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      1 // Copyright 2012 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef V8_PROPERTY_DETAILS_H_
      6 #define V8_PROPERTY_DETAILS_H_
      7 
      8 #include "include/v8.h"
      9 #include "src/allocation.h"
     10 #include "src/utils.h"
     11 
     12 // Ecma-262 3rd 8.6.1
     13 enum PropertyAttributes {
     14   NONE              = v8::None,
     15   READ_ONLY         = v8::ReadOnly,
     16   DONT_ENUM         = v8::DontEnum,
     17   DONT_DELETE       = v8::DontDelete,
     18 
     19   SEALED            = DONT_DELETE,
     20   FROZEN            = SEALED | READ_ONLY,
     21 
     22   STRING            = 8,  // Used to filter symbols and string names
     23   SYMBOLIC          = 16,
     24   PRIVATE_SYMBOL    = 32,
     25 
     26   DONT_SHOW         = DONT_ENUM | SYMBOLIC | PRIVATE_SYMBOL,
     27   ABSENT            = 64  // Used in runtime to indicate a property is absent.
     28   // ABSENT can never be stored in or returned from a descriptor's attributes
     29   // bitfield.  It is only used as a return value meaning the attributes of
     30   // a non-existent property.
     31 };
     32 
     33 
     34 namespace v8 {
     35 namespace internal {
     36 
     37 class Smi;
     38 template<class> class TypeImpl;
     39 struct ZoneTypeConfig;
     40 typedef TypeImpl<ZoneTypeConfig> Type;
     41 class TypeInfo;
     42 
     43 // Type of properties.
     44 // Order of properties is significant.
     45 // Must fit in the BitField PropertyDetails::TypeField.
     46 // A copy of this is in mirror-debugger.js.
     47 enum PropertyType {
     48   // Only in slow mode.
     49   NORMAL                    = 0,
     50   // Only in fast mode.
     51   FIELD                     = 1,
     52   CONSTANT                  = 2,
     53   CALLBACKS                 = 3,
     54   // Only in lookup results, not in descriptors.
     55   HANDLER                   = 4,
     56   INTERCEPTOR               = 5,
     57   // Only used as a marker in LookupResult.
     58   NONEXISTENT               = 6
     59 };
     60 
     61 
     62 class Representation {
     63  public:
     64   enum Kind {
     65     kNone,
     66     kInteger8,
     67     kUInteger8,
     68     kInteger16,
     69     kUInteger16,
     70     kSmi,
     71     kInteger32,
     72     kDouble,
     73     kHeapObject,
     74     kTagged,
     75     kExternal,
     76     kNumRepresentations
     77   };
     78 
     79   Representation() : kind_(kNone) { }
     80 
     81   static Representation None() { return Representation(kNone); }
     82   static Representation Tagged() { return Representation(kTagged); }
     83   static Representation Integer8() { return Representation(kInteger8); }
     84   static Representation UInteger8() { return Representation(kUInteger8); }
     85   static Representation Integer16() { return Representation(kInteger16); }
     86   static Representation UInteger16() { return Representation(kUInteger16); }
     87   static Representation Smi() { return Representation(kSmi); }
     88   static Representation Integer32() { return Representation(kInteger32); }
     89   static Representation Double() { return Representation(kDouble); }
     90   static Representation HeapObject() { return Representation(kHeapObject); }
     91   static Representation External() { return Representation(kExternal); }
     92 
     93   static Representation FromKind(Kind kind) { return Representation(kind); }
     94 
     95   static Representation FromType(Type* type);
     96 
     97   bool Equals(const Representation& other) const {
     98     return kind_ == other.kind_;
     99   }
    100 
    101   bool IsCompatibleForLoad(const Representation& other) const {
