Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 812 insertions, 0 deletions

diff --git a/js/src/vm/Iteration.h b/js/src/vm/Iteration.h
new file mode 100644
index 0000000000..92edaccd65
--- /dev/null
+++ b/js/src/vm/Iteration.h
@@ -0,0 +1,812 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * 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_Iteration_h
+#define vm_Iteration_h
+
+/*
+ * JavaScript iterators.
+ */
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/MemoryReporting.h"
+
+#include "builtin/SelfHostingDefines.h"
+#include "gc/Barrier.h"
+#include "vm/NativeObject.h"
+#include "vm/TypedArrayObject.h"
+
+/*
+ * [SMDOC] For-in enumeration
+ *
+ * A for-in loop in JS iterates over the string-valued, enumerable
+ * property keys of an object and its prototype chain. The order in
+ * which keys appear is specified to the extent that implementations
+ * historically agreed, and implementation-defined beyond that. See
+ * https://tc39.es/ecma262/#sec-enumerate-object-properties for the
+ * gory details. Each key appears only once in the enumeration.
+ *
+ * We enumerate properties using PropertyEnumerator, which creates an
+ * ordered list of PropertyKeys, using ShapePropertyIter for native
+ * objects and calling enumerate hooks where necessary. This list is
+ * used to create a NativeIterator, which contains (among other
+ * things) a trailing array of strings representing the property keys
+ * of the object, and a cursor pointing into that array. This
+ * NativeIterator is wrapped in a PropertyIteratorObject, which is
+ * pushed by JSOp::Iter and used by JSOp::MoreIter and JSOp::EndIter.
+ *
+ * While active, a NativeIterator is registered in a doubly linked
+ * list, rooted in the compartment. When any property is deleted from
+ * an object, this list is used to remove the deleted property from
+ * any active enumerations. See SuppressDeletedProperty. This slows
+ * down deletion but speeds up enumeration, which is generally a good
+ * tradeoff.
+ *
+ * In many cases, objects with the same shape will have the same set
+ * of property keys. (The most common exception is objects with dense
+ * elements, which can be added or removed without changing the shape
+ * of the object.) In such cases, we can reuse an existing iterator by
+ * storing a pointer to the PropertyIteratorObject in the shape's
+ * |cache_| pointer. Before reusing an iterator, we have to verify
+ * that the prototype chain has not changed and no dense elements have
+ * been added, which is done by storing a trailing array of prototype
+ * shapes in the NativeIterator and comparing it against the shapes of
+ * the prototype chain.
+ *
+ * One of the most frequent uses of for-in loops is in loops that look
+ * like this, which iterate over each property of an object and do
+ * something with those values:
+ *   for (var key in obj) {
+ *     if (obj.hasOwnProperty(key)) {
+ *       doSomethingWith(obj[key]);
+ *     }
+ *   }
+ * Most objects don't have any enumerable properties on the prototype
+ * chain. In such cases, we can speed up property access inside the
+ * loop by precomputing some information and storing it in the
+ * iterator.  When we see a pattern like this in Ion, we generate a
+ * call to GetIteratorWithIndices instead of GetIterator. In this
+ * case, in addition to the list of property keys, PropertyEnumerator
+ * will try to generate a list of corresponding PropertyIndex values,
+ * which represent the location of the own property key in the object
+ * (fixed slot/dynamic slot/dense element + offset). This list will be
+ * stored in NativeIterator as yet another trailing array. When
+ * present, it can be used by Ion code to speed up property access
+ * inside for-in loops. See OptimizeIteratorIndices in
+ * IonAnalysis.cpp.
+ */
+
+namespace js {
+
+class ArrayObject;
+class PlainObject;
+class PropertyIteratorObject;
+
+// A PropertyIndex stores information about the location of an own data
+// property in a format that can be stored in a NativeIterator and consumed by
+// jitcode to access properties without needing to use the megamorphic cache.
