in the dictionary.
    int NumberOfEnumElements();
  
    // Copies keys to preallocated fixed array.
    void CopyKeysTo(FixedArray* storage, PropertyAttributes filter);
    // Fill in details for properties into storage.
    void CopyKeysTo(FixedArray* storage);
  
    // Accessors for next enumeration index.
    void SetNextEnumerationIndex(int index) {
      this->fast_set(this, kNextEnumerationIndexIndex, Smi::FromInt(index));
    }
  
    int NextEnumerationIndex() {
      return Smi::cast(FixedArray::get(kNextEnumerationIndexIndex))->value();
    }
  
    // Returns a new array for dictionary usage. Might return Failure.
    static Object* Allocate(int at_least_space_for);
  
    // Ensure enough space for n additional elements.
    Object* EnsureCapacity(int n, Key key);
  
  #ifdef DEBUG
    void Print();
  #endif
    // Returns the key (slow).
    Object* SlowReverseLookup(Object* value);
  
    // Sets the entry to (key, value) pair.
    inline void SetEntry(int entry,
                         Object* key,
                         Object* value,
                         PropertyDetails details);
  
    Object* Add(Key key, Object* value, PropertyDetails details);
  
   protected:
    // Generic at put operation.
    Object* AtPut(Key key, Object* value);
  
    // Add entry to dictionary.
    Object* AddEntry(Key key,
                     Object* value,
                     PropertyDetails details,
                     uint32_t hash);
  
    // Generate new enumeration indices to avoid enumeration index overflow.
    Object* GenerateNewEnumerationIndices();
    static const int kMaxNumberKeyIndex =
        HashTable<Shape, Key>::kPrefixStartIndex;
    static const int kNextEnumerationIndexIndex = kMaxNumberKeyIndex + 1;
  };
  
  
  class StringDictionaryShape {
   public:
    static inline bool IsMatch(String* key, Object* other);
    static inline uint32_t Hash(String* key);
    static inline uint32_t HashForObject(String* key, Object* object);
    static inline Object* AsObject(String* key);
    static const int kPrefixSize = 2;
    static const int kEntrySize = 3;
    static const bool kIsEnumerable = true;
  };
  
  
  class StringDictionary: public Dictionary<StringDictionaryShape, String*> {
   public:
    static inline StringDictionary* cast(Object* obj) {
      ASSERT(obj->IsDictionary());
      return reinterpret_cast<StringDictionary*>(obj);
    }
  
    // Copies enumerable keys to preallocated fixed array.
    void CopyEnumKeysTo(FixedArray* storage, FixedArray* sort_array);
  
    // For transforming properties of a JSObject.
    Object* TransformPropertiesToFastFor(JSObject* obj,
                                         int unused_property_fields);
  };
  
  
  class NumberDictionaryShape {
   public:
    static inline bool IsMatch(uint32_t key, Object* other);
    static inline uint32_t Hash(uint32_t key);
    static inline uint32_t HashForObject(uint32_t key, Object* object);
    static inline Object* AsObject(uint32_t key);
    static const int kPrefixSize = 2;
    static const int kEntrySize = 3;
    static const bool kIsEnumerable = false;
  };
  
  
  class NumberDictionary: public Dictionary<NumberDictionaryShape, uint32_t> {
   public:
    static NumberDictionary* cast(Object* obj) {
      ASSERT(obj->IsDictionary());
      return reinterpret_cast<NumberDictionary*>(obj);
    }
  
    // Type specific at put (default NONE attributes is used when adding).
    Object* AtNumberPut(uint32_t key, Object* value);
    Object* AddNumberEntry(uint32_t key,
                           Object* value,
                           PropertyDetails details);
  
    // Set an existing entry or add a new one if needed.
    Object* Set(uint32_t key, Object* value, PropertyDetails details);
  
    void UpdateMaxNumberKey(uint32_t key);
  
    // If slow elements are required we will never go back to fast-case
    // for the elements kept in this dictionary.  We require slow
    // elements if an element has been added at an index larger than
    // kRequiresSlowElementsLimit or set_requires_slow_elements() has been called
    // when defining a getter or setter with a number key.
    inline bool requires_slow_elements();
    inline void set_requires_slow_elements();
  
    // Get the value of the max number key that has been added to this
    // dictionary.  max_number_key can only be called if
    // requires_slow_elements returns false.
    inline uint32_t max_number_key();
  
    // Remove all entries were key is a number and (from <= key && key < to).
    void RemoveNumberEntries(uint32_t from, uint32_t to);
  
    // Bit masks.
    static const int kRequiresSlowElementsMask = 1;
    static const int kRequiresSlowElementsTagSize = 1;
    static const uint32_t kRequiresSlowElementsLimit = (1 << 29) - 1;
  };
  
  
  // JSFunctionResultCache caches results of some JSFunction invocation.
  // It is a fixed array with fixed structure:
  //   [0]: factory function
  //   [1]: finger index
  //   [2]: current cache size
  //   [3]: dummy field.
  // The rest of array are key/value pairs.
  class JSFunctionResultCache: public FixedArray {
   public:
    static const int kFactoryIndex = 0;
    static const int kFingerIndex = kFactoryIndex + 1;
    static const int kCacheSizeIndex = kFingerIndex + 1;
    static const int kDummyIndex = kCacheSizeIndex + 1;
    static const int kEntriesIndex = kDummyIndex + 1;
  
    static const int kEntrySize = 2;  // key + value
  };
  
  
  // ByteArray represents fixed sized byte arrays.  Used by the outside world,
  // such as PCRE, and also by the memory allocator and garbage collector to
  // fill in free blocks in the heap.
  class ByteArray: public Array {
   public:
    // Setter and getter.
    inline byte get(int index);
    inline void set(int index, byte value);
  
    // Treat contents as an int array.
    inline int get_int(int index);
  
    static int SizeFor(int length) {
      return OBJECT_SIZE_ALIGN(kHeaderSize + length);
    }
    // We use byte arrays for free blocks in the heap.  Given a desired size in
    // bytes that is a multiple of the word size and big enough to hold a byte
    // array, this function returns the number of elements a byte array should
    // have.
    static int LengthFor(int size_in_bytes) {
      ASSERT(IsAligned(size_in_bytes, kPointerSize));
      ASSERT(size_in_bytes >= kHeaderSize);
      return size_in_bytes - kHeaderSize;
    }
  
    // Returns data start address.
    inline Address GetDataStartAddress();
  
    // Returns a pointer to the ByteArray object for a given data start address.
    static inline ByteArray* FromDataStartAddress(Address address);
  
    // Casting.
    static inline ByteArray* cast(Object* obj);
  
    // Dispatched behavior.
    int ByteArraySize() { return SizeFor(length()); }
  #ifdef DEBUG
    void ByteArrayPrint();
    void ByteArrayVerify();
  #endif
  
    // ByteArray headers are not quadword aligned.
    static const int kHeaderSize = Array::kHeaderSize;
    static const int kAlignedSize = Array::kAlignedSize;
  
    // Maximal memory consumption for a single ByteArray.
    static const int kMaxSize = 512 * MB;
    // Maximal length of a single ByteArray.
    static const int kMaxLength = kMaxSize - kHeaderSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ByteArray);
  };
  
  
  // A PixelArray represents a fixed-size byte array with special semantics
  // used for implementing the CanvasPixelArray object. Please see the
  // specification at:
  // http://www.whatwg.org/specs/web-apps/current-work/
  //                      multipage/the-canvas-element.html#canvaspixelarray
  // In particular, write access clamps the value written to 0 or 255 if the
  // value written is outside this range.
  class PixelArray: public Array {
   public:
    // [external_pointer]: The pointer to the external memory area backing this
    // pixel array.
    DECL_ACCESSORS(external_pointer, uint8_t)  // Pointer to the data store.
  
    // Setter and getter.
    inline uint8_t get(int index);
    inline void set(int index, uint8_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber and
    // undefined and clamps the converted value between 0 and 255.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline PixelArray* cast(Object* obj);
  
  #ifdef DEBUG
    void PixelArrayPrint();
    void PixelArrayVerify();
  #endif  // DEBUG
  
    // Maximal acceptable length for a pixel array.
    static const int kMaxLength = 0x3fffffff;
  
    // PixelArray headers are not quadword aligned.
    static const int kExternalPointerOffset = Array::kAlignedSize;
    static const int kHeaderSize = kExternalPointerOffset + kPointerSize;
    static const int kAlignedSize = OBJECT_SIZE_ALIGN(kHeaderSize);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(PixelArray);
  };
  
  
  // An ExternalArray represents a fixed-size array of primitive values
  // which live outside the JavaScript heap. Its subclasses are used to
  // implement the CanvasArray types being defined in the WebGL
  // specification. As of this writing the first public draft is not yet
  // available, but Khronos members can access the draft at:
  //   https://cvs.khronos.org/svn/repos/3dweb/trunk/doc/spec/WebGL-spec.html
  //
  // The semantics of these arrays differ from CanvasPixelArray.
  // Out-of-range values passed to the setter are converted via a C
  // cast, not clamping. Out-of-range indices cause exceptions to be
  // raised rather than being silently ignored.
  class ExternalArray: public Array {
   public:
    // [external_pointer]: The pointer to the external memory area backing this
    // external array.
    DECL_ACCESSORS(external_pointer, void)  // Pointer to the data store.
  
    // Casting.
    static inline ExternalArray* cast(Object* obj);
  
    // Maximal acceptable length for an external array.
    static const int kMaxLength = 0x3fffffff;
  
    // ExternalArray headers are not quadword aligned.
    static const int kExternalPointerOffset = Array::kAlignedSize;
    static const int kHeaderSize = kExternalPointerOffset + kPointerSize;
    static const int kAlignedSize = OBJECT_SIZE_ALIGN(kHeaderSize);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalArray);
  };
  
  
  class ExternalByteArray: public ExternalArray {
   public:
    // Setter and getter.
    inline int8_t get(int index);
    inline void set(int index, int8_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalByteArray* cast(Object* obj);
  
  #ifdef DEBUG
    void ExternalByteArrayPrint();
    void ExternalByteArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalByteArray);
  };
  
  
  class ExternalUnsignedByteArray: public ExternalArray {
   public:
    // Setter and getter.
    inline uint8_t get(int index);
    inline void set(int index, uint8_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalUnsignedByteArray* cast(Object* obj);
  
  #ifdef DEBUG
    void ExternalUnsignedByteArrayPrint();
    void ExternalUnsignedByteArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalUnsignedByteArray);
  };
  
  
  class ExternalShortArray: public ExternalArray {
   public:
    // Setter and getter.
    inline int16_t get(int index);
    inline void set(int index, int16_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalShortArray* cast(Object* obj);
  
  #ifdef DEBUG
    void ExternalShortArrayPrint();
    void ExternalShortArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalShortArray);
  };
  
  
  class ExternalUnsignedShortArray: public ExternalArray {
   public:
    // Setter and getter.
    inline uint16_t get(int index);
    inline void set(int index, uint16_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalUnsignedShortArray* cast(Object* obj);
  
  #ifdef DEBUG
    void ExternalUnsignedShortArrayPrint();
    void ExternalUnsignedShortArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalUnsignedShortArray);
  };
  
  
  class ExternalIntArray: public ExternalArray {
   public:
    // Setter and getter.
    inline int32_t get(int index);
    inline void set(int index, int32_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalIntArray* cast(Object* obj);
  
  #ifdef DEBUG
    void ExternalIntArrayPrint();
    void ExternalIntArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalIntArray);
  };
  
  
  class ExternalUnsignedIntArray: public ExternalArray {
   public:
    // Setter and getter.
    inline uint32_t get(int index);
    inline void set(int index, uint32_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalUnsignedIntArray* cast(Object* obj);
  
  #ifdef DEBUG
    void ExternalUnsignedIntArrayPrint();
    void ExternalUnsignedIntArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalUnsignedIntArray);
  };
  
  
  class ExternalFloatArray: public ExternalArray {
   public:
    // Setter and getter.
    inline float get(int index);
    inline void set(int index, float value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    Object* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalFloatArray* cast(Object* obj);
  
  #ifdef DEBUG
    void ExternalFloatArrayPrint();
    void ExternalFloatArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalFloatArray);
  };
  
  
  // Code describes objects with on-the-fly generated machine code.
  class Code: public HeapObject {
   public:
    // Opaque data type for encapsulating code flags like kind, inline
    // cache state, and arguments count.
    enum Flags { };
  
    enum Kind {
      FUNCTION,
      STUB,
      BUILTIN,
      LOAD_IC,
      KEYED_LOAD_IC,
      CALL_IC,
      STORE_IC,
      KEYED_STORE_IC,
      BINARY_OP_IC,
      // No more than 16 kinds. The value currently encoded in four bits in
      // Flags.
  
