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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef vm_Shape_h
#define vm_Shape_h

#include "mozilla/Attributes.h"
#include "mozilla/GuardObjects.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/Maybe.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/TemplateLib.h"

#include "jsapi.h"
#include "jsfriendapi.h"
#include "jsinfer.h"
#include "jspropertytree.h"
#include "jstypes.h"
#include "NamespaceImports.h"

#include "gc/Barrier.h"
#include "gc/Heap.h"
#include "gc/Marking.h"
#include "gc/Rooting.h"
#include "js/HashTable.h"
#include "js/RootingAPI.h"

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4800)
#pragma warning(push)
#pragma warning(disable:4100) /* Silence unreferenced formal parameter warnings */
#endif

/*
 * In isolation, a Shape represents a property that exists in one or more
 * objects; it has an id, flags, etc. (But it doesn't represent the property's
 * value.)  However, Shapes are always stored in linked linear sequence of
 * Shapes, called "shape lineages". Each shape lineage represents the layout of
 * an entire object.
 *
 * Every JSObject has a pointer, |shape_|, accessible via lastProperty(), to
 * the last Shape in a shape lineage, which identifies the property most
 * recently added to the object.  This pointer permits fast object layout
 * tests. The shape lineage order also dictates the enumeration order for the
 * object; ECMA requires no particular order but this implementation has
 * promised and delivered property definition order.
 *
 * Shape lineages occur in two kinds of data structure.
 *
 * 1. N-ary property trees. Each path from a non-root node to the root node in
 *    a property tree is a shape lineage. Property trees permit full (or
 *    partial) sharing of Shapes between objects that have fully (or partly)
 *    identical layouts. The root is an EmptyShape whose identity is determined
 *    by the object's class, compartment and prototype. These Shapes are shared
 *    and immutable.
 *
 * 2. Dictionary mode lists. Shapes in such lists are said to be "in
 *    dictionary mode", as are objects that point to such Shapes. These Shapes
 *    are unshared, private to a single object, and immutable except for their
 *    links in the dictionary list.
 *
 * All shape lineages are bi-directionally linked, via the |parent| and
 * |kids|/|listp| members.
 *
 * Shape lineages start out life in the property tree. They can be converted
 * (by copying) to dictionary mode lists in the following circumstances.
 *
 * 1. The shape lineage's size reaches MAX_HEIGHT. This reasonable limit avoids
 *    potential worst cases involving shape lineage mutations.
 *
 * 2. A property represented by a non-last Shape in a shape lineage is removed
 *    from an object. (In the last Shape case, obj->shape_ can be easily
 *    adjusted to point to obj->shape_->parent.)  We originally tried lazy
 *    forking of the property tree, but this blows up for delete/add
 *    repetitions.
 *
 * 3. A property represented by a non-last Shape in a shape lineage has its
 *    attributes modified.
 *
 * To find the Shape for a particular property of an object initially requires
 * a linear search. But if the number of searches starting at any particular
 * Shape in the property tree exceeds MAX_LINEAR_SEARCHES and the Shape's
 * lineage has (excluding the EmptyShape) at least MIN_ENTRIES, we create an
 * auxiliary hash table -- the ShapeTable -- that allows faster lookup.
 * Furthermore, a ShapeTable is always created for dictionary mode lists,
 * and it is attached to the last Shape in the lineage. Shape tables for
 * property tree Shapes never change, but shape tables for dictionary mode
 * Shapes can grow and shrink.
 *
 * There used to be a long, math-heavy comment here explaining why property
 * trees are more space-efficient than alternatives.  This was removed in bug
 * 631138; see that bug for the full details.
 *
 * Because many Shapes have similar data, there is actually a secondary type
 * called a BaseShape that holds some of a Shape's data.  Many shapes can share
 * a single BaseShape.
 */

#define JSSLOT_FREE(clasp)  JSCLASS_RESERVED_SLOTS(clasp)

namespace js {

class Bindings;
class Debugger;
class Nursery;
class ObjectImpl;
class StaticBlockObject;

typedef JSPropertyOp         PropertyOp;
typedef JSStrictPropertyOp   StrictPropertyOp;
typedef JSPropertyDescriptor PropertyDescriptor;

/* Limit on the number of slotful properties in an object. */
static const uint32_t SHAPE_INVALID_SLOT = JS_BIT(24) - 1;
static const uint32_t SHAPE_MAXIMUM_SLOT = JS_BIT(24) - 2;

static inline PropertyOp
CastAsPropertyOp(JSObject* object)
{
    return JS_DATA_TO_FUNC_PTR(PropertyOp, object);
}

static inline StrictPropertyOp
CastAsStrictPropertyOp(JSObject* object)
{
    return JS_DATA_TO_FUNC_PTR(StrictPropertyOp, object);
}

/*
 * A representation of ECMA-262 ed. 5's internal Property Descriptor data
 * structure.
 */
struct PropDesc {
  private:
    /*
     * Original object from which this descriptor derives, passed through for
     * the benefit of proxies.  FIXME: Remove this when direct proxies happen.
     */
    Value pd_;

    Value value_, get_, set_;

    /* Property descriptor boolean fields. */
    uint8_t attrs;

    /* Bits indicating which values are set. */
    bool hasGet_ : 1;
    bool hasSet_ : 1;
    bool hasValue_ : 1;
    bool hasWritable_ : 1;
    bool hasEnumerable_ : 1;
    bool hasConfigurable_ : 1;

    /* Or maybe this represents a property's absence, and it's undefined. */
    bool isUndefined_ : 1;

    PropDesc(const Value& v)
      : pd_(UndefinedValue()),
        value_(v),
        get_(UndefinedValue()), set_(UndefinedValue()),
        attrs(0),
        hasGet_(false), hasSet_(false),
        hasValue_(true), hasWritable_(false), hasEnumerable_(false), hasConfigurable_(false),
        isUndefined_(false)
    {
    }

  public:
    friend class AutoPropDescRooter;
    friend void JS::AutoGCRooter::trace(JSTracer* trc);

    enum Enumerability { Enumerable = true, NonEnumerable = false };
    enum Configurability { Configurable = true, NonConfigurable = false };
    enum Writability { Writable = true, NonWritable = false };

    PropDesc();

    static PropDesc undefined() { return PropDesc(); }
    static PropDesc valueOnly(const Value& v) { return PropDesc(v); }

    PropDesc(const Value& v, Writability writable,
             Enumerability enumerable, Configurability configurable)
      : pd_(UndefinedValue()),
        value_(v),
        get_(UndefinedValue()), set_(UndefinedValue()),
        attrs((writable ? 0 : JSPROP_READONLY) |
              (enumerable ? JSPROP_ENUMERATE : 0) |
              (configurable ? 0 : JSPROP_PERMANENT)),
        hasGet_(false), hasSet_(false),
        hasValue_(true), hasWritable_(true), hasEnumerable_(true), hasConfigurable_(true),
        isUndefined_(false)
    {}

    inline PropDesc(const Value& getter, const Value& setter,
                    Enumerability enumerable, Configurability configurable);

    /*
     * 8.10.5 ToPropertyDescriptor(Obj)
     *
     * If checkAccessors is false, skip steps 7.b and 8.b, which throw a
     * TypeError if .get or .set is neither a callable object nor undefined.
     *
     * (DebuggerObject_defineProperty uses this: the .get and .set properties
     * are expected to be Debugger.Object wrappers of functions, which are not
     * themselves callable.)
     */
    bool initialize(JSContext* cx, const Value& v, bool checkAccessors = true);

    /*
     * If IsGenericDescriptor(desc) or IsDataDescriptor(desc) is true, then if
     * the value of an attribute field of desc, considered as a data
     * descriptor, is absent, set it to its default value. Else if the value of
     * an attribute field of desc, considered as an attribute descriptor, is
     * absent, set it to its default value.
     */
    void complete();