+struct PropertyIndex {
+ private:
+  uint32_t asBits_;
+
+ public:
+  enum class Kind : uint32_t { DynamicSlot, FixedSlot, Element, Invalid };
+
+  PropertyIndex(Kind kind, uint32_t index) : asBits_(encode(kind, index)) {}
+
+  static PropertyIndex Invalid() { return PropertyIndex(Kind::Invalid, 0); }
+
+  static PropertyIndex ForElement(uint32_t index) {
+    return PropertyIndex(Kind::Element, index);
+  }
+
+  static PropertyIndex ForSlot(NativeObject* obj, uint32_t index) {
+    if (index < obj->numFixedSlots()) {
+      return PropertyIndex(Kind::FixedSlot, index);
+    } else {
+      return PropertyIndex(Kind::DynamicSlot, index - obj->numFixedSlots());
+    }
+  }
+
+  static constexpr uint32_t KindBits = 2;
+
+  static constexpr uint32_t IndexBits = 32 - KindBits;
+  static constexpr uint32_t IndexLimit = 1 << IndexBits;
+  static constexpr uint32_t IndexMask = (1 << IndexBits) - 1;
+
+  static constexpr uint32_t KindShift = IndexBits;
+
+  static_assert(NativeObject::MAX_FIXED_SLOTS < IndexLimit);
+  static_assert(NativeObject::MAX_SLOTS_COUNT < IndexLimit);
+  static_assert(NativeObject::MAX_DENSE_ELEMENTS_COUNT < IndexLimit);
+
+ private:
+  uint32_t encode(Kind kind, uint32_t index) {
+    MOZ_ASSERT(index < IndexLimit);
+    return (uint32_t(kind) << KindShift) | index;
+  }
+
+ public:
+  Kind kind() const { return Kind(asBits_ >> KindShift); }
+  uint32_t index() const { return asBits_ & IndexMask; }
+};
+
+using PropertyIndexVector = js::Vector<PropertyIndex, 8, js::TempAllocPolicy>;
+
+struct NativeIterator;
+
+class NativeIteratorListNode {
+ protected:
+  // While in compartment->enumerators, these form a doubly linked list.
+  NativeIteratorListNode* prev_ = nullptr;
+  NativeIteratorListNode* next_ = nullptr;
+
+ public:
+  NativeIteratorListNode* prev() { return prev_; }
+  NativeIteratorListNode* next() { return next_; }
+
+  void setPrev(NativeIteratorListNode* prev) { prev_ = prev; }
+  void setNext(NativeIteratorListNode* next) { next_ = next; }
+
+  static constexpr size_t offsetOfNext() {
+    return offsetof(NativeIteratorListNode, next_);
+  }
+
+  static constexpr size_t offsetOfPrev() {
+    return offsetof(NativeIteratorListNode, prev_);
+  }
+
+ private:
+  NativeIterator* asNativeIterator() {
+    return reinterpret_cast<NativeIterator*>(this);
+  }
+
+  friend class NativeIteratorListIter;
+};
+
+class NativeIteratorListHead : public NativeIteratorListNode {
+ private:
+  // Initialize a |Compartment::enumerators| sentinel.
+  NativeIteratorListHead() { prev_ = next_ = this; }
+  friend class JS::Compartment;
+};
+
+class NativeIteratorListIter {
+ private:
+  NativeIteratorListHead* head_;
+  NativeIteratorListNode* curr_;
+
+ public:
+  explicit NativeIteratorListIter(NativeIteratorListHead* head)
+      : head_(head), curr_(head->next()) {}
+
+  bool done() const { return curr_ == head_; }
+
+  NativeIterator* next() {
+    MOZ_ASSERT(!done());
+    NativeIterator* result = curr_->asNativeIterator();
+    curr_ = curr_->next();
+    return result;
+  }
+};
+
+// If an object only has own data properties, we can store a list of
+// PropertyIndex that can be used in Ion to more efficiently access those
+// properties in cases like `for (var key in obj) { ...obj[key]... }`.
+enum class NativeIteratorIndices : uint32_t {
+  // The object being iterated does not support indices.
