Add m-esr52 at 52.6.0

1 files changed, 3798 insertions, 0 deletions

diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
new file mode 100644
index 0000000000..9cbeff6a2e
--- /dev/null
+++ b/js/src/jsarray.cpp
@@ -0,0 +1,3798 @@
+/* -*- 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/. */
+
+#include "jsarray.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/MathAlgorithms.h"
+
+#include <algorithm>
+
+#include "jsapi.h"
+#include "jsatom.h"
+#include "jscntxt.h"
+#include "jsfriendapi.h"
+#include "jsfun.h"
+#include "jsiter.h"
+#include "jsnum.h"
+#include "jsobj.h"
+#include "jstypes.h"
+#include "jsutil.h"
+
+#include "ds/Sort.h"
+#include "gc/Heap.h"
+#include "jit/InlinableNatives.h"
+#include "js/Class.h"
+#include "js/Conversions.h"
+#include "vm/ArgumentsObject.h"
+#include "vm/Interpreter.h"
+#include "vm/SelfHosting.h"
+#include "vm/Shape.h"
+#include "vm/StringBuffer.h"
+#include "vm/TypedArrayCommon.h"
+#include "vm/WrapperObject.h"
+
+#include "jsatominlines.h"
+
+#include "vm/ArgumentsObject-inl.h"
+#include "vm/ArrayObject-inl.h"
+#include "vm/Caches-inl.h"
+#include "vm/Interpreter-inl.h"
+#include "vm/NativeObject-inl.h"
+#include "vm/UnboxedObject-inl.h"
+
+using namespace js;
+using namespace js::gc;
+
+using mozilla::Abs;
+using mozilla::ArrayLength;
+using mozilla::CeilingLog2;
+using mozilla::CheckedInt;
+using mozilla::DebugOnly;
+using mozilla::IsNaN;
+
+using JS::AutoCheckCannotGC;
+using JS::IsArrayAnswer;
+using JS::ToUint32;
+
+bool
+JS::IsArray(JSContext* cx, HandleObject obj, IsArrayAnswer* answer)
+{
+    if (obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>()) {
+        *answer = IsArrayAnswer::Array;
+        return true;
+    }
+
+    if (obj->is<ProxyObject>())
+        return Proxy::isArray(cx, obj, answer);
+
+    *answer = IsArrayAnswer::NotArray;
+    return true;
+}
+
+bool
+JS::IsArray(JSContext* cx, HandleObject obj, bool* isArray)
+{
+    IsArrayAnswer answer;
+    if (!IsArray(cx, obj, &answer))
+        return false;
+
+    if (answer == IsArrayAnswer::RevokedProxy) {
+        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_PROXY_REVOKED);
+        return false;
+    }
+
+    *isArray = answer == IsArrayAnswer::Array;
+    return true;
+}
+
+bool
+js::GetLengthProperty(JSContext* cx, HandleObject obj, uint32_t* lengthp)
+{
+    if (obj->is<ArrayObject>()) {
+        *lengthp = obj->as<ArrayObject>().length();
+        return true;
+    }
+
+    if (obj->is<UnboxedArrayObject>()) {
+        *lengthp = obj->as<UnboxedArrayObject>().length();
+        return true;
+    }
+
+    if (obj->is<ArgumentsObject>()) {
+        ArgumentsObject& argsobj = obj->as<ArgumentsObject>();
+        if (!argsobj.hasOverriddenLength()) {
+            *lengthp = argsobj.initialLength();
+            return true;
+        }
+    }
+
+    RootedValue value(cx);
+    if (!GetProperty(cx, obj, obj, cx->names().length, &value))
+        return false;
+
+    bool overflow;
+    if (!ToLengthClamped(cx, value, lengthp, &overflow)) {
+        if (!overflow)
+            return false;
+        *lengthp = UINT32_MAX;
+    }
+    return true;
+}
+
+/*
+ * Determine if the id represents an array index.
+ *
+ * An id is an array index according to ECMA by (15.4):
+ *
+ * "Array objects give special treatment to a certain class of property names.
+ * A property name P (in the form of a string value) is an array index if and
+ * only if ToString(ToUint32(P)) is equal to P and ToUint32(P) is not equal
+ * to 2^32-1."
+ *
+ * This means the largest allowed index is actually 2^32-2 (4294967294).
+ *
+ * In our implementation, it would be sufficient to check for id.isInt32()
+ * except that by using signed 31-bit integers we miss the top half of the
+ * valid range. This function checks the string representation itself; note
+ * that calling a standard conversion routine might allow strings such as
+ * "08" or "4.0" as array indices, which they are not.
+ *
+ */
+template <typename CharT>
+static bool
+StringIsArrayIndex(const CharT* s, uint32_t length, uint32_t* indexp)
+{
+    const CharT* end = s + length;
+
+    if (length == 0 || length > (sizeof("4294967294") - 1) || !JS7_ISDEC(*s))
+        return false;
+
+    uint32_t c = 0, previous = 0;
+    uint32_t index = JS7_UNDEC(*s++);
+
+    /* Don't allow leading zeros. */
+    if (index == 0 && s != end)
+        return false;
+
+    for (; s < end; s++) {
+        if (!JS7_ISDEC(*s))
+            return false;
+
+        previous = index;
+        c = JS7_UNDEC(*s);
+        index = 10 * index + c;
+    }
+
+    /* Make sure we didn't overflow. */
+    if (previous < (MAX_ARRAY_INDEX / 10) || (previous == (MAX_ARRAY_INDEX / 10) &&
+        c <= (MAX_ARRAY_INDEX % 10))) {
+        MOZ_ASSERT(index <= MAX_ARRAY_INDEX);
+        *indexp = index;
+        return true;
+    }
+
+    return false;
+}
+
+JS_FRIEND_API(bool)
+js::StringIsArrayIndex(JSLinearString* str, uint32_t* indexp)
+{
+    AutoCheckCannotGC nogc;
+    return str->hasLatin1Chars()
+           ? ::StringIsArrayIndex(str->latin1Chars(nogc), str->length(), indexp)
+           : ::StringIsArrayIndex(str->twoByteChars(nogc), str->length(), indexp);
+}
+
+static bool
+ToId(JSContext* cx, double index, MutableHandleId id)
+{
+    if (index == uint32_t(index))
+        return IndexToId(cx, uint32_t(index), id);
+
+    Value tmp = DoubleValue(index);
+    return ValueToId<CanGC>(cx, HandleValue::fromMarkedLocation(&tmp), id);
+}
+
+static bool
+ToId(JSContext* cx, uint32_t index, MutableHandleId id)
+{
+    return IndexToId(cx, index, id);
+}
+
+/*
+ * If the property at the given index exists, get its value into location
+ * pointed by vp and set *hole to false. Otherwise set *hole to true and *vp
+ * to JSVAL_VOID. This function assumes that the location pointed by vp is
+ * properly rooted and can be used as GC-protected storage for temporaries.
+ */
+template <typename IndexType>
+static inline bool
+DoGetElement(JSContext* cx, HandleObject obj, HandleObject receiver,
+             IndexType index, bool* hole, MutableHandleValue vp)
+{
+    RootedId id(cx);
+    if (!ToId(cx, index, &id))
+        return false;
+
+    bool found;
+    if (!HasProperty(cx, obj, id, &found))
+        return false;
+
+    if (found) {
+        if (!GetProperty(cx, obj, receiver, id, vp))
+            return false;
+    } else {
+        vp.setUndefined();
+    }
+    *hole = !found;
+    return true;
+}
+
+template <typename IndexType>
+static void
+AssertGreaterThanZero(IndexType index)
+{
+    MOZ_ASSERT(index >= 0);
+    MOZ_ASSERT(index == floor(index));
+}
+
+template<>
+void
+AssertGreaterThanZero(uint32_t index)
+{
+}
+
+static bool
+GetElement(JSContext* cx, HandleObject obj, HandleObject receiver,
+           uint32_t index, bool* hole, MutableHandleValue vp)
+{
+    AssertGreaterThanZero(index);
+    if (index < GetAnyBoxedOrUnboxedInitializedLength(obj)) {
+        vp.set(GetAnyBoxedOrUnboxedDenseElement(obj, uint32_t(index)));
+        if (!vp.isMagic(JS_ELEMENTS_HOLE)) {
+            *hole = false;
+            return true;
+        }
+    }
+    if (obj->is<ArgumentsObject>()) {
+        if (obj->as<ArgumentsObject>().maybeGetElement(uint32_t(index), vp)) {
+            *hole = false;
+            return true;
+        }
+    }
+
+    return DoGetElement(cx, obj, receiver, index, hole, vp);
+}
+
+template <typename IndexType>
+static inline bool
+GetElement(JSContext* cx, HandleObject obj, IndexType index, bool* hole, MutableHandleValue vp)
+{
+    return GetElement(cx, obj, obj, index, hole, vp);
+}
+
+bool
+ElementAdder::append(JSContext* cx, HandleValue v)
+{
+    MOZ_ASSERT(index_ < length_);
+    if (resObj_) {
+        DenseElementResult result =
+            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, resObj_, index_, v.address(), 1);
+        if (result == DenseElementResult::Failure)
+            return false;
+        if (result == DenseElementResult::Incomplete) {
+            if (!DefineElement(cx, resObj_, index_, v))
+                return false;
+        }
+    } else {
+        vp_[index_] = v;
+    }
+    index_++;
+    return true;
+}
+
+void
+ElementAdder::appendHole()
+{
+    MOZ_ASSERT(getBehavior_ == ElementAdder::CheckHasElemPreserveHoles);
+    MOZ_ASSERT(index_ < length_);
+    if (!resObj_)
+        vp_[index_].setMagic(JS_ELEMENTS_HOLE);
+    index_++;
+}
+
+bool
+js::GetElementsWithAdder(JSContext* cx, HandleObject obj, HandleObject receiver,
+                         uint32_t begin, uint32_t end, ElementAdder* adder)
+{
+    MOZ_ASSERT(begin <= end);
+
+    RootedValue val(cx);
+    for (uint32_t i = begin; i < end; i++) {
+        if (adder->getBehavior() == ElementAdder::CheckHasElemPreserveHoles) {
+            bool hole;
+            if (!GetElement(cx, obj, receiver, i, &hole, &val))
+                return false;
+            if (hole) {
+                adder->appendHole();
+                continue;
+            }
+        } else {
+            MOZ_ASSERT(adder->getBehavior() == ElementAdder::GetElement);
+            if (!GetElement(cx, obj, receiver, i, &val))
+                return false;
+        }
+        if (!adder->append(cx, val))
+            return false;
+    }
+
+    return true;
+}
+
+template <JSValueType Type>
+DenseElementResult
+GetBoxedOrUnboxedDenseElements(JSObject* aobj, uint32_t length, Value* vp)
+{
+    MOZ_ASSERT(!ObjectMayHaveExtraIndexedProperties(aobj));
+
+    if (length > GetBoxedOrUnboxedInitializedLength<Type>(aobj))
+        return DenseElementResult::Incomplete;
+
+    for (size_t i = 0; i < length; i++) {
+        vp[i] = GetBoxedOrUnboxedDenseElement<Type>(aobj, i);
+
+        // No other indexed properties so hole => undefined.
+        if (vp[i].isMagic(JS_ELEMENTS_HOLE))
+            vp[i] = UndefinedValue();
+    }
+
+    return DenseElementResult::Success;
+}
+
+DefineBoxedOrUnboxedFunctor3(GetBoxedOrUnboxedDenseElements,
+                             JSObject*, uint32_t, Value*);
+
+bool
+js::GetElements(JSContext* cx, HandleObject aobj, uint32_t length, Value* vp)
+{
+    if (!ObjectMayHaveExtraIndexedProperties(aobj)) {
+        GetBoxedOrUnboxedDenseElementsFunctor functor(aobj, length, vp);
+        DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, aobj);
+        if (result != DenseElementResult::Incomplete)
+            return result == DenseElementResult::Success;
+    }
+
+    if (aobj->is<ArgumentsObject>()) {
+        ArgumentsObject& argsobj = aobj->as<ArgumentsObject>();
+        if (!argsobj.hasOverriddenLength()) {
+            if (argsobj.maybeGetElements(0, length, vp))
+                return true;
+        }
+    }
+
+    if (js::GetElementsOp op = aobj->getOpsGetElements()) {
+        ElementAdder adder(cx, vp, length, ElementAdder::GetElement);
+        return op(cx, aobj, 0, length, &adder);
+    }
+
+    for (uint32_t i = 0; i < length; i++) {
+        if (!GetElement(cx, aobj, aobj, i, MutableHandleValue::fromMarkedLocation(&vp[i])))
+            return false;
+    }
+
+    return true;
+}
+
+// Set the value of the property at the given index to v. The behavior of this
+// function is currently incoherent and it sometimes defines the property
+// instead. See bug 1163091.
+static bool
+SetArrayElement(JSContext* cx, HandleObject obj, double index, HandleValue v)
+{
+    MOZ_ASSERT(index >= 0);
+
+    if ((obj->is<ArrayObject>() || obj->is<UnboxedArrayObject>()) && !obj->isIndexed() && index <= UINT32_MAX) {
+        DenseElementResult result =
+            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, uint32_t(index), v.address(), 1);
+        if (result != DenseElementResult::Incomplete)
+            return result == DenseElementResult::Success;
+    }
+
+    RootedId id(cx);
+    if (!ToId(cx, index, &id))
+        return false;
+
+    return SetProperty(cx, obj, id, v);
+}
+
+/*
+ * Attempt to delete the element |index| from |obj| as if by
+ * |obj.[[Delete]](index)|.
+ *
+ * If an error occurs while attempting to delete the element (that is, the call
+ * to [[Delete]] threw), return false.
+ *
+ * Otherwise call result.succeed() or result.fail() to indicate whether the
+ * deletion attempt succeeded (that is, whether the call to [[Delete]] returned
+ * true or false).  (Deletes generally fail only when the property is
+ * non-configurable, but proxies may implement different semantics.)
+ */
+static bool
+DeleteArrayElement(JSContext* cx, HandleObject obj, double index, ObjectOpResult& result)
+{
+    MOZ_ASSERT(index >= 0);
+    MOZ_ASSERT(floor(index) == index);
+
+    if (obj->is<ArrayObject>() && !obj->isIndexed() &&
+        !obj->as<NativeObject>().denseElementsAreFrozen())
+    {
+        ArrayObject* aobj = &obj->as<ArrayObject>();
+        if (index <= UINT32_MAX) {
+            uint32_t idx = uint32_t(index);
+            if (idx < aobj->getDenseInitializedLength()) {
+                if (!aobj->maybeCopyElementsForWrite(cx))
+                    return false;
+                if (idx+1 == aobj->getDenseInitializedLength()) {
+                    aobj->setDenseInitializedLength(idx);
+                } else {
+                    aobj->markDenseElementsNotPacked(cx);
+                    aobj->setDenseElement(idx, MagicValue(JS_ELEMENTS_HOLE));
+                }
+                if (!SuppressDeletedElement(cx, obj, idx))
+                    return false;
+            }
+        }
+
+        return result.succeed();
+    }
+
+    RootedId id(cx);
+    if (!ToId(cx, index, &id))
+        return false;
+    return DeleteProperty(cx, obj, id, result);
+}
+
+/* ES6 draft rev 32 (2 Febr 2015) 7.3.7 */
+static bool
+DeletePropertyOrThrow(JSContext* cx, HandleObject obj, double index)
+{
+    ObjectOpResult success;
+    if (!DeleteArrayElement(cx, obj, index, success))
+        return false;
+    if (!success) {
+        RootedId id(cx);
+        RootedValue indexv(cx, NumberValue(index));
+        if (!ValueToId<CanGC>(cx, indexv, &id))
+            return false;
+        return success.reportError(cx, obj, id);
+    }
+    return true;
+}
+
+bool
+js::SetLengthProperty(JSContext* cx, HandleObject obj, double length)
+{
+    RootedValue v(cx, NumberValue(length));
+    return SetProperty(cx, obj, cx->names().length, v);
+}
+
+static bool
+array_length_getter(JSContext* cx, HandleObject obj, HandleId id, MutableHandleValue vp)
+{
+    vp.setNumber(obj->as<ArrayObject>().length());
+    return true;
+}
+
+static bool
+array_length_setter(JSContext* cx, HandleObject obj, HandleId id, MutableHandleValue vp,
+                    ObjectOpResult& result)
+{
+    if (!obj->is<ArrayObject>()) {
+        // This array .length property was found on the prototype
+        // chain. Ideally the setter should not have been called, but since
+        // we're here, do an impression of SetPropertyByDefining.