    /*
     * 8.10.4 FromPropertyDescriptor(Desc)
     *
     * initFromPropertyDescriptor sets pd to undefined and populates all the
     * other fields of this PropDesc from desc.
     *
     * makeObject populates pd based on the other fields of *this, creating a
     * new property descriptor JSObject and defining properties on it.
     */
    void initFromPropertyDescriptor(Handle<PropertyDescriptor> desc);
    bool makeObject(JSContext* cx);

    void setUndefined() { isUndefined_ = true; }

    bool isUndefined() const { return isUndefined_; }

    bool hasGet() const { MOZ_ASSERT(!isUndefined()); return hasGet_; }
    bool hasSet() const { MOZ_ASSERT(!isUndefined()); return hasSet_; }
    bool hasValue() const { MOZ_ASSERT(!isUndefined()); return hasValue_; }
    bool hasWritable() const { MOZ_ASSERT(!isUndefined()); return hasWritable_; }
    bool hasEnumerable() const { MOZ_ASSERT(!isUndefined()); return hasEnumerable_; }
    bool hasConfigurable() const { MOZ_ASSERT(!isUndefined()); return hasConfigurable_; }

    Value pd() const { MOZ_ASSERT(!isUndefined()); return pd_; }
    void clearPd() { pd_ = UndefinedValue(); }

    uint8_t attributes() const { MOZ_ASSERT(!isUndefined()); return attrs; }

    /* 8.10.1 IsAccessorDescriptor(desc) */
    bool isAccessorDescriptor() const {
        return !isUndefined() && (hasGet() || hasSet());
    }

    /* 8.10.2 IsDataDescriptor(desc) */
    bool isDataDescriptor() const {
        return !isUndefined() && (hasValue() || hasWritable());
    }

    /* 8.10.3 IsGenericDescriptor(desc) */
    bool isGenericDescriptor() const {
        return !isUndefined() && !isAccessorDescriptor() && !isDataDescriptor();
    }

    bool configurable() const {
        MOZ_ASSERT(!isUndefined());
        MOZ_ASSERT(hasConfigurable());
        return (attrs & JSPROP_PERMANENT) == 0;
    }

    bool enumerable() const {
        MOZ_ASSERT(!isUndefined());
        MOZ_ASSERT(hasEnumerable());
        return (attrs & JSPROP_ENUMERATE) != 0;
    }

    bool writable() const {
        MOZ_ASSERT(!isUndefined());
        MOZ_ASSERT(hasWritable());
        return (attrs & JSPROP_READONLY) == 0;
    }

    HandleValue value() const {
        MOZ_ASSERT(hasValue());
        return HandleValue::fromMarkedLocation(&value_);
    }

    JSObject * getterObject() const {
        MOZ_ASSERT(!isUndefined());
        MOZ_ASSERT(hasGet());
        return get_.isUndefined() ? nullptr : &get_.toObject();
    }
    JSObject * setterObject() const {
        MOZ_ASSERT(!isUndefined());
        MOZ_ASSERT(hasSet());
        return set_.isUndefined() ? nullptr : &set_.toObject();
    }

    HandleValue getterValue() const {
        MOZ_ASSERT(!isUndefined());
        MOZ_ASSERT(hasGet());
        return HandleValue::fromMarkedLocation(&get_);
    }
    HandleValue setterValue() const {
        MOZ_ASSERT(!isUndefined());
        MOZ_ASSERT(hasSet());
        return HandleValue::fromMarkedLocation(&set_);
    }

    /*
     * Unfortunately the values produced by these methods are used such that
     * we can't assert anything here.  :-(
     */
    PropertyOp getter() const {
        return CastAsPropertyOp(get_.isUndefined() ? nullptr : &get_.toObject());
    }
    StrictPropertyOp setter() const {
        return CastAsStrictPropertyOp(set_.isUndefined() ? nullptr : &set_.toObject());
    }

    /*
     * Throw a TypeError if a getter/setter is present and is neither callable
     * nor undefined. These methods do exactly the type checks that are skipped
     * by passing false as the checkAccessors parameter of initialize.
     */
    bool checkGetter(JSContext* cx);
    bool checkSetter(JSContext* cx);

    bool unwrapDebuggerObjectsInto(JSContext* cx, Debugger* dbg, HandleObject obj,
                                   PropDesc* unwrapped) const;

    bool wrapInto(JSContext* cx, HandleObject obj, const jsid& id, jsid* wrappedId,
                  PropDesc* wrappedDesc) const;
};

class AutoPropDescRooter : private JS::CustomAutoRooter
{
  public:
    explicit AutoPropDescRooter(JSContext* cx
                                MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
      : CustomAutoRooter(cx), skip(cx, &propDesc)
    {
        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
    }

    PropDesc& getPropDesc() { return propDesc; }

    void initFromPropertyDescriptor(Handle<PropertyDescriptor> desc) {
        propDesc.initFromPropertyDescriptor(desc);
    }

    bool makeObject(JSContext* cx) {
        return propDesc.makeObject(cx);
    }

    void setUndefined() { propDesc.setUndefined(); }
    bool isUndefined() const { return propDesc.isUndefined(); }

    bool hasGet() const { return propDesc.hasGet(); }
    bool hasSet() const { return propDesc.hasSet(); }
    bool hasValue() const { return propDesc.hasValue(); }
    bool hasWritable() const { return propDesc.hasWritable(); }
    bool hasEnumerable() const { return propDesc.hasEnumerable(); }
    bool hasConfigurable() const { return propDesc.hasConfigurable(); }

    Value pd() const { return propDesc.pd(); }
    void clearPd() { propDesc.clearPd(); }

    uint8_t attributes() const { return propDesc.attributes(); }

    bool isAccessorDescriptor() const { return propDesc.isAccessorDescriptor(); }
    bool isDataDescriptor() const { return propDesc.isDataDescriptor(); }
    bool isGenericDescriptor() const { return propDesc.isGenericDescriptor(); }
    bool configurable() const { return propDesc.configurable(); }
    bool enumerable() const { return propDesc.enumerable(); }
    bool writable() const { return propDesc.writable(); }

    HandleValue value() const { return propDesc.value(); }
    JSObject* getterObject() const { return propDesc.getterObject(); }
    JSObject* setterObject() const { return propDesc.setterObject(); }
    HandleValue getterValue() const { return propDesc.getterValue(); }
    HandleValue setterValue() const { return propDesc.setterValue(); }

    PropertyOp getter() const { return propDesc.getter(); }
    StrictPropertyOp setter() const { return propDesc.setter(); }

  private:
    virtual void trace(JSTracer* trc);

    PropDesc propDesc;
    SkipRoot skip;
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

/*
 * Shapes use multiplicative hashing, but specialized to
 * minimize footprint.
 */
struct ShapeTable {
    static const uint32_t HASH_BITS     = mozilla::tl::BitSize<HashNumber>::value;
    static const uint32_t MIN_ENTRIES   = 11;

    // This value is low because it's common for a ShapeTable to be created
    // with an entryCount of zero.
    static const uint32_t MIN_SIZE_LOG2 = 2;
    static const uint32_t MIN_SIZE      = JS_BIT(MIN_SIZE_LOG2);

    int             hashShift;          /* multiplicative hash shift */

    uint32_t        entryCount;         /* number of entries in table */
    uint32_t        removedCount;       /* removed entry sentinels in table */
    uint32_t        freelist;           /* SHAPE_INVALID_SLOT or head of slot
                                           freelist in owning dictionary-mode
                                           object */
    js::Shape**     entries;          /* table of ptrs to shared tree nodes */

