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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 // TODO(ishell): remove once FLAG_track_constant_fields is removed.
     11 #include "src/flags.h"
     12 #include "src/utils.h"
     13 
     14 namespace v8 {
     15 namespace internal {
     16 
     17 // ES6 6.1.7.1
     18 enum PropertyAttributes {
     19   NONE = ::v8::None,
     20   READ_ONLY = ::v8::ReadOnly,
     21   DONT_ENUM = ::v8::DontEnum,
     22   DONT_DELETE = ::v8::DontDelete,
     23 
     24   ALL_ATTRIBUTES_MASK = READ_ONLY | DONT_ENUM | DONT_DELETE,
     25 
     26   SEALED = DONT_DELETE,
     27   FROZEN = SEALED | READ_ONLY,
     28 
     29   ABSENT = 64,  // Used in runtime to indicate a property is absent.
     30   // ABSENT can never be stored in or returned from a descriptor's attributes
     31   // bitfield.  It is only used as a return value meaning the attributes of
     32   // a non-existent property.
     33 };
     34 
     35 
     36 enum PropertyFilter {
     37   ALL_PROPERTIES = 0,
     38   ONLY_WRITABLE = 1,
     39   ONLY_ENUMERABLE = 2,
     40   ONLY_CONFIGURABLE = 4,
     41   SKIP_STRINGS = 8,
     42   SKIP_SYMBOLS = 16,
     43   ONLY_ALL_CAN_READ = 32,
     44   ENUMERABLE_STRINGS = ONLY_ENUMERABLE | SKIP_SYMBOLS,
     45 };
     46 // Enable fast comparisons of PropertyAttributes against PropertyFilters.
     47 STATIC_ASSERT(ALL_PROPERTIES == static_cast<PropertyFilter>(NONE));
     48 STATIC_ASSERT(ONLY_WRITABLE == static_cast<PropertyFilter>(READ_ONLY));
     49 STATIC_ASSERT(ONLY_ENUMERABLE == static_cast<PropertyFilter>(DONT_ENUM));
     50 STATIC_ASSERT(ONLY_CONFIGURABLE == static_cast<PropertyFilter>(DONT_DELETE));
     51 STATIC_ASSERT(((SKIP_STRINGS | SKIP_SYMBOLS | ONLY_ALL_CAN_READ) &
     52                ALL_ATTRIBUTES_MASK) == 0);
     53 STATIC_ASSERT(ALL_PROPERTIES ==
     54               static_cast<PropertyFilter>(v8::PropertyFilter::ALL_PROPERTIES));
     55 STATIC_ASSERT(ONLY_WRITABLE ==
     56               static_cast<PropertyFilter>(v8::PropertyFilter::ONLY_WRITABLE));
     57 STATIC_ASSERT(ONLY_ENUMERABLE ==
     58               static_cast<PropertyFilter>(v8::PropertyFilter::ONLY_ENUMERABLE));
     59 STATIC_ASSERT(ONLY_CONFIGURABLE == static_cast<PropertyFilter>(
     60                                        v8::PropertyFilter::ONLY_CONFIGURABLE));
     61 STATIC_ASSERT(SKIP_STRINGS ==
     62               static_cast<PropertyFilter>(v8::PropertyFilter::SKIP_STRINGS));
     63 STATIC_ASSERT(SKIP_SYMBOLS ==
     64               static_cast<PropertyFilter>(v8::PropertyFilter::SKIP_SYMBOLS));
     65 
     66 class Smi;
     67 class TypeInfo;
     68 
     69 // Order of kinds is significant.
     70 // Must fit in the BitField PropertyDetails::KindField.
     71 enum PropertyKind { kData = 0, kAccessor = 1 };
     72 
     73 // Order of modes is significant.
     74 // Must fit in the BitField PropertyDetails::LocationField.
     75 enum PropertyLocation { kField = 0, kDescriptor = 1 };
     76 
     77 // Order of modes is significant.
     78 // Must fit in the BitField PropertyDetails::ConstnessField.
     79 enum PropertyConstness { kMutable = 0, kConst = 1 };
     80 
     81 // TODO(ishell): remove once constant field tracking is done.
