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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 };
     55 
     56 
     57 class Representation {
     58  public:
     59   enum Kind {
     60     kNone,
     61     kInteger8,
     62     kUInteger8,
     63     kInteger16,
     64     kUInteger16,
     65     kSmi,
     66     kInteger32,
     67     kDouble,
     68     kHeapObject,
     69     kTagged,
     70     kExternal,
     71     kNumRepresentations
     72   };
     73 
     74   Representation() : kind_(kNone) { }
     75 
     76   static Representation None() { return Representation(kNone); }
     77   static Representation Tagged() { return Representation(kTagged); }
     78   static Representation Integer8() { return Representation(kInteger8); }
     79   static Representation UInteger8() { return Representation(kUInteger8); }
     80   static Representation Integer16() { return Representation(kInteger16); }
     81   static Representation UInteger16() { return Representation(kUInteger16); }
     82   static Representation Smi() { return Representation(kSmi); }
     83   static Representation Integer32() { return Representation(kInteger32); }
     84   static Representation Double() { return Representation(kDouble); }
     85   static Representation HeapObject() { return Representation(kHeapObject); }
     86   static Representation External() { return Representation(kExternal); }
     87 
     88   static Representation FromKind(Kind kind) { return Representation(kind); }
     89 
     90   static Representation FromType(Type* type);
     91 
     92   bool Equals(const Representation& other) const {
     93     return kind_ == other.kind_;
     94   }
     95 
     96   bool IsCompatibleForLoad(const Representation& other) const {
     97     return (IsDouble() && other.IsDouble()) ||
     98         (!IsDouble() && !other.IsDouble());
     99   }
    100 
    101   bool IsCompatibleForStore(const Representation& other) const {
    102     return Equals(other);
    103   }
    104 
    105   bool is_more_general_than(const Representation& other) const {
    106     if (kind_ == kExternal && other.kind_ == kNone) return true;
    107     if (kind_ == kExternal && other.kind_ == kExternal) return false;
    108     if (kind_ == kNone && other.kind_ == kExternal) return false;
    109 
    110     DCHECK(kind_ != kExternal);
    111     DCHECK(other.kind_ != kExternal);
    112     if (IsHeapObject()) return other.IsNone();
    113     if (kind_ == kUInteger8 && other.kind_ == kInteger8) return false;
    114     if (kind_ == kUInteger16 && other.kind_ == kInteger16) return false;
    115     return kind_ > other.kind_;
    116   }
    117 
    118   bool fits_into(const Representation& other) const {
    119     return other.is_more_general_than(*this) || other.Equals(*this);
    120   }
    121 
    122   Representation generalize(Representation other) {
    123     if (other.fits_into(*this)) return *this;
    124     if (other.is_more_general_than(*this)) return other;
    125     return Representation::Tagged();
    126   }
    127 
    128   int size() const {
    129     DCHECK(!IsNone());
    130     if (IsInteger8() || IsUInteger8()) {
    131       return sizeof(uint8_t);
    132     }
    133     if (IsInteger16() || IsUInteger16()) {
    134       return sizeof(uint16_t);
    135     }
    136     if (IsInteger32()) {
    137       return sizeof(uint32_t);
    138     }
    139     return kPointerSize;
    140   }
    141 
    142   Kind kind() const { return static_cast<Kind>(kind_); }
    143   bool IsNone() const { return kind_ == kNone; }
    144   bool IsInteger8() const { return kind_ == kInteger8; }
    145   bool IsUInteger8() const { return kind_ == kUInteger8; }
    146   bool IsInteger16() const { return kind_ == kInteger16; }
    147   bool IsUInteger16() const { return kind_ == kUInteger16; }
    148   bool IsTagged() const { return kind_ == kTagged; }
    149   bool IsSmi() const { return kind_ == kSmi; }
    150   bool IsSmiOrTagged() const { return IsSmi() || IsTagged(); }
    151   bool IsInteger32() const { return kind_ == kInteger32; }
    152   bool IsSmiOrInteger32() const { return IsSmi() || IsInteger32(); }
    153   bool IsDouble() const { return kind_ == kDouble; }
    154   bool IsHeapObject() const { return kind_ == kHeapObject; }
    155   bool IsExternal() const { return kind_ == kExternal; }
    156   bool IsSpecialization() const {
    157     return IsInteger8() || IsUInteger8() ||
    158       IsInteger16() || IsUInteger16() ||
    159       IsSmi() || IsInteger32() || IsDouble();
    160   }
    161   const char* Mnemonic() const;
    162 
    163  private:
    164   explicit Representation(Kind k) : kind_(k) { }
    165 
    166   // Make sure kind fits in int8.
    167   STATIC_ASSERT(kNumRepresentations <= (1 << kBitsPerByte));
    168 
    169   int8_t kind_;
    170 };
    171 
    172 
    173 static const int kDescriptorIndexBitCount = 10;
    174 // The maximum number of descriptors we want in a descriptor array (should
    175 // fit in a page).