+        const Class* clasp = obj->getClass();
+        return DefineProperty(cx, obj, cx->names().length, vp,
+                              clasp->getGetProperty(), clasp->getSetProperty(),
+                              JSPROP_ENUMERATE, result);
+    }
+
+    Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+    MOZ_ASSERT(arr->lengthIsWritable(),
+               "setter shouldn't be called if property is non-writable");
+
+    return ArraySetLength(cx, arr, id, JSPROP_PERMANENT, vp, result);
+}
+
+struct ReverseIndexComparator
+{
+    bool operator()(const uint32_t& a, const uint32_t& b, bool* lessOrEqualp) {
+        MOZ_ASSERT(a != b, "how'd we get duplicate indexes?");
+        *lessOrEqualp = b <= a;
+        return true;
+    }
+};
+
+bool
+js::CanonicalizeArrayLengthValue(JSContext* cx, HandleValue v, uint32_t* newLen)
+{
+    double d;
+
+    if (!ToUint32(cx, v, newLen))
+        return false;
+
+    if (!ToNumber(cx, v, &d))
+        return false;
+
+    if (d == *newLen)
+        return true;
+
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
+    return false;
+}
+
+/* ES6 draft rev 34 (2015 Feb 20) 9.4.2.4 ArraySetLength */
+bool
+js::ArraySetLength(JSContext* cx, Handle<ArrayObject*> arr, HandleId id,
+                   unsigned attrs, HandleValue value, ObjectOpResult& result)
+{
+    MOZ_ASSERT(id == NameToId(cx->names().length));
+
+    if (!arr->maybeCopyElementsForWrite(cx))
+        return false;
+
+    // Step 1.
+    uint32_t newLen;
+    if (attrs & JSPROP_IGNORE_VALUE) {
+        // The spec has us calling OrdinaryDefineOwnProperty if
+        // Desc.[[Value]] is absent, but our implementation is so different that
+        // this is impossible. Instead, set newLen to the current length and
+        // proceed to step 9.
+        newLen = arr->length();
+    } else {
+        // Step 2 is irrelevant in our implementation.
+
+        // Steps 3-7.
+        MOZ_ASSERT_IF(attrs & JSPROP_IGNORE_VALUE, value.isUndefined());
+        if (!CanonicalizeArrayLengthValue(cx, value, &newLen))
+            return false;
+
+        // Step 8 is irrelevant in our implementation.
+    }
+
+    // Steps 9-11.
+    bool lengthIsWritable = arr->lengthIsWritable();
+#ifdef DEBUG
+    {
+        RootedShape lengthShape(cx, arr->lookupPure(id));
+        MOZ_ASSERT(lengthShape);
+        MOZ_ASSERT(lengthShape->writable() == lengthIsWritable);
+    }
+#endif
+    uint32_t oldLen = arr->length();
+
+    // Part of steps 1.a, 12.a, and 16: Fail if we're being asked to change
+    // enumerability or configurability, or otherwise break the object
+    // invariants. (ES6 checks these by calling OrdinaryDefineOwnProperty, but
+    // in SM, the array length property is hardly ordinary.)
+    if ((attrs & (JSPROP_PERMANENT | JSPROP_IGNORE_PERMANENT)) == 0 ||
+        (attrs & (JSPROP_ENUMERATE | JSPROP_IGNORE_ENUMERATE)) == JSPROP_ENUMERATE ||
+        (attrs & (JSPROP_GETTER | JSPROP_SETTER)) != 0 ||
+        (!lengthIsWritable && (attrs & (JSPROP_READONLY | JSPROP_IGNORE_READONLY)) == 0))
+    {
+        return result.fail(JSMSG_CANT_REDEFINE_PROP);
+    }
+
+    // Steps 12-13 for arrays with non-writable length.
+    if (!lengthIsWritable) {
+        if (newLen == oldLen)
+            return result.succeed();
+
+        return result.fail(JSMSG_CANT_REDEFINE_ARRAY_LENGTH);
+    }
+
+    // Step 19.
+    bool succeeded = true;
+    do {
+        // The initialized length and capacity of an array only need updating
+        // when non-hole elements are added or removed, which doesn't happen
+        // when array length stays the same or increases.
+        if (newLen >= oldLen)
+            break;
+
+        // Attempt to propagate dense-element optimization tricks, if possible,
+        // and avoid the generic (and accordingly slow) deletion code below.
+        // We can only do this if there are only densely-indexed elements.
+        // Once there's a sparse indexed element, there's no good way to know,
+        // save by enumerating all the properties to find it.  But we *have* to
+        // know in case that sparse indexed element is non-configurable, as
+        // that element must prevent any deletions below it.  Bug 586842 should
+        // fix this inefficiency by moving indexed storage to be entirely
+        // separate from non-indexed storage.
+        // A second reason for this optimization to be invalid is an active
+        // for..in iteration over the array. Keys deleted before being reached
+        // during the iteration must not be visited, and suppressing them here
+        // would be too costly.
+        ObjectGroup* arrGroup = arr->getGroup(cx);
+        if (MOZ_UNLIKELY(!arrGroup))
+            return false;
+        if (!arr->isIndexed() && !MOZ_UNLIKELY(arrGroup->hasAllFlags(OBJECT_FLAG_ITERATED))) {
+            if (!arr->maybeCopyElementsForWrite(cx))
+                return false;
+
+            uint32_t oldCapacity = arr->getDenseCapacity();
+            uint32_t oldInitializedLength = arr->getDenseInitializedLength();
+            MOZ_ASSERT(oldCapacity >= oldInitializedLength);
+            if (oldInitializedLength > newLen)
+                arr->setDenseInitializedLength(newLen);
+            if (oldCapacity > newLen)
+                arr->shrinkElements(cx, newLen);
+
+            // We've done the work of deleting any dense elements needing
+            // deletion, and there are no sparse elements.  Thus we can skip
+            // straight to defining the length.
+            break;
+        }
+
+        // Step 15.
+        //
+        // Attempt to delete all elements above the new length, from greatest
+        // to least.  If any of these deletions fails, we're supposed to define
+        // the length to one greater than the index that couldn't be deleted,
+        // *with the property attributes specified*.  This might convert the
+        // length to be not the value specified, yet non-writable.  (You may be
+        // forgiven for thinking these are interesting semantics.)  Example:
+        //
+        //   var arr =
+        //     Object.defineProperty([0, 1, 2, 3], 1, { writable: false });
+        //   Object.defineProperty(arr, "length",
+        //                         { value: 0, writable: false });
+        //
+        // will convert |arr| to an array of non-writable length two, then
+        // throw a TypeError.
+        //
+        // We implement this behavior, in the relevant lops below, by setting
+        // |succeeded| to false.  Then we exit the loop, define the length
+        // appropriately, and only then throw a TypeError, if necessary.
+        uint32_t gap = oldLen - newLen;
+        const uint32_t RemoveElementsFastLimit = 1 << 24;
+        if (gap < RemoveElementsFastLimit) {
+            // If we're removing a relatively small number of elements, just do
+            // it exactly by the spec.
+            while (newLen < oldLen) {
+                // Step 15a.
+                oldLen--;
+
+                // Steps 15b-d.
+                ObjectOpResult deleteSucceeded;
+                if (!DeleteElement(cx, arr, oldLen, deleteSucceeded))
+                    return false;
+                if (!deleteSucceeded) {
+                    newLen = oldLen + 1;
+                    succeeded = false;
+                    break;
+                }
+            }
+        } else {
+            // If we're removing a large number of elements from an array
+            // that's probably sparse, try a different tack.  Get all the own
+            // property names, sift out the indexes in the deletion range into
+            // a vector, sort the vector greatest to least, then delete the
+            // indexes greatest to least using that vector.  See bug 322135.
+            //
+            // This heuristic's kind of a huge guess -- "large number of
+            // elements" and "probably sparse" are completely unprincipled
+            // predictions.  In the long run, bug 586842 will support the right
+            // fix: store sparse elements in a sorted data structure that
+            // permits fast in-reverse-order traversal and concurrent removals.
+
+            Vector<uint32_t> indexes(cx);
+            {
+                AutoIdVector props(cx);
+                if (!GetPropertyKeys(cx, arr, JSITER_OWNONLY | JSITER_HIDDEN, &props))
+                    return false;
+
+                for (size_t i = 0; i < props.length(); i++) {
+                    if (!CheckForInterrupt(cx))
+                        return false;
+
+                    uint32_t index;
+                    if (!IdIsIndex(props[i], &index))
+                        continue;
+
+                    if (index >= newLen && index < oldLen) {
+                        if (!indexes.append(index))
+                            return false;
+                    }
+                }
+            }
+
+            uint32_t count = indexes.length();
+            {
+                // We should use radix sort to be O(n), but this is uncommon
+                // enough that we'll punt til someone complains.
+                Vector<uint32_t> scratch(cx);
+                if (!scratch.resize(count))
+                    return false;
+                MOZ_ALWAYS_TRUE(MergeSort(indexes.begin(), count, scratch.begin(),
+                                          ReverseIndexComparator()));
+            }
+
+            uint32_t index = UINT32_MAX;
+            for (uint32_t i = 0; i < count; i++) {
+                MOZ_ASSERT(indexes[i] < index, "indexes should never repeat");
+                index = indexes[i];
+
+                // Steps 15b-d.
+                ObjectOpResult deleteSucceeded;
+                if (!DeleteElement(cx, arr, index, deleteSucceeded))
+                    return false;
+                if (!deleteSucceeded) {
+                    newLen = index + 1;
+                    succeeded = false;
+                    break;
+                }
+            }
+        }
+    } while (false);
+
+    // Update array length. Technically we should have been doing this
+    // throughout the loop, in step 19.d.iii.
+    arr->setLength(cx, newLen);
+
+    // Step 20.
+    if (attrs & JSPROP_READONLY) {
+        // Yes, we totally drop a non-stub getter/setter from a defineProperty
+        // API call on the floor here.  Given that getter/setter will go away in
+        // the long run, with accessors replacing them both internally and at the
+        // API level, just run with this.
+        RootedShape lengthShape(cx, arr->lookup(cx, id));
+        if (!NativeObject::changeProperty(cx, arr, lengthShape,
+                                          lengthShape->attributes() | JSPROP_READONLY,
+                                          array_length_getter, array_length_setter))
+        {
+            return false;
+        }
+    }
+
+    // All operations past here until the |!succeeded| code must be infallible,
+    // so that all element fields remain properly synchronized.
+
+    // Trim the initialized length, if needed, to preserve the <= length
+    // invariant.  (Capacity was already reduced during element deletion, if
+    // necessary.)
+    ObjectElements* header = arr->getElementsHeader();
+    header->initializedLength = Min(header->initializedLength, newLen);
+
+    if (attrs & JSPROP_READONLY) {
+        header->setNonwritableArrayLength();
+
+        // When an array's length becomes non-writable, writes to indexes
+        // greater than or equal to the length don't change the array.  We
+        // handle this with a check for non-writable length in most places.
+        // But in JIT code every check counts -- so we piggyback the check on
+        // the already-required range check for |index < capacity| by making
+        // capacity of arrays with non-writable length never exceed the length.
+        if (arr->getDenseCapacity() > newLen) {
+            arr->shrinkElements(cx, newLen);
+            arr->getElementsHeader()->capacity = newLen;
+        }
+    }
+
+    if (!succeeded)
+        return result.fail(JSMSG_CANT_TRUNCATE_ARRAY);
+
+    return result.succeed();
+}
+
+bool
+js::WouldDefinePastNonwritableLength(HandleNativeObject obj, uint32_t index)
+{
+    if (!obj->is<ArrayObject>())
+        return false;
+
+    ArrayObject* arr = &obj->as<ArrayObject>();
+    return !arr->lengthIsWritable() && index >= arr->length();
+}
+
+static bool
+array_addProperty(JSContext* cx, HandleObject obj, HandleId id, HandleValue v)
+{
+    Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+
+    uint32_t index;
+    if (!IdIsIndex(id, &index))
+        return true;
+
+    uint32_t length = arr->length();
+    if (index >= length) {
+        MOZ_ASSERT(arr->lengthIsWritable(),
+                   "how'd this element get added if length is non-writable?");
+        arr->setLength(cx, index + 1);
+    }
+    return true;
+}
+
+static inline bool
+ObjectMayHaveExtraIndexedOwnProperties(JSObject* obj)
+{
+    return (!obj->isNative() && !obj->is<UnboxedArrayObject>()) ||
+           obj->isIndexed() ||
+           obj->is<TypedArrayObject>() ||
+           ClassMayResolveId(*obj->runtimeFromAnyThread()->commonNames,
+                             obj->getClass(), INT_TO_JSID(0), obj);
+}
+
+/*
+ * Whether obj may have indexed properties anywhere besides its dense
+ * elements. This includes other indexed properties in its shape hierarchy, and
+ * indexed properties or elements along its prototype chain.
+ */
+bool
+js::ObjectMayHaveExtraIndexedProperties(JSObject* obj)
+{
+    MOZ_ASSERT_IF(obj->hasDynamicPrototype(), !obj->isNative());
+
+    if (ObjectMayHaveExtraIndexedOwnProperties(obj))
+        return true;
+
+    do {
+        MOZ_ASSERT(obj->hasStaticPrototype(),
+                   "dynamic-prototype objects must be non-native, ergo must "
+                   "have failed ObjectMayHaveExtraIndexedOwnProperties");
+
+        obj = obj->staticPrototype();
+        if (!obj)
+            return false; // no extra indexed properties found
+
+        if (ObjectMayHaveExtraIndexedOwnProperties(obj))
+            return true;
+        if (GetAnyBoxedOrUnboxedInitializedLength(obj) != 0)
+            return true;
+    } while (true);
+}
+
+static bool
+AddLengthProperty(ExclusiveContext* cx, HandleArrayObject obj)
+{
+    /*
+     * Add the 'length' property for a newly created array,
+     * and update the elements to be an empty array owned by the object.
+     * The shared emptyObjectElements singleton cannot be used for slow arrays,
+     * as accesses to 'length' will use the elements header.
+     */
+
+    RootedId lengthId(cx, NameToId(cx->names().length));
+    MOZ_ASSERT(!obj->lookup(cx, lengthId));
+
+    return NativeObject::addProperty(cx, obj, lengthId, array_length_getter, array_length_setter,
+                                     SHAPE_INVALID_SLOT,
+                                     JSPROP_PERMANENT | JSPROP_SHARED | JSPROP_SHADOWABLE,
+                                     0, /* allowDictionary = */ false);
+}
+
+static bool
+IsArrayConstructor(const JSObject* obj)
+{
+    // This must only return true if v is *the* Array constructor for the
+    // current compartment; we rely on the fact that any other Array
+    // constructor would be represented as a wrapper.