      // Pseudo-kinds.
      REGEXP = BUILTIN,
      FIRST_IC_KIND = LOAD_IC,
      LAST_IC_KIND = BINARY_OP_IC
    };
  
    enum {
      NUMBER_OF_KINDS = KEYED_STORE_IC + 1
    };
  
  #ifdef ENABLE_DISASSEMBLER
    // Printing
    static const char* Kind2String(Kind kind);
    static const char* ICState2String(InlineCacheState state);
    static const char* PropertyType2String(PropertyType type);
    void Disassemble(const char* name);
  #endif  // ENABLE_DISASSEMBLER
  
    // [instruction_size]: Size of the native instructions
    inline int instruction_size();
    inline void set_instruction_size(int value);
  
    // [relocation_size]: Size of relocation information.
    inline int relocation_size();
    inline void set_relocation_size(int value);
  
    // [sinfo_size]: Size of scope information.
    inline int sinfo_size();
    inline void set_sinfo_size(int value);
  
    // [flags]: Various code flags.
    inline Flags flags();
    inline void set_flags(Flags flags);
  
    // [flags]: Access to specific code flags.
    inline Kind kind();
    inline InlineCacheState ic_state();  // Only valid for IC stubs.
    inline InLoopFlag ic_in_loop();  // Only valid for IC stubs.
    inline PropertyType type();  // Only valid for monomorphic IC stubs.
    inline int arguments_count();  // Only valid for call IC stubs.
  
    // Testers for IC stub kinds.
    inline bool is_inline_cache_stub();
    inline bool is_load_stub() { return kind() == LOAD_IC; }
    inline bool is_keyed_load_stub() { return kind() == KEYED_LOAD_IC; }
    inline bool is_store_stub() { return kind() == STORE_IC; }
    inline bool is_keyed_store_stub() { return kind() == KEYED_STORE_IC; }
    inline bool is_call_stub() { return kind() == CALL_IC; }
  
    // [major_key]: For kind STUB or BINARY_OP_IC, the major key.
    inline CodeStub::Major major_key();
    inline void set_major_key(CodeStub::Major major);
  
    // Flags operations.
    static inline Flags ComputeFlags(Kind kind,
                                     InLoopFlag in_loop = NOT_IN_LOOP,
                                     InlineCacheState ic_state = UNINITIALIZED,
                                     PropertyType type = NORMAL,
                                     int argc = -1);
  
    static inline Flags ComputeMonomorphicFlags(
        Kind kind,
        PropertyType type,
        InLoopFlag in_loop = NOT_IN_LOOP,
        int argc = -1);
  
    static inline Kind ExtractKindFromFlags(Flags flags);
    static inline InlineCacheState ExtractICStateFromFlags(Flags flags);
    static inline InLoopFlag ExtractICInLoopFromFlags(Flags flags);
    static inline PropertyType ExtractTypeFromFlags(Flags flags);
    static inline int ExtractArgumentsCountFromFlags(Flags flags);
    static inline Flags RemoveTypeFromFlags(Flags flags);
  
    // Convert a target address into a code object.
    static inline Code* GetCodeFromTargetAddress(Address address);
  
    // Returns the address of the first instruction.
    inline byte* instruction_start();
  
    // Returns the size of the instructions, padding, and relocation information.
    inline int body_size();
  
    // Returns the address of the first relocation info (read backwards!).
    inline byte* relocation_start();
  
    // Code entry point.
    inline byte* entry();
  
    // Returns true if pc is inside this object's instructions.
    inline bool contains(byte* pc);
  
    // Returns the address of the scope information.
    inline byte* sinfo_start();
  
    // Relocate the code by delta bytes. Called to signal that this code
    // object has been moved by delta bytes.
    void Relocate(intptr_t delta);
  
    // Migrate code described by desc.
    void CopyFrom(const CodeDesc& desc);
  
    // Returns the object size for a given body and sinfo size (Used for
    // allocation).
    static int SizeFor(int body_size, int sinfo_size) {
      ASSERT_SIZE_TAG_ALIGNED(body_size);
      ASSERT_SIZE_TAG_ALIGNED(sinfo_size);
      return RoundUp(kHeaderSize + body_size + sinfo_size, kCodeAlignment);
    }
  
    // Calculate the size of the code object to report for log events. This takes
    // the layout of the code object into account.
    int ExecutableSize() {
      // Check that the assumptions about the layout of the code object holds.
      ASSERT_EQ(static_cast<int>(instruction_start() - address()),
                Code::kHeaderSize);
      return instruction_size() + Code::kHeaderSize;
    }
  
    // Locating source position.
    int SourcePosition(Address pc);
    int SourceStatementPosition(Address pc);
  
    // Casting.
    static inline Code* cast(Object* obj);
  
    // Dispatched behavior.
    int CodeSize() { return SizeFor(body_size(), sinfo_size()); }
    void CodeIterateBody(ObjectVisitor* v);
  #ifdef DEBUG
    void CodePrint();
    void CodeVerify();
  #endif
    // Code entry points are aligned to 32 bytes.
    static const int kCodeAlignmentBits = 5;
    static const int kCodeAlignment = 1 << kCodeAlignmentBits;
    static const int kCodeAlignmentMask = kCodeAlignment - 1;
  
    // Layout description.
    static const int kInstructionSizeOffset = HeapObject::kHeaderSize;
    static const int kRelocationSizeOffset = kInstructionSizeOffset + kIntSize;
    static const int kSInfoSizeOffset = kRelocationSizeOffset + kIntSize;
    static const int kFlagsOffset = kSInfoSizeOffset + kIntSize;
    static const int kKindSpecificFlagsOffset  = kFlagsOffset + kIntSize;
    // Add padding to align the instruction start following right after
    // the Code object header.
    static const int kHeaderSize =
        (kKindSpecificFlagsOffset + kIntSize + kCodeAlignmentMask) &
            ~kCodeAlignmentMask;
  
    // Byte offsets within kKindSpecificFlagsOffset.
    static const int kStubMajorKeyOffset = kKindSpecificFlagsOffset + 1;
  
    // Flags layout.
    static const int kFlagsICStateShift        = 0;
    static const int kFlagsICInLoopShift       = 3;
    static const int kFlagsKindShift           = 4;
    static const int kFlagsTypeShift           = 8;
    static const int kFlagsArgumentsCountShift = 11;
  
    static const int kFlagsICStateMask        = 0x00000007;  // 00000000111
    static const int kFlagsICInLoopMask       = 0x00000008;  // 00000001000
    static const int kFlagsKindMask           = 0x000000F0;  // 00011110000
    static const int kFlagsTypeMask           = 0x00000700;  // 11100000000
    static const int kFlagsArgumentsCountMask = 0xFFFFF800;
  
    static const int kFlagsNotUsedInLookup =
        (kFlagsICInLoopMask | kFlagsTypeMask);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Code);
  };
  
  
  // All heap objects have a Map that describes their structure.
  //  A Map contains information about:
  //  - Size information about the object
  //  - How to iterate over an object (for garbage collection)
  class Map: public HeapObject {
   public:
    // Instance size.
    inline int instance_size();
    inline void set_instance_size(int value);
  
    // Count of properties allocated in the object.
    inline int inobject_properties();
    inline void set_inobject_properties(int value);
  
    // Count of property fields pre-allocated in the object when first allocated.
    inline int pre_allocated_property_fields();
    inline void set_pre_allocated_property_fields(int value);
  
    // Instance type.
    inline InstanceType instance_type();
    inline void set_instance_type(InstanceType value);
  
    // Tells how many unused property fields are available in the
    // instance (only used for JSObject in fast mode).
    inline int unused_property_fields();
    inline void set_unused_property_fields(int value);
  
    // Bit field.
    inline byte bit_field();
    inline void set_bit_field(byte value);
  
    // Bit field 2.
    inline byte bit_field2();
    inline void set_bit_field2(byte value);
  
    // Tells whether the object in the prototype property will be used
    // for instances created from this function.  If the prototype
    // property is set to a value that is not a JSObject, the prototype
    // property will not be used to create instances of the function.
    // See ECMA-262, 13.2.2.
    inline void set_non_instance_prototype(bool value);
    inline bool has_non_instance_prototype();
  
    // Tells whether the instance with this map should be ignored by the
    // __proto__ accessor.
    inline void set_is_hidden_prototype() {
      set_bit_field(bit_field() | (1 << kIsHiddenPrototype));
    }
  
    inline bool is_hidden_prototype() {
      return ((1 << kIsHiddenPrototype) & bit_field()) != 0;
    }
  
    // Records and queries whether the instance has a named interceptor.
    inline void set_has_named_interceptor() {
      set_bit_field(bit_field() | (1 << kHasNamedInterceptor));
    }
  
    inline bool has_named_interceptor() {
      return ((1 << kHasNamedInterceptor) & bit_field()) != 0;
    }
  
    // Records and queries whether the instance has an indexed interceptor.
    inline void set_has_indexed_interceptor() {
      set_bit_field(bit_field() | (1 << kHasIndexedInterceptor));
    }
  
    inline bool has_indexed_interceptor() {
      return ((1 << kHasIndexedInterceptor) & bit_field()) != 0;
    }
  
    // Tells whether the instance is undetectable.
    // An undetectable object is a special class of JSObject: 'typeof' operator
    // returns undefined, ToBoolean returns false. Otherwise it behaves like
    // a normal JS object.  It is useful for implementing undetectable
    // document.all in Firefox & Safari.
    // See https://bugzilla.mozilla.org/show_bug.cgi?id=248549.
    inline void set_is_undetectable() {
      set_bit_field(bit_field() | (1 << kIsUndetectable));
    }
  
    inline bool is_undetectable() {
      return ((1 << kIsUndetectable) & bit_field()) != 0;
    }
  
    // Tells whether the instance has a call-as-function handler.
    inline void set_has_instance_call_handler() {
      set_bit_field(bit_field() | (1 << kHasInstanceCallHandler));
    }
  
    inline bool has_instance_call_handler() {
      return ((1 << kHasInstanceCallHandler) & bit_field()) != 0;
    }
  
    inline void set_is_extensible() {
      set_bit_field2(bit_field2() | (1 << kIsExtensible));
    }
  
    inline bool is_extensible() {
      return ((1 << kIsExtensible) & bit_field2()) != 0;
    }
  
    // Tells whether the instance needs security checks when accessing its
    // properties.
    inline void set_is_access_check_needed(bool access_check_needed);
    inline bool is_access_check_needed();
  
    // [prototype]: implicit prototype object.
    DECL_ACCESSORS(prototype, Object)
  
    // [constructor]: points back to the function responsible for this map.
    DECL_ACCESSORS(constructor, Object)
  
    // [instance descriptors]: describes the object.
    DECL_ACCESSORS(instance_descriptors, DescriptorArray)
  
    // [stub cache]: contains stubs compiled for this map.
    DECL_ACCESSORS(code_cache, Object)
  
    Object* CopyDropDescriptors();
  
    // Returns a copy of the map, with all transitions dropped from the
    // instance descriptors.
    Object* CopyDropTransitions();
  
    // Returns the property index for name (only valid for FAST MODE).
    int PropertyIndexFor(String* name);
  
    // Returns the next free property index (only valid for FAST MODE).
    int NextFreePropertyIndex();
  
    // Returns the number of properties described in instance_descriptors.
    int NumberOfDescribedProperties();
  
    // Casting.
    static inline Map* cast(Object* obj);
  
    // Locate an accessor in the instance descriptor.
    AccessorDescriptor* FindAccessor(String* name);
  
    // Code cache operations.
  
