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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 class 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 ? PropertyConstness::kConst
     84                                : PropertyConstness::kMutable;
     85 
     86 class Representation {
     87  public:
     88   enum Kind {
     89     kNone,
     90     kInteger8,
     91     kUInteger8,
     92     kInteger16,
     93     kUInteger16,
     94     kSmi,
     95     kInteger32,
     96     kDouble,
     97     kHeapObject,
     98     kTagged,
     99     kExternal,
    100     kNumRepresentations
    101   };
    102 
    103   Representation() : kind_(kNone) { }
    104 
    105   static Representation None() { return Representation(kNone); }
    106   static Representation Tagged() { return Representation(kTagged); }
    107   static Representation Integer8() { return Representation(kInteger8); }
    108   static Representation UInteger8() { return Representation(kUInteger8); }
    109   static Representation Integer16() { return Representation(kInteger16); }
    110   static Representation UInteger16() { return Representation(kUInteger16); }
    111   static Representation Smi() { return Representation(kSmi); }
    112   static Representation Integer32() { return Representation(kInteger32); }
    113   static Representation Double() { return Representation(kDouble); }
    114   static Representation HeapObject() { return Representation(kHeapObject); }
    115   static Representation External() { return Representation(kExternal); }
    116 
    117   static Representation FromKind(Kind kind) { return Representation(kind); }
    118 
    119   bool Equals(const Representation& other) const {
    120     return kind_ == other.kind_;
    121   }
    122 
    123   bool IsCompatibleForLoad(const Representation& other) const {
    124     return (IsDouble() && other.IsDouble()) ||
    125         (!IsDouble() && !other.IsDouble());
    126   }
    127 
    128   bool IsCompatibleForStore(const Representation& other) const {
    129     return Equals(other);
    130   }
    131 
    132   bool is_more_general_than(const Representation& other) const {
    133     if (kind_ == kExternal && other.kind_ == kNone) return true;
    134     if (kind_ == kExternal && other.kind_ == kExternal) return false;
    135     if (kind_ == kNone && other.kind_ == kExternal) return false;
    136 
    137     DCHECK_NE(kind_, kExternal);
    138     DCHECK_NE(other.kind_, kExternal);
    139     if (IsHeapObject()) return other.IsNone();
    140     if (kind_ == kUInteger8 && other.kind_ == kInteger8) return false;
    141     if (kind_ == kUInteger16 && other.kind_ == kInteger16) return false;
    142     return kind_ > other.kind_;
    143   }
    144 
    145   bool fits_into(const Representation& other) const {
    146     return other.is_more_general_than(*this) || other.Equals(*this);
    147   }
    148 
    149   Representation generalize(Representation other) {
    150     if (other.fits_into(*this)) return *this;
    151     if (other.is_more_general_than(*this)) return other;
    152     return Representation::Tagged();
    153   }
    154 
    155   int size() const {
    156     DCHECK(!IsNone());
    157     if (IsInteger8() || IsUInteger8()) {
    158       return sizeof(uint8_t);
    159     }
    160     if (IsInteger16() || IsUInteger16()) {
    161       return sizeof(uint16_t);
    162     }
    163     if (IsInteger32()) {
    164       return sizeof(uint32_t);
    165     }
    166     return kPointerSize;
    167   }
    168 
    169   Kind kind() const { return static_cast<Kind>(kind_); }
    170   bool IsNone() const { return kind_ == kNone; }
    171   bool IsInteger8() const { return kind_ == kInteger8; }
    172   bool IsUInteger8() const { return kind_ == kUInteger8; }
    173   bool IsInteger16() const { return kind_ == kInteger16; }
    174   bool IsUInteger16() const { return kind_ == kUInteger16; }
    175   bool IsTagged() const { return kind_ == kTagged; }
    176   bool IsSmi() const { return kind_ == kSmi; }
    177   bool IsSmiOrTagged() const { return IsSmi() || IsTagged(); }
    178   bool IsInteger32() const { return kind_ == kInteger32; }
    179   bool IsSmiOrInteger32() const { return IsSmi() || IsInteger32(); }
    180   bool IsDouble() const { return kind_ == kDouble; }
    181   bool IsHeapObject() const { return kind_ == kHeapObject; }
    182   bool IsExternal() const { return kind_ == kExternal; }
    183   bool IsSpecialization() const {
    184     return IsInteger8() || IsUInteger8() ||
    185       IsInteger16() || IsUInteger16() ||
    186       IsSmi() || IsInteger32() || IsDouble();
    187   }
    188   const char* Mnemonic() const;
    189 
    190  private:
    191   explicit Representation(Kind k) : kind_(k) { }
    192 
    193   // Make sure kind fits in int8.
    194   STATIC_ASSERT(kNumRepresentations <= (1 << kBitsPerByte));
    195 
    196   int8_t kind_;
    197 };
    198 
    199 
    200 static const int kDescriptorIndexBitCount = 10;
    201 static const int kFirstInobjectPropertyOffsetBitCount = 7;
    202 // The maximum number of descriptors we want in a descriptor array.  It should
    203 // fit in a page and also the following should hold:
    204 // kMaxNumberOfDescriptors + kFieldsAdded <= PropertyArray::kMaxLength.