+    return obj->is<JSFunction>() &&
+           obj->as<JSFunction>().isNative() &&
+           obj->as<JSFunction>().native() == ArrayConstructor;
+}
+
+static bool
+IsArrayConstructor(const Value& v)
+{
+    return v.isObject() && IsArrayConstructor(&v.toObject());
+}
+
+bool
+js::IsWrappedArrayConstructor(JSContext* cx, const Value& v, bool* result)
+{
+    if (!v.isObject()) {
+        *result = false;
+        return true;
+    }
+    if (v.toObject().is<WrapperObject>()) {
+        JSObject* obj = CheckedUnwrap(&v.toObject());
+        if (!obj) {
+            JS_ReportErrorASCII(cx, "Permission denied to access object");
+            return false;
+        }
+
+        *result = IsArrayConstructor(obj);
+    } else {
+        *result = false;
+    }
+    return true;
+}
+
+static bool
+IsArraySpecies(JSContext* cx, HandleObject origArray)
+{
+    RootedValue ctor(cx);
+    if (!GetPropertyPure(cx, origArray, NameToId(cx->names().constructor), ctor.address()))
+        return false;
+
+    if (!IsArrayConstructor(ctor))
+        return false;
+
+    RootedObject ctorObj(cx, &ctor.toObject());
+    RootedId speciesId(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().species));
+    JSFunction* getter;
+    if (!GetGetterPure(cx, ctorObj, speciesId, &getter))
+        return false;
+
+    if (!getter)
+        return false;
+
+    return IsSelfHostedFunctionWithName(getter, cx->names().ArraySpecies);
+}
+
+static bool
+ArraySpeciesCreate(JSContext* cx, HandleObject origArray, uint32_t length, MutableHandleObject arr)
+{
+    RootedId createId(cx, NameToId(cx->names().ArraySpeciesCreate));
+    RootedFunction create(cx, JS::GetSelfHostedFunction(cx, "ArraySpeciesCreate", createId, 2));
+    if (!create)
+        return false;
+
+    FixedInvokeArgs<2> args(cx);
+
+    args[0].setObject(*origArray);
+    args[1].set(NumberValue(length));
+
+    RootedValue callee(cx, ObjectValue(*create));
+    RootedValue rval(cx);
+    if (!Call(cx, callee, UndefinedHandleValue, args, &rval))
+        return false;
+
+    MOZ_ASSERT(rval.isObject());
+    arr.set(&rval.toObject());
+    return true;
+}
+
+#if JS_HAS_TOSOURCE
+
+static bool
+array_toSource(JSContext* cx, unsigned argc, Value* vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    if (!args.thisv().isObject()) {
+        ReportIncompatible(cx, args);
+        return false;
+    }
+
+    Rooted<JSObject*> obj(cx, &args.thisv().toObject());
+    RootedValue elt(cx);
+
+    AutoCycleDetector detector(cx, obj);
+    if (!detector.init())
+        return false;
+
+    StringBuffer sb(cx);
+
+    if (detector.foundCycle()) {
+        if (!sb.append("[]"))
+            return false;
+        goto make_string;
+    }
+
+    if (!sb.append('['))
+        return false;
+
+    uint32_t length;
+    if (!GetLengthProperty(cx, obj, &length))
+        return false;
+
+    for (uint32_t index = 0; index < length; index++) {
+        bool hole;
+        if (!CheckForInterrupt(cx) ||
+            !GetElement(cx, obj, index, &hole, &elt)) {
+            return false;
+        }
+
+        /* Get element's character string. */
+        JSString* str;
+        if (hole) {
+            str = cx->runtime()->emptyString;
+        } else {
+            str = ValueToSource(cx, elt);
+            if (!str)
+                return false;
+        }
+
+        /* Append element to buffer. */
+        if (!sb.append(str))
+            return false;
+        if (index + 1 != length) {
+            if (!sb.append(", "))
+                return false;
+        } else if (hole) {
+            if (!sb.append(','))
+                return false;
+        }
+    }
+
+    /* Finalize the buffer. */
+    if (!sb.append(']'))
+        return false;
+
+  make_string:
+    JSString* str = sb.finishString();
+    if (!str)
+        return false;
+
+    args.rval().setString(str);
+    return true;
+}
+
+#endif
+
+struct EmptySeparatorOp
+{
+    bool operator()(JSContext*, StringBuffer& sb) { return true; }
+};
+
+template <typename CharT>
+struct CharSeparatorOp
+{
+    const CharT sep;
+    explicit CharSeparatorOp(CharT sep) : sep(sep) {}
+    bool operator()(JSContext*, StringBuffer& sb) { return sb.append(sep); }
+};
+
+struct StringSeparatorOp
+{
+    HandleLinearString sep;
+
+    explicit StringSeparatorOp(HandleLinearString sep) : sep(sep) {}
+
+    bool operator()(JSContext* cx, StringBuffer& sb) {
+        return sb.append(sep);
+    }
+};
+
+template <typename SeparatorOp, JSValueType Type>
+static DenseElementResult
+ArrayJoinDenseKernel(JSContext* cx, SeparatorOp sepOp, HandleObject obj, uint32_t length,
+                     StringBuffer& sb, uint32_t* numProcessed)
+{
+    // This loop handles all elements up to initializedLength. If
+    // length > initLength we rely on the second loop to add the
+    // other elements.
+    MOZ_ASSERT(*numProcessed == 0);
+    uint32_t initLength = Min<uint32_t>(GetBoxedOrUnboxedInitializedLength<Type>(obj), length);
+    while (*numProcessed < initLength) {
+        if (!CheckForInterrupt(cx))
+            return DenseElementResult::Failure;
+
+        Value elem = GetBoxedOrUnboxedDenseElement<Type>(obj, *numProcessed);
+
+        if (elem.isString()) {
+            if (!sb.append(elem.toString()))
+                return DenseElementResult::Failure;
+        } else if (elem.isNumber()) {
+            if (!NumberValueToStringBuffer(cx, elem, sb))
+                return DenseElementResult::Failure;
+        } else if (elem.isBoolean()) {
+            if (!BooleanToStringBuffer(elem.toBoolean(), sb))
+                return DenseElementResult::Failure;
+        } else if (elem.isObject() || elem.isSymbol()) {
+            /*
+             * Object stringifying could modify the initialized length or make
+             * the array sparse. Delegate it to a separate loop to keep this
+             * one tight.
+             *
+             * Symbol stringifying is a TypeError, so into the slow path
+             * with those as well.
+             */
+            break;
+        } else {
+            MOZ_ASSERT(elem.isMagic(JS_ELEMENTS_HOLE) || elem.isNullOrUndefined());
+        }
+
+        if (++(*numProcessed) != length && !sepOp(cx, sb))
+            return DenseElementResult::Failure;
+    }
+
+    return DenseElementResult::Incomplete;
+}
+
+template <typename SeparatorOp>
+struct ArrayJoinDenseKernelFunctor {
+    JSContext* cx;
+    SeparatorOp sepOp;
+    HandleObject obj;
+    uint32_t length;
+    StringBuffer& sb;
+    uint32_t* numProcessed;
+
+    ArrayJoinDenseKernelFunctor(JSContext* cx, SeparatorOp sepOp, HandleObject obj,
+                                uint32_t length, StringBuffer& sb, uint32_t* numProcessed)
+      : cx(cx), sepOp(sepOp), obj(obj), length(length), sb(sb), numProcessed(numProcessed)
+    {}
+
+    template <JSValueType Type>
+    DenseElementResult operator()() {
+        return ArrayJoinDenseKernel<SeparatorOp, Type>(cx, sepOp, obj, length, sb, numProcessed);
+    }
+};
+
+template <typename SeparatorOp>
+static bool
+ArrayJoinKernel(JSContext* cx, SeparatorOp sepOp, HandleObject obj, uint32_t length,
+               StringBuffer& sb)
+{
+    uint32_t i = 0;
+
+    if (!ObjectMayHaveExtraIndexedProperties(obj)) {
+        ArrayJoinDenseKernelFunctor<SeparatorOp> functor(cx, sepOp, obj, length, sb, &i);
+        DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, obj);
+        if (result == DenseElementResult::Failure)
+            return false;
+    }
+
+    if (i != length) {
+        RootedValue v(cx);
+        while (i < length) {
+            if (!CheckForInterrupt(cx))
+                return false;
+
+            bool hole;
+            if (!GetElement(cx, obj, i, &hole, &v))
+                return false;
+            if (!hole && !v.isNullOrUndefined()) {
+                if (!ValueToStringBuffer(cx, v, sb))
+                    return false;
+            }
+
+            if (++i != length && !sepOp(cx, sb))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+/* ES5 15.4.4.5 */
+bool
+js::array_join(JSContext* cx, unsigned argc, Value* vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.join");
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    // Step 1
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    AutoCycleDetector detector(cx, obj);
+    if (!detector.init())
+        return false;
+
+    if (detector.foundCycle()) {
+        args.rval().setString(cx->names().empty);
+        return true;
+    }
+
+    // Steps 2 and 3
+    uint32_t length;
+    if (!GetLengthProperty(cx, obj, &length))
+        return false;
+
+    // Steps 4 and 5
+    RootedLinearString sepstr(cx);
+    if (args.hasDefined(0)) {
+        JSString *s = ToString<CanGC>(cx, args[0]);
+        if (!s)
+            return false;
+        sepstr = s->ensureLinear(cx);
+        if (!sepstr)
+            return false;
+    } else {
+        sepstr = cx->names().comma;
+    }
+
+    // Step 6 is implicit in the loops below.
+
+    // An optimized version of a special case of steps 7-11: when length==1 and
+    // the 0th element is a string, ToString() of that element is a no-op and
+    // so it can be immediately returned as the result.
+    if (length == 1 && GetAnyBoxedOrUnboxedInitializedLength(obj) == 1) {
+        Value elem0 = GetAnyBoxedOrUnboxedDenseElement(obj, 0);
+        if (elem0.isString()) {
+            args.rval().set(elem0);
+            return true;
+        }
+    }
+
+    StringBuffer sb(cx);
+    if (sepstr->hasTwoByteChars() && !sb.ensureTwoByteChars())
+        return false;
+
+    // The separator will be added |length - 1| times, reserve space for that
+    // so that we don't have to unnecessarily grow the buffer.
+    size_t seplen = sepstr->length();
+    CheckedInt<uint32_t> res = CheckedInt<uint32_t>(seplen) * (length - 1);
+    if (length > 0 && !res.isValid()) {
+        ReportAllocationOverflow(cx);
+        return false;
+    }
+
+    if (length > 0 && !sb.reserve(res.value()))
+        return false;
+
+    // Various optimized versions of steps 7-10.
+    if (seplen == 0) {
+        EmptySeparatorOp op;
+        if (!ArrayJoinKernel(cx, op, obj, length, sb))
+            return false;
+    } else if (seplen == 1) {
+        char16_t c = sepstr->latin1OrTwoByteChar(0);
+        if (c <= JSString::MAX_LATIN1_CHAR) {
+            CharSeparatorOp<Latin1Char> op(c);
+            if (!ArrayJoinKernel(cx, op, obj, length, sb))
+                return false;
+        } else {
+            CharSeparatorOp<char16_t> op(c);
+            if (!ArrayJoinKernel(cx, op, obj, length, sb))
+                return false;
+        }
+    } else {
+        StringSeparatorOp op(sepstr);
+        if (!ArrayJoinKernel(cx, op, obj, length, sb))
+            return false;
+    }
+
+    // Step 11
+    JSString *str = sb.finishString();
+    if (!str)
+        return false;
+
+    args.rval().setString(str);
+    return true;
+}
+
+// ES2017 draft rev f8a9be8ea4bd97237d176907a1e3080dce20c68f
+// 22.1.3.27 Array.prototype.toLocaleString ([ reserved1 [ , reserved2 ] ])
+// ES2017 Intl draft rev 78bbe7d1095f5ff3760ac4017ed366026e4cb276
+// 13.4.1 Array.prototype.toLocaleString ([ locales [ , options ]])
+static bool
+array_toLocaleString(JSContext* cx, unsigned argc, Value* vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    // Step 1
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    // Avoid calling into self-hosted code if the array is empty.
+    if (obj->is<ArrayObject>() && obj->as<ArrayObject>().length() == 0) {
+        args.rval().setString(cx->names().empty);
+        return true;
+    }
+    if (obj->is<UnboxedArrayObject>() && obj->as<UnboxedArrayObject>().length() == 0) {
+        args.rval().setString(cx->names().empty);
+        return true;
+    }
+
+    AutoCycleDetector detector(cx, obj);
+    if (!detector.init())
+        return false;
+
+    if (detector.foundCycle()) {
+        args.rval().setString(cx->names().empty);
+        return true;
+    }
+
+    FixedInvokeArgs<2> args2(cx);
+
+    args2[0].set(args.get(0));
+    args2[1].set(args.get(1));
+
+    // Steps 2-10.
+    RootedValue thisv(cx, ObjectValue(*obj));
+    return CallSelfHostedFunction(cx, cx->names().ArrayToLocaleString, thisv, args2, args.rval());
+}
+
+/* vector must point to rooted memory. */
+static bool
+InitArrayElements(JSContext* cx, HandleObject obj, uint32_t start,
+                  uint32_t count, const Value* vector,
+                  ShouldUpdateTypes updateTypes = ShouldUpdateTypes::Update)
+{
+    MOZ_ASSERT(count <= MAX_ARRAY_INDEX);
+
+    if (count == 0)
+        return true;
+
+    ObjectGroup* group = obj->getGroup(cx);
+    if (!group)
+        return false;
+
+    if (!ObjectMayHaveExtraIndexedProperties(obj)) {
+        DenseElementResult result =
+            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, start, vector, count, updateTypes);
+        if (result != DenseElementResult::Incomplete)
+            return result == DenseElementResult::Success;
+    }
+
+    const Value* end = vector + count;
+    while (vector < end && start <= MAX_ARRAY_INDEX) {
+        if (!CheckForInterrupt(cx) ||
+            !SetArrayElement(cx, obj, start++, HandleValue::fromMarkedLocation(vector++))) {
+            return false;
+        }
+    }
+
+    if (vector == end)
+        return true;
+
+    MOZ_ASSERT(start == MAX_ARRAY_INDEX + 1);
+    RootedValue value(cx);
+    RootedId id(cx);
+    RootedValue indexv(cx);
+    double index = MAX_ARRAY_INDEX + 1;
+    do {
+        value = *vector++;
+        indexv = DoubleValue(index);
+        if (!ValueToId<CanGC>(cx, indexv, &id))
+            return false;
+        if (!SetProperty(cx, obj, id, value))
+            return false;
+        index += 1;
+    } while (vector != end);
+
+    return true;
+}
+
+template <JSValueType Type>
+DenseElementResult
+ArrayReverseDenseKernel(JSContext* cx, HandleObject obj, uint32_t length)
+{
+    /* An empty array or an array with no elements is already reversed. */
+    if (length == 0 || GetBoxedOrUnboxedInitializedLength<Type>(obj) == 0)
+        return DenseElementResult::Success;
+
+    if (Type == JSVAL_TYPE_MAGIC) {
+        if (obj->as<NativeObject>().denseElementsAreFrozen())
+            return DenseElementResult::Incomplete;
+
+        /*
+         * It's actually surprisingly complicated to reverse an array due to the
+         * orthogonality of array length and array capacity while handling
+         * leading and trailing holes correctly.  Reversing seems less likely to
+         * be a common operation than other array mass-mutation methods, so for
+         * now just take a probably-small memory hit (in the absence of too many
+         * holes in the array at its start) and ensure that the capacity is
+         * sufficient to hold all the elements in the array if it were full.
+         */
+        DenseElementResult result = obj->as<NativeObject>().ensureDenseElements(cx, length, 0);
+        if (result != DenseElementResult::Success)
+            return result;
+
+        /* Fill out the array's initialized length to its proper length. */
+        obj->as<NativeObject>().ensureDenseInitializedLength(cx, length, 0);
+    } else {
+        // Unboxed arrays can only be reversed here if their initialized length
+        // matches their actual length. Otherwise the reversal will place holes
+        // at the beginning of the array, which we don't support.
+        if (length != obj->as<UnboxedArrayObject>().initializedLength())
+            return DenseElementResult::Incomplete;
+    }
+
+    RootedValue origlo(cx), orighi(cx);
+
+    uint32_t lo = 0, hi = length - 1;
+    for (; lo < hi; lo++, hi--) {
+        origlo = GetBoxedOrUnboxedDenseElement<Type>(obj, lo);
+        orighi = GetBoxedOrUnboxedDenseElement<Type>(obj, hi);
+        SetBoxedOrUnboxedDenseElementNoTypeChange<Type>(obj, lo, orighi);
+        if (orighi.isMagic(JS_ELEMENTS_HOLE) &&
+            !SuppressDeletedProperty(cx, obj, INT_TO_JSID(lo)))
+        {
+            return DenseElementResult::Failure;
+        }
+        SetBoxedOrUnboxedDenseElementNoTypeChange<Type>(obj, hi, origlo);
+        if (origlo.isMagic(JS_ELEMENTS_HOLE) &&
+            !SuppressDeletedProperty(cx, obj, INT_TO_JSID(hi)))
+        {
+            return DenseElementResult::Failure;
+        }
+    }
+
+    return DenseElementResult::Success;
+}
+
+DefineBoxedOrUnboxedFunctor3(ArrayReverseDenseKernel,
+                             JSContext*, HandleObject, uint32_t);
+
+bool
+js::array_reverse(JSContext* cx, unsigned argc, Value* vp)
+{
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.reverse");
+    CallArgs args = CallArgsFromVp(argc, vp);
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    uint32_t len;
+    if (!GetLengthProperty(cx, obj, &len))
+        return false;
+
+    if (!ObjectMayHaveExtraIndexedProperties(obj)) {
+        ArrayReverseDenseKernelFunctor functor(cx, obj, len);
+        DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, obj);
+        if (result != DenseElementResult::Incomplete) {
+            /*
+             * Per ECMA-262, don't update the length of the array, even if the new
+             * array has trailing holes (and thus the original array began with
+             * holes).
