Add m-esr52 at 52.6.0

1 files changed, 1636 insertions, 0 deletions

diff --git a/js/src/vm/Shape.h b/js/src/vm/Shape.h
new file mode 100644
index 0000000000..978798aaa6
--- /dev/null
+++ b/js/src/vm/Shape.h
@@ -0,0 +1,1636 @@
+/* -*- 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 "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/MemoryMetrics.h"
+#include "js/RootingAPI.h"
+#include "js/UbiNode.h"
+#include "vm/ObjectGroup.h"
+#include "vm/String.h"
+#include "vm/Symbol.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 LINEAR_SEARCHES_MAX 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.
+ *
+ * To save memory, shape tables can be discarded on GC and recreated when
+ * needed. AutoKeepShapeTables can be used to avoid discarding shape tables
+ * for a particular zone. Methods operating on ShapeTables take either an
+ * AutoCheckCannotGC or AutoKeepShapeTables argument, to help ensure tables
+ * are not purged while we're using them.
+ *
+ * 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.
+ *
+ * For getters/setters, an AccessorShape is allocated. This is a slightly fatter
+ * type with extra fields for the getter/setter data.
+ *
+ * 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 TenuringTracer;
+
+typedef JSGetterOp GetterOp;
+typedef JSSetterOp SetterOp;
+
+/* 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;
+
+enum class MaybeAdding { Adding = true, NotAdding = false };
+
+class AutoKeepShapeTables;
+
+/*
+ * Shapes use multiplicative hashing, but specialized to
+ * minimize footprint.
+ */
+class ShapeTable {
+  public:
+    friend class NativeObject;
+    friend class BaseShape;
+    static const uint32_t MIN_ENTRIES   = 11;
+
+    class Entry {
+        // js::Shape pointer tag bit indicating a collision.
+        static const uintptr_t SHAPE_COLLISION = 1;
+        static Shape* const SHAPE_REMOVED; // = SHAPE_COLLISION
+
+        Shape* shape_;
+
+        Entry() = delete;
+        Entry(const Entry&) = delete;
+        Entry& operator=(const Entry&) = delete;
+
+      public:
+        bool isFree() const { return shape_ == nullptr; }
+        bool isRemoved() const { return shape_ == SHAPE_REMOVED; }
+        bool isLive() const { return !isFree() && !isRemoved(); }
+        bool hadCollision() const { return uintptr_t(shape_) & SHAPE_COLLISION; }
+
+        void setFree() { shape_ = nullptr; }
+        void setRemoved() { shape_ = SHAPE_REMOVED; }
+
+        Shape* shape() const {
+            return reinterpret_cast<Shape*>(uintptr_t(shape_) & ~SHAPE_COLLISION);
+        }
+
+        void setShape(Shape* shape) {
+            MOZ_ASSERT(isFree());
+            MOZ_ASSERT(shape);
+            MOZ_ASSERT(shape != SHAPE_REMOVED);
+            shape_ = shape;
+            MOZ_ASSERT(!hadCollision());
+        }
+
+        void flagCollision() {
+            shape_ = reinterpret_cast<Shape*>(uintptr_t(shape_) | SHAPE_COLLISION);
+        }
+        void setPreservingCollision(Shape* shape) {
+            shape_ = reinterpret_cast<Shape*>(uintptr_t(shape) | uintptr_t(hadCollision()));
+        }
+    };
+
+  private:
+    static const uint32_t HASH_BITS     = mozilla::tl::BitSize<HashNumber>::value;
+
+    // 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);
+
+    uint32_t        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 */
+
+    Entry*          entries_;          /* table of ptrs to shared tree nodes */
+
+    template<MaybeAdding Adding>
+    Entry& searchUnchecked(jsid id);
+
+  public:
+    explicit ShapeTable(uint32_t nentries)
+      : hashShift_(HASH_BITS - MIN_SIZE_LOG2),
+        entryCount_(nentries),
+        removedCount_(0),
+        freeList_(SHAPE_INVALID_SLOT),
+        entries_(nullptr)
+    {
+        /* NB: entries is set by init, which must be called. */
+    }
+
+    ~ShapeTable() {
+        js_free(entries_);
+    }
+
+    uint32_t entryCount() const { return entryCount_; }
+
+    uint32_t freeList() const { return freeList_; }
+    void setFreeList(uint32_t slot) { freeList_ = slot; }
+
+    /*
+     * 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_);
+    }
+
+    // init() is fallible and reports OOM to the context.
+    bool init(ExclusiveContext* cx, Shape* lastProp);
+
+    // change() is fallible but does not report OOM.
+    bool change(ExclusiveContext* cx, int log2Delta);
+
+    template<MaybeAdding Adding>
+    MOZ_ALWAYS_INLINE Entry& search(jsid id, const AutoKeepShapeTables&) {
+        return searchUnchecked<Adding>(id);
+    }
+
+    template<MaybeAdding Adding>
+    MOZ_ALWAYS_INLINE Entry& search(jsid id, const JS::AutoCheckCannotGC&) {
+        return searchUnchecked<Adding>(id);
+    }
+
+    void trace(JSTracer* trc);
+#ifdef JSGC_HASH_TABLE_CHECKS
+    void checkAfterMovingGC();
+#endif
+
+  private:
+    Entry& getEntry(uint32_t i) const {
+        MOZ_ASSERT(i < capacity());
+        return entries_[i];
+    }
+    void decEntryCount() {
+        MOZ_ASSERT(entryCount_ > 0);
+        entryCount_--;
+    }
+    void incEntryCount() {
+        entryCount_++;
+        MOZ_ASSERT(entryCount_ + removedCount_ <= capacity());
+    }
+    void incRemovedCount() {
+        removedCount_++;
+        MOZ_ASSERT(entryCount_ + removedCount_ <= capacity());
+    }
+
+    /* By definition, hashShift = HASH_BITS - log2(capacity). */
+    uint32_t capacity() const { return JS_BIT(HASH_BITS - hashShift_); }
+
+    /* 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(ExclusiveContext* cx);
+};
+
+// Ensures no shape tables are purged in the current zone.