    // Clears the code cache.
    inline void ClearCodeCache();
  
    // Update code cache.
    Object* UpdateCodeCache(String* name, Code* code);
  
    // Returns the found code or undefined if absent.
    Object* FindInCodeCache(String* name, Code::Flags flags);
  
    // Returns the non-negative index of the code object if it is in the
    // cache and -1 otherwise.
    int IndexInCodeCache(Object* name, Code* code);
  
    // Removes a code object from the code cache at the given index.
    void RemoveFromCodeCache(String* name, Code* code, int index);
  
    // For every transition in this map, makes the transition's
    // target's prototype pointer point back to this map.
    // This is undone in MarkCompactCollector::ClearNonLiveTransitions().
    void CreateBackPointers();
  
    // Set all map transitions from this map to dead maps to null.
    // Also, restore the original prototype on the targets of these
    // transitions, so that we do not process this map again while
    // following back pointers.
    void ClearNonLiveTransitions(Object* real_prototype);
  
    // Dispatched behavior.
    void MapIterateBody(ObjectVisitor* v);
  #ifdef DEBUG
    void MapPrint();
    void MapVerify();
  #endif
  
    static const int kMaxPreAllocatedPropertyFields = 255;
  
    // Layout description.
    static const int kInstanceSizesOffset = HeapObject::kHeaderSize;
    static const int kInstanceAttributesOffset = kInstanceSizesOffset + kIntSize;
    static const int kPrototypeOffset = kInstanceAttributesOffset + kIntSize;
    static const int kConstructorOffset = kPrototypeOffset + kPointerSize;
    static const int kInstanceDescriptorsOffset =
        kConstructorOffset + kPointerSize;
    static const int kCodeCacheOffset = kInstanceDescriptorsOffset + kPointerSize;
    static const int kPadStart = kCodeCacheOffset + kPointerSize;
    static const int kSize = MAP_SIZE_ALIGN(kPadStart);
  
    // Byte offsets within kInstanceSizesOffset.
    static const int kInstanceSizeOffset = kInstanceSizesOffset + 0;
    static const int kInObjectPropertiesByte = 1;
    static const int kInObjectPropertiesOffset =
        kInstanceSizesOffset + kInObjectPropertiesByte;
    static const int kPreAllocatedPropertyFieldsByte = 2;
    static const int kPreAllocatedPropertyFieldsOffset =
        kInstanceSizesOffset + kPreAllocatedPropertyFieldsByte;
    // The byte at position 3 is not in use at the moment.
  
    // Byte offsets within kInstanceAttributesOffset attributes.
    static const int kInstanceTypeOffset = kInstanceAttributesOffset + 0;
    static const int kUnusedPropertyFieldsOffset = kInstanceAttributesOffset + 1;
    static const int kBitFieldOffset = kInstanceAttributesOffset + 2;
    static const int kBitField2Offset = kInstanceAttributesOffset + 3;
  
    STATIC_CHECK(kInstanceTypeOffset == Internals::kMapInstanceTypeOffset);
  
    // Bit positions for bit field.
    static const int kUnused = 0;  // To be used for marking recently used maps.
    static const int kHasNonInstancePrototype = 1;
    static const int kIsHiddenPrototype = 2;
    static const int kHasNamedInterceptor = 3;
    static const int kHasIndexedInterceptor = 4;
    static const int kIsUndetectable = 5;
    static const int kHasInstanceCallHandler = 6;
    static const int kIsAccessCheckNeeded = 7;
  
    // Bit positions for bit field 2
    static const int kIsExtensible = 0;
  
    // Layout of the default cache. It holds alternating name and code objects.
    static const int kCodeCacheEntrySize = 2;
    static const int kCodeCacheEntryNameOffset = 0;
    static const int kCodeCacheEntryCodeOffset = 1;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Map);
  };
  
  
  // An abstract superclass, a marker class really, for simple structure classes.
  // It doesn't carry much functionality but allows struct classes to me
  // identified in the type system.
  class Struct: public HeapObject {
   public:
    inline void InitializeBody(int object_size);
    static inline Struct* cast(Object* that);
  };
  
  
  // Script describes a script which has been added to the VM.
  class Script: public Struct {
   public:
    // Script types.
    enum Type {
      TYPE_NATIVE = 0,
      TYPE_EXTENSION = 1,
      TYPE_NORMAL = 2
    };
  
    // Script compilation types.
    enum CompilationType {
      COMPILATION_TYPE_HOST = 0,
      COMPILATION_TYPE_EVAL = 1,
      COMPILATION_TYPE_JSON = 2
    };
  
    // [source]: the script source.
    DECL_ACCESSORS(source, Object)
  
    // [name]: the script name.
    DECL_ACCESSORS(name, Object)
  
    // [id]: the script id.
    DECL_ACCESSORS(id, Object)
  
    // [line_offset]: script line offset in resource from where it was extracted.
    DECL_ACCESSORS(line_offset, Smi)
  
    // [column_offset]: script column offset in resource from where it was
    // extracted.
    DECL_ACCESSORS(column_offset, Smi)
  
    // [data]: additional data associated with this script.
    DECL_ACCESSORS(data, Object)
  
    // [context_data]: context data for the context this script was compiled in.
    DECL_ACCESSORS(context_data, Object)
  
    // [wrapper]: the wrapper cache.
    DECL_ACCESSORS(wrapper, Proxy)
  
    // [type]: the script type.
    DECL_ACCESSORS(type, Smi)
  
    // [compilation]: how the the script was compiled.
    DECL_ACCESSORS(compilation_type, Smi)
  
    // [line_ends]: FixedArray of line ends positions.
    DECL_ACCESSORS(line_ends, Object)
  
    // [eval_from_shared]: for eval scripts the shared funcion info for the
    // function from which eval was called.
    DECL_ACCESSORS(eval_from_shared, Object)
  
    // [eval_from_instructions_offset]: the instruction offset in the code for the
    // function from which eval was called where eval was called.
    DECL_ACCESSORS(eval_from_instructions_offset, Smi)
  
    static inline Script* cast(Object* obj);
  
    // If script source is an external string, check that the underlying
    // resource is accessible. Otherwise, always return true.
    inline bool HasValidSource();
  
  #ifdef DEBUG
    void ScriptPrint();
    void ScriptVerify();
  #endif
  
    static const int kSourceOffset = HeapObject::kHeaderSize;
    static const int kNameOffset = kSourceOffset + kPointerSize;
    static const int kLineOffsetOffset = kNameOffset + kPointerSize;
    static const int kColumnOffsetOffset = kLineOffsetOffset + kPointerSize;
    static const int kDataOffset = kColumnOffsetOffset + kPointerSize;
    static const int kContextOffset = kDataOffset + kPointerSize;
    static const int kWrapperOffset = kContextOffset + kPointerSize;
    static const int kTypeOffset = kWrapperOffset + kPointerSize;
    static const int kCompilationTypeOffset = kTypeOffset + kPointerSize;
    static const int kLineEndsOffset = kCompilationTypeOffset + kPointerSize;
    static const int kIdOffset = kLineEndsOffset + kPointerSize;
    static const int kEvalFromSharedOffset = kIdOffset + kPointerSize;
    static const int kEvalFrominstructionsOffsetOffset =
        kEvalFromSharedOffset + kPointerSize;
    static const int kSize = kEvalFrominstructionsOffsetOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Script);
  };
  
  
  // SharedFunctionInfo describes the JSFunction information that can be
  // shared by multiple instances of the function.
  class SharedFunctionInfo: public HeapObject {
   public:
    // [name]: Function name.
    DECL_ACCESSORS(name, Object)
  
    // [code]: Function code.
    DECL_ACCESSORS(code, Code)
  
    // [construct stub]: Code stub for constructing instances of this function.
    DECL_ACCESSORS(construct_stub, Code)
  
    // Returns if this function has been compiled to native code yet.
    inline bool is_compiled();
  
    // [length]: The function length - usually the number of declared parameters.
    // Use up to 2^30 parameters.
    inline int length();
    inline void set_length(int value);
  
    // [formal parameter count]: The declared number of parameters.
    inline int formal_parameter_count();
    inline void set_formal_parameter_count(int value);
  
    // Set the formal parameter count so the function code will be
    // called without using argument adaptor frames.
    inline void DontAdaptArguments();
  
    // [expected_nof_properties]: Expected number of properties for the function.
    inline int expected_nof_properties();
    inline void set_expected_nof_properties(int value);
  
    // [instance class name]: class name for instances.
    DECL_ACCESSORS(instance_class_name, Object)
  
    // [function data]: This field holds some additional data for function.
    // Currently it either has FunctionTemplateInfo to make benefit the API
    // or Proxy wrapping CustomCallGenerator.
    // In the long run we don't want all functions to have this field but
    // we can fix that when we have a better model for storing hidden data
    // on objects.
    DECL_ACCESSORS(function_data, Object)
  
    inline bool IsApiFunction();
    inline FunctionTemplateInfo* get_api_func_data();
    inline bool HasCustomCallGenerator();
  
    // [script info]: Script from which the function originates.
    DECL_ACCESSORS(script, Object)
  
    // [num_literals]: Number of literals used by this function.
    inline int num_literals();
    inline void set_num_literals(int value);
  
    // [start_position_and_type]: Field used to store both the source code
    // position, whether or not the function is a function expression,
    // and whether or not the function is a toplevel function. The two
    // least significants bit indicates whether the function is an
    // expression and the rest contains the source code position.
    inline int start_position_and_type();
    inline void set_start_position_and_type(int value);
  
    // [debug info]: Debug information.
    DECL_ACCESSORS(debug_info, Object)
  
    // [inferred name]: Name inferred from variable or property
    // assignment of this function. Used to facilitate debugging and
    // profiling of JavaScript code written in OO style, where almost
    // all functions are anonymous but are assigned to object
    // properties.
    DECL_ACCESSORS(inferred_name, String)
  
    // Position of the 'function' token in the script source.
    inline int function_token_position();
    inline void set_function_token_position(int function_token_position);
  
    // Position of this function in the script source.
    inline int start_position();
    inline void set_start_position(int start_position);
  
    // End position of this function in the script source.
    inline int end_position();
    inline void set_end_position(int end_position);
  
    // Is this function a function expression in the source code.
    inline bool is_expression();
    inline void set_is_expression(bool value);
  
    // Is this function a top-level function (scripts, evals).
    inline bool is_toplevel();
    inline void set_is_toplevel(bool value);
  
    // Bit field containing various information collected by the compiler to
    // drive optimization.
    inline int compiler_hints();
    inline void set_compiler_hints(int value);
  
    // Add information on assignments of the form this.x = ...;
    void SetThisPropertyAssignmentsInfo(
        bool has_only_simple_this_property_assignments,
        FixedArray* this_property_assignments);
  
    // Clear information on assignments of the form this.x = ...;
    void ClearThisPropertyAssignmentsInfo();
  
    // Indicate that this function only consists of assignments of the form
    // this.x = y; where y is either a constant or refers to an argument.
    inline bool has_only_simple_this_property_assignments();
  
    inline bool try_full_codegen();
    inline void set_try_full_codegen(bool flag);
  
    // Check whether a inlined constructor can be generated with the given
    // prototype.
    bool CanGenerateInlineConstructor(Object* prototype);
  
    // For functions which only contains this property assignments this provides
    // access to the names for the properties assigned.
    DECL_ACCESSORS(this_property_assignments, Object)
    inline int this_property_assignments_count();
    inline void set_this_property_assignments_count(int value);
    String* GetThisPropertyAssignmentName(int index);
    bool IsThisPropertyAssignmentArgument(int index);
    int GetThisPropertyAssignmentArgument(int index);
    Object* GetThisPropertyAssignmentConstant(int index);
  
    // [source code]: Source code for the function.
    bool HasSourceCode();
    Object* GetSourceCode();
  
    // Calculate the instance size.
    int CalculateInstanceSize();
  
    // Calculate the number of in-object properties.
    int CalculateInObjectProperties();
  
    // Dispatched behavior.
    void SharedFunctionInfoIterateBody(ObjectVisitor* v);
    // Set max_length to -1 for unlimited length.
    void SourceCodePrint(StringStream* accumulator, int max_length);
  #ifdef DEBUG
    void SharedFunctionInfoPrint();
    void SharedFunctionInfoVerify();
  #endif
  
    // Casting.
    static inline SharedFunctionInfo* cast(Object* obj);
  
    // Constants.
    static const int kDontAdaptArgumentsSentinel = -1;
  