+             */
+            args.rval().setObject(*obj);
+            return result == DenseElementResult::Success;
+        }
+    }
+
+    RootedValue lowval(cx), hival(cx);
+    for (uint32_t i = 0, half = len / 2; i < half; i++) {
+        bool hole, hole2;
+        if (!CheckForInterrupt(cx) ||
+            !GetElement(cx, obj, i, &hole, &lowval) ||
+            !GetElement(cx, obj, len - i - 1, &hole2, &hival))
+        {
+            return false;
+        }
+
+        if (!hole && !hole2) {
+            if (!SetArrayElement(cx, obj, i, hival))
+                return false;
+            if (!SetArrayElement(cx, obj, len - i - 1, lowval))
+                return false;
+        } else if (hole && !hole2) {
+            if (!SetArrayElement(cx, obj, i, hival))
+                return false;
+            if (!DeletePropertyOrThrow(cx, obj, len - i - 1))
+                return false;
+        } else if (!hole && hole2) {
+            if (!DeletePropertyOrThrow(cx, obj, i))
+                return false;
+            if (!SetArrayElement(cx, obj, len - i - 1, lowval))
+                return false;
+        } else {
+            // No action required.
+        }
+    }
+    args.rval().setObject(*obj);
+    return true;
+}
+
+static inline bool
+CompareStringValues(JSContext* cx, const Value& a, const Value& b, bool* lessOrEqualp)
+{
+    if (!CheckForInterrupt(cx))
+        return false;
+
+    JSString* astr = a.toString();
+    JSString* bstr = b.toString();
+    int32_t result;
+    if (!CompareStrings(cx, astr, bstr, &result))
+        return false;
+
+    *lessOrEqualp = (result <= 0);
+    return true;
+}
+
+static const uint64_t powersOf10[] = {
+    1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, 1000000000000ULL
+};
+
+static inline unsigned
+NumDigitsBase10(uint32_t n)
+{
+    /*
+     * This is just floor_log10(n) + 1
+     * Algorithm taken from
+     * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
+     */
+    uint32_t log2 = CeilingLog2(n);
+    uint32_t t = log2 * 1233 >> 12;
+    return t - (n < powersOf10[t]) + 1;
+}
+
+static inline bool
+CompareLexicographicInt32(const Value& a, const Value& b, bool* lessOrEqualp)
+{
+    int32_t aint = a.toInt32();
+    int32_t bint = b.toInt32();
+
+    /*
+     * If both numbers are equal ... trivial
+     * If only one of both is negative --> arithmetic comparison as char code
+     * of '-' is always less than any other digit
+     * If both numbers are negative convert them to positive and continue
+     * handling ...
+     */
+    if (aint == bint) {
+        *lessOrEqualp = true;
+    } else if ((aint < 0) && (bint >= 0)) {
+        *lessOrEqualp = true;
+    } else if ((aint >= 0) && (bint < 0)) {
+        *lessOrEqualp = false;
+    } else {
+        uint32_t auint = Abs(aint);
+        uint32_t buint = Abs(bint);
+
+        /*
+         *  ... get number of digits of both integers.
+         * If they have the same number of digits --> arithmetic comparison.
+         * If digits_a > digits_b: a < b*10e(digits_a - digits_b).
+         * If digits_b > digits_a: a*10e(digits_b - digits_a) <= b.
+         */
+        unsigned digitsa = NumDigitsBase10(auint);
+        unsigned digitsb = NumDigitsBase10(buint);
+        if (digitsa == digitsb) {
+            *lessOrEqualp = (auint <= buint);
+        } else if (digitsa > digitsb) {
+            MOZ_ASSERT((digitsa - digitsb) < ArrayLength(powersOf10));
+            *lessOrEqualp = (uint64_t(auint) < uint64_t(buint) * powersOf10[digitsa - digitsb]);
+        } else { /* if (digitsb > digitsa) */
+            MOZ_ASSERT((digitsb - digitsa) < ArrayLength(powersOf10));
+            *lessOrEqualp = (uint64_t(auint) * powersOf10[digitsb - digitsa] <= uint64_t(buint));
+        }
+    }
+
+    return true;
+}
+
+template <typename Char1, typename Char2>
+static inline bool
+CompareSubStringValues(JSContext* cx, const Char1* s1, size_t len1, const Char2* s2, size_t len2,
+                       bool* lessOrEqualp)
+{
+    if (!CheckForInterrupt(cx))
+        return false;
+
+    if (!s1 || !s2)
+        return false;
+
+    int32_t result = CompareChars(s1, len1, s2, len2);
+    *lessOrEqualp = (result <= 0);
+    return true;
+}
+
+namespace {
+
+struct SortComparatorStrings
+{
+    JSContext*  const cx;
+
+    explicit SortComparatorStrings(JSContext* cx)
+      : cx(cx) {}
+
+    bool operator()(const Value& a, const Value& b, bool* lessOrEqualp) {
+        return CompareStringValues(cx, a, b, lessOrEqualp);
+    }
+};
+
+struct SortComparatorLexicographicInt32
+{
+    bool operator()(const Value& a, const Value& b, bool* lessOrEqualp) {
+        return CompareLexicographicInt32(a, b, lessOrEqualp);
+    }
+};
+
+struct StringifiedElement
+{
+    size_t charsBegin;
+    size_t charsEnd;
+    size_t elementIndex;
+};
+
+struct SortComparatorStringifiedElements
+{
+    JSContext*          const cx;
+    const StringBuffer& sb;
+
+    SortComparatorStringifiedElements(JSContext* cx, const StringBuffer& sb)
+      : cx(cx), sb(sb) {}
+
+    bool operator()(const StringifiedElement& a, const StringifiedElement& b, bool* lessOrEqualp) {
+        size_t lenA = a.charsEnd - a.charsBegin;
+        size_t lenB = b.charsEnd - b.charsBegin;
+
+        if (sb.isUnderlyingBufferLatin1()) {
+            return CompareSubStringValues(cx, sb.rawLatin1Begin() + a.charsBegin, lenA,
+                                          sb.rawLatin1Begin() + b.charsBegin, lenB,
+                                          lessOrEqualp);
+        }
+
+        return CompareSubStringValues(cx, sb.rawTwoByteBegin() + a.charsBegin, lenA,
+                                      sb.rawTwoByteBegin() + b.charsBegin, lenB,
+                                      lessOrEqualp);
+    }
+};
+
+struct NumericElement
+{
+    double dv;
+    size_t elementIndex;
+};
+
+static bool
+ComparatorNumericLeftMinusRight(const NumericElement& a, const NumericElement& b,
+                                bool* lessOrEqualp)
+{
+    *lessOrEqualp = (a.dv <= b.dv);
+    return true;
+}
+
+static bool
+ComparatorNumericRightMinusLeft(const NumericElement& a, const NumericElement& b,
+                                bool* lessOrEqualp)
+{
+    *lessOrEqualp = (b.dv <= a.dv);
+    return true;
+}
+
+typedef bool (*ComparatorNumeric)(const NumericElement& a, const NumericElement& b,
+                                  bool* lessOrEqualp);
+
+static const ComparatorNumeric SortComparatorNumerics[] = {
+    nullptr,
+    nullptr,
+    ComparatorNumericLeftMinusRight,
+    ComparatorNumericRightMinusLeft
+};
+
+static bool
+ComparatorInt32LeftMinusRight(const Value& a, const Value& b, bool* lessOrEqualp)
+{
+    *lessOrEqualp = (a.toInt32() <= b.toInt32());
+    return true;
+}
+
+static bool
+ComparatorInt32RightMinusLeft(const Value& a, const Value& b, bool* lessOrEqualp)
+{
+    *lessOrEqualp = (b.toInt32() <= a.toInt32());
+    return true;
+}
+
+typedef bool (*ComparatorInt32)(const Value& a, const Value& b, bool* lessOrEqualp);
+
+static const ComparatorInt32 SortComparatorInt32s[] = {
+    nullptr,
+    nullptr,
+    ComparatorInt32LeftMinusRight,
+    ComparatorInt32RightMinusLeft
+};
+
+// Note: Values for this enum must match up with SortComparatorNumerics
+// and SortComparatorInt32s.
+enum ComparatorMatchResult {
+    Match_Failure = 0,
+    Match_None,
+    Match_LeftMinusRight,
+    Match_RightMinusLeft
+};
+
+} // namespace
+
+
+/*
+ * Specialize behavior for comparator functions with particular common bytecode
+ * patterns: namely, |return x - y| and |return y - x|.
+ */
+static ComparatorMatchResult
+MatchNumericComparator(JSContext* cx, const Value& v)
+{
+    if (!v.isObject())
+        return Match_None;
+
+    JSObject& obj = v.toObject();
+    if (!obj.is<JSFunction>())
+        return Match_None;
+
+    JSFunction* fun = &obj.as<JSFunction>();
+    if (!fun->isInterpreted() || fun->isClassConstructor())
+        return Match_None;
+
+    JSScript* script = fun->getOrCreateScript(cx);
+    if (!script)
+        return Match_Failure;
+
+    jsbytecode* pc = script->code();
+
+    uint16_t arg0, arg1;
+    if (JSOp(*pc) != JSOP_GETARG)
+        return Match_None;
+    arg0 = GET_ARGNO(pc);
+    pc += JSOP_GETARG_LENGTH;
+
+    if (JSOp(*pc) != JSOP_GETARG)
+        return Match_None;
+    arg1 = GET_ARGNO(pc);
+    pc += JSOP_GETARG_LENGTH;
+
+    if (JSOp(*pc) != JSOP_SUB)
+        return Match_None;
+    pc += JSOP_SUB_LENGTH;
+
+    if (JSOp(*pc) != JSOP_RETURN)
+        return Match_None;
+
+    if (arg0 == 0 && arg1 == 1)
+        return Match_LeftMinusRight;
+
+    if (arg0 == 1 && arg1 == 0)
+        return Match_RightMinusLeft;
+
+    return Match_None;
+}
+
+template <typename K, typename C>
+static inline bool
+MergeSortByKey(K keys, size_t len, K scratch, C comparator, MutableHandle<GCVector<Value>> vec)
+{
+    MOZ_ASSERT(vec.length() >= len);
+
+    /* Sort keys. */
+    if (!MergeSort(keys, len, scratch, comparator))
+        return false;
+
+    /*
+     * Reorder vec by keys in-place, going element by element.  When an out-of-
+     * place element is encountered, move that element to its proper position,
+     * displacing whatever element was at *that* point to its proper position,
+     * and so on until an element must be moved to the current position.
+     *
+     * At each outer iteration all elements up to |i| are sorted.  If
+     * necessary each inner iteration moves some number of unsorted elements
+     * (including |i|) directly to sorted position.  Thus on completion |*vec|
+     * is sorted, and out-of-position elements have moved once.  Complexity is
+     * Θ(len) + O(len) == O(2*len), with each element visited at most twice.
+     */
+    for (size_t i = 0; i < len; i++) {
+        size_t j = keys[i].elementIndex;
+        if (i == j)
+            continue; // fixed point
+
+        MOZ_ASSERT(j > i, "Everything less than |i| should be in the right place!");
+        Value tv = vec[j];
+        do {
+            size_t k = keys[j].elementIndex;
+            keys[j].elementIndex = j;
+            vec[j].set(vec[k]);
+            j = k;
+        } while (j != i);
+
+        // We could assert the loop invariant that |i == keys[i].elementIndex|
+        // here if we synced |keys[i].elementIndex|.  But doing so would render
+        // the assertion vacuous, so don't bother, even in debug builds.
+        vec[i].set(tv);
+    }
+
+    return true;
+}
+
+/*
+ * Sort Values as strings.
+ *
+ * To minimize #conversions, SortLexicographically() first converts all Values
+ * to strings at once, then sorts the elements by these cached strings.
+ */
+static bool
+SortLexicographically(JSContext* cx, MutableHandle<GCVector<Value>> vec, size_t len)
+{
+    MOZ_ASSERT(vec.length() >= len);
+
+    StringBuffer sb(cx);
+    Vector<StringifiedElement, 0, TempAllocPolicy> strElements(cx);
+
+    /* MergeSort uses the upper half as scratch space. */
+    if (!strElements.resize(2 * len))
+        return false;
+
+    /* Convert Values to strings. */
+    size_t cursor = 0;
+    for (size_t i = 0; i < len; i++) {
+        if (!CheckForInterrupt(cx))
+            return false;
+
+        if (!ValueToStringBuffer(cx, vec[i], sb))
+            return false;
+
+        strElements[i] = { cursor, sb.length(), i };
+        cursor = sb.length();
+    }
+
+    /* Sort Values in vec alphabetically. */
+    return MergeSortByKey(strElements.begin(), len, strElements.begin() + len,
+                          SortComparatorStringifiedElements(cx, sb), vec);
+}
+
+/*
+ * Sort Values as numbers.
+ *
+ * To minimize #conversions, SortNumerically first converts all Values to
+ * numerics at once, then sorts the elements by these cached numerics.
+ */
+static bool
+SortNumerically(JSContext* cx, MutableHandle<GCVector<Value>> vec, size_t len,
+                ComparatorMatchResult comp)
+{
+    MOZ_ASSERT(vec.length() >= len);
+
+    Vector<NumericElement, 0, TempAllocPolicy> numElements(cx);
+
+    /* MergeSort uses the upper half as scratch space. */
+    if (!numElements.resize(2 * len))
+        return false;
+
+    /* Convert Values to numerics. */
+    for (size_t i = 0; i < len; i++) {
+        if (!CheckForInterrupt(cx))
+            return false;
+
+        double dv;
+        if (!ToNumber(cx, vec[i], &dv))
+            return false;
+
+        numElements[i] = { dv, i };
+    }
+
+    /* Sort Values in vec numerically. */
+    return MergeSortByKey(numElements.begin(), len, numElements.begin() + len,
+                          SortComparatorNumerics[comp], vec);
+}
+
+bool
+js::array_sort(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    RootedValue fval(cx);
+
+    if (args.hasDefined(0)) {
+        if (args[0].isPrimitive()) {
+            JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_SORT_ARG);
+            return false;
+        }
+        fval = args[0];     /* non-default compare function */
+    } else {
+        fval.setNull();
+    }
+
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    ComparatorMatchResult comp = MatchNumericComparator(cx, fval);
+    if (comp == Match_Failure)
+        return false;
+
+    if (!fval.isNull() && comp == Match_None) {
+        /*
+         * Non-optimized user supplied comparators perform much better when
+         * called from within a self-hosted sorting function.
+         */
+        RootedAtom selfHostedSortAtom(cx, Atomize(cx, "ArraySort", 9));
+        RootedPropertyName selfHostedSortName(cx, selfHostedSortAtom->asPropertyName());
+        RootedValue selfHostedSortValue(cx);
+
+        if (!GlobalObject::getIntrinsicValue(cx, cx->global(), selfHostedSortName,
+            &selfHostedSortValue)) {
+            return false;
+        }
+
+        MOZ_ASSERT(selfHostedSortValue.isObject());
+        MOZ_ASSERT(selfHostedSortValue.toObject().is<JSFunction>());
+
+        return Call(cx, selfHostedSortValue, args.thisv(), fval, args.rval());
+    }
+
+    uint32_t len;
+    if (!GetLengthProperty(cx, obj, &len))
+        return false;
+    if (len < 2) {
+        /* [] and [a] remain unchanged when sorted. */
+        args.rval().setObject(*obj);
+        return true;
+    }
+
+    /*
+     * We need a temporary array of 2 * len Value to hold the array elements
+     * and the scratch space for merge sort. Check that its size does not
+     * overflow size_t, which would allow for indexing beyond the end of the
+     * malloc'd vector.
+     */
+#if JS_BITS_PER_WORD == 32
+    if (size_t(len) > size_t(-1) / (2 * sizeof(Value))) {
+        ReportAllocationOverflow(cx);
+        return false;
+    }
+#endif
+
+    /*
+     * Initialize vec as a root. We will clear elements of vec one by
+     * one while increasing the rooted amount of vec when we know that the
+     * property at the corresponding index exists and its value must be rooted.
+     *
+     * In this way when sorting a huge mostly sparse array we will not
+     * access the tail of vec corresponding to properties that do not
+     * exist, allowing OS to avoiding committing RAM. See bug 330812.
+     */
+    size_t n, undefs;
+    {
+        Rooted<GCVector<Value>> vec(cx, GCVector<Value>(cx));
+        if (!vec.reserve(2 * size_t(len)))
+            return false;
+
+        /*
+         * By ECMA 262, 15.4.4.11, a property that does not exist (which we
+         * call a "hole") is always greater than an existing property with
+         * value undefined and that is always greater than any other property.
+         * Thus to sort holes and undefs we simply count them, sort the rest
+         * of elements, append undefs after them and then make holes after
+         * undefs.
