text: // Copyright 2012 the V8 project authors. All rights reserved.
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  //       notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  //       copyright notice, this list of conditions and the following
  //       disclaimer in the documentation and/or other materials provided
  //       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 "allocation.h"
  #include "builtins.h"
  #include "list.h"
  #include "property-details.h"
  #include "smart-array-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
  #include "v8checks.h"
  
  
  //
  // Most object types in the V8 JavaScript are described in this file.
  //
  // Inheritance hierarchy:
  // - MaybeObject    (an object or a failure)
  //   - Failure      (immediate for marking failed operation)
  //   - Object
  //     - Smi          (immediate small integer)
  //     - HeapObject   (superclass for everything allocated in the heap)
  //       - JSReceiver  (suitable for property access)
  //         - JSObject
  //           - JSArray
  //           - JSSet
  //           - JSMap
  //           - JSWeakMap
  //           - JSRegExp
  //           - JSFunction
  //           - GlobalObject
  //             - JSGlobalObject
  //             - JSBuiltinsObject
  //           - JSGlobalProxy
  //           - JSValue
  //           - JSMessageObject
  //         - JSProxy
  //           - JSFunctionProxy
  //       - FixedArrayBase
  //         - ByteArray
  //         - FixedArray
  //           - DescriptorArray
  //           - HashTable
  //             - Dictionary
  //             - SymbolTable
  //             - CompilationCacheTable
  //             - CodeCacheHashTable
  //             - MapCache
  //           - Context
  //           - JSFunctionResultCache
  //           - ScopeInfo
  //         - FixedDoubleArray
  //         - ExternalArray
  //           - ExternalPixelArray
  //           - ExternalByteArray
  //           - ExternalUnsignedByteArray
  //           - ExternalShortArray
  //           - ExternalUnsignedShortArray
  //           - ExternalIntArray
  //           - ExternalUnsignedIntArray
  //           - ExternalFloatArray
  //       - String
  //         - SeqString
  //           - SeqAsciiString
  //           - SeqTwoByteString
  //         - SlicedString
  //         - ConsString
  //         - ExternalString
  //           - ExternalAsciiString
  //           - ExternalTwoByteString
  //       - HeapNumber
  //       - Code
  //       - Map
  //       - Oddball
  //       - Foreign
  //       - SharedFunctionInfo
  //       - Struct
  //         - AccessorInfo
  //         - AccessorPair
  //         - 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
  
  namespace v8 {
  namespace internal {
  
  enum ElementsKind {
    // The "fast" kind for elements that only contain SMI values. Must be first
    // to make it possible to efficiently check maps for this kind.
    FAST_SMI_ONLY_ELEMENTS,
  
    // The "fast" kind for tagged values. Must be second to make it possible to
    // efficiently check maps for this and the FAST_SMI_ONLY_ELEMENTS kind
    // together at once.
    FAST_ELEMENTS,
  
    // The "fast" kind for unwrapped, non-tagged double values.
    FAST_DOUBLE_ELEMENTS,
  
    // The "slow" kind.
    DICTIONARY_ELEMENTS,
    NON_STRICT_ARGUMENTS_ELEMENTS,
    // The "fast" kind for external arrays
    EXTERNAL_BYTE_ELEMENTS,
    EXTERNAL_UNSIGNED_BYTE_ELEMENTS,
    EXTERNAL_SHORT_ELEMENTS,
    EXTERNAL_UNSIGNED_SHORT_ELEMENTS,
    EXTERNAL_INT_ELEMENTS,
    EXTERNAL_UNSIGNED_INT_ELEMENTS,
    EXTERNAL_FLOAT_ELEMENTS,
    EXTERNAL_DOUBLE_ELEMENTS,
    EXTERNAL_PIXEL_ELEMENTS,
  
    // Derived constants from ElementsKind
    FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND = EXTERNAL_BYTE_ELEMENTS,
    LAST_EXTERNAL_ARRAY_ELEMENTS_KIND = EXTERNAL_PIXEL_ELEMENTS,
    FIRST_ELEMENTS_KIND = FAST_SMI_ONLY_ELEMENTS,
    LAST_ELEMENTS_KIND = EXTERNAL_PIXEL_ELEMENTS
  };
  
  enum CompareMapMode {
    REQUIRE_EXACT_MAP,
    ALLOW_ELEMENT_TRANSITION_MAPS
  };
  
  const int kElementsKindCount = LAST_ELEMENTS_KIND - FIRST_ELEMENTS_KIND + 1;
  
  void PrintElementsKind(FILE* out, ElementsKind kind);
  
  inline bool IsMoreGeneralElementsKindTransition(ElementsKind from_kind,
                                                  ElementsKind to_kind);
  
  // 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
  };
  
  
  // NormalizedMapSharingMode is used to specify whether a map may be shared
  // by different objects with normalized properties.
  enum NormalizedMapSharingMode {
    UNIQUE_NORMALIZED_MAP,
    SHARED_NORMALIZED_MAP
  };
  
  
  // Indicates whether a get method should implicitly create the object looked up.
  enum CreationFlag {
    ALLOW_CREATION,
    OMIT_CREATION
  };
  
  
  // Instance size sentinel for objects of variable size.
  const int kVariableSizeSentinel = 0;
  
  
  // 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 (e.g. 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_SYMBOL_WITH_ASCII_DATA_TYPE)                                      \
    V(EXTERNAL_ASCII_SYMBOL_TYPE)                                                \
    V(SHORT_EXTERNAL_SYMBOL_TYPE)                                                \
    V(SHORT_EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE)                                \
    V(SHORT_EXTERNAL_ASCII_SYMBOL_TYPE)                                          \
    V(STRING_TYPE)                                                               \
    V(ASCII_STRING_TYPE)                                                         \
    V(CONS_STRING_TYPE)                                                          \
    V(CONS_ASCII_STRING_TYPE)                                                    \
    V(SLICED_STRING_TYPE)                                                        \
    V(EXTERNAL_STRING_TYPE)                                                      \
    V(EXTERNAL_STRING_WITH_ASCII_DATA_TYPE)                                      \
    V(EXTERNAL_ASCII_STRING_TYPE)                                                \
    V(SHORT_EXTERNAL_STRING_TYPE)                                                \
    V(SHORT_EXTERNAL_STRING_WITH_ASCII_DATA_TYPE)                                \
    V(SHORT_EXTERNAL_ASCII_STRING_TYPE)                                          \
    V(PRIVATE_EXTERNAL_ASCII_STRING_TYPE)                                        \
                                                                                 \
    V(MAP_TYPE)                                                                  \
    V(CODE_TYPE)                                                                 \
    V(ODDBALL_TYPE)                                                              \
    V(JS_GLOBAL_PROPERTY_CELL_TYPE)                                              \
                                                                                 \
    V(HEAP_NUMBER_TYPE)                                                          \
    V(FOREIGN_TYPE)                                                              \
    V(BYTE_ARRAY_TYPE)                                                           \
    V(FREE_SPACE_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(EXTERNAL_PIXEL_ARRAY_TYPE)                                                 \
    V(FILLER_TYPE)                                                               \
                                                                                 \
    V(ACCESSOR_INFO_TYPE)                                                        \
    V(ACCESSOR_PAIR_TYPE)                                                        \
    V(ACCESS_CHECK_INFO_TYPE)                                                    \
    V(INTERCEPTOR_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(POLYMORPHIC_CODE_CACHE_TYPE)                                               \
                                                                                 \
    V(FIXED_ARRAY_TYPE)                                                          \
    V(FIXED_DOUBLE_ARRAY_TYPE)                                                   \
    V(SHARED_FUNCTION_INFO_TYPE)                                                 \
                                                                                 \
    V(JS_MESSAGE_OBJECT_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_PROXY_TYPE)                                                             \
    V(JS_WEAK_MAP_TYPE)                                                          \
    V(JS_REGEXP_TYPE)                                                            \
                                                                                 \
    V(JS_FUNCTION_TYPE)                                                          \
    V(JS_FUNCTION_PROXY_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,                                                               \
      kVariableSizeSentinel,                                                     \
      symbol,                                                                    \
      Symbol)                                                                    \
    V(ASCII_SYMBOL_TYPE,                                                         \
      kVariableSizeSentinel,                                                     \
      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_SYMBOL_WITH_ASCII_DATA_TYPE,                                      \
      ExternalTwoByteString::kSize,                                              \
      external_symbol_with_ascii_data,                                           \
      ExternalSymbolWithAsciiData)                                               \
    V(EXTERNAL_ASCII_SYMBOL_TYPE,                                                \
      ExternalAsciiString::kSize,                                                \
      external_ascii_symbol,                                                     \
      ExternalAsciiSymbol)                                                       \
    V(SHORT_EXTERNAL_SYMBOL_TYPE,                                                \
      ExternalTwoByteString::kShortSize,                                         \
      short_external_symbol,                                                     \
      ShortExternalSymbol)                                                       \
    V(SHORT_EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE,                                \
      ExternalTwoByteString::kShortSize,                                         \
      short_external_symbol_with_ascii_data,                                     \
      ShortExternalSymbolWithAsciiData)                                          \
    V(SHORT_EXTERNAL_ASCII_SYMBOL_TYPE,                                          \
      ExternalAsciiString::kShortSize,                                           \
      short_external_ascii_symbol,                                               \
      ShortExternalAsciiSymbol)                                                  \
    V(STRING_TYPE,                                                               \
      kVariableSizeSentinel,                                                     \
      string,                                                                    \
      String)                                                                    \
    V(ASCII_STRING_TYPE,                                                         \
      kVariableSizeSentinel,                                                     \
      ascii_string,                                                              \
      AsciiString)                                                               \
    V(CONS_STRING_TYPE,                                                          \
      ConsString::kSize,                                                         \
      cons_string,                                                               \
      ConsString)                                                                \
    V(CONS_ASCII_STRING_TYPE,                                                    \
      ConsString::kSize,                                                         \
      cons_ascii_string,                                                         \
      ConsAsciiString)                                                           \
    V(SLICED_STRING_TYPE,                                                        \
      SlicedString::kSize,                                                       \
      sliced_string,                                                             \
      SlicedString)                                                              \
    V(SLICED_ASCII_STRING_TYPE,                                                  \
      SlicedString::kSize,                                                       \
      sliced_ascii_string,                                                       \
      SlicedAsciiString)                                                         \
    V(EXTERNAL_STRING_TYPE,                                                      \
      ExternalTwoByteString::kSize,                                              \
      external_string,                                                           \
      ExternalString)                                                            \
    V(EXTERNAL_STRING_WITH_ASCII_DATA_TYPE,                                      \
      ExternalTwoByteString::kSize,                                              \
      external_string_with_ascii_data,                                           \
      ExternalStringWithAsciiData)                                               \
    V(EXTERNAL_ASCII_STRING_TYPE,                                                \
      ExternalAsciiString::kSize,                                                \
      external_ascii_string,                                                     \
      ExternalAsciiString)                                                       \
    V(SHORT_EXTERNAL_STRING_TYPE,                                                \
      ExternalTwoByteString::kShortSize,                                         \
      short_external_string,                                                     \
      ShortExternalString)                                                       \
    V(SHORT_EXTERNAL_STRING_WITH_ASCII_DATA_TYPE,                                \
      ExternalTwoByteString::kShortSize,                                         \
      short_external_string_with_ascii_data,                                     \
      ShortExternalStringWithAsciiData)                                          \
    V(SHORT_EXTERNAL_ASCII_STRING_TYPE,                                          \
      ExternalAsciiString::kShortSize,                                           \
      short_external_ascii_string,                                               \
      ShortExternalAsciiString)
  
  // 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(ACCESSOR_PAIR, AccessorPair, accessor_pair)                                \
    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)                                         \
    V(POLYMORPHIC_CODE_CACHE, PolymorphicCodeCache, polymorphic_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 = 0x2,
    kSlicedStringTag = 0x3
  };
  const uint32_t kIsIndirectStringMask = 0x1;
  const uint32_t kIsIndirectStringTag = 0x1;
  STATIC_ASSERT((kSeqStringTag & kIsIndirectStringMask) == 0);
  STATIC_ASSERT((kExternalStringTag & kIsIndirectStringMask) == 0);
  STATIC_ASSERT(
      (kConsStringTag & kIsIndirectStringMask) == kIsIndirectStringTag);
  STATIC_ASSERT(
      (kSlicedStringTag & kIsIndirectStringMask) == kIsIndirectStringTag);
  
  // Use this mask to distinguish between cons and slice only after making
  // sure that the string is one of the two (an indirect string).
  const uint32_t kSlicedNotConsMask = kSlicedStringTag & ~kConsStringTag;
  STATIC_ASSERT(IS_POWER_OF_TWO(kSlicedNotConsMask) && kSlicedNotConsMask != 0);
  
  // If bit 7 is clear, then bit 3 indicates whether this two-byte
  // string actually contains ASCII data.
  const uint32_t kAsciiDataHintMask = 0x08;
  const uint32_t kAsciiDataHintTag = 0x08;
  
  // If bit 7 is clear and string representation indicates an external string,
  // then bit 4 indicates whether the data pointer is cached.
  const uint32_t kShortExternalStringMask = 0x10;
  const uint32_t kShortExternalStringTag = 0x10;
  
  
  // 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 = kTwoByteStringTag | kSymbolTag | kSeqStringTag,
    ASCII_SYMBOL_TYPE = kAsciiStringTag | kSymbolTag | kSeqStringTag,
    CONS_SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag | kConsStringTag,
    CONS_ASCII_SYMBOL_TYPE = kAsciiStringTag | kSymbolTag | kConsStringTag,
    SHORT_EXTERNAL_SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag |
                                 kExternalStringTag | kShortExternalStringTag,
    SHORT_EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE =
        kTwoByteStringTag | kSymbolTag | kExternalStringTag |
        kAsciiDataHintTag | kShortExternalStringTag,
    SHORT_EXTERNAL_ASCII_SYMBOL_TYPE = kAsciiStringTag | kExternalStringTag |
                                       kSymbolTag | kShortExternalStringTag,
    EXTERNAL_SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag | kExternalStringTag,
    EXTERNAL_SYMBOL_WITH_ASCII_DATA_TYPE =
        kTwoByteStringTag | kSymbolTag | kExternalStringTag | kAsciiDataHintTag,
    EXTERNAL_ASCII_SYMBOL_TYPE =
        kAsciiStringTag | kSymbolTag | kExternalStringTag,
    STRING_TYPE = kTwoByteStringTag | kSeqStringTag,
    ASCII_STRING_TYPE = kAsciiStringTag | kSeqStringTag,
    CONS_STRING_TYPE = kTwoByteStringTag | kConsStringTag,
    CONS_ASCII_STRING_TYPE = kAsciiStringTag | kConsStringTag,
    SLICED_STRING_TYPE = kTwoByteStringTag | kSlicedStringTag,
    SLICED_ASCII_STRING_TYPE = kAsciiStringTag | kSlicedStringTag,
    SHORT_EXTERNAL_STRING_TYPE =
        kTwoByteStringTag | kExternalStringTag | kShortExternalStringTag,
    SHORT_EXTERNAL_STRING_WITH_ASCII_DATA_TYPE =
        kTwoByteStringTag | kExternalStringTag |
        kAsciiDataHintTag | kShortExternalStringTag,
    SHORT_EXTERNAL_ASCII_STRING_TYPE =
        kAsciiStringTag | kExternalStringTag | kShortExternalStringTag,
    EXTERNAL_STRING_TYPE = kTwoByteStringTag | kExternalStringTag,
    EXTERNAL_STRING_WITH_ASCII_DATA_TYPE =
        kTwoByteStringTag | kExternalStringTag | kAsciiDataHintTag,
    // LAST_STRING_TYPE
    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,
    FOREIGN_TYPE,
    BYTE_ARRAY_TYPE,
    FREE_SPACE_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,
    EXTERNAL_DOUBLE_ARRAY_TYPE,
    EXTERNAL_PIXEL_ARRAY_TYPE,  // LAST_EXTERNAL_ARRAY_TYPE
    FIXED_DOUBLE_ARRAY_TYPE,
    FILLER_TYPE,  // LAST_DATA_TYPE
  
    // Structs.
    ACCESSOR_INFO_TYPE,
    ACCESSOR_PAIR_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,
    POLYMORPHIC_CODE_CACHE_TYPE,
    // The following two instance types are only used when ENABLE_DEBUGGER_SUPPORT
    // is defined. However as include/v8.h contain some of the instance type
    // constants always having them avoids them getting different numbers
    // depending on whether ENABLE_DEBUGGER_SUPPORT is defined or not.
    DEBUG_INFO_TYPE,
    BREAK_POINT_INFO_TYPE,
  
    FIXED_ARRAY_TYPE,
    SHARED_FUNCTION_INFO_TYPE,
  
    JS_MESSAGE_OBJECT_TYPE,
  
    // All the following types are subtypes of JSReceiver, which corresponds to
    // objects in the JS sense. The first and the last type in this range are
    // the two forms of function. This organization enables using the same
    // compares for checking the JS_RECEIVER/SPEC_OBJECT range and the
    // NONCALLABLE_JS_OBJECT range.
    JS_FUNCTION_PROXY_TYPE,  // FIRST_JS_RECEIVER_TYPE, FIRST_JS_PROXY_TYPE
    JS_PROXY_TYPE,  // LAST_JS_PROXY_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_SET_TYPE,
    JS_MAP_TYPE,
    JS_WEAK_MAP_TYPE,
  
    JS_REGEXP_TYPE,
  
    JS_FUNCTION_TYPE,  // LAST_JS_OBJECT_TYPE, LAST_JS_RECEIVER_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_PIXEL_ARRAY_TYPE,
    // Boundary for promotion to old data space/old pointer space.
    LAST_DATA_TYPE = FILLER_TYPE,
    // Boundary for objects represented as JSReceiver (i.e. JSObject or JSProxy).
    // Note that there is no range for JSObject or JSProxy, since their subtypes
    // are not continuous in this enum! The enum ranges instead reflect the
    // external class names, where proxies are treated as either ordinary objects,
    // or functions.
    FIRST_JS_RECEIVER_TYPE = JS_FUNCTION_PROXY_TYPE,
    LAST_JS_RECEIVER_TYPE = LAST_TYPE,
    // Boundaries for testing the types represented as JSObject
    FIRST_JS_OBJECT_TYPE = JS_VALUE_TYPE,
    LAST_JS_OBJECT_TYPE = LAST_TYPE,
    // Boundaries for testing the types represented as JSProxy
    FIRST_JS_PROXY_TYPE = JS_FUNCTION_PROXY_TYPE,
    LAST_JS_PROXY_TYPE = JS_PROXY_TYPE,
    // Boundaries for testing whether the type is a JavaScript object.
    FIRST_SPEC_OBJECT_TYPE = FIRST_JS_RECEIVER_TYPE,
    LAST_SPEC_OBJECT_TYPE = LAST_JS_RECEIVER_TYPE,
    // Boundaries for testing the types for which typeof is "object".
    FIRST_NONCALLABLE_SPEC_OBJECT_TYPE = JS_PROXY_TYPE,
    LAST_NONCALLABLE_SPEC_OBJECT_TYPE = JS_REGEXP_TYPE,
    // Note that the types for which typeof is "function" are not continuous.
    // Define this so that we can put assertions on discrete checks.
    NUM_OF_CALLABLE_SPEC_OBJECT_TYPES = 2
  };
  
  const int kExternalArrayTypeCount =
      LAST_EXTERNAL_ARRAY_TYPE - FIRST_EXTERNAL_ARRAY_TYPE + 1;
  
  STATIC_CHECK(JS_OBJECT_TYPE == Internals::kJSObjectType);
  STATIC_CHECK(FIRST_NONSTRING_TYPE == Internals::kFirstNonstringType);
  STATIC_CHECK(FOREIGN_TYPE == Internals::kForeignType);
  
  
  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 DictionaryElementsAccessor;
  class ElementsAccessor;
  class FixedArrayBase;
  class ObjectVisitor;
  class StringStream;
  class Failure;
  
  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);
  
  
  class MaybeObject BASE_EMBEDDED {
   public:
    inline bool IsFailure();
    inline bool IsRetryAfterGC();
    inline bool IsOutOfMemory();
    inline bool IsException();
    INLINE(bool IsTheHole());
    inline bool ToObject(Object** obj) {
      if (IsFailure()) return false;
      *obj = reinterpret_cast<Object*>(this);
      return true;
    }
    inline Failure* ToFailureUnchecked() {
      ASSERT(IsFailure());
      return reinterpret_cast<Failure*>(this);
    }
    inline Object* ToObjectUnchecked() {
      ASSERT(!IsFailure());
      return reinterpret_cast<Object*>(this);
    }
    inline Object* ToObjectChecked() {
      CHECK(!IsFailure());
      return reinterpret_cast<Object*>(this);
    }
  
    template<typename T>
    inline bool To(T** obj) {
      if (IsFailure()) return false;
      *obj = T::cast(reinterpret_cast<Object*>(this));
      return true;
    }
  
  #ifdef OBJECT_PRINT
    // Prints this object with details.
    inline void Print() {
      Print(stdout);
    }
    inline void PrintLn() {
      PrintLn(stdout);
    }
    void Print(FILE* out);
    void PrintLn(FILE* out);
  #endif
  #ifdef DEBUG
    // Verifies the object.
    void Verify();
  #endif
  };
  
  
  #define OBJECT_TYPE_LIST(V)                    \
    V(Smi)                                       \
    V(HeapObject)                                \
    V(Number)                                    \
  
