diff -r 000000000000 -r 6474c204b198 js/src/jsarray.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jsarray.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,3357 @@
+/* -*- 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/DebugOnly.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/MathAlgorithms.h"
+
+#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 "vm/ArgumentsObject.h"
+#include "vm/ForkJoin.h"
+#include "vm/Interpreter.h"
+#include "vm/NumericConversions.h"
+#include "vm/Shape.h"
+#include "vm/StringBuffer.h"
+
+#include "jsatominlines.h"
+
+#include "vm/ArgumentsObject-inl.h"
+#include "vm/ArrayObject-inl.h"
+#include "vm/Interpreter-inl.h"
+#include "vm/Runtime-inl.h"
+
+using namespace js;
+using namespace js::gc;
+using namespace js::types;
+
+using mozilla::Abs;
+using mozilla::ArrayLength;
+using mozilla::CeilingLog2;
+using mozilla::DebugOnly;
+using mozilla::IsNaN;
+using mozilla::PointerRangeSize;
+
+bool
+js::GetLengthProperty(JSContext *cx, HandleObject obj, uint32_t *lengthp)
+{
+    if (obj->is<ArrayObject>()) {
+        *lengthp = obj->as<ArrayObject>().length();
+        return true;
+    }
+
+    if (obj->is<ArgumentsObject>()) {
+        ArgumentsObject &argsobj = obj->as<ArgumentsObject>();
+        if (!argsobj.hasOverriddenLength()) {
+            *lengthp = argsobj.initialLength();
+            return true;
+        }
+    }
+
+    RootedValue value(cx);
+    if (!JSObject::getProperty(cx, obj, obj, cx->names().length, &value))
+        return false;
+
+    if (value.isInt32()) {
+        *lengthp = uint32_t(value.toInt32()); // uint32_t cast does ToUint32
+        return true;
+    }
+
+    return ToUint32(cx, value, lengthp);
+}
+
+/*
+ * 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 JSVAL_IS_INT(id)
+ * 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.
+ *
+ */
+JS_FRIEND_API(bool)
+js::StringIsArrayIndex(JSLinearString *str, uint32_t *indexp)
+{
+    const jschar *s = str->chars();
+    uint32_t length = str->length();
+    const jschar *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))) {
+        JS_ASSERT(index <= MAX_ARRAY_INDEX);
+        *indexp = index;
+        return true;
+    }
+
+    return false;
+}
+
+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;
+
+    RootedObject obj2(cx);
+    RootedShape prop(cx);
+    if (!JSObject::lookupGeneric(cx, obj, id, &obj2, &prop))
+        return false;
+
+    if (!prop) {
+        vp.setUndefined();
+        *hole = true;
+    } else {
+        if (!JSObject::getGeneric(cx, obj, receiver, id, vp))
+            return false;
+        *hole = false;
+    }
+    return true;
+}
+
+template<typename IndexType>
+static void
+AssertGreaterThanZero(IndexType index)
+{
+    JS_ASSERT(index >= 0);
+    JS_ASSERT(index == floor(index));
+}
+
+template<>
+void
+AssertGreaterThanZero(uint32_t index)
+{
+}
+
+template<typename IndexType>
+static bool
+GetElement(JSContext *cx, HandleObject obj, HandleObject receiver,
+           IndexType index, bool *hole, MutableHandleValue vp)
+{
+    AssertGreaterThanZero(index);
+    if (obj->isNative() && index < obj->getDenseInitializedLength()) {
+        vp.set(obj->getDenseElement(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);
+}
+
+static bool
+GetElementsSlow(JSContext *cx, HandleObject aobj, uint32_t length, Value *vp)
+{
+    for (uint32_t i = 0; i < length; i++) {
+        if (!JSObject::getElement(cx, aobj, aobj, i, MutableHandleValue::fromMarkedLocation(&vp[i])))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+js::GetElements(JSContext *cx, HandleObject aobj, uint32_t length, Value *vp)
+{
+    if (aobj->is<ArrayObject>() && length <= aobj->getDenseInitializedLength() &&
+        !ObjectMayHaveExtraIndexedProperties(aobj))
+    {
+        /* No other indexed properties so hole = undefined */
+        const Value *srcbeg = aobj->getDenseElements();
+        const Value *srcend = srcbeg + length;
+        const Value *src = srcbeg;
+        for (Value *dst = vp; src < srcend; ++dst, ++src)
+            *dst = src->isMagic(JS_ELEMENTS_HOLE) ? UndefinedValue() : *src;
+        return true;
+    }
+
+    if (aobj->is<ArgumentsObject>()) {
+        ArgumentsObject &argsobj = aobj->as<ArgumentsObject>();
+        if (!argsobj.hasOverriddenLength()) {
+            if (argsobj.maybeGetElements(0, length, vp))
+                return true;
+        }
+    }
+
+    return GetElementsSlow(cx, aobj, length, vp);
+}
+
+/*
+ * Set the value of the property at the given index to v assuming v is rooted.
+ */
+static bool
+SetArrayElement(JSContext *cx, HandleObject obj, double index, HandleValue v)
+{
+    JS_ASSERT(index >= 0);
+
+    if (obj->is<ArrayObject>() && !obj->isIndexed()) {
+        Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+        /* Predicted/prefetched code should favor the remains-dense case. */
+        JSObject::EnsureDenseResult result = JSObject::ED_SPARSE;
+        do {
+            if (index > uint32_t(-1))
+                break;
+            uint32_t idx = uint32_t(index);
+            if (idx >= arr->length() && !arr->lengthIsWritable()) {
+                JS_ReportErrorFlagsAndNumber(cx, JSREPORT_ERROR, js_GetErrorMessage, nullptr,
+                                             JSMSG_CANT_REDEFINE_ARRAY_LENGTH);
+                return false;
+            }
+            result = arr->ensureDenseElements(cx, idx, 1);
+            if (result != JSObject::ED_OK)
+                break;
+            if (idx >= arr->length())
+                arr->setLengthInt32(idx + 1);
+            arr->setDenseElementWithType(cx, idx, v);
+            return true;
+        } while (false);
+
+        if (result == JSObject::ED_FAILED)
+            return false;
+        JS_ASSERT(result == JSObject::ED_SPARSE);
+    }
+
+    RootedId id(cx);
+    if (!ToId(cx, index, &id))
+        return false;
+
+    RootedValue tmp(cx, v);
+    return JSObject::setGeneric(cx, obj, obj, id, &tmp, true);
+}
+
+/*
+ * 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 set *succeeded 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, bool *succeeded)
+{
+    JS_ASSERT(index >= 0);
+    JS_ASSERT(floor(index) == index);
+
+    if (obj->is<ArrayObject>() && !obj->isIndexed()) {
+        if (index <= UINT32_MAX) {
+            uint32_t idx = uint32_t(index);
+            if (idx < obj->getDenseInitializedLength()) {
+                obj->markDenseElementsNotPacked(cx);
+                obj->setDenseElement(idx, MagicValue(JS_ELEMENTS_HOLE));
+                if (!js_SuppressDeletedElement(cx, obj, idx))
+                    return false;
+            }
+        }
+
+        *succeeded = true;
+        return true;
+    }
+
+    if (index <= UINT32_MAX)
+        return JSObject::deleteElement(cx, obj, uint32_t(index), succeeded);
+
+    return JSObject::deleteByValue(cx, obj, DoubleValue(index), succeeded);
+}
+
+/* ES6 20130308 draft 9.3.5 */
+static bool
+DeletePropertyOrThrow(JSContext *cx, HandleObject obj, double index)
+{
+    bool succeeded;
+    if (!DeleteArrayElement(cx, obj, index, &succeeded))
+        return false;
+    if (succeeded)
+        return true;
+
+    RootedId id(cx);
+    RootedValue indexv(cx, NumberValue(index));
+    if (!ValueToId<CanGC>(cx, indexv, &id))
+        return false;
+    return obj->reportNotConfigurable(cx, id, JSREPORT_ERROR);
+}
+
+bool
+js::SetLengthProperty(JSContext *cx, HandleObject obj, double length)
+{
+    RootedValue v(cx, NumberValue(length));
+    return JSObject::setProperty(cx, obj, obj, cx->names().length, &v, true);
+}
+
+/*
+ * Since SpiderMonkey supports cross-class prototype-based delegation, we have
+ * to be careful about the length getter and setter being called on an object
+ * not of Array class. For the getter, we search obj's prototype chain for the
+ * array that caused this getter to be invoked. In the setter case to overcome
+ * the JSPROP_SHARED attribute, we must define a shadowing length property.
