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// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_OBJECTS_PROPERTY_DETAILS_H_
#define V8_OBJECTS_PROPERTY_DETAILS_H_
#include "include/v8.h"
#include "src/base/bit-field.h"
#include "src/common/globals.h"
#include "src/flags/flags.h"
#include "src/utils/allocation.h"
namespace v8 {
namespace internal {
// ES6 6.1.7.1
enum PropertyAttributes {
NONE = ::v8::None,
READ_ONLY = ::v8::ReadOnly,
DONT_ENUM = ::v8::DontEnum,
DONT_DELETE = ::v8::DontDelete,
ALL_ATTRIBUTES_MASK = READ_ONLY | DONT_ENUM | DONT_DELETE,
SEALED = DONT_DELETE,
FROZEN = SEALED | READ_ONLY,
ABSENT = 64, // Used in runtime to indicate a property is absent.
// ABSENT can never be stored in or returned from a descriptor's attributes
// bitfield. It is only used as a return value meaning the attributes of
// a non-existent property.
};
// Number of distinct bits in PropertyAttributes.
static const int kPropertyAttributesBitsCount = 3;
static const int kPropertyAttributesCombinationsCount =
1 << kPropertyAttributesBitsCount;
enum PropertyFilter {
ALL_PROPERTIES = 0,
ONLY_WRITABLE = 1,
ONLY_ENUMERABLE = 2,
ONLY_CONFIGURABLE = 4,
SKIP_STRINGS = 8,
SKIP_SYMBOLS = 16,
ONLY_ALL_CAN_READ = 32,
PRIVATE_NAMES_ONLY = 64,
ENUMERABLE_STRINGS = ONLY_ENUMERABLE | SKIP_SYMBOLS,
};
// Enable fast comparisons of PropertyAttributes against PropertyFilters.
STATIC_ASSERT(ALL_PROPERTIES == static_cast<PropertyFilter>(NONE));
STATIC_ASSERT(ONLY_WRITABLE == static_cast<PropertyFilter>(READ_ONLY));
STATIC_ASSERT(ONLY_ENUMERABLE == static_cast<PropertyFilter>(DONT_ENUM));
STATIC_ASSERT(ONLY_CONFIGURABLE == static_cast<PropertyFilter>(DONT_DELETE));
STATIC_ASSERT(((SKIP_STRINGS | SKIP_SYMBOLS | ONLY_ALL_CAN_READ) &
ALL_ATTRIBUTES_MASK) == 0);
STATIC_ASSERT(ALL_PROPERTIES ==
static_cast<PropertyFilter>(v8::PropertyFilter::ALL_PROPERTIES));
STATIC_ASSERT(ONLY_WRITABLE ==
static_cast<PropertyFilter>(v8::PropertyFilter::ONLY_WRITABLE));
STATIC_ASSERT(ONLY_ENUMERABLE ==
static_cast<PropertyFilter>(v8::PropertyFilter::ONLY_ENUMERABLE));
STATIC_ASSERT(ONLY_CONFIGURABLE == static_cast<PropertyFilter>(
v8::PropertyFilter::ONLY_CONFIGURABLE));
STATIC_ASSERT(SKIP_STRINGS ==
static_cast<PropertyFilter>(v8::PropertyFilter::SKIP_STRINGS));
STATIC_ASSERT(SKIP_SYMBOLS ==
static_cast<PropertyFilter>(v8::PropertyFilter::SKIP_SYMBOLS));
// Assert that kPropertyAttributesBitsCount value matches the definition of
// ALL_ATTRIBUTES_MASK.
STATIC_ASSERT((ALL_ATTRIBUTES_MASK == (READ_ONLY | DONT_ENUM | DONT_DELETE)) ==
(kPropertyAttributesBitsCount == 3));
class Smi;
class TypeInfo;
// Order of kinds is significant.
// Must fit in the BitField PropertyDetails::KindField.
enum PropertyKind { kData = 0, kAccessor = 1 };
// Order of modes is significant.