+class MOZ_RAII AutoKeepShapeTables
+{
+    ExclusiveContext* cx_;
+    bool prev_;
+
+    AutoKeepShapeTables(const AutoKeepShapeTables&) = delete;
+    void operator=(const AutoKeepShapeTables&) = delete;
+
+  public:
+    explicit inline AutoKeepShapeTables(ExclusiveContext* cx);
+    inline ~AutoKeepShapeTables();
+};
+
+/*
+ * Use the reserved attribute bit to mean shadowability.
+ */
+#define JSPROP_SHADOWABLE       JSPROP_INTERNAL_USE_BIT
+
+/*
+ * 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 zone 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 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 AccessorShape;
+class Shape;
+class UnownedBaseShape;
+struct StackBaseShape;
+
+class BaseShape : public gc::TenuredCell
+{
+  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,
+
+        /* (0x2 and 0x4 are unused) */
+
+        /*
+         * 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,
+        /* (0x40 is unused) */
+        HAD_ELEMENTS_ACCESS =   0x80,
+        WATCHED             =  0x100,
+        ITERATED_SINGLETON  =  0x200,
+        NEW_GROUP_UNKNOWN   =  0x400,
+        UNCACHEABLE_PROTO   =  0x800,
+        IMMUTABLE_PROTOTYPE = 0x1000,
+
+        // See JSObject::isQualifiedVarObj().
+        QUALIFIED_VAROBJ    = 0x2000,
+
+        // 0x4000 is unused.
+
+        // For a function used as an interpreted constructor, whether a 'new'
+        // type had constructor information cleared.
+        NEW_SCRIPT_CLEARED  = 0x8000,
+
+        OBJECT_FLAG_MASK    = 0xfff8
+    };
+
+  private:
+    const Class*        clasp_;        /* Class of referring object. */
+    uint32_t            flags;          /* Vector of above flags. */
+    uint32_t            slotSpan_;      /* Object slot span for BaseShapes at
+                                         * dictionary last properties. */
+
+    /* For owned BaseShapes, the canonical unowned BaseShape. */
+    GCPtrUnownedBaseShape unowned_;
+
+    /* For owned BaseShapes, the shape's shape table. */
+    ShapeTable*      table_;
+
+#if JS_BITS_PER_WORD == 32
+    // Ensure sizeof(BaseShape) is a multiple of gc::CellSize.
+    uint32_t padding_;
+#endif
+
+    BaseShape(const BaseShape& base) = delete;
+    BaseShape& operator=(const BaseShape& other) = delete;
+
+  public:
+    void finalize(FreeOp* fop);
+
+    explicit inline BaseShape(const StackBaseShape& base);
+
+    /* Not defined: BaseShapes must not be stack allocated. */
+    ~BaseShape();
+
+    const Class* clasp() const { return clasp_; }
+
+    bool isOwned() const { return !!(flags & OWNED_SHAPE); }
+
+    static void copyFromUnowned(BaseShape& dest, UnownedBaseShape& src);
+    inline void adoptUnowned(UnownedBaseShape* other);
+
+    void setOwned(UnownedBaseShape* unowned) {
+        flags |= OWNED_SHAPE;
+        unowned_ = unowned;
+    }
+
+    uint32_t getObjectFlags() const { return flags & OBJECT_FLAG_MASK; }
+
+    bool hasTable() const { MOZ_ASSERT_IF(table_, isOwned()); return table_ != nullptr; }
+    void setTable(ShapeTable* table) { MOZ_ASSERT(isOwned()); table_ = table; }
+
+    ShapeTable* maybeTable(const AutoKeepShapeTables&) const {
+        MOZ_ASSERT_IF(table_, isOwned());
+        return table_;
+    }
+    ShapeTable* maybeTable(const JS::AutoCheckCannotGC&) const {
+        MOZ_ASSERT_IF(table_, isOwned());
+        return table_;
+    }
+    void maybePurgeTable() {
+        if (table_ && table_->freeList() == SHAPE_INVALID_SLOT) {
+            js_delete(table_);
+            table_ = nullptr;
+        }
+    }
+
+    uint32_t slotSpan() const { MOZ_ASSERT(isOwned()); return slotSpan_; }
+    void setSlotSpan(uint32_t slotSpan) { MOZ_ASSERT(isOwned()); slotSpan_ = slotSpan; }
+
+    /*
+     * Lookup base shapes from the zone's baseShapes table, adding if not
+     * already found.
