Move CopyElements to the accessor of the target.

src/elements.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 128 matching lines @@
 
 
 static Failure* ThrowArrayLengthRangeError(Heap* heap) {
   HandleScope scope(heap->isolate());
   return heap->isolate()->Throw(
       *heap->isolate()->factory()->NewRangeError("invalid_array_length",
           HandleVector<Object>(NULL, 0)));
 }
 
 
-static void CopyObjectToObjectElements(FixedArray* from,
+static void CopyObjectToObjectElements(FixedArrayBase* from_base,
                                        ElementsKind from_kind,
                                        uint32_t from_start,
-                                       FixedArray* to,
+                                       FixedArrayBase* to_base,
                                        ElementsKind to_kind,
                                        uint32_t to_start,
                                        int raw_copy_size) {
-  ASSERT(to->map() != HEAP->fixed_cow_array_map());
+  ASSERT(to_base->map() != HEAP->fixed_cow_array_map());
   AssertNoAllocation no_allocation;
   int copy_size = raw_copy_size;
   if (raw_copy_size < 0) {
     ASSERT(raw_copy_size == ElementsAccessor::kCopyToEnd ||
            raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
-    copy_size = Min(from->length() - from_start,
-                    to->length() - to_start);
+    copy_size = Min(from_base->length() - from_start,
+                    to_base->length() - to_start);
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
       int start = to_start + copy_size;
-      int length = to->length() - start;
+      int length = to_base->length() - start;
       if (length > 0) {
-        Heap* heap = from->GetHeap();
-        MemsetPointer(to->data_start() + start, heap->the_hole_value(), length);
+        Heap* heap = from_base->GetHeap();
+        MemsetPointer(FixedArray::cast(to_base)->data_start() + start,
+                      heap->the_hole_value(), length);
       }
     }
   }
-  ASSERT((copy_size + static_cast<int>(to_start)) <= to->length() &&
-         (copy_size + static_cast<int>(from_start)) <= from->length());
+  ASSERT((copy_size + static_cast<int>(to_start)) <= to_base->length() &&
+         (copy_size + static_cast<int>(from_start)) <= from_base->length());
   if (copy_size == 0) return;
+  FixedArray* from = FixedArray::cast(from_base);
+  FixedArray* to = FixedArray::cast(to_base);
   ASSERT(IsFastSmiOrObjectElementsKind(from_kind));
   ASSERT(IsFastSmiOrObjectElementsKind(to_kind));
   Address to_address = to->address() + FixedArray::kHeaderSize;
   Address from_address = from->address() + FixedArray::kHeaderSize;
   CopyWords(reinterpret_cast<Object**>(to_address) + to_start,
             reinterpret_cast<Object**>(from_address) + from_start,
             copy_size);
   if (IsFastObjectElementsKind(from_kind) &&
       IsFastObjectElementsKind(to_kind)) {
     Heap* heap = from->GetHeap();
     if (!heap->InNewSpace(to)) {
       heap->RecordWrites(to->address(),
                          to->OffsetOfElementAt(to_start),
                          copy_size);
     }
     heap->incremental_marking()->RecordWrites(to);
   }
 }
 
 
-static void CopyDictionaryToObjectElements(SeededNumberDictionary* from,
+static void CopyDictionaryToObjectElements(FixedArrayBase* from_base,
                                            uint32_t from_start,
-                                           FixedArray* to,
+                                           FixedArrayBase* to_base,
                                            ElementsKind to_kind,
                                            uint32_t to_start,
                                            int raw_copy_size) {
+  SeededNumberDictionary* from = SeededNumberDictionary::cast(from_base);
   AssertNoAllocation no_allocation;
   int copy_size = raw_copy_size;
   Heap* heap = from->GetHeap();
   if (raw_copy_size < 0) {
     ASSERT(raw_copy_size == ElementsAccessor::kCopyToEnd ||
            raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
     copy_size = from->max_number_key() + 1 - from_start;
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
       int start = to_start + copy_size;
-      int length = to->length() - start;
+      int length = to_base->length() - start;
       if (length > 0) {
         Heap* heap = from->GetHeap();
-        MemsetPointer(to->data_start() + start, heap->the_hole_value(), length);
+        MemsetPointer(FixedArray::cast(to_base)->data_start() + start,
+                      heap->the_hole_value(), length);
       }
     }
   }
-  ASSERT(to != from);
+  ASSERT(to_base != from_base);
   ASSERT(IsFastSmiOrObjectElementsKind(to_kind));
   if (copy_size == 0) return;
+  FixedArray* to = FixedArray::cast(to_base);
   uint32_t to_length = to->length();
   if (to_start + copy_size > to_length) {
     copy_size = to_length - to_start;
   }
   for (int i = 0; i < copy_size; i++) {
     int entry = from->FindEntry(i + from_start);
     if (entry != SeededNumberDictionary::kNotFound) {
       Object* value = from->ValueAt(entry);
       ASSERT(!value->IsTheHole());
       to->set(i + to_start, value, SKIP_WRITE_BARRIER);
     } else {
       to->set_the_hole(i + to_start);
     }
   }
   if (IsFastObjectElementsKind(to_kind)) {
     if (!heap->InNewSpace(to)) {
       heap->RecordWrites(to->address(),
                          to->OffsetOfElementAt(to_start),
                          copy_size);
     }
     heap->incremental_marking()->RecordWrites(to);
   }
 }
 