  #define HEAP_OBJECT_TYPE_LIST(V)               \
    V(HeapNumber)                                \
    V(String)                                    \
    V(Symbol)                                    \
    V(SeqString)                                 \
    V(ExternalString)                            \
    V(ConsString)                                \
    V(SlicedString)                              \
    V(ExternalTwoByteString)                     \
    V(ExternalAsciiString)                       \
    V(SeqTwoByteString)                          \
    V(SeqAsciiString)                            \
                                                 \
    V(ExternalArray)                             \
    V(ExternalByteArray)                         \
    V(ExternalUnsignedByteArray)                 \
    V(ExternalShortArray)                        \
    V(ExternalUnsignedShortArray)                \
    V(ExternalIntArray)                          \
    V(ExternalUnsignedIntArray)                  \
    V(ExternalFloatArray)                        \
    V(ExternalDoubleArray)                       \
    V(ExternalPixelArray)                        \
    V(ByteArray)                                 \
    V(FreeSpace)                                 \
    V(JSReceiver)                                \
    V(JSObject)                                  \
    V(JSContextExtensionObject)                  \
    V(Map)                                       \
    V(DescriptorArray)                           \
    V(DeoptimizationInputData)                   \
    V(DeoptimizationOutputData)                  \
    V(FixedArray)                                \
    V(FixedDoubleArray)                          \
    V(Context)                                   \
    V(GlobalContext)                             \
    V(ScopeInfo)                                 \
    V(JSFunction)                                \
    V(Code)                                      \
    V(Oddball)                                   \
    V(SharedFunctionInfo)                        \
    V(JSValue)                                   \
    V(JSMessageObject)                           \
    V(StringWrapper)                             \
    V(Foreign)                                   \
    V(Boolean)                                   \
    V(JSArray)                                   \
    V(JSProxy)                                   \
    V(JSFunctionProxy)                           \
    V(JSSet)                                     \
    V(JSMap)                                     \
    V(JSWeakMap)                                 \
    V(JSRegExp)                                  \
    V(HashTable)                                 \
    V(Dictionary)                                \
    V(SymbolTable)                               \
    V(JSFunctionResultCache)                     \
    V(NormalizedMapCache)                        \
    V(CompilationCacheTable)                     \
    V(CodeCacheHashTable)                        \
    V(PolymorphicCodeCacheHashTable)             \
    V(MapCache)                                  \
    V(Primitive)                                 \
    V(GlobalObject)                              \
    V(JSGlobalObject)                            \
    V(JSBuiltinsObject)                          \
    V(JSGlobalProxy)                             \
    V(UndetectableObject)                        \
    V(AccessCheckNeeded)                         \
    V(JSGlobalPropertyCell)                      \
  
  
  class JSReceiver;
  
  // 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 : public MaybeObject {
   public:
    // Type testing.
  #define IS_TYPE_FUNCTION_DECL(type_)  inline bool Is##type_();
    OBJECT_TYPE_LIST(IS_TYPE_FUNCTION_DECL)
    HEAP_OBJECT_TYPE_LIST(IS_TYPE_FUNCTION_DECL)
  #undef IS_TYPE_FUNCTION_DECL
  
    inline bool IsFixedArrayBase();
  
    // 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
  
    INLINE(bool IsSpecObject());
    INLINE(bool IsSpecFunction());
  
    // Oddball testing.
    INLINE(bool IsUndefined());
    INLINE(bool IsNull());
    INLINE(bool IsTheHole());  // Shadows MaybeObject's implementation.
    INLINE(bool IsTrue());
    INLINE(bool IsFalse());
    inline bool IsArgumentsMarker();
    inline bool NonFailureIsHeapObject();
  
    // Filler objects (fillers and free space objects).
    inline bool IsFiller();
  
    // Extract the number.
    inline double Number();
  
    // Returns true if the object is of the correct type to be used as a
    // implementation of a JSObject's elements.
    inline bool HasValidElements();
  
    inline bool HasSpecificClassOf(String* name);
  
    MUST_USE_RESULT MaybeObject* 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.
    MUST_USE_RESULT MaybeObject* ToObject(Context* global_context);
  
    // Converts this to a Smi if possible.
    // Failure is returned otherwise.
    MUST_USE_RESULT inline MaybeObject* ToSmi();
  
    void Lookup(String* name, LookupResult* result);
  
    // Property access.
    MUST_USE_RESULT inline MaybeObject* GetProperty(String* key);
    MUST_USE_RESULT inline MaybeObject* GetProperty(
        String* key,
        PropertyAttributes* attributes);
    MUST_USE_RESULT MaybeObject* GetPropertyWithReceiver(
        Object* receiver,
        String* key,
        PropertyAttributes* attributes);
  
    static Handle<Object> GetProperty(Handle<Object> object,
                                      Handle<Object> receiver,
                                      LookupResult* result,
                                      Handle<String> key,
                                      PropertyAttributes* attributes);
  
    MUST_USE_RESULT MaybeObject* GetProperty(Object* receiver,
                                             LookupResult* result,
                                             String* key,
                                             PropertyAttributes* attributes);
  
    MUST_USE_RESULT MaybeObject* GetPropertyWithDefinedGetter(Object* receiver,
                                                              JSReceiver* getter);
  
    static Handle<Object> GetElement(Handle<Object> object, uint32_t index);
    inline MaybeObject* GetElement(uint32_t index);
    // For use when we know that no exception can be thrown.
    inline Object* GetElementNoExceptionThrown(uint32_t index);
    MaybeObject* GetElementWithReceiver(Object* receiver, uint32_t index);
  
    // Return the object's prototype (might be Heap::null_value()).
    Object* GetPrototype();
  
    // Returns the permanent hash code associated with this object depending on
    // the actual object type.  Might return a failure in case no hash was
    // created yet or GC was caused by creation.
    MUST_USE_RESULT MaybeObject* GetHash(CreationFlag flag);
  
    // Checks whether this object has the same value as the given one.  This
    // function is implemented according to ES5, section 9.12 and can be used
    // to implement the Harmony "egal" function.
    bool SameValue(Object* other);
  
    // Tries to convert an object to an array index.  Returns true and sets
    // the output parameter if it succeeds.
    inline bool ToArrayIndex(uint32_t* index);
  
    // 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
    // Verify a pointer is a valid object pointer.
    static void VerifyPointer(Object* p);
  #endif
  
    // Prints this object without details.
    inline void ShortPrint() {
      ShortPrint(stdout);
    }
    void ShortPrint(FILE* out);
  
    // 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.
    inline void SmiPrint() {
      SmiPrint(stdout);
    }
    void SmiPrint(FILE* out);
    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:
  // +-------------------------+---+--+--+
  // |.........unused..........|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).
  
  // Failure type tag info.
  const int kFailureTypeTagSize = 2;
  const int kFailureTypeTagMask = (1 << kFailureTypeTagSize) - 1;
  
  class Failure: public MaybeObject {
   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 Isolate::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;
  
    inline bool IsInternalError() const;
    inline bool IsOutOfMemoryException() const;
  
    static inline Failure* RetryAfterGC(AllocationSpace space);
    static inline Failure* RetryAfterGC();  // NEW_SPACE
    static inline Failure* Exception();
    static inline Failure* InternalError();
    static inline Failure* OutOfMemoryException();
    // Casting.
    static inline Failure* cast(MaybeObject* object);
  
    // Dispatched behavior.
    inline void FailurePrint() {
      FailurePrint(stdout);
    }
    void FailurePrint(FILE* out);
    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 (e.g. 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, i.e. 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();
  
    static inline MapWord FromRawValue(uintptr_t value) {
      return MapWord(value);
    }
  
    inline uintptr_t ToRawValue() {
      return value_;
    }
  
   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);
    // The no-write-barrier version.  This is OK if the object is white and in
    // new space, or if the value is an immortal immutable object, like the maps
    // of primitive (non-JS) objects like strings, heap numbers etc.
    inline void set_map_no_write_barrier(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);
  
    // The Heap the object was allocated in. Used also to access Isolate.
    inline Heap* GetHeap();
  
    // Convenience method to get current isolate. This method can be
    // accessed only when its result is the same as
    // Isolate::Current(), it ASSERTs this. See also comment for GetHeap.
    inline Isolate* GetIsolate();
  
    // 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);
  
    // 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);
  
    // 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 invoke write barrier, 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 OBJECT_PRINT
    inline void HeapObjectPrint() {
      HeapObjectPrint(stdout);
    }
    void HeapObjectPrint(FILE* out);
    void PrintHeader(FILE* out, const char* id);
  #endif
  
  #ifdef DEBUG
    void HeapObjectVerify();
    inline void VerifyObjectField(int offset);
    inline void VerifySmiField(int offset);
  
    // 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);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(HeapObject);
  };
  
  
  #define SLOT_ADDR(obj, offset) \
    reinterpret_cast<Object**>((obj)->address() + offset)
  
  // This class describes a body of an object of a fixed size
  // in which all pointer fields are located in the [start_offset, end_offset)
  // interval.
  template<int start_offset, int end_offset, int size>
  class FixedBodyDescriptor {
   public:
    static const int kStartOffset = start_offset;
    static const int kEndOffset = end_offset;
    static const int kSize = size;
  
    static inline void IterateBody(HeapObject* obj, ObjectVisitor* v);
  
    template<typename StaticVisitor>
    static inline void IterateBody(HeapObject* obj) {
      StaticVisitor::VisitPointers(SLOT_ADDR(obj, start_offset),
                                   SLOT_ADDR(obj, end_offset));
    }
  };
  
  
  // This class describes a body of an object of a variable size
  // in which all pointer fields are located in the [start_offset, object_size)
  // interval.
  template<int start_offset>
  class FlexibleBodyDescriptor {
   public:
    static const int kStartOffset = start_offset;
  
    static inline void IterateBody(HeapObject* obj,
                                   int object_size,
                                   ObjectVisitor* v);
  
    template<typename StaticVisitor>
    static inline void IterateBody(HeapObject* obj, int object_size) {
      StaticVisitor::VisitPointers(SLOT_ADDR(obj, start_offset),
                                   SLOT_ADDR(obj, object_size));
    }
  };
  
  #undef SLOT_ADDR
  
  
  // 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();
    inline void HeapNumberPrint() {
      HeapNumberPrint(stdout);
    }
    void HeapNumberPrint(FILE* out);
    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!
    static const int kMantissaOffset = kValueOffset;
    static const int kExponentOffset = kValueOffset + 4;
  
    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 kMantissaBits = 52;
    static const int kExponentBits = 11;
    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);
  };
  
  
  enum EnsureElementsMode {
    DONT_ALLOW_DOUBLE_ELEMENTS,
    ALLOW_COPIED_DOUBLE_ELEMENTS,
    ALLOW_CONVERTED_DOUBLE_ELEMENTS
  };
  
  
  // JSReceiver includes types on which properties can be defined, i.e.,
  // JSObject and JSProxy.
  class JSReceiver: public HeapObject {
   public:
    enum DeleteMode {
      NORMAL_DELETION,
      STRICT_DELETION,
      FORCE_DELETION
    };
  
    // Casting.
    static inline JSReceiver* cast(Object* obj);
  
    static Handle<Object> SetProperty(Handle<JSReceiver> object,
                                      Handle<String> key,
                                      Handle<Object> value,
                                      PropertyAttributes attributes,
                                      StrictModeFlag strict_mode);
    // Can cause GC.
    MUST_USE_RESULT MaybeObject* SetProperty(String* key,
                                             Object* value,
                                             PropertyAttributes attributes,
                                             StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetProperty(LookupResult* result,
                                             String* key,
                                             Object* value,
                                             PropertyAttributes attributes,
                                             StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetPropertyWithDefinedSetter(JSReceiver* setter,
                                                              Object* value);
  
    MUST_USE_RESULT MaybeObject* DeleteProperty(String* name, DeleteMode mode);
    MUST_USE_RESULT MaybeObject* DeleteElement(uint32_t index, DeleteMode mode);
  
    // Set the index'th array element.
    // Can cause GC, or return failure if GC is required.
    MUST_USE_RESULT MaybeObject* SetElement(uint32_t index,
                                            Object* value,
                                            StrictModeFlag strict_mode,
                                            bool check_prototype);
  
    // Tests for the fast common case for property enumeration.
    bool IsSimpleEnum();
  
    // 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();
  
    inline PropertyAttributes GetPropertyAttribute(String* name);
    PropertyAttributes GetPropertyAttributeWithReceiver(JSReceiver* receiver,
                                                        String* name);
    PropertyAttributes GetLocalPropertyAttribute(String* name);
  
    // Can cause a GC.
    inline bool HasProperty(String* name);
    inline bool HasLocalProperty(String* name);
    inline bool HasElement(uint32_t index);
  
    // Return the object's prototype (might be Heap::null_value()).
    inline Object* GetPrototype();
  
    // Set the object's prototype (only JSReceiver and null are allowed).
    MUST_USE_RESULT MaybeObject* SetPrototype(Object* value,
                                              bool skip_hidden_prototypes);
  
    // Retrieves a permanent object identity hash code. The undefined value might
    // be returned in case no hash was created yet and OMIT_CREATION was used.
    inline MUST_USE_RESULT MaybeObject* GetIdentityHash(CreationFlag flag);
  
    // 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);
  
   protected:
    Smi* GenerateIdentityHash();
  
   private:
    PropertyAttributes GetPropertyAttribute(JSReceiver* receiver,
                                            LookupResult* result,
                                            String* name,
                                            bool continue_search);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSReceiver);
  };
  
  // 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 JSReceiver {
   public:
    // [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 can be in two general modes: fast and slow. Each mode
    // corrensponds to a set of object representations of elements that
    // have something in common.
    //
    // In the fast mode elements is a FixedArray and so each element can
    // be quickly accessed. This fact is used in the generated code. The
    // elements array can have one of three maps in this mode:
    // fixed_array_map, non_strict_arguments_elements_map or
    // fixed_cow_array_map (for copy-on-write arrays). In the latter case
    // the elements array may be shared by a few objects and so before
    // writing to any element the array must be copied. Use
    // EnsureWritableFastElements in this case.
    //
    // In the slow mode the elements is either a NumberDictionary, an
    // ExternalArray, or a FixedArray parameter map for a (non-strict)
    // arguments object.
    DECL_ACCESSORS(elements, FixedArrayBase)
    inline void initialize_elements();
    MUST_USE_RESULT inline MaybeObject* ResetElements();
    inline ElementsKind GetElementsKind();
    inline ElementsAccessor* GetElementsAccessor();
    inline bool HasFastSmiOnlyElements();
    inline bool HasFastElements();
    // Returns if an object has either FAST_ELEMENT or FAST_SMI_ONLY_ELEMENT
    // elements.  TODO(danno): Rename HasFastTypeElements to HasFastElements() and
    // HasFastElements to HasFastObjectElements.
    inline bool HasFastTypeElements();
    inline bool HasFastDoubleElements();
    inline bool HasNonStrictArgumentsElements();
    inline bool HasDictionaryElements();
    inline bool HasExternalPixelElements();
    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 HasExternalDoubleElements();
    bool HasFastArgumentsElements();
    bool HasDictionaryArgumentsElements();
    inline SeededNumberDictionary* element_dictionary();  // Gets slow elements.
  
    inline void set_map_and_elements(
        Map* map,
        FixedArrayBase* value,
        WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
  
    // Requires: HasFastElements().
    MUST_USE_RESULT inline MaybeObject* EnsureWritableFastElements();
  
    // Collects elements starting at index 0.
    // Undefined values are placed after non-undefined values.
    // Returns the number of non-undefined values.
    MUST_USE_RESULT MaybeObject* PrepareElementsForSort(uint32_t limit);
    // As PrepareElementsForSort, but only on objects where elements is
    // a dictionary, and it will stay a dictionary.
    MUST_USE_RESULT MaybeObject* PrepareSlowElementsForSort(uint32_t limit);
  
    MUST_USE_RESULT MaybeObject* GetPropertyWithCallback(Object* receiver,
                                                         Object* structure,
                                                         String* name);
  
    // Can cause GC.
    MUST_USE_RESULT MaybeObject* SetPropertyForResult(LookupResult* result,
                                             String* key,
                                             Object* value,
                                             PropertyAttributes attributes,
                                             StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetPropertyWithFailedAccessCheck(
        LookupResult* result,
        String* name,
        Object* value,
        bool check_prototype,
        StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetPropertyWithCallback(
        Object* structure,
        String* name,
        Object* value,
        JSObject* holder,
        StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetPropertyWithInterceptor(
        String* name,
        Object* value,
        PropertyAttributes attributes,
        StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetPropertyPostInterceptor(
        String* name,
        Object* value,
        PropertyAttributes attributes,
        StrictModeFlag strict_mode);
  
    static Handle<Object> SetLocalPropertyIgnoreAttributes(
        Handle<JSObject> object,
        Handle<String> key,
        Handle<Object> value,
        PropertyAttributes attributes);
  
    // Can cause GC.
    MUST_USE_RESULT MaybeObject* SetLocalPropertyIgnoreAttributes(
        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.
    static Handle<Object> SetNormalizedProperty(Handle<JSObject> object,
                                                Handle<String> key,
                                                Handle<Object> value,
                                                PropertyDetails details);
  
    MUST_USE_RESULT MaybeObject* SetNormalizedProperty(String* name,
                                                       Object* value,
                                                       PropertyDetails details);
  
    // Deletes the named property in a normalized object.
    MUST_USE_RESULT MaybeObject* DeleteNormalizedProperty(String* name,
                                                          DeleteMode mode);
  
    // Retrieve interceptors.
    InterceptorInfo* GetNamedInterceptor();
    InterceptorInfo* GetIndexedInterceptor();
  
    // Used from JSReceiver.
    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);
  
    MUST_USE_RESULT MaybeObject* DefineAccessor(String* name,
                                                bool is_getter,
                                                Object* fun,
                                                PropertyAttributes attributes);
    Object* LookupAccessor(String* name, bool is_getter);
  
    MUST_USE_RESULT MaybeObject* DefineAccessor(AccessorInfo* info);
  
    // Used from Object::GetProperty().
    MaybeObject* GetPropertyWithFailedAccessCheck(
        Object* receiver,
        LookupResult* result,
        String* name,
        PropertyAttributes* attributes);
    MaybeObject* GetPropertyWithInterceptor(
        JSReceiver* receiver,
        String* name,
        PropertyAttributes* attributes);
    MaybeObject* GetPropertyPostInterceptor(
        JSReceiver* receiver,
        String* name,
        PropertyAttributes* attributes);
    MaybeObject* GetLocalPropertyPostInterceptor(JSReceiver* 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();
  
    // 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 in an auxiliary structure kept 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, and if it's a detached proxy, then you can't have
    // hidden properties.
  
    // Sets a hidden property on this object. Returns this object if successful,
    // undefined if called on a detached proxy.
    static Handle<Object> SetHiddenProperty(Handle<JSObject> obj,
                                            Handle<String> key,
                                            Handle<Object> value);
    // Returns a failure if a GC is required.
    MaybeObject* SetHiddenProperty(String* key, Object* value);
    // Gets the value of a hidden property with the given key. Returns undefined
    // if the property doesn't exist (or if called on a detached proxy),
    // otherwise returns the value set for the key.
    Object* GetHiddenProperty(String* key);
    // Deletes a hidden property. Deleting a non-existing property is
    // considered successful.
    void DeleteHiddenProperty(String* key);
    // Returns true if the object has a property with the hidden symbol as name.
    bool HasHiddenProperties();
  
    static int GetIdentityHash(Handle<JSObject> obj);
    MUST_USE_RESULT MaybeObject* GetIdentityHash(CreationFlag flag);
    MUST_USE_RESULT MaybeObject* SetIdentityHash(Object* hash, CreationFlag flag);
  
    static Handle<Object> DeleteProperty(Handle<JSObject> obj,
                                         Handle<String> name);
    MUST_USE_RESULT MaybeObject* DeleteProperty(String* name, DeleteMode mode);
  
    static Handle<Object> DeleteElement(Handle<JSObject> obj, uint32_t index);
    MUST_USE_RESULT MaybeObject* DeleteElement(uint32_t index, DeleteMode mode);
  
    inline void ValidateSmiOnlyElements();
  
    // Makes sure that this object can contain HeapObject as elements.
    inline MaybeObject* EnsureCanContainHeapObjectElements();
  
    // Makes sure that this object can contain the specified elements.
    inline MaybeObject* EnsureCanContainElements(Object** elements,
                                                 uint32_t count,
                                                 EnsureElementsMode mode);
    inline MaybeObject* EnsureCanContainElements(FixedArrayBase* elements,
                                                 EnsureElementsMode mode);
    MaybeObject* EnsureCanContainElements(Arguments* arguments,
                                          uint32_t first_arg,
                                          uint32_t arg_count,
                                          EnsureElementsMode mode);
  
    // 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();
    // Returns true if the elements of JSObject contains only values that can be
    // represented in a FixedDoubleArray and has at least one value that can only
    // be represented as a double and not a Smi.
    bool ShouldConvertToFastDoubleElements(bool* has_smi_only_elements);
  
    // Tells whether the index'th element is present.
    bool HasElementWithReceiver(JSReceiver* receiver, uint32_t index);
  
    // Computes the new capacity when expanding the elements of a JSObject.
    static int NewElementsCapacity(int old_capacity) {
      // (old_capacity + 50%) + 16
      return old_capacity + (old_capacity >> 1) + 16;
    }
  
    // Tells whether the index'th element is present and how it is stored.
    enum LocalElementType {
      // There is no element with given index.
      UNDEFINED_ELEMENT,
  
      // Element with given index is handled by interceptor.
      INTERCEPTED_ELEMENT,
  
      // Element with given index is character in string.
      STRING_CHARACTER_ELEMENT,
  
      // Element with given index is stored in fast backing store.
      FAST_ELEMENT,
  
      // Element with given index is stored in slow backing store.
      DICTIONARY_ELEMENT
    };
  
    LocalElementType HasLocalElement(uint32_t index);
  
    bool HasElementWithInterceptor(JSReceiver* receiver, uint32_t index);
    bool HasElementPostInterceptor(JSReceiver* receiver, uint32_t index);
  
    MUST_USE_RESULT MaybeObject* SetFastElement(uint32_t index,
                                                Object* value,
                                                StrictModeFlag strict_mode,
                                                bool check_prototype);
  
    MUST_USE_RESULT MaybeObject* SetDictionaryElement(uint32_t index,
                                                      Object* value,
                                                      StrictModeFlag strict_mode,
                                                      bool check_prototype);
  
    MUST_USE_RESULT MaybeObject* SetFastDoubleElement(
        uint32_t index,
        Object* value,
        StrictModeFlag strict_mode,
        bool check_prototype = true);
  
  
    static Handle<Object> SetOwnElement(Handle<JSObject> object,
                                        uint32_t index,
                                        Handle<Object> value,
                                        StrictModeFlag strict_mode);
  