+     */
+    static UnownedBaseShape* getUnowned(ExclusiveContext* cx, 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 offsetOfFlags() { return offsetof(BaseShape, flags); }
+
+    static const JS::TraceKind TraceKind = JS::TraceKind::BaseShape;
+
+    void traceChildren(JSTracer* trc);
+    void traceChildrenSkipShapeTable(JSTracer* trc);
+
+#ifdef DEBUG
+    bool canSkipMarkingShapeTable(Shape* lastShape);
+#endif
+
+  private:
+    static void staticAsserts() {
+        JS_STATIC_ASSERT(offsetof(BaseShape, clasp_) == offsetof(js::shadow::BaseShape, clasp_));
+        static_assert(sizeof(BaseShape) % gc::CellSize == 0,
+                      "Things inheriting from gc::Cell must have a size that's "
+                      "a multiple of gc::CellSize");
+    }
+
+    void traceShapeTable(JSTracer* trc);
+};
+
+class UnownedBaseShape : public BaseShape {};
+
+UnownedBaseShape*
+BaseShape::unowned()
+{
+    return isOwned() ? baseUnowned() : toUnowned();
+}
+
+UnownedBaseShape*
+BaseShape::toUnowned()
+{
+    MOZ_ASSERT(!isOwned() && !unowned_);
+    return static_cast<UnownedBaseShape*>(this);
+}
+
+UnownedBaseShape*
+BaseShape::baseUnowned()
+{
+    MOZ_ASSERT(isOwned() && unowned_);
+    return unowned_;
+}
+
+/* Entries for the per-zone baseShapes set of unowned base shapes. */
+struct StackBaseShape : public DefaultHasher<ReadBarriered<UnownedBaseShape*>>
+{
+    uint32_t flags;
+    const Class* clasp;
+
+    explicit StackBaseShape(BaseShape* base)
+      : flags(base->flags & BaseShape::OBJECT_FLAG_MASK),
+        clasp(base->clasp_)
+    {}
+
+    inline StackBaseShape(ExclusiveContext* cx, const Class* clasp, uint32_t objectFlags);
+    explicit inline StackBaseShape(Shape* shape);
+
+    struct Lookup
+    {
+        uint32_t flags;
+        const Class* clasp;
+
+        MOZ_IMPLICIT Lookup(const StackBaseShape& base)
+          : flags(base.flags), clasp(base.clasp)
+        {}
+
+        MOZ_IMPLICIT Lookup(UnownedBaseShape* base)
+          : flags(base->getObjectFlags()), clasp(base->clasp())
+        {
+            MOZ_ASSERT(!base->isOwned());
+        }
+    };
+
+    static inline HashNumber hash(const Lookup& lookup);
+    static inline bool match(ReadBarriered<UnownedBaseShape*> key, const Lookup& lookup);
+};
+
+static MOZ_ALWAYS_INLINE js::HashNumber
+HashId(jsid id)
+{
+    // HashGeneric alone would work, but bits of atom and symbol addresses
+    // could then be recovered from the hash code. See bug 1330769.
+    if (MOZ_LIKELY(JSID_IS_ATOM(id)))
+        return JSID_TO_ATOM(id)->hash();
+    if (JSID_IS_SYMBOL(id))
+        return JSID_TO_SYMBOL(id)->hash();
+    return mozilla::HashGeneric(JSID_BITS(id));
+}
+
+template <>
+struct DefaultHasher<jsid>
+{
+    typedef jsid Lookup;
+    static HashNumber hash(jsid id) {
+        return HashId(id);
+    }
+    static bool match(jsid id1, jsid id2) {
+        return id1 == id2;
+    }
+};
+
+using BaseShapeSet = JS::GCHashSet<ReadBarriered<UnownedBaseShape*>,
+                                   StackBaseShape,
+                                   SystemAllocPolicy>;
+
+class Shape : public gc::TenuredCell
+{
+    friend class ::JSObject;
+    friend class ::JSFunction;
+    friend class NativeObject;
+    friend class PropertyTree;
+    friend class TenuringTracer;
+    friend struct StackBaseShape;
+    friend struct StackShape;
+    friend class JS::ubi::Concrete<Shape>;
+    friend class js::gc::RelocationOverlay;
+
+  protected:
+    GCPtrBaseShape base_;
+    PreBarrieredId propid_;
+
+    enum 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
+    };
+
+    uint32_t            slotInfo;       /* mask of above info */
+    uint8_t             attrs;          /* attributes, see jsapi.h JSPROP_* */
+    uint8_t             flags;          /* flags, see below for defines */
+
+    GCPtrShape   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 */
+        GCPtrShape* 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_ */
+    };
+
+    template<MaybeAdding Adding = MaybeAdding::NotAdding>
+    static inline Shape* search(ExclusiveContext* cx, Shape* start, jsid id);
+
+    template<MaybeAdding Adding = MaybeAdding::NotAdding>
+    static inline MOZ_MUST_USE bool search(ExclusiveContext* cx, Shape* start, jsid id,
+                                           const AutoKeepShapeTables&,
+                                           Shape** pshape, ShapeTable::Entry** pentry);
+
+    static inline Shape* searchNoHashify(Shape* start, jsid id);
+
+    void removeFromDictionary(NativeObject* obj);
+    void insertIntoDictionary(GCPtrShape* dictp);
+
+    inline void initDictionaryShape(const StackShape& child, uint32_t nfixed,
+                                    GCPtrShape* 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(ExclusiveContext* cx, Shape* shape);