 
 MUST_USE_RESULT static MaybeObject* CopyDoubleToObjectElements(
-    FixedDoubleArray* from,
+    FixedArrayBase* from_base,
     uint32_t from_start,
-    FixedArray* to,
+    FixedArrayBase* to_base,
     ElementsKind to_kind,
     uint32_t to_start,
     int raw_copy_size) {
   ASSERT(IsFastSmiOrObjectElementsKind(to_kind));
   int copy_size = raw_copy_size;
   if (raw_copy_size < 0) {
     ASSERT(raw_copy_size == ElementsAccessor::kCopyToEnd ||
            raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
-    copy_size = Min(from->length() - from_start,
-                    to->length() - to_start);
+    copy_size = Min(from_base->length() - from_start,
+                    to_base->length() - to_start);
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
       // Also initialize the area that will be copied over since HeapNumber
       // allocation below can cause an incremental marking step, requiring all
       // existing heap objects to be propertly initialized.
       int start = to_start;
-      int length = to->length() - start;
+      int length = to_base->length() - start;
       if (length > 0) {
-        Heap* heap = from->GetHeap();
-        MemsetPointer(to->data_start() + start, heap->the_hole_value(), length);
+        Heap* heap = from_base->GetHeap();
+        MemsetPointer(FixedArray::cast(to_base)->data_start() + start,
+                      heap->the_hole_value(), length);
       }
     }
   }
-  ASSERT((copy_size + static_cast<int>(to_start)) <= to->length() &&
-         (copy_size + static_cast<int>(from_start)) <= from->length());
-  if (copy_size == 0) return from;
+  ASSERT((copy_size + static_cast<int>(to_start)) <= to_base->length() &&
+         (copy_size + static_cast<int>(from_start)) <= from_base->length());
+  if (copy_size == 0) return from_base;
+  FixedDoubleArray* from = FixedDoubleArray::cast(from_base);
+  FixedArray* to = FixedArray::cast(to_base);
   for (int i = 0; i < copy_size; ++i) {
     if (IsFastSmiElementsKind(to_kind)) {
       UNIMPLEMENTED();
       return Failure::Exception();
     } else {
       MaybeObject* maybe_value = from->get(i + from_start);
       Object* value;
       ASSERT(IsFastObjectElementsKind(to_kind));
       // Because Double -> Object elements transitions allocate HeapObjects
       // iteratively, the allocate must succeed within a single GC cycle,
       // otherwise the retry after the GC will also fail. In order to ensure
       // that no GC is triggered, allocate HeapNumbers from old space if they
       // can't be taken from new space.
       if (!maybe_value->ToObject(&value)) {
         ASSERT(maybe_value->IsRetryAfterGC() || maybe_value->IsOutOfMemory());
         Heap* heap = from->GetHeap();
         MaybeObject* maybe_value_object =
             heap->AllocateHeapNumber(from->get_scalar(i + from_start),
                                      TENURED);
         if (!maybe_value_object->ToObject(&value)) return maybe_value_object;
       }
       to->set(i + to_start, value, UPDATE_WRITE_BARRIER);
     }
   }
   return to;
 }
 