    // Empty handle is returned if the element cannot be set to the given value.
    static MUST_USE_RESULT Handle<Object> SetElement(Handle<JSObject> object,
                                                     uint32_t index,
                                                     Handle<Object> value,
                                                     StrictModeFlag strict_mode);
  
    // A Failure object is returned if GC is needed.
    MUST_USE_RESULT MaybeObject* SetElement(uint32_t index,
                                            Object* value,
                                            StrictModeFlag strict_mode,
                                            bool check_prototype);
  
    // Returns the index'th element.
    // The undefined object if index is out of bounds.
    MaybeObject* GetElementWithInterceptor(Object* receiver, uint32_t index);
  
    enum SetFastElementsCapacityMode {
      kAllowSmiOnlyElements,
      kForceSmiOnlyElements,
      kDontAllowSmiOnlyElements
    };
  
    // Replace the elements' backing store with fast elements of the given
    // capacity.  Update the length for JSArrays.  Returns the new backing
    // store.
    MUST_USE_RESULT MaybeObject* SetFastElementsCapacityAndLength(
        int capacity,
        int length,
        SetFastElementsCapacityMode set_capacity_mode);
    MUST_USE_RESULT MaybeObject* SetFastDoubleElementsCapacityAndLength(
        int capacity,
        int 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);
  
    // 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 int GetInternalFieldOffset(int index);
    inline Object* GetInternalField(int index);
    inline void SetInternalField(int index, Object* value);
    inline void SetInternalField(int index, Smi* value);
  
    // 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);
    MUST_USE_RESULT MaybeObject* SetElementWithCallbackSetterInPrototypes(
        uint32_t index, Object* value, bool* found, StrictModeFlag strict_mode);
    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.
    MUST_USE_RESULT MaybeObject* 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.
    MUST_USE_RESULT MaybeObject* AddConstantFunctionProperty(
        String* name,
        JSFunction* function,
        PropertyAttributes attributes);
  
    MUST_USE_RESULT MaybeObject* ReplaceSlowProperty(
        String* name,
        Object* value,
        PropertyAttributes attributes);
  
    // Returns a new map with all transitions dropped from the object's current
    // map and the ElementsKind set.
    static Handle<Map> GetElementsTransitionMap(Handle<JSObject> object,
                                                ElementsKind to_kind);
    MUST_USE_RESULT MaybeObject* GetElementsTransitionMap(
        ElementsKind elements_kind);
  
    static Handle<Object> TransitionElementsKind(Handle<JSObject> object,
                                                 ElementsKind to_kind);
  
    MUST_USE_RESULT MaybeObject* TransitionElementsKind(ElementsKind to_kind);
  
    // 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.
    MUST_USE_RESULT MaybeObject* 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.
    MUST_USE_RESULT MaybeObject* ConvertDescriptorToField(
        String* name,
        Object* new_value,
        PropertyAttributes attributes);
  
    // Add a property to a fast-case object.
    MUST_USE_RESULT MaybeObject* AddFastProperty(String* name,
                                                 Object* value,
                                                 PropertyAttributes attributes);
  
    // Add a property to a slow-case object.
    MUST_USE_RESULT MaybeObject* AddSlowProperty(String* name,
                                                 Object* value,
                                                 PropertyAttributes attributes);
  
    // Add a property to an object.
    MUST_USE_RESULT MaybeObject* AddProperty(String* name,
                                             Object* value,
                                             PropertyAttributes attributes,
                                             StrictModeFlag strict_mode);
  
    // 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.
    static void NormalizeProperties(Handle<JSObject> object,
                                    PropertyNormalizationMode mode,
                                    int expected_additional_properties);
  
    MUST_USE_RESULT MaybeObject* NormalizeProperties(
        PropertyNormalizationMode mode,
        int expected_additional_properties);
  
    // Convert and update the elements backing store to be a
    // SeededNumberDictionary dictionary.  Returns the backing after conversion.
    static Handle<SeededNumberDictionary> NormalizeElements(
        Handle<JSObject> object);
  
    MUST_USE_RESULT MaybeObject* NormalizeElements();
  
    static void UpdateMapCodeCache(Handle<JSObject> object,
                                   Handle<String> name,
                                   Handle<Code> code);
  
    MUST_USE_RESULT MaybeObject* UpdateMapCodeCache(String* name, Code* code);
  
    // Transform slow named properties to fast variants.
    // Returns failure if allocation failed.
    static void TransformToFastProperties(Handle<JSObject> object,
                                          int unused_property_fields);
  
    MUST_USE_RESULT MaybeObject* 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 int GetInObjectPropertyOffset(int index);
    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.  Fill the pre-allocated fields with
    // pre_allocated_value and the rest with filler_value.
    // Note: this call does not update write barrier, the caller is responsible
    // to ensure that |filler_value| can be collected without WB here.
    inline void InitializeBody(Map* map,
                               Object* pre_allocated_value,
                               Object* filler_value);
  
    // Check whether this object references another object
    bool ReferencesObject(Object* obj);
  
    // Casting.
    static inline JSObject* cast(Object* obj);
  
    // Disalow further properties to be added to the object.
    static Handle<Object> PreventExtensions(Handle<JSObject> object);
    MUST_USE_RESULT MaybeObject* PreventExtensions();
  
  
    // Dispatched behavior.
    void JSObjectShortPrint(StringStream* accumulator);
  #ifdef OBJECT_PRINT
    inline void JSObjectPrint() {
      JSObjectPrint(stdout);
    }
    void JSObjectPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSObjectVerify();
  #endif
  #ifdef OBJECT_PRINT
    inline void PrintProperties() {
      PrintProperties(stdout);
    }
    void PrintProperties(FILE* out);
  
    inline void PrintElements() {
      PrintElements(stdout);
    }
    void PrintElements(FILE* out);
  #endif
  
    void PrintElementsTransition(
        FILE* file, ElementsKind from_kind, FixedArrayBase* from_elements,
        ElementsKind to_kind, FixedArrayBase* to_elements);
  
  #ifdef DEBUG
    // 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 fast properties for the JSObject. Used to
    // restrict the number of map transitions to avoid an explosion in
    // the number of maps for objects used as dictionaries.
    inline int MaxFastProperties();
  
    // Maximal number of elements (numbered 0 .. kMaxElementCount - 1).
    // Also maximal value of JSArray's length property.
    static const uint32_t kMaxElementCount = 0xffffffffu;
  
    // Constants for heuristics controlling conversion of fast elements
    // to slow elements.
  
    // Maximal gap that can be introduced by adding an element beyond
    // the current elements length.
    static const uint32_t kMaxGap = 1024;
  
    // Maximal length of fast elements array that won't be checked for
    // being dense enough on expansion.
    static const int kMaxUncheckedFastElementsLength = 5000;
  
    // Same as above but for old arrays. This limit is more strict. We
    // don't want to be wasteful with long lived objects.
    static const int kMaxUncheckedOldFastElementsLength = 500;
  
    static const int kInitialMaxFastElementArray = 100000;
    static const int kMaxFastProperties = 12;
    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);
  
    class BodyDescriptor : public FlexibleBodyDescriptor<kPropertiesOffset> {
     public:
      static inline int SizeOf(Map* map, HeapObject* object);
    };
  
   private:
    friend class DictionaryElementsAccessor;
  
    MUST_USE_RESULT MaybeObject* GetElementWithCallback(Object* receiver,
                                                        Object* structure,
                                                        uint32_t index,
                                                        Object* holder);
    MaybeObject* SetElementWithCallback(Object* structure,
                                        uint32_t index,
                                        Object* value,
                                        JSObject* holder,
                                        StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetElementWithInterceptor(
        uint32_t index,
        Object* value,
        StrictModeFlag strict_mode,
        bool check_prototype);
    MUST_USE_RESULT MaybeObject* SetElementWithoutInterceptor(
        uint32_t index,
        Object* value,
        StrictModeFlag strict_mode,
        bool check_prototype);
  
    // Searches the prototype chain for a callback setter and sets the property
    // with the setter if it finds one. The '*found' flag indicates whether
    // a setter was found or not.
    // This function can cause GC and can return a failure result with
    // '*found==true'.
    MUST_USE_RESULT MaybeObject* SetPropertyWithCallbackSetterInPrototypes(
        String* name,
        Object* value,
        PropertyAttributes attributes,
        bool* found,
        StrictModeFlag strict_mode);
  
    MUST_USE_RESULT MaybeObject* DeletePropertyPostInterceptor(String* name,
                                                               DeleteMode mode);
    MUST_USE_RESULT MaybeObject* DeletePropertyWithInterceptor(String* name);
  
    MUST_USE_RESULT MaybeObject* DeleteElementWithInterceptor(uint32_t index);
  
    MUST_USE_RESULT MaybeObject* DeleteFastElement(uint32_t index);
    MUST_USE_RESULT MaybeObject* DeleteDictionaryElement(uint32_t index,
                                                         DeleteMode mode);
  
    bool ReferencesObjectFromElements(FixedArray* elements,
                                      ElementsKind kind,
                                      Object* object);
    bool HasElementInElements(FixedArray* elements,
                              ElementsKind kind,
                              uint32_t index);
  
    // Returns true if most of the elements backing storage is used.
    bool HasDenseElements();
  
    // Gets the current elements capacity and the number of used elements.
    void GetElementsCapacityAndUsage(int* capacity, int* used);
  
    bool CanSetCallback(String* name);
    MUST_USE_RESULT MaybeObject* SetElementCallback(
        uint32_t index,
        Object* structure,
        PropertyAttributes attributes);
    MUST_USE_RESULT MaybeObject* SetPropertyCallback(
        String* name,
        Object* structure,
        PropertyAttributes attributes);
    MUST_USE_RESULT MaybeObject* DefineGetterSetter(
        String* name,
        PropertyAttributes attributes);
  
    void LookupInDescriptor(String* name, LookupResult* result);
  
    // Returns the hidden properties backing store object, currently
    // a StringDictionary, stored on this object.
    // If no hidden properties object has been put on this object,
    // return undefined, unless create_if_absent is true, in which case
    // a new dictionary is created, added to this object, and returned.
    MaybeObject* GetHiddenPropertiesDictionary(bool create_if_absent);
    // Updates the existing hidden properties dictionary.
    MaybeObject* SetHiddenPropertiesDictionary(StringDictionary* dictionary);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSObject);
  };
  
  
  // Common superclass for FixedArrays that allow implementations to share
  // common accessors and some code paths.
  class FixedArrayBase: public HeapObject {
   public:
    // [length]: length of the array.
    inline int length();
    inline void set_length(int value);
  
    inline static FixedArrayBase* cast(Object* object);
  
    // Layout description.
    // Length is smi tagged when it is stored.
    static const int kLengthOffset = HeapObject::kHeaderSize;
    static const int kHeaderSize = kLengthOffset + kPointerSize;
  };
  
  
  class FixedDoubleArray;
  
  // FixedArray describes fixed-sized arrays with element type Object*.
  class FixedArray: public FixedArrayBase {
   public:
    // Setter and getter for elements.
    inline Object* get(int index);
    // Setter that uses write barrier.
    inline void set(int index, Object* value);
    inline bool is_the_hole(int index);
  
    // 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);
    // TODO(isolates): duplicate.
    inline void set_undefined(Heap* heap, int index);
    inline void set_null(int index);
    // TODO(isolates): duplicate.
    inline void set_null(Heap* heap, int index);
    inline void set_the_hole(int index);
  
    // Setters with less debug checks for the GC to use.
    inline void set_unchecked(int index, Smi* value);
    inline void set_null_unchecked(Heap* heap, int index);
    inline void set_unchecked(Heap* heap, int index, Object* value,
                              WriteBarrierMode mode);
  
    // Gives access to raw memory which stores the array's data.
    inline Object** data_start();
  
    inline Object** GetFirstElementAddress();
    inline bool ContainsOnlySmisOrHoles();
  
    // Copy operations.
    MUST_USE_RESULT inline MaybeObject* Copy();
    MUST_USE_RESULT MaybeObject* CopySize(int new_length);
  
    // Add the elements of a JSArray to this FixedArray.
    MUST_USE_RESULT MaybeObject* AddKeysFromJSArray(JSArray* array);
  
    // Compute the union of this and other.
    MUST_USE_RESULT MaybeObject* 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);
  
    // Maximal allowed size, in bytes, of a single FixedArray.
    // Prevents overflowing size computations, as well as extreme memory
    // consumption.
    static const int kMaxSize = 128 * MB * kPointerSize;
    // Maximally allowed length of a FixedArray.
    static const int kMaxLength = (kMaxSize - kHeaderSize) / kPointerSize;
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void FixedArrayPrint() {
      FixedArrayPrint(stdout);
    }
    void FixedArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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);
  
    class BodyDescriptor : public FlexibleBodyDescriptor<kHeaderSize> {
     public:
      static inline int SizeOf(Map* map, HeapObject* object) {
        return SizeFor(reinterpret_cast<FixedArray*>(object)->length());
      }
    };
  
   protected:
    // Set operation on FixedArray without using write barriers. Can
    // only be used for storing old space objects or smis.
    static inline void NoWriteBarrierSet(FixedArray* array,
                                         int index,
                                         Object* value);
  
    // Set operation on FixedArray without incremental write barrier. Can
    // only be used if the object is guaranteed to be white (whiteness witness
    // is present).
    static inline void NoIncrementalWriteBarrierSet(FixedArray* array,
                                                    int index,
                                                    Object* value);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(FixedArray);
  };
  
  
  // FixedDoubleArray describes fixed-sized arrays with element type double.
  class FixedDoubleArray: public FixedArrayBase {
   public:
    inline void Initialize(FixedArray* from);
    inline void Initialize(FixedDoubleArray* from);
    inline void Initialize(SeededNumberDictionary* from);
  
    // Setter and getter for elements.
    inline double get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, double value);
    inline void set_the_hole(int index);
  
    // Checking for the hole.
    inline bool is_the_hole(int index);
  
    // Copy operations
    MUST_USE_RESULT inline MaybeObject* Copy();
  
    // Garbage collection support.
    inline static int SizeFor(int length) {
      return kHeaderSize + length * kDoubleSize;
    }
  
    // Code Generation support.
    static int OffsetOfElementAt(int index) { return SizeFor(index); }
  
    inline static bool is_the_hole_nan(double value);
    inline static double hole_nan_as_double();
    inline static double canonical_not_the_hole_nan_as_double();
  
    // Casting.
    static inline FixedDoubleArray* cast(Object* obj);
  
    // Maximal allowed size, in bytes, of a single FixedDoubleArray.
    // 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) / kDoubleSize;
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void FixedDoubleArrayPrint() {
      FixedDoubleArrayPrint(stdout);
    }
    void FixedDoubleArrayPrint(FILE* out);
  #endif
  
  #ifdef DEBUG
    void FixedDoubleArrayVerify();
  #endif
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(FixedDoubleArray);
  };
  
  
  class IncrementalMarking;
  
  
  // DescriptorArrays are fixed arrays used to hold instance descriptors.
  // The format of the these objects is:
  // TODO(1399): It should be possible to make room for bit_field3 in the map
  //             without overloading the instance descriptors field in the map
  //             (and storing it in the DescriptorArray when the map has one).
  //   [0]: storage for bit_field3 for Map owning this object (Smi)
  //   [1]: point to a fixed array with (value, detail) pairs.
  //   [2]: next enumeration index (Smi), or pointer to small fixed array:
  //          [0]: next enumeration index (Smi)
  //          [1]: pointer to fixed array with enum cache
  //   [3]: first key
  //   [length() - 1]: last key
  //
  class DescriptorArray: public FixedArray {
   public:
    // Returns true for both shared empty_descriptor_array and for smis, which the
    // map uses to encode additional bit fields when the descriptor array is not
    // yet used.
    inline bool IsEmpty();
  
    // Returns the number of descriptors in the array.
    int number_of_descriptors() {
      ASSERT(length() > kFirstIndex || IsEmpty());
      int len = length();
      return len <= kFirstIndex ? 0 : len - 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()) {
        set(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);
    }
  
    // TODO(1399): It should be possible to make room for bit_field3 in the map
    //             without overloading the instance descriptors field in the map
    //             (and storing it in the DescriptorArray when the map has one).
    inline int bit_field3_storage();
    inline void set_bit_field3_storage(int value);
  
    // 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);
  
    class WhitenessWitness {
     public:
      inline explicit WhitenessWitness(DescriptorArray* array);
      inline ~WhitenessWitness();
  
     private:
      IncrementalMarking* marking_;
    };
  
    // Accessor for complete descriptor.
    inline void Get(int descriptor_number, Descriptor* desc);
    inline void Set(int descriptor_number,
                    Descriptor* desc,
                    const WhitenessWitness&);
  
    // Transfer complete descriptor from another descriptor array to
    // this one.
    inline void CopyFrom(int index,
                         DescriptorArray* src,
                         int src_index,
                         const WhitenessWitness&);
  
    // 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.
    MUST_USE_RESULT MaybeObject* 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.
    MUST_USE_RESULT MaybeObject* RemoveTransitions();
  
    // Sort the instance descriptors by the hash codes of their keys.
    // Does not check for duplicates.
    void SortUnchecked(const WhitenessWitness&);
  
    // Sort the instance descriptors by the hash codes of their keys.
    // Checks the result for duplicates.
    void Sort(const WhitenessWitness&);
  
    // Search the instance descriptors for given name.
    inline int Search(String* name);
  
    // As the above, but uses DescriptorLookupCache and updates it when
    // necessary.
    inline int SearchWithCache(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.
    MUST_USE_RESULT static MaybeObject* 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 kBitField3StorageIndex = 0;
    static const int kContentArrayIndex = 1;
    static const int kEnumerationIndexIndex = 2;
    static const int kFirstIndex = 3;
  
    // 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 kBitField3StorageOffset = FixedArray::kHeaderSize;
    static const int kContentArrayOffset = kBitField3StorageOffset + kPointerSize;
    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 OBJECT_PRINT
    // Print all the descriptors.
    inline void PrintDescriptors() {
      PrintDescriptors(stdout);
    }
    void PrintDescriptors(FILE* out);
  #endif
  
  #ifdef DEBUG
    // 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 NoIncrementalWriteBarrierSwap(
        FixedArray* array, int first, int second);
  
    // Swap descriptor first and second.
    inline void NoIncrementalWriteBarrierSwapDescriptors(
        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 == the_hole 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 Key>
  class BaseShape {
   public:
    static const bool UsesSeed = false;
    static uint32_t Hash(Key key) { return 0; }
    static uint32_t SeededHash(Key key, uint32_t seed) {
      ASSERT(UsesSeed);
      return Hash(key);
    }
    static uint32_t HashForObject(Key key, Object* object) { return 0; }
    static uint32_t SeededHashForObject(Key key, uint32_t seed, Object* object) {
      ASSERT(UsesSeed);
      return HashForObject(key, object);
    }
  };
  
  template<typename Shape, typename Key>
  class HashTable: public FixedArray {
   public:
    // Wrapper methods
    inline uint32_t Hash(Key key) {
      if (Shape::UsesSeed) {
        return Shape::SeededHash(key,
            GetHeap()->HashSeed());
      } else {
        return Shape::Hash(key);
      }
    }
  
    inline uint32_t HashForObject(Key key, Object* object) {
      if (Shape::UsesSeed) {
        return Shape::SeededHashForObject(key,
            GetHeap()->HashSeed(), object);
      } else {
        return Shape::HashForObject(key, object);
      }
    }
  
    // 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.
    MUST_USE_RESULT static MaybeObject* Allocate(
        int at_least_space_for,
        PretenureFlag pretenure = NOT_TENURED);
  
    // Computes the required capacity for a table holding the given
    // number of elements. May be more than HashTable::kMaxCapacity.
    static int ComputeCapacity(int at_least_space_for);
  
    // Returns the key at entry.
    Object* KeyAt(int entry) { return get(EntryToIndex(entry)); }
  
    // Tells whether k is a real key.  The hole and undefined are not allowed
    // as keys and can be used to indicate missing or deleted elements.
    bool IsKey(Object* k) {
      return !k->IsTheHole() && !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 kNotFound.
    inline int FindEntry(Key key);
    int FindEntry(Isolate* isolate, 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) {
      set(kNumberOfElementsIndex, Smi::FromInt(nof));
    }
  
    // Update the number of deleted elements in the hash table.
    void SetNumberOfDeletedElements(int nod) {
      set(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);
      set(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);
    }
  
    // Rehashes this hash-table into the new table.
    MUST_USE_RESULT MaybeObject* Rehash(HashTable* new_table, Key key);
  
    // Attempt to shrink hash table after removal of key.
    MUST_USE_RESULT MaybeObject* Shrink(Key key);
  
    // Ensure enough space for n additional elements.
    MUST_USE_RESULT MaybeObject* 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.
    MUST_USE_RESULT virtual MaybeObject* AsObject() = 0;
    // Required.
    virtual ~HashTableKey() {}
  };
  
  
  class SymbolTableShape : public BaseShape<HashTableKey*> {
   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);
    }
    MUST_USE_RESULT static inline MaybeObject* AsObject(HashTableKey* key) {
      return key->AsObject();
    }
  
    static const int kPrefixSize = 0;
    static const int kEntrySize = 1;
  };
  
  class SeqAsciiString;
  
  // 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.
    MUST_USE_RESULT MaybeObject* LookupSymbol(Vector<const char> str, Object** s);
    MUST_USE_RESULT MaybeObject* LookupAsciiSymbol(Vector<const char> str,
                                                   Object** s);
    MUST_USE_RESULT MaybeObject* LookupSubStringAsciiSymbol(
        Handle<SeqAsciiString> str,
        int from,
        int length,
        Object** s);
    MUST_USE_RESULT MaybeObject* LookupTwoByteSymbol(Vector<const uc16> str,
                                                     Object** s);
    MUST_USE_RESULT MaybeObject* 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:
    MUST_USE_RESULT MaybeObject* LookupKey(HashTableKey* key, Object** s);
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(SymbolTable);
  };
  
  
  class MapCacheShape : public BaseShape<HashTableKey*> {
   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);
    }
  