+  Unavailable = 0,
+
+  // The object being iterated supports indices, but none have been
+  // allocated, because it has not yet been iterated by Ion code that
+  // can use indices-based access.
+  AvailableOnRequest = 1,
+
+  // The object being iterated had indices allocated, but they were
+  // disabled due to a deleted property.
+  Disabled = 2,
+
+  // The object being iterated had indices allocated, and they are
+  // still valid.
+  Valid = 3
+};
+
+struct NativeIterator : public NativeIteratorListNode {
+ private:
+  // Object being iterated.  Non-null except in NativeIterator sentinels,
+  // the empty iterator singleton (for iterating |null| or |undefined|), and
+  // inactive iterators.
+  GCPtr<JSObject*> objectBeingIterated_ = {};
+
+  // Internal iterator object.
+  const GCPtr<JSObject*> iterObj_ = {};
+
+  // The end of GCPtr<Shape*>s that appear directly after |this|, as part of an
+  // overall allocation that stores |*this|, shapes, iterated strings, and maybe
+  // indices. Once this has been fully initialized, it also equals the start of
+  // iterated strings.
+  GCPtr<Shape*>* shapesEnd_;  // initialized by constructor
+
+  // The next property, pointing into an array of strings directly after any
+  // GCPtr<Shape*>s that appear directly after |*this|, as part of an overall
+  // allocation that stores |*this|, shapes, iterated strings, and maybe
+  // indices.
+  GCPtr<JSLinearString*>* propertyCursor_;  // initialized by constructor
+
+  // The limit/end of properties to iterate. Once |this| has been fully
+  // initialized, it also equals the start of indices, if indices are present,
+  // or the end of the full allocation storing |*this|, shapes, and strings, if
+  // indices are not present. Beware! This value may change as properties are
+  // deleted from the observed object.
+  GCPtr<JSLinearString*>* propertiesEnd_;  // initialized by constructor
+
+  HashNumber shapesHash_;  // initialized by constructor
+
+ public:
+  // For cacheable native iterators, whether the iterator is currently
+  // active.  Not serialized by XDR.
+  struct Flags {
+    // This flag is set when all shapes and properties associated with this
+    // NativeIterator have been initialized, such that |shapesEnd_|, in
+    // addition to being the end of shapes, is also the beginning of
+    // properties.
+    //
+    // This flag is only *not* set when a NativeIterator is in the process
+    // of being constructed.  At such time |shapesEnd_| accounts only for
+    // shapes that have been initialized -- potentially none of them.
+    // Instead, |propertyCursor_| is initialized to the ultimate/actual
+    // start of properties and must be used instead of |propertiesBegin()|,
+    // which asserts that this flag is present to guard against misuse.
+    static constexpr uint32_t Initialized = 0x1;
+
+    // This flag indicates that this NativeIterator is currently being used
+    // to enumerate an object's properties and has not yet been closed.
+    static constexpr uint32_t Active = 0x2;
+
+    // This flag indicates that the object being enumerated by this
+    // |NativeIterator| had a property deleted from it before it was
+    // visited, forcing the properties array in this to be mutated to
+    // remove it.
+    static constexpr uint32_t HasUnvisitedPropertyDeletion = 0x4;
+
+    // Whether this is the shared empty iterator object used for iterating over
+    // null/undefined.
+    static constexpr uint32_t IsEmptyIteratorSingleton = 0x8;
+
+    // If any of these bits are set on a |NativeIterator|, it isn't
+    // currently reusable.  (An active |NativeIterator| can't be stolen
+    // *right now*; a |NativeIterator| that's had its properties mutated
+    // can never be reused, because it would give incorrect results.)