+         */
+        undefs = 0;
+        bool allStrings = true;
+        bool allInts = true;
+        bool extraIndexed = ObjectMayHaveExtraIndexedProperties(obj);
+        RootedValue v(cx);
+        for (uint32_t i = 0; i < len; i++) {
+            if (!CheckForInterrupt(cx))
+                return false;
+
+            /* Clear vec[newlen] before including it in the rooted set. */
+            bool hole;
+            if (!GetElement(cx, obj, i, &hole, &v))
+                return false;
+            if (hole)
+                continue;
+            if (v.isUndefined()) {
+                ++undefs;
+                continue;
+            }
+            vec.infallibleAppend(v);
+            allStrings = allStrings && v.isString();
+            allInts = allInts && v.isInt32();
+        }
+
+
+        /*
+         * If the array only contains holes, we're done.  But if it contains
+         * undefs, those must be sorted to the front of the array.
+         */
+        n = vec.length();
+        if (n == 0 && undefs == 0) {
+            args.rval().setObject(*obj);
+            return true;
+        }
+
+        /* Here len == n + undefs + number_of_holes. */
+        if (fval.isNull()) {
+            /*
+             * Sort using the default comparator converting all elements to
+             * strings.
+             */
+            if (allStrings) {
+                JS_ALWAYS_TRUE(vec.resize(n * 2));
+                if (!MergeSort(vec.begin(), n, vec.begin() + n, SortComparatorStrings(cx)))
+                    return false;
+            } else if (allInts) {
+                JS_ALWAYS_TRUE(vec.resize(n * 2));
+                if (!MergeSort(vec.begin(), n, vec.begin() + n,
+                               SortComparatorLexicographicInt32())) {
+                    return false;
+                }
+            } else {
+                if (!SortLexicographically(cx, &vec, n))
+                    return false;
+            }
+        } else {
+            if (allInts) {
+                JS_ALWAYS_TRUE(vec.resize(n * 2));
+                if (!MergeSort(vec.begin(), n, vec.begin() + n, SortComparatorInt32s[comp]))
+                    return false;
+            } else {
+                if (!SortNumerically(cx, &vec, n, comp))
+                    return false;
+            }
+        }
+
+        ShouldUpdateTypes updateTypes = !extraIndexed && (allStrings || allInts)
+                                        ? ShouldUpdateTypes::DontUpdate
+                                        : ShouldUpdateTypes::Update;
+        if (!InitArrayElements(cx, obj, 0, uint32_t(n), vec.begin(), updateTypes))
+            return false;
+    }
+
+    /* Set undefs that sorted after the rest of elements. */
+    while (undefs != 0) {
+        --undefs;
+        if (!CheckForInterrupt(cx) || !SetArrayElement(cx, obj, n++, UndefinedHandleValue))
+            return false;
+    }
+
+    /* Re-create any holes that sorted to the end of the array. */
+    while (len > n) {
+        if (!CheckForInterrupt(cx) || !DeletePropertyOrThrow(cx, obj, --len))
+            return false;
+    }
+    args.rval().setObject(*obj);
+    return true;
+}
+
+bool
+js::NewbornArrayPush(JSContext* cx, HandleObject obj, const Value& v)
+{
+    Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+
+    MOZ_ASSERT(!v.isMagic());
+    MOZ_ASSERT(arr->lengthIsWritable());
+
+    uint32_t length = arr->length();
+    MOZ_ASSERT(length <= arr->getDenseCapacity());
+
+    if (!arr->ensureElements(cx, length + 1))
+        return false;
+
+    arr->setDenseInitializedLength(length + 1);
+    arr->setLengthInt32(length + 1);
+    arr->initDenseElementWithType(cx, length, v);
+    return true;
+}
+
+/* ES5 15.4.4.7 */
+bool
+js::array_push(JSContext* cx, unsigned argc, Value* vp)
+{
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.push");
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    /* Steps 2-3. */
+    uint32_t length;
+    if (!GetLengthProperty(cx, obj, &length))
+        return false;
+
+    if (!ObjectMayHaveExtraIndexedProperties(obj)) {
+        DenseElementResult result =
+            SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, length,
+                                                      args.array(), args.length());
+        if (result != DenseElementResult::Incomplete) {
+            if (result == DenseElementResult::Failure)
+                return false;
+
+            uint32_t newlength = length + args.length();
+            args.rval().setNumber(newlength);
+
+            // SetOrExtendAnyBoxedOrUnboxedDenseElements takes care of updating the
+            // length for boxed and unboxed arrays. Handle updates to the length of
+            // non-arrays here.
+            bool isArray;
+            if (!IsArray(cx, obj, &isArray))
+                return false;
+
+            if (!isArray)
+                return SetLengthProperty(cx, obj, newlength);
+
+            return true;
+        }
+    }
+
+    /* Steps 4-5. */
+    if (!InitArrayElements(cx, obj, length, args.length(), args.array()))
+        return false;
+
+    /* Steps 6-7. */
+    double newlength = length + double(args.length());
+    args.rval().setNumber(newlength);
+    return SetLengthProperty(cx, obj, newlength);
+}
+
+/* ES6 20130308 draft 15.4.4.6. */
+bool
+js::array_pop(JSContext* cx, unsigned argc, Value* vp)
+{
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.pop");
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    /* Steps 2-3. */
+    uint32_t index;
+    if (!GetLengthProperty(cx, obj, &index))
+        return false;
+
+    /* Steps 4-5. */
+    if (index == 0) {
+        /* Step 4b. */
+        args.rval().setUndefined();
+    } else {
+        /* Step 5a. */
+        index--;
+
+        /* Step 5b, 5e. */
+        bool hole;
+        if (!GetElement(cx, obj, index, &hole, args.rval()))
+            return false;
+
+        /* Step 5c. */
+        if (!hole && !DeletePropertyOrThrow(cx, obj, index))
+            return false;
+    }
+
+    /* Steps 4a, 5d. */
+    return SetLengthProperty(cx, obj, index);
+}
+
+template <JSValueType Type>
+static inline DenseElementResult
+ShiftMoveBoxedOrUnboxedDenseElements(JSObject* obj)
+{
+    MOZ_ASSERT(HasBoxedOrUnboxedDenseElements<Type>(obj));
+
+    /*
+     * At this point the length and initialized length have already been
+     * decremented and the result fetched, so just shift the array elements
+     * themselves.
+     */
+    size_t initlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
+    if (Type == JSVAL_TYPE_MAGIC) {
+        obj->as<NativeObject>().moveDenseElementsNoPreBarrier(0, 1, initlen);
+    } else {
+        uint8_t* data = obj->as<UnboxedArrayObject>().elements();
+        size_t elementSize = UnboxedTypeSize(Type);
+        memmove(data, data + elementSize, initlen * elementSize);
+    }
+
+    return DenseElementResult::Success;
+}
+
+DefineBoxedOrUnboxedFunctor1(ShiftMoveBoxedOrUnboxedDenseElements, JSObject*);
+
+void
+js::ArrayShiftMoveElements(JSObject* obj)
+{
+    MOZ_ASSERT_IF(obj->is<ArrayObject>(), obj->as<ArrayObject>().lengthIsWritable());
+
+    ShiftMoveBoxedOrUnboxedDenseElementsFunctor functor(obj);
+    JS_ALWAYS_TRUE(CallBoxedOrUnboxedSpecialization(functor, obj) == DenseElementResult::Success);
+}
+
+template <JSValueType Type>
+DenseElementResult
+ArrayShiftDenseKernel(JSContext* cx, HandleObject obj, MutableHandleValue rval)
+{
+    if (ObjectMayHaveExtraIndexedProperties(obj))
+        return DenseElementResult::Incomplete;
+
+    RootedObjectGroup group(cx, obj->getGroup(cx));
+    if (MOZ_UNLIKELY(!group))
+        return DenseElementResult::Failure;
+
+    if (MOZ_UNLIKELY(group->hasAllFlags(OBJECT_FLAG_ITERATED)))
+        return DenseElementResult::Incomplete;
+
+    size_t initlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
+    if (initlen == 0)
+        return DenseElementResult::Incomplete;
+
+    rval.set(GetBoxedOrUnboxedDenseElement<Type>(obj, 0));
+    if (rval.isMagic(JS_ELEMENTS_HOLE))
+        rval.setUndefined();
+
+    DenseElementResult result = MoveBoxedOrUnboxedDenseElements<Type>(cx, obj, 0, 1, initlen - 1);
+    if (result != DenseElementResult::Success)
+        return result;
+
+    SetBoxedOrUnboxedInitializedLength<Type>(cx, obj, initlen - 1);
+    return DenseElementResult::Success;
+}
+
+DefineBoxedOrUnboxedFunctor3(ArrayShiftDenseKernel,
+                             JSContext*, HandleObject, MutableHandleValue);
+
+/* ES5 15.4.4.9 */
+bool
+js::array_shift(JSContext* cx, unsigned argc, Value* vp)
+{
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.shift");
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    /* Steps 2-3. */
+    uint32_t len;
+    if (!GetLengthProperty(cx, obj, &len))
+        return false;
+
+    /* Step 4. */
+    if (len == 0) {
+        /* Step 4a. */
+        if (!SetLengthProperty(cx, obj, 0))
+            return false;
+
+        /* Step 4b. */
+        args.rval().setUndefined();
+        return true;
+    }
+
+    uint32_t newlen = len - 1;
+
+    /* Fast paths. */
+    ArrayShiftDenseKernelFunctor functor(cx, obj, args.rval());
+    DenseElementResult result = CallBoxedOrUnboxedSpecialization(functor, obj);
+    if (result != DenseElementResult::Incomplete) {
+        if (result == DenseElementResult::Failure)
+            return false;
+
+        return SetLengthProperty(cx, obj, newlen);
+    }
+
+    /* Steps 5, 10. */
+    bool hole;
+    if (!GetElement(cx, obj, uint32_t(0), &hole, args.rval()))
+        return false;
+
+    /* Steps 6-7. */
+    RootedValue value(cx);
+    for (uint32_t i = 0; i < newlen; i++) {
+        if (!CheckForInterrupt(cx))
+            return false;
+        if (!GetElement(cx, obj, i + 1, &hole, &value))
+            return false;
+        if (hole) {
+            if (!DeletePropertyOrThrow(cx, obj, i))
+                return false;
+        } else {
+            if (!SetArrayElement(cx, obj, i, value))
+                return false;
+        }
+    }
+
+    /* Step 8. */
+    if (!DeletePropertyOrThrow(cx, obj, newlen))
+        return false;
+
+    /* Step 9. */
+    return SetLengthProperty(cx, obj, newlen);
+}
+
+bool
+js::array_unshift(JSContext* cx, unsigned argc, Value* vp)
+{
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.unshift");
+    CallArgs args = CallArgsFromVp(argc, vp);
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    uint32_t length;
+    if (!GetLengthProperty(cx, obj, &length))
+        return false;
+
+    double newlen = length;
+    if (args.length() > 0) {
+        /* Slide up the array to make room for all args at the bottom. */
+        if (length > 0) {
+            // Only include a fast path for boxed arrays. Unboxed arrays can'nt
+            // be optimized here because unshifting temporarily places holes at
+            // the start of the array.
+            bool optimized = false;
+            do {
+                if (!obj->is<ArrayObject>())
+                    break;
+                if (ObjectMayHaveExtraIndexedProperties(obj))
+                    break;
+                ArrayObject* aobj = &obj->as<ArrayObject>();
+                if (!aobj->lengthIsWritable())
+                    break;
+                DenseElementResult result = aobj->ensureDenseElements(cx, length, args.length());
+                if (result != DenseElementResult::Success) {
+                    if (result == DenseElementResult::Failure)
+                        return false;
+                    MOZ_ASSERT(result == DenseElementResult::Incomplete);
+                    break;
+                }
+                aobj->moveDenseElements(args.length(), 0, length);
+                for (uint32_t i = 0; i < args.length(); i++)
+                    aobj->setDenseElement(i, MagicValue(JS_ELEMENTS_HOLE));
+                optimized = true;
+            } while (false);
+
+            if (!optimized) {
+                double last = length;
+                double upperIndex = last + args.length();
+                RootedValue value(cx);
+                do {
+                    --last, --upperIndex;
+                    bool hole;
+                    if (!CheckForInterrupt(cx))
+                        return false;
+                    if (!GetElement(cx, obj, last, &hole, &value))
+                        return false;
+                    if (hole) {
+                        if (!DeletePropertyOrThrow(cx, obj, upperIndex))
+                            return false;
+                    } else {
+                        if (!SetArrayElement(cx, obj, upperIndex, value))
+                            return false;
+                    }
+                } while (last != 0);
+            }
+        }
+
+        /* Copy from args to the bottom of the array. */
+        if (!InitArrayElements(cx, obj, 0, args.length(), args.array()))
+            return false;
+
+        newlen += args.length();
+    }
+    if (!SetLengthProperty(cx, obj, newlen))
+        return false;
+
+    /* Follow Perl by returning the new array length. */
+    args.rval().setNumber(newlen);
+    return true;
+}
+
+/*
+ * Returns true if this is a dense or unboxed array whose |count| properties
+ * starting from |startingIndex| may be accessed (get, set, delete) directly
+ * through its contiguous vector of elements without fear of getters, setters,
+ * etc. along the prototype chain, or of enumerators requiring notification of
+ * modifications.
+ */
+static inline bool
+CanOptimizeForDenseStorage(HandleObject arr, uint32_t startingIndex, uint32_t count, JSContext* cx)
+{
+    /* If the desired properties overflow dense storage, we can't optimize. */
+    if (UINT32_MAX - startingIndex < count)
+        return false;
+
+    /* There's no optimizing possible if it's not an array. */
+    if (!arr->is<ArrayObject>() && !arr->is<UnboxedArrayObject>())
+        return false;
+
+    /* If it's a frozen array, always pick the slow path */
+    if (arr->is<ArrayObject>() && arr->as<ArrayObject>().denseElementsAreFrozen())
+        return false;
+
+    /*
+     * Don't optimize if the array might be in the midst of iteration.  We
+     * rely on this to be able to safely move dense array elements around with
+     * just a memmove (see NativeObject::moveDenseArrayElements), without worrying
+     * about updating any in-progress enumerators for properties implicitly
+     * deleted if a hole is moved from one location to another location not yet
+     * visited.  See bug 690622.
+     */
+    ObjectGroup* arrGroup = arr->getGroup(cx);
+    if (!arrGroup) {
+        cx->recoverFromOutOfMemory();
+        return false;
+    }
+    if (MOZ_UNLIKELY(arrGroup->hasAllFlags(OBJECT_FLAG_ITERATED)))
+        return false;
+
+    /*
+     * Another potential wrinkle: what if the enumeration is happening on an
+     * object which merely has |arr| on its prototype chain?
+     */
+    if (arr->isDelegate())
+        return false;
+
+    /*
+     * Now watch out for getters and setters along the prototype chain or in
+     * other indexed properties on the object.  (Note that non-writable length
+     * is subsumed by the initializedLength comparison.)