    MUST_USE_RESULT static inline MaybeObject* 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);
    MUST_USE_RESULT MaybeObject* 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.
    // Returns false if the put wasn't performed due to property being read only.
    // Returns true on successful put.
    bool ValueAtPut(int entry, Object* value) {
      // Check that this value can actually be written.
      PropertyDetails details = DetailsAt(entry);
      // If a value has not been initilized we allow writing to it even if
      // it is read only (a declared const that has not been initialized).
      if (details.IsReadOnly() && !ValueAt(entry)->IsTheHole()) {
        return false;
      }
      this->set(HashTable<Shape, Key>::EntryToIndex(entry) + 1, value);
      return true;
    }
  
    // 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);
  
    // Attempt to shrink the dictionary after deletion of key.
    MUST_USE_RESULT MaybeObject* Shrink(Key key);
  
    // 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();
  
    enum SortMode { UNSORTED, SORTED };
    // Copies keys to preallocated fixed array.
    void CopyKeysTo(FixedArray* storage,
                    PropertyAttributes filter,
                    SortMode sort_mode);
    // Fill in details for properties into storage.
    void CopyKeysTo(FixedArray* storage, int index, SortMode sort_mode);
  
    // Accessors for next enumeration index.
    void SetNextEnumerationIndex(int index) {
      this->set(kNextEnumerationIndexIndex, Smi::FromInt(index));
    }
  
    int NextEnumerationIndex() {
      return Smi::cast(FixedArray::get(kNextEnumerationIndexIndex))->value();
    }
  
    // Returns a new array for dictionary usage. Might return Failure.
    MUST_USE_RESULT static MaybeObject* Allocate(int at_least_space_for);
  
    // Ensure enough space for n additional elements.
    MUST_USE_RESULT MaybeObject* EnsureCapacity(int n, Key key);
  
  #ifdef OBJECT_PRINT
    inline void Print() {
      Print(stdout);
    }
    void Print(FILE* out);
  #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);
    inline void SetEntry(int entry,
                         Object* key,
                         Object* value,
                         PropertyDetails details);
  
    MUST_USE_RESULT MaybeObject* Add(Key key,
                                     Object* value,
                                     PropertyDetails details);
  
   protected:
    // Generic at put operation.
    MUST_USE_RESULT MaybeObject* AtPut(Key key, Object* value);
  
    // Add entry to dictionary.
    MUST_USE_RESULT MaybeObject* AddEntry(Key key,
                                          Object* value,
                                          PropertyDetails details,
                                          uint32_t hash);
  
    // Generate new enumeration indices to avoid enumeration index overflow.
    MUST_USE_RESULT MaybeObject* GenerateNewEnumerationIndices();
    static const int kMaxNumberKeyIndex =
        HashTable<Shape, Key>::kPrefixStartIndex;
    static const int kNextEnumerationIndexIndex = kMaxNumberKeyIndex + 1;
  };
  
  
  class StringDictionaryShape : public BaseShape<String*> {
   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);
    MUST_USE_RESULT static inline MaybeObject* 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.
    MUST_USE_RESULT MaybeObject* TransformPropertiesToFastFor(
        JSObject* obj,
        int unused_property_fields);
  
    // Find entry for key, otherwise return kNotFound. Optimized version of
    // HashTable::FindEntry.
    int FindEntry(String* key);
  };
  
  
  class NumberDictionaryShape : public BaseShape<uint32_t> {
   public:
    static inline bool IsMatch(uint32_t key, Object* other);
    MUST_USE_RESULT static inline MaybeObject* AsObject(uint32_t key);
    static const int kEntrySize = 3;
    static const bool kIsEnumerable = false;
  };
  
  
  class SeededNumberDictionaryShape : public NumberDictionaryShape {
   public:
    static const bool UsesSeed = true;
    static const int kPrefixSize = 2;
  
    static inline uint32_t SeededHash(uint32_t key, uint32_t seed);
    static inline uint32_t SeededHashForObject(uint32_t key,
                                               uint32_t seed,
                                               Object* object);
  };
  
  
  class UnseededNumberDictionaryShape : public NumberDictionaryShape {
   public:
    static const int kPrefixSize = 0;
  
    static inline uint32_t Hash(uint32_t key);
    static inline uint32_t HashForObject(uint32_t key, Object* object);
  };
  
  
  class SeededNumberDictionary
      : public Dictionary<SeededNumberDictionaryShape, uint32_t> {
   public:
    static SeededNumberDictionary* cast(Object* obj) {
      ASSERT(obj->IsDictionary());
      return reinterpret_cast<SeededNumberDictionary*>(obj);
    }
  
    // Type specific at put (default NONE attributes is used when adding).
    MUST_USE_RESULT MaybeObject* AtNumberPut(uint32_t key, Object* value);
    MUST_USE_RESULT MaybeObject* AddNumberEntry(uint32_t key,
                                                Object* value,
                                                PropertyDetails details);
  
    // Set an existing entry or add a new one if needed.
    // Return the updated dictionary.
    MUST_USE_RESULT static Handle<SeededNumberDictionary> Set(
        Handle<SeededNumberDictionary> dictionary,
        uint32_t index,
        Handle<Object> value,
        PropertyDetails details);
  
    MUST_USE_RESULT MaybeObject* 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();
  
    // Bit masks.
    static const int kRequiresSlowElementsMask = 1;
    static const int kRequiresSlowElementsTagSize = 1;
    static const uint32_t kRequiresSlowElementsLimit = (1 << 29) - 1;
  };
  
  
  class UnseededNumberDictionary
      : public Dictionary<UnseededNumberDictionaryShape, uint32_t> {
   public:
    static UnseededNumberDictionary* cast(Object* obj) {
      ASSERT(obj->IsDictionary());
      return reinterpret_cast<UnseededNumberDictionary*>(obj);
    }
  
    // Type specific at put (default NONE attributes is used when adding).
    MUST_USE_RESULT MaybeObject* AtNumberPut(uint32_t key, Object* value);
    MUST_USE_RESULT MaybeObject* AddNumberEntry(uint32_t key, Object* value);
  
    // Set an existing entry or add a new one if needed.
    // Return the updated dictionary.
    MUST_USE_RESULT static Handle<UnseededNumberDictionary> Set(
        Handle<UnseededNumberDictionary> dictionary,
        uint32_t index,
        Handle<Object> value);
  
    MUST_USE_RESULT MaybeObject* Set(uint32_t key, Object* value);
  };
  
  
  template <int entrysize>
  class ObjectHashTableShape : public BaseShape<Object*> {
   public:
    static inline bool IsMatch(Object* key, Object* other);
    static inline uint32_t Hash(Object* key);
    static inline uint32_t HashForObject(Object* key, Object* object);
    MUST_USE_RESULT static inline MaybeObject* AsObject(Object* key);
    static const int kPrefixSize = 0;
    static const int kEntrySize = entrysize;
  };
  
  
  // ObjectHashSet holds keys that are arbitrary objects by using the identity
  // hash of the key for hashing purposes.
  class ObjectHashSet: public HashTable<ObjectHashTableShape<1>, Object*> {
   public:
    static inline ObjectHashSet* cast(Object* obj) {
      ASSERT(obj->IsHashTable());
      return reinterpret_cast<ObjectHashSet*>(obj);
    }
  
    // Looks up whether the given key is part of this hash set.
    bool Contains(Object* key);
  
    // Adds the given key to this hash set.
    MUST_USE_RESULT MaybeObject* Add(Object* key);
  
    // Removes the given key from this hash set.
    MUST_USE_RESULT MaybeObject* Remove(Object* key);
  };
  
  
  // ObjectHashTable maps keys that are arbitrary objects to object values by
  // using the identity hash of the key for hashing purposes.
  class ObjectHashTable: public HashTable<ObjectHashTableShape<2>, Object*> {
   public:
    static inline ObjectHashTable* cast(Object* obj) {
      ASSERT(obj->IsHashTable());
      return reinterpret_cast<ObjectHashTable*>(obj);
    }
  
    // Looks up the value associated with the given key. The undefined value is
    // returned in case the key is not present.
    Object* Lookup(Object* key);
  
    // Adds (or overwrites) the value associated with the given key. Mapping a
    // key to the undefined value causes removal of the whole entry.
    MUST_USE_RESULT MaybeObject* Put(Object* key, Object* value);
  
   private:
    friend class MarkCompactCollector;
  
    void AddEntry(int entry, Object* key, Object* value);
    void RemoveEntry(int entry);
  
    // Returns the index to the value of an entry.
    static inline int EntryToValueIndex(int entry) {
      return EntryToIndex(entry) + 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
  
    static const int kFactoryOffset = kHeaderSize;
    static const int kFingerOffset = kFactoryOffset + kPointerSize;
    static const int kCacheSizeOffset = kFingerOffset + kPointerSize;
  
    inline void MakeZeroSize();
    inline void Clear();
  
    inline int size();
    inline void set_size(int size);
    inline int finger_index();
    inline void set_finger_index(int finger_index);
  
    // Casting
    static inline JSFunctionResultCache* cast(Object* obj);
  
  #ifdef DEBUG
    void JSFunctionResultCacheVerify();
  #endif
  };
  
  
  // ScopeInfo represents information about different scopes of a source
  // program  and the allocation of the scope's variables. Scope information
  // is stored in a compressed form in ScopeInfo objects and is used
  // at runtime (stack dumps, deoptimization, etc.).
  
  // This object provides quick access to scope info details for runtime
  // routines.
  class ScopeInfo : public FixedArray {
   public:
    static inline ScopeInfo* cast(Object* object);
  
    // Return the type of this scope.
    ScopeType Type();
  
    // Does this scope call eval?
    bool CallsEval();
  
    // Return the language mode of this scope.
    LanguageMode language_mode();
  
    // Does this scope make a non-strict eval call?
    bool CallsNonStrictEval() {
      return CallsEval() && (language_mode() == CLASSIC_MODE);
    }
  
    // Return the total number of locals allocated on the stack and in the
    // context. This includes the parameters that are allocated in the context.
    int LocalCount();
  
    // Return the number of stack slots for code. This number consists of two
    // parts:
    //  1. One stack slot per stack allocated local.
    //  2. One stack slot for the function name if it is stack allocated.
    int StackSlotCount();
  
    // Return the number of context slots for code if a context is allocated. This
    // number consists of three parts:
    //  1. Size of fixed header for every context: Context::MIN_CONTEXT_SLOTS
    //  2. One context slot per context allocated local.
    //  3. One context slot for the function name if it is context allocated.
    // Parameters allocated in the context count as context allocated locals. If
    // no contexts are allocated for this scope ContextLength returns 0.
    int ContextLength();
  
    // Is this scope the scope of a named function expression?
    bool HasFunctionName();
  
    // Return if this has context allocated locals.
    bool HasHeapAllocatedLocals();
  
    // Return if contexts are allocated for this scope.
    bool HasContext();
  
    // Return the function_name if present.
    String* FunctionName();
  
    // Return the name of the given parameter.
    String* ParameterName(int var);
  
    // Return the name of the given local.
    String* LocalName(int var);
  
    // Return the name of the given stack local.
    String* StackLocalName(int var);
  
    // Return the name of the given context local.
    String* ContextLocalName(int var);
  
    // Return the mode of the given context local.
    VariableMode ContextLocalMode(int var);
  
    // Return the initialization flag of the given context local.
    InitializationFlag ContextLocalInitFlag(int var);
  
    // Lookup support for serialized scope info. Returns the
    // the stack slot index for a given slot name if the slot is
    // present; otherwise returns a value < 0. The name must be a symbol
    // (canonicalized).
    int StackSlotIndex(String* name);
  
    // Lookup support for serialized scope info. Returns the
    // context slot index for a given slot name if the slot is present; otherwise
    // returns a value < 0. The name must be a symbol (canonicalized).
    // If the slot is present and mode != NULL, sets *mode to the corresponding
    // mode for that variable.
    int ContextSlotIndex(String* name,
                         VariableMode* mode,
                         InitializationFlag* init_flag);
  
    // Lookup support for serialized scope info. Returns the
    // parameter index for a given parameter name if the parameter is present;
    // otherwise returns a value < 0. The name must be a symbol (canonicalized).
    int ParameterIndex(String* name);
  
    // Lookup support for serialized scope info. Returns the
    // function context slot index if the function name is present (named
    // function expressions, only), otherwise returns a value < 0. The name
    // must be a symbol (canonicalized).
    int FunctionContextSlotIndex(String* name, VariableMode* mode);
  
    static Handle<ScopeInfo> Create(Scope* scope);
  
    // Serializes empty scope info.
    static ScopeInfo* Empty();
  
  #ifdef DEBUG
    void Print();
  #endif
  
    // The layout of the static part of a ScopeInfo is as follows. Each entry is
    // numeric and occupies one array slot.
    // 1. A set of properties of the scope
    // 2. The number of parameters. This only applies to function scopes. For
    //    non-function scopes this is 0.
    // 3. The number of non-parameter variables allocated on the stack.
    // 4. The number of non-parameter and parameter variables allocated in the
    //    context.
  #define FOR_EACH_NUMERIC_FIELD(V)          \
    V(Flags)                                 \
    V(ParameterCount)                        \
    V(StackLocalCount)                       \
    V(ContextLocalCount)
  
  #define FIELD_ACCESSORS(name)                            \
    void Set##name(int value) {                            \
      set(k##name, Smi::FromInt(value));                   \
    }                                                      \
    int name() {                                           \
      if (length() > 0) {                                  \
        return Smi::cast(get(k##name))->value();           \
      } else {                                             \
        return 0;                                          \
      }                                                    \
    }
    FOR_EACH_NUMERIC_FIELD(FIELD_ACCESSORS)
  #undef FIELD_ACCESSORS
  
   private:
    enum {
  #define DECL_INDEX(name) k##name,
    FOR_EACH_NUMERIC_FIELD(DECL_INDEX)
  #undef DECL_INDEX
  #undef FOR_EACH_NUMERIC_FIELD
    kVariablePartIndex
    };
  
    // The layout of the variable part of a ScopeInfo is as follows:
    // 1. ParameterEntries:
    //    This part stores the names of the parameters for function scopes. One
    //    slot is used per parameter, so in total this part occupies
    //    ParameterCount() slots in the array. For other scopes than function
    //    scopes ParameterCount() is 0.
    // 2. StackLocalEntries:
    //    Contains the names of local variables that are allocated on the stack,
    //    in increasing order of the stack slot index. One slot is used per stack
    //    local, so in total this part occupies StackLocalCount() slots in the
    //    array.
    // 3. ContextLocalNameEntries:
    //    Contains the names of local variables and parameters that are allocated
    //    in the context. They are stored in increasing order of the context slot
    //    index starting with Context::MIN_CONTEXT_SLOTS. One slot is used per
    //    context local, so in total this part occupies ContextLocalCount() slots
    //    in the array.
    // 4. ContextLocalInfoEntries:
    //    Contains the variable modes and initialization flags corresponding to
    //    the context locals in ContextLocalNameEntries. One slot is used per
    //    context local, so in total this part occupies ContextLocalCount()
    //    slots in the array.
    // 5. FunctionNameEntryIndex:
    //    If the scope belongs to a named function expression this part contains
    //    information about the function variable. It always occupies two array
    //    slots:  a. The name of the function variable.
    //            b. The context or stack slot index for the variable.
    int ParameterEntriesIndex();
    int StackLocalEntriesIndex();
    int ContextLocalNameEntriesIndex();
    int ContextLocalInfoEntriesIndex();
    int FunctionNameEntryIndex();
  
    // Location of the function variable for named function expressions.
    enum FunctionVariableInfo {
      NONE,     // No function name present.
      STACK,    // Function
      CONTEXT,
      UNUSED
    };
  
    // Properties of scopes.
    class TypeField:             public BitField<ScopeType,            0, 3> {};
    class CallsEvalField:        public BitField<bool,                 3, 1> {};
    class LanguageModeField:     public BitField<LanguageMode,         4, 2> {};
    class FunctionVariableField: public BitField<FunctionVariableInfo, 6, 2> {};
    class FunctionVariableMode:  public BitField<VariableMode,         8, 3> {};
  
    // BitFields representing the encoded information for context locals in the
    // ContextLocalInfoEntries part.
    class ContextLocalMode:      public BitField<VariableMode,         0, 3> {};
    class ContextLocalInitFlag:  public BitField<InitializationFlag,   3, 1> {};
  };
  
  
  // The cache for maps used by normalized (dictionary mode) objects.
  // Such maps do not have property descriptors, so a typical program
  // needs very limited number of distinct normalized maps.
  class NormalizedMapCache: public FixedArray {
   public:
    static const int kEntries = 64;
  
    MUST_USE_RESULT MaybeObject* Get(JSObject* object,
                                     PropertyNormalizationMode mode);
  
    void Clear();
  
    // Casting
    static inline NormalizedMapCache* cast(Object* obj);
  
  #ifdef DEBUG
    void NormalizedMapCacheVerify();
  #endif
  };
  
  
  // ByteArray represents fixed sized byte arrays.  Used for the relocation info
  // that is attached to code objects.
  class ByteArray: public FixedArrayBase {
   public:
    inline int Size() { return RoundUp(length() + kHeaderSize, kPointerSize); }
  
    // 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_POINTER_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.
    inline int ByteArraySize() {
      return SizeFor(this->length());
    }
  #ifdef OBJECT_PRINT
    inline void ByteArrayPrint() {
      ByteArrayPrint(stdout);
    }
    void ByteArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ByteArrayVerify();
  #endif
  
    // Layout description.
    static const int kAlignedSize = OBJECT_POINTER_ALIGN(kHeaderSize);
  
    // 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);
  };
  
  
  // FreeSpace represents fixed sized areas of the heap that are not currently in
  // use.  Used by the heap and GC.
  class FreeSpace: public HeapObject {
   public:
    // [size]: size of the free space including the header.
    inline int size();
    inline void set_size(int value);
  
    inline int Size() { return size(); }
  
    // Casting.
    static inline FreeSpace* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void FreeSpacePrint() {
      FreeSpacePrint(stdout);
    }
    void FreeSpacePrint(FILE* out);
  #endif
  #ifdef DEBUG
    void FreeSpaceVerify();
  #endif
  
    // Layout description.
    // Size is smi tagged when it is stored.
    static const int kSizeOffset = HeapObject::kHeaderSize;
    static const int kHeaderSize = kSizeOffset + kPointerSize;
  
    static const int kAlignedSize = OBJECT_POINTER_ALIGN(kHeaderSize);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(FreeSpace);
  };
  
  
  // 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 FixedArrayBase {
   public:
    inline bool is_the_hole(int index) { return false; }
  
    // [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 =
        POINTER_SIZE_ALIGN(FixedArrayBase::kLengthOffset + kPointerSize);
    static const int kHeaderSize = kExternalPointerOffset + kPointerSize;
    static const int kAlignedSize = OBJECT_POINTER_ALIGN(kHeaderSize);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalArray);
  };
  
  
  // A ExternalPixelArray 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 ExternalPixelArray: public ExternalArray {
   public:
    inline uint8_t* external_pixel_pointer();
  
    // Setter and getter.
    inline uint8_t get_scalar(int index);
    inline MaybeObject* 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 ExternalPixelArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalPixelArrayPrint() {
      ExternalPixelArrayPrint(stdout);
    }
    void ExternalPixelArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalPixelArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalPixelArray);
  };
  
  
  class ExternalByteArray: public ExternalArray {
   public:
    // Setter and getter.
    inline int8_t get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, int8_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalByteArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalByteArrayPrint() {
      ExternalByteArrayPrint(stdout);
    }
    void ExternalByteArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalByteArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalByteArray);
  };
  
  
  class ExternalUnsignedByteArray: public ExternalArray {
   public:
    // Setter and getter.
    inline uint8_t get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, uint8_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalUnsignedByteArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalUnsignedByteArrayPrint() {
      ExternalUnsignedByteArrayPrint(stdout);
    }
    void ExternalUnsignedByteArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalUnsignedByteArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalUnsignedByteArray);
  };
  
  
  class ExternalShortArray: public ExternalArray {
   public:
    // Setter and getter.
    inline int16_t get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, int16_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalShortArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalShortArrayPrint() {
      ExternalShortArrayPrint(stdout);
    }
    void ExternalShortArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalShortArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalShortArray);
  };
  
  
  class ExternalUnsignedShortArray: public ExternalArray {
   public:
    // Setter and getter.
    inline uint16_t get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, uint16_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalUnsignedShortArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalUnsignedShortArrayPrint() {
      ExternalUnsignedShortArrayPrint(stdout);
    }
    void ExternalUnsignedShortArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalUnsignedShortArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalUnsignedShortArray);
  };
  
  
  class ExternalIntArray: public ExternalArray {
   public:
    // Setter and getter.
    inline int32_t get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, int32_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalIntArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalIntArrayPrint() {
      ExternalIntArrayPrint(stdout);
    }
    void ExternalIntArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalIntArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalIntArray);
  };
  
  
  class ExternalUnsignedIntArray: public ExternalArray {
   public:
    // Setter and getter.
    inline uint32_t get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, uint32_t value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalUnsignedIntArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalUnsignedIntArrayPrint() {
      ExternalUnsignedIntArrayPrint(stdout);
    }
    void ExternalUnsignedIntArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalUnsignedIntArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalUnsignedIntArray);
  };
  
  
  class ExternalFloatArray: public ExternalArray {
   public:
    // Setter and getter.
    inline float get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, float value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalFloatArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalFloatArrayPrint() {
      ExternalFloatArrayPrint(stdout);
    }
    void ExternalFloatArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ExternalFloatArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalFloatArray);
  };
  
  
  class ExternalDoubleArray: public ExternalArray {
   public:
    // Setter and getter.
    inline double get_scalar(int index);
    inline MaybeObject* get(int index);
    inline void set(int index, double value);
  
    // This accessor applies the correct conversion from Smi, HeapNumber
    // and undefined.
    MaybeObject* SetValue(uint32_t index, Object* value);
  
    // Casting.
    static inline ExternalDoubleArray* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void ExternalDoubleArrayPrint() {
      ExternalDoubleArrayPrint(stdout);
    }
    void ExternalDoubleArrayPrint(FILE* out);
  #endif  // OBJECT_PRINT
  #ifdef DEBUG
    void ExternalDoubleArrayVerify();
  #endif  // DEBUG
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ExternalDoubleArray);
  };
  