    205 static const int kMaxNumberOfDescriptors = (1 << kDescriptorIndexBitCount) - 4;
    206 static const int kInvalidEnumCacheSentinel =
    207     (1 << kDescriptorIndexBitCount) - 1;
    208 
    209 enum class PropertyCellType {
    210   // Meaningful when a property cell does not contain the hole.
    211   kUndefined,     // The PREMONOMORPHIC of property cells.
    212   kConstant,      // Cell has been assigned only once.
    213   kConstantType,  // Cell has been assigned only one type.
    214   kMutable,       // Cell will no longer be tracked as constant.
    215 
    216   // Meaningful when a property cell contains the hole.
    217   kUninitialized = kUndefined,  // Cell has never been initialized.
    218   kInvalidated = kConstant,     // Cell has been deleted, invalidated or never
    219                                 // existed.
    220 
    221   // For dictionaries not holding cells.
    222   kNoCell = kMutable,
    223 };
    224 
    225 enum class PropertyCellConstantType {
    226   kSmi,
    227   kStableMap,
    228 };
    229 
    230 
    231 // PropertyDetails captures type and attributes for a property.
    232 // They are used both in property dictionaries and instance descriptors.
    233 class PropertyDetails BASE_EMBEDDED {
    234  public:
    235   // Property details for dictionary mode properties/elements.
    236   PropertyDetails(PropertyKind kind, PropertyAttributes attributes,
    237                   PropertyCellType cell_type, int dictionary_index = 0) {
    238     value_ = KindField::encode(kind) | LocationField::encode(kField) |
    239              AttributesField::encode(attributes) |
    240              DictionaryStorageField::encode(dictionary_index) |
    241              PropertyCellTypeField::encode(cell_type);
    242   }
    243 
    244   // Property details for fast mode properties.
    245   PropertyDetails(PropertyKind kind, PropertyAttributes attributes,
    246                   PropertyLocation location, PropertyConstness constness,
    247                   Representation representation, int field_index = 0) {
    248     value_ = KindField::encode(kind) | AttributesField::encode(attributes) |
    249              LocationField::encode(location) |
    250              ConstnessField::encode(constness) |
    251              RepresentationField::encode(EncodeRepresentation(representation)) |
    252              FieldIndexField::encode(field_index);
    253   }
    254 
    255   static PropertyDetails Empty(
    256       PropertyCellType cell_type = PropertyCellType::kNoCell) {
    257     return PropertyDetails(kData, NONE, cell_type);
    258   }
    259 
    260   int pointer() const { return DescriptorPointer::decode(value_); }
    261 
    262   PropertyDetails set_pointer(int i) const {
    263     return PropertyDetails(value_, i);
    264   }
    265 
    266   PropertyDetails set_cell_type(PropertyCellType type) const {
    267     PropertyDetails details = *this;
    268     details.value_ = PropertyCellTypeField::update(details.value_, type);
    269     return details;
    270   }
    271 
    272   PropertyDetails set_index(int index) const {
    273     PropertyDetails details = *this;
    274     details.value_ = DictionaryStorageField::update(details.value_, index);
    275     return details;
    276   }
    277 
    278   PropertyDetails CopyWithRepresentation(Representation representation) const {
    279     return PropertyDetails(value_, representation);
    280   }
    281   PropertyDetails CopyWithConstness(PropertyConstness constness) const {
    282     return PropertyDetails(value_, constness);
    283   }
    284   PropertyDetails CopyAddAttributes(PropertyAttributes new_attributes) const {
    285     new_attributes =
    286         static_cast<PropertyAttributes>(attributes() | new_attributes);
    287     return PropertyDetails(value_, new_attributes);
    288   }
    289 
    290   // Conversion for storing details as Object*.
    291   explicit inline PropertyDetails(Smi* smi);
    292   inline Smi* AsSmi() const;
    293 
    294   static uint8_t EncodeRepresentation(Representation representation) {
    295     return representation.kind();
    296   }
    297 
    298   static Representation DecodeRepresentation(uint32_t bits) {
    299     return Representation::FromKind(static_cast<Representation::Kind>(bits));
    300   }
    301 
    302   PropertyKind kind() const { return KindField::decode(value_); }
    303   PropertyLocation location() const { return LocationField::decode(value_); }
    304   PropertyConstness constness() const { return ConstnessField::decode(value_); }
    305 
    306   PropertyAttributes attributes() const {
    307     return AttributesField::decode(value_);
    308   }
    309 
    310   int dictionary_index() const {
    311     return DictionaryStorageField::decode(value_);
    312   }
    313 
    314   Representation representation() const {
    315     return DecodeRepresentation(RepresentationField::decode(value_));
    316   }
    317 
    318   int field_index() const { return FieldIndexField::decode(value_); }
    319 
    320   inline int field_width_in_words() const;
    321 
    322   static bool IsValidIndex(int index) {
    323     return DictionaryStorageField::is_valid(index);
    324   }
    325 
    326   bool IsReadOnly() const { return (attributes() & READ_ONLY) != 0; }
    327   bool IsConfigurable() const { return (attributes() & DONT_DELETE) == 0; }
    328   bool IsDontEnum() const { return (attributes() & DONT_ENUM) != 0; }
    329   bool IsEnumerable() const { return !IsDontEnum(); }
    330   PropertyCellType cell_type() const {
    331     return PropertyCellTypeField::decode(value_);
    332   }
    333 
    334   // Bit fields in value_ (type, shift, size). Must be public so the
    335   // constants can be embedded in generated code.
