Make use of ArrayObjects in favor of generic JS objects.

ArrayObjects has been a thing for years but been under-used. About time
they are used where prudent.

14 files changed, 57 insertions, 96 deletions

diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index c524184d6..ea6baeec7 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -6281,8 +6281,8 @@ ParseNode::getConstantValue(ExclusiveContext* cx, AllowConstantObjects allowObje
         }
         MOZ_ASSERT(idx == count);
 
-        JSObject* obj = ObjectGroup::newArrayObject(cx, values.begin(), values.length(),
-                                                    newKind, arrayKind);
+        ArrayObject* obj = ObjectGroup::newArrayObject(cx, values.begin(), values.length(),
+                                                       newKind, arrayKind);
         if (!obj)
             return false;
 
diff --git a/js/src/jit/BaselineCompiler.cpp b/js/src/jit/BaselineCompiler.cpp
index 3fa5a80ed..93e3759b9 100644
--- a/js/src/jit/BaselineCompiler.cpp
+++ b/js/src/jit/BaselineCompiler.cpp
@@ -2055,7 +2055,7 @@ BaselineCompiler::emit_JSOP_SPREADCALLARRAY()
     return emit_JSOP_NEWARRAY();
 }
 
-typedef JSObject* (*NewArrayCopyOnWriteFn)(JSContext*, HandleArrayObject, gc::InitialHeap);
+typedef ArrayObject* (*NewArrayCopyOnWriteFn)(JSContext*, HandleArrayObject, gc::InitialHeap);
 const VMFunction jit::NewArrayCopyOnWriteInfo =
     FunctionInfo<NewArrayCopyOnWriteFn>(js::NewDenseCopyOnWriteArray, "NewDenseCopyOnWriteArray");
 
@@ -4136,14 +4136,14 @@ BaselineCompiler::emit_JSOP_REST()
 {
     frame.syncStack(0);
 
-    JSObject* templateObject =
+    ArrayObject* templateObject =
         ObjectGroup::newArrayObject(cx, nullptr, 0, TenuredObject,
                                     ObjectGroup::NewArrayKind::UnknownIndex);
     if (!templateObject)
         return false;
 
     // Call IC.
-    ICRest_Fallback::Compiler compiler(cx, &templateObject->as<ArrayObject>());
+    ICRest_Fallback::Compiler compiler(cx, templateObject);
     if (!emitOpIC(compiler.getStub(&stubSpace_)))
         return false;
 
diff --git a/js/src/jit/BaselineIC.cpp b/js/src/jit/BaselineIC.cpp
index 28e263ac7..2b0822655 100644
--- a/js/src/jit/BaselineIC.cpp
+++ b/js/src/jit/BaselineIC.cpp
@@ -5765,10 +5765,10 @@ static bool
 CopyArray(JSContext* cx, HandleArrayObject arr, MutableHandleValue result)
 {
     uint32_t length = arr->length();
-    JSObject* nobj = NewFullyAllocatedArrayTryReuseGroup(cx, arr, length, TenuredObject);
+    ArrayObject* nobj = NewFullyAllocatedArrayTryReuseGroup(cx, arr, length, TenuredObject);
     if (!nobj)
         return false;
-    EnsureArrayGroupAnalyzed(cx, nobj);
+    EnsureArrayGroupAnalyzed(cx, nobj); //XXX
     CopyBoxedOrUnboxedDenseElements(cx, nobj, arr, 0, 0, length);
 
     result.setObject(*nobj);
@@ -8547,8 +8547,8 @@ static bool DoRestFallback(JSContext* cx, BaselineFrame* frame, ICRest_Fallback*
     unsigned numRest = numActuals > numFormals ? numActuals - numFormals : 0;
     Value* rest = frame->argv() + numFormals;
 