+    void handoffTableTo(Shape* newShape);
+
+    void setParent(Shape* p) {
+        MOZ_ASSERT_IF(p && !p->hasMissingSlot() && !inDictionary(),
+                      p->maybeSlot() <= maybeSlot());
+        MOZ_ASSERT_IF(p && !inDictionary(),
+                      hasSlot() == (p->maybeSlot() != maybeSlot()));
+        parent = p;
+    }
+
+    bool ensureOwnBaseShape(ExclusiveContext* cx) {
+        if (base()->isOwned())
+            return true;
+        return makeOwnBaseShape(cx);
+    }
+
+    bool makeOwnBaseShape(ExclusiveContext* cx);
+
+    MOZ_ALWAYS_INLINE MOZ_MUST_USE bool maybeCreateTableForLookup(ExclusiveContext* cx);
+
+  public:
+    bool hasTable() const { return base()->hasTable(); }
+
+    ShapeTable* maybeTable(const AutoKeepShapeTables& keep) const {
+        return base()->maybeTable(keep);
+    }
+    ShapeTable* maybeTable(const JS::AutoCheckCannotGC& check) const {
+        return base()->maybeTable(check);
+    }
+
+    template <typename T>
+    MOZ_MUST_USE ShapeTable* ensureTableForDictionary(ExclusiveContext* cx, const T& nogc) {
+        MOZ_ASSERT(inDictionary());
+        if (ShapeTable* table = maybeTable(nogc))
+            return table;
+        if (!hashify(cx, this))
+            return nullptr;
+        ShapeTable* table = maybeTable(nogc);
+        MOZ_ASSERT(table);
+        return table;
+    }
+
+    void addSizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf,
+                                JS::ShapeInfo* info) const
+    {
+        JS::AutoCheckCannotGC nogc;
+        if (ShapeTable* table = maybeTable(nogc)) {
+            if (inDictionary())
+                info->shapesMallocHeapDictTables += table->sizeOfIncludingThis(mallocSizeOf);
+            else
+                info->shapesMallocHeapTreeTables += table->sizeOfIncludingThis(mallocSizeOf);
+        }
+
+        if (!inDictionary() && kids.isHash())
+            info->shapesMallocHeapTreeKids += kids.toHash()->sizeOfIncludingThis(mallocSizeOf);
+    }
+
+    bool isAccessorShape() const {
+        MOZ_ASSERT_IF(flags & ACCESSOR_SHAPE, getAllocKind() == gc::AllocKind::ACCESSOR_SHAPE);
+        return flags & ACCESSOR_SHAPE;
+    }
+    AccessorShape& asAccessorShape() const {
+        MOZ_ASSERT(isAccessorShape());
+        return *(AccessorShape*)this;
+    }
+
+    const GCPtrShape& previous() const { return parent; }
+
+    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);
+        }
+
+        explicit Range(Shape* shape) : cursor((ExclusiveContext*) nullptr, shape) {
+            JS_STATIC_ASSERT(allowGC == NoGC);
+        }
+
+        bool empty() const {
+            return !cursor || cursor->isEmptyShape();
+        }
+
+        Shape& front() const {
+            MOZ_ASSERT(!empty());
+            return *cursor;
+        }
+
+        void popFront() {
+            MOZ_ASSERT(!empty());
+            cursor = cursor->parent;
+        }
+    };
+
+    const Class* getObjectClass() const {
+        return base()->clasp_;
+    }
+
+    static Shape* setObjectFlags(ExclusiveContext* cx,
+                                 BaseShape::Flag flag, TaggedProto proto, Shape* last);
+
+    uint32_t getObjectFlags() const { return base()->getObjectFlags(); }
+    bool hasAllObjectFlags(BaseShape::Flag flags) const {
+        MOZ_ASSERT(flags);
+        MOZ_ASSERT(!(flags & ~BaseShape::OBJECT_FLAG_MASK));
+        return (base()->flags & flags) == flags;
+    }
+
+  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 stored in per-object dictionary, not shared property tree. */
+        IN_DICTIONARY   = 0x01,
+
+        /*
+         * Slotful property was stored to more than once. This is used as a
+         * hint for type inference.
+         */
+        OVERWRITTEN     = 0x02,
+
+        /*
+         * This shape is an AccessorShape, a fat Shape that can store
+         * getter/setter information.
+         */
+        ACCESSOR_SHAPE  = 0x04,
+
+        /* Flags used to speed up isBigEnoughForAShapeTable(). */
+        HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE = 0x08,
+        CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE = 0x10,
+    };
+
+    /* 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) = delete;
+
+    /* Allocate a new shape based on the given StackShape. */
+    static inline Shape* new_(ExclusiveContext* cx, Handle<StackShape> other, uint32_t nfixed);
+
+    /*
+     * 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;
+    }
+
+    inline GetterOp getter() const;
+    bool hasDefaultGetter() const { return !getter(); }
+    GetterOp getterOp() const { MOZ_ASSERT(!hasGetterValue()); return getter(); }
+    inline JSObject* getterObject() const;
+    bool hasGetterObject() const { return hasGetterValue() && getterObject(); }
+
+    // Per ES5, decode null getterObj as the undefined value, which encodes as null.