    // Layout description.
    // Pointer fields.
    static const int kNameOffset = HeapObject::kHeaderSize;
    static const int kCodeOffset = kNameOffset + kPointerSize;
    static const int kConstructStubOffset = kCodeOffset + kPointerSize;
    static const int kInstanceClassNameOffset =
        kConstructStubOffset + kPointerSize;
    static const int kFunctionDataOffset =
        kInstanceClassNameOffset + kPointerSize;
    static const int kScriptOffset = kFunctionDataOffset + kPointerSize;
    static const int kDebugInfoOffset = kScriptOffset + kPointerSize;
    static const int kInferredNameOffset = kDebugInfoOffset + kPointerSize;
    static const int kThisPropertyAssignmentsOffset =
        kInferredNameOffset + kPointerSize;
    // Integer fields.
    static const int kLengthOffset =
        kThisPropertyAssignmentsOffset + kPointerSize;
    static const int kFormalParameterCountOffset = kLengthOffset + kIntSize;
    static const int kExpectedNofPropertiesOffset =
        kFormalParameterCountOffset + kIntSize;
    static const int kNumLiteralsOffset = kExpectedNofPropertiesOffset + kIntSize;
    static const int kStartPositionAndTypeOffset =
        kNumLiteralsOffset + kIntSize;
    static const int kEndPositionOffset = kStartPositionAndTypeOffset + kIntSize;
    static const int kFunctionTokenPositionOffset = kEndPositionOffset + kIntSize;
    static const int kCompilerHintsOffset =
        kFunctionTokenPositionOffset + kIntSize;
    static const int kThisPropertyAssignmentsCountOffset =
        kCompilerHintsOffset + kIntSize;
    // Total size.
    static const int kSize = kThisPropertyAssignmentsCountOffset + kIntSize;
    static const int kAlignedSize = POINTER_SIZE_ALIGN(kSize);
  
   private:
    // Bit positions in start_position_and_type.
    // The source code start position is in the 30 most significant bits of
    // the start_position_and_type field.
    static const int kIsExpressionBit = 0;
    static const int kIsTopLevelBit   = 1;
    static const int kStartPositionShift = 2;
    static const int kStartPositionMask = ~((1 << kStartPositionShift) - 1);
  
    // Bit positions in compiler_hints.
    static const int kHasOnlySimpleThisPropertyAssignments = 0;
    static const int kTryFullCodegen = 1;
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(SharedFunctionInfo);
  };
  
  
  // JSFunction describes JavaScript functions.
  class JSFunction: public JSObject {
   public:
    // [prototype_or_initial_map]:
    DECL_ACCESSORS(prototype_or_initial_map, Object)
  
    // [shared_function_info]: The information about the function that
    // can be shared by instances.
    DECL_ACCESSORS(shared, SharedFunctionInfo)
  
    // [context]: The context for this function.
    inline Context* context();
    inline Object* unchecked_context();
    inline void set_context(Object* context);
  
    // [code]: The generated code object for this function.  Executed
    // when the function is invoked, e.g. foo() or new foo(). See
    // [[Call]] and [[Construct]] description in ECMA-262, section
    // 8.6.2, page 27.
    inline Code* code();
    inline void set_code(Code* value);
  
    // Tells whether this function is builtin.
    inline bool IsBuiltin();
  
    // [literals]: Fixed array holding the materialized literals.
    //
    // If the function contains object, regexp or array literals, the
    // literals array prefix contains the object, regexp, and array
    // function to be used when creating these literals.  This is
    // necessary so that we do not dynamically lookup the object, regexp
    // or array functions.  Performing a dynamic lookup, we might end up
    // using the functions from a new context that we should not have
    // access to.
    DECL_ACCESSORS(literals, FixedArray)
  
    // The initial map for an object created by this constructor.
    inline Map* initial_map();
    inline void set_initial_map(Map* value);
    inline bool has_initial_map();
  
    // Get and set the prototype property on a JSFunction. If the
    // function has an initial map the prototype is set on the initial
    // map. Otherwise, the prototype is put in the initial map field
    // until an initial map is needed.
    inline bool has_prototype();
    inline bool has_instance_prototype();
    inline Object* prototype();
    inline Object* instance_prototype();
    Object* SetInstancePrototype(Object* value);
    Object* SetPrototype(Object* value);
  
    // Accessor for this function's initial map's [[class]]
    // property. This is primarily used by ECMA native functions.  This
    // method sets the class_name field of this function's initial map
    // to a given value. It creates an initial map if this function does
    // not have one. Note that this method does not copy the initial map
    // if it has one already, but simply replaces it with the new value.
    // Instances created afterwards will have a map whose [[class]] is
    // set to 'value', but there is no guarantees on instances created
    // before.
    Object* SetInstanceClassName(String* name);
  
    // Returns if this function has been compiled to native code yet.
    inline bool is_compiled();
  
    // Casting.
    static inline JSFunction* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void JSFunctionPrint();
    void JSFunctionVerify();
  #endif
  
    // Returns the number of allocated literals.
    inline int NumberOfLiterals();
  
    // Retrieve the global context from a function's literal array.
    static Context* GlobalContextFromLiterals(FixedArray* literals);
  
    // Layout descriptors.
    static const int kPrototypeOrInitialMapOffset = JSObject::kHeaderSize;
    static const int kSharedFunctionInfoOffset =
        kPrototypeOrInitialMapOffset + kPointerSize;
    static const int kContextOffset = kSharedFunctionInfoOffset + kPointerSize;
    static const int kLiteralsOffset = kContextOffset + kPointerSize;
    static const int kSize = kLiteralsOffset + kPointerSize;
  
    // Layout of the literals array.
    static const int kLiteralsPrefixSize = 1;
    static const int kLiteralGlobalContextIndex = 0;
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSFunction);
  };
  
  
  // JSGlobalProxy's prototype must be a JSGlobalObject or null,
  // and the prototype is hidden. JSGlobalProxy always delegates
  // property accesses to its prototype if the prototype is not null.
  //
  // A JSGlobalProxy can be reinitialized which will preserve its identity.
  //
  // Accessing a JSGlobalProxy requires security check.
  
  class JSGlobalProxy : public JSObject {
   public:
    // [context]: the owner global context of this proxy object.
    // It is null value if this object is not used by any context.
    DECL_ACCESSORS(context, Object)
  
    // Casting.
    static inline JSGlobalProxy* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void JSGlobalProxyPrint();
    void JSGlobalProxyVerify();
  #endif
  
    // Layout description.
    static const int kContextOffset = JSObject::kHeaderSize;
    static const int kSize = kContextOffset + kPointerSize;
  
   private:
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSGlobalProxy);
  };
  
  
  // Forward declaration.
  class JSBuiltinsObject;
  
  // Common super class for JavaScript global objects and the special
  // builtins global objects.
  class GlobalObject: public JSObject {
   public:
    // [builtins]: the object holding the runtime routines written in JS.
    DECL_ACCESSORS(builtins, JSBuiltinsObject)
  
    // [global context]: the global context corresponding to this global object.
    DECL_ACCESSORS(global_context, Context)
  
    // [global receiver]: the global receiver object of the context
    DECL_ACCESSORS(global_receiver, JSObject)
  
    // Retrieve the property cell used to store a property.
    Object* GetPropertyCell(LookupResult* result);
  
    // Ensure that the global object has a cell for the given property name.
    Object* EnsurePropertyCell(String* name);
  
    // Casting.
    static inline GlobalObject* cast(Object* obj);
  
    // Layout description.
    static const int kBuiltinsOffset = JSObject::kHeaderSize;
    static const int kGlobalContextOffset = kBuiltinsOffset + kPointerSize;
    static const int kGlobalReceiverOffset = kGlobalContextOffset + kPointerSize;
    static const int kHeaderSize = kGlobalReceiverOffset + kPointerSize;
  
   private:
    friend class AGCCVersionRequiresThisClassToHaveAFriendSoHereItIs;
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(GlobalObject);
  };
  
  
  // JavaScript global object.
  class JSGlobalObject: public GlobalObject {
   public:
  
    // Casting.
    static inline JSGlobalObject* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void JSGlobalObjectPrint();
    void JSGlobalObjectVerify();
  #endif
  
    // Layout description.
    static const int kSize = GlobalObject::kHeaderSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSGlobalObject);
  };
  
  
  // Builtins global object which holds the runtime routines written in
  // JavaScript.
  class JSBuiltinsObject: public GlobalObject {
   public:
    // Accessors for the runtime routines written in JavaScript.
    inline Object* javascript_builtin(Builtins::JavaScript id);
    inline void set_javascript_builtin(Builtins::JavaScript id, Object* value);
  
    // Accessors for code of the runtime routines written in JavaScript.
    inline Code* javascript_builtin_code(Builtins::JavaScript id);
    inline void set_javascript_builtin_code(Builtins::JavaScript id, Code* value);
  
    // Casting.
    static inline JSBuiltinsObject* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void JSBuiltinsObjectPrint();
    void JSBuiltinsObjectVerify();
  #endif
  
    // Layout description.  The size of the builtins object includes
    // room for two pointers per runtime routine written in javascript
    // (function and code object).
    static const int kJSBuiltinsCount = Builtins::id_count;
    static const int kJSBuiltinsOffset = GlobalObject::kHeaderSize;
    static const int kJSBuiltinsCodeOffset =
        GlobalObject::kHeaderSize + (kJSBuiltinsCount * kPointerSize);
    static const int kSize =
        kJSBuiltinsCodeOffset + (kJSBuiltinsCount * kPointerSize);
  
    static int OffsetOfFunctionWithId(Builtins::JavaScript id) {
      return kJSBuiltinsOffset + id * kPointerSize;
    }
  
    static int OffsetOfCodeWithId(Builtins::JavaScript id) {
      return kJSBuiltinsCodeOffset + id * kPointerSize;
    }
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSBuiltinsObject);
  };
  
  
  // Representation for JS Wrapper objects, String, Number, Boolean, Date, etc.
  class JSValue: public JSObject {
   public:
    // [value]: the object being wrapped.
    DECL_ACCESSORS(value, Object)
  
    // Casting.
    static inline JSValue* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void JSValuePrint();
    void JSValueVerify();
  #endif
  
    // Layout description.
    static const int kValueOffset = JSObject::kHeaderSize;
    static const int kSize = kValueOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSValue);
  };
  
  // Regular expressions
  // The regular expression holds a single reference to a FixedArray in
  // the kDataOffset field.
  // The FixedArray contains the following data:
  // - tag : type of regexp implementation (not compiled yet, atom or irregexp)
  // - reference to the original source string
  // - reference to the original flag string
  // If it is an atom regexp
  // - a reference to a literal string to search for
  // If it is an irregexp regexp:
  // - a reference to code for ASCII inputs (bytecode or compiled).
  // - a reference to code for UC16 inputs (bytecode or compiled).
  // - max number of registers used by irregexp implementations.
  // - number of capture registers (output values) of the regexp.
  class JSRegExp: public JSObject {
   public:
    // Meaning of Type:
    // NOT_COMPILED: Initial value. No data has been stored in the JSRegExp yet.
    // ATOM: A simple string to match against using an indexOf operation.
    // IRREGEXP: Compiled with Irregexp.
    // IRREGEXP_NATIVE: Compiled to native code with Irregexp.
    enum Type { NOT_COMPILED, ATOM, IRREGEXP };
    enum Flag { NONE = 0, GLOBAL = 1, IGNORE_CASE = 2, MULTILINE = 4 };
  
    class Flags {
     public:
      explicit Flags(uint32_t value) : value_(value) { }
      bool is_global() { return (value_ & GLOBAL) != 0; }
      bool is_ignore_case() { return (value_ & IGNORE_CASE) != 0; }
      bool is_multiline() { return (value_ & MULTILINE) != 0; }
      uint32_t value() { return value_; }
     private:
      uint32_t value_;
    };
  
    DECL_ACCESSORS(data, Object)
  
    inline Type TypeTag();
    inline int CaptureCount();
    inline Flags GetFlags();
    inline String* Pattern();
    inline Object* DataAt(int index);
    // Set implementation data after the object has been prepared.
    inline void SetDataAt(int index, Object* value);
    static int code_index(bool is_ascii) {
      if (is_ascii) {
        return kIrregexpASCIICodeIndex;
      } else {
        return kIrregexpUC16CodeIndex;
      }
    }
  
    static inline JSRegExp* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void JSRegExpVerify();
  #endif
  
    static const int kDataOffset = JSObject::kHeaderSize;
    static const int kSize = kDataOffset + kPointerSize;
  