-    JSObject* obj = ObjectGroup::newArrayObject(cx, rest, numRest, GenericObject,
-                                                ObjectGroup::NewArrayKind::UnknownIndex);
+    ArrayObject* obj = ObjectGroup::newArrayObject(cx, rest, numRest, GenericObject,
+                                                   ObjectGroup::NewArrayKind::UnknownIndex);
     if (!obj)
         return false;
     res.setObject(*obj);
diff --git a/js/src/jit/CodeGenerator.cpp b/js/src/jit/CodeGenerator.cpp
index 485e881fe..ae9c61031 100644
--- a/js/src/jit/CodeGenerator.cpp
+++ b/js/src/jit/CodeGenerator.cpp
@@ -5169,11 +5169,11 @@ static JSObject*
 NewArrayWithGroup(JSContext* cx, uint32_t length, HandleObjectGroup group,
                   bool convertDoubleElements)
 {
-    JSObject* res = NewFullyAllocatedArrayTryUseGroup(cx, group, length);
+    ArrayObject* res = NewFullyAllocatedArrayTryUseGroup(cx, group, length);
     if (!res)
         return nullptr;
     if (convertDoubleElements)
-        res->as<ArrayObject>().setShouldConvertDoubleElements();
+        res->setShouldConvertDoubleElements();
     return res;
 }
 
@@ -5319,7 +5319,7 @@ CodeGenerator::visitNewArrayCopyOnWrite(LNewArrayCopyOnWrite* lir)
     masm.bind(ool->rejoin());
 }
 
-typedef JSObject* (*ArrayConstructorOneArgFn)(JSContext*, HandleObjectGroup, int32_t length);
+typedef ArrayObject* (*ArrayConstructorOneArgFn)(JSContext*, HandleObjectGroup, int32_t length);
 static const VMFunction ArrayConstructorOneArgInfo =
     FunctionInfo<ArrayConstructorOneArgFn>(ArrayConstructorOneArg, "ArrayConstructorOneArg");
 
@@ -7765,7 +7765,7 @@ CodeGenerator::visitSinCos(LSinCos *lir)
     masm.freeStack(sizeof(double) * 2);
 }
 
-typedef JSObject* (*StringSplitFn)(JSContext*, HandleObjectGroup, HandleString, HandleString, uint32_t);
+typedef ArrayObject* (*StringSplitFn)(JSContext*, HandleObjectGroup, HandleString, HandleString, uint32_t);
 static const VMFunction StringSplitInfo =
     FunctionInfo<StringSplitFn>(js::str_split_string, "str_split_string");
 
diff --git a/js/src/jit/Recover.cpp b/js/src/jit/Recover.cpp
index 6fd71f377..8fe6ee3fb 100644
--- a/js/src/jit/Recover.cpp
+++ b/js/src/jit/Recover.cpp
@@ -1355,7 +1355,7 @@ RNewArray::recover(JSContext* cx, SnapshotIterator& iter) const
     RootedValue result(cx);
     RootedObjectGroup group(cx, templateObject->group());
 
-    JSObject* resultObject = NewFullyAllocatedArrayTryUseGroup(cx, group, count_);
+    ArrayObject* resultObject = NewFullyAllocatedArrayTryUseGroup(cx, group, count_);
     if (!resultObject)
         return false;
 
diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
index da692c1b5..0d6f78fcf 100644
--- a/js/src/jsarray.cpp
+++ b/js/src/jsarray.cpp
@@ -2811,7 +2811,7 @@ SliceSlowly(JSContext* cx, HandleObject obj, HandleObject receiver,
 }
 
 static bool
-SliceSparse(JSContext* cx, HandleObject obj, uint32_t begin, uint32_t end, HandleObject result)
+SliceSparse(JSContext* cx, HandleObject obj, uint32_t begin, uint32_t end, HandleArrayObject result)
 {
     MOZ_ASSERT(begin <= end);
 
@@ -2866,7 +2866,7 @@ ArraySliceOrdinary(JSContext* cx, HandleObject obj, uint32_t length, uint32_t be
         if (initlen > begin)
             count = Min<size_t>(initlen - begin, end - begin);
 