     82 const PropertyConstness kDefaultFieldConstness =
     83     FLAG_track_constant_fields ? kConst : kMutable;
     84 
     85 class Representation {
     86  public:
     87   enum Kind {
     88     kNone,
     89     kInteger8,
     90     kUInteger8,
     91     kInteger16,
     92     kUInteger16,
     93     kSmi,
     94     kInteger32,
     95     kDouble,
     96     kHeapObject,
     97     kTagged,
     98     kExternal,
     99     kNumRepresentations
    100   };
    101 
    102   Representation() : kind_(kNone) { }
    103 
    104   static Representation None() { return Representation(kNone); }
    105   static Representation Tagged() { return Representation(kTagged); }
    106   static Representation Integer8() { return Representation(kInteger8); }
    107   static Representation UInteger8() { return Representation(kUInteger8); }
    108   static Representation Integer16() { return Representation(kInteger16); }
    109   static Representation UInteger16() { return Representation(kUInteger16); }
    110   static Representation Smi() { return Representation(kSmi); }
    111   static Representation Integer32() { return Representation(kInteger32); }
    112   static Representation Double() { return Representation(kDouble); }
    113   static Representation HeapObject() { return Representation(kHeapObject); }
    114   static Representation External() { return Representation(kExternal); }
    115 
    116   static Representation FromKind(Kind kind) { return Representation(kind); }
    117 
    118   bool Equals(const Representation& other) const {
    119     return kind_ == other.kind_;
    120   }
    121 
    122   bool IsCompatibleForLoad(const Representation& other) const {
    123     return (IsDouble() && other.IsDouble()) ||
    124         (!IsDouble() && !other.IsDouble());
    125   }
    126 
    127   bool IsCompatibleForStore(const Representation& other) const {
    128     return Equals(other);
    129   }
    130 
    131   bool is_more_general_than(const Representation& other) const {
    132     if (kind_ == kExternal && other.kind_ == kNone) return true;
    133     if (kind_ == kExternal && other.kind_ == kExternal) return false;
    134     if (kind_ == kNone && other.kind_ == kExternal) return false;
    135 
    136     DCHECK(kind_ != kExternal);
    137     DCHECK(other.kind_ != kExternal);
    138     if (IsHeapObject()) return other.IsNone();
    139     if (kind_ == kUInteger8 && other.kind_ == kInteger8) return false;
    140     if (kind_ == kUInteger16 && other.kind_ == kInteger16) return false;
    141     return kind_ > other.kind_;
    142   }
    143 
    144   bool fits_into(const Representation& other) const {
    145     return other.is_more_general_than(*this) || other.Equals(*this);
    146   }
    147 
    148   Representation generalize(Representation other) {
    149     if (other.fits_into(*this)) return *this;
    150     if (other.is_more_general_than(*this)) return other;
    151     return Representation::Tagged();
    152   }
    153 
    154   int size() const {
    155     DCHECK(!IsNone());
    156     if (IsInteger8() || IsUInteger8()) {
    157       return sizeof(uint8_t);
    158     }
    159     if (IsInteger16() || IsUInteger16()) {
    160       return sizeof(uint16_t);
    161     }
    162     if (IsInteger32()) {
    163       return sizeof(uint32_t);
    164     }
    165     return kPointerSize;
    166   }
    167 
    168   Kind kind() const { return static_cast<Kind>(kind_); }
    169   bool IsNone() const { return kind_ == kNone; }
    170   bool IsInteger8() const { return kind_ == kInteger8; }
    171   bool IsUInteger8() const { return kind_ == kUInteger8; }
    172   bool IsInteger16() const { return kind_ == kInteger16; }
    173   bool IsUInteger16() const { return kind_ == kUInteger16; }
    174   bool IsTagged() const { return kind_ == kTagged; }
    175   bool IsSmi() const { return kind_ == kSmi; }
    176   bool IsSmiOrTagged() const { return IsSmi() || IsTagged(); }
    177   bool IsInteger32() const { return kind_ == kInteger32; }
    178   bool IsSmiOrInteger32() const { return IsSmi() || IsInteger32(); }
    179   bool IsDouble() const { return kind_ == kDouble; }
    180   bool IsHeapObject() const { return kind_ == kHeapObject; }
    181   bool IsExternal() const { return kind_ == kExternal; }
    182   bool IsSpecialization() const {
    183     return IsInteger8() || IsUInteger8() ||
    184       IsInteger16() || IsUInteger16() ||
    185       IsSmi() || IsInteger32() || IsDouble();
    186   }
    187   const char* Mnemonic() const;
    188 
    189  private:
    190   explicit Representation(Kind k) : kind_(k) { }
    191 
    192   // Make sure kind fits in int8.
    193   STATIC_ASSERT(kNumRepresentations <= (1 << kBitsPerByte));
    194 
    195   int8_t kind_;
    196 };
    197 
    198 
    199 static const int kDescriptorIndexBitCount = 10;
    200 // The maximum number of descriptors we want in a descriptor array (should
    201 // fit in a page).