+ */
+static bool
+array_length_getter(JSContext *cx, HandleObject obj_, HandleId id, MutableHandleValue vp)
+{
+    RootedObject obj(cx, obj_);
+    do {
+        if (obj->is<ArrayObject>()) {
+            vp.setNumber(obj->as<ArrayObject>().length());
+            return true;
+        }
+        if (!JSObject::getProto(cx, obj, &obj))
+            return false;
+    } while (obj);
+    return true;
+}
+
+static bool
+array_length_setter(JSContext *cx, HandleObject obj, HandleId id, bool strict, MutableHandleValue vp)
+{
+    if (!obj->is<ArrayObject>()) {
+        return JSObject::defineProperty(cx, obj, cx->names().length, vp,
+                                        nullptr, nullptr, JSPROP_ENUMERATE);
+    }
+
+    Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+    MOZ_ASSERT(arr->lengthIsWritable(),
+               "setter shouldn't be called if property is non-writable");
+    return ArraySetLength<SequentialExecution>(cx, arr, id, JSPROP_PERMANENT, vp, strict);
+}
+
+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;
+    }
+};
+
+template <ExecutionMode mode>
+bool
+js::CanonicalizeArrayLengthValue(typename ExecutionModeTraits<mode>::ContextType cx,
+                                 HandleValue v, uint32_t *newLen)
+{
+    double d;
+
+    if (mode == ParallelExecution) {
+        if (v.isObject())
+            return false;
+
+        if (!NonObjectToUint32(cx, v, newLen))
+            return false;
+
+        if (!NonObjectToNumber(cx, v, &d))
+            return false;
+    } else {
+        if (!ToUint32(cx->asJSContext(), v, newLen))
+            return false;
+
+        if (!ToNumber(cx->asJSContext(), v, &d))
+            return false;
+    }
+
+    if (d == *newLen)
+        return true;
+
+    if (cx->isJSContext())
+        JS_ReportErrorNumber(cx->asJSContext(), js_GetErrorMessage, nullptr,
+                             JSMSG_BAD_ARRAY_LENGTH);
+    return false;
+}
+
+template bool
+js::CanonicalizeArrayLengthValue<SequentialExecution>(JSContext *cx,
+                                                      HandleValue v, uint32_t *newLen);
+template bool
+js::CanonicalizeArrayLengthValue<ParallelExecution>(ForkJoinContext *cx,
+                                                    HandleValue v, uint32_t *newLen);
+
+/* ES6 20130308 draft 8.4.2.4 ArraySetLength */
+template <ExecutionMode mode>
+bool
+js::ArraySetLength(typename ExecutionModeTraits<mode>::ContextType cxArg,
+                   Handle<ArrayObject*> arr, HandleId id,
+                   unsigned attrs, HandleValue value, bool setterIsStrict)
+{
+    MOZ_ASSERT(cxArg->isThreadLocal(arr));
+    MOZ_ASSERT(id == NameToId(cxArg->names().length));
+
+    /* Steps 1-2 are irrelevant in our implementation. */
+
+    /* Steps 3-5. */
+    uint32_t newLen;
+    if (!CanonicalizeArrayLengthValue<mode>(cxArg, value, &newLen))
+        return false;
+
+    // Abort if we're being asked to change enumerability or configurability.
+    // (The length property of arrays is non-configurable, so such attempts
+    // must fail.)  This behavior is spread throughout the ArraySetLength spec
+    // algorithm, but we only need check it once as our array implementation
+    // is internally so different from the spec algorithm.  (ES5 and ES6 define
+    // behavior by delegating to the default define-own-property algorithm --
+    // OrdinaryDefineOwnProperty in ES6, the default [[DefineOwnProperty]] in
+    // ES5 -- but we reimplement all the conflict-detection bits ourselves here
+    // so that we can use a customized length representation.)
+    if (!(attrs & JSPROP_PERMANENT) || (attrs & JSPROP_ENUMERATE)) {
+        if (!setterIsStrict)
+            return true;
+        // Bail for strict mode in parallel execution, as we need to go back
+        // to sequential mode to throw the error.
+        if (mode == ParallelExecution)
+            return false;
+        return Throw(cxArg->asJSContext(), id, JSMSG_CANT_REDEFINE_PROP);
+    }
+
+    /* Steps 6-7. */
+    bool lengthIsWritable = arr->lengthIsWritable();
+#ifdef DEBUG
+    {
+        RootedShape lengthShape(cxArg, arr->nativeLookupPure(id));
+        MOZ_ASSERT(lengthShape);
+        MOZ_ASSERT(lengthShape->writable() == lengthIsWritable);
+    }
+#endif
+
+    uint32_t oldLen = arr->length();
+
+    /* Steps 8-9 for arrays with non-writable length. */
+    if (!lengthIsWritable) {
+        if (newLen == oldLen)
+            return true;
+
+        if (!cxArg->isJSContext())
+            return false;
+
+        if (setterIsStrict) {
+            return JS_ReportErrorFlagsAndNumber(cxArg->asJSContext(),
+                                                JSREPORT_ERROR, js_GetErrorMessage, nullptr,
+                                                JSMSG_CANT_REDEFINE_ARRAY_LENGTH);
+        }
+
+        return JSObject::reportReadOnly(cxArg->asJSContext(), id,
+                                        JSREPORT_STRICT | JSREPORT_WARNING);
+    }
+
+    /* Step 8. */
+    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.
+        if (!arr->isIndexed()) {
+            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(cxArg, 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;
+        }
+
+        // Bail from parallel execution if need to perform step 15, which is
+        // unsafe and isn't a common case.
+        if (mode == ParallelExecution)
+            return false;
+
+        JSContext *cx = cxArg->asJSContext();
+
+        // 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. */
+                bool deleteSucceeded;
+                if (!JSObject::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 (!GetPropertyNames(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 (!js_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. */
+                bool deleteSucceeded;
+                if (!JSObject::deleteElement(cx, arr, index, &deleteSucceeded))
+                    return false;
+                if (!deleteSucceeded) {
+                    newLen = index + 1;
+                    succeeded = false;
+                    break;
+                }
+            }
+        }
+    } while (false);
+
+    /* Steps 12, 16. */
+
+    // 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(cxArg, mode == ParallelExecution
+                            ? arr->nativeLookupPure(id)
+                            : arr->nativeLookup(cxArg->asJSContext(), id));
+    if (!JSObject::changeProperty<mode>(cxArg, arr, lengthShape, attrs,
+                                        JSPROP_PERMANENT | JSPROP_READONLY | JSPROP_SHARED,
+                                        array_length_getter, array_length_setter))
+    {
+        return false;
+    }
+
+    if (mode == ParallelExecution) {
+        // Overflowing int32 requires changing TI state.
+        if (newLen > INT32_MAX)
+            return false;
+        arr->setLengthInt32(newLen);
+    } else {
+        JSContext *cx = cxArg->asJSContext();
+        arr->setLength(cx, newLen);
+    }
+
+
+    // 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(cxArg, newLen);
+            arr->getElementsHeader()->capacity = newLen;
+        }
+    }
+
+    if (setterIsStrict && !succeeded) {
+        // We can't have arrived here under ParallelExecution, as we have
+        // returned from the function before step 15 above.
+        JSContext *cx = cxArg->asJSContext();
+        RootedId elementId(cx);
+        if (!IndexToId(cx, newLen - 1, &elementId))
+            return false;
+        return arr->reportNotConfigurable(cx, elementId);
+    }
+
+    return true;
+}
+
+template bool
+js::ArraySetLength<SequentialExecution>(JSContext *cx, Handle<ArrayObject*> arr,
+                                        HandleId id, unsigned attrs, HandleValue value,
+                                        bool setterIsStrict);
+template bool
+js::ArraySetLength<ParallelExecution>(ForkJoinContext *cx, Handle<ArrayObject*> arr,
+                                      HandleId id, unsigned attrs, HandleValue value,
+                                      bool setterIsStrict);
+
+bool
+js::WouldDefinePastNonwritableLength(ThreadSafeContext *cx,
+                                     HandleObject obj, uint32_t index, bool strict,
+                                     bool *definesPast)
+{
+    if (!obj->is<ArrayObject>()) {
+        *definesPast = false;
+        return true;
+    }
+
+    Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+    uint32_t length = arr->length();
+    if (index < length) {
+        *definesPast = false;
+        return true;
+    }
+
+    if (arr->lengthIsWritable()) {
+        *definesPast = false;
+        return true;
+    }
+
+    *definesPast = true;
+
+    // Error in strict mode code or warn with strict option.
+    unsigned flags = strict ? JSREPORT_ERROR : (JSREPORT_STRICT | JSREPORT_WARNING);
+    if (cx->isForkJoinContext())
+        return cx->asForkJoinContext()->reportError(ParallelBailoutUnsupportedVM, flags);
+
+    if (!cx->isJSContext())
+        return true;
+
+    JSContext *ncx = cx->asJSContext();
+
+    if (!strict && !ncx->options().extraWarnings())
+        return true;
+
+    // XXX include the index and maybe array length in the error message
+    return JS_ReportErrorFlagsAndNumber(ncx, flags, js_GetErrorMessage, nullptr,
+                                        JSMSG_CANT_DEFINE_PAST_ARRAY_LENGTH);
+}
+
+static bool
+array_addProperty(JSContext *cx, HandleObject obj, HandleId id, MutableHandleValue vp)
+{
+    Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+
+    uint32_t index;
+    if (!js_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;
+}
+
+bool
+js::ObjectMayHaveExtraIndexedProperties(JSObject *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.
+     */
+
+    JS_ASSERT(obj->isNative());
+
+    if (obj->isIndexed())
+        return true;
+
+    /*
+     * Walk up the prototype chain and see if this indexed element already
+     * exists. If we hit the end of the prototype chain, it's safe to set the
+     * element on the original object.
+     */
+    while ((obj = obj->getProto()) != nullptr) {
+        /*
+         * If the prototype is a non-native object (possibly a dense array), or
+         * a native object (possibly a slow array) that has indexed properties,
+         * return true.