+     */
+    return !ObjectMayHaveExtraIndexedProperties(arr) &&
+           startingIndex + count <= GetAnyBoxedOrUnboxedInitializedLength(arr);
+}
+
+/* ES 2016 draft Mar 25, 2016 22.1.3.26. */
+bool
+js::array_splice(JSContext* cx, unsigned argc, Value* vp)
+{
+    return array_splice_impl(cx, argc, vp, true);
+}
+
+static inline bool
+ArraySpliceCopy(JSContext* cx, HandleObject arr, HandleObject obj,
+                uint32_t actualStart, uint32_t actualDeleteCount)
+{
+    /* Steps 14, 15, 15.e. */
+    RootedValue fromValue(cx);
+    for (uint32_t k = 0; k < actualDeleteCount; k++) {
+        /* Step 15.a (implicit). */
+
+        if (!CheckForInterrupt(cx))
+            return false;
+
+        /* Steps 15.b-c, 15.d.i-ii. */
+        bool hole;
+        if (!GetElement(cx, obj, actualStart + k, &hole, &fromValue))
+            return false;
+
+        /* Step 15.d. */
+        if (!hole) {
+            /* Step 15.d.iii-iv. */
+            if (!DefineElement(cx, arr, k, fromValue))
+                return false;
+        }
+    }
+
+    /* Steps 16-17. */
+    return SetLengthProperty(cx, arr, actualDeleteCount);
+}
+
+bool
+js::array_splice_impl(JSContext* cx, unsigned argc, Value* vp, bool returnValueIsUsed)
+{
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.splice");
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    /* Step 2. */
+    uint32_t len;
+    if (!GetLengthProperty(cx, obj, &len))
+        return false;
+
+    /* Step 3. */
+    double relativeStart;
+    if (!ToInteger(cx, args.get(0), &relativeStart))
+        return false;
+
+    /* Step 4. */
+    uint32_t actualStart;
+    if (relativeStart < 0)
+        actualStart = Max(len + relativeStart, 0.0);
+    else
+        actualStart = Min(relativeStart, double(len));
+
+    /* Step 5. */
+    uint32_t actualDeleteCount;
+    if (args.length() == 0) {
+        /* Step 5.b. */
+        actualDeleteCount = 0;
+    } else if (args.length() == 1) {
+        /* Step 6.b. */
+        actualDeleteCount = len - actualStart;
+    } else {
+        /* Steps 7.b. */
+        double deleteCountDouble;
+        RootedValue cnt(cx, args[1]);
+        if (!ToInteger(cx, cnt, &deleteCountDouble))
+            return false;
+
+        /* Step 7.c. */
+        actualDeleteCount = Min(Max(deleteCountDouble, 0.0), double(len - actualStart));
+    }
+
+    /* Step 8 (implicit). */
+
+    MOZ_ASSERT(len - actualStart >= actualDeleteCount);
+
+    RootedObject arr(cx);
+    if (IsArraySpecies(cx, obj)) {
+        if (CanOptimizeForDenseStorage(obj, actualStart, actualDeleteCount, cx)) {
+            if (returnValueIsUsed) {
+                /* Step 9. */
+                arr = NewFullyAllocatedArrayTryReuseGroup(cx, obj, actualDeleteCount);
+                if (!arr)
+                    return false;
+
+                /* Steps 10-11. */
+                DebugOnly<DenseElementResult> result =
+                    CopyAnyBoxedOrUnboxedDenseElements(cx, arr, obj, 0, actualStart, actualDeleteCount);
+                MOZ_ASSERT(result.value == DenseElementResult::Success);
+
+                /* Step 12 (implicit). */
+            }
+        } else {
+            /* Step 9. */
+            arr = NewFullyAllocatedArrayTryReuseGroup(cx, obj, actualDeleteCount);
+            if (!arr)
+                return false;
+
+            /* Steps 10-12. */
+            if (!ArraySpliceCopy(cx, arr, obj, actualStart, actualDeleteCount))
+                return false;
+        }
+    } else {
+        /* Steps 9. */
+        if (!ArraySpeciesCreate(cx, obj, actualDeleteCount, &arr))
+            return false;
+
+        /* Steps 10-12. */
+        if (!ArraySpliceCopy(cx, arr, obj, actualStart, actualDeleteCount))
+            return false;
+    }
+
+    /* Step 14. */
+    uint32_t itemCount = (args.length() >= 2) ? (args.length() - 2) : 0;
+
+    if (itemCount < actualDeleteCount) {
+        /* Step 15: the array is being shrunk. */
+        uint32_t sourceIndex = actualStart + actualDeleteCount;
+        uint32_t targetIndex = actualStart + itemCount;
+        uint32_t finalLength = len - actualDeleteCount + itemCount;
+
+        if (CanOptimizeForDenseStorage(obj, 0, len, cx)) {
+            /* Steps 15.a-b. */
+            DenseElementResult result =
+                MoveAnyBoxedOrUnboxedDenseElements(cx, obj, targetIndex, sourceIndex,
+                                                   len - sourceIndex);
+            MOZ_ASSERT(result != DenseElementResult::Incomplete);
+            if (result == DenseElementResult::Failure)
+                return false;
+
+            /* Steps 15.c-d. */
+            SetAnyBoxedOrUnboxedInitializedLength(cx, obj, finalLength);
+        } else {
+            /*
+             * This is all very slow if the length is very large. We don't yet
+             * have the ability to iterate in sorted order, so we just do the
+             * pessimistic thing and let CheckForInterrupt handle the
+             * fallout.
+             */
+
+            /* Steps 15.a-b. */
+            RootedValue fromValue(cx);
+            for (uint32_t from = sourceIndex, to = targetIndex; from < len; from++, to++) {
+                /* Steps 15.b.i-ii (implicit). */
+
+                if (!CheckForInterrupt(cx))
+                    return false;
+
+                /* Steps 15.b.iii, 15.b.iv.1. */
+                bool hole;
+                if (!GetElement(cx, obj, from, &hole, &fromValue))
+                    return false;
+
+                /* Steps 15.b.iv. */
+                if (hole) {
+                    /* Steps 15.b.v.1. */
+                    if (!DeletePropertyOrThrow(cx, obj, to))
+                        return false;
+                } else {
+                    /* Step 15.b.iv.2. */
+                    if (!SetArrayElement(cx, obj, to, fromValue))
+                        return false;
+                }
+            }
+
+            /* Steps 15.c-d. */
+            for (uint32_t k = len; k > finalLength; k--) {
+                /* Steps 15.d.i-ii. */
+                if (!DeletePropertyOrThrow(cx, obj, k - 1))
+                    return false;
+            }
+        }
+    } else if (itemCount > actualDeleteCount) {
+        /* Step 16. */
+
+        /*
+         * Optimize only if the array is already dense and we can extend it to
+         * its new length.  It would be wrong to extend the elements here for a
+         * number of reasons.
+         *
+         * First, this could cause us to fall into the fast-path below.  This
+         * would cause elements to be moved into places past the non-writable
+         * length.  And when the dense initialized length is updated, that'll
+         * cause the |in| operator to think that those elements actually exist,
+         * even though, properly, setting them must fail.
+         *
+         * Second, extending the elements here will trigger assertions inside
+         * ensureDenseElements that the elements aren't being extended past the
+         * length of a non-writable array.  This is because extending elements
+         * will extend capacity -- which might extend them past a non-writable
+         * length, violating the |capacity <= length| invariant for such
+         * arrays.  And that would make the various JITted fast-path method
+         * implementations of [].push, [].unshift, and so on wrong.
+         *
+         * If the array length is non-writable, this method *will* throw.  For
+         * simplicity, have the slow-path code do it.  (Also note that the slow
+         * path may validly *not* throw -- if all the elements being moved are
+         * holes.)
+         */
+        if (obj->is<ArrayObject>()) {
+            Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+            if (arr->lengthIsWritable()) {
+                DenseElementResult result =
+                    arr->ensureDenseElements(cx, len, itemCount - actualDeleteCount);
+                if (result == DenseElementResult::Failure)
+                    return false;
+            }
+        }
+
+        if (CanOptimizeForDenseStorage(obj, len, itemCount - actualDeleteCount, cx)) {
+            DenseElementResult result =
+                MoveAnyBoxedOrUnboxedDenseElements(cx, obj, actualStart + itemCount,
+                                                   actualStart + actualDeleteCount,
+                                                   len - (actualStart + actualDeleteCount));
+            MOZ_ASSERT(result != DenseElementResult::Incomplete);
+            if (result == DenseElementResult::Failure)
+                return false;
+
+            /* Steps 16.a-b. */
+            SetAnyBoxedOrUnboxedInitializedLength(cx, obj, len + itemCount - actualDeleteCount);
+        } else {
+            RootedValue fromValue(cx);
+            for (double k = len - actualDeleteCount; k > actualStart; k--) {
+                if (!CheckForInterrupt(cx))
+                    return false;
+
+                /* Step 16.b.i. */
+                double from = k + actualDeleteCount - 1;
+
+                /* Step 16.b.ii. */
+                double to = k + itemCount - 1;
+
+                /* Steps 16.b.iii, 16.b.iv.1. */
+                bool hole;
+                if (!GetElement(cx, obj, from, &hole, &fromValue))
+                    return false;
+
+                /* Steps 16.b.iv. */
+                if (hole) {
+                    /* Step 16.b.v.1. */
+                    if (!DeletePropertyOrThrow(cx, obj, to))
+                        return false;
+                } else {
+                    /* Step 16.b.iv.2. */
+                    if (!SetArrayElement(cx, obj, to, fromValue))
+                        return false;
+                }
+            }
+        }
+    }
+
+    /* Step 13 (reordered). */
+    Value* items = args.array() + 2;
+
+    /* Steps 17-18. */
+    for (uint32_t k = actualStart, i = 0; i < itemCount; i++, k++) {
+        /* Step 18.a (implicit). */
+
+        /* Step 18.b. */
+        if (!SetArrayElement(cx, obj, k, HandleValue::fromMarkedLocation(&items[i])))
+            return false;
+    }
+
+    /* Step 19. */
+    double finalLength = double(len) - actualDeleteCount + itemCount;
+    if (!SetLengthProperty(cx, obj, finalLength))
+        return false;
+
+    /* Step 20. */
+    if (returnValueIsUsed)
+        args.rval().setObject(*arr);
+
+    return true;
+}
+
+struct SortComparatorIndexes
+{
+    bool operator()(uint32_t a, uint32_t b, bool* lessOrEqualp) {
+        *lessOrEqualp = (a <= b);
+        return true;
+    }
+};
+
+// Returns all indexed properties in the range [begin, end) found on |obj| or
+// its proto chain. This function does not handle proxies, objects with
+// resolve/lookupProperty hooks or indexed getters, as those can introduce
+// new properties. In those cases, *success is set to |false|.
+static bool
+GetIndexedPropertiesInRange(JSContext* cx, HandleObject obj, uint32_t begin, uint32_t end,
+                            Vector<uint32_t>& indexes, bool* success)
+{
+    *success = false;
+
+    // First, look for proxies or class hooks that can introduce extra
+    // properties.
+    JSObject* pobj = obj;
+    do {
+        if (!pobj->isNative() || pobj->getClass()->getResolve() || pobj->getOpsLookupProperty())
+            return true;
+    } while ((pobj = pobj->staticPrototype()));
+
+    // Collect indexed property names.
+    pobj = obj;
+    do {
+        // Append dense elements.
+        NativeObject* nativeObj = &pobj->as<NativeObject>();
+        uint32_t initLen = nativeObj->getDenseInitializedLength();
+        for (uint32_t i = begin; i < initLen && i < end; i++) {
+            if (nativeObj->getDenseElement(i).isMagic(JS_ELEMENTS_HOLE))
+                continue;
+            if (!indexes.append(i))
+                return false;
+        }
+
+        // Append typed array elements.
+        if (pobj->is<TypedArrayObject>()) {
+            uint32_t len = pobj->as<TypedArrayObject>().length();
+            for (uint32_t i = begin; i < len && i < end; i++) {
+                if (!indexes.append(i))
+                    return false;
+            }
+        }
+
+        // Append sparse elements.
+        if (pobj->isIndexed()) {
+            Shape::Range<NoGC> r(pobj->as<NativeObject>().lastProperty());
+            for (; !r.empty(); r.popFront()) {
+                Shape& shape = r.front();
+                jsid id = shape.propid();
+                if (!JSID_IS_INT(id))
+                    continue;
+
+                uint32_t i = uint32_t(JSID_TO_INT(id));
+                if (!(begin <= i && i < end))
+                    continue;
+
+                // Watch out for getters, they can add new properties.
+                if (!shape.hasDefaultGetter())
+                    return true;
+
+                if (!indexes.append(i))
+                    return false;
+            }
+        }
+    } while ((pobj = pobj->staticPrototype()));
+
+    // Sort the indexes.
+    Vector<uint32_t> tmp(cx);
+    size_t n = indexes.length();
+    if (!tmp.resize(n))
+        return false;
+    if (!MergeSort(indexes.begin(), n, tmp.begin(), SortComparatorIndexes()))
+        return false;
+
+    // Remove duplicates.
+    if (!indexes.empty()) {
+        uint32_t last = 0;
+        for (size_t i = 1, len = indexes.length(); i < len; i++) {
+            uint32_t elem = indexes[i];
+            if (indexes[last] != elem) {
+                last++;
+                indexes[last] = elem;
+            }
+        }
+        if (!indexes.resize(last + 1))
+            return false;
+    }
+
+    *success = true;
+    return true;
+}
+
+static bool
+SliceSlowly(JSContext* cx, HandleObject obj, HandleObject receiver,
+            uint32_t begin, uint32_t end, HandleObject result)
+{
+    RootedValue value(cx);
+    for (uint32_t slot = begin; slot < end; slot++) {
+        bool hole;
+        if (!CheckForInterrupt(cx) ||
+            !GetElement(cx, obj, receiver, slot, &hole, &value))
+        {
+            return false;
+        }
+        if (!hole && !DefineElement(cx, result, slot - begin, value))
+            return false;
+    }
+    return true;
+}
+
+static bool
+SliceSparse(JSContext* cx, HandleObject obj, uint32_t begin, uint32_t end, HandleObject result)
+{
+    MOZ_ASSERT(begin <= end);
+
+    Vector<uint32_t> indexes(cx);
+    bool success;
+    if (!GetIndexedPropertiesInRange(cx, obj, begin, end, indexes, &success))
+        return false;
+
+    if (!success)
+        return SliceSlowly(cx, obj, obj, begin, end, result);
+
+    RootedValue value(cx);
+    for (size_t i = 0, len = indexes.length(); i < len; i++) {
+        uint32_t index = indexes[i];
+        MOZ_ASSERT(begin <= index && index < end);
+
+        bool hole;
+        if (!GetElement(cx, obj, obj, index, &hole, &value))
+            return false;
+
+        if (!hole && !DefineElement(cx, result, index - begin, value))
+            return false;
+    }
+
+    return true;
+}
+
+template <typename T>
+static inline uint32_t
+NormalizeSliceTerm(T value, uint32_t length)
+{
+    if (value < 0) {
+        value += length;
+        if (value < 0)
+            return 0;
+    } else if (double(value) > double(length)) {
+        return length;
+    }
+    return uint32_t(value);
+}
+
+static bool
+ArraySliceOrdinary(JSContext* cx, HandleObject obj, uint32_t length, uint32_t begin, uint32_t end,
+                   MutableHandleObject arr)
+{
+    if (begin > end)
+        begin = end;
+
+    if (!ObjectMayHaveExtraIndexedProperties(obj)) {
+        size_t initlen = GetAnyBoxedOrUnboxedInitializedLength(obj);
+        size_t count = 0;
+        if (initlen > begin)
+            count = Min<size_t>(initlen - begin, end - begin);
+
+        RootedObject narr(cx, NewFullyAllocatedArrayTryReuseGroup(cx, obj, count));
+        if (!narr)
+            return false;
+        SetAnyBoxedOrUnboxedArrayLength(cx, narr, end - begin);
+
+        if (count) {
+            DebugOnly<DenseElementResult> result =
+                CopyAnyBoxedOrUnboxedDenseElements(cx, narr, obj, 0, begin, count);
+            MOZ_ASSERT(result.value == DenseElementResult::Success);
+        }
+        arr.set(narr);
+        return true;
+    }
+
+    RootedObject narr(cx, NewPartlyAllocatedArrayTryReuseGroup(cx, obj, end - begin));
+    if (!narr)
+        return false;
+
+    if (js::GetElementsOp op = obj->getOpsGetElements()) {
+        ElementAdder adder(cx, narr, end - begin, ElementAdder::CheckHasElemPreserveHoles);
+        if (!op(cx, obj, begin, end, &adder))
+            return false;
+
+        arr.set(narr);
+        return true;
+    }
+
+    if (obj->isNative() && obj->isIndexed() && end - begin > 1000) {
+        if (!SliceSparse(cx, obj, begin, end, narr))
+            return false;
+    } else {
+        if (!SliceSlowly(cx, obj, obj, begin, end, narr))
+            return false;
+    }
+
+    arr.set(narr);
+    return true;
+}
+
+/* ES 2016 draft Mar 25, 2016 22.1.3.23. */
+bool
+js::array_slice(JSContext* cx, unsigned argc, Value* vp)
+{
+    AutoSPSEntry pseudoFrame(cx->runtime(), "Array.prototype.slice");
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    /* Step 2. */
+    uint32_t length;
+    if (!GetLengthProperty(cx, obj, &length))
+        return false;
+
+    uint32_t k = 0;
+    uint32_t final = length;
+    if (args.length() > 0) {
+        double d;
+        /* Step 3. */
+        if (!ToInteger(cx, args[0], &d))
+            return false;
+
+        /* Step 4. */
+        k = NormalizeSliceTerm(d, length);
+
+        if (args.hasDefined(1)) {
+            /* Step 5. */
+            if (!ToInteger(cx, args[1], &d))
+                return false;
+
+            /* Step 6. */
+            final = NormalizeSliceTerm(d, length);
+        }
+    }
+
+    /* Step 7. */
+    uint32_t count = final > k ? final - k : 0;
+
+    RootedObject arr(cx);
+    if (IsArraySpecies(cx, obj)) {
+        /* Steps 8-11: Optimized for ordinary array. */
+        if (!ArraySliceOrdinary(cx, obj, length, k, final, &arr))
+            return false;
+
+        /* Step 12. */
+        args.rval().setObject(*arr);
+        return true;
+    }
+
+    /* Step 8. */
+    if (!ArraySpeciesCreate(cx, obj, count, &arr))
+        return false;
+
+    /* Step 9. */
+    uint32_t n = 0;
+
+    /* Step 10. */
+    RootedValue kValue(cx);
+    while (k < final) {
+        if (!CheckForInterrupt(cx))
+            return false;
+
+        /* Steps 10.a-b, and 10.c.i. */
+        bool kNotPresent;
+        if (!GetElement(cx, obj, k, &kNotPresent, &kValue))
+            return false;
+
+        /* Step 10.c. */
+        if (!kNotPresent) {
+            /* Steps 10.c.ii. */
+            if (!DefineElement(cx, arr, n, kValue))
+                return false;
+        }
+        /* Step 10.d. */
+        k++;
+
+        /* Step 10.e. */
+        n++;
+    }
+
+    /* Step 11. */
+    if (!SetLengthProperty(cx, arr, n))
+        return false;
+
+    /* Step 12. */
+    args.rval().setObject(*arr);
+    return true;
+}
+
+template <JSValueType Type>
+DenseElementResult
+ArraySliceDenseKernel(JSContext* cx, JSObject* obj, int32_t beginArg, int32_t endArg, JSObject* result)
+{
+    int32_t length = GetAnyBoxedOrUnboxedArrayLength(obj);
+
+    uint32_t begin = NormalizeSliceTerm(beginArg, length);
+    uint32_t end = NormalizeSliceTerm(endArg, length);
+
+    if (begin > end)
+        begin = end;
+
+    size_t initlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
+    if (initlen > begin) {
+        size_t count = Min<size_t>(initlen - begin, end - begin);
+        if (count) {
+            DenseElementResult rv = EnsureBoxedOrUnboxedDenseElements<Type>(cx, result, count);
+            if (rv != DenseElementResult::Success)
+                return rv;
+            CopyBoxedOrUnboxedDenseElements<Type, Type>(cx, result, obj, 0, begin, count);
+        }
+    }
+
+    SetAnyBoxedOrUnboxedArrayLength(cx, result, end - begin);
+    return DenseElementResult::Success;
+}
+
+DefineBoxedOrUnboxedFunctor5(ArraySliceDenseKernel,
+                             JSContext*, JSObject*, int32_t, int32_t, JSObject*);
+
+JSObject*
+js::array_slice_dense(JSContext* cx, HandleObject obj, int32_t begin, int32_t end,
+                      HandleObject result)
+{
+    if (result && IsArraySpecies(cx, obj)) {
+        ArraySliceDenseKernelFunctor functor(cx, obj, begin, end, result);
+        DenseElementResult rv = CallBoxedOrUnboxedSpecialization(functor, result);
+        MOZ_ASSERT(rv != DenseElementResult::Incomplete);
+        return rv == DenseElementResult::Success ? result : nullptr;
+    }
+
+    // Slower path if the JIT wasn't able to allocate an object inline.