// Must fit in the BitField PropertyDetails::LocationField.
enum PropertyLocation { kField = 0, kDescriptor = 1 };
// Order of modes is significant.
// Must fit in the BitField PropertyDetails::ConstnessField.
enum class PropertyConstness { kMutable = 0, kConst = 1 };
class Representation {
public:
enum Kind {
kNone,
kSmi,
kDouble,
kHeapObject,
kTagged,
// This representation is used for WasmObject fields and basically means
// that the actual field type information must be taken from the Wasm RTT
// associated with the map.
kWasmValue,
kNumRepresentations
};
Representation() : kind_(kNone) {}
static Representation None() { return Representation(kNone); }
static Representation Tagged() { return Representation(kTagged); }
static Representation Smi() { return Representation(kSmi); }
static Representation Double() { return Representation(kDouble); }
static Representation HeapObject() { return Representation(kHeapObject); }
static Representation WasmValue() { return Representation(kWasmValue); }
static Representation FromKind(Kind kind) { return Representation(kind); }
bool Equals(const Representation& other) const {
return kind_ == other.kind_;
}
bool IsCompatibleForLoad(const Representation& other) const {
return IsDouble() == other.IsDouble();
}
bool IsCompatibleForStore(const Representation& other) const {
return Equals(other);
}
// Returns true if a change from this representation to a more general one
// might cause a map deprecation.
bool MightCauseMapDeprecation() const {
// HeapObject to tagged representation change can be done in-place.
// Boxed double to tagged transition is always done in-place.
// Note that WasmValue is not supposed to be changed at all (the only
// representation it fits into is WasmValue), so for the sake of predicate
// correctness we treat it as in-place "changeable".
if (IsTagged() || IsHeapObject() || IsDouble() || IsWasmValue()) {
return false;
}
// None to double and smi to double representation changes require
// deprecation, because doubles might require box allocation, see
// CanBeInPlaceChangedTo().
DCHECK(IsNone() || IsSmi());
return true;
}
bool CanBeInPlaceChangedTo(const Representation& other) const {
if (Equals(other)) return true;
if (IsWasmValue() || other.IsWasmValue()) return false;
// If it's just a representation generalization case (i.e. property kind and
// attributes stays unchanged) it's fine to transition from None to anything
// but double without any modification to the object, because the default
// uninitialized value for representation None can be overwritten by both
// smi and tagged values. Doubles, however, would require a box allocation.
if (IsNone()) return !other.IsDouble();
if (!other.IsTagged()) return false;
DCHECK(IsSmi() || IsDouble() || IsHeapObject());
return true;
}
// Return the most generic representation that this representation can be
// changed to in-place. If an in-place representation change is not allowed,
// then this will return the current representation.
Representation MostGenericInPlaceChange() const {
if (IsWasmValue()) return Representation::WasmValue();
return Representation::Tagged();
}
bool is_more_general_than(const Representation& other) const {
if (IsWasmValue()) return false;
if (IsHeapObject()) return other.IsNone();
return kind_ > other.kind_;
}
bool fits_into(const Representation& other) const {
return other.is_more_general_than(*this) || other.Equals(*this);
}
Representation generalize(Representation other) {
if (other.fits_into(*this)) return *this;
if (other.is_more_general_than(*this)) return other;
return Representation::Tagged();
}
int size() const {
DCHECK(!IsNone());
if (IsDouble()) return kDoubleSize;
DCHECK(IsTagged() || IsSmi() || IsHeapObject());
return kTaggedSize;
}
Kind kind() const { return static_cast<Kind>(kind_); }
bool IsNone() const { return kind_ == kNone; }
bool IsWasmValue() const { return kind_ == kWasmValue; }
bool IsTagged() const { return kind_ == kTagged; }
bool IsSmi() const { return kind_ == kSmi; }
bool IsSmiOrTagged() const { return IsSmi() || IsTagged(); }
bool IsDouble() const { return kind_ == kDouble; }
bool IsHeapObject() const { return kind_ == kHeapObject; }
const char* Mnemonic() const {
switch (kind_) {
case kNone:
return "v";
case kTagged:
return "t";
case kSmi:
return "s";
case kDouble:
return "d";
case kHeapObject:
return "h";
case kWasmValue:
return "w";
}
UNREACHABLE();
}
private:
explicit Representation(Kind k) : kind_(k) {}
// Make sure kind fits in int8.