+         */
+        if (!obj->isNative())
+            return true;
+        if (obj->isIndexed())
+            return true;
+        if (obj->getDenseInitializedLength() > 0)
+            return true;
+        if (obj->is<TypedArrayObject>())
+            return true;
+    }
+
+    return false;
+}
+
+const Class ArrayObject::class_ = {
+    "Array",
+    JSCLASS_HAS_CACHED_PROTO(JSProto_Array),
+    array_addProperty,
+    JS_DeletePropertyStub,   /* delProperty */
+    JS_PropertyStub,         /* getProperty */
+    JS_StrictPropertyStub,   /* setProperty */
+    JS_EnumerateStub,
+    JS_ResolveStub,
+    JS_ConvertStub,
+    nullptr,
+    nullptr,        /* call        */
+    nullptr,        /* hasInstance */
+    nullptr,        /* construct   */
+    nullptr         /* trace       */
+};
+
+static bool
+AddLengthProperty(ExclusiveContext *cx, HandleObject 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));
+    JS_ASSERT(!obj->nativeLookup(cx, lengthId));
+
+    return JSObject::addProperty(cx, obj, lengthId, array_length_getter, array_length_setter,
+                                 SHAPE_INVALID_SLOT, JSPROP_PERMANENT | JSPROP_SHARED, 0,
+                                 /* allowDictionary = */ false);
+}
+
+#if JS_HAS_TOSOURCE
+MOZ_ALWAYS_INLINE bool
+IsArray(HandleValue v)
+{
+    return v.isObject() && v.toObject().is<ArrayObject>();
+}
+
+MOZ_ALWAYS_INLINE bool
+array_toSource_impl(JSContext *cx, CallArgs args)
+{
+    JS_ASSERT(IsArray(args.thisv()));
+
+    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;
+}
+
+static bool
+array_toSource(JSContext *cx, unsigned argc, Value *vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+    CallArgs args = CallArgsFromVp(argc, vp);
+    return CallNonGenericMethod<IsArray, array_toSource_impl>(cx, args);
+}
+#endif
+
+struct EmptySeparatorOp
+{
+    bool operator()(JSContext *, StringBuffer &sb) { return true; }
+};
+
+struct CharSeparatorOp
+{
+    jschar sep;
+    CharSeparatorOp(jschar sep) : sep(sep) {};
+    bool operator()(JSContext *, StringBuffer &sb) { return sb.append(sep); }
+};
+
+struct StringSeparatorOp
+{
+    const jschar *sepchars;
+    size_t seplen;
+
+    StringSeparatorOp(const jschar *sepchars, size_t seplen)
+      : sepchars(sepchars), seplen(seplen) {};
+
+    bool operator()(JSContext *cx, StringBuffer &sb) {
+        return sb.append(sepchars, seplen);
+    }
+};
+
+template <bool Locale, typename SeparatorOp>
+static bool
+ArrayJoinKernel(JSContext *cx, SeparatorOp sepOp, HandleObject obj, uint32_t length,
+               StringBuffer &sb)
+{
+    uint32_t i = 0;
+
+    if (!Locale && obj->is<ArrayObject>() && !ObjectMayHaveExtraIndexedProperties(obj)) {
+        // This loop handles all elements up to initializedLength. If
+        // length > initLength we rely on the second loop to add the
+        // other elements.
+        uint32_t initLength = obj->getDenseInitializedLength();
+        while (i < initLength) {
+            if (!CheckForInterrupt(cx))
+                return false;
+
+            const Value &elem = obj->getDenseElement(i);
+
+            if (elem.isString()) {
+                if (!sb.append(elem.toString()))
+                    return false;
+            } else if (elem.isNumber()) {
+                if (!NumberValueToStringBuffer(cx, elem, sb))
+                    return false;
+            } else if (elem.isBoolean()) {
+                if (!BooleanToStringBuffer(elem.toBoolean(), sb))
+                    return false;
+            } else if (elem.isObject()) {
+                /*
+                 * Object stringifying could modify the initialized length or make
+                 * the array sparse. Delegate it to a separate loop to keep this
+                 * one tight.
+                 */
+                break;
+            } else {
+                JS_ASSERT(elem.isMagic(JS_ELEMENTS_HOLE) || elem.isNullOrUndefined());
+            }
+
+            if (++i != length && !sepOp(cx, sb))
+                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 (Locale) {
+                    JSObject *robj = ToObject(cx, v);
+                    if (!robj)
+                        return false;
+                    RootedId id(cx, NameToId(cx->names().toLocaleString));
+                    if (!robj->callMethod(cx, id, 0, nullptr, &v))
+                        return false;
+                }
+                if (!ValueToStringBuffer(cx, v, sb))
+                    return false;
+            }
+
+            if (++i != length && !sepOp(cx, sb))
+                return false;
+        }
+    }
+
+    return true;
+}
+
+template <bool Locale>
+static bool
+ArrayJoin(JSContext *cx, CallArgs &args)
+{
+    // This method is shared by Array.prototype.join and
+    // Array.prototype.toLocaleString. The steps in ES5 are nearly the same, so
+    // the annotations in this function apply to both toLocaleString and join.
+
+    // 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
+    RootedString sepstr(cx, nullptr);
+    const jschar *sepchars;
+    size_t seplen;
+    if (!Locale && args.hasDefined(0)) {
+        sepstr = ToString<CanGC>(cx, args[0]);
+        if (!sepstr)
+            return false;
+        sepchars = sepstr->getChars(cx);
+        if (!sepchars)
+            return false;
+        seplen = sepstr->length();
+    } else {
+        HandlePropertyName comma = cx->names().comma;
+        sepstr = comma;
+        sepchars = comma->chars();
+        seplen = comma->length();
+    }
+
+    JS::Anchor<JSString*> anchor(sepstr);
+
+    // 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 && !Locale && obj->is<ArrayObject>() &&
+        obj->getDenseInitializedLength() == 1)
+    {
+        const Value &elem0 = obj->getDenseElement(0);
+        if (elem0.isString()) {
+            args.rval().setString(elem0.toString());
+            return true;
+        }
+    }
+
+    StringBuffer sb(cx);
+
+    // The separator will be added |length - 1| times, reserve space for that
+    // so that we don't have to unnecessarily grow the buffer.
+    if (length > 0 && !sb.reserve(seplen * (length - 1)))
+        return false;
+
+    // Various optimized versions of steps 7-10.
+    if (seplen == 0) {
+        EmptySeparatorOp op;
+        if (!ArrayJoinKernel<Locale>(cx, op, obj, length, sb))
+            return false;
+    } else if (seplen == 1) {
+        CharSeparatorOp op(sepchars[0]);
+        if (!ArrayJoinKernel<Locale>(cx, op, obj, length, sb))
+            return false;
+    } else {
+        StringSeparatorOp op(sepchars, seplen);
+        if (!ArrayJoinKernel<Locale>(cx, op, obj, length, sb))
+            return false;
+    }
+
+    // Step 11
+    JSString *str = sb.finishString();
+    if (!str)
+        return false;
+    args.rval().setString(str);
+    return true;
+}
+
+/* ES5 15.4.4.2. NB: The algorithm here differs from the one in ES3. */
+static bool
+array_toString(JSContext *cx, unsigned argc, Value *vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    CallArgs args = CallArgsFromVp(argc, vp);
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    RootedValue join(cx, args.calleev());
+    if (!JSObject::getProperty(cx, obj, obj, cx->names().join, &join))
+        return false;
+
+    if (!js_IsCallable(join)) {
+        JSString *str = JS_BasicObjectToString(cx, obj);
+        if (!str)
+            return false;
+        args.rval().setString(str);
+        return true;
+    }
+
+    InvokeArgs args2(cx);
+    if (!args2.init(0))
+        return false;
+
+    args2.setCallee(join);
+    args2.setThis(ObjectValue(*obj));
+
+    /* Do the call. */
+    if (!Invoke(cx, args2))
+        return false;
+    args.rval().set(args2.rval());
+    return true;
+}
+
+/* ES5 15.4.4.3 */
+static bool
+array_toLocaleString(JSContext *cx, unsigned argc, Value *vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    CallArgs args = CallArgsFromVp(argc, vp);
+    return ArrayJoin<true>(cx, args);
+}
+
+/* ES5 15.4.4.5 */
+static bool
+array_join(JSContext *cx, unsigned argc, Value *vp)
+{
+    JS_CHECK_RECURSION(cx, return false);
+
+    CallArgs args = CallArgsFromVp(argc, vp);
+    return ArrayJoin<false>(cx, args);
+}
+
+static inline bool
+InitArrayTypes(JSContext *cx, TypeObject *type, const Value *vector, unsigned count)
+{
+    if (!type->unknownProperties()) {
+        AutoEnterAnalysis enter(cx);
+
+        HeapTypeSet *types = type->getProperty(cx, JSID_VOID);
+        if (!types)
+            return false;
+
+        for (unsigned i = 0; i < count; i++) {
+            if (vector[i].isMagic(JS_ELEMENTS_HOLE))
+                continue;
+            Type valtype = GetValueType(vector[i]);
+            types->addType(cx, valtype);
+        }
+    }
+    return true;
+}
+
+enum ShouldUpdateTypes
+{
+    UpdateTypes = true,
+    DontUpdateTypes = false
+};
+
+/* vector must point to rooted memory. */
+static bool
+InitArrayElements(JSContext *cx, HandleObject obj, uint32_t start, uint32_t count, const Value *vector, ShouldUpdateTypes updateTypes)
+{
+    JS_ASSERT(count <= MAX_ARRAY_INDEX);
+
+    if (count == 0)
+        return true;
+
+    types::TypeObject *type = obj->getType(cx);
+    if (!type)
+        return false;
+    if (updateTypes && !InitArrayTypes(cx, type, vector, count))
+        return false;
+
+    /*
+     * Optimize for dense arrays so long as adding the given set of elements
+     * wouldn't otherwise make the array slow or exceed a non-writable array
+     * length.