+    JS::AutoValueArray<4> argv(cx);
+    argv[0].setUndefined();
+    argv[1].setObject(*obj);
+    argv[2].setInt32(begin);
+    argv[3].setInt32(end);
+    if (!array_slice(cx, 2, argv.begin()))
+        return nullptr;
+    return &argv[0].toObject();
+}
+
+static bool
+array_isArray(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    bool isArray = false;
+    if (args.get(0).isObject()) {
+        RootedObject obj(cx, &args[0].toObject());
+        if (!IsArray(cx, obj, &isArray))
+            return false;
+    }
+    args.rval().setBoolean(isArray);
+    return true;
+}
+
+static bool
+ArrayFromCallArgs(JSContext* cx, CallArgs& args, HandleObject proto = nullptr)
+{
+    JSObject* obj = NewCopiedArrayForCallingAllocationSite(cx, args.array(), args.length(), proto);
+    if (!obj)
+        return false;
+
+    args.rval().setObject(*obj);
+    return true;
+}
+
+static bool
+array_of(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    if (IsArrayConstructor(args.thisv()) || !IsConstructor(args.thisv())) {
+        // IsArrayConstructor(this) will usually be true in practice. This is
+        // the most common path.
+        return ArrayFromCallArgs(cx, args);
+    }
+
+    // Step 4.
+    RootedObject obj(cx);
+    {
+        FixedConstructArgs<1> cargs(cx);
+
+        cargs[0].setNumber(args.length());
+
+        if (!Construct(cx, args.thisv(), cargs, args.thisv(), &obj))
+            return false;
+    }
+
+    // Step 8.
+    for (unsigned k = 0; k < args.length(); k++) {
+        if (!DefineElement(cx, obj, k, args[k]))
+            return false;
+    }
+
+    // Steps 9-10.
+    if (!SetLengthProperty(cx, obj, args.length()))
+        return false;
+
+    // Step 11.
+    args.rval().setObject(*obj);
+    return true;
+}
+
+static const JSFunctionSpec array_methods[] = {
+#if JS_HAS_TOSOURCE
+    JS_FN(js_toSource_str,      array_toSource,     0,0),
+#endif
+    JS_SELF_HOSTED_FN(js_toString_str, "ArrayToString",      0,0),
+    JS_FN(js_toLocaleString_str,       array_toLocaleString, 0,0),
+
+    /* Perl-ish methods. */
+    JS_INLINABLE_FN("join",     array_join,         1,0, ArrayJoin),
+    JS_FN("reverse",            array_reverse,      0,0),
+    JS_FN("sort",               array_sort,         1,0),
+    JS_INLINABLE_FN("push",     array_push,         1,0, ArrayPush),
+    JS_INLINABLE_FN("pop",      array_pop,          0,0, ArrayPop),
+    JS_INLINABLE_FN("shift",    array_shift,        0,0, ArrayShift),
+    JS_FN("unshift",            array_unshift,      1,0),
+    JS_INLINABLE_FN("splice",   array_splice,       2,0, ArraySplice),
+
+    /* Pythonic sequence methods. */
+    JS_SELF_HOSTED_FN("concat",      "ArrayConcat",      1,0),
+    JS_INLINABLE_FN("slice",    array_slice,        2,0, ArraySlice),
+
+    JS_SELF_HOSTED_FN("lastIndexOf", "ArrayLastIndexOf", 1,0),
+    JS_SELF_HOSTED_FN("indexOf",     "ArrayIndexOf",     1,0),
+    JS_SELF_HOSTED_FN("forEach",     "ArrayForEach",     1,0),
+    JS_SELF_HOSTED_FN("map",         "ArrayMap",         1,0),
+    JS_SELF_HOSTED_FN("filter",      "ArrayFilter",      1,0),
+    JS_SELF_HOSTED_FN("reduce",      "ArrayReduce",      1,0),
+    JS_SELF_HOSTED_FN("reduceRight", "ArrayReduceRight", 1,0),
+    JS_SELF_HOSTED_FN("some",        "ArraySome",        1,0),
+    JS_SELF_HOSTED_FN("every",       "ArrayEvery",       1,0),
+
+    /* ES6 additions */
+    JS_SELF_HOSTED_FN("find",        "ArrayFind",        1,0),
+    JS_SELF_HOSTED_FN("findIndex",   "ArrayFindIndex",   1,0),
+    JS_SELF_HOSTED_FN("copyWithin",  "ArrayCopyWithin",  3,0),
+
+    JS_SELF_HOSTED_FN("fill",        "ArrayFill",        3,0),
+
+    JS_SELF_HOSTED_SYM_FN(iterator,  "ArrayValues",      0,0),
+    JS_SELF_HOSTED_FN("entries",     "ArrayEntries",     0,0),
+    JS_SELF_HOSTED_FN("keys",        "ArrayKeys",        0,0),
+#ifdef NIGHTLY_BUILD
+    JS_SELF_HOSTED_FN("values",      "ArrayValues",      0,0),
+#endif
+
+    /* ES7 additions */
+    JS_SELF_HOSTED_FN("includes",    "ArrayIncludes",    2,0),
+    JS_FS_END
+};
+
+static const JSFunctionSpec array_static_methods[] = {
+    JS_INLINABLE_FN("isArray",       array_isArray,        1,0, ArrayIsArray),
+    JS_SELF_HOSTED_FN("concat",      "ArrayStaticConcat", 2,0),
+    JS_SELF_HOSTED_FN("lastIndexOf", "ArrayStaticLastIndexOf", 2,0),
+    JS_SELF_HOSTED_FN("indexOf",     "ArrayStaticIndexOf", 2,0),
+    JS_SELF_HOSTED_FN("forEach",     "ArrayStaticForEach", 2,0),
+    JS_SELF_HOSTED_FN("map",         "ArrayStaticMap",   2,0),
+    JS_SELF_HOSTED_FN("filter",      "ArrayStaticFilter", 2,0),
+    JS_SELF_HOSTED_FN("every",       "ArrayStaticEvery", 2,0),
+    JS_SELF_HOSTED_FN("some",        "ArrayStaticSome",  2,0),
+    JS_SELF_HOSTED_FN("reduce",      "ArrayStaticReduce", 2,0),
+    JS_SELF_HOSTED_FN("reduceRight", "ArrayStaticReduceRight", 2,0),
+    JS_SELF_HOSTED_FN("join",        "ArrayStaticJoin", 2,0),
+    JS_SELF_HOSTED_FN("reverse",     "ArrayStaticReverse", 1,0),
+    JS_SELF_HOSTED_FN("sort",        "ArrayStaticSort", 2,0),
+    JS_SELF_HOSTED_FN("push",        "ArrayStaticPush", 2,0),
+    JS_SELF_HOSTED_FN("pop",         "ArrayStaticPop", 1,0),
+    JS_SELF_HOSTED_FN("shift",       "ArrayStaticShift", 1,0),
+    JS_SELF_HOSTED_FN("unshift",     "ArrayStaticUnshift", 2,0),
+    JS_SELF_HOSTED_FN("splice",      "ArrayStaticSplice", 3,0),
+    JS_SELF_HOSTED_FN("slice",       "ArrayStaticSlice", 3,0),
+    JS_SELF_HOSTED_FN("from",        "ArrayFrom", 3,0),
+    JS_FN("of",                 array_of,           0,0),
+
+    JS_FS_END
+};
+
+const JSPropertySpec array_static_props[] = {
+    JS_SELF_HOSTED_SYM_GET(species, "ArraySpecies", 0),
+    JS_PS_END
+};
+
+static inline bool
+ArrayConstructorImpl(JSContext* cx, CallArgs& args, bool isConstructor)
+{
+    RootedObject proto(cx);
+    if (isConstructor) {
+        if (!GetPrototypeFromCallableConstructor(cx, args, &proto))
+            return false;
+    } else {
+        // We're emulating |new Array(n)| with |std_Array(n)| in self-hosted JS,
+        // and the proto should be %ArrayPrototype% regardless of the callee.
+        proto = GlobalObject::getOrCreateArrayPrototype(cx, cx->global());
+        if (!proto)
+            return false;
+    }
+
+    if (args.length() != 1 || !args[0].isNumber())
+        return ArrayFromCallArgs(cx, args, proto);
+
+    uint32_t length;
+    if (args[0].isInt32()) {
+        int32_t i = args[0].toInt32();
+        if (i < 0) {
+            JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
+            return false;
+        }
+        length = uint32_t(i);
+    } else {
+        double d = args[0].toDouble();
+        length = ToUint32(d);
+        if (d != double(length)) {
+            JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
+            return false;
+        }
+    }
+
+    JSObject* obj = NewPartlyAllocatedArrayForCallingAllocationSite(cx, length, proto);
+    if (!obj)
+        return false;
+
+    args.rval().setObject(*obj);
+    return true;
+}
+
+/* ES5 15.4.2 */
+bool
+js::ArrayConstructor(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    return ArrayConstructorImpl(cx, args, /* isConstructor = */ true);
+}
+
+bool
+js::array_construct(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    MOZ_ASSERT(!args.isConstructing());
+    MOZ_ASSERT(args.length() == 1);
+    MOZ_ASSERT(args[0].isNumber());
+    return ArrayConstructorImpl(cx, args, /* isConstructor = */ false);
+}
+
+JSObject*
+js::ArrayConstructorOneArg(JSContext* cx, HandleObjectGroup group, int32_t lengthInt)
+{
+    if (lengthInt < 0) {
+        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
+        return nullptr;
+    }
+
+    uint32_t length = uint32_t(lengthInt);
+    return NewPartlyAllocatedArrayTryUseGroup(cx, group, length);
+}
+
+static JSObject*
+CreateArrayPrototype(JSContext* cx, JSProtoKey key)
+{
+    MOZ_ASSERT(key == JSProto_Array);
+    RootedObject proto(cx, cx->global()->getOrCreateObjectPrototype(cx));
+    if (!proto)
+        return nullptr;
+
+    RootedObjectGroup group(cx, ObjectGroup::defaultNewGroup(cx, &ArrayObject::class_,
+                                                             TaggedProto(proto)));
+    if (!group)
+        return nullptr;
+
+    RootedShape shape(cx, EmptyShape::getInitialShape(cx, &ArrayObject::class_, TaggedProto(proto),
+                                                      gc::AllocKind::OBJECT0));
+    if (!shape)
+        return nullptr;
+
+    AutoSetNewObjectMetadata metadata(cx);
+    RootedArrayObject arrayProto(cx, ArrayObject::createArray(cx, gc::AllocKind::OBJECT4,
+                                                              gc::TenuredHeap, shape, group, 0,
+                                                              metadata));
+    if (!arrayProto ||
+        !JSObject::setSingleton(cx, arrayProto) ||
+        !arrayProto->setDelegate(cx) ||
+        !AddLengthProperty(cx, arrayProto))
+    {
+        return nullptr;
+    }
+
+    /*
+     * The default 'new' group of Array.prototype is required by type inference
+     * to have unknown properties, to simplify handling of e.g. heterogenous
+     * arrays in JSON and script literals and allows setDenseArrayElement to
+     * be used without updating the indexed type set for such default arrays.
+     */
+    if (!JSObject::setNewGroupUnknown(cx, &ArrayObject::class_, arrayProto))
+        return nullptr;
+
+    return arrayProto;
+}
+
+static bool
+array_proto_finish(JSContext* cx, JS::HandleObject ctor, JS::HandleObject proto)
+{
+    // Add Array.prototype[@@unscopables]. ECMA-262 draft (2016 Mar 19) 22.1.3.32.
+    RootedObject unscopables(cx, NewObjectWithGivenProto<PlainObject>(cx, nullptr, TenuredObject));
+    if (!unscopables)
+        return false;
+
+    RootedValue value(cx, BooleanValue(true));
+    if (!DefineProperty(cx, unscopables, cx->names().copyWithin, value) ||
+        !DefineProperty(cx, unscopables, cx->names().entries, value) ||
+        !DefineProperty(cx, unscopables, cx->names().fill, value) ||
+        !DefineProperty(cx, unscopables, cx->names().find, value) ||
+        !DefineProperty(cx, unscopables, cx->names().findIndex, value) ||
+        !DefineProperty(cx, unscopables, cx->names().includes, value) ||
+        !DefineProperty(cx, unscopables, cx->names().keys, value) ||
+        !DefineProperty(cx, unscopables, cx->names().values, value))
+    {
+        return false;
+    }
+
+    RootedId id(cx, SYMBOL_TO_JSID(cx->wellKnownSymbols().get(JS::SymbolCode::unscopables)));
+    value.setObject(*unscopables);
+    return DefineProperty(cx, proto, id, value, nullptr, nullptr, JSPROP_READONLY);
+}
+
+static const ClassOps ArrayObjectClassOps = {
+    array_addProperty,
+    nullptr, /* delProperty */
+    nullptr, /* getProperty */
+    nullptr, /* setProperty */
+    nullptr, /* enumerate */
+    nullptr, /* resolve */
+    nullptr, /* mayResolve */
+    nullptr, /* finalize */
+    nullptr, /* call */
+    nullptr, /* hasInstance */
+    nullptr, /* construct */
+    nullptr, /* trace */
+};
+
+static const ClassSpec ArrayObjectClassSpec = {
+    GenericCreateConstructor<ArrayConstructor, 1, AllocKind::FUNCTION, &jit::JitInfo_Array>,
+    CreateArrayPrototype,
+    array_static_methods,
+    array_static_props,
+    array_methods,
+    nullptr,
+    array_proto_finish
+};
+
+const Class ArrayObject::class_ = {
+    "Array",
+    JSCLASS_HAS_CACHED_PROTO(JSProto_Array) | JSCLASS_DELAY_METADATA_BUILDER,
+    &ArrayObjectClassOps,
+    &ArrayObjectClassSpec
+};
+
+/*
+ * Array allocation functions.