    176 static const int kMaxNumberOfDescriptors =
    177     (1 << kDescriptorIndexBitCount) - 2;
    178 static const int kInvalidEnumCacheSentinel =
    179     (1 << kDescriptorIndexBitCount) - 1;
    180 
    181 
    182 // PropertyDetails captures type and attributes for a property.
    183 // They are used both in property dictionaries and instance descriptors.
    184 class PropertyDetails BASE_EMBEDDED {
    185  public:
    186   PropertyDetails(PropertyAttributes attributes,
    187                   PropertyType type,
    188                   int index) {
    189     value_ = TypeField::encode(type)
    190         | AttributesField::encode(attributes)
    191         | DictionaryStorageField::encode(index);
    192 
    193     DCHECK(type == this->type());
    194     DCHECK(attributes == this->attributes());
    195   }
    196 
    197   PropertyDetails(PropertyAttributes attributes,
    198                   PropertyType type,
    199                   Representation representation,
    200                   int field_index = 0) {
    201     value_ = TypeField::encode(type)
    202         | AttributesField::encode(attributes)
    203         | RepresentationField::encode(EncodeRepresentation(representation))
    204         | FieldIndexField::encode(field_index);
    205   }
    206 
    207   int pointer() const { return DescriptorPointer::decode(value_); }
    208 
    209   PropertyDetails set_pointer(int i) { return PropertyDetails(value_, i); }
    210 
    211   PropertyDetails CopyWithRepresentation(Representation representation) const {
    212     return PropertyDetails(value_, representation);
    213   }
    214   PropertyDetails CopyAddAttributes(PropertyAttributes new_attributes) {
    215     new_attributes =
    216         static_cast<PropertyAttributes>(attributes() | new_attributes);
    217     return PropertyDetails(value_, new_attributes);
    218   }
    219 
    220   // Conversion for storing details as Object*.
    221   explicit inline PropertyDetails(Smi* smi);
    222   inline Smi* AsSmi() const;
    223 
    224   static uint8_t EncodeRepresentation(Representation representation) {
    225     return representation.kind();
    226   }
    227 
    228   static Representation DecodeRepresentation(uint32_t bits) {
    229     return Representation::FromKind(static_cast<Representation::Kind>(bits));
    230   }
    231 
    232   PropertyType type() const { return TypeField::decode(value_); }
    233 
    234   PropertyAttributes attributes() const {
    235     return AttributesField::decode(value_);
    236   }
    237 
    238   int dictionary_index() const {
    239     return DictionaryStorageField::decode(value_);
    240   }
    241 
    242   Representation representation() const {
    243     DCHECK(type() != NORMAL);
    244     return DecodeRepresentation(RepresentationField::decode(value_));
    245   }
    246 
    247   int field_index() const {
    248     return FieldIndexField::decode(value_);
    249   }
    250 
    251   inline PropertyDetails AsDeleted() const;
    252 
    253   static bool IsValidIndex(int index) {
    254     return DictionaryStorageField::is_valid(index);
    255   }
    256 
    257   bool IsReadOnly() const { return (attributes() & READ_ONLY) != 0; }
    258   bool IsConfigurable() const { return (attributes() & DONT_DELETE) == 0; }
    259   bool IsDontEnum() const { return (attributes() & DONT_ENUM) != 0; }
    260   bool IsDeleted() const { return DeletedField::decode(value_) != 0;}
    261 
    262   // Bit fields in value_ (type, shift, size). Must be public so the
    263   // constants can be embedded in generated code.
    264   class TypeField : public BitField<PropertyType, 0, 2> {};
    265   class AttributesField : public BitField<PropertyAttributes, 2, 3> {};
    266 
    267   // Bit fields for normalized objects.
    268   class DeletedField : public BitField<uint32_t, 5, 1> {};
    269   class DictionaryStorageField : public BitField<uint32_t, 6, 24> {};
    270 
    271   // Bit fields for fast objects.
    272   class RepresentationField : public BitField<uint32_t, 5, 4> {};
    273   class DescriptorPointer
    274       : public BitField<uint32_t, 9, kDescriptorIndexBitCount> {};  // NOLINT
    275   class FieldIndexField
    276       : public BitField<uint32_t, 9 + kDescriptorIndexBitCount,
    277                         kDescriptorIndexBitCount> {};  // NOLINT
    278   // All bits for fast objects must fix in a smi.
    279   STATIC_ASSERT(9 + kDescriptorIndexBitCount + kDescriptorIndexBitCount <= 31);
    280 
    281   static const int kInitialIndex = 1;
    282 
    283  private:
    284   PropertyDetails(int value, int pointer) {
    285     value_ = DescriptorPointer::update(value, pointer);
    286   }
    287   PropertyDetails(int value, Representation representation) {
    288     value_ = RepresentationField::update(
    289         value, EncodeRepresentation(representation));
    290   }
    291   PropertyDetails(int value, PropertyAttributes attributes) {
    292     value_ = AttributesField::update(value, attributes);
    293   }
    294 
    295   uint32_t value_;
    296 };
    297 
    298 } }  // namespace v8::internal
    299 
    300 #endif  // V8_PROPERTY_DETAILS_H_
    301