+    static constexpr uint32_t NotReusable =
+        Active | HasUnvisitedPropertyDeletion;
+  };
+
+ private:
+  static constexpr uint32_t FlagsBits = 4;
+  static constexpr uint32_t IndicesBits = 2;
+
+  static constexpr uint32_t FlagsMask = (1 << FlagsBits) - 1;
+
+  static constexpr uint32_t PropCountShift = IndicesBits + FlagsBits;
+  static constexpr uint32_t PropCountBits = 32 - PropCountShift;
+
+ public:
+  static constexpr uint32_t IndicesShift = FlagsBits;
+  static constexpr uint32_t IndicesMask = ((1 << IndicesBits) - 1)
+                                          << IndicesShift;
+
+  static constexpr uint32_t PropCountLimit = 1 << PropCountBits;
+
+ private:
+  // Stores Flags bits and indices state in the lower bits and the initial
+  // property count above them.
+  uint32_t flagsAndCount_ = 0;
+
+#ifdef DEBUG
+  // If true, this iterator may contain indexed properties that came from
+  // objects on the prototype chain. This is used by certain debug assertions.
+  bool maybeHasIndexedPropertiesFromProto_ = false;
+#endif
+
+  // END OF PROPERTIES
+
+  // No further fields appear after here *in NativeIterator*, but this class is
+  // always allocated with space tacked on immediately after |this| to store
+  // shapes p to |shapesEnd_|, iterated property names after that up to
+  // |propertiesEnd_|, and maybe PropertyIndex values up to |indices_end()|.
+
+ public:
+  /**
+   * Initialize a NativeIterator properly allocated for |props.length()|
+   * properties and |numShapes| shapes. If |indices| is non-null, also
+   * allocates room for |indices.length()| PropertyIndex values. In this case,
+   * |indices.length()| must equal |props.length()|.
+   *
+   * Despite being a constructor, THIS FUNCTION CAN REPORT ERRORS.  Users
+   * MUST set |*hadError = false| on entry and consider |*hadError| on return
+   * to mean this function failed.
+   */
+  NativeIterator(JSContext* cx, Handle<PropertyIteratorObject*> propIter,
+                 Handle<JSObject*> objBeingIterated, HandleIdVector props,
+                 bool supportsIndices, PropertyIndexVector* indices,
+                 uint32_t numShapes, bool* hadError);
+
+  JSObject* objectBeingIterated() const { return objectBeingIterated_; }
+
+  void initObjectBeingIterated(JSObject& obj) {
+    MOZ_ASSERT(!objectBeingIterated_);
+    objectBeingIterated_.init(&obj);
+  }
+  void clearObjectBeingIterated() {
+    MOZ_ASSERT(objectBeingIterated_);
+    objectBeingIterated_ = nullptr;
+  }
+
+  GCPtr<Shape*>* shapesBegin() const {
+    static_assert(
+        alignof(GCPtr<Shape*>) <= alignof(NativeIterator),
+        "NativeIterator must be aligned to begin storing "
+        "GCPtr<Shape*>s immediately after it with no required padding");
+    const NativeIterator* immediatelyAfter = this + 1;
+    auto* afterNonConst = const_cast<NativeIterator*>(immediatelyAfter);
+    return reinterpret_cast<GCPtr<Shape*>*>(afterNonConst);
+  }
+
+  GCPtr<Shape*>* shapesEnd() const { return shapesEnd_; }
+
+  uint32_t shapeCount() const {
+    return mozilla::PointerRangeSize(shapesBegin(), shapesEnd());
+  }
+
+  GCPtr<JSLinearString*>* propertiesBegin() const {
+    static_assert(
+        alignof(GCPtr<Shape*>) >= alignof(GCPtr<JSLinearString*>),
+        "GCPtr<JSLinearString*>s for properties must be able to appear "
+        "directly after any GCPtr<Shape*>s after this NativeIterator, "
+        "with no padding space required for correct alignment");
+    static_assert(
+        alignof(NativeIterator) >= alignof(GCPtr<JSLinearString*>),
+        "GCPtr<JSLinearString*>s for properties must be able to appear "
+        "directly after this NativeIterator when no GCPtr<Shape*>s are "
+        "present, with no padding space required for correct "
+        "alignment");
+
+    // We *could* just check the assertion below if we wanted, but the
+    // incompletely-initialized NativeIterator case matters for so little
+    // code that we prefer not imposing the condition-check on every single
+    // user.