    ShapeTable(uint32_t nentries)
      : hashShift(HASH_BITS - MIN_SIZE_LOG2),
        entryCount(nentries),
        removedCount(0),
        freelist(SHAPE_INVALID_SLOT)
    {
        /* NB: entries is set by init, which must be called. */
    }

    ~ShapeTable() {
        js_free(entries);
    }

    /* By definition, hashShift = HASH_BITS - log2(capacity). */
    uint32_t capacity() const { return JS_BIT(HASH_BITS - hashShift); }

    /* Computes the size of the entries array for a given capacity. */
    static size_t sizeOfEntries(size_t cap) { return cap * sizeof(Shape*); }

    /*
     * This counts the ShapeTable object itself (which must be
     * heap-allocated) and its |entries| array.
     */
    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return mallocSizeOf(this) + mallocSizeOf(entries);
    }

    /* Whether we need to grow.  We want to do this if the load factor is >= 0.75 */
    bool needsToGrow() const {
        uint32_t size = capacity();
        return entryCount + removedCount >= size - (size >> 2);
    }

    /*
     * Try to grow the table.  On failure, reports out of memory on cx
     * and returns false.  This will make any extant pointers into the
     * table invalid.  Don't call this unless needsToGrow() is true.
     */
    bool grow(ThreadSafeContext* cx);

    /*
     * NB: init and change are fallible but do not report OOM, so callers can
     * cope or ignore. They do however use the context's calloc_ method in
     * order to update the malloc counter on success.
     */
    bool            init(ThreadSafeContext* cx, Shape* lastProp);
    bool            change(int log2Delta, ThreadSafeContext* cx);
    Shape**         search(jsid id, bool adding);
};

/*
 * Reuse the API-only JSPROP_INDEX attribute to mean shadowability.
 */
#define JSPROP_SHADOWABLE       JSPROP_INDEX

/*
 * Shapes encode information about both a property lineage *and* a particular
 * property. This information is split across the Shape and the BaseShape
 * at shape->base(). Both Shape and BaseShape can be either owned or unowned
 * by, respectively, the Object or Shape referring to them.
 *
 * Owned Shapes are used in dictionary objects, and form a doubly linked list
 * whose entries are all owned by that dictionary. Unowned Shapes are all in
 * the property tree.
 *
 * Owned BaseShapes are used for shapes which have shape tables, including
 * the last properties in all dictionaries. Unowned BaseShapes compactly store
 * information common to many shapes. In a given compartment there is a single
 * BaseShape for each combination of BaseShape information. This information
 * is cloned in owned BaseShapes so that information can be quickly looked up
 * for a given object or shape without regard to whether the base shape is
 * owned or not.
 *
 * All combinations of owned/unowned Shapes/BaseShapes are possible:
 *
 * Owned Shape, Owned BaseShape:
 *
 *     Last property in a dictionary object. The BaseShape is transferred from
 *     property to property as the object's last property changes.
 *
 * Owned Shape, Unowned BaseShape:
 *
 *     Property in a dictionary object other than the last one.
 *
 * Unowned Shape, Owned BaseShape:
 *
 *     Property in the property tree which has a shape table.
 *
 * Unowned Shape, Unowned BaseShape:
 *
 *     Property in the property tree which does not have a shape table.
 *
 * BaseShapes additionally encode some information about the referring object
 * itself. This includes the object's class, parent and various flags that may
 * be set for the object. Except for the class, this information is mutable and
 * may change when the object has an established property lineage. On such
 * changes the entire property lineage is not updated, but rather only the
 * last property (and its base shape). This works because only the object's
 * last property is used to query information about the object. Care must be
 * taken to call JSObject::canRemoveLastProperty when unwinding an object to
 * an earlier property, however.
 */

class Shape;
class UnownedBaseShape;
struct StackBaseShape;

namespace gc {
void MergeCompartments(JSCompartment* source, JSCompartment* target);
}

static inline void
GetterSetterWriteBarrierPost(JSRuntime* rt, JSObject** objp)
{
#ifdef JSGC_GENERATIONAL
    JS::shadow::Runtime* shadowRuntime = JS::shadow::Runtime::asShadowRuntime(rt);
    shadowRuntime->gcStoreBufferPtr()->putRelocatableCell(reinterpret_cast<gc::Cell**>(objp));
#endif
}

static inline void
GetterSetterWriteBarrierPostRemove(JSRuntime* rt, JSObject** objp)
{
#ifdef JSGC_GENERATIONAL
    JS::shadow::Runtime* shadowRuntime = JS::shadow::Runtime::asShadowRuntime(rt);
    shadowRuntime->gcStoreBufferPtr()->removeRelocatableCell(reinterpret_cast<gc::Cell**>(objp));
#endif
}

class BaseShape : public gc::BarrieredCell<BaseShape>
{
  public:
    friend class Shape;
    friend struct StackBaseShape;
    friend struct StackShape;
    friend void gc::MergeCompartments(JSCompartment* source, JSCompartment* target);

    enum Flag {
        /* Owned by the referring shape. */
        OWNED_SHAPE        = 0x1,

        /* getterObj/setterObj are active in unions below. */
        HAS_GETTER_OBJECT  = 0x2,
        HAS_SETTER_OBJECT  = 0x4,

        /*
         * Flags set which describe the referring object. Once set these cannot
         * be unset (except during object densification of sparse indexes), and
         * are transferred from shape to shape as the object's last property
         * changes.
         *
         * If you add a new flag here, please add appropriate code to
         * JSObject::dump to dump it as part of object representation.
         */

        DELEGATE            =    0x8,
        NOT_EXTENSIBLE      =   0x10,
        INDEXED             =   0x20,
        BOUND_FUNCTION      =   0x40,
        VAROBJ              =   0x80,
        WATCHED             =  0x100,
        ITERATED_SINGLETON  =  0x200,
        NEW_TYPE_UNKNOWN    =  0x400,
        UNCACHEABLE_PROTO   =  0x800,
        HAD_ELEMENTS_ACCESS = 0x1000,

        OBJECT_FLAG_MASK    = 0x1ff8
    };

  private:
    const Class*        clasp_;        /* Class of referring object. */
    HeapPtrObject       parent;         /* Parent of referring object. */
    HeapPtrObject       metadata;       /* Optional holder of metadata about
                                         * the referring object. */
    JSCompartment*      compartment_;  /* Compartment shape belongs to. */
    uint32_t            flags;          /* Vector of above flags. */
    uint32_t            slotSpan_;      /* Object slot span for BaseShapes at
                                         * dictionary last properties. */

    union {
        PropertyOp      rawGetter;      /* getter hook for shape */
        JSObject*       getterObj;     /* user-defined callable "get" object or
                                           null if shape->hasGetterValue() */
    };

    union {
        StrictPropertyOp rawSetter;     /* setter hook for shape */
        JSObject*       setterObj;     /* user-defined callable "set" object or
                                           null if shape->hasSetterValue() */
    };

    /* For owned BaseShapes, the canonical unowned BaseShape. */
    HeapPtr<UnownedBaseShape> unowned_;

    /* For owned BaseShapes, the shape's shape table. */
    ShapeTable*      table_;

    BaseShape(const BaseShape& base) MOZ_DELETE;

  public:
    void finalize(FreeOp* fop);

    BaseShape(JSCompartment* comp, const Class* clasp, JSObject* parent, JSObject* metadata,
              uint32_t objectFlags)
    {
        JS_ASSERT(!(objectFlags & ~OBJECT_FLAG_MASK));
        mozilla::PodZero(this);
        this->clasp_ = clasp;
        this->parent = parent;
        this->metadata = metadata;
        this->flags = objectFlags;
        this->compartment_ = comp;
    }