  
  // DeoptimizationInputData is a fixed array used to hold the deoptimization
  // data for code generated by the Hydrogen/Lithium compiler.  It also
  // contains information about functions that were inlined.  If N different
  // functions were inlined then first N elements of the literal array will
  // contain these functions.
  //
  // It can be empty.
  class DeoptimizationInputData: public FixedArray {
   public:
    // Layout description.  Indices in the array.
    static const int kTranslationByteArrayIndex = 0;
    static const int kInlinedFunctionCountIndex = 1;
    static const int kLiteralArrayIndex = 2;
    static const int kOsrAstIdIndex = 3;
    static const int kOsrPcOffsetIndex = 4;
    static const int kFirstDeoptEntryIndex = 5;
  
    // Offsets of deopt entry elements relative to the start of the entry.
    static const int kAstIdOffset = 0;
    static const int kTranslationIndexOffset = 1;
    static const int kArgumentsStackHeightOffset = 2;
    static const int kPcOffset = 3;
    static const int kDeoptEntrySize = 4;
  
    // Simple element accessors.
  #define DEFINE_ELEMENT_ACCESSORS(name, type)      \
    type* name() {                                  \
      return type::cast(get(k##name##Index));       \
    }                                               \
    void Set##name(type* value) {                   \
      set(k##name##Index, value);                   \
    }
  
    DEFINE_ELEMENT_ACCESSORS(TranslationByteArray, ByteArray)
    DEFINE_ELEMENT_ACCESSORS(InlinedFunctionCount, Smi)
    DEFINE_ELEMENT_ACCESSORS(LiteralArray, FixedArray)
    DEFINE_ELEMENT_ACCESSORS(OsrAstId, Smi)
    DEFINE_ELEMENT_ACCESSORS(OsrPcOffset, Smi)
  
  #undef DEFINE_ELEMENT_ACCESSORS
  
    // Accessors for elements of the ith deoptimization entry.
  #define DEFINE_ENTRY_ACCESSORS(name, type)                       \
    type* name(int i) {                                            \
      return type::cast(get(IndexForEntry(i) + k##name##Offset));  \
    }                                                              \
    void Set##name(int i, type* value) {                           \
      set(IndexForEntry(i) + k##name##Offset, value);              \
    }
  
    DEFINE_ENTRY_ACCESSORS(AstId, Smi)
    DEFINE_ENTRY_ACCESSORS(TranslationIndex, Smi)
    DEFINE_ENTRY_ACCESSORS(ArgumentsStackHeight, Smi)
    DEFINE_ENTRY_ACCESSORS(Pc, Smi)
  
  #undef DEFINE_ENTRY_ACCESSORS
  
    int DeoptCount() {
      return (length() - kFirstDeoptEntryIndex) / kDeoptEntrySize;
    }
  
    // Allocates a DeoptimizationInputData.
    MUST_USE_RESULT static MaybeObject* Allocate(int deopt_entry_count,
                                                 PretenureFlag pretenure);
  
    // Casting.
    static inline DeoptimizationInputData* cast(Object* obj);
  
  #ifdef ENABLE_DISASSEMBLER
    void DeoptimizationInputDataPrint(FILE* out);
  #endif
  
   private:
    static int IndexForEntry(int i) {
      return kFirstDeoptEntryIndex + (i * kDeoptEntrySize);
    }
  
    static int LengthFor(int entry_count) {
      return IndexForEntry(entry_count);
    }
  };
  
  
  // DeoptimizationOutputData is a fixed array used to hold the deoptimization
  // data for code generated by the full compiler.
  // The format of the these objects is
  //   [i * 2]: Ast ID for ith deoptimization.
  //   [i * 2 + 1]: PC and state of ith deoptimization
  class DeoptimizationOutputData: public FixedArray {
   public:
    int DeoptPoints() { return length() / 2; }
    Smi* AstId(int index) { return Smi::cast(get(index * 2)); }
    void SetAstId(int index, Smi* id) { set(index * 2, id); }
    Smi* PcAndState(int index) { return Smi::cast(get(1 + index * 2)); }
    void SetPcAndState(int index, Smi* offset) { set(1 + index * 2, offset); }
  
    static int LengthOfFixedArray(int deopt_points) {
      return deopt_points * 2;
    }
  
    // Allocates a DeoptimizationOutputData.
    MUST_USE_RESULT static MaybeObject* Allocate(int number_of_deopt_points,
                                                 PretenureFlag pretenure);
  
    // Casting.
    static inline DeoptimizationOutputData* cast(Object* obj);
  
  #if defined(OBJECT_PRINT) || defined(ENABLE_DISASSEMBLER)
    void DeoptimizationOutputDataPrint(FILE* out);
  #endif
  };
  
  
  class SafepointEntry;
  
  
  // 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.
    // FLAGS_MIN_VALUE and FLAGS_MAX_VALUE are specified to ensure that
    // enumeration type has correct value range (see Issue 830 for more details).
    enum Flags {
      FLAGS_MIN_VALUE = kMinInt,
      FLAGS_MAX_VALUE = kMaxInt
    };
  
    enum Kind {
      FUNCTION,
      OPTIMIZED_FUNCTION,
      STUB,
      BUILTIN,
      LOAD_IC,
      KEYED_LOAD_IC,
      CALL_IC,
      KEYED_CALL_IC,
      STORE_IC,
      KEYED_STORE_IC,
      UNARY_OP_IC,
      BINARY_OP_IC,
      COMPARE_IC,
      TO_BOOLEAN_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 = TO_BOOLEAN_IC
    };
  
    enum {
      NUMBER_OF_KINDS = LAST_IC_KIND + 1
    };
  
    typedef int ExtraICState;
  
    static const ExtraICState kNoExtraICState = 0;
  
  #ifdef ENABLE_DISASSEMBLER
    // Printing
    static const char* Kind2String(Kind kind);
    static const char* ICState2String(InlineCacheState state);
    static const char* PropertyType2String(PropertyType type);
    static void PrintExtraICState(FILE* out, Kind kind, ExtraICState extra);
    inline void Disassemble(const char* name) {
      Disassemble(name, stdout);
    }
    void Disassemble(const char* name, FILE* out);
  #endif  // ENABLE_DISASSEMBLER
  
    // [instruction_size]: Size of the native instructions
    inline int instruction_size();
    inline void set_instruction_size(int value);
  
    // [relocation_info]: Code relocation information
    DECL_ACCESSORS(relocation_info, ByteArray)
    void InvalidateRelocation();
  
    // [handler_table]: Fixed array containing offsets of exception handlers.
    DECL_ACCESSORS(handler_table, FixedArray)
  
    // [deoptimization_data]: Array containing data for deopt.
    DECL_ACCESSORS(deoptimization_data, FixedArray)
  
    // [gc_metadata]: Field used to hold GC related metadata. The contents of this
    // field does not have to be traced during garbage collection since
    // it is only used by the garbage collector itself.
    DECL_ACCESSORS(gc_metadata, Object)
  
    // Unchecked accessors to be used during GC.
    inline ByteArray* unchecked_relocation_info();
    inline FixedArray* unchecked_deoptimization_data();
  
    inline int relocation_size();
  
    // [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 ExtraICState extra_ic_state();  // 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; }
    inline bool is_keyed_call_stub() { return kind() == KEYED_CALL_IC; }
    inline bool is_unary_op_stub() { return kind() == UNARY_OP_IC; }
    inline bool is_binary_op_stub() { return kind() == BINARY_OP_IC; }
    inline bool is_compare_ic_stub() { return kind() == COMPARE_IC; }
    inline bool is_to_boolean_ic_stub() { return kind() == TO_BOOLEAN_IC; }
  
    // [major_key]: For kind STUB or BINARY_OP_IC, the major key.
    inline int major_key();
    inline void set_major_key(int value);
  
    // For stubs, tells whether they should always exist, so that they can be
    // called from other stubs.
    inline bool is_pregenerated();
    inline void set_is_pregenerated(bool value);
  
    // [optimizable]: For FUNCTION kind, tells if it is optimizable.
    inline bool optimizable();
    inline void set_optimizable(bool value);
  
    // [has_deoptimization_support]: For FUNCTION kind, tells if it has
    // deoptimization support.
    inline bool has_deoptimization_support();
    inline void set_has_deoptimization_support(bool value);
  
    // [has_debug_break_slots]: For FUNCTION kind, tells if it has
    // been compiled with debug break slots.
    inline bool has_debug_break_slots();
    inline void set_has_debug_break_slots(bool value);
  
    // [compiled_with_optimizing]: For FUNCTION kind, tells if it has
    // been compiled with IsOptimizing set to true.
    inline bool is_compiled_optimizable();
    inline void set_compiled_optimizable(bool value);
  
    // [allow_osr_at_loop_nesting_level]: For FUNCTION kind, tells for
    // how long the function has been marked for OSR and therefore which
    // level of loop nesting we are willing to do on-stack replacement
    // for.
    inline void set_allow_osr_at_loop_nesting_level(int level);
    inline int allow_osr_at_loop_nesting_level();
  
    // [stack_slots]: For kind OPTIMIZED_FUNCTION, the number of stack slots
    // reserved in the code prologue.
    inline unsigned stack_slots();
    inline void set_stack_slots(unsigned slots);
  
    // [safepoint_table_start]: For kind OPTIMIZED_CODE, the offset in
    // the instruction stream where the safepoint table starts.
    inline unsigned safepoint_table_offset();
    inline void set_safepoint_table_offset(unsigned offset);
  
    // [stack_check_table_start]: For kind FUNCTION, the offset in the
    // instruction stream where the stack check table starts.
    inline unsigned stack_check_table_offset();
    inline void set_stack_check_table_offset(unsigned offset);
  
    // [check type]: For kind CALL_IC, tells how to check if the
    // receiver is valid for the given call.
    inline CheckType check_type();
    inline void set_check_type(CheckType value);
  
    // [type-recording unary op type]: For kind UNARY_OP_IC.
    inline byte unary_op_type();
    inline void set_unary_op_type(byte value);
  
    // [type-recording binary op type]: For kind BINARY_OP_IC.
    inline byte binary_op_type();
    inline void set_binary_op_type(byte value);
    inline byte binary_op_result_type();
    inline void set_binary_op_result_type(byte value);
  
    // [compare state]: For kind COMPARE_IC, tells what state the stub is in.
    inline byte compare_state();
    inline void set_compare_state(byte value);
  
    // [to_boolean_foo]: For kind TO_BOOLEAN_IC tells what state the stub is in.
    inline byte to_boolean_state();
    inline void set_to_boolean_state(byte value);
  
    // For kind STUB, major_key == CallFunction, tells whether there is
    // a function cache in the instruction stream.
    inline bool has_function_cache();
    inline void set_has_function_cache(bool flag);
  
    // Get the safepoint entry for the given pc.
    SafepointEntry GetSafepointEntry(Address pc);
  
    // Mark this code object as not having a stack check table.  Assumes kind
    // is FUNCTION.
    void SetNoStackCheckTable();
  
    // Find the first map in an IC stub.
    Map* FindFirstMap();
  
    // Flags operations.
    static inline Flags ComputeFlags(
        Kind kind,
        InlineCacheState ic_state = UNINITIALIZED,
        ExtraICState extra_ic_state = kNoExtraICState,
        PropertyType type = NORMAL,
        int argc = -1,
        InlineCacheHolderFlag holder = OWN_MAP);
  
    static inline Flags ComputeMonomorphicFlags(
        Kind kind,
        PropertyType type,
        ExtraICState extra_ic_state = kNoExtraICState,
        InlineCacheHolderFlag holder = OWN_MAP,
        int argc = -1);
  
    static inline InlineCacheState ExtractICStateFromFlags(Flags flags);
    static inline PropertyType ExtractTypeFromFlags(Flags flags);
    static inline Kind ExtractKindFromFlags(Flags flags);
    static inline InlineCacheHolderFlag ExtractCacheHolderFromFlags(Flags flags);
    static inline ExtraICState ExtractExtraICStateFromFlags(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);
  
    // Convert an entry address into an object.
    static inline Object* GetObjectFromEntryAddress(Address location_of_address);
  
    // Returns the address of the first instruction.
    inline byte* instruction_start();
  
    // Returns the address right after the last instruction.
    inline byte* instruction_end();
  
    // 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);
  
    // 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 (used for allocation).
    static int SizeFor(int body_size) {
      ASSERT_SIZE_TAG_ALIGNED(body_size);
      return RoundUp(kHeaderSize + body_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()); }
    inline void CodeIterateBody(ObjectVisitor* v);
  
    template<typename StaticVisitor>
    inline void CodeIterateBody(Heap* heap);
  #ifdef OBJECT_PRINT
    inline void CodePrint() {
      CodePrint(stdout);
    }
    void CodePrint(FILE* out);
  #endif
  #ifdef DEBUG
    void CodeVerify();
  #endif
  
    // Max loop nesting marker used to postpose OSR. We don't take loop
    // nesting that is deeper than 5 levels into account.
    static const int kMaxLoopNestingMarker = 6;
  
    // Layout description.
    static const int kInstructionSizeOffset = HeapObject::kHeaderSize;
    static const int kRelocationInfoOffset = kInstructionSizeOffset + kIntSize;
    static const int kHandlerTableOffset = kRelocationInfoOffset + kPointerSize;
    static const int kDeoptimizationDataOffset =
        kHandlerTableOffset + kPointerSize;
    static const int kGCMetadataOffset = kDeoptimizationDataOffset + kPointerSize;
    static const int kFlagsOffset = kGCMetadataOffset + kPointerSize;
  
    static const int kKindSpecificFlagsOffset = kFlagsOffset + kIntSize;
    static const int kKindSpecificFlagsSize = 2 * kIntSize;
  
    static const int kHeaderPaddingStart = kKindSpecificFlagsOffset +
        kKindSpecificFlagsSize;
  
    // Add padding to align the instruction start following right after
    // the Code object header.
    static const int kHeaderSize =
        (kHeaderPaddingStart + kCodeAlignmentMask) & ~kCodeAlignmentMask;
  
    // Byte offsets within kKindSpecificFlagsOffset.
    static const int kStubMajorKeyOffset = kKindSpecificFlagsOffset;
    static const int kOptimizableOffset = kKindSpecificFlagsOffset;
    static const int kStackSlotsOffset = kKindSpecificFlagsOffset;
    static const int kCheckTypeOffset = kKindSpecificFlagsOffset;
  
    static const int kUnaryOpTypeOffset = kStubMajorKeyOffset + 1;
    static const int kBinaryOpTypeOffset = kStubMajorKeyOffset + 1;
    static const int kCompareStateOffset = kStubMajorKeyOffset + 1;
    static const int kToBooleanTypeOffset = kStubMajorKeyOffset + 1;
    static const int kHasFunctionCacheOffset = kStubMajorKeyOffset + 1;
  
    static const int kFullCodeFlags = kOptimizableOffset + 1;
    class FullCodeFlagsHasDeoptimizationSupportField:
        public BitField<bool, 0, 1> {};  // NOLINT
    class FullCodeFlagsHasDebugBreakSlotsField: public BitField<bool, 1, 1> {};
    class FullCodeFlagsIsCompiledOptimizable: public BitField<bool, 2, 1> {};
  
    static const int kBinaryOpReturnTypeOffset = kBinaryOpTypeOffset + 1;
  
    static const int kAllowOSRAtLoopNestingLevelOffset = kFullCodeFlags + 1;
  
    static const int kSafepointTableOffsetOffset = kStackSlotsOffset + kIntSize;
    static const int kStackCheckTableOffsetOffset = kStackSlotsOffset + kIntSize;
  
    // Flags layout.  BitField<type, shift, size>.
    class ICStateField: public BitField<InlineCacheState, 0, 3> {};
    class TypeField: public BitField<PropertyType, 3, 4> {};
    class KindField: public BitField<Kind, 7, 4> {};
    class CacheHolderField: public BitField<InlineCacheHolderFlag, 11, 1> {};
    class ExtraICStateField: public BitField<ExtraICState, 12, 2> {};
    class IsPregeneratedField: public BitField<bool, 14, 1> {};
  
    // Signed field cannot be encoded using the BitField class.
    static const int kArgumentsCountShift = 15;
    static const int kArgumentsCountMask = ~((1 << kArgumentsCountShift) - 1);
  
    static const int kFlagsNotUsedInLookup =
        TypeField::kMask | CacheHolderField::kMask;
  
   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.
    // Size in bytes or kVariableSizeSentinel if instances do not have
    // a fixed 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);
  
    // Bit field 3.
    // TODO(1399): It should be possible to make room for bit_field3 in the map
    // without overloading the instance descriptors field (and storing it in the
    // DescriptorArray when the map has one).
    inline int bit_field3();
    inline void set_bit_field3(int 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 function has special prototype property. If not, prototype
    // property will not be created when accessed (will return undefined),
    // and construction from this function will not be allowed.
    inline void set_function_with_prototype(bool value);
    inline bool function_with_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(bool value);
    inline bool is_extensible();
  
    inline void set_elements_kind(ElementsKind elements_kind) {
      ASSERT(elements_kind < kElementsKindCount);
      ASSERT(kElementsKindCount <= (1 << kElementsKindBitCount));
      set_bit_field2((bit_field2() & ~kElementsKindMask) |
          (elements_kind << kElementsKindShift));
      ASSERT(this->elements_kind() == elements_kind);
    }
  
    inline ElementsKind elements_kind() {
      return static_cast<ElementsKind>(
          (bit_field2() & kElementsKindMask) >> kElementsKindShift);
    }
  
    // Tells whether the instance has fast elements that are only Smis.
    inline bool has_fast_smi_only_elements() {
      return elements_kind() == FAST_SMI_ONLY_ELEMENTS;
    }
  
    // Tells whether the instance has fast elements.
    inline bool has_fast_elements() {
      return elements_kind() == FAST_ELEMENTS;
    }
  
    inline bool has_fast_double_elements() {
      return elements_kind() == FAST_DOUBLE_ELEMENTS;
    }
  
    inline bool has_non_strict_arguments_elements() {
      return elements_kind() == NON_STRICT_ARGUMENTS_ELEMENTS;
    }
  
    inline bool has_external_array_elements() {
      ElementsKind kind(elements_kind());
      return kind >= FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND &&
          kind <= LAST_EXTERNAL_ARRAY_ELEMENTS_KIND;
    }
  
    inline bool has_dictionary_elements() {
      return elements_kind() == DICTIONARY_ELEMENTS;
    }
  
    inline bool has_slow_elements_kind() {
      return elements_kind() == DICTIONARY_ELEMENTS
          || elements_kind() == NON_STRICT_ARGUMENTS_ELEMENTS;
    }
  
    static bool IsValidElementsTransition(ElementsKind from_kind,
                                          ElementsKind to_kind);
  
    // Tells whether the map is attached to SharedFunctionInfo
    // (for inobject slack tracking).
    inline void set_attached_to_shared_function_info(bool value);
  
    inline bool attached_to_shared_function_info();
  
    // Tells whether the map is shared between objects that may have different
    // behavior. If true, the map should never be modified, instead a clone
    // should be created and modified.
    inline void set_is_shared(bool value);
  
    inline bool is_shared();
  
    // 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)
  
    inline JSFunction* unchecked_constructor();
  
    // Should only be called by the code that initializes map to set initial valid
    // value of the instance descriptor member.
    inline void init_instance_descriptors();
  
    // [instance descriptors]: describes the object.
    DECL_ACCESSORS(instance_descriptors, DescriptorArray)
  
    // Sets the instance descriptor array for the map to be an empty descriptor
    // array.
    inline void clear_instance_descriptors();
  
    // [stub cache]: contains stubs compiled for this map.
    DECL_ACCESSORS(code_cache, Object)
  
    // [prototype transitions]: cache of prototype transitions.
    // Prototype transition is a transition that happens
    // when we change object's prototype to a new one.
    // Cache format:
    //    0: finger - index of the first free cell in the cache
    //    1 + 2 * i: prototype
    //    2 + 2 * i: target map
    DECL_ACCESSORS(prototype_transitions, FixedArray)
  
    inline FixedArray* unchecked_prototype_transitions();
  
    static const int kProtoTransitionHeaderSize = 1;
    static const int kProtoTransitionNumberOfEntriesOffset = 0;
    static const int kProtoTransitionElementsPerEntry = 2;
    static const int kProtoTransitionPrototypeOffset = 0;
    static const int kProtoTransitionMapOffset = 1;
  
    inline int NumberOfProtoTransitions() {
      FixedArray* cache = prototype_transitions();
      if (cache->length() == 0) return 0;
      return
          Smi::cast(cache->get(kProtoTransitionNumberOfEntriesOffset))->value();
    }
  
    inline void SetNumberOfProtoTransitions(int value) {
      FixedArray* cache = prototype_transitions();
      ASSERT(cache->length() != 0);
      cache->set_unchecked(kProtoTransitionNumberOfEntriesOffset,
                           Smi::FromInt(value));
    }
  
    // Lookup in the map's instance descriptors and fill out the result
    // with the given holder if the name is found. The holder may be
    // NULL when this function is used from the compiler.
    void LookupInDescriptors(JSObject* holder,
                             String* name,
                             LookupResult* result);
  
    MUST_USE_RESULT MaybeObject* CopyDropDescriptors();
  
    MUST_USE_RESULT MaybeObject* CopyNormalized(PropertyNormalizationMode mode,
                                                NormalizedMapSharingMode sharing);
  
    // Returns a copy of the map, with all transitions dropped from the
    // instance descriptors.
    MUST_USE_RESULT MaybeObject* 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(Heap* heap);
  
    // Update code cache.
    static void UpdateCodeCache(Handle<Map> map,
                                Handle<String> name,
                                Handle<Code> code);
    MUST_USE_RESULT MaybeObject* 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();
  
    void CreateOneBackPointer(Map* transition_target);
  
    // 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(Heap* heap, Object* real_prototype);
  
    // Computes a hash value for this map, to be used in HashTables and such.
    int Hash();
  