+    MOZ_ASSERT(isInitialized(),
+               "NativeIterator must be initialized, or else |shapesEnd_| "
+               "isn't necessarily the start of properties and instead "
+               "|propertyCursor_| is");
+
+    return reinterpret_cast<GCPtr<JSLinearString*>*>(shapesEnd_);
+  }
+
+  GCPtr<JSLinearString*>* propertiesEnd() const { return propertiesEnd_; }
+
+  GCPtr<JSLinearString*>* nextProperty() const { return propertyCursor_; }
+
+  PropertyIndex* indicesBegin() const {
+    // PropertyIndex must be able to be appear directly after the properties
+    // array, with no padding required for correct alignment.
+    static_assert(alignof(GCPtr<JSLinearString*>) >= alignof(PropertyIndex));
+    return reinterpret_cast<PropertyIndex*>(propertiesEnd_);
+  }
+
+  PropertyIndex* indicesEnd() const {
+    MOZ_ASSERT(indicesState() == NativeIteratorIndices::Valid);
+    return indicesBegin() + numKeys() * sizeof(PropertyIndex);
+  }
+
+  MOZ_ALWAYS_INLINE JS::Value nextIteratedValueAndAdvance() {
+    if (propertyCursor_ >= propertiesEnd_) {
+      MOZ_ASSERT(propertyCursor_ == propertiesEnd_);
+      return JS::MagicValue(JS_NO_ITER_VALUE);
+    }
+
+    JSLinearString* str = *propertyCursor_;
+    incCursor();
+    return JS::StringValue(str);
+  }
+
+  void resetPropertyCursorForReuse() {
+    MOZ_ASSERT(isInitialized());
+
+    // This function is called unconditionally on IteratorClose, so
+    // unvisited properties might have been deleted, so we can't assert
+    // this NativeIterator is reusable.  (Should we not bother resetting
+    // the cursor in that case?)
+
+    // Note: JIT code inlines |propertyCursor_| resetting when an iterator
+    //       ends: see |CodeGenerator::visitIteratorEnd|.
+    propertyCursor_ = propertiesBegin();
+  }
+
+  bool previousPropertyWas(JS::Handle<JSLinearString*> str) {
+    MOZ_ASSERT(isInitialized());
+    return propertyCursor_ > propertiesBegin() && propertyCursor_[-1] == str;
+  }
+
+  size_t numKeys() const {
+    return mozilla::PointerRangeSize(propertiesBegin(), propertiesEnd());
+  }
+
+  void trimLastProperty() {
+    MOZ_ASSERT(isInitialized());
+    propertiesEnd_--;
+
+    // This invokes the pre barrier on this property, since it's no longer
+    // going to be marked, and it ensures that any existing remembered set
+    // entry will be dropped.
+    *propertiesEnd_ = nullptr;
+
+    // Indices are no longer valid.
+    disableIndices();
+  }
+
+  JSObject* iterObj() const { return iterObj_; }
+
+  void incCursor() {
+    MOZ_ASSERT(isInitialized());
+    propertyCursor_++;
+  }
+
+  HashNumber shapesHash() const { return shapesHash_; }
+
+  bool isInitialized() const { return flags() & Flags::Initialized; }
+
+  size_t allocationSize() const;
+
+#ifdef DEBUG
+  void setMaybeHasIndexedPropertiesFromProto() {
+    maybeHasIndexedPropertiesFromProto_ = true;
+  }
+  bool maybeHasIndexedPropertiesFromProto() const {
+    return maybeHasIndexedPropertiesFromProto_;
+  }
+#endif
+
+ private:
+  uint32_t flags() const { return flagsAndCount_ & FlagsMask; }
+
+  NativeIteratorIndices indicesState() const {
+    return NativeIteratorIndices((flagsAndCount_ & IndicesMask) >>
+                                 IndicesShift);
+  }
+
+  uint32_t initialPropertyCount() const {
+    return flagsAndCount_ >> PropCountShift;
+  }
+
+  static uint32_t initialFlagsAndCount(uint32_t count) {
+    // No flags are initially set.