    BaseShape(JSCompartment* comp, const Class* clasp, JSObject* parent, JSObject* metadata,
              uint32_t objectFlags, uint8_t attrs,
              PropertyOp rawGetter, StrictPropertyOp rawSetter)
    {
        JS_ASSERT(!(objectFlags & ~OBJECT_FLAG_MASK));
        mozilla::PodZero(this);
        this->clasp_ = clasp;
        this->parent = parent;
        this->metadata = metadata;
        this->flags = objectFlags;
        this->rawGetter = rawGetter;
        this->rawSetter = rawSetter;
        if ((attrs & JSPROP_GETTER) && rawGetter) {
            this->flags |= HAS_GETTER_OBJECT;
            GetterSetterWriteBarrierPost(runtimeFromMainThread(), &this->getterObj);
        }
        if ((attrs & JSPROP_SETTER) && rawSetter) {
            this->flags |= HAS_SETTER_OBJECT;
            GetterSetterWriteBarrierPost(runtimeFromMainThread(), &this->setterObj);
        }
        this->compartment_ = comp;
    }

    inline BaseShape(const StackBaseShape& base);

    /* Not defined: BaseShapes must not be stack allocated. */
    ~BaseShape();

    BaseShape& operator=(const BaseShape& other) {
        clasp_ = other.clasp_;
        parent = other.parent;
        metadata = other.metadata;
        flags = other.flags;
        slotSpan_ = other.slotSpan_;
        if (flags & HAS_GETTER_OBJECT) {
            getterObj = other.getterObj;
            GetterSetterWriteBarrierPost(runtimeFromMainThread(), &getterObj);
        } else {
            if (rawGetter)
                GetterSetterWriteBarrierPostRemove(runtimeFromMainThread(), &getterObj);
            rawGetter = other.rawGetter;
        }
        if (flags & HAS_SETTER_OBJECT) {
            setterObj = other.setterObj;
            GetterSetterWriteBarrierPost(runtimeFromMainThread(), &setterObj);
        } else {
            if (rawSetter)
                GetterSetterWriteBarrierPostRemove(runtimeFromMainThread(), &setterObj);
            rawSetter = other.rawSetter;
        }
        compartment_ = other.compartment_;
        return *this;
    }

    const Class* clasp() const { return clasp_; }

    bool isOwned() const { return !!(flags & OWNED_SHAPE); }

    bool matchesGetterSetter(PropertyOp rawGetter, StrictPropertyOp rawSetter) const {
        return rawGetter == this->rawGetter && rawSetter == this->rawSetter;
    }

    inline void adoptUnowned(UnownedBaseShape* other);

    void setOwned(UnownedBaseShape* unowned) {
        flags |= OWNED_SHAPE;
        this->unowned_ = unowned;
    }

    JSObject* getObjectParent() const { return parent; }
    JSObject* getObjectMetadata() const { return metadata; }
    uint32_t getObjectFlags() const { return flags & OBJECT_FLAG_MASK; }

    bool hasGetterObject() const { return !!(flags & HAS_GETTER_OBJECT); }
    JSObject* getterObject() const { JS_ASSERT(hasGetterObject()); return getterObj; }

    bool hasSetterObject() const { return !!(flags & HAS_SETTER_OBJECT); }
    JSObject* setterObject() const { JS_ASSERT(hasSetterObject()); return setterObj; }

    bool hasTable() const { JS_ASSERT_IF(table_, isOwned()); return table_ != nullptr; }
    ShapeTable& table() const { JS_ASSERT(table_ && isOwned()); return *table_; }
    void setTable(ShapeTable* table) { JS_ASSERT(isOwned()); table_ = table; }

    uint32_t slotSpan() const { JS_ASSERT(isOwned()); return slotSpan_; }
    void setSlotSpan(uint32_t slotSpan) { JS_ASSERT(isOwned()); slotSpan_ = slotSpan; }

    JSCompartment* compartment() const { return compartment_; }

    /*
     * Lookup base shapes from the compartment's baseShapes table, adding if
     * not already found.
     */
    static UnownedBaseShape* getUnowned(ExclusiveContext* cx, StackBaseShape& base);

    /*
     * Lookup base shapes from the compartment's baseShapes table, returning
     * nullptr if not found.
     */
    static UnownedBaseShape* lookupUnowned(ThreadSafeContext* cx, const StackBaseShape& base);

    /* Get the canonical base shape. */
    inline UnownedBaseShape* unowned();

    /* Get the canonical base shape for an owned one. */
    inline UnownedBaseShape* baseUnowned();

    /* Get the canonical base shape for an unowned one (i.e. identity). */
    inline UnownedBaseShape* toUnowned();

    /* Check that an owned base shape is consistent with its unowned base. */
    void assertConsistency();

    /* For JIT usage */
    static inline size_t offsetOfParent() { return offsetof(BaseShape, parent); }
    static inline size_t offsetOfFlags() { return offsetof(BaseShape, flags); }

    static inline ThingRootKind rootKind() { return THING_ROOT_BASE_SHAPE; }

    void markChildren(JSTracer* trc) {
        if (hasGetterObject())
            gc::MarkObjectUnbarriered(trc, &getterObj, "getter");

        if (hasSetterObject())
            gc::MarkObjectUnbarriered(trc, &setterObj, "setter");

        if (isOwned())
            gc::MarkBaseShape(trc, &unowned_, "base");

        if (parent)
            gc::MarkObject(trc, &parent, "parent");

        if (metadata)
            gc::MarkObject(trc, &metadata, "metadata");
    }

  private:
    static void staticAsserts() {
        JS_STATIC_ASSERT(offsetof(BaseShape, clasp_) == offsetof(js::shadow::BaseShape, clasp_));
    }
};

class UnownedBaseShape : public BaseShape {};

inline void
BaseShape::adoptUnowned(UnownedBaseShape* other)
{
    // This is a base shape owned by a dictionary object, update it to reflect the
    // unowned base shape of a new last property.
    JS_ASSERT(isOwned());

    uint32_t span = slotSpan();
    ShapeTable* table = &this->table();

    *this = *other;
    setOwned(other);
    setTable(table);
    setSlotSpan(span);

    assertConsistency();
}

UnownedBaseShape*
BaseShape::unowned()
{
    return isOwned() ? baseUnowned() : toUnowned();
}

UnownedBaseShape*
BaseShape::toUnowned()
{
    JS_ASSERT(!isOwned() && !unowned_); return static_cast<UnownedBaseShape*>(this);
}

UnownedBaseShape*
BaseShape::baseUnowned()
{
    JS_ASSERT(isOwned() && unowned_); return unowned_;
}

/* Entries for the per-compartment baseShapes set of unowned base shapes. */
struct StackBaseShape
{
    typedef const StackBaseShape* Lookup;

    uint32_t flags;
    const Class* clasp;
    JSObject* parent;
    JSObject* metadata;
    PropertyOp rawGetter;
    StrictPropertyOp rawSetter;
    JSCompartment* compartment;

    explicit StackBaseShape(BaseShape* base)
      : flags(base->flags & BaseShape::OBJECT_FLAG_MASK),
        clasp(base->clasp_),
        parent(base->parent),
        metadata(base->metadata),
        rawGetter(nullptr),
        rawSetter(nullptr),
        compartment(base->compartment())
    {}

    inline StackBaseShape(ThreadSafeContext* cx, const Class* clasp,
                          JSObject* parent, JSObject* metadata, uint32_t objectFlags);
    inline StackBaseShape(Shape* shape);

    void updateGetterSetter(uint8_t attrs, PropertyOp rawGetter, StrictPropertyOp rawSetter) {
        flags &= ~(BaseShape::HAS_GETTER_OBJECT | BaseShape::HAS_SETTER_OBJECT);
        if ((attrs & JSPROP_GETTER) && rawGetter) {
            JS_ASSERT(!IsPoisonedPtr(rawGetter));
            flags |= BaseShape::HAS_GETTER_OBJECT;
        }
        if ((attrs & JSPROP_SETTER) && rawSetter) {
            JS_ASSERT(!IsPoisonedPtr(rawSetter));
            flags |= BaseShape::HAS_SETTER_OBJECT;
        }

        this->rawGetter = rawGetter;
        this->rawSetter = rawSetter;
    }

    static inline HashNumber hash(const StackBaseShape* lookup);
    static inline bool match(UnownedBaseShape* key, const StackBaseShape* lookup);