+    Value getterValue() const {
+        MOZ_ASSERT(hasGetterValue());
+        if (JSObject* getterObj = getterObject())
+            return ObjectValue(*getterObj);
+        return UndefinedValue();
+    }
+
+    Value getterOrUndefined() const {
+        return hasGetterValue() ? getterValue() : UndefinedValue();
+    }
+
+    inline SetterOp setter() const;
+    bool hasDefaultSetter() const { return !setter(); }
+    SetterOp setterOp() const { MOZ_ASSERT(!hasSetterValue()); return setter(); }
+    inline JSObject* setterObject() const;
+    bool hasSetterObject() const { return hasSetterValue() && setterObject(); }
+
+    // Per ES5, decode null setterObj as the undefined value, which encodes as null.
+    Value setterValue() const {
+        MOZ_ASSERT(hasSetterValue());
+        if (JSObject* setterObj = setterObject())
+            return ObjectValue(*setterObj);
+        return UndefinedValue();
+    }
+
+    Value setterOrUndefined() const {
+        return hasSetterValue() ? setterValue() : UndefinedValue();
+    }
+
+    void setOverwritten() {
+        flags |= OVERWRITTEN;
+    }
+    bool hadOverwrite() const {
+        return flags & OVERWRITTEN;
+    }
+
+    void update(GetterOp getter, SetterOp 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,
+                                    other->getter(), other->setter());
+    }
+
+    inline bool matches(const StackShape& other) const;
+
+    bool matchesParamsAfterId(BaseShape* base, uint32_t aslot, unsigned aattrs, unsigned aflags,
+                              GetterOp rawGetter, SetterOp rawSetter) const
+    {
+        return base->unowned() == this->base()->unowned() &&
+               maybeSlot() == aslot &&
+               attrs == aattrs &&
+               getter() == rawGetter &&
+               setter() == rawSetter;
+    }
+
+    bool set(JSContext* cx, HandleNativeObject obj, HandleObject receiver, MutableHandleValue vp,
+             ObjectOpResult& result);
+
+    BaseShape* base() const { return base_.get(); }
+
+    bool hasSlot() const {
+        return (attrs & JSPROP_SHARED) == 0;
+    }
+    uint32_t slot() const { MOZ_ASSERT(hasSlot() && !hasMissingSlot()); return maybeSlot(); }
+    uint32_t maybeSlot() const {
+        return slotInfo & SLOT_MASK;
+    }
+
+    bool isEmptyShape() const {
+        MOZ_ASSERT_IF(JSID_IS_EMPTY(propid_), hasMissingSlot());
+        return JSID_IS_EMPTY(propid_);
+    }
+
+    uint32_t slotSpan(const Class* clasp) const {
+        MOZ_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) {
+        MOZ_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) {
+        MOZ_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();
+        MOZ_ASSERT(count < LINEAR_SEARCHES_MAX);
+        slotInfo = slotInfo & ~LINEAR_SEARCHES_MASK;
+        slotInfo = slotInfo | ((count + 1) << LINEAR_SEARCHES_SHIFT);
+    }
+
+    const PreBarrieredId& propid() const {
+        MOZ_ASSERT(!isEmptyShape());
+        MOZ_ASSERT(!JSID_IS_VOID(propid_));
+        return propid_;
+    }
+    PreBarrieredId& propidRef() { MOZ_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;
+    }
+
+    bool hasShadowable() const { return attrs & JSPROP_SHADOWABLE; }
+
+    uint32_t entryCount() {
+        JS::AutoCheckCannotGC nogc;
+        if (ShapeTable* table = maybeTable(nogc))
+            return table->entryCount();
+        uint32_t count = 0;
+        for (Shape::Range<NoGC> r(this); !r.empty(); r.popFront())
+            ++count;
+        return count;
+    }
+
+  private:
+    bool isBigEnoughForAShapeTableSlow() {
+        uint32_t count = 0;
+        for (Shape::Range<NoGC> r(this); !r.empty(); r.popFront()) {
+            ++count;
+            if (count >= ShapeTable::MIN_ENTRIES)
+                return true;
+        }
+        return false;
+    }
+    void clearCachedBigEnoughForShapeTable() {
+        flags &= ~(HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE | CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE);
+    }
+
+  public:
+    bool isBigEnoughForAShapeTable() {
+        MOZ_ASSERT(!hasTable());
+
+        // isBigEnoughForAShapeTableSlow is pretty inefficient so we only call
+        // it once and cache the result.