    336   class KindField : public BitField<PropertyKind, 0, 1> {};
    337   class LocationField : public BitField<PropertyLocation, KindField::kNext, 1> {
    338   };
    339   class ConstnessField
    340       : public BitField<PropertyConstness, LocationField::kNext, 1> {};
    341   class AttributesField
    342       : public BitField<PropertyAttributes, ConstnessField::kNext, 3> {};
    343   static const int kAttributesReadOnlyMask =
    344       (READ_ONLY << AttributesField::kShift);
    345   static const int kAttributesDontDeleteMask =
    346       (DONT_DELETE << AttributesField::kShift);
    347   static const int kAttributesDontEnumMask =
    348       (DONT_ENUM << AttributesField::kShift);
    349 
    350   // Bit fields for normalized objects.
    351   class PropertyCellTypeField
    352       : public BitField<PropertyCellType, AttributesField::kNext, 2> {};
    353   class DictionaryStorageField
    354       : public BitField<uint32_t, PropertyCellTypeField::kNext, 23> {};
    355 
    356   // Bit fields for fast objects.
    357   class RepresentationField
    358       : public BitField<uint32_t, AttributesField::kNext, 4> {};
    359   class DescriptorPointer
    360       : public BitField<uint32_t, RepresentationField::kNext,
    361                         kDescriptorIndexBitCount> {};  // NOLINT
    362   class FieldIndexField : public BitField<uint32_t, DescriptorPointer::kNext,
    363                                           kDescriptorIndexBitCount> {
    364   };  // NOLINT
    365 
    366   // All bits for both fast and slow objects must fit in a smi.
    367   STATIC_ASSERT(DictionaryStorageField::kNext <= 31);
    368   STATIC_ASSERT(FieldIndexField::kNext <= 31);
    369 
    370   static const int kInitialIndex = 1;
    371 
    372 #ifdef OBJECT_PRINT
    373   // For our gdb macros, we should perhaps change these in the future.
    374   void Print(bool dictionary_mode);
    375 #endif
    376 
    377   enum PrintMode {
    378     kPrintAttributes = 1 << 0,
    379     kPrintFieldIndex = 1 << 1,
    380     kPrintRepresentation = 1 << 2,
    381     kPrintPointer = 1 << 3,
    382 
    383     kForProperties = kPrintFieldIndex,
    384     kForTransitions = kPrintAttributes,
    385     kPrintFull = -1,
    386   };
    387   void PrintAsSlowTo(std::ostream& out);
    388   void PrintAsFastTo(std::ostream& out, PrintMode mode = kPrintFull);
    389 
    390  private:
    391   PropertyDetails(int value, int pointer) {
    392     value_ = DescriptorPointer::update(value, pointer);
    393   }
    394   PropertyDetails(int value, Representation representation) {
    395     value_ = RepresentationField::update(
    396         value, EncodeRepresentation(representation));
    397   }
    398   PropertyDetails(int value, PropertyConstness constness) {
    399     value_ = ConstnessField::update(value, constness);
    400   }
    401   PropertyDetails(int value, PropertyAttributes attributes) {
    402     value_ = AttributesField::update(value, attributes);
    403   }
    404 
    405   uint32_t value_;
    406 };
    407 
    408 // kField location is more general than kDescriptor, kDescriptor generalizes
    409 // only to itself.
    410 inline bool IsGeneralizableTo(PropertyLocation a, PropertyLocation b) {
    411   return b == kField || a == kDescriptor;
    412 }
    413 
    414 // PropertyConstness::kMutable constness is more general than
    415 // VariableMode::kConst, VariableMode::kConst generalizes only to itself.
    416 inline bool IsGeneralizableTo(PropertyConstness a, PropertyConstness b) {
    417   return b == PropertyConstness::kMutable || a == PropertyConstness::kConst;
    418 }
    419 
    420 inline PropertyConstness GeneralizeConstness(PropertyConstness a,
    421                                              PropertyConstness b) {
    422   return a == PropertyConstness::kMutable ? PropertyConstness::kMutable : b;
    423 }
    424 
    425 std::ostream& operator<<(std::ostream& os,
    426                          const PropertyAttributes& attributes);
    427 }  // namespace internal
    428 }  // namespace v8
    429 
    430 #endif  // V8_PROPERTY_DETAILS_H_
    431