Source/JavaScriptCore/runtime/JSTypeInfo.h

// -*- mode: c++; c-basic-offset: 4 -*-
/*
 * Copyright (C) 2008-2019 Apple Inc. All rights reserved.
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#pragma once

// This file would be called TypeInfo.h, but that conflicts with <typeinfo.h>
// in the STL on systems without case-sensitive file systems. 

#include "JSType.h"

namespace JSC {

class LLIntOffsetsExtractor;

// Inline flags.

static constexpr unsigned MasqueradesAsUndefined = 1; // WebCore uses MasqueradesAsUndefined to make document.all undetectable.
static constexpr unsigned ImplementsDefaultHasInstance = 1 << 1;
static constexpr unsigned OverridesGetCallData = 1 << 2; // Need this flag if you implement [[Callable]] interface, which means overriding getCallData. The object may not be callable since getCallData can say it is not callable.
static constexpr unsigned OverridesGetOwnPropertySlot = 1 << 3;
static constexpr unsigned OverridesToThis = 1 << 4; // If this is false then this returns something other than 'this'. Non-object cells that are visible to JS have this set as do some exotic objects.
static constexpr unsigned HasStaticPropertyTable = 1 << 5;
static constexpr unsigned TypeInfoPerCellBit = 1 << 7; // Unlike other inline flags, this will only be set on the cell itself and will not be set on the Structure.

// Out of line flags.

static constexpr unsigned ImplementsHasInstance = 1 << 8;
static constexpr unsigned OverridesGetPropertyNames = 1 << 9;
static constexpr unsigned ProhibitsPropertyCaching = 1 << 10;
static constexpr unsigned GetOwnPropertySlotIsImpure = 1 << 11;
static constexpr unsigned NewImpurePropertyFiresWatchpoints = 1 << 12;
static constexpr unsigned IsImmutablePrototypeExoticObject = 1 << 13;
static constexpr unsigned GetOwnPropertySlotIsImpureForPropertyAbsence = 1 << 14;
static constexpr unsigned InterceptsGetOwnPropertySlotByIndexEvenWhenLengthIsNotZero = 1 << 15;
static constexpr unsigned StructureIsImmortal = 1 << 16;
static constexpr unsigned HasPutPropertySecurityCheck = 1 << 17;

class TypeInfo {
public:
    typedef uint8_t InlineTypeFlags;
    typedef uint16_t OutOfLineTypeFlags;

    TypeInfo(JSType type, unsigned flags = 0)
        : TypeInfo(type, flags & 0xff, flags >> 8)
    {
        ASSERT(!(flags >> 24));
    }

    TypeInfo(JSType type, InlineTypeFlags inlineTypeFlags, OutOfLineTypeFlags outOfLineTypeFlags)
        : m_type(type)
        , m_flags(inlineTypeFlags)
        , m_flags2(outOfLineTypeFlags)
    {
    }

    JSType type() const { return static_cast<JSType>(m_type); }
    bool isObject() const { return isObject(type()); }
    static bool isObject(JSType type) { return type >= ObjectType; }
    bool isFinalObject() const { return type() == FinalObjectType; }
    bool isNumberObject() const { return type() == NumberObjectType; }

    unsigned flags() const { return (static_cast<unsigned>(m_flags2) << 8) | static_cast<unsigned>(m_flags); }
    bool masqueradesAsUndefined() const { return isSetOnFlags1(MasqueradesAsUndefined); }
    bool implementsHasInstance() const { return isSetOnFlags2(ImplementsHasInstance); }
    bool implementsDefaultHasInstance() const { return isSetOnFlags1(ImplementsDefaultHasInstance); }
    bool overridesGetCallData() const { return isSetOnFlags1(OverridesGetCallData); }
    bool overridesGetOwnPropertySlot() const { return overridesGetOwnPropertySlot(inlineTypeFlags()); }
    static bool overridesGetOwnPropertySlot(InlineTypeFlags flags) { return flags & OverridesGetOwnPropertySlot; }
    static bool hasStaticPropertyTable(InlineTypeFlags flags) { return flags & HasStaticPropertyTable; }
    static bool perCellBit(InlineTypeFlags flags) { return flags & TypeInfoPerCellBit; }
    bool overridesToThis() const { return isSetOnFlags1(OverridesToThis); }
    bool structureIsImmortal() const { return isSetOnFlags2(StructureIsImmortal); }
    bool overridesGetPropertyNames() const { return isSetOnFlags2(OverridesGetPropertyNames); }
    bool prohibitsPropertyCaching() const { return isSetOnFlags2(ProhibitsPropertyCaching); }
    bool getOwnPropertySlotIsImpure() const { return isSetOnFlags2(GetOwnPropertySlotIsImpure); }
    bool getOwnPropertySlotIsImpureForPropertyAbsence() const { return isSetOnFlags2(GetOwnPropertySlotIsImpureForPropertyAbsence); }
    bool hasPutPropertySecurityCheck() const { return isSetOnFlags2(HasPutPropertySecurityCheck); }
    bool newImpurePropertyFiresWatchpoints() const { return isSetOnFlags2(NewImpurePropertyFiresWatchpoints); }
    bool isImmutablePrototypeExoticObject() const { return isSetOnFlags2(IsImmutablePrototypeExoticObject); }
    bool interceptsGetOwnPropertySlotByIndexEvenWhenLengthIsNotZero() const { return isSetOnFlags2(InterceptsGetOwnPropertySlotByIndexEvenWhenLengthIsNotZero); }

    static bool isArgumentsType(JSType type)
    {
        return type == DirectArgumentsType
            || type == ScopedArgumentsType
            || type == ClonedArgumentsType;
    }

    static ptrdiff_t flagsOffset()
    {
        return OBJECT_OFFSETOF(TypeInfo, m_flags);
    }

    static ptrdiff_t typeOffset()
    {
        return OBJECT_OFFSETOF(TypeInfo, m_type);
    }

    // Since the Structure doesn't track TypeInfoPerCellBit, we need to make sure we copy it.
    static InlineTypeFlags mergeInlineTypeFlags(InlineTypeFlags structureFlags, InlineTypeFlags oldCellFlags)
    {
        return structureFlags | (oldCellFlags & static_cast<InlineTypeFlags>(TypeInfoPerCellBit));
    }

    InlineTypeFlags inlineTypeFlags() const { return m_flags; }
    OutOfLineTypeFlags outOfLineTypeFlags() const { return m_flags2; }

private:
    friend class LLIntOffsetsExtractor;

    bool isSetOnFlags1(unsigned flag) const { ASSERT(flag <= (1 << 7)); return m_flags & flag; }
    bool isSetOnFlags2(unsigned flag) const { ASSERT(flag >= (1 << 8)); return m_flags2 & (flag >> 8); }

    uint8_t m_type;
    uint8_t m_flags;
    uint16_t m_flags2;
};

} // namespace JSC