+
+        if (flags & HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE) {
+            bool res = flags & CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE;
+            MOZ_ASSERT(res == isBigEnoughForAShapeTableSlow());
+            return res;
+        }
+
+        MOZ_ASSERT(!(flags & CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE));
+
+        bool res = isBigEnoughForAShapeTableSlow();
+        if (res)
+            flags |= CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE;
+        flags |= HAS_CACHED_BIG_ENOUGH_FOR_SHAPE_TABLE;
+        return res;
+    }
+
+#ifdef DEBUG
+    void dump(FILE* fp) const;
+    void dumpSubtree(int level, FILE* fp) const;
+#endif
+
+    void sweep();
+    void finalize(FreeOp* fop);
+    void removeChild(Shape* child);
+
+    static const JS::TraceKind TraceKind = JS::TraceKind::Shape;
+
+    void traceChildren(JSTracer* trc);
+
+    inline Shape* search(ExclusiveContext* cx, jsid id);
+    MOZ_ALWAYS_INLINE Shape* searchLinear(jsid id);
+
+    void fixupAfterMovingGC();
+    void fixupGetterSetterForBarrier(JSTracer* trc);
+    void updateBaseShapeAfterMovingGC();
+
+    /* For JIT usage */
+    static inline size_t offsetOfBase() { return offsetof(Shape, base_); }
+    static inline size_t offsetOfSlotInfo() { return offsetof(Shape, slotInfo); }
+    static inline uint32_t fixedSlotsMask() { return FIXED_SLOTS_MASK; }
+
+  private:
+    void fixupDictionaryShapeAfterMovingGC();
+    void fixupShapeTreeAfterMovingGC();
+
+    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);
+    }
+};
+
+/* Fat Shape used for accessor properties. */
+class AccessorShape : public Shape
+{
+    friend class Shape;
+    friend class NativeObject;
+
+    union {
+        GetterOp rawGetter;     /* getter hook for shape */
+        JSObject* getterObj;    /* user-defined callable "get" object or
+                                   null if shape->hasGetterValue() */
+    };
+    union {
+        SetterOp rawSetter;     /* setter hook for shape */
+        JSObject* setterObj;    /* user-defined callable "set" object or
+                                   null if shape->hasSetterValue() */
+    };
+
+  public:
+    /* Get a shape identical to this one, without parent/kids information. */
+    inline AccessorShape(const StackShape& other, uint32_t nfixed);
+};
+
+inline
+StackBaseShape::StackBaseShape(Shape* shape)
+  : flags(shape->getObjectFlags()),
+    clasp(shape->getObjectClass())
+{}
+
+class MOZ_RAII AutoRooterGetterSetter
+{
+    class Inner final : private JS::CustomAutoRooter
+    {
+      public:
+        inline Inner(ExclusiveContext* cx, uint8_t attrs, GetterOp* pgetter_, SetterOp* psetter_);
+
+      private:
+        virtual void trace(JSTracer* trc);
+
+        uint8_t attrs;
+        GetterOp* pgetter;
+        SetterOp* psetter;
+    };
+
+  public:
+    inline AutoRooterGetterSetter(ExclusiveContext* cx, uint8_t attrs,
+                                  GetterOp* pgetter, SetterOp* psetter
+                                  MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
+    inline AutoRooterGetterSetter(ExclusiveContext* cx, uint8_t attrs,
+                                  JSNative* pgetter, JSNative* 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)
+    { }
+
+    static Shape* new_(ExclusiveContext* cx, Handle<UnownedBaseShape*> base, uint32_t nfixed);
+
+    /*
+     * 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, size_t nfixed, uint32_t objectFlags = 0);
+    static Shape* getInitialShape(ExclusiveContext* cx, const Class* clasp,
+                                  TaggedProto proto, 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);
+};
+
+// InitialShapeProto stores either:
+//
+// * A TaggedProto (or ReadBarriered<TaggedProto>).
+//
+// * A JSProtoKey. This is used instead of the TaggedProto if the proto is one
+//   of the global's builtin prototypes. For instance, if the proto is the
+//   initial Object.prototype, we use key_ = JSProto_Object, proto_ = nullptr.
+//
+// Using the JSProtoKey here is an optimization that lets us share more shapes
+// across compartments within a zone.
+template <typename PtrType>
+class InitialShapeProto
+{
+    template <typename T> friend class InitialShapeProto;
+
+    JSProtoKey key_;
+    PtrType proto_;
+
+  public:
+    InitialShapeProto()
+      : key_(JSProto_LIMIT), proto_()
+    {}
+
+    InitialShapeProto(JSProtoKey key, TaggedProto proto)
+      : key_(key), proto_(proto)
+    {}
+
+    template <typename T>
+    explicit InitialShapeProto(const InitialShapeProto<T>& other)
+      : key_(other.key()), proto_(other.proto_)
+    {}
+
+    explicit InitialShapeProto(TaggedProto proto)
+      : key_(JSProto_LIMIT), proto_(proto)
+    {}
+    explicit InitialShapeProto(JSProtoKey key)
+      : key_(key), proto_(nullptr)
+    {
+        MOZ_ASSERT(key < JSProto_LIMIT);
+    }
+
+    HashNumber hashCode() const {
+        return proto_.hashCode() ^ HashNumber(key_);
+    }
+    template <typename T>
+    bool match(const InitialShapeProto<T>& other) const {
+        return key_ == other.key_ &&
+               proto_.uniqueId() == other.proto_.unbarrieredGet().uniqueId();
+    }
+
+    JSProtoKey key() const {
+        return key_;
+    }
+    const PtrType& proto() const {
+        return proto_;
+    }
+    void setProto(TaggedProto proto) {
+        proto_ = proto;
+    }
+};
+
+/*
+ * Entries for the per-zone initialShapes set indexing initial shapes for
+ * objects in the zone 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.