    // Indices in the data array.
    static const int kTagIndex = 0;
    static const int kSourceIndex = kTagIndex + 1;
    static const int kFlagsIndex = kSourceIndex + 1;
    static const int kDataIndex = kFlagsIndex + 1;
    // The data fields are used in different ways depending on the
    // value of the tag.
    // Atom regexps (literal strings).
    static const int kAtomPatternIndex = kDataIndex;
  
    static const int kAtomDataSize = kAtomPatternIndex + 1;
  
    // Irregexp compiled code or bytecode for ASCII. If compilation
    // fails, this fields hold an exception object that should be
    // thrown if the regexp is used again.
    static const int kIrregexpASCIICodeIndex = kDataIndex;
    // Irregexp compiled code or bytecode for UC16.  If compilation
    // fails, this fields hold an exception object that should be
    // thrown if the regexp is used again.
    static const int kIrregexpUC16CodeIndex = kDataIndex + 1;
    // Maximal number of registers used by either ASCII or UC16.
    // Only used to check that there is enough stack space
    static const int kIrregexpMaxRegisterCountIndex = kDataIndex + 2;
    // Number of captures in the compiled regexp.
    static const int kIrregexpCaptureCountIndex = kDataIndex + 3;
  
    static const int kIrregexpDataSize = kIrregexpCaptureCountIndex + 1;
  
    // Offsets directly into the data fixed array.
    static const int kDataTagOffset =
        FixedArray::kHeaderSize + kTagIndex * kPointerSize;
    static const int kDataAsciiCodeOffset =
        FixedArray::kHeaderSize + kIrregexpASCIICodeIndex * kPointerSize;
    static const int kDataUC16CodeOffset =
        FixedArray::kHeaderSize + kIrregexpUC16CodeIndex * kPointerSize;
    static const int kIrregexpCaptureCountOffset =
        FixedArray::kHeaderSize + kIrregexpCaptureCountIndex * kPointerSize;
  
    // In-object fields.
    static const int kSourceFieldIndex = 0;
    static const int kGlobalFieldIndex = 1;
    static const int kIgnoreCaseFieldIndex = 2;
    static const int kMultilineFieldIndex = 3;
    static const int kLastIndexFieldIndex = 4;
  };
  
  
  class CompilationCacheShape {
   public:
    static inline bool IsMatch(HashTableKey* key, Object* value) {
      return key->IsMatch(value);
    }
  
    static inline uint32_t Hash(HashTableKey* key) {
      return key->Hash();
    }
  
    static inline uint32_t HashForObject(HashTableKey* key, Object* object) {
      return key->HashForObject(object);
    }
  
    static Object* AsObject(HashTableKey* key) {
      return key->AsObject();
    }
  
    static const int kPrefixSize = 0;
    static const int kEntrySize = 2;
  };
  
  
  class CompilationCacheTable: public HashTable<CompilationCacheShape,
                                                HashTableKey*> {
   public:
    // Find cached value for a string key, otherwise return null.
    Object* Lookup(String* src);
    Object* LookupEval(String* src, Context* context);
    Object* LookupRegExp(String* source, JSRegExp::Flags flags);
    Object* Put(String* src, Object* value);
    Object* PutEval(String* src, Context* context, Object* value);
    Object* PutRegExp(String* src, JSRegExp::Flags flags, FixedArray* value);
  
    static inline CompilationCacheTable* cast(Object* obj);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(CompilationCacheTable);
  };
  
  
  class CodeCache: public Struct {
   public:
    DECL_ACCESSORS(default_cache, FixedArray)
    DECL_ACCESSORS(normal_type_cache, Object)
  
    // Add the code object to the cache.
    Object* Update(String* name, Code* code);
  
    // Lookup code object in the cache. Returns code object if found and undefined
    // if not.
    Object* Lookup(String* name, Code::Flags flags);
  
    // Get the internal index of a code object in the cache. Returns -1 if the
    // code object is not in that cache. This index can be used to later call
    // RemoveByIndex. The cache cannot be modified between a call to GetIndex and
    // RemoveByIndex.
    int GetIndex(Object* name, Code* code);
  
    // Remove an object from the cache with the provided internal index.
    void RemoveByIndex(Object* name, Code* code, int index);
  
    static inline CodeCache* cast(Object* obj);
  
  #ifdef DEBUG
    void CodeCachePrint();
    void CodeCacheVerify();
  #endif
  
    static const int kDefaultCacheOffset = HeapObject::kHeaderSize;
    static const int kNormalTypeCacheOffset =
        kDefaultCacheOffset + kPointerSize;
    static const int kSize = kNormalTypeCacheOffset + kPointerSize;
  
   private:
    Object* UpdateDefaultCache(String* name, Code* code);
    Object* UpdateNormalTypeCache(String* name, Code* code);
    Object* LookupDefaultCache(String* name, Code::Flags flags);
    Object* LookupNormalTypeCache(String* name, Code::Flags flags);
  
    // Code cache layout of the default cache. Elements are alternating name and
    // code objects for non normal load/store/call IC's.
    static const int kCodeCacheEntrySize = 2;
    static const int kCodeCacheEntryNameOffset = 0;
    static const int kCodeCacheEntryCodeOffset = 1;
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(CodeCache);
  };
  
  
  class CodeCacheHashTableShape {
   public:
    static inline bool IsMatch(HashTableKey* key, Object* value) {
      return key->IsMatch(value);
    }
  
    static inline uint32_t Hash(HashTableKey* key) {
      return key->Hash();
    }
  
    static inline uint32_t HashForObject(HashTableKey* key, Object* object) {
      return key->HashForObject(object);
    }
  
    static Object* AsObject(HashTableKey* key) {
      return key->AsObject();
    }
  
    static const int kPrefixSize = 0;
    static const int kEntrySize = 2;
  };
  
  
  class CodeCacheHashTable: public HashTable<CodeCacheHashTableShape,
                                             HashTableKey*> {
   public:
    Object* Lookup(String* name, Code::Flags flags);
    Object* Put(String* name, Code* code);
  
    int GetIndex(String* name, Code::Flags flags);
    void RemoveByIndex(int index);
  
    static inline CodeCacheHashTable* cast(Object* obj);
  
    // Initial size of the fixed array backing the hash table.
    static const int kInitialSize = 64;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(CodeCacheHashTable);
  };
  
  
  enum AllowNullsFlag {ALLOW_NULLS, DISALLOW_NULLS};
  enum RobustnessFlag {ROBUST_STRING_TRAVERSAL, FAST_STRING_TRAVERSAL};
  
  
  class StringHasher {
   public:
    inline StringHasher(int length);
  
    // Returns true if the hash of this string can be computed without
    // looking at the contents.
    inline bool has_trivial_hash();
  
    // Add a character to the hash and update the array index calculation.
    inline void AddCharacter(uc32 c);
  
    // Adds a character to the hash but does not update the array index
    // calculation.  This can only be called when it has been verified
    // that the input is not an array index.
    inline void AddCharacterNoIndex(uc32 c);
  
    // Returns the value to store in the hash field of a string with
    // the given length and contents.
    uint32_t GetHashField();
  
    // Returns true if the characters seen so far make up a legal array
    // index.
    bool is_array_index() { return is_array_index_; }
  
    bool is_valid() { return is_valid_; }
  
    void invalidate() { is_valid_ = false; }
  
   private:
  
    uint32_t array_index() {
      ASSERT(is_array_index());
      return array_index_;
    }
  
    inline uint32_t GetHash();
  
    int length_;
    uint32_t raw_running_hash_;
    uint32_t array_index_;
    bool is_array_index_;
    bool is_first_char_;
    bool is_valid_;
    friend class TwoCharHashTableKey;
  };
  
  
  // The characteristics of a string are stored in its map.  Retrieving these
  // few bits of information is moderately expensive, involving two memory
  // loads where the second is dependent on the first.  To improve efficiency
  // the shape of the string is given its own class so that it can be retrieved
  // once and used for several string operations.  A StringShape is small enough
  // to be passed by value and is immutable, but be aware that flattening a
  // string can potentially alter its shape.  Also be aware that a GC caused by
  // something else can alter the shape of a string due to ConsString
  // shortcutting.  Keeping these restrictions in mind has proven to be error-
  // prone and so we no longer put StringShapes in variables unless there is a
  // concrete performance benefit at that particular point in the code.
  class StringShape BASE_EMBEDDED {
   public:
    inline explicit StringShape(String* s);
    inline explicit StringShape(Map* s);
    inline explicit StringShape(InstanceType t);
    inline bool IsSequential();
    inline bool IsExternal();
    inline bool IsCons();
    inline bool IsExternalAscii();
    inline bool IsExternalTwoByte();
    inline bool IsSequentialAscii();
    inline bool IsSequentialTwoByte();
    inline bool IsSymbol();
    inline StringRepresentationTag representation_tag();
    inline uint32_t full_representation_tag();
    inline uint32_t size_tag();
  #ifdef DEBUG
    inline uint32_t type() { return type_; }
    inline void invalidate() { valid_ = false; }
    inline bool valid() { return valid_; }
  #else
    inline void invalidate() { }
  #endif
   private:
    uint32_t type_;
  #ifdef DEBUG
    inline void set_valid() { valid_ = true; }
    bool valid_;
  #else
    inline void set_valid() { }
  #endif
  };
  
  
  // The String abstract class captures JavaScript string values:
  //
  // Ecma-262:
  //  4.3.16 String Value
  //    A string value is a member of the type String and is a finite
  //    ordered sequence of zero or more 16-bit unsigned integer values.
  //
  // All string values have a length field.
  class String: public HeapObject {
   public:
    // Get and set the length of the string.
    inline int length();
    inline void set_length(int value);
  
    // Get and set the hash field of the string.
    inline uint32_t hash_field();
    inline void set_hash_field(uint32_t value);
  
    inline bool IsAsciiRepresentation();
    inline bool IsTwoByteRepresentation();
  
    // Check whether this string is an external two-byte string that in
    // fact contains only ascii characters.
    //
    // Such strings may appear when the embedder prefers two-byte
    // representations even for ascii data.
    inline bool IsExternalTwoByteStringWithAsciiChars();
  
    // Get and set individual two byte chars in the string.
    inline void Set(int index, uint16_t value);
    // Get individual two byte char in the string.  Repeated calls
    // to this method are not efficient unless the string is flat.
    inline uint16_t Get(int index);
  
    // Try to flatten the top level ConsString that is hiding behind this
    // string.  This is a no-op unless the string is a ConsString.  Flatten
    // mutates the ConsString and might return a failure.
    Object* SlowTryFlatten(PretenureFlag pretenure);
  
    // Try to flatten the string.  Checks first inline to see if it is necessary.
    // Do not handle allocation failures.  After calling TryFlatten, the
    // string could still be a ConsString, in which case a failure is returned.
    // Use FlattenString from Handles.cc to be sure to flatten.
    inline Object* TryFlatten(PretenureFlag pretenure = NOT_TENURED);
  
    Vector<const char> ToAsciiVector();
    Vector<const uc16> ToUC16Vector();
  
    // Mark the string as an undetectable object. It only applies to
    // ascii and two byte string types.
    bool MarkAsUndetectable();
  
    // Return a substring.
    Object* SubString(int from, int to, PretenureFlag pretenure = NOT_TENURED);
  
    // String equality operations.
    inline bool Equals(String* other);
    bool IsEqualTo(Vector<const char> str);
  
    // Return a UTF8 representation of the string.  The string is null
    // terminated but may optionally contain nulls.  Length is returned
    // in length_output if length_output is not a null pointer  The string
    // should be nearly flat, otherwise the performance of this method may
    // be very slow (quadratic in the length).  Setting robustness_flag to
    // ROBUST_STRING_TRAVERSAL invokes behaviour that is robust  This means it
    // handles unexpected data without causing assert failures and it does not
    // do any heap allocations.  This is useful when printing stack traces.
    SmartPointer<char> ToCString(AllowNullsFlag allow_nulls,
                                 RobustnessFlag robustness_flag,
                                 int offset,
                                 int length,
                                 int* length_output = 0);
    SmartPointer<char> ToCString(
        AllowNullsFlag allow_nulls = DISALLOW_NULLS,
        RobustnessFlag robustness_flag = FAST_STRING_TRAVERSAL,
        int* length_output = 0);
  
    int Utf8Length();
  
    // Return a 16 bit Unicode representation of the string.
    // The string should be nearly flat, otherwise the performance of
    // of this method may be very bad.  Setting robustness_flag to
    // ROBUST_STRING_TRAVERSAL invokes behaviour that is robust  This means it
    // handles unexpected data without causing assert failures and it does not
    // do any heap allocations.  This is useful when printing stack traces.
    SmartPointer<uc16> ToWideCString(
        RobustnessFlag robustness_flag = FAST_STRING_TRAVERSAL);
  
    // Tells whether the hash code has been computed.
    inline bool HasHashCode();
  
    // Returns a hash value used for the property table
    inline uint32_t Hash();
  
    static uint32_t ComputeHashField(unibrow::CharacterStream* buffer,
                                     int length);
  
    static bool ComputeArrayIndex(unibrow::CharacterStream* buffer,
                                  uint32_t* index,
                                  int length);
  
    // Externalization.
    bool MakeExternal(v8::String::ExternalStringResource* resource);
    bool MakeExternal(v8::String::ExternalAsciiStringResource* resource);
  
    // Conversion.
    inline bool AsArrayIndex(uint32_t* index);
  
    // Casting.
    static inline String* cast(Object* obj);
  
    void PrintOn(FILE* out);
  
    // For use during stack traces.  Performs rudimentary sanity check.
    bool LooksValid();
  
    // Dispatched behavior.
    void StringShortPrint(StringStream* accumulator);
  #ifdef DEBUG
    void StringPrint();
    void StringVerify();
  #endif
    inline bool IsFlat();
  
    // Layout description.
    static const int kLengthOffset = HeapObject::kHeaderSize;
    static const int kHashFieldOffset = kLengthOffset + kIntSize;
    static const int kSize = kHashFieldOffset + kIntSize;
    // Notice: kSize is not pointer-size aligned if pointers are 64-bit.
  