-        RootedObject narr(cx, NewFullyAllocatedArrayTryReuseGroup(cx, obj, count));
+        RootedArrayObject narr(cx, NewFullyAllocatedArrayTryReuseGroup(cx, obj, count));
         if (!narr)
             return false;
 
@@ -2882,7 +2882,7 @@ ArraySliceOrdinary(JSContext* cx, HandleObject obj, uint32_t length, uint32_t be
         return true;
     }
 
-    RootedObject narr(cx, NewPartlyAllocatedArrayTryReuseGroup(cx, obj, end - begin));
+    RootedArrayObject narr(cx, NewPartlyAllocatedArrayTryReuseGroup(cx, obj, end - begin));
     if (!narr)
         return false;
 
@@ -3069,7 +3069,7 @@ array_isArray(JSContext* cx, unsigned argc, Value* vp)
 static bool
 ArrayFromCallArgs(JSContext* cx, CallArgs& args, HandleObject proto = nullptr)
 {
-    JSObject* obj = NewCopiedArrayForCallingAllocationSite(cx, args.array(), args.length(), proto);
+    ArrayObject* obj = NewCopiedArrayForCallingAllocationSite(cx, args.array(), args.length(), proto);
     if (!obj)
         return false;
 
@@ -3234,7 +3234,7 @@ ArrayConstructorImpl(JSContext* cx, CallArgs& args, bool isConstructor)
         }
     }
 
-    JSObject* obj = NewPartlyAllocatedArrayForCallingAllocationSite(cx, length, proto);
+    ArrayObject* obj = NewPartlyAllocatedArrayForCallingAllocationSite(cx, length, proto);
     if (!obj)
         return false;
 
@@ -3260,7 +3260,7 @@ js::array_construct(JSContext* cx, unsigned argc, Value* vp)
     return ArrayConstructorImpl(cx, args, /* isConstructor = */ false);
 }
 
-JSObject*
+ArrayObject*
 js::ArrayConstructorOneArg(JSContext* cx, HandleObjectGroup group, int32_t lengthInt)
 {
     if (lengthInt < 0) {
@@ -3555,7 +3555,7 @@ js::NewDenseFullyAllocatedArrayWithTemplate(JSContext* cx, uint32_t length, JSOb
     return arr;
 }
 
-JSObject*
+ArrayObject*
 js::NewDenseCopyOnWriteArray(JSContext* cx, HandleArrayObject templateObject, gc::InitialHeap heap)
 {
     MOZ_ASSERT(!gc::IsInsideNursery(templateObject));
@@ -3573,7 +3573,7 @@ js::NewDenseCopyOnWriteArray(JSContext* cx, HandleArrayObject templateObject, gc
 // specified group cannot be used, ensure that the created array at least has
 // the given [[Prototype]].
 template <uint32_t maxLength>
-static inline JSObject*
+static inline ArrayObject*
 NewArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
                     NewObjectKind newKind = GenericObject)
 {
@@ -3603,14 +3603,14 @@ NewArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length
     return res;
 }
 
-JSObject*
+ArrayObject*
 js::NewFullyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
                                       NewObjectKind newKind)
 {
     return NewArrayTryUseGroup<UINT32_MAX>(cx, group, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewPartlyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length)
 {
     return NewArrayTryUseGroup<ArrayObject::EagerAllocationMaxLength>(cx, group, length);
@@ -3624,7 +3624,7 @@ js::NewPartlyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup g
 // |length| is larger than the input object's initialized length (in which case
 // UnboxedArrayObject::MaximumCapacity might be exceeded).
 template <uint32_t maxLength>
-static inline JSObject*
+static inline ArrayObject*
 NewArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
                       NewObjectKind newKind = GenericObject)
 {
@@ -3641,20 +3641,20 @@ NewArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
     return NewArrayTryUseGroup<maxLength>(cx, group, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewFullyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
                                         NewObjectKind newKind)
 {
     return NewArrayTryReuseGroup<UINT32_MAX>(cx, obj, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewPartlyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length)
 {
     return NewArrayTryReuseGroup<ArrayObject::EagerAllocationMaxLength>(cx, obj, length);
 }
 