+    MOZ_ASSERT(count < PropCountLimit);
+    return count << PropCountShift;
+  }
+
+  void setFlags(uint32_t flags) {
+    MOZ_ASSERT((flags & ~FlagsMask) == 0);
+    flagsAndCount_ = (flagsAndCount_ & ~FlagsMask) | flags;
+  }
+
+  void setIndicesState(NativeIteratorIndices indices) {
+    uint32_t indicesBits = uint32_t(indices) << IndicesShift;
+    flagsAndCount_ = (flagsAndCount_ & ~IndicesMask) | indicesBits;
+  }
+
+  bool indicesAllocated() const {
+    return indicesState() >= NativeIteratorIndices::Disabled;
+  }
+
+  void markInitialized() {
+    MOZ_ASSERT(flags() == 0);
+    setFlags(Flags::Initialized);
+  }
+
+  bool isUnlinked() const { return !prev_ && !next_; }
+
+ public:
+  // Whether this is the shared empty iterator object used for iterating over
+  // null/undefined.
+  bool isEmptyIteratorSingleton() const {
+    // Note: equivalent code is inlined in MacroAssembler::iteratorClose.
+    bool res = flags() & Flags::IsEmptyIteratorSingleton;
+    MOZ_ASSERT_IF(
+        res, flags() == (Flags::Initialized | Flags::IsEmptyIteratorSingleton));
+    MOZ_ASSERT_IF(res, !objectBeingIterated_);
+    MOZ_ASSERT_IF(res, initialPropertyCount() == 0);
+    MOZ_ASSERT_IF(res, shapeCount() == 0);
+    MOZ_ASSERT_IF(res, isUnlinked());
+    return res;
+  }
+  void markEmptyIteratorSingleton() {
+    flagsAndCount_ |= Flags::IsEmptyIteratorSingleton;
+
+    // isEmptyIteratorSingleton() has various debug assertions.
+    MOZ_ASSERT(isEmptyIteratorSingleton());
+  }
+
+  bool isActive() const {
+    MOZ_ASSERT(isInitialized());
+
+    return flags() & Flags::Active;
+  }
+
+  void markActive() {
+    MOZ_ASSERT(isInitialized());
+    MOZ_ASSERT(!isEmptyIteratorSingleton());
+
+    flagsAndCount_ |= Flags::Active;
+  }
+
+  void markInactive() {
+    MOZ_ASSERT(isInitialized());
+    MOZ_ASSERT(!isEmptyIteratorSingleton());
+
+    flagsAndCount_ &= ~Flags::Active;
+  }
+
+  bool isReusable() const {
+    MOZ_ASSERT(isInitialized());
+
+    // Cached NativeIterators are reusable if they're not currently active
+    // and their properties array hasn't been mutated, i.e. if only
+    // |Flags::Initialized| is set.  Using |Flags::NotReusable| to test
+    // would also work, but this formulation is safer against memory
+    // corruption.
+    return flags() == Flags::Initialized;
+  }
+
+  void markHasUnvisitedPropertyDeletion() {
+    MOZ_ASSERT(isInitialized());
+    MOZ_ASSERT(!isEmptyIteratorSingleton());
+
+    flagsAndCount_ |= Flags::HasUnvisitedPropertyDeletion;
+  }
+
+  bool hasValidIndices() const {
+    return indicesState() == NativeIteratorIndices::Valid;
+  }
+
+  bool indicesAvailableOnRequest() const {
+    return indicesState() == NativeIteratorIndices::AvailableOnRequest;
+  }
+
+  // Indicates the native iterator may walk prototype properties.
+  bool mayHavePrototypeProperties() {
+    // If we can use indices for this iterator, we know it doesn't have
+    // prototype properties, and so we use this as a check for prototype
+    // properties.
+    return !hasValidIndices() && !indicesAvailableOnRequest();
+  }
+
+  void disableIndices() {
+    // If we have allocated indices, set the state to Disabled.