    // For RootedGeneric<StackBaseShape*>
    static inline js::ThingRootKind rootKind() { return js::THING_ROOT_CUSTOM; }
    void trace(JSTracer* trc);
};

inline
BaseShape::BaseShape(const StackBaseShape& base)
{
    mozilla::PodZero(this);
    this->clasp_ = base.clasp;
    this->parent = base.parent;
    this->metadata = base.metadata;
    this->flags = base.flags;
    this->rawGetter = base.rawGetter;
    this->rawSetter = base.rawSetter;
    if ((base.flags & HAS_GETTER_OBJECT) && base.rawGetter)
        GetterSetterWriteBarrierPost(runtimeFromMainThread(), &this->getterObj);
    if ((base.flags & HAS_SETTER_OBJECT) && base.rawSetter)
        GetterSetterWriteBarrierPost(runtimeFromMainThread(), &this->setterObj);
    this->compartment_ = base.compartment;
}

typedef HashSet<ReadBarriered<UnownedBaseShape>,
                StackBaseShape,
                SystemAllocPolicy> BaseShapeSet;


class Shape : public gc::BarrieredCell<Shape>
{
    friend class ::JSObject;
    friend class ::JSFunction;
    friend class js::Bindings;
    friend class js::Nursery;
    friend class js::ObjectImpl;
    friend class js::PropertyTree;
    friend class js::StaticBlockObject;
    friend struct js::StackShape;
    friend struct js::StackBaseShape;

  protected:
    HeapPtrBaseShape    base_;
    EncapsulatedId      propid_;

    JS_ENUM_HEADER(SlotInfo, uint32_t)
    {
        /* Number of fixed slots in objects with this shape. */
        // FIXED_SLOTS_MAX is the biggest count of fixed slots a Shape can store
        FIXED_SLOTS_MAX        = 0x1f,
        FIXED_SLOTS_SHIFT      = 27,
        FIXED_SLOTS_MASK       = uint32_t(FIXED_SLOTS_MAX << FIXED_SLOTS_SHIFT),

        /*
         * numLinearSearches starts at zero and is incremented initially on
         * search() calls. Once numLinearSearches reaches LINEAR_SEARCHES_MAX,
         * the table is created on the next search() call. The table can also
         * be created when hashifying for dictionary mode.
         */
        LINEAR_SEARCHES_MAX    = 0x7,
        LINEAR_SEARCHES_SHIFT  = 24,
        LINEAR_SEARCHES_MASK   = LINEAR_SEARCHES_MAX << LINEAR_SEARCHES_SHIFT,

        /*
         * Mask to get the index in object slots for shapes which hasSlot().
         * For !hasSlot() shapes in the property tree with a parent, stores the
         * parent's slot index (which may be invalid), and invalid for all
         * other shapes.
         */
        SLOT_MASK              = JS_BIT(24) - 1
    } JS_ENUM_FOOTER(SlotInfo);

    uint32_t            slotInfo;       /* mask of above info */
    uint8_t             attrs;          /* attributes, see jsapi.h JSPROP_* */
    uint8_t             flags;          /* flags, see below for defines */

    HeapPtrShape        parent;        /* parent node, reverse for..in order */
    /* kids is valid when !inDictionary(), listp is valid when inDictionary(). */
    union {
        KidsPointer kids;       /* null, single child, or a tagged ptr
                                   to many-kids data structure */
        HeapPtrShape* listp;    /* dictionary list starting at shape_
                                   has a double-indirect back pointer,
                                   either to the next shape's parent if not
                                   last, else to obj->shape_ */
    };

    static inline Shape* search(ExclusiveContext* cx, Shape* start, jsid id,
                                Shape*** pspp, bool adding = false);
    static inline Shape* searchThreadLocal(ThreadSafeContext* cx, Shape* start, jsid id,
                                           Shape*** pspp, bool adding = false);
    static inline Shape* searchNoHashify(Shape* start, jsid id);

    void removeFromDictionary(ObjectImpl* obj);
    void insertIntoDictionary(HeapPtrShape* dictp);

    void initDictionaryShape(const StackShape& child, uint32_t nfixed, HeapPtrShape* dictp) {
        new (this) Shape(child, nfixed);
        this->flags |= IN_DICTIONARY;

        this->listp = nullptr;
        insertIntoDictionary(dictp);
    }

    /* Replace the base shape of the last shape in a non-dictionary lineage with base. */
    static Shape* replaceLastProperty(ExclusiveContext* cx, StackBaseShape& base,
                                      TaggedProto proto, HandleShape shape);

    /*
     * This function is thread safe if every shape in the lineage of |shape|
     * is thread local, which is the case when we clone the entire shape
     * lineage in preparation for converting an object to dictionary mode.
     */
    static bool hashify(ThreadSafeContext* cx, Shape* shape);
    void handoffTableTo(Shape* newShape);

    void setParent(Shape* p) {
        JS_ASSERT_IF(p && !p->hasMissingSlot() && !inDictionary(),
                     p->maybeSlot() <= maybeSlot());
        JS_ASSERT_IF(p && !inDictionary(),
                     hasSlot() == (p->maybeSlot() != maybeSlot()));
        parent = p;
    }

    bool ensureOwnBaseShape(ThreadSafeContext* cx) {
        if (base()->isOwned())
            return true;
        return makeOwnBaseShape(cx);
    }

    bool makeOwnBaseShape(ThreadSafeContext* cx);

  public:
    bool hasTable() const { return base()->hasTable(); }
    ShapeTable& table() const { return base()->table(); }

    void addSizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf,
                                size_t* propTableSize, size_t* kidsSize) const {
        if (hasTable())
            *propTableSize += table().sizeOfIncludingThis(mallocSizeOf);

        if (!inDictionary() && kids.isHash())
            *kidsSize += kids.toHash()->sizeOfIncludingThis(mallocSizeOf);
    }

    bool isNative() const {
        JS_ASSERT(!(flags & NON_NATIVE) == getObjectClass()->isNative());
        return !(flags & NON_NATIVE);
    }

    const HeapPtrShape& previous() const { return parent; }
    JSCompartment* compartment() const { return base()->compartment(); }

    template <AllowGC allowGC>
    class Range {
      protected:
        friend class Shape;

        typename MaybeRooted<Shape*, allowGC>::RootType cursor;

      public:
        Range(ExclusiveContext* cx, Shape* shape) : cursor(cx, shape) {
            JS_STATIC_ASSERT(allowGC == CanGC);
        }

        Range(Shape* shape) : cursor((ExclusiveContext*) nullptr, shape) {
            JS_STATIC_ASSERT(allowGC == NoGC);
        }

        bool empty() const {
            return !cursor || cursor->isEmptyShape();
        }