+     */
+    using ShapeProto = InitialShapeProto<ReadBarriered<TaggedProto>>;
+    ShapeProto proto;
+
+    /* State used to determine a match on an initial shape. */
+    struct Lookup {
+        using ShapeProto = InitialShapeProto<TaggedProto>;
+        const Class* clasp;
+        ShapeProto proto;
+        uint32_t nfixed;
+        uint32_t baseFlags;
+
+        Lookup(const Class* clasp, ShapeProto proto, uint32_t nfixed, uint32_t baseFlags)
+          : clasp(clasp), proto(proto), nfixed(nfixed), baseFlags(baseFlags)
+        {}
+    };
+
+    inline InitialShapeEntry();
+    inline InitialShapeEntry(Shape* shape, const Lookup::ShapeProto& proto);
+
+    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; }
+
+    bool needsSweep() {
+        Shape* ushape = shape.unbarrieredGet();
+        JSObject* protoObj = proto.proto().raw();
+        return (gc::IsAboutToBeFinalizedUnbarriered(&ushape) ||
+                (proto.proto().isObject() && gc::IsAboutToBeFinalizedUnbarriered(&protoObj)));
+    }
+};
+
+using InitialShapeSet = JS::GCHashSet<InitialShapeEntry, InitialShapeEntry, SystemAllocPolicy>;
+
+struct StackShape
+{
+    /* For performance, StackShape only roots when absolutely necessary. */
+    UnownedBaseShape* base;
+    jsid propid;
+    GetterOp rawGetter;
+    SetterOp rawSetter;
+    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),
+        rawGetter(nullptr),
+        rawSetter(nullptr),
+        slot_(slot),
+        attrs(uint8_t(attrs)),
+        flags(uint8_t(flags))
+    {
+        MOZ_ASSERT(base);
+        MOZ_ASSERT(!JSID_IS_VOID(propid));
+        MOZ_ASSERT(slot <= SHAPE_INVALID_SLOT);
+        MOZ_ASSERT_IF(attrs & (JSPROP_GETTER | JSPROP_SETTER), attrs & JSPROP_SHARED);
+    }
+
+    explicit StackShape(Shape* shape)
+      : base(shape->base()->unowned()),
+        propid(shape->propidRef()),
+        rawGetter(shape->getter()),
+        rawSetter(shape->setter()),
+        slot_(shape->maybeSlot()),
+        attrs(shape->attrs),
+        flags(shape->flags)
+    {}
+
+    void updateGetterSetter(GetterOp rawGetter, SetterOp rawSetter) {
+        if (rawGetter || rawSetter || (attrs & (JSPROP_GETTER|JSPROP_SETTER)))
+            flags |= Shape::ACCESSOR_SHAPE;
+        else
+            flags &= ~Shape::ACCESSOR_SHAPE;
+
+        this->rawGetter = rawGetter;
+        this->rawSetter = rawSetter;
+    }
+
+    bool hasSlot() const { return (attrs & JSPROP_SHARED) == 0; }
+    bool hasMissingSlot() const { return maybeSlot() == SHAPE_INVALID_SLOT; }
+
+    uint32_t slot() const { MOZ_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) {
+        MOZ_ASSERT(slot <= SHAPE_INVALID_SLOT);
+        slot_ = slot;
+    }
+
+    bool isAccessorShape() const {
+        return flags & Shape::ACCESSOR_SHAPE;
+    }
+
+    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) ^ HashId(propid);
+        hash = mozilla::RotateLeft(hash, 4) ^ uintptr_t(rawGetter);
+        hash = mozilla::RotateLeft(hash, 4) ^ uintptr_t(rawSetter);
+        return hash;
+    }
+
+    // Traceable implementation.
+    static void trace(StackShape* stackShape, JSTracer* trc) { stackShape->trace(trc); }
+    void trace(JSTracer* trc);
+};
+
+template <typename Outer>
+class StackShapeOperations {
+    const StackShape& ss() const { return static_cast<const Outer*>(this)->get(); }
+
+  public:
+    bool hasSlot() const { return ss().hasSlot(); }
+    bool hasMissingSlot() const { return ss().hasMissingSlot(); }
+    uint32_t slot() const { return ss().slot(); }
+    uint32_t maybeSlot() const { return ss().maybeSlot(); }
+    uint32_t slotSpan() const { return ss().slotSpan(); }
+    bool isAccessorShape() const { return ss().isAccessorShape(); }
+    uint8_t attrs() const { return ss().attrs; }
+};
+
+template <typename Outer>
+class MutableStackShapeOperations : public StackShapeOperations<Outer> {
+    StackShape& ss() { return static_cast<Outer*>(this)->get(); }
+
+  public:
+    void updateGetterSetter(GetterOp rawGetter, SetterOp rawSetter) {
+        ss().updateGetterSetter(rawGetter, rawSetter);
+    }
+    void setSlot(uint32_t slot) { ss().setSlot(slot); }
+    void setBase(UnownedBaseShape* base) { ss().base = base; }
+    void setAttrs(uint8_t attrs) { ss().attrs = attrs; }
+};
+
+template <>
+class RootedBase<StackShape> : public MutableStackShapeOperations<JS::Rooted<StackShape>>
+{};
+
+template <>
+class HandleBase<StackShape> : public StackShapeOperations<JS::Handle<StackShape>>
+{};
+
+template <>
+class MutableHandleBase<StackShape>
+  : public MutableStackShapeOperations<JS::MutableHandle<StackShape>>
+{};
+
+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)
+{
+#ifdef DEBUG
+    gc::AllocKind allocKind = getAllocKind();
+    MOZ_ASSERT_IF(other.isAccessorShape(), allocKind == gc::AllocKind::ACCESSOR_SHAPE);
+    MOZ_ASSERT_IF(allocKind == gc::AllocKind::SHAPE, !other.isAccessorShape());
+#endif
+
+    MOZ_ASSERT_IF(attrs & (JSPROP_GETTER | JSPROP_SETTER), attrs & JSPROP_SHARED);
+    kids.setNull();
+}
+
+// This class is used to add a post barrier on the AccessorShape's getter/setter
+// objects. It updates the pointers and the shape's entry in the parent's
+// KidsHash table.