+    // This will ensure that we don't use them, but we still
+    // free them correctly.
+    if (indicesState() == NativeIteratorIndices::Valid) {
+      setIndicesState(NativeIteratorIndices::Disabled);
+    }
+  }
+
+  void link(NativeIteratorListNode* other) {
+    MOZ_ASSERT(isInitialized());
+
+    // The shared iterator used for for-in with null/undefined is immutable and
+    // shouldn't be linked.
+    MOZ_ASSERT(!isEmptyIteratorSingleton());
+
+    // A NativeIterator cannot appear in the enumerator list twice.
+    MOZ_ASSERT(isUnlinked());
+
+    setNext(other);
+    setPrev(other->prev());
+
+    other->prev()->setNext(this);
+    other->setPrev(this);
+  }
+  void unlink() {
+    MOZ_ASSERT(isInitialized());
+    MOZ_ASSERT(!isEmptyIteratorSingleton());
+
+    next()->setPrev(prev());
+    prev()->setNext(next());
+    setNext(nullptr);
+    setPrev(nullptr);
+  }
+
+  void trace(JSTracer* trc);
+
+  static constexpr size_t offsetOfObjectBeingIterated() {
+    return offsetof(NativeIterator, objectBeingIterated_);
+  }
+
+  static constexpr size_t offsetOfShapesEnd() {
+    return offsetof(NativeIterator, shapesEnd_);
+  }
+
+  static constexpr size_t offsetOfPropertyCursor() {
+    return offsetof(NativeIterator, propertyCursor_);
+  }
+
+  static constexpr size_t offsetOfPropertiesEnd() {
+    return offsetof(NativeIterator, propertiesEnd_);
+  }
+
+  static constexpr size_t offsetOfFlagsAndCount() {
+    return offsetof(NativeIterator, flagsAndCount_);
+  }
+
+  static constexpr size_t offsetOfFirstShape() {
+    // Shapes are stored directly after |this|.
+    return sizeof(NativeIterator);
+  }
+};
+
+class PropertyIteratorObject : public NativeObject {
+  static const JSClassOps classOps_;
+
+  enum { IteratorSlot, SlotCount };
+
+ public:
+  static const JSClass class_;
+
+  NativeIterator* getNativeIterator() const {
+    return maybePtrFromReservedSlot<NativeIterator>(IteratorSlot);
+  }
+  void initNativeIterator(js::NativeIterator* ni) {
+    initReservedSlot(IteratorSlot, PrivateValue(ni));
+  }
+
+  size_t sizeOfMisc(mozilla::MallocSizeOf mallocSizeOf) const;
+
+  static size_t offsetOfIteratorSlot() {
+    return getFixedSlotOffset(IteratorSlot);
+  }
+
+ private:
+  static void trace(JSTracer* trc, JSObject* obj);
+  static void finalize(JS::GCContext* gcx, JSObject* obj);
+};
+
+class ArrayIteratorObject : public NativeObject {
+ public:
+  static const JSClass class_;
+};
+
+ArrayIteratorObject* NewArrayIteratorTemplate(JSContext* cx);
+ArrayIteratorObject* NewArrayIterator(JSContext* cx);
+
+class StringIteratorObject : public NativeObject {
+ public:
+  static const JSClass class_;
+};
+
+StringIteratorObject* NewStringIteratorTemplate(JSContext* cx);
+StringIteratorObject* NewStringIterator(JSContext* cx);
+
+class RegExpStringIteratorObject : public NativeObject {
+ public:
+  static const JSClass class_;
+};
+
+RegExpStringIteratorObject* NewRegExpStringIteratorTemplate(JSContext* cx);
+RegExpStringIteratorObject* NewRegExpStringIterator(JSContext* cx);
+
+[[nodiscard]] bool EnumerateProperties(JSContext* cx, HandleObject obj,
+                                       MutableHandleIdVector props);
+
+PropertyIteratorObject* LookupInIteratorCache(JSContext* cx, HandleObject obj);
+PropertyIteratorObject* LookupInShapeIteratorCache(JSContext* cx,