        Shape& front() const {
            JS_ASSERT(!empty());
            return *cursor;
        }

        void popFront() {
            JS_ASSERT(!empty());
            cursor = cursor->parent;
        }
    };

    const Class* getObjectClass() const {
        return base()->clasp_;
    }
    JSObject* getObjectParent() const { return base()->parent; }
    JSObject* getObjectMetadata() const { return base()->metadata; }

    static Shape* setObjectParent(ExclusiveContext* cx,
                                  JSObject* obj, TaggedProto proto, Shape* last);
    static Shape* setObjectMetadata(JSContext* cx,
                                    JSObject* metadata, TaggedProto proto, Shape* last);
    static Shape* setObjectFlag(ExclusiveContext* cx,
                                BaseShape::Flag flag, TaggedProto proto, Shape* last);

    uint32_t getObjectFlags() const { return base()->getObjectFlags(); }
    bool hasObjectFlag(BaseShape::Flag flag) const {
        JS_ASSERT(!(flag & ~BaseShape::OBJECT_FLAG_MASK));
        return !!(base()->flags & flag);
    }

  protected:
    /*
     * Implementation-private bits stored in shape->flags. See public: enum {}
     * flags further below, which were allocated FCFS over time, so interleave
     * with these bits.
     */
    enum {
        /* Property is placeholder for a non-native class. */
        NON_NATIVE      = 0x01,

        /* Property stored in per-object dictionary, not shared property tree. */
        IN_DICTIONARY   = 0x02,

        UNUSED_BITS     = 0x3C
    };

    /* Get a shape identical to this one, without parent/kids information. */
    inline Shape(const StackShape& other, uint32_t nfixed);

    /* Used by EmptyShape (see jsscopeinlines.h). */
    inline Shape(UnownedBaseShape* base, uint32_t nfixed);

    /* Copy constructor disabled, to avoid misuse of the above form. */
    Shape(const Shape& other) MOZ_DELETE;

    /*
     * Whether this shape has a valid slot value. This may be true even if
     * !hasSlot() (see SlotInfo comment above), and may be false even if
     * hasSlot() if the shape is being constructed and has not had a slot
     * assigned yet. After construction, hasSlot() implies !hasMissingSlot().
     */
    bool hasMissingSlot() const { return maybeSlot() == SHAPE_INVALID_SLOT; }

  public:
    bool inDictionary() const {
        return (flags & IN_DICTIONARY) != 0;
    }

    PropertyOp getter() const { return base()->rawGetter; }
    bool hasDefaultGetter() const {return !base()->rawGetter; }
    PropertyOp getterOp() const { JS_ASSERT(!hasGetterValue()); return base()->rawGetter; }
    JSObject* getterObject() const { JS_ASSERT(hasGetterValue()); return base()->getterObj; }

    // Per ES5, decode null getterObj as the undefined value, which encodes as null.
    Value getterValue() const {
        JS_ASSERT(hasGetterValue());
        return base()->getterObj ? ObjectValue(*base()->getterObj) : UndefinedValue();
    }

    Value getterOrUndefined() const {
        return (hasGetterValue() && base()->getterObj)
               ? ObjectValue(*base()->getterObj)
               : UndefinedValue();
    }

    StrictPropertyOp setter() const { return base()->rawSetter; }
    bool hasDefaultSetter() const  { return !base()->rawSetter; }
    StrictPropertyOp setterOp() const { JS_ASSERT(!hasSetterValue()); return base()->rawSetter; }
    JSObject* setterObject() const { JS_ASSERT(hasSetterValue()); return base()->setterObj; }

    // Per ES5, decode null setterObj as the undefined value, which encodes as null.
    Value setterValue() const {
        JS_ASSERT(hasSetterValue());
        return base()->setterObj ? ObjectValue(*base()->setterObj) : UndefinedValue();
    }

    Value setterOrUndefined() const {
        return (hasSetterValue() && base()->setterObj)
               ? ObjectValue(*base()->setterObj)
               : UndefinedValue();
    }

    void update(PropertyOp getter, StrictPropertyOp setter, uint8_t attrs);

    bool matches(const Shape* other) const {
        return propid_.get() == other->propid_.get() &&
               matchesParamsAfterId(other->base(), other->maybeSlot(), other->attrs, other->flags);
    }

    inline bool matches(const StackShape& other) const;

    bool matchesParamsAfterId(BaseShape* base, uint32_t aslot, unsigned aattrs, unsigned aflags) const
    {
        return base->unowned() == this->base()->unowned() &&
               maybeSlot() == aslot &&
               attrs == aattrs;
    }

    bool get(JSContext* cx, HandleObject receiver, JSObject* obj, JSObject* pobj, MutableHandleValue vp);
    bool set(JSContext* cx, HandleObject obj, HandleObject receiver, bool strict, MutableHandleValue vp);

    BaseShape* base() const { return base_.get(); }

    bool hasSlot() const {
        return (attrs & JSPROP_SHARED) == 0;
    }
    uint32_t slot() const { JS_ASSERT(hasSlot() && !hasMissingSlot()); return maybeSlot(); }
    uint32_t maybeSlot() const {
        return slotInfo & SLOT_MASK;
    }

    bool isEmptyShape() const {
        JS_ASSERT_IF(JSID_IS_EMPTY(propid_), hasMissingSlot());
        return JSID_IS_EMPTY(propid_);
    }

    uint32_t slotSpan(const Class* clasp) const {
        JS_ASSERT(!inDictionary());
        uint32_t free = JSSLOT_FREE(clasp);
        return hasMissingSlot() ? free : Max(free, maybeSlot() + 1);
    }

    uint32_t slotSpan() const {
        return slotSpan(getObjectClass());
    }

    void setSlot(uint32_t slot) {
        JS_ASSERT(slot <= SHAPE_INVALID_SLOT);
        slotInfo = slotInfo & ~Shape::SLOT_MASK;
        slotInfo = slotInfo | slot;
    }

    uint32_t numFixedSlots() const {
        return (slotInfo >> FIXED_SLOTS_SHIFT);
    }

    void setNumFixedSlots(uint32_t nfixed) {
        JS_ASSERT(nfixed < FIXED_SLOTS_MAX);
        slotInfo = slotInfo & ~FIXED_SLOTS_MASK;
        slotInfo = slotInfo | (nfixed << FIXED_SLOTS_SHIFT);
    }

    uint32_t numLinearSearches() const {
        return (slotInfo & LINEAR_SEARCHES_MASK) >> LINEAR_SEARCHES_SHIFT;
    }

    void incrementNumLinearSearches() {
        uint32_t count = numLinearSearches();
        JS_ASSERT(count < LINEAR_SEARCHES_MAX);
        slotInfo = slotInfo & ~LINEAR_SEARCHES_MASK;
        slotInfo = slotInfo | ((count + 1) << LINEAR_SEARCHES_SHIFT);
    }

    const EncapsulatedId& propid() const {
        JS_ASSERT(!isEmptyShape());
        JS_ASSERT(!JSID_IS_VOID(propid_));
        return propid_;
    }
    EncapsulatedId& propidRef() { JS_ASSERT(!JSID_IS_VOID(propid_)); return propid_; }
    jsid propidRaw() const {
        // Return the actual jsid, not an internal reference.
        return propid();
    }

    uint8_t attributes() const { return attrs; }
    bool configurable() const { return (attrs & JSPROP_PERMANENT) == 0; }
    bool enumerable() const { return (attrs & JSPROP_ENUMERATE) != 0; }
    bool writable() const {
        return (attrs & JSPROP_READONLY) == 0;
    }
    bool hasGetterValue() const { return attrs & JSPROP_GETTER; }
    bool hasSetterValue() const { return attrs & JSPROP_SETTER; }

    bool isDataDescriptor() const {
        return (attrs & (JSPROP_SETTER | JSPROP_GETTER)) == 0;
    }
    bool isAccessorDescriptor() const {
        return (attrs & (JSPROP_SETTER | JSPROP_GETTER)) != 0;
    }

    PropDesc::Writability writability() const {
        return (attrs & JSPROP_READONLY) ? PropDesc::NonWritable : PropDesc::Writable;
    }
    PropDesc::Enumerability enumerability() const {
        return (attrs & JSPROP_ENUMERATE) ? PropDesc::Enumerable : PropDesc::NonEnumerable;
    }
    PropDesc::Configurability configurability() const {
        return (attrs & JSPROP_PERMANENT) ? PropDesc::NonConfigurable : PropDesc::Configurable;
    }