 
-static void CopyDoubleToDoubleElements(FixedDoubleArray* from,
+static void CopyDoubleToDoubleElements(FixedArrayBase* from_base,
                                        uint32_t from_start,
-                                       FixedDoubleArray* to,
+                                       FixedArrayBase* to_base,
                                        uint32_t to_start,
                                        int raw_copy_size) {
   int copy_size = raw_copy_size;
   if (raw_copy_size < 0) {
     ASSERT(raw_copy_size == ElementsAccessor::kCopyToEnd ||
            raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
-    copy_size = Min(from->length() - from_start,
-                    to->length() - to_start);
+    copy_size = Min(from_base->length() - from_start,
+                    to_base->length() - to_start);
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
-      for (int i = to_start + copy_size; i < to->length(); ++i) {
-        to->set_the_hole(i);
+      for (int i = to_start + copy_size; i < to_base->length(); ++i) {
+        FixedDoubleArray::cast(to_base)->set_the_hole(i);
       }
     }
   }
-  ASSERT((copy_size + static_cast<int>(to_start)) <= to->length() &&
-         (copy_size + static_cast<int>(from_start)) <= from->length());
+  ASSERT((copy_size + static_cast<int>(to_start)) <= to_base->length() &&
+         (copy_size + static_cast<int>(from_start)) <= from_base->length());
   if (copy_size == 0) return;
+  FixedDoubleArray* from = FixedDoubleArray::cast(from_base);
+  FixedDoubleArray* to = FixedDoubleArray::cast(to_base);
   Address to_address = to->address() + FixedDoubleArray::kHeaderSize;
   Address from_address = from->address() + FixedDoubleArray::kHeaderSize;
   to_address += kDoubleSize * to_start;
   from_address += kDoubleSize * from_start;
   int words_per_double = (kDoubleSize / kPointerSize);
   CopyWords(reinterpret_cast<Object**>(to_address),
             reinterpret_cast<Object**>(from_address),
             words_per_double * copy_size);
 }
 
 
-static void CopySmiToDoubleElements(FixedArray* from,
+static void CopySmiToDoubleElements(FixedArrayBase* from_base,
                                     uint32_t from_start,
-                                    FixedDoubleArray* to,
+                                    FixedArrayBase* to_base,
                                     uint32_t to_start,
                                     int raw_copy_size) {
   int copy_size = raw_copy_size;
   if (raw_copy_size < 0) {
     ASSERT(raw_copy_size == ElementsAccessor::kCopyToEnd ||
            raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
-    copy_size = from->length() - from_start;
+    copy_size = from_base->length() - from_start;
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
-      for (int i = to_start + copy_size; i < to->length(); ++i) {
-        to->set_the_hole(i);
+      for (int i = to_start + copy_size; i < to_base->length(); ++i) {
+        FixedDoubleArray::cast(to_base)->set_the_hole(i);
       }
     }
   }
-  ASSERT((copy_size + static_cast<int>(to_start)) <= to->length() &&
-         (copy_size + static_cast<int>(from_start)) <= from->length());
+  ASSERT((copy_size + static_cast<int>(to_start)) <= to_base->length() &&
+         (copy_size + static_cast<int>(from_start)) <= from_base->length());
   if (copy_size == 0) return;
+  FixedArray* from = FixedArray::cast(from_base);
+  FixedDoubleArray* to = FixedDoubleArray::cast(to_base);
   Object* the_hole = from->GetHeap()->the_hole_value();
   for (uint32_t from_end = from_start + static_cast<uint32_t>(copy_size);
        from_start < from_end; from_start++, to_start++) {
     Object* hole_or_smi = from->get(from_start);
     if (hole_or_smi == the_hole) {
       to->set_the_hole(to_start);
     } else {
       to->set(to_start, Smi::cast(hole_or_smi)->value());
     }
   }
 }
 