+     */
+    do {
+        if (!obj->is<ArrayObject>())
+            break;
+        if (ObjectMayHaveExtraIndexedProperties(obj))
+            break;
+
+        if (obj->shouldConvertDoubleElements())
+            break;
+
+        Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+
+        if (!arr->lengthIsWritable() && start + count > arr->length())
+            break;
+
+        JSObject::EnsureDenseResult result = arr->ensureDenseElements(cx, start, count);
+        if (result != JSObject::ED_OK) {
+            if (result == JSObject::ED_FAILED)
+                return false;
+            JS_ASSERT(result == JSObject::ED_SPARSE);
+            break;
+        }
+
+        uint32_t newlen = start + count;
+        if (newlen > arr->length())
+            arr->setLengthInt32(newlen);
+
+        JS_ASSERT(count < UINT32_MAX / sizeof(Value));
+        arr->copyDenseElements(start, vector, count);
+        JS_ASSERT_IF(count != 0, !arr->getDenseElement(newlen - 1).isMagic(JS_ELEMENTS_HOLE));
+        return true;
+    } while (false);
+
+    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;
+
+    JS_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) ||
+            !JSObject::setGeneric(cx, obj, obj, id, &value, true))
+        {
+            return false;
+        }
+        index += 1;
+    } while (vector != end);
+
+    return true;
+}
+
+static bool
+array_reverse(JSContext *cx, unsigned argc, Value *vp)
+{
+    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;
+
+    do {
+        if (!obj->is<ArrayObject>())
+            break;
+        if (ObjectMayHaveExtraIndexedProperties(obj))
+            break;
+
+        /* An empty array or an array with no elements is already reversed. */
+        if (len == 0 || obj->getDenseCapacity() == 0) {
+            args.rval().setObject(*obj);
+            return true;
+        }
+
+        /*
+         * 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.
+         */
+        JSObject::EnsureDenseResult result = obj->ensureDenseElements(cx, len, 0);
+        if (result != JSObject::ED_OK) {
+            if (result == JSObject::ED_FAILED)
+                return false;
+            JS_ASSERT(result == JSObject::ED_SPARSE);
+            break;
+        }
+
+        /* Fill out the array's initialized length to its proper length. */
+        obj->ensureDenseInitializedLength(cx, len, 0);
+
+        RootedValue origlo(cx), orighi(cx);
+
+        uint32_t lo = 0, hi = len - 1;
+        for (; lo < hi; lo++, hi--) {
+            origlo = obj->getDenseElement(lo);
+            orighi = obj->getDenseElement(hi);
+            obj->setDenseElement(lo, orighi);
+            if (orighi.isMagic(JS_ELEMENTS_HOLE) &&
+                !js_SuppressDeletedProperty(cx, obj, INT_TO_JSID(lo))) {
+                return false;
+            }
+            obj->setDenseElement(hi, origlo);
+            if (origlo.isMagic(JS_ELEMENTS_HOLE) &&
+                !js_SuppressDeletedProperty(cx, obj, INT_TO_JSID(hi))) {
+                return false;
+            }
+        }
+
+        /*
+         * 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 true;
+    } while (false);
+
+    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;
+}
+
+namespace {
+
+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) {
+            JS_ASSERT((digitsa - digitsb) < ArrayLength(powersOf10));
+            *lessOrEqualp = (uint64_t(auint) < uint64_t(buint) * powersOf10[digitsa - digitsb]);
+        } else { /* if (digitsb > digitsa) */
+            JS_ASSERT((digitsb - digitsa) < ArrayLength(powersOf10));
+            *lessOrEqualp = (uint64_t(auint) * powersOf10[digitsb - digitsa] <= uint64_t(buint));
+        }
+    }
+
+    return true;
+}
+
+static inline bool
+CompareSubStringValues(JSContext *cx, const jschar *s1, size_t l1,
+                       const jschar *s2, size_t l2, bool *lessOrEqualp)
+{
+    if (!CheckForInterrupt(cx))
+        return false;
+
+    if (!s1 || !s2)
+        return false;
+
+    int32_t result = CompareChars(s1, l1, s2, l2);
+    *lessOrEqualp = (result <= 0);
+    return true;
+}
+
+struct SortComparatorStrings
+{
+    JSContext   *const cx;
+
+    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) {
+        return CompareSubStringValues(cx, sb.begin() + a.charsBegin, a.charsEnd - a.charsBegin,
+                                      sb.begin() + b.charsBegin, b.charsEnd - b.charsBegin,
+                                      lessOrEqualp);
+    }
+};
+
+struct SortComparatorFunction
+{
+    JSContext          *const cx;
+    const Value        &fval;
+    FastInvokeGuard    &fig;
+
+    SortComparatorFunction(JSContext *cx, const Value &fval, FastInvokeGuard &fig)
+      : cx(cx), fval(fval), fig(fig) { }
+
+    bool operator()(const Value &a, const Value &b, bool *lessOrEqualp);
+};
+
+bool
+SortComparatorFunction::operator()(const Value &a, const Value &b, bool *lessOrEqualp)
+{
+    /*
+     * array_sort deals with holes and undefs on its own and they should not
+     * come here.
+     */
+    JS_ASSERT(!a.isMagic() && !a.isUndefined());
+    JS_ASSERT(!a.isMagic() && !b.isUndefined());
+
+    if (!CheckForInterrupt(cx))
+        return false;
+
+    InvokeArgs &args = fig.args();
+    if (!args.init(2))
+        return false;
+
+    args.setCallee(fval);
+    args.setThis(UndefinedValue());
+    args[0].set(a);
+    args[1].set(b);
+
+    if (!fig.invoke(cx))
+        return false;
+
+    double cmp;
+    if (!ToNumber(cx, args.rval(), &cmp))
+        return false;
+
+    /*
+     * XXX eport some kind of error here if cmp is NaN? ECMA talks about
+     * 'consistent compare functions' that don't return NaN, but is silent
+     * about what the result should be. So we currently ignore it.
+     */
+    *lessOrEqualp = (IsNaN(cmp) || cmp <= 0);
+    return true;
+}
+
+struct NumericElement
+{
+    double dv;
+    size_t elementIndex;
+};
+
+bool
+ComparatorNumericLeftMinusRight(const NumericElement &a, const NumericElement &b,
+                                bool *lessOrEqualp)
+{
+    *lessOrEqualp = (a.dv <= b.dv);
+    return true;
+}
+
+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);
+
+ComparatorNumeric SortComparatorNumerics[] = {
+    nullptr,
+    nullptr,
+    ComparatorNumericLeftMinusRight,
+    ComparatorNumericRightMinusLeft
+};
+
+bool
+ComparatorInt32LeftMinusRight(const Value &a, const Value &b, bool *lessOrEqualp)
+{
+    *lessOrEqualp = (a.toInt32() <= b.toInt32());
+    return true;
+}
+
+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);
+
+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
+};
+
+/*
+ * Specialize behavior for comparator functions with particular common bytecode
+ * patterns: namely, |return x - y| and |return y - x|.
+ */
+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())
+        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, AutoValueVector *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] = (*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] = 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.
+ */
+bool
+SortLexicographically(JSContext *cx, AutoValueVector *vec, size_t len)
+{
+    JS_ASSERT(vec->length() >= len);
+
+    StringBuffer sb(cx);
+    Vector<StringifiedElement, 0, TempAllocPolicy> strElements(cx);
+
+    /* MergeSort uses the upper half as scratch space. */
+    if (!strElements.reserve(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;
+
+        StringifiedElement el = { cursor, sb.length(), i };
+        strElements.infallibleAppend(el);
+        cursor = sb.length();
+    }
+
+    /* Resize strElements so we can perform MergeSort. */
+    JS_ALWAYS_TRUE(strElements.resize(2 * len));
+
+    /* 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.