    202 static const int kMaxNumberOfDescriptors =
    203     (1 << kDescriptorIndexBitCount) - 2;
    204 static const int kInvalidEnumCacheSentinel =
    205     (1 << kDescriptorIndexBitCount) - 1;
    206 
    207 enum class PropertyCellType {
    208   // Meaningful when a property cell does not contain the hole.
    209   kUndefined,     // The PREMONOMORPHIC of property cells.
    210   kConstant,      // Cell has been assigned only once.
    211   kConstantType,  // Cell has been assigned only one type.
    212   kMutable,       // Cell will no longer be tracked as constant.
    213 
    214   // Meaningful when a property cell contains the hole.
    215   kUninitialized = kUndefined,  // Cell has never been initialized.
    216   kInvalidated = kConstant,     // Cell has been deleted, invalidated or never
    217                                 // existed.
    218 
    219   // For dictionaries not holding cells.
    220   kNoCell = kMutable,
    221 };
    222 
    223 enum class PropertyCellConstantType {
    224   kSmi,
    225   kStableMap,
    226 };
    227 
    228 
    229 // PropertyDetails captures type and attributes for a property.
    230 // They are used both in property dictionaries and instance descriptors.
    231 class PropertyDetails BASE_EMBEDDED {
    232  public:
    233   // Property details for dictionary mode properties/elements.
    234   PropertyDetails(PropertyKind kind, PropertyAttributes attributes, int index,
    235                   PropertyCellType cell_type) {
    236     value_ = KindField::encode(kind) | LocationField::encode(kField) |
    237              AttributesField::encode(attributes) |
    238              DictionaryStorageField::encode(index) |
    239              PropertyCellTypeField::encode(cell_type);
    240   }
    241 
    242   // Property details for fast mode properties.
    243   PropertyDetails(PropertyKind kind, PropertyAttributes attributes,
    244                   PropertyLocation location, PropertyConstness constness,
    245                   Representation representation, int field_index = 0) {
    246     value_ = KindField::encode(kind) | AttributesField::encode(attributes) |
    247              LocationField::encode(location) |
    248              ConstnessField::encode(constness) |
    249              RepresentationField::encode(EncodeRepresentation(representation)) |
    250              FieldIndexField::encode(field_index);
    251   }
    252 
    253   static PropertyDetails Empty(
    254       PropertyCellType cell_type = PropertyCellType::kNoCell) {
    255     return PropertyDetails(kData, NONE, 0, cell_type);
    256   }
    257 
    258   int pointer() const { return DescriptorPointer::decode(value_); }
    259 
    260   PropertyDetails set_pointer(int i) const {
    261     return PropertyDetails(value_, i);
    262   }
    263 
    264   PropertyDetails set_cell_type(PropertyCellType type) const {
    265     PropertyDetails details = *this;
    266     details.value_ = PropertyCellTypeField::update(details.value_, type);
    267     return details;
    268   }
    269 
    270   PropertyDetails set_index(int index) const {
    271     PropertyDetails details = *this;
    272     details.value_ = DictionaryStorageField::update(details.value_, index);
    273     return details;
    274   }
    275 
    276   PropertyDetails CopyWithRepresentation(Representation representation) const {
    277     return PropertyDetails(value_, representation);
    278   }
    279   PropertyDetails CopyWithConstness(PropertyConstness constness) const {
    280     return PropertyDetails(value_, constness);
    281   }
    282   PropertyDetails CopyAddAttributes(PropertyAttributes new_attributes) const {
    283     new_attributes =
    284         static_cast<PropertyAttributes>(attributes() | new_attributes);
    285     return PropertyDetails(value_, new_attributes);
    286   }
    287 
    288   // Conversion for storing details as Object*.
    289   explicit inline PropertyDetails(Smi* smi);
    290   inline Smi* AsSmi() const;
    291 
    292   static uint8_t EncodeRepresentation(Representation representation) {
    293     return representation.kind();
    294   }
    295 
    296   static Representation DecodeRepresentation(uint32_t bits) {
    297     return Representation::FromKind(static_cast<Representation::Kind>(bits));
    298   }
    299 
    300   PropertyKind kind() const { return KindField::decode(value_); }
    301   PropertyLocation location() const { return LocationField::decode(value_); }
    302   PropertyConstness constness() const { return ConstnessField::decode(value_); }
    303 
    304   PropertyAttributes attributes() const {
    305     return AttributesField::decode(value_);
    306   }
    307 
    308   int dictionary_index() const {
    309     return DictionaryStorageField::decode(value_);
    310   }
    311 
    312   Representation representation() const {
    313     return DecodeRepresentation(RepresentationField::decode(value_));
    314   }
    315 
    316   int field_index() const { return FieldIndexField::decode(value_); }
    317 
    318   inline int field_width_in_words() const;
    319 
    320   static bool IsValidIndex(int index) {
    321     return DictionaryStorageField::is_valid(index);
    322   }
    323 
    324   bool IsReadOnly() const { return (attributes() & READ_ONLY) != 0; }
    325   bool IsConfigurable() const { return (attributes() & DONT_DELETE) == 0; }
    326   bool IsDontEnum() const { return (attributes() & DONT_ENUM) != 0; }
    327   bool IsEnumerable() const { return !IsDontEnum(); }
    328   PropertyCellType cell_type() const {
    329     return PropertyCellTypeField::decode(value_);
    330   }
    331 
    332   // Bit fields in value_ (type, shift, size). Must be public so the
    333   // constants can be embedded in generated code.