    // Compares this map to another to see if they describe equivalent objects.
    // If |mode| is set to CLEAR_INOBJECT_PROPERTIES, |other| is treated as if
    // it had exactly zero inobject properties.
    // The "shared" flags of both this map and |other| are ignored.
    bool EquivalentToForNormalization(Map* other, PropertyNormalizationMode mode);
  
    // Returns true if this map and |other| describe equivalent objects.
    // The "shared" flags of both this map and |other| are ignored.
    bool EquivalentTo(Map* other) {
      return EquivalentToForNormalization(other, KEEP_INOBJECT_PROPERTIES);
    }
  
    // Returns the contents of this map's descriptor array for the given string.
    // May return NULL. |safe_to_add_transition| is set to false and NULL
    // is returned if adding transitions is not allowed.
    Object* GetDescriptorContents(String* sentinel_name,
                                  bool* safe_to_add_transitions);
  
    // Returns the map that this map transitions to if its elements_kind
    // is changed to |elements_kind|, or NULL if no such map is cached yet.
    // |safe_to_add_transitions| is set to false if adding transitions is not
    // allowed.
    Map* LookupElementsTransitionMap(ElementsKind elements_kind,
                                     bool* safe_to_add_transition);
  
    // Adds an entry to this map's descriptor array for a transition to
    // |transitioned_map| when its elements_kind is changed to |elements_kind|.
    MaybeObject* AddElementsTransition(ElementsKind elements_kind,
                                       Map* transitioned_map);
  
    // Returns the transitioned map for this map with the most generic
    // elements_kind that's found in |candidates|, or null handle if no match is
    // found at all.
    Handle<Map> FindTransitionedMap(MapHandleList* candidates);
    Map* FindTransitionedMap(MapList* candidates);
  
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void MapPrint() {
      MapPrint(stdout);
    }
    void MapPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void MapVerify();
    void SharedMapVerify();
  #endif
  
    inline int visitor_id();
    inline void set_visitor_id(int visitor_id);
  
    typedef void (*TraverseCallback)(Map* map, void* data);
  
    void TraverseTransitionTree(TraverseCallback callback, void* data);
  
    static const int kMaxCachedPrototypeTransitions = 256;
  
    Object* GetPrototypeTransition(Object* prototype);
  
    MaybeObject* PutPrototypeTransition(Object* prototype, Map* map);
  
    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;
    // Storage for instance descriptors is overloaded to also contain additional
    // map flags when unused (bit_field3). When the map has instance descriptors,
    // the flags are transferred to the instance descriptor array and accessed
    // through an extra indirection.
    // TODO(1399): It should be possible to make room for bit_field3 in the map
    // without overloading the instance descriptors field, but the map is
    // currently perfectly aligned to 32 bytes and extending it at all would
    // double its size.  After the increment GC work lands, this size restriction
    // could be loosened and bit_field3 moved directly back in the map.
    static const int kInstanceDescriptorsOrBitField3Offset =
        kConstructorOffset + kPointerSize;
    static const int kCodeCacheOffset =
        kInstanceDescriptorsOrBitField3Offset + kPointerSize;
    static const int kPrototypeTransitionsOffset =
        kCodeCacheOffset + kPointerSize;
    static const int kPadStart = kPrototypeTransitionsOffset + kPointerSize;
    static const int kSize = MAP_POINTER_ALIGN(kPadStart);
  
    // Layout of pointer fields. Heap iteration code relies on them
    // being continuously allocated.
    static const int kPointerFieldsBeginOffset = Map::kPrototypeOffset;
    static const int kPointerFieldsEndOffset =
        Map::kPrototypeTransitionsOffset + kPointerSize;
  
    // 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;
    static const int kVisitorIdByte = 3;
    static const int kVisitorIdOffset = kInstanceSizesOffset + kVisitorIdByte;
  
    // 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;
    static const int kFunctionWithPrototype = 1;
    static const int kStringWrapperSafeForDefaultValueOf = 2;
    static const int kAttachedToSharedFunctionInfo = 3;
    // No bits can be used after kElementsKindFirstBit, they are all reserved for
    // storing ElementKind.
    static const int kElementsKindShift = 4;
    static const int kElementsKindBitCount = 4;
  
    // Derived values from bit field 2
    static const int kElementsKindMask = (-1 << kElementsKindShift) &
        ((1 << (kElementsKindShift + kElementsKindBitCount)) - 1);
    static const int8_t kMaximumBitField2FastElementValue = static_cast<int8_t>(
        (FAST_ELEMENTS + 1) << Map::kElementsKindShift) - 1;
    static const int8_t kMaximumBitField2FastSmiOnlyElementValue =
        static_cast<int8_t>((FAST_SMI_ONLY_ELEMENTS + 1) <<
                            Map::kElementsKindShift) - 1;
  
    // Bit positions for bit field 3
    static const int kIsShared = 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;
  
    typedef FixedBodyDescriptor<kPointerFieldsBeginOffset,
                                kPointerFieldsEndOffset,
                                kSize> BodyDescriptor;
  
   private:
    String* elements_transition_sentinel_name();
    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 be
  // 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
    };
  
    // [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, Foreign)
  
    // [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 OBJECT_PRINT
    inline void ScriptPrint() {
      ScriptPrint(stdout);
    }
    void ScriptPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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);
  };
  
  
  // List of builtin functions we want to identify to improve code
  // generation.
  //
  // Each entry has a name of a global object property holding an object
  // optionally followed by ".prototype", a name of a builtin function
  // on the object (the one the id is set for), and a label.
  //
  // Installation of ids for the selected builtin functions is handled
  // by the bootstrapper.
  //
  // NOTE: Order is important: math functions should be at the end of
  // the list and MathFloor should be the first math function.
  #define FUNCTIONS_WITH_ID_LIST(V)                   \
    V(Array.prototype, push, ArrayPush)               \
    V(Array.prototype, pop, ArrayPop)                 \
    V(Function.prototype, apply, FunctionApply)       \
    V(String.prototype, charCodeAt, StringCharCodeAt) \
    V(String.prototype, charAt, StringCharAt)         \
    V(String, fromCharCode, StringFromCharCode)       \
    V(Math, floor, MathFloor)                         \
    V(Math, round, MathRound)                         \
    V(Math, ceil, MathCeil)                           \
    V(Math, abs, MathAbs)                             \
    V(Math, log, MathLog)                             \
    V(Math, sin, MathSin)                             \
    V(Math, cos, MathCos)                             \
    V(Math, tan, MathTan)                             \
    V(Math, asin, MathASin)                           \
    V(Math, acos, MathACos)                           \
    V(Math, atan, MathATan)                           \
    V(Math, exp, MathExp)                             \
    V(Math, sqrt, MathSqrt)                           \
    V(Math, pow, MathPow)                             \
    V(Math, random, MathRandom)                       \
    V(Math, max, MathMax)                             \
    V(Math, min, MathMin)
  
  
  enum BuiltinFunctionId {
  #define DECLARE_FUNCTION_ID(ignored1, ignore2, name)    \
    k##name,
    FUNCTIONS_WITH_ID_LIST(DECLARE_FUNCTION_ID)
  #undef DECLARE_FUNCTION_ID
    // Fake id for a special case of Math.pow. Note, it continues the
    // list of math functions.
    kMathPowHalf,
    kFirstMathFunctionId = kMathFloor
  };
  
  
  // 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)
  
    // [scope_info]: Scope info.
    DECL_ACCESSORS(scope_info, ScopeInfo)
  
    // [construct stub]: Code stub for constructing instances of this function.
    DECL_ACCESSORS(construct_stub, Code)
  
    inline Code* unchecked_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);
  
    // Inobject slack tracking is the way to reclaim unused inobject space.
    //
    // The instance size is initially determined by adding some slack to
    // expected_nof_properties (to allow for a few extra properties added
    // after the constructor). There is no guarantee that the extra space
    // will not be wasted.
    //
    // Here is the algorithm to reclaim the unused inobject space:
    // - Detect the first constructor call for this SharedFunctionInfo.
    //   When it happens enter the "in progress" state: remember the
    //   constructor's initial_map and install a special construct stub that
    //   counts constructor calls.
    // - While the tracking is in progress create objects filled with
    //   one_pointer_filler_map instead of undefined_value. This way they can be
    //   resized quickly and safely.
    // - Once enough (kGenerousAllocationCount) objects have been created
    //   compute the 'slack' (traverse the map transition tree starting from the
    //   initial_map and find the lowest value of unused_property_fields).
    // - Traverse the transition tree again and decrease the instance size
    //   of every map. Existing objects will resize automatically (they are
    //   filled with one_pointer_filler_map). All further allocations will
    //   use the adjusted instance size.
    // - Decrease expected_nof_properties so that an allocations made from
    //   another context will use the adjusted instance size too.
    // - Exit "in progress" state by clearing the reference to the initial_map
    //   and setting the regular construct stub (generic or inline).
    //
    //  The above is the main event sequence. Some special cases are possible
    //  while the tracking is in progress:
    //
    // - GC occurs.
    //   Check if the initial_map is referenced by any live objects (except this
    //   SharedFunctionInfo). If it is, continue tracking as usual.
    //   If it is not, clear the reference and reset the tracking state. The
    //   tracking will be initiated again on the next constructor call.
    //
    // - The constructor is called from another context.
    //   Immediately complete the tracking, perform all the necessary changes
    //   to maps. This is  necessary because there is no efficient way to track
    //   multiple initial_maps.
    //   Proceed to create an object in the current context (with the adjusted
    //   size).
    //
    // - A different constructor function sharing the same SharedFunctionInfo is
    //   called in the same context. This could be another closure in the same
    //   context, or the first function could have been disposed.
    //   This is handled the same way as the previous case.
    //
    //  Important: inobject slack tracking is not attempted during the snapshot
    //  creation.
  
    static const int kGenerousAllocationCount = 8;
  
    // [construction_count]: Counter for constructor calls made during
    // the tracking phase.
    inline int construction_count();
    inline void set_construction_count(int value);
  
    // [initial_map]: initial map of the first function called as a constructor.
    // Saved for the duration of the tracking phase.
    // This is a weak link (GC resets it to undefined_value if no other live
    // object reference this map).
    DECL_ACCESSORS(initial_map, Object)
  
    // True if the initial_map is not undefined and the countdown stub is
    // installed.
    inline bool IsInobjectSlackTrackingInProgress();
  
    // Starts the tracking.
    // Stores the initial map and installs the countdown stub.
    // IsInobjectSlackTrackingInProgress is normally true after this call,
    // except when tracking have not been started (e.g. the map has no unused
    // properties or the snapshot is being built).
    void StartInobjectSlackTracking(Map* map);
  
    // Completes the tracking.
    // IsInobjectSlackTrackingInProgress is false after this call.
    void CompleteInobjectSlackTracking();
  
    // Clears the initial_map before the GC marking phase to ensure the reference
    // is weak. IsInobjectSlackTrackingInProgress is false after this call.
    void DetachInitialMap();
  
    // Restores the link to the initial map after the GC marking phase.
    // IsInobjectSlackTrackingInProgress is true after this call.
    void AttachInitialMap(Map* map);
  
    // False if there are definitely no live objects created from this function.
    // True if live objects _may_ exist (existence not guaranteed).
    // May go back from true to false after GC.
    DECL_BOOLEAN_ACCESSORS(live_objects_may_exist)
  
    // [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 Smi identifying a builtin function.
    // 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 HasBuiltinFunctionId();
    inline BuiltinFunctionId builtin_function_id();
  
    // [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)
  
    // The function's name if it is non-empty, otherwise the inferred name.
    String* DebugName();
  
    // 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.
    DECL_BOOLEAN_ACCESSORS(is_expression)
  
    // Is this function a top-level function (scripts, evals).
    DECL_BOOLEAN_ACCESSORS(is_toplevel)
  
    // Bit field containing various information collected by the compiler to
    // drive optimization.
    inline int compiler_hints();
    inline void set_compiler_hints(int value);
  
    // A counter used to determine when to stress the deoptimizer with a
    // deopt.
    inline Smi* deopt_counter();
    inline void set_deopt_counter(Smi* counter);
  
    // 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();
  
    // Indicates if this function can be lazy compiled.
    // This is used to determine if we can safely flush code from a function
    // when doing GC if we expect that the function will no longer be used.
    DECL_BOOLEAN_ACCESSORS(allows_lazy_compilation)
  
    // Indicates how many full GCs this function has survived with assigned
    // code object. Used to determine when it is relatively safe to flush
    // this code object and replace it with lazy compilation stub.
    // Age is reset when GC notices that the code object is referenced
    // from the stack or compilation cache.
    inline int code_age();
    inline void set_code_age(int age);
  
    // Indicates whether optimizations have been disabled for this
    // shared function info. If a function is repeatedly optimized or if
    // we cannot optimize the function we disable optimization to avoid
    // spending time attempting to optimize it again.
    DECL_BOOLEAN_ACCESSORS(optimization_disabled)
  
    // Indicates the language mode of the function's code as defined by the
    // current harmony drafts for the next ES language standard. Possible
    // values are:
    // 1. CLASSIC_MODE - Unrestricted syntax and semantics, same as in ES5.
    // 2. STRICT_MODE - Restricted syntax and semantics, same as in ES5.
    // 3. EXTENDED_MODE - Only available under the harmony flag, not part of ES5.
    inline LanguageMode language_mode();
    inline void set_language_mode(LanguageMode language_mode);
  
    // Indicates whether the language mode of this function is CLASSIC_MODE.
    inline bool is_classic_mode();
  
    // Indicates whether the language mode of this function is EXTENDED_MODE.
    inline bool is_extended_mode();
  
    // False if the function definitely does not allocate an arguments object.
    DECL_BOOLEAN_ACCESSORS(uses_arguments)
  
    // True if the function has any duplicated parameter names.
    DECL_BOOLEAN_ACCESSORS(has_duplicate_parameters)
  
    // Indicates whether the function is a native function.
    // These needs special treatment in .call and .apply since
    // null passed as the receiver should not be translated to the
    // global object.
    DECL_BOOLEAN_ACCESSORS(native)
  
    // Indicates that the function was created by the Function function.
    // Though it's anonymous, toString should treat it as if it had the name
    // "anonymous".  We don't set the name itself so that the system does not
    // see a binding for it.
    DECL_BOOLEAN_ACCESSORS(name_should_print_as_anonymous)
  
    // Indicates whether the function is a bound function created using
    // the bind function.
    DECL_BOOLEAN_ACCESSORS(bound)
  
    // Indicates that the function is anonymous (the name field can be set
    // through the API, which does not change this flag).
    DECL_BOOLEAN_ACCESSORS(is_anonymous)
  
    // Indicates whether or not the code in the shared function support
    // deoptimization.
    inline bool has_deoptimization_support();
  
    // Enable deoptimization support through recompiled code.
    void EnableDeoptimizationSupport(Code* recompiled);
  
    // Disable (further) attempted optimization of all functions sharing this
    // shared function info.  The function is the one we actually tried to
    // optimize.
    void DisableOptimization(JSFunction* function);
  
    // Lookup the bailout ID and ASSERT that it exists in the non-optimized
    // code, returns whether it asserted (i.e., always true if assertions are
    // disabled).
    bool VerifyBailoutId(int id);
  
    // Check whether a inlined constructor can be generated with the given
    // prototype.
    bool CanGenerateInlineConstructor(Object* prototype);
  
    // Prevents further attempts to generate inline constructors.
    // To be called if generation failed for any reason.
    void ForbidInlineConstructor();
  
    // 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();
  
    inline int opt_count();
    inline void set_opt_count(int opt_count);
  
    // Source size of this function.
    int SourceSize();
  
    // Calculate the instance size.
    int CalculateInstanceSize();
  
    // Calculate the number of in-object properties.
    int CalculateInObjectProperties();
  
    // Dispatched behavior.
    // Set max_length to -1 for unlimited length.
    void SourceCodePrint(StringStream* accumulator, int max_length);
  #ifdef OBJECT_PRINT
    inline void SharedFunctionInfoPrint() {
      SharedFunctionInfoPrint(stdout);
    }
    void SharedFunctionInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void SharedFunctionInfoVerify();
  #endif
  
    // Helpers to compile the shared code.  Returns true on success, false on
    // failure (e.g., stack overflow during compilation).
    static bool EnsureCompiled(Handle<SharedFunctionInfo> shared,
                               ClearExceptionFlag flag);
    static bool CompileLazy(Handle<SharedFunctionInfo> shared,
                            ClearExceptionFlag flag);
  
    // 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 kScopeInfoOffset = kCodeOffset + kPointerSize;
    static const int kConstructStubOffset = kScopeInfoOffset + 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 kInitialMapOffset =
        kInferredNameOffset + kPointerSize;
    static const int kThisPropertyAssignmentsOffset =
        kInitialMapOffset + kPointerSize;
    static const int kDeoptCounterOffset =
        kThisPropertyAssignmentsOffset + kPointerSize;
  #if V8_HOST_ARCH_32_BIT
    // Smi fields.
    static const int kLengthOffset =
        kDeoptCounterOffset + kPointerSize;
    static const int kFormalParameterCountOffset = kLengthOffset + kPointerSize;
    static const int kExpectedNofPropertiesOffset =
        kFormalParameterCountOffset + kPointerSize;
    static const int kNumLiteralsOffset =
        kExpectedNofPropertiesOffset + kPointerSize;
    static const int kStartPositionAndTypeOffset =
        kNumLiteralsOffset + kPointerSize;
    static const int kEndPositionOffset =
        kStartPositionAndTypeOffset + kPointerSize;
    static const int kFunctionTokenPositionOffset =
        kEndPositionOffset + kPointerSize;
    static const int kCompilerHintsOffset =
        kFunctionTokenPositionOffset + kPointerSize;
    static const int kThisPropertyAssignmentsCountOffset =
        kCompilerHintsOffset + kPointerSize;
    static const int kOptCountOffset =
        kThisPropertyAssignmentsCountOffset + kPointerSize;
    // Total size.
    static const int kSize = kOptCountOffset + kPointerSize;
  #else
    // The only reason to use smi fields instead of int fields
    // is to allow iteration without maps decoding during
    // garbage collections.
    // To avoid wasting space on 64-bit architectures we use
    // the following trick: we group integer fields into pairs
    // First integer in each pair is shifted left by 1.
    // By doing this we guarantee that LSB of each kPointerSize aligned
    // word is not set and thus this word cannot be treated as pointer
    // to HeapObject during old space traversal.
    static const int kLengthOffset =
        kDeoptCounterOffset + kPointerSize;
    static const int kFormalParameterCountOffset =
        kLengthOffset + kIntSize;
  
    static const int kExpectedNofPropertiesOffset =
        kFormalParameterCountOffset + kIntSize;
    static const int kNumLiteralsOffset =
        kExpectedNofPropertiesOffset + kIntSize;
  
    static const int kEndPositionOffset =
        kNumLiteralsOffset + kIntSize;
    static const int kStartPositionAndTypeOffset =
        kEndPositionOffset + kIntSize;
  
    static const int kFunctionTokenPositionOffset =
        kStartPositionAndTypeOffset + kIntSize;
    static const int kCompilerHintsOffset =
        kFunctionTokenPositionOffset + kIntSize;
  
    static const int kThisPropertyAssignmentsCountOffset =
        kCompilerHintsOffset + kIntSize;
    static const int kOptCountOffset =
        kThisPropertyAssignmentsCountOffset + kIntSize;
  
    // Total size.
    static const int kSize = kOptCountOffset + kIntSize;
  
  #endif
  
    // The construction counter for inobject slack tracking is stored in the
    // most significant byte of compiler_hints which is otherwise unused.
    // Its offset depends on the endian-ness of the architecture.
  #if __BYTE_ORDER == __LITTLE_ENDIAN
    static const int kConstructionCountOffset = kCompilerHintsOffset + 3;
  #elif __BYTE_ORDER == __BIG_ENDIAN
    static const int kConstructionCountOffset = kCompilerHintsOffset + 0;
  #else
  #error Unknown byte ordering
  #endif
  
    static const int kAlignedSize = POINTER_SIZE_ALIGN(kSize);
  
    typedef FixedBodyDescriptor<kNameOffset,
                                kThisPropertyAssignmentsOffset + kPointerSize,
                                kSize> BodyDescriptor;
  
    // 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 kCodeAgeSize = 3;
    static const int kCodeAgeMask = (1 << kCodeAgeSize) - 1;
  
    enum CompilerHints {
      kHasOnlySimpleThisPropertyAssignments,
      kAllowLazyCompilation,
      kLiveObjectsMayExist,
      kCodeAgeShift,
      kOptimizationDisabled = kCodeAgeShift + kCodeAgeSize,
      kStrictModeFunction,
      kExtendedModeFunction,
      kUsesArguments,
      kHasDuplicateParameters,
      kNative,
      kBoundFunction,
      kIsAnonymous,
      kNameShouldPrintAsAnonymous,
      kCompilerHintsCount  // Pseudo entry
    };
  
   private:
  #if V8_HOST_ARCH_32_BIT
    // On 32 bit platforms, compiler hints is a smi.
    static const int kCompilerHintsSmiTagSize = kSmiTagSize;
    static const int kCompilerHintsSize = kPointerSize;
  #else
    // On 64 bit platforms, compiler hints is not a smi, see comment above.
    static const int kCompilerHintsSmiTagSize = 0;
    static const int kCompilerHintsSize = kIntSize;
  #endif
  
    STATIC_ASSERT(SharedFunctionInfo::kCompilerHintsCount <=
                  SharedFunctionInfo::kCompilerHintsSize * kBitsPerByte);
  
   public:
    // Constants for optimizing codegen for strict mode function and
    // native tests.
    // Allows to use byte-width instructions.
    static const int kStrictModeBitWithinByte =
        (kStrictModeFunction + kCompilerHintsSmiTagSize) % kBitsPerByte;
  
    static const int kExtendedModeBitWithinByte =
        (kExtendedModeFunction + kCompilerHintsSmiTagSize) % kBitsPerByte;
  
    static const int kNativeBitWithinByte =
        (kNative + kCompilerHintsSmiTagSize) % kBitsPerByte;
  