+ */
+bool
+SortNumerically(JSContext *cx, AutoValueVector *vec, size_t len, ComparatorMatchResult comp)
+{
+    JS_ASSERT(vec->length() >= len);
+
+    Vector<NumericElement, 0, TempAllocPolicy> numElements(cx);
+
+    /* MergeSort uses the upper half as scratch space. */
+    if (!numElements.reserve(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->handleAt(i), &dv))
+            return false;
+
+        NumericElement el = { dv, i };
+        numElements.infallibleAppend(el);
+    }
+
+    /* Resize strElements so we can perform MergeSort. */
+    JS_ALWAYS_TRUE(numElements.resize(2 * len));
+
+    /* Sort Values in vec numerically. */
+    return MergeSortByKey(numElements.begin(), len, numElements.begin() + len,
+                          SortComparatorNumerics[comp], vec);
+}
+
+} /* namespace anonymous */
+
+bool
+js::array_sort(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    RootedValue fvalRoot(cx);
+    Value &fval = fvalRoot.get();
+
+    if (args.hasDefined(0)) {
+        if (args[0].isPrimitive()) {
+            JS_ReportErrorNumber(cx, js_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;
+
+    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))) {
+        js_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;
+    {
+        AutoValueVector vec(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;
+        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 {
+            ComparatorMatchResult comp = MatchNumericComparator(cx, fval);
+            if (comp == Match_Failure)
+                return false;
+
+            if (comp != Match_None) {
+                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;
+                }
+            } else {
+                FastInvokeGuard fig(cx, fval);
+                MOZ_ASSERT(!InParallelSection(),
+                           "Array.sort() can't currently be used from parallel code");
+                JS_ALWAYS_TRUE(vec.resize(n * 2));
+                if (!MergeSort(vec.begin(), n, vec.begin() + n,
+                               SortComparatorFunction(cx, fval, fig)))
+                {
+                    return false;
+                }
+            }
+        }
+
+        if (!InitArrayElements(cx, obj, 0, uint32_t(n), vec.begin(), DontUpdateTypes))
+            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>());
+
+    JS_ASSERT(!v.isMagic());
+    JS_ASSERT(arr->lengthIsWritable());
+
+    uint32_t length = arr->length();
+    JS_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)
+{
+    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;
+
+    /* Fast path for native objects with dense elements. */
+    do {
+        if (!obj->isNative() || obj->is<TypedArrayObject>())
+            break;
+
+        if (obj->is<ArrayObject>() && !obj->as<ArrayObject>().lengthIsWritable())
+            break;
+
+        if (ObjectMayHaveExtraIndexedProperties(obj))
+            break;
+
+        uint32_t argCount = args.length();
+        JSObject::EnsureDenseResult result = obj->ensureDenseElements(cx, length, argCount);
+        if (result == JSObject::ED_FAILED)
+            return false;
+
+        if (result == JSObject::ED_OK) {
+            for (uint32_t i = 0, index = length; i < argCount; index++, i++)
+                obj->setDenseElementWithType(cx, index, args[i]);
+            uint32_t newlength = length + argCount;
+            args.rval().setNumber(newlength);
+            if (obj->is<ArrayObject>()) {
+                obj->as<ArrayObject>().setLengthInt32(newlength);
+                return true;
+            }
+            return SetLengthProperty(cx, obj, newlength);
+        }
+
+        MOZ_ASSERT(result == JSObject::ED_SPARSE);
+    } while (false);
+
+    /* Steps 4-5. */
+    if (!InitArrayElements(cx, obj, length, args.length(), args.array(), UpdateTypes))
+        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)
+{
+    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;
+    }
+
+    // If this was an array, then there are no elements above the one we just
+    // deleted (if we deleted an element).  Thus we can shrink the dense
+    // initialized length accordingly.  (This is fine even if the array length
+    // is non-writable: length-changing occurs after element-deletion effects.)
+    // Don't do anything if this isn't an array, as any deletion above has no
+    // effect on any elements after the "last" one indicated by the "length"
+    // property.
+    if (obj->is<ArrayObject>() && obj->getDenseInitializedLength() > index)
+        obj->setDenseInitializedLength(index);
+
+    /* Steps 4a, 5d. */
+    return SetLengthProperty(cx, obj, index);
+}
+
+void
+js::ArrayShiftMoveElements(JSObject *obj)
+{
+    JS_ASSERT(obj->is<ArrayObject>());
+    JS_ASSERT(obj->as<ArrayObject>().lengthIsWritable());
+
+    /*
+     * At this point the length and initialized length have already been
+     * decremented and the result fetched, so just shift the array elements
+     * themselves.
+     */
+    uint32_t initlen = obj->getDenseInitializedLength();
+    obj->moveDenseElementsNoPreBarrier(0, 1, initlen);
+}
+
+/* ES5 15.4.4.9 */
+bool
+js::array_shift(JSContext *cx, unsigned argc, Value *vp)
+{
+    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. */
+    if (obj->is<ArrayObject>() &&
+        obj->getDenseInitializedLength() > 0 &&
+        newlen < obj->getDenseCapacity() &&
+        !ObjectMayHaveExtraIndexedProperties(obj))
+    {
+        args.rval().set(obj->getDenseElement(0));
+        if (args.rval().isMagic(JS_ELEMENTS_HOLE))
+            args.rval().setUndefined();
+
+        obj->moveDenseElements(0, 1, obj->getDenseInitializedLength() - 1);
+        obj->setDenseInitializedLength(obj->getDenseInitializedLength() - 1);
+
+        if (!SetLengthProperty(cx, obj, newlen))
+            return false;
+
+        return js_SuppressDeletedProperty(cx, obj, INT_TO_JSID(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);
+}
+
+static bool
+array_unshift(JSContext *cx, unsigned argc, Value *vp)
+{
+    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) {
+            bool optimized = false;
+            do {
+                if (!obj->is<ArrayObject>())
+                    break;
+                if (ObjectMayHaveExtraIndexedProperties(obj))
+                    break;
+                if (!obj->as<ArrayObject>().lengthIsWritable())
+                    break;
+                JSObject::EnsureDenseResult result = obj->ensureDenseElements(cx, length, args.length());
+                if (result != JSObject::ED_OK) {
+                    if (result == JSObject::ED_FAILED)
+                        return false;
+                    JS_ASSERT(result == JSObject::ED_SPARSE);
+                    break;
+                }
+                obj->moveDenseElements(args.length(), 0, length);
+                for (uint32_t i = 0; i < args.length(); i++)
+                    obj->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(), UpdateTypes))
+            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;
+}
+
+static inline void
+TryReuseArrayType(JSObject *obj, ArrayObject *narr)
+{
+    /*
+     * Try to change the type of a newly created array narr to the same type
+     * as obj. This can only be performed if the original object is an array
+     * and has the same prototype.
+     */
+    JS_ASSERT(narr->getProto()->hasNewType(&ArrayObject::class_, narr->type()));
+
+    if (obj->is<ArrayObject>() && !obj->hasSingletonType() && obj->getProto() == narr->getProto())
+        narr->setType(obj->type());
+}
+
+/*
+ * Returns true if this is a dense 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>())
+        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 JSObject::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.
+     *
+     * Another potential wrinkle: what if the enumeration is happening on an
+     * object which merely has |arr| on its prototype chain?  It turns out this
+     * case can't happen, because any dense array used as the prototype of
+     * another object is first slowified, for type inference's sake.
+     */
+    types::TypeObject *arrType = arr->getType(cx);
+    if (MOZ_UNLIKELY(!arrType || arrType->hasAllFlags(OBJECT_FLAG_ITERATED)))
+        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 <= arr->getDenseInitializedLength();
+}
+
+/* ES5 15.4.4.12. */
+bool
+js::array_splice(JSContext *cx, unsigned argc, Value *vp)
+{
+    return array_splice_impl(cx, argc, vp, true);
+}
+
+bool
+js::array_splice_impl(JSContext *cx, unsigned argc, Value *vp, bool returnValueIsUsed)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    /* Steps 3-4. */
+    uint32_t len;
+    if (!GetLengthProperty(cx, obj, &len))
+        return false;
+
+    /* Step 5. */
+    double relativeStart;
+    if (!ToInteger(cx, args.get(0), &relativeStart))
+        return false;
+
+    /* Step 6. */
+    uint32_t actualStart;
+    if (relativeStart < 0)
+        actualStart = Max(len + relativeStart, 0.0);
+    else
+        actualStart = Min(relativeStart, double(len));
+
+    /* Step 7. */
+    uint32_t actualDeleteCount;
+    if (args.length() != 1) {
+        double deleteCountDouble;
+        RootedValue cnt(cx, args.length() >= 2 ? args[1] : Int32Value(0));
+        if (!ToInteger(cx, cnt, &deleteCountDouble))
+            return false;
+        actualDeleteCount = Min(Max(deleteCountDouble, 0.0), double(len - actualStart));
+    } else {
+        /*
+         * Non-standard: if start was specified but deleteCount was omitted,
+         * delete to the end of the array.  See bug 668024 for discussion.
+         */
+        actualDeleteCount = len - actualStart;
+    }
+
+    JS_ASSERT(len - actualStart >= actualDeleteCount);
+
+    /* Steps 2, 8-9. */
+    Rooted<ArrayObject*> arr(cx);
+    if (CanOptimizeForDenseStorage(obj, actualStart, actualDeleteCount, cx)) {
+        if (returnValueIsUsed) {
+            arr = NewDenseCopiedArray(cx, actualDeleteCount, obj, actualStart);
+            if (!arr)
+                return false;
+            TryReuseArrayType(obj, arr);
+        }
+    } else {
+        arr = NewDenseAllocatedArray(cx, actualDeleteCount);
+        if (!arr)
+            return false;
+        TryReuseArrayType(obj, arr);
+
+        RootedValue fromValue(cx);
+        for (uint32_t k = 0; k < actualDeleteCount; k++) {
+            bool hole;
+            if (!CheckForInterrupt(cx) ||
+                !GetElement(cx, obj, actualStart + k, &hole, &fromValue) ||
+                (!hole && !JSObject::defineElement(cx, arr, k, fromValue)))
+            {
+                return false;
+            }
+        }
+    }
+
+    /* Step 11. */
+    uint32_t itemCount = (args.length() >= 2) ? (args.length() - 2) : 0;
+
+    if (itemCount < actualDeleteCount) {
+        /* Step 12: 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 12(a)-(b). */
+            obj->moveDenseElements(targetIndex, sourceIndex, len - sourceIndex);
+
+            /*
+             * Update the initialized length. Do so before shrinking so that we
+             * can apply the write barrier to the old slots.