    102     return (IsDouble() && other.IsDouble()) ||
    103         (!IsDouble() && !other.IsDouble());
    104   }
    105 
    106   bool IsCompatibleForStore(const Representation& other) const {
    107     return Equals(other);
    108   }
    109 
    110   bool is_more_general_than(const Representation& other) const {
    111     if (kind_ == kExternal && other.kind_ == kNone) return true;
    112     if (kind_ == kExternal && other.kind_ == kExternal) return false;
    113     if (kind_ == kNone && other.kind_ == kExternal) return false;
    114 
    115     ASSERT(kind_ != kExternal);
    116     ASSERT(other.kind_ != kExternal);
    117     if (IsHeapObject()) return other.IsNone();
    118     if (kind_ == kUInteger8 && other.kind_ == kInteger8) return false;
    119     if (kind_ == kUInteger16 && other.kind_ == kInteger16) return false;
    120     return kind_ > other.kind_;
    121   }
    122 
    123   bool fits_into(const Representation& other) const {
    124     return other.is_more_general_than(*this) || other.Equals(*this);
    125   }
    126 
    127   bool CanContainDouble(double value);
    128 
    129   Representation generalize(Representation other) {
    130     if (other.fits_into(*this)) return *this;
    131     if (other.is_more_general_than(*this)) return other;
    132     return Representation::Tagged();
    133   }
    134 
    135   int size() const {
    136     ASSERT(!IsNone());
    137     if (IsInteger8() || IsUInteger8()) {
    138       return sizeof(uint8_t);
    139     }
    140     if (IsInteger16() || IsUInteger16()) {
    141       return sizeof(uint16_t);
    142     }
    143     if (IsInteger32()) {
    144       return sizeof(uint32_t);
    145     }
    146     return kPointerSize;
    147   }
    148 
    149   Kind kind() const { return static_cast<Kind>(kind_); }
    150   bool IsNone() const { return kind_ == kNone; }
    151   bool IsInteger8() const { return kind_ == kInteger8; }
    152   bool IsUInteger8() const { return kind_ == kUInteger8; }
    153   bool IsInteger16() const { return kind_ == kInteger16; }
    154   bool IsUInteger16() const { return kind_ == kUInteger16; }
    155   bool IsTagged() const { return kind_ == kTagged; }
    156   bool IsSmi() const { return kind_ == kSmi; }
    157   bool IsSmiOrTagged() const { return IsSmi() || IsTagged(); }
    158   bool IsInteger32() const { return kind_ == kInteger32; }
    159   bool IsSmiOrInteger32() const { return IsSmi() || IsInteger32(); }
    160   bool IsDouble() const { return kind_ == kDouble; }
    161   bool IsHeapObject() const { return kind_ == kHeapObject; }
    162   bool IsExternal() const { return kind_ == kExternal; }
    163   bool IsSpecialization() const {
    164     return IsInteger8() || IsUInteger8() ||
    165       IsInteger16() || IsUInteger16() ||
    166       IsSmi() || IsInteger32() || IsDouble();
    167   }
    168   const char* Mnemonic() const;
    169 
    170  private:
    171   explicit Representation(Kind k) : kind_(k) { }
    172 
    173   // Make sure kind fits in int8.
    174   STATIC_ASSERT(kNumRepresentations <= (1 << kBitsPerByte));
    175 
    176   int8_t kind_;
    177 };
    178 
    179 
    180 static const int kDescriptorIndexBitCount = 10;
    181 // The maximum number of descriptors we want in a descriptor array (should
    182 // fit in a page).
    183 static const int kMaxNumberOfDescriptors =
    184     (1 << kDescriptorIndexBitCount) - 2;
    185 static const int kInvalidEnumCacheSentinel =
    186     (1 << kDescriptorIndexBitCount) - 1;
    187 
    188 
    189 // PropertyDetails captures type and attributes for a property.
    190 // They are used both in property dictionaries and instance descriptors.