+                                                   HandleObject obj);
+
+PropertyIteratorObject* GetIterator(JSContext* cx, HandleObject obj);
+PropertyIteratorObject* GetIteratorWithIndices(JSContext* cx, HandleObject obj);
+
+PropertyIteratorObject* ValueToIterator(JSContext* cx, HandleValue vp);
+
+void CloseIterator(JSObject* obj);
+
+bool IteratorCloseForException(JSContext* cx, HandleObject obj);
+
+void UnwindIteratorForUncatchableException(JSObject* obj);
+
+extern bool SuppressDeletedProperty(JSContext* cx, HandleObject obj, jsid id);
+
+extern bool SuppressDeletedElement(JSContext* cx, HandleObject obj,
+                                   uint32_t index);
+
+#ifdef DEBUG
+extern void AssertDenseElementsNotIterated(NativeObject* obj);
+#else
+inline void AssertDenseElementsNotIterated(NativeObject* obj) {}
+#endif
+
+/*
+ * IteratorMore() returns the next iteration value. If no value is available,
+ * MagicValue(JS_NO_ITER_VALUE) is returned.
+ */
+inline Value IteratorMore(JSObject* iterobj) {
+  NativeIterator* ni =
+      iterobj->as<PropertyIteratorObject>().getNativeIterator();
+  return ni->nextIteratedValueAndAdvance();
+}
+
+/*
+ * Create an object of the form { value: VALUE, done: DONE }.
+ * ES 2017 draft 7.4.7.
+ */
+extern PlainObject* CreateIterResultObject(JSContext* cx, HandleValue value,
+                                           bool done);
+
+/*
+ * Global Iterator constructor.
+ * Iterator Helpers proposal 2.1.3.
+ */
+class IteratorObject : public NativeObject {
+ public:
+  static const JSClass class_;
+  static const JSClass protoClass_;
+};
+
+/*
+ * Wrapper for iterators created via Iterator.from.
+ * Iterator Helpers proposal 2.1.3.3.1.1.
+ */
+class WrapForValidIteratorObject : public NativeObject {
+ public:
+  static const JSClass class_;
+
+  enum { IteratorSlot, NextMethodSlot, SlotCount };
+
+  static_assert(
+      IteratorSlot == WRAP_FOR_VALID_ITERATOR_ITERATOR_SLOT,
+      "IteratedSlot must match self-hosting define for iterator object slot.");
+
+  static_assert(
+      NextMethodSlot == WRAP_FOR_VALID_ITERATOR_NEXT_METHOD_SLOT,
+      "NextMethodSlot must match self-hosting define for next method slot.");
+};
+
+WrapForValidIteratorObject* NewWrapForValidIterator(JSContext* cx);
+
+/*
+ * Generator-esque object returned by Iterator Helper methods.
+ */
+class IteratorHelperObject : public NativeObject {
+ public:
+  static const JSClass class_;
+
+  enum {
+    // The implementation (an instance of one of the generators in
+    // builtin/Iterator.js).
+    // Never null.
+    GeneratorSlot,
+
+    SlotCount,
+  };
+
+  static_assert(GeneratorSlot == ITERATOR_HELPER_GENERATOR_SLOT,
+                "GeneratorSlot must match self-hosting define for generator "
+                "object slot.");
+};
+
+IteratorHelperObject* NewIteratorHelper(JSContext* cx);
+
+bool IterableToArray(JSContext* cx, HandleValue iterable,
+                     MutableHandle<ArrayObject*> array);
+
+// Typed arrays and classes with an enumerate hook can have extra properties not
+// included in the shape's property map or the object's dense elements.
+static inline bool ClassCanHaveExtraEnumeratedProperties(const JSClass* clasp) {
+  return IsTypedArrayClass(clasp) || clasp->getNewEnumerate() ||
+         clasp->getEnumerate();
+}
+
+} /* namespace js */
+
+#endif /* vm_Iteration_h */