+             */
+            obj->setDenseInitializedLength(finalLength);
+
+            /* Steps 12(c)-(d). */
+            obj->shrinkElements(cx, 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 12(a)-(b). */
+            RootedValue fromValue(cx);
+            for (uint32_t from = sourceIndex, to = targetIndex; from < len; from++, to++) {
+                if (!CheckForInterrupt(cx))
+                    return false;
+
+                bool hole;
+                if (!GetElement(cx, obj, from, &hole, &fromValue))
+                    return false;
+                if (hole) {
+                    if (!DeletePropertyOrThrow(cx, obj, to))
+                        return false;
+                } else {
+                    if (!SetArrayElement(cx, obj, to, fromValue))
+                        return false;
+                }
+            }
+
+            /* Steps 12(c)-(d). */
+            for (uint32_t k = len; k > finalLength; k--) {
+                if (!DeletePropertyOrThrow(cx, obj, k - 1))
+                    return false;
+            }
+        }
+    } else if (itemCount > actualDeleteCount) {
+        /* Step 13. */
+
+        /*
+         * 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()) {
+                JSObject::EnsureDenseResult res =
+                    arr->ensureDenseElements(cx, arr->length(), itemCount - actualDeleteCount);
+                if (res == JSObject::ED_FAILED)
+                    return false;
+            }
+        }
+
+        if (CanOptimizeForDenseStorage(obj, len, itemCount - actualDeleteCount, cx)) {
+            obj->moveDenseElements(actualStart + itemCount,
+                                   actualStart + actualDeleteCount,
+                                   len - (actualStart + actualDeleteCount));
+            obj->setDenseInitializedLength(len + itemCount - actualDeleteCount);
+        } else {
+            RootedValue fromValue(cx);
+            for (double k = len - actualDeleteCount; k > actualStart; k--) {
+                if (!CheckForInterrupt(cx))
+                    return false;
+
+                double from = k + actualDeleteCount - 1;
+                double to = k + itemCount - 1;
+
+                bool hole;
+                if (!GetElement(cx, obj, from, &hole, &fromValue))
+                    return false;
+
+                if (hole) {
+                    if (!DeletePropertyOrThrow(cx, obj, to))
+                        return false;
+                } else {
+                    if (!SetArrayElement(cx, obj, to, fromValue))
+                        return false;
+                }
+            }
+        }
+    }
+
+    /* Step 10. */
+    Value *items = args.array() + 2;
+
+    /* Steps 14-15. */
+    for (uint32_t k = actualStart, i = 0; i < itemCount; i++, k++) {
+        if (!SetArrayElement(cx, obj, k, HandleValue::fromMarkedLocation(&items[i])))
+            return false;
+    }
+
+    /* Step 16. */
+    double finalLength = double(len) - actualDeleteCount + itemCount;
+    if (!SetLengthProperty(cx, obj, finalLength))
+        return false;
+
+    /* Step 17. */
+    if (returnValueIsUsed)
+        args.rval().setObject(*arr);
+
+    return true;
+}
+
+#ifdef JS_ION
+bool
+js::array_concat_dense(JSContext *cx, Handle<ArrayObject*> arr1, Handle<ArrayObject*> arr2,
+                       Handle<ArrayObject*> result)
+{
+    uint32_t initlen1 = arr1->getDenseInitializedLength();
+    JS_ASSERT(initlen1 == arr1->length());
+
+    uint32_t initlen2 = arr2->getDenseInitializedLength();
+    JS_ASSERT(initlen2 == arr2->length());
+
+    /* No overflow here due to nelements limit. */
+    uint32_t len = initlen1 + initlen2;
+
+    if (!result->ensureElements(cx, len))
+        return false;
+
+    JS_ASSERT(!result->getDenseInitializedLength());
+    result->setDenseInitializedLength(len);
+
+    result->initDenseElements(0, arr1->getDenseElements(), initlen1);
+    result->initDenseElements(initlen1, arr2->getDenseElements(), initlen2);
+    result->setLengthInt32(len);
+    return true;
+}
+#endif /* JS_ION */
+
+/*
+ * Python-esque sequence operations.
+ */
+bool
+js::array_concat(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Treat our |this| object as the first argument; see ECMA 15.4.4.4. */
+    Value *p = args.array() - 1;
+
+    /* Create a new Array object and root it using *vp. */
+    RootedObject aobj(cx, ToObject(cx, args.thisv()));
+    if (!aobj)
+        return false;
+
+    Rooted<ArrayObject*> narr(cx);
+    uint32_t length;
+    if (aobj->is<ArrayObject>() && !aobj->isIndexed()) {
+        length = aobj->as<ArrayObject>().length();
+        uint32_t initlen = aobj->getDenseInitializedLength();
+        narr = NewDenseCopiedArray(cx, initlen, aobj, 0);
+        if (!narr)
+            return false;
+        TryReuseArrayType(aobj, narr);
+        narr->setLength(cx, length);
+        args.rval().setObject(*narr);
+        if (argc == 0)
+            return true;
+        argc--;
+        p++;
+    } else {
+        narr = NewDenseEmptyArray(cx);
+        if (!narr)
+            return false;
+        args.rval().setObject(*narr);
+        length = 0;
+    }
+
+    /* Loop over [0, argc] to concat args into narr, expanding all Arrays. */
+    for (unsigned i = 0; i <= argc; i++) {
+        if (!CheckForInterrupt(cx))
+            return false;
+        HandleValue v = HandleValue::fromMarkedLocation(&p[i]);
+        if (v.isObject()) {
+            RootedObject obj(cx, &v.toObject());
+            if (ObjectClassIs(obj, ESClass_Array, cx)) {
+                uint32_t alength;
+                if (!GetLengthProperty(cx, obj, &alength))
+                    return false;
+                RootedValue tmp(cx);
+                for (uint32_t slot = 0; slot < alength; slot++) {
+                    bool hole;
+                    if (!CheckForInterrupt(cx) || !GetElement(cx, obj, slot, &hole, &tmp))
+                        return false;
+
+                    /*
+                     * Per ECMA 262, 15.4.4.4, step 9, ignore nonexistent
+                     * properties.
+                     */
+                    if (!hole && !SetArrayElement(cx, narr, length + slot, tmp))
+                        return false;
+                }
+                length += alength;
+                continue;
+            }
+        }
+
+        if (!SetArrayElement(cx, narr, length, v))
+            return false;
+        length++;
+    }
+
+    return SetLengthProperty(cx, narr, length);
+}
+
+static bool
+array_slice(JSContext *cx, unsigned argc, Value *vp)
+{
+    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;
+
+    uint32_t begin = 0;
+    uint32_t end = length;
+    if (args.length() > 0) {
+        double d;
+        if (!ToInteger(cx, args[0], &d))
+            return false;
+        if (d < 0) {
+            d += length;
+            if (d < 0)
+                d = 0;
+        } else if (d > length) {
+            d = length;
+        }
+        begin = (uint32_t)d;
+
+        if (args.hasDefined(1)) {
+            if (!ToInteger(cx, args[1], &d))
+                return false;
+            if (d < 0) {
+                d += length;
+                if (d < 0)
+                    d = 0;
+            } else if (d > length) {
+                d = length;
+            }
+            end = (uint32_t)d;
+        }
+    }
+
+    if (begin > end)
+        begin = end;
+
+    Rooted<ArrayObject*> narr(cx);
+    narr = NewDenseAllocatedArray(cx, end - begin);
+    if (!narr)
+        return false;
+    TryReuseArrayType(obj, narr);
+
+    if (obj->is<ArrayObject>() && !ObjectMayHaveExtraIndexedProperties(obj)) {
+        if (obj->getDenseInitializedLength() > begin) {
+            uint32_t numSourceElements = obj->getDenseInitializedLength() - begin;
+            uint32_t initLength = Min(numSourceElements, end - begin);
+            narr->setDenseInitializedLength(initLength);
+            narr->initDenseElements(0, &obj->getDenseElement(begin), initLength);
+        }
+        args.rval().setObject(*narr);
+        return true;
+    }
+
+    if (js::SliceOp op = obj->getOps()->slice) {
+        // Ensure that we have dense elements, so that DOM can use js::UnsafeDefineElement.