    191 class PropertyDetails BASE_EMBEDDED {
    192  public:
    193   PropertyDetails(PropertyAttributes attributes,
    194                   PropertyType type,
    195                   int index) {
    196     value_ = TypeField::encode(type)
    197         | AttributesField::encode(attributes)
    198         | DictionaryStorageField::encode(index);
    199 
    200     ASSERT(type == this->type());
    201     ASSERT(attributes == this->attributes());
    202   }
    203 
    204   PropertyDetails(PropertyAttributes attributes,
    205                   PropertyType type,
    206                   Representation representation,
    207                   int field_index = 0) {
    208     value_ = TypeField::encode(type)
    209         | AttributesField::encode(attributes)
    210         | RepresentationField::encode(EncodeRepresentation(representation))
    211         | FieldIndexField::encode(field_index);
    212   }
    213 
    214   int pointer() const { return DescriptorPointer::decode(value_); }
    215 
    216   PropertyDetails set_pointer(int i) { return PropertyDetails(value_, i); }
    217 
    218   PropertyDetails CopyWithRepresentation(Representation representation) const {
    219     return PropertyDetails(value_, representation);
    220   }
    221   PropertyDetails CopyAddAttributes(PropertyAttributes new_attributes) {
    222     new_attributes =
    223         static_cast<PropertyAttributes>(attributes() | new_attributes);
    224     return PropertyDetails(value_, new_attributes);
    225   }
    226 
    227   // Conversion for storing details as Object*.
    228   explicit inline PropertyDetails(Smi* smi);
    229   inline Smi* AsSmi() const;
    230 
    231   static uint8_t EncodeRepresentation(Representation representation) {
    232     return representation.kind();
    233   }
    234 
    235   static Representation DecodeRepresentation(uint32_t bits) {
    236     return Representation::FromKind(static_cast<Representation::Kind>(bits));
    237   }
    238 
    239   PropertyType type() const { return TypeField::decode(value_); }
    240 
    241   PropertyAttributes attributes() const {
    242     return AttributesField::decode(value_);
    243   }
    244 
    245   int dictionary_index() const {
    246     return DictionaryStorageField::decode(value_);
    247   }
    248 
    249   Representation representation() const {
    250     ASSERT(type() != NORMAL);
    251     return DecodeRepresentation(RepresentationField::decode(value_));
    252   }
    253 
    254   int field_index() const {
    255     return FieldIndexField::decode(value_);
    256   }
    257 
    258   inline PropertyDetails AsDeleted() const;
    259 
    260   static bool IsValidIndex(int index) {
    261     return DictionaryStorageField::is_valid(index);
    262   }
    263 
    264   bool IsReadOnly() const { return (attributes() & READ_ONLY) != 0; }
    265   bool IsDontDelete() const { return (attributes() & DONT_DELETE) != 0; }
    266   bool IsDontEnum() const { return (attributes() & DONT_ENUM) != 0; }
    267   bool IsDeleted() const { return DeletedField::decode(value_) != 0;}
    268 
    269   // Bit fields in value_ (type, shift, size). Must be public so the
    270   // constants can be embedded in generated code.
    271   class TypeField:                public BitField<PropertyType,       0,  3> {};
    272   class AttributesField:          public BitField<PropertyAttributes, 3,  3> {};
    273 
    274   // Bit fields for normalized objects.
    275   class DeletedField:             public BitField<uint32_t,           6,  1> {};
    276   class DictionaryStorageField:   public BitField<uint32_t,           7, 24> {};
    277 
    278   // Bit fields for fast objects.
    279   class RepresentationField:      public BitField<uint32_t,           6,  4> {};
    280   class DescriptorPointer:        public BitField<uint32_t, 10,
    281       kDescriptorIndexBitCount> {};  // NOLINT
    282   class FieldIndexField:          public BitField<uint32_t,
    283       10 + kDescriptorIndexBitCount,
    284       kDescriptorIndexBitCount> {};  // NOLINT
    285   // All bits for fast objects must fix in a smi.
    286   STATIC_ASSERT(10 + kDescriptorIndexBitCount + kDescriptorIndexBitCount <= 31);
    287 
    288   static const int kInitialIndex = 1;
    289 
    290  private:
    291   PropertyDetails(int value, int pointer) {
    292     value_ = DescriptorPointer::update(value, pointer);
    293   }
    294   PropertyDetails(int value, Representation representation) {
    295     value_ = RepresentationField::update(
    296         value, EncodeRepresentation(representation));
    297   }
    298   PropertyDetails(int value, PropertyAttributes attributes) {
    299     value_ = AttributesField::update(value, attributes);
    300   }
    301 
    302   uint32_t value_;
    303 };
    304 
    305 } }  // namespace v8::internal
    306 
    307 #endif  // V8_PROPERTY_DETAILS_H_
    308