    /*
     * For ES5 compatibility, we allow properties with PropertyOp-flavored
     * setters to be shadowed when set. The "own" property thereby created in
     * the directly referenced object will have the same getter and setter as
     * the prototype property. See bug 552432.
     */
    bool shadowable() const {
        JS_ASSERT_IF(isDataDescriptor(), writable());
        return hasSlot() || (attrs & JSPROP_SHADOWABLE);
    }

    uint32_t entryCount() {
        if (hasTable())
            return table().entryCount;
        uint32_t count = 0;
        for (Shape::Range<NoGC> r(this); !r.empty(); r.popFront())
            ++count;
        return count;
    }

    bool isBigEnoughForAShapeTable() {
        JS_ASSERT(!hasTable());
        Shape* shape = this;
        uint32_t count = 0;
        for (Shape::Range<NoGC> r(shape); !r.empty(); r.popFront()) {
            ++count;
            if (count >= ShapeTable::MIN_ENTRIES)
                return true;
        }
        return false;
    }

#ifdef DEBUG
    void dump(JSContext* cx, FILE* fp) const;
    void dumpSubtree(JSContext* cx, int level, FILE* fp) const;
#endif

    void sweep();
    void finalize(FreeOp* fop);
    void removeChild(Shape* child);

    static inline ThingRootKind rootKind() { return THING_ROOT_SHAPE; }

    void markChildren(JSTracer* trc) {
        MarkBaseShape(trc, &base_, "base");
        gc::MarkId(trc, &propidRef(), "propid");
        if (parent)
            MarkShape(trc, &parent, "parent");
    }

    inline Shape* search(ExclusiveContext* cx, jsid id);
    inline Shape* searchLinear(jsid id);

    /* For JIT usage */
    static inline size_t offsetOfBase() { return offsetof(Shape, base_); }

  private:
    static void staticAsserts() {
        JS_STATIC_ASSERT(offsetof(Shape, base_) == offsetof(js::shadow::Shape, base));
        JS_STATIC_ASSERT(offsetof(Shape, slotInfo) == offsetof(js::shadow::Shape, slotInfo));
        JS_STATIC_ASSERT(FIXED_SLOTS_SHIFT == js::shadow::Shape::FIXED_SLOTS_SHIFT);
        static_assert(js::shadow::Object::MAX_FIXED_SLOTS <= FIXED_SLOTS_MAX,
                      "verify numFixedSlots() bitfield is big enough");
    }
};

inline
StackBaseShape::StackBaseShape(Shape* shape)
  : flags(shape->getObjectFlags()),
    clasp(shape->getObjectClass()),
    parent(shape->getObjectParent()),
    metadata(shape->getObjectMetadata()),
    compartment(shape->compartment())
{
    updateGetterSetter(shape->attrs, shape->getter(), shape->setter());
}

class AutoRooterGetterSetter
{
    class Inner : private JS::CustomAutoRooter
    {
      public:
        inline Inner(ThreadSafeContext* cx, uint8_t attrs,
                     PropertyOp* pgetter_, StrictPropertyOp* psetter_);

      private:
        virtual void trace(JSTracer* trc);

        uint8_t attrs;
        PropertyOp* pgetter;
        StrictPropertyOp* psetter;
        SkipRoot getterRoot, setterRoot;
    };

  public:
    inline AutoRooterGetterSetter(ThreadSafeContext* cx, uint8_t attrs,
                                  PropertyOp* pgetter, StrictPropertyOp* psetter
                                  MOZ_GUARD_OBJECT_NOTIFIER_PARAM);

  private:
    mozilla::Maybe<Inner> inner;
    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
};

struct EmptyShape : public js::Shape
{
    EmptyShape(UnownedBaseShape* base, uint32_t nfixed)
      : js::Shape(base, nfixed)
    {
        // Only empty shapes can be NON_NATIVE.
        if (!getObjectClass()->isNative())
            flags |= NON_NATIVE;
    }

    /*
     * Lookup an initial shape matching the given parameters, creating an empty
     * shape if none was found.
     */
    static Shape* getInitialShape(ExclusiveContext* cx, const Class* clasp,
                                  TaggedProto proto, JSObject* metadata,
                                  JSObject* parent, size_t nfixed, uint32_t objectFlags = 0);
    static Shape* getInitialShape(ExclusiveContext* cx, const Class* clasp,
                                  TaggedProto proto, JSObject* metadata,
                                  JSObject* parent, gc::AllocKind kind, uint32_t objectFlags = 0);

    /*
     * Reinsert an alternate initial shape, to be returned by future
     * getInitialShape calls, until the new shape becomes unreachable in a GC
     * and the table entry is purged.
     */
    static void insertInitialShape(ExclusiveContext* cx, HandleShape shape, HandleObject proto);

    /*
     * Some object subclasses are allocated with a built-in set of properties.
     * The first time such an object is created, these built-in properties must
     * be set manually, to compute an initial shape.  Afterward, that initial
     * shape can be reused for newly-created objects that use the subclass's
     * standard prototype.  This method should be used in a post-allocation
     * init method, to ensure that objects of such subclasses compute and cache
     * the initial shape, if it hasn't already been computed.
     */
    template<class ObjectSubclass>
    static inline bool
    ensureInitialCustomShape(ExclusiveContext* cx, Handle<ObjectSubclass*> obj);
};

/*
 * Entries for the per-compartment initialShapes set indexing initial shapes
 * for objects in the compartment and the associated types.
 */
struct InitialShapeEntry
{
    /*
     * Initial shape to give to the object. This is an empty shape, except for
     * certain classes (e.g. String, RegExp) which may add certain baked-in
     * properties.
     */
    ReadBarriered<Shape> shape;

    /*
     * Matching prototype for the entry. The shape of an object determines its
     * prototype, but the prototype cannot be determined from the shape itself.
     */
    TaggedProto proto;

    /* State used to determine a match on an initial shape. */
    struct Lookup {
        const Class* clasp;
        TaggedProto hashProto;
        TaggedProto matchProto;
        JSObject* hashParent;
        JSObject* matchParent;
        JSObject* hashMetadata;
        JSObject* matchMetadata;
        uint32_t nfixed;
        uint32_t baseFlags;
        Lookup(const Class* clasp, TaggedProto proto, JSObject* parent, JSObject* metadata,
               uint32_t nfixed, uint32_t baseFlags)
          : clasp(clasp),
            hashProto(proto), matchProto(proto),
            hashParent(parent), matchParent(parent),
            hashMetadata(metadata), matchMetadata(metadata),
            nfixed(nfixed), baseFlags(baseFlags)
        {}