-JSObject*
+ArrayObject*
 js::NewFullyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length,
                                                    NewObjectKind newKind)
 {
@@ -3664,7 +3664,7 @@ js::NewFullyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length,
     return NewArrayTryUseGroup<UINT32_MAX>(cx, group, length, newKind);
 }
 
-JSObject*
+ArrayObject*
 js::NewPartlyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length, HandleObject proto)
 {
     RootedObjectGroup group(cx, ObjectGroup::callingAllocationSiteGroup(cx, JSProto_Array, proto));
@@ -3673,44 +3673,12 @@ js::NewPartlyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length
     return NewArrayTryUseGroup<ArrayObject::EagerAllocationMaxLength>(cx, group, length);
 }
 
-bool
-js::MaybeAnalyzeBeforeCreatingLargeArray(ExclusiveContext* cx, HandleObjectGroup group,
-                                         const Value* vp, size_t length)
-{
-    static const size_t EagerPreliminaryObjectAnalysisThreshold = 800;
-
-    // Force analysis to see if an unboxed array can be used when making a
-    // sufficiently large array, to avoid excessive analysis and copying later
-    // on. If this is the first array of its group that is being created, first
-    // make a dummy array with the initial elements of the array we are about
-    // to make, so there is some basis for the unboxed array analysis.
-    if (length > EagerPreliminaryObjectAnalysisThreshold) {
-        if (PreliminaryObjectArrayWithTemplate* objects = group->maybePreliminaryObjects()) {
-            if (objects->empty()) {
-                size_t nlength = Min<size_t>(length, 100);
-                JSObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, nlength);
-                if (!obj)
-                    return false;
-                DebugOnly<DenseElementResult> result =
-                    SetOrExtendBoxedOrUnboxedDenseElements(cx, obj, 0, vp, nlength,
-                                                           ShouldUpdateTypes::Update);
-                MOZ_ASSERT(result.value == DenseElementResult::Success);
-            }
-            objects->maybeAnalyze(cx, group, /* forceAnalyze = */ true);
-        }
-    }
-    return true;
-}
-
-JSObject*
+ArrayObject*
 js::NewCopiedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group,
                               const Value* vp, size_t length, NewObjectKind newKind,
                               ShouldUpdateTypes updateTypes)
 {
-    if (!MaybeAnalyzeBeforeCreatingLargeArray(cx, group, vp, length))
-        return nullptr;
-
-    JSObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, length, newKind);
+    ArrayObject* obj = NewFullyAllocatedArrayTryUseGroup(cx, group, length, newKind);
     if (!obj)
         return nullptr;
 
@@ -3722,7 +3690,7 @@ js::NewCopiedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group,
     return obj;
 }
 
-JSObject*
+ArrayObject*
 js::NewCopiedArrayForCallingAllocationSite(JSContext* cx, const Value* vp, size_t length,
                                            HandleObject proto /* = nullptr */)
 {
diff --git a/js/src/jsarray.h b/js/src/jsarray.h
index e22cde881..ecde87c3b 100644
--- a/js/src/jsarray.h
+++ b/js/src/jsarray.h
@@ -72,30 +72,30 @@ extern ArrayObject*
 NewDenseFullyAllocatedArrayWithTemplate(JSContext* cx, uint32_t length, JSObject* templateObject);
 
 /* Create a dense array with the same copy-on-write elements as another object. */
-extern JSObject*
+extern ArrayObject*
 NewDenseCopyOnWriteArray(JSContext* cx, HandleArrayObject templateObject, gc::InitialHeap heap);
 
 // The methods below can create either boxed or unboxed arrays.
 