    334   class KindField : public BitField<PropertyKind, 0, 1> {};
    335   class LocationField : public BitField<PropertyLocation, KindField::kNext, 1> {
    336   };
    337   class ConstnessField
    338       : public BitField<PropertyConstness, LocationField::kNext, 1> {};
    339   class AttributesField
    340       : public BitField<PropertyAttributes, ConstnessField::kNext, 3> {};
    341   static const int kAttributesReadOnlyMask =
    342       (READ_ONLY << AttributesField::kShift);
    343 
    344   // Bit fields for normalized objects.
    345   class PropertyCellTypeField
    346       : public BitField<PropertyCellType, AttributesField::kNext, 2> {};
    347   class DictionaryStorageField
    348       : public BitField<uint32_t, PropertyCellTypeField::kNext, 23> {};
    349 
    350   // Bit fields for fast objects.
    351   class RepresentationField
    352       : public BitField<uint32_t, AttributesField::kNext, 4> {};
    353   class DescriptorPointer
    354       : public BitField<uint32_t, RepresentationField::kNext,
    355                         kDescriptorIndexBitCount> {};  // NOLINT
    356   class FieldIndexField : public BitField<uint32_t, DescriptorPointer::kNext,
    357                                           kDescriptorIndexBitCount> {
    358   };  // NOLINT
    359 
    360   // All bits for both fast and slow objects must fit in a smi.
    361   STATIC_ASSERT(DictionaryStorageField::kNext <= 31);
    362   STATIC_ASSERT(FieldIndexField::kNext <= 31);
    363 
    364   static const int kInitialIndex = 1;
    365 
    366 #ifdef OBJECT_PRINT
    367   // For our gdb macros, we should perhaps change these in the future.
    368   void Print(bool dictionary_mode);
    369 #endif
    370 
    371   enum PrintMode {
    372     kPrintAttributes = 1 << 0,
    373     kPrintFieldIndex = 1 << 1,
    374     kPrintRepresentation = 1 << 2,
    375     kPrintPointer = 1 << 3,
    376 
    377     kForProperties = kPrintFieldIndex,
    378     kForTransitions = kPrintAttributes,
    379     kPrintFull = -1,
    380   };
    381   void PrintAsSlowTo(std::ostream& out);
    382   void PrintAsFastTo(std::ostream& out, PrintMode mode = kPrintFull);
    383 
    384  private:
    385   PropertyDetails(int value, int pointer) {
    386     value_ = DescriptorPointer::update(value, pointer);
    387   }
    388   PropertyDetails(int value, Representation representation) {
    389     value_ = RepresentationField::update(
    390         value, EncodeRepresentation(representation));
    391   }
    392   PropertyDetails(int value, PropertyConstness constness) {
    393     value_ = ConstnessField::update(value, constness);
    394   }
    395   PropertyDetails(int value, PropertyAttributes attributes) {
    396     value_ = AttributesField::update(value, attributes);
    397   }
    398 
    399   uint32_t value_;
    400 };
    401 
    402 // kField location is more general than kDescriptor, kDescriptor generalizes
    403 // only to itself.
    404 inline bool IsGeneralizableTo(PropertyLocation a, PropertyLocation b) {
    405   return b == kField || a == kDescriptor;
    406 }
    407 
    408 // kMutable constness is more general than kConst, kConst generalizes only to
    409 // itself.
    410 inline bool IsGeneralizableTo(PropertyConstness a, PropertyConstness b) {
    411   return b == kMutable || a == kConst;
    412 }
    413 
    414 inline PropertyConstness GeneralizeConstness(PropertyConstness a,
    415                                              PropertyConstness b) {
    416   return a == kMutable ? kMutable : b;
    417 }
    418 
    419 std::ostream& operator<<(std::ostream& os,
    420                          const PropertyAttributes& attributes);
    421 }  // namespace internal
    422 }  // namespace v8
    423 
    424 #endif  // V8_PROPERTY_DETAILS_H_
    425