#ifdef JSGC_GENERATIONAL
        /*
         * For use by generational GC post barriers. Look up an entry whose
         * parent and metadata fields may have been moved, but was hashed with
         * the original values.
         */
        Lookup(const Class* clasp, TaggedProto proto,
               JSObject* hashParent, JSObject* matchParent,
               JSObject* hashMetadata, JSObject* matchMetadata,
               uint32_t nfixed, uint32_t baseFlags)
          : clasp(clasp),
            hashProto(proto), matchProto(proto),
            hashParent(hashParent), matchParent(matchParent),
            hashMetadata(hashMetadata), matchMetadata(matchMetadata),
            nfixed(nfixed), baseFlags(baseFlags)
        {}
#endif
    };

    inline InitialShapeEntry();
    inline InitialShapeEntry(const ReadBarriered<Shape>& shape, TaggedProto proto);

    inline Lookup getLookup() const;

    static inline HashNumber hash(const Lookup& lookup);
    static inline bool match(const InitialShapeEntry& key, const Lookup& lookup);
    static void rekey(InitialShapeEntry& k, const InitialShapeEntry& newKey) { k = newKey; }
};

typedef HashSet<InitialShapeEntry, InitialShapeEntry, SystemAllocPolicy> InitialShapeSet;

struct StackShape
{
    /* For performance, StackShape only roots when absolutely necessary. */
    UnownedBaseShape* base;
    jsid             propid;
    uint32_t         slot_;
    uint8_t          attrs;
    uint8_t          flags;

    explicit StackShape(UnownedBaseShape* base, jsid propid, uint32_t slot,
                        unsigned attrs, unsigned flags)
      : base(base),
        propid(propid),
        slot_(slot),
        attrs(uint8_t(attrs)),
        flags(uint8_t(flags))
    {
        JS_ASSERT(base);
        JS_ASSERT(!JSID_IS_VOID(propid));
        JS_ASSERT(slot <= SHAPE_INVALID_SLOT);
        JS_ASSERT_IF(attrs & (JSPROP_GETTER | JSPROP_SETTER), attrs & JSPROP_SHARED);
    }

    StackShape(Shape* shape)
      : base(shape->base()->unowned()),
        propid(shape->propidRef()),
        slot_(shape->maybeSlot()),
        attrs(shape->attrs),
        flags(shape->flags)
    {}

    bool hasSlot() const { return (attrs & JSPROP_SHARED) == 0; }
    bool hasMissingSlot() const { return maybeSlot() == SHAPE_INVALID_SLOT; }

    uint32_t slot() const { JS_ASSERT(hasSlot() && !hasMissingSlot()); return slot_; }
    uint32_t maybeSlot() const { return slot_; }

    uint32_t slotSpan() const {
        uint32_t free = JSSLOT_FREE(base->clasp_);
        return hasMissingSlot() ? free : (maybeSlot() + 1);
    }

    void setSlot(uint32_t slot) {
        JS_ASSERT(slot <= SHAPE_INVALID_SLOT);
        slot_ = slot;
    }

    HashNumber hash() const {
        HashNumber hash = uintptr_t(base);

        /* Accumulate from least to most random so the low bits are most random. */
        hash = mozilla::RotateLeft(hash, 4) ^ attrs;
        hash = mozilla::RotateLeft(hash, 4) ^ slot_;
        hash = mozilla::RotateLeft(hash, 4) ^ JSID_BITS(propid);
        return hash;
    }

    // For RootedGeneric<StackShape*>
    static inline js::ThingRootKind rootKind() { return js::THING_ROOT_CUSTOM; }
    void trace(JSTracer* trc);
};

} /* namespace js */

/* js::Shape pointer tag bit indicating a collision. */
#define SHAPE_COLLISION                 (uintptr_t(1))
#define SHAPE_REMOVED                   ((js::Shape*) SHAPE_COLLISION)

/* Functions to get and set shape pointer values and collision flags. */

inline bool
SHAPE_IS_FREE(js::Shape* shape)
{
    return shape == nullptr;
}

inline bool
SHAPE_IS_REMOVED(js::Shape* shape)
{
    return shape == SHAPE_REMOVED;
}

inline bool
SHAPE_IS_LIVE(js::Shape* shape)
{
    return shape > SHAPE_REMOVED;
}

inline void
SHAPE_FLAG_COLLISION(js::Shape** spp, js::Shape* shape)
{
    *spp = reinterpret_cast<js::Shape*>(uintptr_t(shape) | SHAPE_COLLISION);
}

inline bool
SHAPE_HAD_COLLISION(js::Shape* shape)
{
    return uintptr_t(shape) & SHAPE_COLLISION;
}

inline js::Shape*
SHAPE_CLEAR_COLLISION(js::Shape* shape)
{
    return reinterpret_cast<js::Shape*>(uintptr_t(shape) & ~SHAPE_COLLISION);
}

inline js::Shape*
SHAPE_FETCH(js::Shape** spp)
{
    return SHAPE_CLEAR_COLLISION(*spp);
}

inline void
SHAPE_STORE_PRESERVING_COLLISION(js::Shape** spp, js::Shape* shape)
{
    *spp = reinterpret_cast<js::Shape*>(uintptr_t(shape) |
                                        uintptr_t(SHAPE_HAD_COLLISION(*spp)));
}

namespace js {

inline
Shape::Shape(const StackShape& other, uint32_t nfixed)
  : base_(other.base),
    propid_(other.propid),
    slotInfo(other.maybeSlot() | (nfixed << FIXED_SLOTS_SHIFT)),
    attrs(other.attrs),
    flags(other.flags),
    parent(nullptr)
{
    JS_ASSERT_IF(attrs & (JSPROP_GETTER | JSPROP_SETTER), attrs & JSPROP_SHARED);
    kids.setNull();
}

inline
Shape::Shape(UnownedBaseShape* base, uint32_t nfixed)
  : base_(base),
    propid_(JSID_EMPTY),
    slotInfo(SHAPE_INVALID_SLOT | (nfixed << FIXED_SLOTS_SHIFT)),
    attrs(JSPROP_SHARED),
    flags(0),
    parent(nullptr)
{
    JS_ASSERT(base);
    kids.setNull();
}

inline Shape*
Shape::searchLinear(jsid id)
{
    /*
     * Non-dictionary shapes can acquire a table at any point the main thread
     * is operating on it, so other threads inspecting such shapes can't use
     * their table without racing. This function can be called from any thread
     * on any non-dictionary shape.
     */
    JS_ASSERT(!inDictionary());

    for (Shape* shape = this; shape; ) {
        if (shape->propidRef() == id)
            return shape;
        shape = shape->parent;
    }

    return nullptr;
}

/*
 * Keep this function in sync with search. It neither hashifies the start
 * shape nor increments linear search count.
 */
inline Shape*
Shape::searchNoHashify(Shape* start, jsid id)
{
    /*
     * If we have a table, search in the shape table, else do a linear
     * search. We never hashify into a table in parallel.
     */
    if (start->hasTable()) {
        Shape** spp = start->table().search(id, false);
        return SHAPE_FETCH(spp);
    }

    return start->searchLinear(id);
}

inline bool
Shape::matches(const StackShape& other) const
{
    return propid_.get() == other.propid &&
           matchesParamsAfterId(other.base, other.slot_, other.attrs, other.flags);
}

template<> struct RootKind<Shape*> : SpecificRootKind<Shape*, THING_ROOT_SHAPE> {};
template<> struct RootKind<BaseShape*> : SpecificRootKind<BaseShape*, THING_ROOT_BASE_SHAPE> {};

// Property lookup hooks on objects are required to return a non-nullptr shape
// to signify that the property has been found. For cases where the property is
// not actually represented by a Shape, use a dummy value. This includes all
// properties of non-native objects, and dense elements for native objects.
// Use separate APIs for these two cases.

static inline void
MarkNonNativePropertyFound(MutableHandleShape propp)
{
    propp.set(reinterpret_cast<Shape*>(1));
}

template <AllowGC allowGC>
static inline void
MarkDenseOrTypedArrayElementFound(typename MaybeRooted<Shape*, allowGC>::MutableHandleType propp)
{
    propp.set(reinterpret_cast<Shape*>(1));
}

static inline bool
IsImplicitDenseOrTypedArrayElement(Shape* prop)
{
    return prop == reinterpret_cast<Shape*>(1);
}

} // namespace js

#ifdef _MSC_VER
#pragma warning(pop)
#pragma warning(pop)
#endif

namespace JS {
template<> class AnchorPermitted<js::Shape*> { };
template<> class AnchorPermitted<const js::Shape*> { };
}

#endif /* vm_Shape_h */