+class ShapeGetterSetterRef : public gc::BufferableRef
+{
+    AccessorShape* shape_;
+
+  public:
+    explicit ShapeGetterSetterRef(AccessorShape* shape) : shape_(shape) {}
+    void trace(JSTracer* trc) override { shape_->fixupGetterSetterForBarrier(trc); }
+};
+
+static inline void
+GetterSetterWriteBarrierPost(AccessorShape* shape)
+{
+    MOZ_ASSERT(shape);
+    if (shape->hasGetterObject()) {
+        gc::StoreBuffer* sb = reinterpret_cast<gc::Cell*>(shape->getterObject())->storeBuffer();
+        if (sb) {
+            sb->putGeneric(ShapeGetterSetterRef(shape));
+            return;
+        }
+    }
+    if (shape->hasSetterObject()) {
+        gc::StoreBuffer* sb = reinterpret_cast<gc::Cell*>(shape->setterObject())->storeBuffer();
+        if (sb) {
+            sb->putGeneric(ShapeGetterSetterRef(shape));
+            return;
+        }
+    }
+}
+
+inline
+AccessorShape::AccessorShape(const StackShape& other, uint32_t nfixed)
+  : Shape(other, nfixed),
+    rawGetter(other.rawGetter),
+    rawSetter(other.rawSetter)
+{
+    MOZ_ASSERT(getAllocKind() == gc::AllocKind::ACCESSOR_SHAPE);
+    GetterSetterWriteBarrierPost(this);
+}
+
+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)
+{
+    MOZ_ASSERT(base);
+    kids.setNull();
+}
+
+inline GetterOp
+Shape::getter() const
+{
+    return isAccessorShape() ? asAccessorShape().rawGetter : nullptr;
+}
+
+inline SetterOp
+Shape::setter() const
+{
+    return isAccessorShape() ? asAccessorShape().rawSetter : nullptr;
+}
+
+inline JSObject*
+Shape::getterObject() const
+{
+    MOZ_ASSERT(hasGetterValue());
+    return asAccessorShape().getterObj;
+}
+
+inline JSObject*
+Shape::setterObject() const
+{
+    MOZ_ASSERT(hasSetterValue());
+    return asAccessorShape().setterObj;
+}
+
+inline void
+Shape::initDictionaryShape(const StackShape& child, uint32_t nfixed, GCPtrShape* dictp)
+{
+    if (child.isAccessorShape())
+        new (this) AccessorShape(child, nfixed);
+    else
+        new (this) Shape(child, nfixed);
+    this->flags |= IN_DICTIONARY;
+
+    this->listp = nullptr;
+    if (dictp)
+        insertIntoDictionary(dictp);
+}
+
+inline Shape*
+Shape::searchLinear(jsid id)
+{
+    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.
+     */
+    JS::AutoCheckCannotGC nogc;
+    if (ShapeTable* table = start->maybeTable(nogc)) {
+        ShapeTable::Entry& entry = table->search<MaybeAdding::NotAdding>(id, nogc);
+        return entry.shape();
+    }
+
+    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,
+                                other.rawGetter, other.rawSetter);
+}
+
+// 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.
+
+template <AllowGC allowGC>
+static inline void
+MarkNonNativePropertyFound(typename MaybeRooted<Shape*, allowGC>::MutableHandleType 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);
+}
+
+static inline bool
+IsImplicitNonNativeProperty(Shape* prop)
+{
+    return prop == reinterpret_cast<Shape*>(1);
+}
+
+Shape*
+ReshapeForAllocKind(JSContext* cx, Shape* shape, TaggedProto proto,
+                    gc::AllocKind allocKind);
+
+} // namespace js
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#pragma warning(pop)
+#endif
+
+// JS::ubi::Nodes can point to Shapes and BaseShapes; they're js::gc::Cell
+// instances that occupy a compartment.
+namespace JS {
+namespace ubi {
+
+template<>
+class Concrete<js::Shape> : TracerConcrete<js::Shape> {
+  protected:
+    explicit Concrete(js::Shape *ptr) : TracerConcrete<js::Shape>(ptr) { }
+
+  public:
+    static void construct(void *storage, js::Shape *ptr) { new (storage) Concrete(ptr); }
+
+    Size size(mozilla::MallocSizeOf mallocSizeOf) const override;
+
+    const char16_t* typeName() const override { return concreteTypeName; }
+    static const char16_t concreteTypeName[];
+};
+
+template<>
+class Concrete<js::BaseShape> : TracerConcrete<js::BaseShape> {
+  protected:
+    explicit Concrete(js::BaseShape *ptr) : TracerConcrete<js::BaseShape>(ptr) { }
+
+  public:
+    static void construct(void *storage, js::BaseShape *ptr) { new (storage) Concrete(ptr); }
+
+    Size size(mozilla::MallocSizeOf mallocSizeOf) const override;
+
+    const char16_t* typeName() const override { return concreteTypeName; }
+    static const char16_t concreteTypeName[];
+};
+
+} // namespace ubi
+} // namespace JS
+
+#endif /* vm_Shape_h */