    // Maximum number of characters to consider when trying to convert a string
    // value into an array index.
    static const int kMaxArrayIndexSize = 10;
  
    // Max ascii char code.
    static const int kMaxAsciiCharCode = unibrow::Utf8::kMaxOneByteChar;
    static const unsigned kMaxAsciiCharCodeU = unibrow::Utf8::kMaxOneByteChar;
    static const int kMaxUC16CharCode = 0xffff;
  
    // Minimum length for a cons string.
    static const int kMinNonFlatLength = 13;
  
    // Mask constant for checking if a string has a computed hash code
    // and if it is an array index.  The least significant bit indicates
    // whether a hash code has been computed.  If the hash code has been
    // computed the 2nd bit tells whether the string can be used as an
    // array index.
    static const int kHashComputedMask = 1;
    static const int kIsArrayIndexMask = 1 << 1;
    static const int kNofLengthBitFields = 2;
  
    // Shift constant retrieving hash code from hash field.
    static const int kHashShift = kNofLengthBitFields;
  
    // Array index strings this short can keep their index in the hash
    // field.
    static const int kMaxCachedArrayIndexLength = 7;
  
    // For strings which are array indexes the hash value has the string length
    // mixed into the hash, mainly to avoid a hash value of zero which would be
    // the case for the string '0'. 24 bits are used for the array index value.
    static const int kArrayIndexHashLengthShift = 24 + kNofLengthBitFields;
    static const int kArrayIndexHashMask = (1 << kArrayIndexHashLengthShift) - 1;
    static const int kArrayIndexValueBits =
        kArrayIndexHashLengthShift - kHashShift;
  
    // Value of empty hash field indicating that the hash is not computed.
    static const int kEmptyHashField = 0;
  
    // Maximal string length.
    static const int kMaxLength = (1 << (32 - 2)) - 1;
  
    // Max length for computing hash. For strings longer than this limit the
    // string length is used as the hash value.
    static const int kMaxHashCalcLength = 16383;
  
    // Limit for truncation in short printing.
    static const int kMaxShortPrintLength = 1024;
  
    // Support for regular expressions.
    const uc16* GetTwoByteData();
    const uc16* GetTwoByteData(unsigned start);
  
    // Support for StringInputBuffer
    static const unibrow::byte* ReadBlock(String* input,
                                          unibrow::byte* util_buffer,
                                          unsigned capacity,
                                          unsigned* remaining,
                                          unsigned* offset);
    static const unibrow::byte* ReadBlock(String** input,
                                          unibrow::byte* util_buffer,
                                          unsigned capacity,
                                          unsigned* remaining,
                                          unsigned* offset);
  
    // Helper function for flattening strings.
    template <typename sinkchar>
    static void WriteToFlat(String* source,
                            sinkchar* sink,
                            int from,
                            int to);
  
   protected:
    class ReadBlockBuffer {
     public:
      ReadBlockBuffer(unibrow::byte* util_buffer_,
                      unsigned cursor_,
                      unsigned capacity_,
                      unsigned remaining_) :
        util_buffer(util_buffer_),
        cursor(cursor_),
        capacity(capacity_),
        remaining(remaining_) {
      }
      unibrow::byte* util_buffer;
      unsigned       cursor;
      unsigned       capacity;
      unsigned       remaining;
    };
  
    static inline const unibrow::byte* ReadBlock(String* input,
                                                 ReadBlockBuffer* buffer,
                                                 unsigned* offset,
                                                 unsigned max_chars);
    static void ReadBlockIntoBuffer(String* input,
                                    ReadBlockBuffer* buffer,
                                    unsigned* offset_ptr,
                                    unsigned max_chars);
  
   private:
    // Slow case of String::Equals.  This implementation works on any strings
    // but it is most efficient on strings that are almost flat.
    bool SlowEquals(String* other);
  
    // Slow case of AsArrayIndex.
    bool SlowAsArrayIndex(uint32_t* index);
  
    // Compute and set the hash code.
    uint32_t ComputeAndSetHash();
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(String);
  };
  
  
  // The SeqString abstract class captures sequential string values.
  class SeqString: public String {
   public:
  
    // Casting.
    static inline SeqString* cast(Object* obj);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(SeqString);
  };
  
  
  // The AsciiString class captures sequential ascii string objects.
  // Each character in the AsciiString is an ascii character.
  class SeqAsciiString: public SeqString {
   public:
    // Dispatched behavior.
    inline uint16_t SeqAsciiStringGet(int index);
    inline void SeqAsciiStringSet(int index, uint16_t value);
  
    // Get the address of the characters in this string.
    inline Address GetCharsAddress();
  
    inline char* GetChars();
  
    // Casting
    static inline SeqAsciiString* cast(Object* obj);
  
    // Garbage collection support.  This method is called by the
    // garbage collector to compute the actual size of an AsciiString
    // instance.
    inline int SeqAsciiStringSize(InstanceType instance_type);
  
    // Computes the size for an AsciiString instance of a given length.
    static int SizeFor(int length) {
      return OBJECT_SIZE_ALIGN(kHeaderSize + length * kCharSize);
    }
  
    // Layout description.
    static const int kHeaderSize = String::kSize;
    static const int kAlignedSize = POINTER_SIZE_ALIGN(kHeaderSize);
  
    // Maximal memory usage for a single sequential ASCII string.
    static const int kMaxSize = 512 * MB;
    // Maximal length of a single sequential ASCII string.
    // Q.v. String::kMaxLength which is the maximal size of concatenated strings.
    static const int kMaxLength = (kMaxSize - kHeaderSize);
  
    // Support for StringInputBuffer.
    inline void SeqAsciiStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                                  unsigned* offset,
                                                  unsigned chars);
    inline const unibrow::byte* SeqAsciiStringReadBlock(unsigned* remaining,
                                                        unsigned* offset,
                                                        unsigned chars);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(SeqAsciiString);
  };
  
  
  // The TwoByteString class captures sequential unicode string objects.
  // Each character in the TwoByteString is a two-byte uint16_t.
  class SeqTwoByteString: public SeqString {
   public:
    // Dispatched behavior.
    inline uint16_t SeqTwoByteStringGet(int index);
    inline void SeqTwoByteStringSet(int index, uint16_t value);
  
    // Get the address of the characters in this string.
    inline Address GetCharsAddress();
  
    inline uc16* GetChars();
  
    // For regexp code.
    const uint16_t* SeqTwoByteStringGetData(unsigned start);
  
    // Casting
    static inline SeqTwoByteString* cast(Object* obj);
  
    // Garbage collection support.  This method is called by the
    // garbage collector to compute the actual size of a TwoByteString
    // instance.
    inline int SeqTwoByteStringSize(InstanceType instance_type);
  
    // Computes the size for a TwoByteString instance of a given length.
    static int SizeFor(int length) {
      return OBJECT_SIZE_ALIGN(kHeaderSize + length * kShortSize);
    }
  
    // Layout description.
    static const int kHeaderSize = String::kSize;
    static const int kAlignedSize = POINTER_SIZE_ALIGN(kHeaderSize);
  
    // Maximal memory usage for a single sequential two-byte string.
    static const int kMaxSize = 512 * MB;
    // Maximal length of a single sequential two-byte string.
    // Q.v. String::kMaxLength which is the maximal size of concatenated strings.
    static const int kMaxLength = (kMaxSize - kHeaderSize) / sizeof(uint16_t);
  
    // Support for StringInputBuffer.
    inline void SeqTwoByteStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                                    unsigned* offset_ptr,
                                                    unsigned chars);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(SeqTwoByteString);
  };
  
  
  // The ConsString class describes string values built by using the
  // addition operator on strings.  A ConsString is a pair where the
  // first and second components are pointers to other string values.
  // One or both components of a ConsString can be pointers to other
  // ConsStrings, creating a binary tree of ConsStrings where the leaves
  // are non-ConsString string values.  The string value represented by
  // a ConsString can be obtained by concatenating the leaf string
  // values in a left-to-right depth-first traversal of the tree.
  class ConsString: public String {
   public:
    // First string of the cons cell.
    inline String* first();
    // Doesn't check that the result is a string, even in debug mode.  This is
    // useful during GC where the mark bits confuse the checks.
    inline Object* unchecked_first();
    inline void set_first(String* first,
                          WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
  
    // Second string of the cons cell.
    inline String* second();
    // Doesn't check that the result is a string, even in debug mode.  This is
    // useful during GC where the mark bits confuse the checks.
    inline Object* unchecked_second();
    inline void set_second(String* second,
                           WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
  
    // Dispatched behavior.
    uint16_t ConsStringGet(int index);
  
    // Casting.
    static inline ConsString* cast(Object* obj);
  
    // Garbage collection support.  This method is called during garbage
    // collection to iterate through the heap pointers in the body of
    // the ConsString.
    void ConsStringIterateBody(ObjectVisitor* v);
  
    // Layout description.
    static const int kFirstOffset = POINTER_SIZE_ALIGN(String::kSize);
    static const int kSecondOffset = kFirstOffset + kPointerSize;
    static const int kSize = kSecondOffset + kPointerSize;
  
    // Support for StringInputBuffer.
    inline const unibrow::byte* ConsStringReadBlock(ReadBlockBuffer* buffer,
                                                    unsigned* offset_ptr,
                                                    unsigned chars);
    inline void ConsStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                              unsigned* offset_ptr,
                                              unsigned chars);
  
    // Minimum length for a cons string.
    static const int kMinLength = 13;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ConsString);
  };
  
  
  // The ExternalString class describes string values that are backed by
  // a string resource that lies outside the V8 heap.  ExternalStrings
  // consist of the length field common to all strings, a pointer to the
  // external resource.  It is important to ensure (externally) that the
  // resource is not deallocated while the ExternalString is live in the
  // V8 heap.
  //
  // The API expects that all ExternalStrings are created through the
  // API.  Therefore, ExternalStrings should not be used internally.
  class ExternalString: public String {
   public:
    // Casting
    static inline ExternalString* cast(Object* obj);
  
    // Layout description.
    static const int kResourceOffset = POINTER_SIZE_ALIGN(String::kSize);
    static const int kSize = kResourceOffset + kPointerSize;
  
    STATIC_CHECK(kResourceOffset == Internals::kStringResourceOffset);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalString);
  };
  
  
  // The ExternalAsciiString class is an external string backed by an
  // ASCII string.
  class ExternalAsciiString: public ExternalString {
   public:
    typedef v8::String::ExternalAsciiStringResource Resource;
  
    // The underlying resource.
    inline Resource* resource();
    inline void set_resource(Resource* buffer);
  
    // Dispatched behavior.
    uint16_t ExternalAsciiStringGet(int index);
  
    // Casting.
    static inline ExternalAsciiString* cast(Object* obj);
  
    // Garbage collection support.
    void ExternalAsciiStringIterateBody(ObjectVisitor* v);
  