-extern JSObject*
+extern ArrayObject*
 NewFullyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length,
                                   NewObjectKind newKind = GenericObject);
 
-extern JSObject*
+extern ArrayObject*
 NewPartlyAllocatedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group, size_t length);
 
-extern JSObject*
+extern ArrayObject*
 NewFullyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length,
                                     NewObjectKind newKind = GenericObject);
 
-extern JSObject*
+extern ArrayObject*
 NewPartlyAllocatedArrayTryReuseGroup(JSContext* cx, JSObject* obj, size_t length);
 
-extern JSObject*
+extern ArrayObject*
 NewFullyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length,
                                                NewObjectKind newKind = GenericObject);
 
-extern JSObject*
+extern ArrayObject*
 NewPartlyAllocatedArrayForCallingAllocationSite(JSContext* cx, size_t length, HandleObject proto);
 
 enum class ShouldUpdateTypes
@@ -104,17 +104,13 @@ enum class ShouldUpdateTypes
     DontUpdate
 };
 
-extern bool
-MaybeAnalyzeBeforeCreatingLargeArray(ExclusiveContext* cx, HandleObjectGroup group,
-                                     const Value* vp, size_t length);
-
-extern JSObject*
+extern ArrayObject*
 NewCopiedArrayTryUseGroup(ExclusiveContext* cx, HandleObjectGroup group,
                           const Value* vp, size_t length,
                           NewObjectKind newKind = GenericObject,
                           ShouldUpdateTypes updateTypes = ShouldUpdateTypes::Update);
 
-extern JSObject*
+extern ArrayObject*
 NewCopiedArrayForCallingAllocationSite(JSContext* cx, const Value* vp, size_t length,
                                        HandleObject proto = nullptr);
 
@@ -202,7 +198,7 @@ array_splice(JSContext* cx, unsigned argc, js::Value* vp);
 extern bool
 NewbornArrayPush(JSContext* cx, HandleObject obj, const Value& v);
 
-extern JSObject*
+extern ArrayObject*
 ArrayConstructorOneArg(JSContext* cx, HandleObjectGroup group, int32_t lengthInt);
 
 #ifdef DEBUG
diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index 7765b1197..d7db5129d 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -2369,7 +2369,7 @@ js::str_replace_string_raw(JSContext* cx, HandleString string, HandleString patt
 }
 
 // ES 2016 draft Mar 25, 2016 21.1.3.17 steps 4, 8, 12-18.
-static JSObject*
+static ArrayObject*
 SplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleLinearString sep,
             HandleObjectGroup group)
 {
@@ -2466,7 +2466,7 @@ SplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleLinearS
 }
 
 // Fast-path for splitting a string into a character array via split("").
-static JSObject*
+static ArrayObject*
 CharSplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleObjectGroup group)
 {
     size_t strLength = str->length();
@@ -2491,7 +2491,7 @@ CharSplitHelper(JSContext* cx, HandleLinearString str, uint32_t limit, HandleObj
 }
 
 // ES 2016 draft Mar 25, 2016 21.1.3.17 steps 4, 8, 12-18.
-JSObject*
+ArrayObject*
 js::str_split_string(JSContext* cx, HandleObjectGroup group, HandleString str, HandleString sep, uint32_t limit)
 
 {
diff --git a/js/src/jsstr.h b/js/src/jsstr.h
index 38fbfa85e..68175c826 100644
--- a/js/src/jsstr.h
+++ b/js/src/jsstr.h
@@ -465,7 +465,7 @@ FileEscapedString(FILE* fp, const char* chars, size_t length, uint32_t quote)
     return res;
 }
 
-JSObject*
+ArrayObject*
 str_split_string(JSContext* cx, HandleObjectGroup group, HandleString str, HandleString sep,
                  uint32_t limit);
 
diff --git a/js/src/vm/JSONParser.cpp b/js/src/vm/JSONParser.cpp
index 01883bb15..e50da3bc4 100644
--- a/js/src/vm/JSONParser.cpp
+++ b/js/src/vm/JSONParser.cpp
@@ -606,8 +606,8 @@ JSONParserBase::finishArray(MutableHandleValue vp, ElementVector& elements)
 {
     MOZ_ASSERT(&elements == &stack.back().elements());
 