 
-static void CopyPackedSmiToDoubleElements(FixedArray* from,
+static void CopyPackedSmiToDoubleElements(FixedArrayBase* from_base,
                                           uint32_t from_start,
-                                          FixedDoubleArray* to,
+                                          FixedArrayBase* to_base,
                                           uint32_t to_start,
                                           int packed_size,
                                           int raw_copy_size) {
   int copy_size = raw_copy_size;
   uint32_t to_end;
   if (raw_copy_size < 0) {
     ASSERT(raw_copy_size == ElementsAccessor::kCopyToEnd ||
            raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
-    copy_size = from->length() - from_start;
+    copy_size = from_base->length() - from_start;
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
-      to_end = to->length();
+      to_end = to_base->length();
       for (uint32_t i = to_start + copy_size; i < to_end; ++i) {
-        to->set_the_hole(i);
+        FixedDoubleArray::cast(to_base)->set_the_hole(i);
       }
     } else {
       to_end = to_start + static_cast<uint32_t>(copy_size);
     }
   } else {
     to_end = to_start + static_cast<uint32_t>(copy_size);
   }
-  ASSERT(static_cast<int>(to_end) <= to->length());
+  ASSERT(static_cast<int>(to_end) <= to_base->length());
   ASSERT(packed_size >= 0 && packed_size <= copy_size);
-  ASSERT((copy_size + static_cast<int>(to_start)) <= to->length() &&
-         (copy_size + static_cast<int>(from_start)) <= from->length());
+  ASSERT((copy_size + static_cast<int>(to_start)) <= to_base->length() &&
+         (copy_size + static_cast<int>(from_start)) <= from_base->length());
   if (copy_size == 0) return;
+  FixedArray* from = FixedArray::cast(from_base);
+  FixedDoubleArray* to = FixedDoubleArray::cast(to_base);
   for (uint32_t from_end = from_start + static_cast<uint32_t>(packed_size);
        from_start < from_end; from_start++, to_start++) {
     Object* smi = from->get(from_start);
     ASSERT(!smi->IsTheHole());
     to->set(to_start, Smi::cast(smi)->value());
   }
 }
 
 
-static void CopyObjectToDoubleElements(FixedArray* from,
+static void CopyObjectToDoubleElements(FixedArrayBase* from_base,
                                        uint32_t from_start,
-                                       FixedDoubleArray* to,
+                                       FixedArrayBase* to_base,
                                        uint32_t to_start,
                                        int raw_copy_size) {
   int copy_size = raw_copy_size;
   if (raw_copy_size < 0) {
     ASSERT(raw_copy_size == ElementsAccessor::kCopyToEnd ||
            raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
-    copy_size = from->length() - from_start;
+    copy_size = from_base->length() - from_start;
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
-      for (int i = to_start + copy_size; i < to->length(); ++i) {
-        to->set_the_hole(i);
+      for (int i = to_start + copy_size; i < to_base->length(); ++i) {
+        FixedDoubleArray::cast(to_base)->set_the_hole(i);
       }
     }
   }
-  ASSERT((copy_size + static_cast<int>(to_start)) <= to->length() &&
-         (copy_size + static_cast<int>(from_start)) <= from->length());
+  ASSERT((copy_size + static_cast<int>(to_start)) <= to_base->length() &&
+         (copy_size + static_cast<int>(from_start)) <= from_base->length());
   if (copy_size == 0) return;
+  FixedArray* from = FixedArray::cast(from_base);
+  FixedDoubleArray* to = FixedDoubleArray::cast(to_base);
   Object* the_hole = from->GetHeap()->the_hole_value();
   for (uint32_t from_end = from_start + copy_size;
        from_start < from_end; from_start++, to_start++) {
     Object* hole_or_object = from->get(from_start);
     if (hole_or_object == the_hole) {
       to->set_the_hole(to_start);
     } else {
       to->set(to_start, hole_or_object->Number());
     }
   }
 }
 
 
-static void CopyDictionaryToDoubleElements(SeededNumberDictionary* from,
+static void CopyDictionaryToDoubleElements(FixedArrayBase* from_base,
                                            uint32_t from_start,
-                                           FixedDoubleArray* to,
+                                           FixedArrayBase* to_base,
                                            uint32_t to_start,
                                            int raw_copy_size) {
+  SeededNumberDictionary* from = SeededNumberDictionary::cast(from_base);
   int copy_size = raw_copy_size;
   if (copy_size < 0) {
     ASSERT(copy_size == ElementsAccessor::kCopyToEnd ||
            copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole);
     copy_size = from->max_number_key() + 1 - from_start;
     if (raw_copy_size == ElementsAccessor::kCopyToEndAndInitializeToHole) {
-      for (int i = to_start + copy_size; i < to->length(); ++i) {
-        to->set_the_hole(i);
+      for (int i = to_start + copy_size; i < to_base->length(); ++i) {
+        FixedDoubleArray::cast(to_base)->set_the_hole(i);
       }
     }
   }
   if (copy_size == 0) return;
+  FixedDoubleArray* to = FixedDoubleArray::cast(to_base);
   uint32_t to_length = to->length();
   if (to_start + copy_size > to_length) {
     copy_size = to_length - to_start;
   }
   for (int i = 0; i < copy_size; i++) {
     int entry = from->FindEntry(i + from_start);
     if (entry != SeededNumberDictionary::kNotFound) {
       to->set(i + to_start, from->ValueAt(entry)->Number());
     } else {
       to->set_the_hole(i + to_start);
@@ skipping 72 matching lines @@
   }
 