+ */
+
+static inline bool
+EnsureNewArrayElements(ExclusiveContext* cx, ArrayObject* obj, uint32_t length)
+{
+    /*
+     * If ensureElements creates dynamically allocated slots, then having
+     * fixedSlots is a waste.
+     */
+    DebugOnly<uint32_t> cap = obj->getDenseCapacity();
+
+    if (!obj->ensureElements(cx, length))
+        return false;
+
+    MOZ_ASSERT_IF(cap, !obj->hasDynamicElements());
+
+    return true;
+}
+
+template <uint32_t maxLength>
+static MOZ_ALWAYS_INLINE ArrayObject*
+NewArray(ExclusiveContext* cxArg, uint32_t length,
+         HandleObject protoArg, NewObjectKind newKind = GenericObject)
+{
+    gc::AllocKind allocKind = GuessArrayGCKind(length);
+    MOZ_ASSERT(CanBeFinalizedInBackground(allocKind, &ArrayObject::class_));
+    allocKind = GetBackgroundAllocKind(allocKind);
+
+    RootedObject proto(cxArg, protoArg);
+    if (!proto && !GetBuiltinPrototype(cxArg, JSProto_Array, &proto))
+        return nullptr;
+
+    Rooted<TaggedProto> taggedProto(cxArg, TaggedProto(proto));
+    bool isCachable = NewObjectWithTaggedProtoIsCachable(cxArg, taggedProto, newKind, &ArrayObject::class_);
+    if (isCachable) {
+        JSContext* cx = cxArg->asJSContext();
+        NewObjectCache& cache = cx->caches.newObjectCache;
+        NewObjectCache::EntryIndex entry = -1;
+        if (cache.lookupProto(&ArrayObject::class_, proto, allocKind, &entry)) {
+            gc::InitialHeap heap = GetInitialHeap(newKind, &ArrayObject::class_);
+            AutoSetNewObjectMetadata metadata(cx);
+            JSObject* obj = cache.newObjectFromHit(cx, entry, heap);
+            if (obj) {
+                /* Fixup the elements pointer and length, which may be incorrect. */
+                ArrayObject* arr = &obj->as<ArrayObject>();
+                arr->setFixedElements();
+                arr->setLength(cx, length);
+                if (maxLength > 0 &&
+                    !EnsureNewArrayElements(cx, arr, std::min(maxLength, length)))
+                {
+                    return nullptr;
+                }
+                return arr;
+            }
+        }
+    }
+
+    RootedObjectGroup group(cxArg, ObjectGroup::defaultNewGroup(cxArg, &ArrayObject::class_,
+                                                                TaggedProto(proto)));
+    if (!group)
+        return nullptr;
+
+    /*
+     * Get a shape with zero fixed slots, regardless of the size class.
+     * See JSObject::createArray.
+     */
+    RootedShape shape(cxArg, EmptyShape::getInitialShape(cxArg, &ArrayObject::class_,
+                                                         TaggedProto(proto),
+                                                         gc::AllocKind::OBJECT0));
+    if (!shape)
+        return nullptr;
+
+    AutoSetNewObjectMetadata metadata(cxArg);
+    RootedArrayObject arr(cxArg, ArrayObject::createArray(cxArg, allocKind,
+                                                          GetInitialHeap(newKind, &ArrayObject::class_),
+                                                          shape, group, length, metadata));
+    if (!arr)
+        return nullptr;
+
+    if (shape->isEmptyShape()) {
+        if (!AddLengthProperty(cxArg, arr))
+            return nullptr;
+        shape = arr->lastProperty();
+        EmptyShape::insertInitialShape(cxArg, shape, proto);
+    }
+
+    if (newKind == SingletonObject && !JSObject::setSingleton(cxArg, arr))
+        return nullptr;
+
+    if (isCachable) {
+        NewObjectCache& cache = cxArg->asJSContext()->caches.newObjectCache;
+        NewObjectCache::EntryIndex entry = -1;
+        cache.lookupProto(&ArrayObject::class_, proto, allocKind, &entry);
+        cache.fillProto(entry, &ArrayObject::class_, taggedProto, allocKind, arr);
+    }
+
+    if (maxLength > 0 && !EnsureNewArrayElements(cxArg, arr, std::min(maxLength, length)))
+        return nullptr;
+
+    probes::CreateObject(cxArg, arr);
+    return arr;
+}
+
+ArrayObject * JS_FASTCALL
+js::NewDenseEmptyArray(JSContext* cx, HandleObject proto /* = nullptr */,
+                       NewObjectKind newKind /* = GenericObject */)
+{
+    return NewArray<0>(cx, 0, proto, newKind);
+}
+
+ArrayObject * JS_FASTCALL
+js::NewDenseFullyAllocatedArray(ExclusiveContext* cx, uint32_t length,
+                                HandleObject proto /* = nullptr */,
+                                NewObjectKind newKind /* = GenericObject */)
+{
+    return NewArray<UINT32_MAX>(cx, length, proto, newKind);
+}
+
+ArrayObject * JS_FASTCALL
+js::NewDensePartlyAllocatedArray(ExclusiveContext* cx, uint32_t length,
+                                 HandleObject proto /* = nullptr */,
+                                 NewObjectKind newKind /* = GenericObject */)
+{
+    return NewArray<ArrayObject::EagerAllocationMaxLength>(cx, length, proto, newKind);
+}
+
+ArrayObject * JS_FASTCALL
+js::NewDenseUnallocatedArray(ExclusiveContext* cx, uint32_t length,
+                             HandleObject proto /* = nullptr */,
+                             NewObjectKind newKind /* = GenericObject */)
+{
+    return NewArray<0>(cx, length, proto, newKind);
+}
+
+// values must point at already-rooted Value objects
+ArrayObject*
+js::NewDenseCopiedArray(ExclusiveContext* cx, uint32_t length, const Value* values,
+                        HandleObject proto /* = nullptr */,
+                        NewObjectKind newKind /* = GenericObject */)
+{
+    ArrayObject* arr = NewArray<UINT32_MAX>(cx, length, proto, newKind);
+    if (!arr)
+        return nullptr;
+
+    MOZ_ASSERT(arr->getDenseCapacity() >= length);
+
+    arr->setDenseInitializedLength(values ? length : 0);
+
+    if (values)
+        arr->initDenseElements(0, values, length);
+
+    return arr;
+}
+
+ArrayObject*
+js::NewDenseFullyAllocatedArrayWithTemplate(JSContext* cx, uint32_t length, JSObject* templateObject)
+{
+    AutoSetNewObjectMetadata metadata(cx);
+    gc::AllocKind allocKind = GuessArrayGCKind(length);
+    MOZ_ASSERT(CanBeFinalizedInBackground(allocKind, &ArrayObject::class_));
+    allocKind = GetBackgroundAllocKind(allocKind);
+
+    RootedObjectGroup group(cx, templateObject->group());
+    RootedShape shape(cx, templateObject->as<ArrayObject>().lastProperty());
+
+    gc::InitialHeap heap = GetInitialHeap(GenericObject, &ArrayObject::class_);
+    Rooted<ArrayObject*> arr(cx, ArrayObject::createArray(cx, allocKind,
+                                                          heap, shape, group, length, metadata));
+    if (!arr)
+        return nullptr;
+
+    if (!EnsureNewArrayElements(cx, arr, length))
+        return nullptr;
+
+    probes::CreateObject(cx, arr);
+
+    return arr;
+}
+
+JSObject*
+js::NewDenseCopyOnWriteArray(JSContext* cx, HandleArrayObject templateObject, gc::InitialHeap heap)
+{
+    MOZ_ASSERT(!gc::IsInsideNursery(templateObject));
+
+    ArrayObject* arr = ArrayObject::createCopyOnWriteArray(cx, heap, templateObject);
+    if (!arr)
+        return nullptr;
+
+    probes::CreateObject(cx, arr);
+    return arr;
+}
+
+// Return a new boxed or unboxed array with the specified length and allocated
+// capacity (up to maxLength), using the specified group if possible. If the
+// specified group cannot be used, ensure that the created array at least has
+// the given [[Prototype]].
+template <uint32_t maxLength>
+static inline JSObject*
+NewArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
+                    NewObjectKind newKind = GenericObject)
+{
+    MOZ_ASSERT(newKind != SingletonObject);
+
+    if (group->maybePreliminaryObjects())
+        group->maybePreliminaryObjects()->maybeAnalyze(cx, group);
+
+    if (group->shouldPreTenure() || group->maybePreliminaryObjects())
+        newKind = TenuredObject;
+
+    RootedObject proto(cx, group->proto().toObject());
+    if (group->maybeUnboxedLayout()) {
+        if (length > UnboxedArrayObject::MaximumCapacity)
+            return NewArray<maxLength>(cx, length, proto, newKind);
+        return UnboxedArrayObject::create(cx, group, length, newKind, maxLength);
+    }
+
+    ArrayObject* res = NewArray<maxLength>(cx, length, proto, newKind);
+    if (!res)
+        return nullptr;
+
+    res->setGroup(group);
+
+    // If the length calculation overflowed, make sure that is marked for the
+    // new group.
+    if (res->length() > INT32_MAX)
+        res->setLength(cx, res->length());
+
+    if (PreliminaryObjectArray* preliminaryObjects = group->maybePreliminaryObjects())
+        preliminaryObjects->registerNewObject(res);
+
+    return res;
+}
+
+JSObject*
+js::NewFullyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
+                                      NewObjectKind newKind)
+{
+    return NewArrayTryUseGroup<UINT32_MAX>(cx, group, length, newKind);
+}
+
+JSObject*
+js::NewPartlyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length)
+{
+    return NewArrayTryUseGroup<ArrayObject::EagerAllocationMaxLength>(cx, group, length);
+}
+
+// Return a new array with the default prototype and specified allocated
+// capacity and length. If possible, try to reuse the group of the input
+// object. The resulting array will either reuse the input object's group or
+// will have unknown property types. Additionally, the result will have the
+// same boxed/unboxed elements representation as the input object, unless
+// |length| is larger than the input object's initialized length (in which case
+// UnboxedArrayObject::MaximumCapacity might be exceeded).
+template <uint32_t maxLength>
+static inline JSObject*
+NewArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
+                      NewObjectKind newKind = GenericObject)
+{
+    if (!obj->is<ArrayObject>() && !obj->is<UnboxedArrayObject>())
+        return NewArray<maxLength>(cx, length, nullptr, newKind);
+
+    if (obj->staticPrototype() != cx->global()->maybeGetArrayPrototype())
+        return NewArray<maxLength>(cx, length, nullptr, newKind);
+
+    RootedObjectGroup group(cx, obj->getGroup(cx));
+    if (!group)
+        return nullptr;
+
+    return NewArrayTryUseGroup<maxLength>(cx, group, length, newKind);
+}
+
+JSObject*
+js::NewFullyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
+                                        NewObjectKind newKind)
+{
+    return NewArrayTryReuseGroup<UINT32_MAX>(cx, obj, length, newKind);
+}
+
+JSObject*
+js::NewPartlyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length)
+{
+    return NewArrayTryReuseGroup<ArrayObject::EagerAllocationMaxLength>(cx, obj, length);
+}
+
+JSObject*
+js::NewFullyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length,
+                                                   NewObjectKind newKind)
+{
+    RootedObjectGroup group(cx, ObjectGroup::callingAllocationSiteGroup(cx, JSProto_Array));
+    if (!group)
+        return nullptr;
+    return NewArrayTryUseGroup<UINT32_MAX>(cx, group, length, newKind);
+}
+
+JSObject*
+js::NewPartlyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length, HandleObject proto)
+{
+    RootedObjectGroup group(cx, ObjectGroup::callingAllocationSiteGroup(cx, JSProto_Array, proto));
+    if (!group)
+        return nullptr;
+    return NewArrayTryUseGroup<ArrayObject::EagerAllocationMaxLength>(cx, group, length);
+}
+
+bool
+js::MaybeAnalyzeBeforeCreatingLargeArray(ExclusiveContext* cx, HandleObjectGroup group,
+                                         const Value* vp, size_t length)
+{
+    static const size_t EagerPreliminaryObjectAnalysisThreshold = 800;
+
+    // Force analysis to see if an unboxed array can be used when making a
+    // sufficiently large array, to avoid excessive analysis and copying later
+    // on. If this is the first array of its group that is being created, first
+    // make a dummy array with the initial elements of the array we are about
+    // to make, so there is some basis for the unboxed array analysis.
+    if (length > EagerPreliminaryObjectAnalysisThreshold) {
+        if (PreliminaryObjectArrayWithTemplate* objects = group->maybePreliminaryObjects()) {
+            if (objects->empty()) {
+                size_t nlength = Min<size_t>(length, 100);
+                JSObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, nlength);
+                if (!obj)
+                    return false;
+                DebugOnly<DenseElementResult> result =
+                    SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, 0, vp, nlength,
+                                                              ShouldUpdateTypes::Update);
+                MOZ_ASSERT(result.value == DenseElementResult::Success);
+            }
+            objects->maybeAnalyze(cx, group, /* forceAnalyze = */ true);
+        }
+    }
+    return true;
+}
+
+JSObject*
+js::NewCopiedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group,
+                              const Value* vp, size_t length, NewObjectKind newKind,
+                              ShouldUpdateTypes updateTypes)
+{
+    if (!MaybeAnalyzeBeforeCreatingLargeArray(cx, group, vp, length))
+        return nullptr;
+
+    JSObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, length, newKind);
+    if (!obj)
+        return nullptr;
+
+    DenseElementResult result =
+        SetOrExtendAnyBoxedOrUnboxedDenseElements(cx, obj, 0, vp, length, updateTypes);
+    if (result == DenseElementResult::Failure)
+        return nullptr;
+    if (result == DenseElementResult::Success)
+        return obj;
+
+    MOZ_ASSERT(obj->is<UnboxedArrayObject>());
+    if (!UnboxedArrayObject::convertToNative(cx->asJSContext(), obj))
+        return nullptr;
+
+    result = SetOrExtendBoxedOrUnboxedDenseElements<JSVAL_TYPE_MAGIC>(cx, obj, 0, vp, length,
+                                                                      updateTypes);
+    MOZ_ASSERT(result != DenseElementResult::Incomplete);
+    if (result == DenseElementResult::Failure)
+        return nullptr;
+
+    return obj;
+}
+
+JSObject*
+js::NewCopiedArrayForCallingAllocationSite(JSContext* cx, const Value* vp, size_t length,
+                                           HandleObject proto /* = nullptr */)
+{
+    RootedObjectGroup group(cx, ObjectGroup::callingAllocationSiteGroup(cx, JSProto_Array, proto));
+    if (!group)
+        return nullptr;
+    return NewCopiedArrayTryUseGroup(cx, group, vp, length);
+}
+
+bool
+js::NewValuePair(JSContext* cx, const Value& val1, const Value& val2, MutableHandleValue rval)
+{
+    JS::AutoValueArray<2> vec(cx);
+    vec[0].set(val1);
+    vec[1].set(val2);
+
+    JSObject* aobj = js::NewDenseCopiedArray(cx, 2, vec.begin());
+    if (!aobj)
+        return false;
+    rval.setObject(*aobj);
+    return true;
+}
+
+#ifdef DEBUG
+bool
+js::ArrayInfo(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    RootedObject obj(cx);
+
+    for (unsigned i = 0; i < args.length(); i++) {
+        HandleValue arg = args[i];
+
+        UniqueChars bytes = DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, arg, nullptr);
+        if (!bytes)
+            return false;
+        if (arg.isPrimitive() ||
+            !(obj = arg.toObjectOrNull())->is<ArrayObject>()) {
+            fprintf(stderr, "%s: not array\n", bytes.get());
+            continue;
+        }
+        fprintf(stderr, "%s: (len %u", bytes.get(), obj->as<ArrayObject>().length());
+        fprintf(stderr, ", capacity %u", obj->as<ArrayObject>().getDenseCapacity());
+        fputs(")\n", stderr);
+    }
+
+    args.rval().setUndefined();
+    return true;
+}
+#endif