    // Support for StringInputBuffer.
    const unibrow::byte* ExternalAsciiStringReadBlock(unsigned* remaining,
                                                      unsigned* offset,
                                                      unsigned chars);
    inline void ExternalAsciiStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                                       unsigned* offset,
                                                       unsigned chars);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalAsciiString);
  };
  
  
  // The ExternalTwoByteString class is an external string backed by a UTF-16
  // encoded string.
  class ExternalTwoByteString: public ExternalString {
   public:
    typedef v8::String::ExternalStringResource Resource;
  
    // The underlying string resource.
    inline Resource* resource();
    inline void set_resource(Resource* buffer);
  
    // Dispatched behavior.
    uint16_t ExternalTwoByteStringGet(int index);
  
    // For regexp code.
    const uint16_t* ExternalTwoByteStringGetData(unsigned start);
  
    // Casting.
    static inline ExternalTwoByteString* cast(Object* obj);
  
    // Garbage collection support.
    void ExternalTwoByteStringIterateBody(ObjectVisitor* v);
  
    // Support for StringInputBuffer.
    void ExternalTwoByteStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                                  unsigned* offset_ptr,
                                                  unsigned chars);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalTwoByteString);
  };
  
  
  // Utility superclass for stack-allocated objects that must be updated
  // on gc.  It provides two ways for the gc to update instances, either
  // iterating or updating after gc.
  class Relocatable BASE_EMBEDDED {
   public:
    inline Relocatable() : prev_(top_) { top_ = this; }
    virtual ~Relocatable() {
      ASSERT_EQ(top_, this);
      top_ = prev_;
    }
    virtual void IterateInstance(ObjectVisitor* v) { }
    virtual void PostGarbageCollection() { }
  
    static void PostGarbageCollectionProcessing();
    static int ArchiveSpacePerThread();
    static char* ArchiveState(char* to);
    static char* RestoreState(char* from);
    static void Iterate(ObjectVisitor* v);
    static void Iterate(ObjectVisitor* v, Relocatable* top);
    static char* Iterate(ObjectVisitor* v, char* t);
   private:
    static Relocatable* top_;
    Relocatable* prev_;
  };
  
  
  // A flat string reader provides random access to the contents of a
  // string independent of the character width of the string.  The handle
  // must be valid as long as the reader is being used.
  class FlatStringReader : public Relocatable {
   public:
    explicit FlatStringReader(Handle<String> str);
    explicit FlatStringReader(Vector<const char> input);
    void PostGarbageCollection();
    inline uc32 Get(int index);
    int length() { return length_; }
   private:
    String** str_;
    bool is_ascii_;
    int length_;
    const void* start_;
  };
  
  
  // Note that StringInputBuffers are not valid across a GC!  To fix this
  // it would have to store a String Handle instead of a String* and
  // AsciiStringReadBlock would have to be modified to use memcpy.
  //
  // StringInputBuffer is able to traverse any string regardless of how
  // deeply nested a sequence of ConsStrings it is made of.  However,
  // performance will be better if deep strings are flattened before they
  // are traversed.  Since flattening requires memory allocation this is
  // not always desirable, however (esp. in debugging situations).
  class StringInputBuffer: public unibrow::InputBuffer<String, String*, 1024> {
   public:
    virtual void Seek(unsigned pos);
    inline StringInputBuffer(): unibrow::InputBuffer<String, String*, 1024>() {}
    inline StringInputBuffer(String* backing):
        unibrow::InputBuffer<String, String*, 1024>(backing) {}
  };
  
  
  class SafeStringInputBuffer
    : public unibrow::InputBuffer<String, String**, 256> {
   public:
    virtual void Seek(unsigned pos);
    inline SafeStringInputBuffer()
        : unibrow::InputBuffer<String, String**, 256>() {}
    inline SafeStringInputBuffer(String** backing)
        : unibrow::InputBuffer<String, String**, 256>(backing) {}
  };
  
  
  template <typename T>
  class VectorIterator {
   public:
    VectorIterator(T* d, int l) : data_(Vector<const T>(d, l)), index_(0) { }
    explicit VectorIterator(Vector<const T> data) : data_(data), index_(0) { }
    T GetNext() { return data_[index_++]; }
    bool has_more() { return index_ < data_.length(); }
   private:
    Vector<const T> data_;
    int index_;
  };
  
  
  // The Oddball describes objects null, undefined, true, and false.
  class Oddball: public HeapObject {
   public:
    // [to_string]: Cached to_string computed at startup.
    DECL_ACCESSORS(to_string, String)
  
    // [to_number]: Cached to_number computed at startup.
    DECL_ACCESSORS(to_number, Object)
  
    // Casting.
    static inline Oddball* cast(Object* obj);
  
    // Dispatched behavior.
    void OddballIterateBody(ObjectVisitor* v);
  #ifdef DEBUG
    void OddballVerify();
  #endif
  
    // Initialize the fields.
    Object* Initialize(const char* to_string, Object* to_number);
  
    // Layout description.
    static const int kToStringOffset = HeapObject::kHeaderSize;
    static const int kToNumberOffset = kToStringOffset + kPointerSize;
    static const int kSize = kToNumberOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Oddball);
  };
  
  
  class JSGlobalPropertyCell: public HeapObject {
   public:
    // [value]: value of the global property.
    DECL_ACCESSORS(value, Object)
  
    // Casting.
    static inline JSGlobalPropertyCell* cast(Object* obj);
  
    // Dispatched behavior.
    void JSGlobalPropertyCellIterateBody(ObjectVisitor* v);
  #ifdef DEBUG
    void JSGlobalPropertyCellVerify();
    void JSGlobalPropertyCellPrint();
  #endif
  
    // Layout description.
    static const int kValueOffset = HeapObject::kHeaderSize;
    static const int kSize = kValueOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSGlobalPropertyCell);
  };
  
  
  
  // Proxy describes objects pointing from JavaScript to C structures.
  // Since they cannot contain references to JS HeapObjects they can be
  // placed in old_data_space.
  class Proxy: public HeapObject {
   public:
    // [proxy]: field containing the address.
    inline Address proxy();
    inline void set_proxy(Address value);
  
    // Casting.
    static inline Proxy* cast(Object* obj);
  
    // Dispatched behavior.
    inline void ProxyIterateBody(ObjectVisitor* v);
  #ifdef DEBUG
    void ProxyPrint();
    void ProxyVerify();
  #endif
  
    // Layout description.
  
    static const int kProxyOffset = HeapObject::kHeaderSize;
    static const int kSize = kProxyOffset + kPointerSize;
  
    STATIC_CHECK(kProxyOffset == Internals::kProxyProxyOffset);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Proxy);
  };
  
  
  // The JSArray describes JavaScript Arrays
  //  Such an array can be in one of two modes:
  //    - fast, backing storage is a FixedArray and length <= elements.length();
  //       Please note: push and pop can be used to grow and shrink the array.
  //    - slow, backing storage is a HashTable with numbers as keys.
  class JSArray: public JSObject {
   public:
    // [length]: The length property.
    DECL_ACCESSORS(length, Object)
  
    // Overload the length setter to skip write barrier when the length
    // is set to a smi. This matches the set function on FixedArray.
    inline void set_length(Smi* length);
  
    Object* JSArrayUpdateLengthFromIndex(uint32_t index, Object* value);
  
    // Initialize the array with the given capacity. The function may
    // fail due to out-of-memory situations, but only if the requested
    // capacity is non-zero.
    Object* Initialize(int capacity);
  
    // Set the content of the array to the content of storage.
    inline void SetContent(FixedArray* storage);
  
    // Casting.
    static inline JSArray* cast(Object* obj);
  
    // Uses handles.  Ensures that the fixed array backing the JSArray has at
    // least the stated size.
    inline void EnsureSize(int minimum_size_of_backing_fixed_array);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void JSArrayPrint();
    void JSArrayVerify();
  #endif
  
    // Number of element slots to pre-allocate for an empty array.
    static const int kPreallocatedArrayElements = 4;
  
    // Layout description.
    static const int kLengthOffset = JSObject::kHeaderSize;
    static const int kSize = kLengthOffset + kPointerSize;
  
   private:
    // Expand the fixed array backing of a fast-case JSArray to at least
    // the requested size.
    void Expand(int minimum_size_of_backing_fixed_array);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSArray);
  };
  
  
  // JSRegExpResult is just a JSArray with a specific initial map.
  // This initial map adds in-object properties for "index" and "input"
  // properties, as assigned by RegExp.prototype.exec, which allows
  // faster creation of RegExp exec results.
  // This class just holds constants used when creating the result.
  // After creation the result must be treated as a JSArray in all regards.
  class JSRegExpResult: public JSArray {
   public:
    // Offsets of object fields.
    static const int kIndexOffset = JSArray::kSize;
    static const int kInputOffset = kIndexOffset + kPointerSize;
    static const int kSize = kInputOffset + kPointerSize;
    // Indices of in-object properties.
    static const int kIndexIndex = 0;
    static const int kInputIndex = 1;
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSRegExpResult);
  };
  
  
  // An accessor must have a getter, but can have no setter.
  //
  // When setting a property, V8 searches accessors in prototypes.
  // If an accessor was found and it does not have a setter,
  // the request is ignored.
  //
  // If the accessor in the prototype has the READ_ONLY property attribute, then
  // a new value is added to the local object when the property is set.
  // This shadows the accessor in the prototype.
  class AccessorInfo: public Struct {
   public:
    DECL_ACCESSORS(getter, Object)
    DECL_ACCESSORS(setter, Object)
    DECL_ACCESSORS(data, Object)
    DECL_ACCESSORS(name, Object)
    DECL_ACCESSORS(flag, Smi)
    DECL_ACCESSORS(load_stub_cache, Object)
  
    inline bool all_can_read();
    inline void set_all_can_read(bool value);
  
    inline bool all_can_write();
    inline void set_all_can_write(bool value);
  
    inline bool prohibits_overwriting();
    inline void set_prohibits_overwriting(bool value);
  
    inline PropertyAttributes property_attributes();
    inline void set_property_attributes(PropertyAttributes attributes);
  
    static inline AccessorInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void AccessorInfoPrint();
    void AccessorInfoVerify();
  #endif
  
    static const int kGetterOffset = HeapObject::kHeaderSize;
    static const int kSetterOffset = kGetterOffset + kPointerSize;
    static const int kDataOffset = kSetterOffset + kPointerSize;
    static const int kNameOffset = kDataOffset + kPointerSize;
    static const int kFlagOffset = kNameOffset + kPointerSize;
    static const int kLoadStubCacheOffset = kFlagOffset + kPointerSize;
    static const int kSize = kLoadStubCacheOffset + kPointerSize;
  
   private:
    // Bit positions in flag.
    static const int kAllCanReadBit = 0;
    static const int kAllCanWriteBit = 1;
    static const int kProhibitsOverwritingBit = 2;
    class AttributesField: public BitField<PropertyAttributes, 3, 3> {};
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(AccessorInfo);
  };
  
  
  class AccessCheckInfo: public Struct {
   public:
    DECL_ACCESSORS(named_callback, Object)
    DECL_ACCESSORS(indexed_callback, Object)
    DECL_ACCESSORS(data, Object)
  
    static inline AccessCheckInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void AccessCheckInfoPrint();
    void AccessCheckInfoVerify();
  #endif
  
    static const int kNamedCallbackOffset   = HeapObject::kHeaderSize;
    static const int kIndexedCallbackOffset = kNamedCallbackOffset + kPointerSize;
    static const int kDataOffset = kIndexedCallbackOffset + kPointerSize;
    static const int kSize = kDataOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(AccessCheckInfo);
  };
  
  
  class InterceptorInfo: public Struct {
   public:
    DECL_ACCESSORS(getter, Object)
    DECL_ACCESSORS(setter, Object)
    DECL_ACCESSORS(query, Object)
    DECL_ACCESSORS(deleter, Object)
    DECL_ACCESSORS(enumerator, Object)
    DECL_ACCESSORS(data, Object)
  
    static inline InterceptorInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void InterceptorInfoPrint();
    void InterceptorInfoVerify();
  #endif
  
    static const int kGetterOffset = HeapObject::kHeaderSize;
    static const int kSetterOffset = kGetterOffset + kPointerSize;
    static const int kQueryOffset = kSetterOffset + kPointerSize;
    static const int kDeleterOffset = kQueryOffset + kPointerSize;
    static const int kEnumeratorOffset = kDeleterOffset + kPointerSize;
    static const int kDataOffset = kEnumeratorOffset + kPointerSize;
    static const int kSize = kDataOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(InterceptorInfo);
  };
  
  
  class CallHandlerInfo: public Struct {
   public:
    DECL_ACCESSORS(callback, Object)
    DECL_ACCESSORS(data, Object)
  
    static inline CallHandlerInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void CallHandlerInfoPrint();
    void CallHandlerInfoVerify();
  #endif
  
    static const int kCallbackOffset = HeapObject::kHeaderSize;
    static const int kDataOffset = kCallbackOffset + kPointerSize;
    static const int kSize = kDataOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(CallHandlerInfo);
  };
  
  
  class TemplateInfo: public Struct {
   public:
    DECL_ACCESSORS(tag, Object)
    DECL_ACCESSORS(property_list, Object)
  