+        JSObject::EnsureDenseResult result = narr->ensureDenseElements(cx, 0, end - begin);
+        if (result == JSObject::ED_FAILED)
+             return false;
+
+        if (result == JSObject::ED_OK) {
+            if (!op(cx, obj, begin, end, narr))
+                return false;
+
+            args.rval().setObject(*narr);
+            return true;
+        }
+
+        // Fallthrough
+        JS_ASSERT(result == JSObject::ED_SPARSE);
+    }
+
+
+    if (!SliceSlowly(cx, obj, obj, begin, end, narr))
+        return false;
+
+    args.rval().setObject(*narr);
+    return true;
+}
+
+JS_FRIEND_API(bool)
+js::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 && !JSObject::defineElement(cx, result, slot - begin, value))
+            return false;
+    }
+    return true;
+}
+
+/* ES5 15.4.4.20. */
+static bool
+array_filter(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    /* Step 1. */
+    RootedObject obj(cx, ToObject(cx, args.thisv()));
+    if (!obj)
+        return false;
+
+    /* Step 2-3. */
+    uint32_t len;
+    if (!GetLengthProperty(cx, obj, &len))
+        return false;
+
+    /* Step 4. */
+    if (args.length() == 0) {
+        js_ReportMissingArg(cx, args.calleev(), 0);
+        return false;
+    }
+    RootedObject callable(cx, ValueToCallable(cx, args[0], args.length() - 1));
+    if (!callable)
+        return false;
+
+    /* Step 5. */
+    RootedValue thisv(cx, args.length() >= 2 ? args[1] : UndefinedValue());
+
+    /* Step 6. */
+    RootedObject arr(cx, NewDenseAllocatedArray(cx, 0));
+    if (!arr)
+        return false;
+    TypeObject *newtype = GetTypeCallerInitObject(cx, JSProto_Array);
+    if (!newtype)
+        return false;
+    arr->setType(newtype);
+
+    /* Step 7. */
+    uint32_t k = 0;
+
+    /* Step 8. */
+    uint32_t to = 0;
+
+    /* Step 9. */
+    JS_ASSERT(!InParallelSection());
+    FastInvokeGuard fig(cx, ObjectValue(*callable));
+    InvokeArgs &args2 = fig.args();
+    RootedValue kValue(cx);
+    while (k < len) {
+        if (!CheckForInterrupt(cx))
+            return false;
+
+        /* Step a, b, and c.i. */
+        bool kNotPresent;
+        if (!GetElement(cx, obj, k, &kNotPresent, &kValue))
+            return false;
+
+        /* Step c.ii-iii. */
+        if (!kNotPresent) {
+            if (!args2.init(3))
+                return false;
+            args2.setCallee(ObjectValue(*callable));
+            args2.setThis(thisv);
+            args2[0].set(kValue);
+            args2[1].setNumber(k);
+            args2[2].setObject(*obj);
+            if (!fig.invoke(cx))
+                return false;
+
+            if (ToBoolean(args2.rval())) {
+                if (!SetArrayElement(cx, arr, to, kValue))
+                    return false;
+                to++;
+            }
+        }
+
+        /* Step d. */
+        k++;
+    }
+
+    /* Step 10. */
+    args.rval().setObject(*arr);
+    return true;
+}
+
+static bool
+array_isArray(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    bool isArray = args.length() > 0 && IsObjectWithClass(args[0], ESClass_Array, cx);
+    args.rval().setBoolean(isArray);
+    return true;
+}
+
+static bool
+IsArrayConstructor(const Value &v)
+{
+    // 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 v.isObject() &&
+           v.toObject().is<JSFunction>() &&
+           v.toObject().as<JSFunction>().isNative() &&
+           v.toObject().as<JSFunction>().native() == js_Array;
+}
+
+static bool
+ArrayFromCallArgs(JSContext *cx, RootedTypeObject &type, CallArgs &args)
+{
+    if (!InitArrayTypes(cx, type, args.array(), args.length()))
+        return false;
+    JSObject *obj = (args.length() == 0)
+        ? NewDenseEmptyArray(cx)
+        : NewDenseCopiedArray(cx, args.length(), args.array());
+    if (!obj)
+        return false;
+    obj->setType(type);
+    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.
+        RootedTypeObject type(cx, GetTypeCallerInitObject(cx, JSProto_Array));
+        if (!type)
+            return false;
+        return ArrayFromCallArgs(cx, type, args);
+    }
+
+    // Step 4.
+    RootedObject obj(cx);
+    {
+        RootedValue v(cx);
+        Value argv[1] = {NumberValue(args.length())};
+        if (!InvokeConstructor(cx, args.thisv(), 1, argv, v.address()))
+            return false;
+        obj = ToObject(cx, v);
+        if (!obj)
+            return false;
+    }
+
+    // Step 8.
+    for (unsigned k = 0; k < args.length(); k++) {
+        if (!JSObject::defineElement(cx, obj, k, args[k]))
+            return false;
+    }
+
+    // Steps 9-10.
+    RootedValue v(cx, NumberValue(args.length()));
+    if (!JSObject::setProperty(cx, obj, obj, cx->names().length, &v, true))
+        return false;
+
+    // Step 11.
+    args.rval().setObject(*obj);
+    return true;
+}
+
+#define GENERIC JSFUN_GENERIC_NATIVE
+
+static const JSFunctionSpec array_methods[] = {
+#if JS_HAS_TOSOURCE
+    JS_FN(js_toSource_str,      array_toSource,     0,0),
+#endif
+    JS_FN(js_toString_str,      array_toString,     0,0),
+    JS_FN(js_toLocaleString_str,array_toLocaleString,0,0),
+
+    /* Perl-ish methods. */
+    JS_FN("join",               array_join,         1,JSFUN_GENERIC_NATIVE),
+    JS_FN("reverse",            array_reverse,      0,JSFUN_GENERIC_NATIVE),
+    JS_FN("sort",               array_sort,         1,JSFUN_GENERIC_NATIVE),
+    JS_FN("push",               array_push,         1,JSFUN_GENERIC_NATIVE),
+    JS_FN("pop",                array_pop,          0,JSFUN_GENERIC_NATIVE),
+    JS_FN("shift",              array_shift,        0,JSFUN_GENERIC_NATIVE),
+    JS_FN("unshift",            array_unshift,      1,JSFUN_GENERIC_NATIVE),
+    JS_FN("splice",             array_splice,       2,JSFUN_GENERIC_NATIVE),
+
+    /* Pythonic sequence methods. */
+    JS_FN("concat",             array_concat,       1,JSFUN_GENERIC_NATIVE),
+    JS_FN("slice",              array_slice,        2,JSFUN_GENERIC_NATIVE),
+
+    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("reduce",      "ArrayReduce",      1,0),
+    JS_SELF_HOSTED_FN("reduceRight", "ArrayReduceRight", 1,0),
+    JS_FN("filter",             array_filter,       1,JSFUN_GENERIC_NATIVE),
+    JS_SELF_HOSTED_FN("some",        "ArraySome",        1,0),
+    JS_SELF_HOSTED_FN("every",       "ArrayEvery",       1,0),
+
+#ifdef ENABLE_PARALLEL_JS
+    /* Parallelizable and pure methods. */
+    JS_SELF_HOSTED_FN("mapPar",      "ArrayMapPar",      2,0),
+    JS_SELF_HOSTED_FN("reducePar",   "ArrayReducePar",   2,0),
+    JS_SELF_HOSTED_FN("scanPar",     "ArrayScanPar",     2,0),
+    JS_SELF_HOSTED_FN("scatterPar",  "ArrayScatterPar",  5,0),
+    JS_SELF_HOSTED_FN("filterPar",   "ArrayFilterPar",   2,0),
+#endif
+
+    /* ES6 additions */
+    JS_SELF_HOSTED_FN("find",        "ArrayFind",        1,0),
+    JS_SELF_HOSTED_FN("findIndex",   "ArrayFindIndex",   1,0),
+
+    JS_SELF_HOSTED_FN("fill",        "ArrayFill",        3,0),
+
+    JS_SELF_HOSTED_FN("@@iterator",  "ArrayValues",      0,0),
+    JS_SELF_HOSTED_FN("entries",     "ArrayEntries",     0,0),
+    JS_SELF_HOSTED_FN("keys",        "ArrayKeys",        0,0),
+    JS_FS_END
+};
+
+static const JSFunctionSpec array_static_methods[] = {
+    JS_FN("isArray",            array_isArray,      1,0),
+    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("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_FN("of",                 array_of,           0,0),
+
+#ifdef ENABLE_PARALLEL_JS
+    JS_SELF_HOSTED_FN("build",       "ArrayStaticBuild", 2,0),
+    /* Parallelizable and pure static methods. */
+    JS_SELF_HOSTED_FN("buildPar",    "ArrayStaticBuildPar", 3,0),
+#endif
+
+    JS_FS_END
+};
+
+/* ES5 15.4.2 */
+bool
+js_Array(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    RootedTypeObject type(cx, GetTypeCallerInitObject(cx, JSProto_Array));
+    if (!type)
+        return false;
+
+    if (args.length() != 1 || !args[0].isNumber())
+        return ArrayFromCallArgs(cx, type, args);
+
+    uint32_t length;
+    if (args[0].isInt32()) {
+        int32_t i = args[0].toInt32();
+        if (i < 0) {
+            JS_ReportErrorNumber(cx, js_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_ReportErrorNumber(cx, js_GetErrorMessage, nullptr, JSMSG_BAD_ARRAY_LENGTH);
+            return false;
+        }
+    }
+
+    /*
+     * Allocate dense elements eagerly for small arrays, to avoid reallocating
+     * elements when filling the array.