  #if __BYTE_ORDER == __LITTLE_ENDIAN
    static const int kStrictModeByteOffset = kCompilerHintsOffset +
        (kStrictModeFunction + kCompilerHintsSmiTagSize) / kBitsPerByte;
    static const int kExtendedModeByteOffset = kCompilerHintsOffset +
        (kExtendedModeFunction + kCompilerHintsSmiTagSize) / kBitsPerByte;
    static const int kNativeByteOffset = kCompilerHintsOffset +
        (kNative + kCompilerHintsSmiTagSize) / kBitsPerByte;
  #elif __BYTE_ORDER == __BIG_ENDIAN
    static const int kStrictModeByteOffset = kCompilerHintsOffset +
        (kCompilerHintsSize - 1) -
        ((kStrictModeFunction + kCompilerHintsSmiTagSize) / kBitsPerByte);
    static const int kExtendedModeByteOffset = kCompilerHintsOffset +
        (kCompilerHintsSize - 1) -
        ((kExtendedModeFunction + kCompilerHintsSmiTagSize) / kBitsPerByte);
    static const int kNativeByteOffset = kCompilerHintsOffset +
        (kCompilerHintsSize - 1) -
        ((kNative + kCompilerHintsSmiTagSize) / kBitsPerByte);
  #else
  #error Unknown byte ordering
  #endif
  
   private:
    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]: The information about the function that
    // can be shared by instances.
    DECL_ACCESSORS(shared, SharedFunctionInfo)
  
    inline SharedFunctionInfo* unchecked_shared();
  
    // [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* code);
    inline void ReplaceCode(Code* code);
  
    inline Code* unchecked_code();
  
    // Tells whether this function is builtin.
    inline bool IsBuiltin();
  
    // Tells whether or not the function needs arguments adaption.
    inline bool NeedsArgumentsAdaption();
  
    // Tells whether or not this function has been optimized.
    inline bool IsOptimized();
  
    // Tells whether or not this function can be optimized.
    inline bool IsOptimizable();
  
    // Mark this function for lazy recompilation. The function will be
    // recompiled the next time it is executed.
    void MarkForLazyRecompilation();
  
    // Helpers to compile this function.  Returns true on success, false on
    // failure (e.g., stack overflow during compilation).
    static bool CompileLazy(Handle<JSFunction> function,
                            ClearExceptionFlag flag);
    static bool CompileOptimized(Handle<JSFunction> function,
                                 int osr_ast_id,
                                 ClearExceptionFlag flag);
  
    // Tells whether or not the function is already marked for lazy
    // recompilation.
    inline bool IsMarkedForLazyRecompilation();
  
    // Check whether or not this function is inlineable.
    bool IsInlineable();
  
    // [literals_or_bindings]: Fixed array holding either
    // the materialized literals or the bindings of a bound function.
    //
    // 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.
    //
    // On bound functions, the array is a (copy-on-write) fixed-array containing
    // the function that was bound, bound this-value and any bound
    // arguments. Bound functions never contain literals.
    DECL_ACCESSORS(literals_or_bindings, FixedArray)
  
    inline FixedArray* literals();
    inline void set_literals(FixedArray* literals);
  
    inline FixedArray* function_bindings();
    inline void set_function_bindings(FixedArray* bindings);
  
    // 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);
    MUST_USE_RESULT MaybeObject* SetPrototype(Object* value);
  
    // After prototype is removed, it will not be created when accessed, and
    // [[Construct]] from this function will not be allowed.
    Object* RemovePrototype();
    inline bool should_have_prototype();
  
    // 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();
  
    // [next_function_link]: Field for linking functions. This list is treated as
    // a weak list by the GC.
    DECL_ACCESSORS(next_function_link, Object)
  
    // Prints the name of the function using PrintF.
    inline void PrintName() {
      PrintName(stdout);
    }
    void PrintName(FILE* out);
  
    // Casting.
    static inline JSFunction* cast(Object* obj);
  
    // Iterates the objects, including code objects indirectly referenced
    // through pointers to the first instruction in the code object.
    void JSFunctionIterateBody(int object_size, ObjectVisitor* v);
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void JSFunctionPrint() {
      JSFunctionPrint(stdout);
    }
    void JSFunctionPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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. The last property (from kNonWeakFieldsEndOffset to
    // kSize) is weak and has special handling during garbage collection.
    static const int kCodeEntryOffset = JSObject::kHeaderSize;
    static const int kPrototypeOrInitialMapOffset =
        kCodeEntryOffset + kPointerSize;
    static const int kSharedFunctionInfoOffset =
        kPrototypeOrInitialMapOffset + kPointerSize;
    static const int kContextOffset = kSharedFunctionInfoOffset + kPointerSize;
    static const int kLiteralsOffset = kContextOffset + kPointerSize;
    static const int kNonWeakFieldsEndOffset = kLiteralsOffset + kPointerSize;
    static const int kNextFunctionLinkOffset = kNonWeakFieldsEndOffset;
    static const int kSize = kNextFunctionLinkOffset + kPointerSize;
  
    // Layout of the literals array.
    static const int kLiteralsPrefixSize = 1;
    static const int kLiteralGlobalContextIndex = 0;
  
    // Layout of the bound-function binding array.
    static const int kBoundFunctionIndex = 0;
    static const int kBoundThisIndex = 1;
    static const int kBoundArgumentsStartIndex = 2;
  
   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 global 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 OBJECT_PRINT
    inline void JSGlobalProxyPrint() {
      JSGlobalProxyPrint(stdout);
    }
    void JSGlobalProxyPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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;
  class JSGlobalPropertyCell;
  
  // 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.
    JSGlobalPropertyCell* GetPropertyCell(LookupResult* result);
  
    // This is like GetProperty, but is used when you know the lookup won't fail
    // by throwing an exception.  This is for the debug and builtins global
    // objects, where it is known which properties can be expected to be present
    // on the object.
    Object* GetPropertyNoExceptionThrown(String* key) {
      Object* answer = GetProperty(key)->ToObjectUnchecked();
      return answer;
    }
  
    // Ensure that the global object has a cell for the given property name.
    static Handle<JSGlobalPropertyCell> EnsurePropertyCell(
        Handle<GlobalObject> global,
        Handle<String> name);
    // TODO(kmillikin): This function can be eliminated once the stub cache is
    // full handlified (and the static helper can be written directly).
    MUST_USE_RESULT MaybeObject* 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:
    DISALLOW_IMPLICIT_CONSTRUCTORS(GlobalObject);
  };
  
  
  // JavaScript global object.
  class JSGlobalObject: public GlobalObject {
   public:
    // Casting.
    static inline JSGlobalObject* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void JSGlobalObjectPrint() {
      JSGlobalObjectPrint(stdout);
    }
    void JSGlobalObjectPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void JSBuiltinsObjectPrint() {
      JSBuiltinsObjectPrint(stdout);
    }
    void JSBuiltinsObjectPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void JSValuePrint() {
      JSValuePrint(stdout);
    }
    void JSValuePrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSValueVerify();
  #endif
  
    // Layout description.
    static const int kValueOffset = JSObject::kHeaderSize;
    static const int kSize = kValueOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSValue);
  };
  
  
  // Representation of message objects used for error reporting through
  // the API. The messages are formatted in JavaScript so this object is
  // a real JavaScript object. The information used for formatting the
  // error messages are not directly accessible from JavaScript to
  // prevent leaking information to user code called during error
  // formatting.
  class JSMessageObject: public JSObject {
   public:
    // [type]: the type of error message.
    DECL_ACCESSORS(type, String)
  
    // [arguments]: the arguments for formatting the error message.
    DECL_ACCESSORS(arguments, JSArray)
  
    // [script]: the script from which the error message originated.
    DECL_ACCESSORS(script, Object)
  
    // [stack_trace]: the stack trace for this error message.
    DECL_ACCESSORS(stack_trace, Object)
  
    // [stack_frames]: an array of stack frames for this error object.
    DECL_ACCESSORS(stack_frames, Object)
  
    // [start_position]: the start position in the script for the error message.
    inline int start_position();
    inline void set_start_position(int value);
  
    // [end_position]: the end position in the script for the error message.
    inline int end_position();
    inline void set_end_position(int value);
  
    // Casting.
    static inline JSMessageObject* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void JSMessageObjectPrint() {
      JSMessageObjectPrint(stdout);
    }
    void JSMessageObjectPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSMessageObjectVerify();
  #endif
  
    // Layout description.
    static const int kTypeOffset = JSObject::kHeaderSize;
    static const int kArgumentsOffset = kTypeOffset + kPointerSize;
    static const int kScriptOffset = kArgumentsOffset + kPointerSize;
    static const int kStackTraceOffset = kScriptOffset + kPointerSize;
    static const int kStackFramesOffset = kStackTraceOffset + kPointerSize;
    static const int kStartPositionOffset = kStackFramesOffset + kPointerSize;
    static const int kEndPositionOffset = kStartPositionOffset + kPointerSize;
    static const int kSize = kEndPositionOffset + kPointerSize;
  
    typedef FixedBodyDescriptor<HeapObject::kMapOffset,
                                kStackFramesOffset + kPointerSize,
                                kSize> BodyDescriptor;
  };
  
  
  // 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), or a smi
  // used for tracking the last usage (used for code flushing).
  // - a reference to code for UC16 inputs (bytecode or compiled), or a smi
  // used for tracking the last usage (used for code flushing)..
  // - 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);
  
    // Used during GC when flushing code or setting age.
    inline Object* DataAtUnchecked(int index);
    inline void SetDataAtUnchecked(int index, Object* value, Heap* heap);
    inline Type TypeTagUnchecked();
  
    static int code_index(bool is_ascii) {
      if (is_ascii) {
        return kIrregexpASCIICodeIndex;
      } else {
        return kIrregexpUC16CodeIndex;
      }
    }
  
    static int saved_code_index(bool is_ascii) {
      if (is_ascii) {
        return kIrregexpASCIICodeSavedIndex;
      } else {
        return kIrregexpUC16CodeSavedIndex;
      }
    }
  
    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;
  
    // Saved instance of Irregexp compiled code or bytecode for ASCII that
    // is a potential candidate for flushing.
    static const int kIrregexpASCIICodeSavedIndex = kDataIndex + 2;
    // Saved instance of Irregexp compiled code or bytecode for UC16 that is
    // a potential candidate for flushing.
    static const int kIrregexpUC16CodeSavedIndex = kDataIndex + 3;
  
    // 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 + 4;
    // Number of captures in the compiled regexp.
    static const int kIrregexpCaptureCountIndex = kDataIndex + 5;
  
    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;
    static const int kInObjectFieldCount = 5;
  
    // The uninitialized value for a regexp code object.
    static const int kUninitializedValue = -1;
  
    // The compilation error value for the regexp code object. The real error
    // object is in the saved code field.
    static const int kCompilationErrorValue = -2;
  
    // When we store the sweep generation at which we moved the code from the
    // code index to the saved code index we mask it of to be in the [0:255]
    // range.
    static const int kCodeAgeMask = 0xff;
  };
  
  
  class CompilationCacheShape : public BaseShape<HashTableKey*> {
   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);
    }
  
    MUST_USE_RESULT static MaybeObject* 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,
                       LanguageMode language_mode,
                       int scope_position);
    Object* LookupRegExp(String* source, JSRegExp::Flags flags);
    MaybeObject* Put(String* src, Object* value);
    MaybeObject* PutEval(String* src,
                         Context* context,
                         SharedFunctionInfo* value,
                         int scope_position);
    MaybeObject* PutRegExp(String* src, JSRegExp::Flags flags, FixedArray* value);
  
    // Remove given value from cache.
    void Remove(Object* 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.
    MUST_USE_RESULT MaybeObject* 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 OBJECT_PRINT
    inline void CodeCachePrint() {
      CodeCachePrint(stdout);
    }
    void CodeCachePrint(FILE* out);
  #endif
  #ifdef DEBUG
    void CodeCacheVerify();
  #endif
  
    static const int kDefaultCacheOffset = HeapObject::kHeaderSize;
    static const int kNormalTypeCacheOffset =
        kDefaultCacheOffset + kPointerSize;
    static const int kSize = kNormalTypeCacheOffset + kPointerSize;
  
   private:
    MUST_USE_RESULT MaybeObject* UpdateDefaultCache(String* name, Code* code);
    MUST_USE_RESULT MaybeObject* 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 BaseShape<HashTableKey*> {
   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);
    }
  
    MUST_USE_RESULT static MaybeObject* 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);
    MUST_USE_RESULT MaybeObject* 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);
  };
  
  
  class PolymorphicCodeCache: public Struct {
   public:
    DECL_ACCESSORS(cache, Object)
  
    static void Update(Handle<PolymorphicCodeCache> cache,
                       MapHandleList* maps,
                       Code::Flags flags,
                       Handle<Code> code);
  
    MUST_USE_RESULT MaybeObject* Update(MapHandleList* maps,
                                        Code::Flags flags,
                                        Code* code);
  
    // Returns an undefined value if the entry is not found.
    Handle<Object> Lookup(MapHandleList* maps, Code::Flags flags);
  
    static inline PolymorphicCodeCache* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void PolymorphicCodeCachePrint() {
      PolymorphicCodeCachePrint(stdout);
    }
    void PolymorphicCodeCachePrint(FILE* out);
  #endif
  #ifdef DEBUG
    void PolymorphicCodeCacheVerify();
  #endif
  
    static const int kCacheOffset = HeapObject::kHeaderSize;
    static const int kSize = kCacheOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(PolymorphicCodeCache);
  };
  
  
  class PolymorphicCodeCacheHashTable
      : public HashTable<CodeCacheHashTableShape, HashTableKey*> {
   public:
    Object* Lookup(MapHandleList* maps, int code_kind);
  
    MUST_USE_RESULT MaybeObject* Put(MapHandleList* maps,
                                     int code_kind,
                                     Code* code);
  
    static inline PolymorphicCodeCacheHashTable* cast(Object* obj);
  
    static const int kInitialSize = 64;
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(PolymorphicCodeCacheHashTable);
  };
  
  
  enum AllowNullsFlag {ALLOW_NULLS, DISALLOW_NULLS};
  enum RobustnessFlag {ROBUST_STRING_TRAVERSAL, FAST_STRING_TRAVERSAL};
  
  
  class StringHasher {
   public:
    explicit inline StringHasher(int length, uint32_t seed);
  
    // 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; }
  
    // Calculated hash value for a string consisting of 1 to
    // String::kMaxArrayIndexSize digits with no leading zeros (except "0").
    // value is represented decimal value.
    static uint32_t MakeArrayIndexHash(uint32_t value, int length);
  
    // No string is allowed to have a hash of zero.  That value is reserved
    // for internal properties.  If the hash calculation yields zero then we
    // use 27 instead.
    static const int kZeroHash = 27;
  
   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;
  };
  
  
  // Calculates string hash.
  template <typename schar>
  inline uint32_t HashSequentialString(const schar* chars,
                                       int length,
                                       uint32_t seed);
  
  
  // 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 IsSliced();
    inline bool IsIndirect();
    inline bool IsExternalAscii();
    inline bool IsExternalTwoByte();
    inline bool IsSequentialAscii();
    inline bool IsSequentialTwoByte();
    inline bool IsSymbol();
    inline StringRepresentationTag representation_tag();
    inline uint32_t encoding_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:
    // Representation of the flat content of a String.
    // A non-flat string doesn't have flat content.
    // A flat string has content that's encoded as a sequence of either
    // ASCII chars or two-byte UC16.
    // Returned by String::GetFlatContent().
    class FlatContent {
     public:
      // Returns true if the string is flat and this structure contains content.
      bool IsFlat() { return state_ != NON_FLAT; }
      // Returns true if the structure contains ASCII content.
      bool IsAscii() { return state_ == ASCII; }
      // Returns true if the structure contains two-byte content.
      bool IsTwoByte() { return state_ == TWO_BYTE; }
  
      // Return the ASCII content of the string. Only use if IsAscii() returns
      // true.
      Vector<const char> ToAsciiVector() {
        ASSERT_EQ(ASCII, state_);
        return Vector<const char>::cast(buffer_);
      }
      // Return the two-byte content of the string. Only use if IsTwoByte()
      // returns true.
      Vector<const uc16> ToUC16Vector() {
        ASSERT_EQ(TWO_BYTE, state_);
        return Vector<const uc16>::cast(buffer_);
      }
  
     private:
      enum State { NON_FLAT, ASCII, TWO_BYTE };
  
      // Constructors only used by String::GetFlatContent().
      explicit FlatContent(Vector<const char> chars)
          : buffer_(Vector<const byte>::cast(chars)),
            state_(ASCII) { }
      explicit FlatContent(Vector<const uc16> chars)
          : buffer_(Vector<const byte>::cast(chars)),
            state_(TWO_BYTE) { }
      FlatContent() : buffer_(), state_(NON_FLAT) { }
  
      Vector<const byte> buffer_;
      State state_;
  
      friend class String;
    };
  
    // 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);
  
    // Returns whether this string has only ASCII chars, i.e. all of them can
    // be ASCII encoded.  This might be the case even if the string is
    // two-byte.  Such strings may appear when the embedder prefers
    // two-byte external representations even for ASCII data.
    inline bool IsAsciiRepresentation();
    inline bool IsTwoByteRepresentation();
  
    // Cons and slices have an encoding flag that may not represent the actual
    // encoding of the underlying string.  This is taken into account here.
    // Requires: this->IsFlat()
    inline bool IsAsciiRepresentationUnderneath();
    inline bool IsTwoByteRepresentationUnderneath();
  
    // NOTE: this should be considered only a hint.  False negatives are
    // possible.
    inline bool HasOnlyAsciiChars();
  
    // 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 string.  Checks first inline to see if it is
    // necessary.  Does nothing if the string is not a cons string.
    // Flattening allocates a sequential string with the same data as
    // the given string and mutates the cons string to a degenerate
    // form, where the first component is the new sequential string and
    // the second component is the empty string.  If allocation fails,
    // this function returns a failure.  If flattening succeeds, this
    // function returns the sequential string that is now the first
    // component of the cons string.
    //
    // Degenerate cons strings are handled specially by the garbage
    // collector (see IsShortcutCandidate).
    //
    // Use FlattenString from Handles.cc to flatten even in case an
    // allocation failure happens.
    inline MaybeObject* TryFlatten(PretenureFlag pretenure = NOT_TENURED);
  
    // Convenience function.  Has exactly the same behavior as
    // TryFlatten(), except in the case of failure returns the original
    // string.
    inline String* TryFlattenGetString(PretenureFlag pretenure = NOT_TENURED);
  
    // Tries to return the content of a flat string as a structure holding either
    // a flat vector of char or of uc16.
    // If the string isn't flat, and therefore doesn't have flat content, the
    // returned structure will report so, and can't provide a vector of either
    // kind.
    FlatContent GetFlatContent();
  
    // Returns the parent of a sliced string or first part of a flat cons string.
    // Requires: StringShape(this).IsIndirect() && this->IsFlat()
    inline String* GetUnderlying();
  
    // Mark the string as an undetectable object. It only applies to
    // ASCII and two byte string types.
    bool MarkAsUndetectable();
  
    // Return a substring.
    MUST_USE_RESULT MaybeObject* SubString(int from,
                                           int to,
                                           PretenureFlag pretenure = NOT_TENURED);
  
    // String equality operations.
    inline bool Equals(String* other);
    bool IsEqualTo(Vector<const char> str);
    bool IsAsciiEqualTo(Vector<const char> str);
    bool IsTwoByteEqualTo(Vector<const uc16> 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.
    SmartArrayPointer<char> ToCString(AllowNullsFlag allow_nulls,
                                      RobustnessFlag robustness_flag,
                                      int offset,
                                      int length,
                                      int* length_output = 0);
    SmartArrayPointer<char> ToCString(
        AllowNullsFlag allow_nulls = DISALLOW_NULLS,
        RobustnessFlag robustness_flag = FAST_STRING_TRAVERSAL,
        int* length_output = 0);
  
    inline int Utf8Length() { return Utf8Length(this, 0, length()); }
    static int Utf8Length(String* input, int from, int to);
  
    // 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.
    SmartArrayPointer<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,
                                     uint32_t seed);
  
    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 OBJECT_PRINT
    inline void StringPrint() {
      StringPrint(stdout);
    }
    void StringPrint(FILE* out);
  
    char* ToAsciiArray();
  #endif
  #ifdef DEBUG
    void StringVerify();
  #endif
    inline bool IsFlat();
  
    // Layout description.
    static const int kLengthOffset = HeapObject::kHeaderSize;
    static const int kHashFieldOffset = kLengthOffset + kPointerSize;
    static const int kSize = kHashFieldOffset + kPointerSize;
  
    // 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;
  
    // 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 kHashNotComputedMask = 1;
    static const int kIsNotArrayIndexMask = 1 << 1;
    static const int kNofHashBitFields = 2;
  
    // Shift constant retrieving hash code from hash field.
    static const int kHashShift = kNofHashBitFields;
  
    // Only these bits are relevant in the hash, since the top two are shifted
    // out.
    static const uint32_t kHashBitMask = 0xffffffffu >> kHashShift;
  
    // 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 kArrayIndexValueBits = 24;
    static const int kArrayIndexLengthBits =
        kBitsPerInt - kArrayIndexValueBits - kNofHashBitFields;
  
    STATIC_CHECK((kArrayIndexLengthBits > 0));
    STATIC_CHECK(kMaxArrayIndexSize < (1 << kArrayIndexLengthBits));
  
    static const int kArrayIndexHashLengthShift =
        kArrayIndexValueBits + kNofHashBitFields;
  
    static const int kArrayIndexHashMask = (1 << kArrayIndexHashLengthShift) - 1;
  
    static const int kArrayIndexValueMask =
        ((1 << kArrayIndexValueBits) - 1) << kHashShift;
  
    // Check that kMaxCachedArrayIndexLength + 1 is a power of two so we
    // could use a mask to test if the length of string is less than or equal to
    // kMaxCachedArrayIndexLength.
    STATIC_CHECK(IS_POWER_OF_TWO(kMaxCachedArrayIndexLength + 1));
  
    static const int kContainsCachedArrayIndexMask =
        (~kMaxCachedArrayIndexLength << kArrayIndexHashLengthShift) |
        kIsNotArrayIndexMask;
  