  #ifdef DEBUG
    void TemplateInfoVerify();
  #endif
  
    static const int kTagOffset          = HeapObject::kHeaderSize;
    static const int kPropertyListOffset = kTagOffset + kPointerSize;
    static const int kHeaderSize         = kPropertyListOffset + kPointerSize;
   protected:
    friend class AGCCVersionRequiresThisClassToHaveAFriendSoHereItIs;
    DISALLOW_IMPLICIT_CONSTRUCTORS(TemplateInfo);
  };
  
  
  class FunctionTemplateInfo: public TemplateInfo {
   public:
    DECL_ACCESSORS(serial_number, Object)
    DECL_ACCESSORS(call_code, Object)
    DECL_ACCESSORS(property_accessors, Object)
    DECL_ACCESSORS(prototype_template, Object)
    DECL_ACCESSORS(parent_template, Object)
    DECL_ACCESSORS(named_property_handler, Object)
    DECL_ACCESSORS(indexed_property_handler, Object)
    DECL_ACCESSORS(instance_template, Object)
    DECL_ACCESSORS(class_name, Object)
    DECL_ACCESSORS(signature, Object)
    DECL_ACCESSORS(instance_call_handler, Object)
    DECL_ACCESSORS(access_check_info, Object)
    DECL_ACCESSORS(flag, Smi)
  
    // Following properties use flag bits.
    DECL_BOOLEAN_ACCESSORS(hidden_prototype)
    DECL_BOOLEAN_ACCESSORS(undetectable)
    // If the bit is set, object instances created by this function
    // requires access check.
    DECL_BOOLEAN_ACCESSORS(needs_access_check)
  
    static inline FunctionTemplateInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void FunctionTemplateInfoPrint();
    void FunctionTemplateInfoVerify();
  #endif
  
    static const int kSerialNumberOffset = TemplateInfo::kHeaderSize;
    static const int kCallCodeOffset = kSerialNumberOffset + kPointerSize;
    static const int kPropertyAccessorsOffset = kCallCodeOffset + kPointerSize;
    static const int kPrototypeTemplateOffset =
        kPropertyAccessorsOffset + kPointerSize;
    static const int kParentTemplateOffset =
        kPrototypeTemplateOffset + kPointerSize;
    static const int kNamedPropertyHandlerOffset =
        kParentTemplateOffset + kPointerSize;
    static const int kIndexedPropertyHandlerOffset =
        kNamedPropertyHandlerOffset + kPointerSize;
    static const int kInstanceTemplateOffset =
        kIndexedPropertyHandlerOffset + kPointerSize;
    static const int kClassNameOffset = kInstanceTemplateOffset + kPointerSize;
    static const int kSignatureOffset = kClassNameOffset + kPointerSize;
    static const int kInstanceCallHandlerOffset = kSignatureOffset + kPointerSize;
    static const int kAccessCheckInfoOffset =
        kInstanceCallHandlerOffset + kPointerSize;
    static const int kFlagOffset = kAccessCheckInfoOffset + kPointerSize;
    static const int kSize = kFlagOffset + kPointerSize;
  
   private:
    // Bit position in the flag, from least significant bit position.
    static const int kHiddenPrototypeBit   = 0;
    static const int kUndetectableBit      = 1;
    static const int kNeedsAccessCheckBit  = 2;
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(FunctionTemplateInfo);
  };
  
  
  class ObjectTemplateInfo: public TemplateInfo {
   public:
    DECL_ACCESSORS(constructor, Object)
    DECL_ACCESSORS(internal_field_count, Object)
  
    static inline ObjectTemplateInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void ObjectTemplateInfoPrint();
    void ObjectTemplateInfoVerify();
  #endif
  
    static const int kConstructorOffset = TemplateInfo::kHeaderSize;
    static const int kInternalFieldCountOffset =
        kConstructorOffset + kPointerSize;
    static const int kSize = kInternalFieldCountOffset + kPointerSize;
  };
  
  
  class SignatureInfo: public Struct {
   public:
    DECL_ACCESSORS(receiver, Object)
    DECL_ACCESSORS(args, Object)
  
    static inline SignatureInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void SignatureInfoPrint();
    void SignatureInfoVerify();
  #endif
  
    static const int kReceiverOffset = Struct::kHeaderSize;
    static const int kArgsOffset     = kReceiverOffset + kPointerSize;
    static const int kSize           = kArgsOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(SignatureInfo);
  };
  
  
  class TypeSwitchInfo: public Struct {
   public:
    DECL_ACCESSORS(types, Object)
  
    static inline TypeSwitchInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void TypeSwitchInfoPrint();
    void TypeSwitchInfoVerify();
  #endif
  
    static const int kTypesOffset = Struct::kHeaderSize;
    static const int kSize        = kTypesOffset + kPointerSize;
  };
  
  
  #ifdef ENABLE_DEBUGGER_SUPPORT
  // The DebugInfo class holds additional information for a function being
  // debugged.
  class DebugInfo: public Struct {
   public:
    // The shared function info for the source being debugged.
    DECL_ACCESSORS(shared, SharedFunctionInfo)
    // Code object for the original code.
    DECL_ACCESSORS(original_code, Code)
    // Code object for the patched code. This code object is the code object
    // currently active for the function.
    DECL_ACCESSORS(code, Code)
    // Fixed array holding status information for each active break point.
    DECL_ACCESSORS(break_points, FixedArray)
  
    // Check if there is a break point at a code position.
    bool HasBreakPoint(int code_position);
    // Get the break point info object for a code position.
    Object* GetBreakPointInfo(int code_position);
    // Clear a break point.
    static void ClearBreakPoint(Handle<DebugInfo> debug_info,
                                int code_position,
                                Handle<Object> break_point_object);
    // Set a break point.
    static void SetBreakPoint(Handle<DebugInfo> debug_info, int code_position,
                              int source_position, int statement_position,
                              Handle<Object> break_point_object);
    // Get the break point objects for a code position.
    Object* GetBreakPointObjects(int code_position);
    // Find the break point info holding this break point object.
    static Object* FindBreakPointInfo(Handle<DebugInfo> debug_info,
                                      Handle<Object> break_point_object);
    // Get the number of break points for this function.
    int GetBreakPointCount();
  
    static inline DebugInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void DebugInfoPrint();
    void DebugInfoVerify();
  #endif
  
    static const int kSharedFunctionInfoIndex = Struct::kHeaderSize;
    static const int kOriginalCodeIndex = kSharedFunctionInfoIndex + kPointerSize;
    static const int kPatchedCodeIndex = kOriginalCodeIndex + kPointerSize;
    static const int kActiveBreakPointsCountIndex =
        kPatchedCodeIndex + kPointerSize;
    static const int kBreakPointsStateIndex =
        kActiveBreakPointsCountIndex + kPointerSize;
    static const int kSize = kBreakPointsStateIndex + kPointerSize;
  
   private:
    static const int kNoBreakPointInfo = -1;
  
    // Lookup the index in the break_points array for a code position.
    int GetBreakPointInfoIndex(int code_position);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(DebugInfo);
  };
  
  
  // The BreakPointInfo class holds information for break points set in a
  // function. The DebugInfo object holds a BreakPointInfo object for each code
  // position with one or more break points.
  class BreakPointInfo: public Struct {
   public:
    // The position in the code for the break point.
    DECL_ACCESSORS(code_position, Smi)
    // The position in the source for the break position.
    DECL_ACCESSORS(source_position, Smi)
    // The position in the source for the last statement before this break
    // position.
    DECL_ACCESSORS(statement_position, Smi)
    // List of related JavaScript break points.
    DECL_ACCESSORS(break_point_objects, Object)
  
    // Removes a break point.
    static void ClearBreakPoint(Handle<BreakPointInfo> info,
                                Handle<Object> break_point_object);
    // Set a break point.
    static void SetBreakPoint(Handle<BreakPointInfo> info,
                              Handle<Object> break_point_object);
    // Check if break point info has this break point object.
    static bool HasBreakPointObject(Handle<BreakPointInfo> info,
                                    Handle<Object> break_point_object);
    // Get the number of break points for this code position.
    int GetBreakPointCount();
  
    static inline BreakPointInfo* cast(Object* obj);
  
  #ifdef DEBUG
    void BreakPointInfoPrint();
    void BreakPointInfoVerify();
  #endif
  
    static const int kCodePositionIndex = Struct::kHeaderSize;
    static const int kSourcePositionIndex = kCodePositionIndex + kPointerSize;
    static const int kStatementPositionIndex =
        kSourcePositionIndex + kPointerSize;
    static const int kBreakPointObjectsIndex =
        kStatementPositionIndex + kPointerSize;
    static const int kSize = kBreakPointObjectsIndex + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(BreakPointInfo);
  };
  #endif  // ENABLE_DEBUGGER_SUPPORT
  
  
  #undef DECL_BOOLEAN_ACCESSORS
  #undef DECL_ACCESSORS
  
  
  // Abstract base class for visiting, and optionally modifying, the
  // pointers contained in Objects. Used in GC and serialization/deserialization.
  class ObjectVisitor BASE_EMBEDDED {
   public:
    virtual ~ObjectVisitor() {}
  
    // Visits a contiguous arrays of pointers in the half-open range
    // [start, end). Any or all of the values may be modified on return.
    virtual void VisitPointers(Object** start, Object** end) = 0;
  
    // To allow lazy clearing of inline caches the visitor has
    // a rich interface for iterating over Code objects..
  
    // Visits a code target in the instruction stream.
    virtual void VisitCodeTarget(RelocInfo* rinfo);
  
    // Visits a runtime entry in the instruction stream.
    virtual void VisitRuntimeEntry(RelocInfo* rinfo) {}
  
    // Visits the resource of an ASCII or two-byte string.
    virtual void VisitExternalAsciiString(
        v8::String::ExternalAsciiStringResource** resource) {}
    virtual void VisitExternalTwoByteString(
        v8::String::ExternalStringResource** resource) {}
  
    // Visits a debug call target in the instruction stream.
    virtual void VisitDebugTarget(RelocInfo* rinfo);
  
    // Handy shorthand for visiting a single pointer.
    virtual void VisitPointer(Object** p) { VisitPointers(p, p + 1); }
  
    // Visits a contiguous arrays of external references (references to the C++
    // heap) in the half-open range [start, end). Any or all of the values
    // may be modified on return.
    virtual void VisitExternalReferences(Address* start, Address* end) {}
  
    inline void VisitExternalReference(Address* p) {
      VisitExternalReferences(p, p + 1);
    }
  
  #ifdef DEBUG
    // Intended for serialization/deserialization checking: insert, or
    // check for the presence of, a tag at this position in the stream.
    virtual void Synchronize(const char* tag) {}
  #else
    inline void Synchronize(const char* tag) {}
  #endif
  };
  
  
  // BooleanBit is a helper class for setting and getting a bit in an
  // integer or Smi.
  class BooleanBit : public AllStatic {
   public:
    static inline bool get(Smi* smi, int bit_position) {
      return get(smi->value(), bit_position);
    }
  
    static inline bool get(int value, int bit_position) {
      return (value & (1 << bit_position)) != 0;
    }
  
    static inline Smi* set(Smi* smi, int bit_position, bool v) {
      return Smi::FromInt(set(smi->value(), bit_position, v));
    }
  
    static inline int set(int value, int bit_position, bool v) {
      if (v) {
        value |= (1 << bit_position);
      } else {
        value &= ~(1 << bit_position);
      }
      return value;
    }
  };
  
  } }  // namespace v8::internal
  
  #endif  // V8_OBJECTS_H_
  