   virtual bool HasElement(Object* receiver,
                           JSObject* holder,
                           uint32_t key,
                           FixedArrayBase* backing_store) {
     if (backing_store == NULL) {
       backing_store = holder->elements();
     }
     return ElementsAccessorSubclass::HasElementImpl(
-        receiver, holder, key, BackingStore::cast(backing_store));
+        receiver, holder, key, backing_store);
   }
 
   MUST_USE_RESULT virtual MaybeObject* Get(Object* receiver,
                                            JSObject* holder,
                                            uint32_t key,
                                            FixedArrayBase* backing_store) {
     if (backing_store == NULL) {
       backing_store = holder->elements();
     }
     return ElementsAccessorSubclass::GetImpl(
-        receiver, holder, key, BackingStore::cast(backing_store));
+        receiver, holder, key, backing_store);
   }
 
   MUST_USE_RESULT static MaybeObject* GetImpl(Object* receiver,
                                               JSObject* obj,
                                               uint32_t key,
-                                              BackingStore* backing_store) {
+                                              FixedArrayBase* backing_store) {
     return (key < ElementsAccessorSubclass::GetCapacityImpl(backing_store))
-           ? backing_store->get(key)
+           ? BackingStore::cast(backing_store)->get(key)
            : backing_store->GetHeap()->the_hole_value();
   }
 
   MUST_USE_RESULT virtual PropertyAttributes GetAttributes(
       Object* receiver,
       JSObject* holder,
       uint32_t key,
       FixedArrayBase* backing_store) {
     if (backing_store == NULL) {
       backing_store = holder->elements();
@@ skipping 15 matching lines @@
 
   MUST_USE_RESULT virtual PropertyType GetType(
       Object* receiver,
       JSObject* holder,
       uint32_t key,
       FixedArrayBase* backing_store) {
     if (backing_store == NULL) {
       backing_store = holder->elements();
     }
     return ElementsAccessorSubclass::GetTypeImpl(
-        receiver, holder, key, BackingStore::cast(backing_store));
+        receiver, holder, key, backing_store);
   }
 
   MUST_USE_RESULT static PropertyType GetTypeImpl(
         Object* receiver,
         JSObject* obj,
         uint32_t key,
-        BackingStore* backing_store) {
+        FixedArrayBase* backing_store) {
     if (key >= ElementsAccessorSubclass::GetCapacityImpl(backing_store)) {
       return NONEXISTENT;
     }
-    return backing_store->is_the_hole(key) ? NONEXISTENT : FIELD;
+    return BackingStore::cast(backing_store)->is_the_hole(key)
+        ? NONEXISTENT : FIELD;
   }
 
   MUST_USE_RESULT virtual AccessorPair* GetAccessorPair(
       Object* receiver,
       JSObject* holder,
       uint32_t key,
       FixedArrayBase* backing_store) {
     if (backing_store == NULL) {
       backing_store = holder->elements();
     }
     return ElementsAccessorSubclass::GetAccessorPairImpl(
-        receiver, holder, key, BackingStore::cast(backing_store));
+        receiver, holder, key, backing_store);
   }
 
   MUST_USE_RESULT static AccessorPair* GetAccessorPairImpl(
         Object* receiver,
         JSObject* obj,
         uint32_t key,
-        BackingStore* backing_store) {
+        FixedArrayBase* backing_store) {
     return NULL;
   }
 
   MUST_USE_RESULT virtual MaybeObject* SetLength(JSArray* array,
                                                  Object* length) {
     return ElementsAccessorSubclass::SetLengthImpl(
-        array, length, BackingStore::cast(array->elements()));
+        array, length, array->elements());
   }
 
   MUST_USE_RESULT static MaybeObject* SetLengthImpl(
       JSObject* obj,
       Object* length,
-      BackingStore* backing_store);
+      FixedArrayBase* backing_store);
 