STATIC_ASSERT(kNumRepresentations <= (1 << kBitsPerByte));
int8_t kind_;
};
static const int kDescriptorIndexBitCount = 10;
static const int kFirstInobjectPropertyOffsetBitCount = 7;
// The maximum number of descriptors we want in a descriptor array. It should
// fit in a page and also the following should hold:
// kMaxNumberOfDescriptors + kFieldsAdded <= PropertyArray::kMaxLength.
static const int kMaxNumberOfDescriptors = (1 << kDescriptorIndexBitCount) - 4;
static const int kInvalidEnumCacheSentinel =
(1 << kDescriptorIndexBitCount) - 1;
// A PropertyCell's property details contains a cell type that is meaningful if
// the cell is still valid (does not hold the hole).
enum class PropertyCellType {
kMutable, // Cell will no longer be tracked as constant.
kUndefined, // The PREMONOMORPHIC of property cells.
kConstant, // Cell has been assigned only once.
kConstantType, // Cell has been assigned only one type.
// Value for dictionaries not holding cells, must be 0:
kNoCell = kMutable,
};
// PropertyDetails captures type and attributes for a property.
// They are used both in property dictionaries and instance descriptors.
class PropertyDetails {
public:
// Property details for global dictionary properties.
PropertyDetails(PropertyKind kind, PropertyAttributes attributes,
PropertyCellType cell_type, int dictionary_index = 0) {
value_ = KindField::encode(kind) | LocationField::encode(kField) |
AttributesField::encode(attributes) |
// We track PropertyCell constness via PropertyCellTypeField,
// so we set ConstnessField to kMutable to simplify DCHECKs related
// to non-global property constness tracking.
ConstnessField::encode(PropertyConstness::kMutable) |
DictionaryStorageField::encode(dictionary_index) |
PropertyCellTypeField::encode(cell_type);
}
// Property details for dictionary mode properties/elements.
PropertyDetails(PropertyKind kind, PropertyAttributes attributes,
PropertyConstness constness, int dictionary_index = 0) {
value_ = KindField::encode(kind) | LocationField::encode(kField) |
AttributesField::encode(attributes) |
ConstnessField::encode(constness) |
DictionaryStorageField::encode(dictionary_index) |
PropertyCellTypeField::encode(PropertyCellType::kNoCell);
}
// Property details for fast mode properties.
PropertyDetails(PropertyKind kind, PropertyAttributes attributes,
PropertyLocation location, PropertyConstness constness,
Representation representation, int field_index = 0) {
value_ = KindField::encode(kind) | AttributesField::encode(attributes) |
LocationField::encode(location) |
ConstnessField::encode(constness) |
RepresentationField::encode(EncodeRepresentation(representation)) |
FieldIndexField::encode(field_index);
}
static PropertyDetails Empty(
PropertyCellType cell_type = PropertyCellType::kNoCell) {
return PropertyDetails(kData, NONE, cell_type);
}
bool operator==(PropertyDetails const& other) {
return value_ == other.value_;
}
bool operator!=(PropertyDetails const& other) {
return value_ != other.value_;
}
int pointer() const { return DescriptorPointer::decode(value_); }
PropertyDetails set_pointer(int i) const {
return PropertyDetails(value_, i);
}
PropertyDetails set_cell_type(PropertyCellType type) const {
PropertyDetails details = *this;
details.value_ = PropertyCellTypeField::update(details.value_, type);
return details;
}
PropertyDetails set_index(int index) const {
PropertyDetails details = *this;
details.value_ = DictionaryStorageField::update(details.value_, index);
return details;
}
PropertyDetails CopyWithRepresentation(Representation representation) const {
return PropertyDetails(value_, representation);
}
PropertyDetails CopyWithConstness(PropertyConstness constness) const {
return PropertyDetails(value_, constness);
}
PropertyDetails CopyAddAttributes(PropertyAttributes new_attributes) const {
new_attributes =
static_cast<PropertyAttributes>(attributes() | new_attributes);
return PropertyDetails(value_, new_attributes);
}
// Conversion for storing details as Object.