-    JSObject* obj = ObjectGroup::newArrayObject(cx, elements.begin(), elements.length(),
-                                                GenericObject);
+    ArrayObject* obj = ObjectGroup::newArrayObject(cx, elements.begin(), elements.length(),
+                                                   GenericObject);
     if (!obj)
         return false;
 
diff --git a/js/src/vm/ObjectGroup.cpp b/js/src/vm/ObjectGroup.cpp
index a227b7c9c..c2866f5ae 100644
--- a/js/src/vm/ObjectGroup.cpp
+++ b/js/src/vm/ObjectGroup.cpp
@@ -774,7 +774,7 @@ GetValueTypeForTable(const Value& v)
     return type;
 }
 
-/* static */ JSObject*
+/* static */ ArrayObject*
 ObjectGroup::newArrayObject(ExclusiveContext* cx,
                             const Value* vp, size_t length,
                             NewObjectKind newKind, NewArrayKind arrayKind)
@@ -854,11 +854,8 @@ ObjectGroup::newArrayObject(ExclusiveContext* cx,
     }
 
     // The type of the elements being added will already be reflected in type
-    // information, but make sure when creating an unboxed array that the
-    // common element type is suitable for the unboxed representation.
+    // information.
     ShouldUpdateTypes updateTypes = ShouldUpdateTypes::DontUpdate;
-    if (!MaybeAnalyzeBeforeCreatingLargeArray(cx, group, vp, length))
-        return nullptr;
     if (group->maybePreliminaryObjects())
         group->maybePreliminaryObjects()->maybeAnalyze(cx, group);
 
diff --git a/js/src/vm/ObjectGroup.h b/js/src/vm/ObjectGroup.h
index 4e24de9f1..553cb8366 100644
--- a/js/src/vm/ObjectGroup.h
+++ b/js/src/vm/ObjectGroup.h
@@ -505,11 +505,11 @@ class ObjectGroup : public gc::TenuredCell
         UnknownIndex  // Make an array with an unknown element type.
     };
 
-    // Create an ArrayObject or UnboxedArrayObject with the specified elements
-    // and a group specialized for the elements.
-    static JSObject* newArrayObject(ExclusiveContext* cx, const Value* vp, size_t length,
-                                    NewObjectKind newKind,
-                                    NewArrayKind arrayKind = NewArrayKind::Normal);
+    // Create an ArrayObject with the specified elements and a group specialized
+    // for the elements.
+    static ArrayObject* newArrayObject(ExclusiveContext* cx, const Value* vp, size_t length,
+                                       NewObjectKind newKind,
+                                       NewArrayKind arrayKind = NewArrayKind::Normal);
 
     // Create a PlainObject or UnboxedPlainObject with the specified properties
     // and a group specialized for those properties.
diff --git a/js/src/vm/Stack.cpp b/js/src/vm/Stack.cpp
index 87e95c893..c5f2cf5f3 100644
--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -82,7 +82,7 @@ InterpreterFrame::isNonGlobalEvalFrame() const
     return isEvalFrame() && script()->bodyScope()->as<EvalScope>().isNonGlobal();
 }
 
-JSObject*
+ArrayObject*
 InterpreterFrame::createRestParameter(JSContext* cx)
 {
     MOZ_ASSERT(script()->hasRest());
diff --git a/js/src/vm/Stack.h b/js/src/vm/Stack.h
index 552738d89..dc9306c99 100644
--- a/js/src/vm/Stack.h
+++ b/js/src/vm/Stack.h
@@ -523,7 +523,7 @@ class InterpreterFrame
     ArgumentsObject& argsObj() const;
     void initArgsObj(ArgumentsObject& argsobj);
 
-    JSObject* createRestParameter(JSContext* cx);
+    ArrayObject* createRestParameter(JSContext* cx);
 
     /*
      * Environment chain