+     */
+    RootedObject obj(cx);
+    obj = (length <= ArrayObject::EagerAllocationMaxLength)
+          ? NewDenseAllocatedArray(cx, length)
+          : NewDenseUnallocatedArray(cx, length);
+    if (!obj)
+        return false;
+    Rooted<ArrayObject*> arr(cx, &obj->as<ArrayObject>());
+
+    arr->setType(type);
+
+    /* If the length calculation overflowed, make sure that is marked for the new type. */
+    if (arr->length() > INT32_MAX)
+        arr->setLength(cx, arr->length());
+
+    args.rval().setObject(*arr);
+    return true;
+}
+
+JSObject *
+js_InitArrayClass(JSContext *cx, HandleObject obj)
+{
+    JS_ASSERT(obj->isNative());
+
+    Rooted<GlobalObject*> global(cx, &obj->as<GlobalObject>());
+
+    RootedObject proto(cx, global->getOrCreateObjectPrototype(cx));
+    if (!proto)
+        return nullptr;
+
+    RootedTypeObject type(cx, cx->getNewType(&ArrayObject::class_, proto.get()));
+    if (!type)
+        return nullptr;
+
+    JSObject *metadata = nullptr;
+    if (!NewObjectMetadata(cx, &metadata))
+        return nullptr;
+
+    RootedShape shape(cx, EmptyShape::getInitialShape(cx, &ArrayObject::class_, TaggedProto(proto),
+                                                      proto->getParent(), metadata,
+                                                      gc::FINALIZE_OBJECT0));
+    if (!shape)
+        return nullptr;
+
+    RootedObject arrayProto(cx, JSObject::createArray(cx, gc::FINALIZE_OBJECT4, gc::TenuredHeap, shape, type, 0));
+    if (!arrayProto || !JSObject::setSingletonType(cx, arrayProto) || !AddLengthProperty(cx, arrayProto))
+        return nullptr;
+
+    RootedFunction ctor(cx);
+    ctor = global->createConstructor(cx, js_Array, cx->names().Array, 1);
+    if (!ctor)
+        return nullptr;
+
+    /*
+     * The default 'new' type 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::setNewTypeUnknown(cx, &ArrayObject::class_, arrayProto))
+        return nullptr;
+
+    if (!LinkConstructorAndPrototype(cx, ctor, arrayProto))
+        return nullptr;
+
+    if (!DefinePropertiesAndBrand(cx, arrayProto, nullptr, array_methods) ||
+        !DefinePropertiesAndBrand(cx, ctor, nullptr, array_static_methods))
+    {
+        return nullptr;
+    }
+
+    if (!GlobalObject::initBuiltinConstructor(cx, global, JSProto_Array, ctor, arrayProto))
+        return nullptr;
+
+    return arrayProto;
+}
+
+/*
+ * Array allocation functions.
+ */
+
+static inline bool
+EnsureNewArrayElements(ExclusiveContext *cx, JSObject *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;
+
+    JS_ASSERT_IF(cap, !obj->hasDynamicElements());
+
+    return true;
+}
+
+template<bool allocateCapacity>
+static MOZ_ALWAYS_INLINE ArrayObject *
+NewArray(ExclusiveContext *cxArg, uint32_t length,
+         JSObject *protoArg, NewObjectKind newKind = GenericObject)
+{
+    gc::AllocKind allocKind = GuessArrayGCKind(length);
+    JS_ASSERT(CanBeFinalizedInBackground(allocKind, &ArrayObject::class_));
+    allocKind = GetBackgroundAllocKind(allocKind);
+
+    NewObjectCache::EntryIndex entry = -1;
+    if (JSContext *cx = cxArg->maybeJSContext()) {
+        NewObjectCache &cache = cx->runtime()->newObjectCache;
+        if (newKind == GenericObject &&
+            !cx->compartment()->hasObjectMetadataCallback() &&
+            cache.lookupGlobal(&ArrayObject::class_, cx->global(), allocKind, &entry))
+        {
+            gc::InitialHeap heap = GetInitialHeap(newKind, &ArrayObject::class_);
+            JSObject *obj = cache.newObjectFromHit<NoGC>(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 (allocateCapacity && !EnsureNewArrayElements(cx, arr, length))
+                    return nullptr;
+                return arr;
+            } else {
+                RootedObject proto(cxArg, protoArg);
+                obj = cache.newObjectFromHit<CanGC>(cx, entry, heap);
+                JS_ASSERT(!obj);
+                protoArg = proto;
+            }
+        }
+    }
+
+    RootedObject proto(cxArg, protoArg);
+    if (protoArg)
+        JS::PoisonPtr(&protoArg);
+
+    if (!proto && !GetBuiltinPrototype(cxArg, JSProto_Array, &proto))
+        return nullptr;
+
+    RootedTypeObject type(cxArg, cxArg->getNewType(&ArrayObject::class_, proto.get()));
+    if (!type)
+        return nullptr;
+
+    JSObject *metadata = nullptr;
+    if (!NewObjectMetadata(cxArg, &metadata))
+        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), cxArg->global(),
+                                                         metadata, gc::FINALIZE_OBJECT0));
+    if (!shape)
+        return nullptr;
+
+    Rooted<ArrayObject*> arr(cxArg, JSObject::createArray(cxArg, allocKind,
+                                                          GetInitialHeap(newKind, &ArrayObject::class_),
+                                                          shape, type, length));
+    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::setSingletonType(cxArg, arr))
+        return nullptr;
+
+    if (entry != -1) {
+        cxArg->asJSContext()->runtime()->newObjectCache.fillGlobal(entry, &ArrayObject::class_,
+                                                                   cxArg->global(), allocKind, arr);
+    }
+
+    if (allocateCapacity && !EnsureNewArrayElements(cxArg, arr, length))
+        return nullptr;
+
+    probes::CreateObject(cxArg, arr);
+    return arr;
+}
+
+ArrayObject * JS_FASTCALL
+js::NewDenseEmptyArray(JSContext *cx, JSObject *proto /* = nullptr */,
+                       NewObjectKind newKind /* = GenericObject */)
+{
+    return NewArray<false>(cx, 0, proto, newKind);
+}
+
+ArrayObject * JS_FASTCALL
+js::NewDenseAllocatedArray(ExclusiveContext *cx, uint32_t length, JSObject *proto /* = nullptr */,
+                           NewObjectKind newKind /* = GenericObject */)
+{
+    return NewArray<true>(cx, length, proto, newKind);
+}
+
+ArrayObject * JS_FASTCALL
+js::NewDenseUnallocatedArray(ExclusiveContext *cx, uint32_t length, JSObject *proto /* = nullptr */,
+                             NewObjectKind newKind /* = GenericObject */)
+{
+    return NewArray<false>(cx, length, proto, newKind);
+}
+
+ArrayObject *
+js::NewDenseCopiedArray(JSContext *cx, uint32_t length, HandleObject src, uint32_t elementOffset,
+                        JSObject *proto /* = nullptr */)
+{
+    JS_ASSERT(!src->isIndexed());
+
+    ArrayObject* arr = NewArray<true>(cx, length, proto);
+    if (!arr)
+        return nullptr;
+
+    JS_ASSERT(arr->getDenseCapacity() >= length);
+
+    const Value* vp = src->getDenseElements() + elementOffset;
+    arr->setDenseInitializedLength(vp ? length : 0);
+
+    if (vp)
+        arr->initDenseElements(0, vp, length);
+
+    return arr;
+}
+
+// values must point at already-rooted Value objects
+ArrayObject *
+js::NewDenseCopiedArray(JSContext *cx, uint32_t length, const Value *values,
+                        JSObject *proto /* = nullptr */, NewObjectKind newKind /* = GenericObject */)
+{
+    ArrayObject* arr = NewArray<true>(cx, length, proto);
+    if (!arr)
+        return nullptr;
+
+    JS_ASSERT(arr->getDenseCapacity() >= length);
+
+    arr->setDenseInitializedLength(values ? length : 0);
+
+    if (values)
+        arr->initDenseElements(0, values, length);
+
+    return arr;
+}
+
+ArrayObject *
+js::NewDenseAllocatedArrayWithTemplate(JSContext *cx, uint32_t length, JSObject *templateObject)
+{
+    gc::AllocKind allocKind = GuessArrayGCKind(length);
+    JS_ASSERT(CanBeFinalizedInBackground(allocKind, &ArrayObject::class_));
+    allocKind = GetBackgroundAllocKind(allocKind);
+
+    RootedTypeObject type(cx, templateObject->type());
+    if (!type)
+        return nullptr;
+
+    RootedShape shape(cx, templateObject->lastProperty());
+    if (!shape)
+        return nullptr;
+
+    gc::InitialHeap heap = GetInitialHeap(GenericObject, &ArrayObject::class_);
+    Rooted<ArrayObject *> arr(cx, JSObject::createArray(cx, allocKind, heap, shape, type, length));
+    if (!arr)
+        return nullptr;
+
+    if (!EnsureNewArrayElements(cx, arr, length))
+        return nullptr;
+
+    probes::CreateObject(cx, arr);
+
+    return arr;
+}
+
+#ifdef DEBUG
+bool
+js_ArrayInfo(JSContext *cx, unsigned argc, Value *vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    JSObject *obj;
+
+    for (unsigned i = 0; i < args.length(); i++) {
+        RootedValue arg(cx, args[i]);
+
+        char *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);
+            js_free(bytes);
+            continue;
+        }
+        fprintf(stderr, "%s: (len %u", bytes, obj->as<ArrayObject>().length());
+        fprintf(stderr, ", capacity %u", obj->getDenseCapacity());
+        fputs(")\n", stderr);
+        js_free(bytes);
+    }
+
+    args.rval().setUndefined();
+    return true;
+}
+#endif