explicit inline PropertyDetails(Smi smi);
inline Smi AsSmi() const;
static uint8_t EncodeRepresentation(Representation representation) {
return representation.kind();
}
static Representation DecodeRepresentation(uint32_t bits) {
return Representation::FromKind(static_cast<Representation::Kind>(bits));
}
PropertyKind kind() const { return KindField::decode(value_); }
PropertyLocation location() const { return LocationField::decode(value_); }
PropertyConstness constness() const { return ConstnessField::decode(value_); }
PropertyAttributes attributes() const {
return AttributesField::decode(value_);
}
bool HasKindAndAttributes(PropertyKind kind, PropertyAttributes attributes) {
return (value_ & (KindField::kMask | AttributesField::kMask)) ==
(KindField::encode(kind) | AttributesField::encode(attributes));
}
int dictionary_index() const {
return DictionaryStorageField::decode(value_);
}
Representation representation() const {
return DecodeRepresentation(RepresentationField::decode(value_));
}
int field_index() const { return FieldIndexField::decode(value_); }
inline int field_width_in_words() const;
static bool IsValidIndex(int index) {
return DictionaryStorageField::is_valid(index);
}
bool IsReadOnly() const { return (attributes() & READ_ONLY) != 0; }
bool IsConfigurable() const { return (attributes() & DONT_DELETE) == 0; }
bool IsDontEnum() const { return (attributes() & DONT_ENUM) != 0; }
bool IsEnumerable() const { return !IsDontEnum(); }
PropertyCellType cell_type() const {
return PropertyCellTypeField::decode(value_);
}
bool operator==(const PropertyDetails& b) const { return value_ == b.value_; }
// Bit fields in value_ (type, shift, size). Must be public so the
// constants can be embedded in generated code.
using KindField = base::BitField<PropertyKind, 0, 1>;
using LocationField = KindField::Next<PropertyLocation, 1>;
using ConstnessField = LocationField::Next<PropertyConstness, 1>;
using AttributesField = ConstnessField::Next<PropertyAttributes, 3>;
static const int kAttributesReadOnlyMask =
(READ_ONLY << AttributesField::kShift);
static const int kAttributesDontDeleteMask =
(DONT_DELETE << AttributesField::kShift);
static const int kAttributesDontEnumMask =
(DONT_ENUM << AttributesField::kShift);
// Bit fields for normalized/dictionary mode objects.
using PropertyCellTypeField = AttributesField::Next<PropertyCellType, 2>;
using DictionaryStorageField = PropertyCellTypeField::Next<uint32_t, 23>;
// Bit fields for fast objects.
using RepresentationField = AttributesField::Next<uint32_t, 3>;
using DescriptorPointer =
RepresentationField::Next<uint32_t, kDescriptorIndexBitCount>;
using FieldIndexField =
DescriptorPointer::Next<uint32_t, kDescriptorIndexBitCount>;
// All bits for both fast and slow objects must fit in a smi.
STATIC_ASSERT(DictionaryStorageField::kLastUsedBit < 31);
STATIC_ASSERT(FieldIndexField::kLastUsedBit < 31);
// DictionaryStorageField must be the last field, so that overflowing it
// doesn't overwrite other fields.
STATIC_ASSERT(DictionaryStorageField::kLastUsedBit == 30);
// All bits for non-global dictionary mode objects except enumeration index
// must fit in a byte.