    // Value of empty hash field indicating that the hash is not computed.
    static const int kEmptyHashField =
        kIsNotArrayIndexMask | kHashNotComputedMask;
  
    // Value of hash field containing computed hash equal to zero.
    static const int kZeroHash = kIsNotArrayIndexMask;
  
    // 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);
  
    static inline bool IsAscii(const char* chars, int length) {
      const char* limit = chars + length;
  #ifdef V8_HOST_CAN_READ_UNALIGNED
      ASSERT(kMaxAsciiCharCode == 0x7F);
      const uintptr_t non_ascii_mask = kUintptrAllBitsSet / 0xFF * 0x80;
      while (chars <= limit - sizeof(uintptr_t)) {
        if (*reinterpret_cast<const uintptr_t*>(chars) & non_ascii_mask) {
          return false;
        }
        chars += sizeof(uintptr_t);
      }
  #endif
      while (chars < limit) {
        if (static_cast<uint8_t>(*chars) > kMaxAsciiCharCodeU) return false;
        ++chars;
      }
      return true;
    }
  
    static inline bool IsAscii(const uc16* chars, int length) {
      const uc16* limit = chars + length;
      while (chars < limit) {
        if (*chars > kMaxAsciiCharCodeU) return false;
        ++chars;
      }
      return true;
    }
  
   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:
    // 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.
    MUST_USE_RESULT MaybeObject* SlowTryFlatten(PretenureFlag pretenure);
  
    static inline bool IsHashFieldComputed(uint32_t field);
  
    // 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);
  
    // Layout description.
    static const int kHeaderSize = String::kSize;
  
   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:
    static const bool kHasAsciiEncoding = true;
  
    // 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_POINTER_ALIGN(kHeaderSize + length * kCharSize);
    }
  
    // Maximal memory usage for a single sequential ASCII string.
    static const int kMaxSize = 512 * MB - 1;
    // 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:
    static const bool kHasAsciiEncoding = false;
  
    // 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_POINTER_ALIGN(kHeaderSize + length * kShortSize);
    }
  
    // Maximal memory usage for a single sequential two-byte string.
    static const int kMaxSize = 512 * MB - 1;
    // 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);
  
    // 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;
  
    typedef FixedBodyDescriptor<kFirstOffset, kSecondOffset + kPointerSize, kSize>
            BodyDescriptor;
  
  #ifdef DEBUG
    void ConsStringVerify();
  #endif
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(ConsString);
  };
  
  
  // The Sliced String class describes strings that are substrings of another
  // sequential string.  The motivation is to save time and memory when creating
  // a substring.  A Sliced String is described as a pointer to the parent,
  // the offset from the start of the parent string and the length.  Using
  // a Sliced String therefore requires unpacking of the parent string and
  // adding the offset to the start address.  A substring of a Sliced String
  // are not nested since the double indirection is simplified when creating
  // such a substring.
  // Currently missing features are:
  //  - handling externalized parent strings
  //  - external strings as parent
  //  - truncating sliced string to enable otherwise unneeded parent to be GC'ed.
  class SlicedString: public String {
   public:
    inline String* parent();
    inline void set_parent(String* parent);
    inline int offset();
    inline void set_offset(int offset);
  
    // Dispatched behavior.
    uint16_t SlicedStringGet(int index);
  
    // Casting.
    static inline SlicedString* cast(Object* obj);
  
    // Layout description.
    static const int kParentOffset = POINTER_SIZE_ALIGN(String::kSize);
    static const int kOffsetOffset = kParentOffset + kPointerSize;
    static const int kSize = kOffsetOffset + kPointerSize;
  
    // Support for StringInputBuffer
    inline const unibrow::byte* SlicedStringReadBlock(ReadBlockBuffer* buffer,
                                                      unsigned* offset_ptr,
                                                      unsigned chars);
    inline void SlicedStringReadBlockIntoBuffer(ReadBlockBuffer* buffer,
                                                unsigned* offset_ptr,
                                                unsigned chars);
    // Minimum length for a sliced string.
    static const int kMinLength = 13;
  
    typedef FixedBodyDescriptor<kParentOffset,
                                kOffsetOffset + kPointerSize, kSize>
            BodyDescriptor;
  
  #ifdef DEBUG
    void SlicedStringVerify();
  #endif
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(SlicedString);
  };
  
  
  // 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 kShortSize = kResourceOffset + kPointerSize;
    static const int kResourceDataOffset = kResourceOffset + kPointerSize;
    static const int kSize = kResourceDataOffset + kPointerSize;
  
    // Return whether external string is short (data pointer is not cached).
    inline bool is_short();
  
    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:
    static const bool kHasAsciiEncoding = true;
  
    typedef v8::String::ExternalAsciiStringResource Resource;
  
    // The underlying resource.
    inline const Resource* resource();
    inline void set_resource(const Resource* buffer);
  
    // Update the pointer cache to the external character array.
    // The cached pointer is always valid, as the external character array does =
    // not move during lifetime.  Deserialization is the only exception, after
    // which the pointer cache has to be refreshed.
    inline void update_data_cache();
  
    inline const char* GetChars();
  
    // Dispatched behavior.
    inline uint16_t ExternalAsciiStringGet(int index);
  
    // Casting.
    static inline ExternalAsciiString* cast(Object* obj);
  
    // Garbage collection support.
    inline void ExternalAsciiStringIterateBody(ObjectVisitor* v);
  
    template<typename StaticVisitor>
    inline void ExternalAsciiStringIterateBody();
  
    // 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:
    static const bool kHasAsciiEncoding = false;
  
    typedef v8::String::ExternalStringResource Resource;
  
    // The underlying string resource.
    inline const Resource* resource();
    inline void set_resource(const Resource* buffer);
  
    // Update the pointer cache to the external character array.
    // The cached pointer is always valid, as the external character array does =
    // not move during lifetime.  Deserialization is the only exception, after
    // which the pointer cache has to be refreshed.
    inline void update_data_cache();
  
    inline const uint16_t* GetChars();
  
    // Dispatched behavior.
    inline uint16_t ExternalTwoByteStringGet(int index);
  
    // For regexp code.
    inline const uint16_t* ExternalTwoByteStringGetData(unsigned start);
  
    // Casting.
    static inline ExternalTwoByteString* cast(Object* obj);
  
    // Garbage collection support.
    inline void ExternalTwoByteStringIterateBody(ObjectVisitor* v);
  
    template<typename StaticVisitor>
    inline void ExternalTwoByteStringIterateBody();
  
  
    // 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:
    explicit inline Relocatable(Isolate* isolate);
    inline virtual ~Relocatable();
    virtual void IterateInstance(ObjectVisitor* v) { }
    virtual void PostGarbageCollection() { }
  
    static void PostGarbageCollectionProcessing();
    static int ArchiveSpacePerThread();
    static char* ArchiveState(Isolate* isolate, char* to);
    static char* RestoreState(Isolate* isolate, char* from);
    static void Iterate(ObjectVisitor* v);
    static void Iterate(ObjectVisitor* v, Relocatable* top);
    static char* Iterate(ObjectVisitor* v, char* t);
   private:
    Isolate* isolate_;
    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:
    FlatStringReader(Isolate* isolate, Handle<String> str);
    FlatStringReader(Isolate* isolate, 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>() {}
    explicit 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>() {}
    explicit 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)
  
    inline byte kind();
    inline void set_kind(byte kind);
  
    // Casting.
    static inline Oddball* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef DEBUG
    void OddballVerify();
  #endif
  
    // Initialize the fields.
    MUST_USE_RESULT MaybeObject* Initialize(const char* to_string,
                                            Object* to_number,
                                            byte kind);
  
    // Layout description.
    static const int kToStringOffset = HeapObject::kHeaderSize;
    static const int kToNumberOffset = kToStringOffset + kPointerSize;
    static const int kKindOffset = kToNumberOffset + kPointerSize;
    static const int kSize = kKindOffset + kPointerSize;
  
    static const byte kFalse = 0;
    static const byte kTrue = 1;
    static const byte kNotBooleanMask = ~1;
    static const byte kTheHole = 2;
    static const byte kNull = 3;
    static const byte kArgumentMarker = 4;
    static const byte kUndefined = 5;
    static const byte kOther = 6;
  
    // The ToNumber value of a hidden oddball is a negative smi.
    static const int kLeastHiddenOddballNumber = -5;
  
    typedef FixedBodyDescriptor<kToStringOffset,
                                kToNumberOffset + kPointerSize,
                                kSize> BodyDescriptor;
  
   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);
  
  #ifdef DEBUG
    void JSGlobalPropertyCellVerify();
  #endif
  #ifdef OBJECT_PRINT
    inline void JSGlobalPropertyCellPrint() {
      JSGlobalPropertyCellPrint(stdout);
    }
    void JSGlobalPropertyCellPrint(FILE* out);
  #endif
  
    // Layout description.
    static const int kValueOffset = HeapObject::kHeaderSize;
    static const int kSize = kValueOffset + kPointerSize;
  
    typedef FixedBodyDescriptor<kValueOffset,
                                kValueOffset + kPointerSize,
                                kSize> BodyDescriptor;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSGlobalPropertyCell);
  };
  
  
  // The JSProxy describes EcmaScript Harmony proxies
  class JSProxy: public JSReceiver {
   public:
    // [handler]: The handler property.
    DECL_ACCESSORS(handler, Object)
  
    // [hash]: The hash code property (undefined if not initialized yet).
    DECL_ACCESSORS(hash, Object)
  
    // Casting.
    static inline JSProxy* cast(Object* obj);
  
    bool HasPropertyWithHandler(String* name);
    bool HasElementWithHandler(uint32_t index);
  
    MUST_USE_RESULT MaybeObject* GetPropertyWithHandler(
        Object* receiver,
        String* name);
    MUST_USE_RESULT MaybeObject* GetElementWithHandler(
        Object* receiver,
        uint32_t index);
  
    MUST_USE_RESULT MaybeObject* SetPropertyWithHandler(
        String* name,
        Object* value,
        PropertyAttributes attributes,
        StrictModeFlag strict_mode);
    MUST_USE_RESULT MaybeObject* SetElementWithHandler(
        uint32_t index,
        Object* value,
        StrictModeFlag strict_mode);
  
    // If the handler defines an accessor property, invoke its setter
    // (or throw if only a getter exists) and set *found to true. Otherwise false.
    MUST_USE_RESULT MaybeObject* SetPropertyWithHandlerIfDefiningSetter(
        String* name,
        Object* value,
        PropertyAttributes attributes,
        StrictModeFlag strict_mode,
        bool* found);
  
    MUST_USE_RESULT MaybeObject* DeletePropertyWithHandler(
        String* name,
        DeleteMode mode);
    MUST_USE_RESULT MaybeObject* DeleteElementWithHandler(
        uint32_t index,
        DeleteMode mode);
  
    MUST_USE_RESULT PropertyAttributes GetPropertyAttributeWithHandler(
        JSReceiver* receiver,
        String* name);
    MUST_USE_RESULT PropertyAttributes GetElementAttributeWithHandler(
        JSReceiver* receiver,
        uint32_t index);
  
    MUST_USE_RESULT MaybeObject* GetIdentityHash(CreationFlag flag);
  
    // Turn this into an (empty) JSObject.
    void Fix();
  
    // Initializes the body after the handler slot.
    inline void InitializeBody(int object_size, Object* value);
  
    // Invoke a trap by name. If the trap does not exist on this's handler,
    // but derived_trap is non-NULL, invoke that instead.  May cause GC.
    Handle<Object> CallTrap(const char* name,
                            Handle<Object> derived_trap,
                            int argc,
                            Handle<Object> args[]);
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void JSProxyPrint() {
      JSProxyPrint(stdout);
    }
    void JSProxyPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSProxyVerify();
  #endif
  
    // Layout description. We add padding so that a proxy has the same
    // size as a virgin JSObject. This is essential for becoming a JSObject
    // upon freeze.
    static const int kHandlerOffset = HeapObject::kHeaderSize;
    static const int kHashOffset = kHandlerOffset + kPointerSize;
    static const int kPaddingOffset = kHashOffset + kPointerSize;
    static const int kSize = JSObject::kHeaderSize;
    static const int kHeaderSize = kPaddingOffset;
    static const int kPaddingSize = kSize - kPaddingOffset;
  
    STATIC_CHECK(kPaddingSize >= 0);
  
    typedef FixedBodyDescriptor<kHandlerOffset,
                                kPaddingOffset,
                                kSize> BodyDescriptor;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSProxy);
  };
  
  
  class JSFunctionProxy: public JSProxy {
   public:
    // [call_trap]: The call trap.
    DECL_ACCESSORS(call_trap, Object)
  
    // [construct_trap]: The construct trap.
    DECL_ACCESSORS(construct_trap, Object)
  
    // Casting.
    static inline JSFunctionProxy* cast(Object* obj);
  
    // Dispatched behavior.
  #ifdef OBJECT_PRINT
    inline void JSFunctionProxyPrint() {
      JSFunctionProxyPrint(stdout);
    }
    void JSFunctionProxyPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSFunctionProxyVerify();
  #endif
  
    // Layout description.
    static const int kCallTrapOffset = JSProxy::kPaddingOffset;
    static const int kConstructTrapOffset = kCallTrapOffset + kPointerSize;
    static const int kPaddingOffset = kConstructTrapOffset + kPointerSize;
    static const int kSize = JSFunction::kSize;
    static const int kPaddingSize = kSize - kPaddingOffset;
  
    STATIC_CHECK(kPaddingSize >= 0);
  
    typedef FixedBodyDescriptor<kHandlerOffset,
                                kConstructTrapOffset + kPointerSize,
                                kSize> BodyDescriptor;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSFunctionProxy);
  };
  
  
  // The JSSet describes EcmaScript Harmony sets
  class JSSet: public JSObject {
   public:
    // [set]: the backing hash set containing keys.
    DECL_ACCESSORS(table, Object)
  
    // Casting.
    static inline JSSet* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void JSSetPrint() {
      JSSetPrint(stdout);
    }
    void JSSetPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSSetVerify();
  #endif
  
    static const int kTableOffset = JSObject::kHeaderSize;
    static const int kSize = kTableOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSSet);
  };
  
  
  // The JSMap describes EcmaScript Harmony maps
  class JSMap: public JSObject {
   public:
    // [table]: the backing hash table mapping keys to values.
    DECL_ACCESSORS(table, Object)
  
    // Casting.
    static inline JSMap* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void JSMapPrint() {
      JSMapPrint(stdout);
    }
    void JSMapPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSMapVerify();
  #endif
  
    static const int kTableOffset = JSObject::kHeaderSize;
    static const int kSize = kTableOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSMap);
  };
  
  
  // The JSWeakMap describes EcmaScript Harmony weak maps
  class JSWeakMap: public JSObject {
   public:
    // [table]: the backing hash table mapping keys to values.
    DECL_ACCESSORS(table, Object)
  
    // [next]: linked list of encountered weak maps during GC.
    DECL_ACCESSORS(next, Object)
  
    // Casting.
    static inline JSWeakMap* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void JSWeakMapPrint() {
      JSWeakMapPrint(stdout);
    }
    void JSWeakMapPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void JSWeakMapVerify();
  #endif
  
    static const int kTableOffset = JSObject::kHeaderSize;
    static const int kNextOffset = kTableOffset + kPointerSize;
    static const int kSize = kNextOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(JSWeakMap);
  };
  
  
  // Foreign 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 Foreign: public HeapObject {
   public:
    // [address]: field containing the address.
    inline Address foreign_address();
    inline void set_foreign_address(Address value);
  
    // Casting.
    static inline Foreign* cast(Object* obj);
  
    // Dispatched behavior.
    inline void ForeignIterateBody(ObjectVisitor* v);
  
    template<typename StaticVisitor>
    inline void ForeignIterateBody();
  
  #ifdef OBJECT_PRINT
    inline void ForeignPrint() {
      ForeignPrint(stdout);
    }
    void ForeignPrint(FILE* out);
  #endif
  #ifdef DEBUG
    void ForeignVerify();
  #endif
  
    // Layout description.
  
    static const int kForeignAddressOffset = HeapObject::kHeaderSize;
    static const int kSize = kForeignAddressOffset + kPointerSize;
  
    STATIC_CHECK(kForeignAddressOffset == Internals::kForeignAddressOffset);
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(Foreign);
  };
  
  
  // 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);
  
    MUST_USE_RESULT MaybeObject* 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.
    MUST_USE_RESULT MaybeObject* Initialize(int capacity);
  
    // Initializes the array to a certain length.
    inline bool AllowsSetElementsLength();
    MUST_USE_RESULT MaybeObject* SetElementsLength(Object* length);
  
    // Set the content of the array to the content of storage.
    inline MaybeObject* SetContent(FixedArrayBase* 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 OBJECT_PRINT
    inline void JSArrayPrint() {
      JSArrayPrint(stdout);
    }
    void JSArrayPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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)
  
    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 OBJECT_PRINT
    inline void AccessorInfoPrint() {
      AccessorInfoPrint(stdout);
    }
    void AccessorInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 kSize = kFlagOffset + 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);
  };
  
  
  // Support for JavaScript accessors: A pair of a getter and a setter. Each
  // accessor can either be
  //   * a pointer to a JavaScript function or proxy: a real accessor
  //   * undefined: considered an accessor by the spec, too, strangely enough
  //   * the hole: an accessor which has not been set
  //   * a pointer to a map: a transition used to ensure map sharing
  class AccessorPair: public Struct {
   public:
    DECL_ACCESSORS(getter, Object)
    DECL_ACCESSORS(setter, Object)
  
    static inline AccessorPair* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    void AccessorPairPrint(FILE* out = stdout);
  #endif
  #ifdef DEBUG
    void AccessorPairVerify();
  #endif
  
    static const int kGetterOffset = HeapObject::kHeaderSize;
    static const int kSetterOffset = kGetterOffset + kPointerSize;
    static const int kSize = kSetterOffset + kPointerSize;
  
   private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(AccessorPair);
  };
  
  
  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 OBJECT_PRINT
    inline void AccessCheckInfoPrint() {
      AccessCheckInfoPrint(stdout);
    }
    void AccessCheckInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void InterceptorInfoPrint() {
      InterceptorInfoPrint(stdout);
    }
    void InterceptorInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void CallHandlerInfoPrint() {
      CallHandlerInfoPrint(stdout);
    }
    void CallHandlerInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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;
  
   private:
    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)
    DECL_BOOLEAN_ACCESSORS(read_only_prototype)
  
    static inline FunctionTemplateInfo* cast(Object* obj);
  
  #ifdef OBJECT_PRINT
    inline void FunctionTemplateInfoPrint() {
      FunctionTemplateInfoPrint(stdout);
    }
    void FunctionTemplateInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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;
    static const int kReadOnlyPrototypeBit = 3;
  
    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 OBJECT_PRINT
    inline void ObjectTemplateInfoPrint() {
      ObjectTemplateInfoPrint(stdout);
    }
    void ObjectTemplateInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void SignatureInfoPrint() {
      SignatureInfoPrint(stdout);
    }
    void SignatureInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void TypeSwitchInfoPrint() {
      TypeSwitchInfoPrint(stdout);
    }
    void TypeSwitchInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void DebugInfoPrint() {
      DebugInfoPrint(stdout);
    }
    void DebugInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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 OBJECT_PRINT
    inline void BreakPointInfoPrint() {
      BreakPointInfoPrint(stdout);
    }
    void BreakPointInfoPrint(FILE* out);
  #endif
  #ifdef DEBUG
    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
  
  #define VISITOR_SYNCHRONIZATION_TAGS_LIST(V)                            \
    V(kSymbolTable, "symbol_table", "(Symbols)")                          \
    V(kExternalStringsTable, "external_strings_table", "(External strings)") \
    V(kStrongRootList, "strong_root_list", "(Strong roots)")              \
    V(kSymbol, "symbol", "(Symbol)")                                      \
    V(kBootstrapper, "bootstrapper", "(Bootstrapper)")                    \
    V(kTop, "top", "(Isolate)")                                           \
    V(kRelocatable, "relocatable", "(Relocatable)")                       \
    V(kDebug, "debug", "(Debugger)")                                      \
    V(kCompilationCache, "compilationcache", "(Compilation cache)")       \
    V(kHandleScope, "handlescope", "(Handle scope)")                      \
    V(kBuiltins, "builtins", "(Builtins)")                                \
    V(kGlobalHandles, "globalhandles", "(Global handles)")                \
    V(kThreadManager, "threadmanager", "(Thread manager)")                \
    V(kExtensions, "Extensions", "(Extensions)")
  
  class VisitorSynchronization : public AllStatic {
   public:
  #define DECLARE_ENUM(enum_item, ignore1, ignore2) enum_item,
    enum SyncTag {
      VISITOR_SYNCHRONIZATION_TAGS_LIST(DECLARE_ENUM)
      kNumberOfSyncTags
    };
  #undef DECLARE_ENUM
  
    static const char* const kTags[kNumberOfSyncTags];
    static const char* const kTagNames[kNumberOfSyncTags];
  };
  
  // 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 code entry in a JS function.
    virtual void VisitCodeEntry(Address entry_address);
  
    // Visits a global property cell reference in the instruction stream.
    virtual void VisitGlobalPropertyCell(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); }
  
    // Visit pointer embedded into a code object.
    virtual void VisitEmbeddedPointer(RelocInfo* rinfo);
  
    // 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) {}
  
    virtual void VisitExternalReference(RelocInfo* rinfo);
  
    inline void VisitExternalReference(Address* p) {
      VisitExternalReferences(p, p + 1);
    }
  
    // Visits a handle that has an embedder-assigned class ID.
    virtual void VisitEmbedderReference(Object** p, uint16_t class_id) {}
  
    // Intended for serialization/deserialization checking: insert, or
    // check for the presence of, a tag at this position in the stream.
    // Also used for marking up GC roots in heap snapshots.
    virtual void Synchronize(VisitorSynchronization::SyncTag tag) {}
  };
  
  
  class StructBodyDescriptor : public
    FlexibleBodyDescriptor<HeapObject::kHeaderSize> {
   public:
    static inline int SizeOf(Map* map, HeapObject* object) {
      return map->instance_size();
    }
  };
  
  
  // 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_
  