STATIC_ASSERT(KindField::kLastUsedBit < 8);
STATIC_ASSERT(ConstnessField::kLastUsedBit < 8);
STATIC_ASSERT(AttributesField::kLastUsedBit < 8);
STATIC_ASSERT(LocationField::kLastUsedBit < 8);
static const int kInitialIndex = 1;
static constexpr PropertyConstness kConstIfDictConstnessTracking =
V8_DICT_PROPERTY_CONST_TRACKING_BOOL ? PropertyConstness::kConst
: PropertyConstness::kMutable;
#ifdef OBJECT_PRINT
// For our gdb macros, we should perhaps change these in the future.
void Print(bool dictionary_mode);
#endif
enum PrintMode {
kPrintAttributes = 1 << 0,
kPrintFieldIndex = 1 << 1,
kPrintRepresentation = 1 << 2,
kPrintPointer = 1 << 3,
kForProperties = kPrintFieldIndex,
kForTransitions = kPrintAttributes,
kPrintFull = -1,
};
void PrintAsSlowTo(std::ostream& out, bool print_dict_index);
void PrintAsFastTo(std::ostream& out, PrintMode mode = kPrintFull);
// Encodes those property details for non-global dictionary properties
// with an enumeration index of 0 as a single byte.
uint8_t ToByte() {
// We only care about the value of KindField, ConstnessField, and
// AttributesField. LocationField is also stored, but it will always be
// kField. We've statically asserted earlier that all those fields fit into
// a byte together.
// PropertyCellTypeField comes next, its value must be kNoCell == 0 for
// dictionary mode PropertyDetails anyway.
DCHECK_EQ(PropertyCellType::kNoCell, cell_type());
STATIC_ASSERT(static_cast<int>(PropertyCellType::kNoCell) == 0);
// Only to be used when the enum index isn't actually maintained
// by the PropertyDetails:
DCHECK_EQ(0, dictionary_index());
return value_;
}
// Only to be used for bytes obtained by ToByte. In particular, only used for
// non-global dictionary properties.
static PropertyDetails FromByte(uint8_t encoded_details) {
// The 0-extension to 32bit sets PropertyCellType to kNoCell and
// enumeration index to 0, as intended. Everything else is obtained from
// |encoded_details|.
PropertyDetails details(encoded_details);
DCHECK_EQ(0, details.dictionary_index());
DCHECK_EQ(PropertyLocation::kField, details.location());
DCHECK_EQ(PropertyCellType::kNoCell, details.cell_type());
return details;
}
private:
PropertyDetails(int value, int pointer) {
value_ = DescriptorPointer::update(value, pointer);
}
PropertyDetails(int value, Representation representation) {
value_ = RepresentationField::update(value,
EncodeRepresentation(representation));
}
PropertyDetails(int value, PropertyConstness constness) {
value_ = ConstnessField::update(value, constness);
}
PropertyDetails(int value, PropertyAttributes attributes) {
value_ = AttributesField::update(value, attributes);
}
explicit PropertyDetails(uint32_t value) : value_{value} {}
uint32_t value_;
};
// kField location is more general than kDescriptor, kDescriptor generalizes
// only to itself.
inline bool IsGeneralizableTo(PropertyLocation a, PropertyLocation b) {
return b == kField || a == kDescriptor;
}
// PropertyConstness::kMutable constness is more general than
// VariableMode::kConst, VariableMode::kConst generalizes only to itself.
inline bool IsGeneralizableTo(PropertyConstness a, PropertyConstness b) {
return b == PropertyConstness::kMutable || a == PropertyConstness::kConst;
}
inline PropertyConstness GeneralizeConstness(PropertyConstness a,
PropertyConstness b) {
return a == PropertyConstness::kMutable ? PropertyConstness::kMutable : b;
}
V8_EXPORT_PRIVATE std::ostream& operator<<(
std::ostream& os, const Representation& representation);
V8_EXPORT_PRIVATE std::ostream& operator<<(
std::ostream& os, const PropertyAttributes& attributes);
V8_EXPORT_PRIVATE std::ostream& operator<<(std::ostream& os,
PropertyConstness constness);
V8_EXPORT_PRIVATE std::ostream& operator<<(std::ostream& os,
PropertyCellType type);
} // namespace internal
} // namespace v8
#endif // V8_OBJECTS_PROPERTY_DETAILS_H_
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