   MUST_USE_RESULT virtual MaybeObject* SetCapacityAndLength(
       JSArray* array,
       int capacity,
       int length) {
     return ElementsAccessorSubclass::SetFastElementsCapacityAndLength(
         array,
         capacity,
         length);
   }
 
   MUST_USE_RESULT static MaybeObject* SetFastElementsCapacityAndLength(
       JSObject* obj,
       int capacity,
       int length) {
     UNIMPLEMENTED();
     return obj;
   }
 
   MUST_USE_RESULT virtual MaybeObject* Delete(JSObject* obj,
                                               uint32_t key,
                                               JSReceiver::DeleteMode mode) = 0;
 
   MUST_USE_RESULT static MaybeObject* CopyElementsImpl(FixedArrayBase* from,
                                                        uint32_t from_start,
                                                        FixedArrayBase* to,
-                                                       ElementsKind to_kind,
+                                                       ElementsKind from_kind,
                                                        uint32_t to_start,
                                                        int packed_size,
                                                        int copy_size) {
     UNREACHABLE();
     return NULL;
   }
 
   MUST_USE_RESULT virtual MaybeObject* CopyElements(JSObject* from_holder,
                                                     uint32_t from_start,
                                                     FixedArrayBase* to,
-                                                    ElementsKind to_kind,
+                                                    ElementsKind from_kind,
                                                     uint32_t to_start,
                                                     int copy_size,
                                                     FixedArrayBase* from) {
     int packed_size = kPackedSizeNotKnown;
     if (from == NULL) {
       from = from_holder->elements();
     }
 
     if (from_holder) {
-      ElementsKind elements_kind = from_holder->GetElementsKind();
-      bool is_packed = IsFastPackedElementsKind(elements_kind) &&
+      bool is_packed = IsFastPackedElementsKind(from_kind) &&
           from_holder->IsJSArray();
       if (is_packed) {
         packed_size = Smi::cast(JSArray::cast(from_holder)->length())->value();
         if (copy_size >= 0 && packed_size > copy_size) {
           packed_size = copy_size;
         }
       }
     }
     return ElementsAccessorSubclass::CopyElementsImpl(
-        from, from_start, to, to_kind, to_start, packed_size, copy_size);
+        from, from_start, to, from_kind, to_start, packed_size, copy_size);
   }
 
   MUST_USE_RESULT virtual MaybeObject* AddElementsToFixedArray(
       Object* receiver,
       JSObject* holder,
       FixedArray* to,
       FixedArrayBase* from) {
     int len0 = to->length();
 #ifdef DEBUG
     if (FLAG_enable_slow_asserts) {
       for (int i = 0; i < len0; i++) {
         ASSERT(!to->get(i)->IsTheHole());
       }
     }
 #endif
     if (from == NULL) {
       from = holder->elements();
     }
-    BackingStore* backing_store = BackingStore::cast(from);
-    uint32_t len1 = ElementsAccessorSubclass::GetCapacityImpl(backing_store);
 
     // Optimize if 'other' is empty.
     // We cannot optimize if 'this' is empty, as other may have holes.
+    uint32_t len1 = ElementsAccessorSubclass::GetCapacityImpl(from);
     if (len1 == 0) return to;
 
     // Compute how many elements are not in other.
     uint32_t extra = 0;
     for (uint32_t y = 0; y < len1; y++) {
-      uint32_t key =
-          ElementsAccessorSubclass::GetKeyForIndexImpl(backing_store, y);
+      uint32_t key = ElementsAccessorSubclass::GetKeyForIndexImpl(from, y);
       if (ElementsAccessorSubclass::HasElementImpl(
-              receiver, holder, key, backing_store)) {
+              receiver, holder, key, from)) {
         MaybeObject* maybe_value =
-            ElementsAccessorSubclass::GetImpl(receiver, holder,
-                                              key, backing_store);
+            ElementsAccessorSubclass::GetImpl(receiver, holder, key, from);
         Object* value;
-        if (!maybe_value->ToObject(&value)) return maybe_value;
+        if (!maybe_value->To(&value)) return maybe_value;
         ASSERT(!value->IsTheHole());
         if (!HasKey(to, value)) {
           extra++;
         }
       }
     }
 
     if (extra == 0) return to;
 
     // Allocate the result
     FixedArray* result;
-    MaybeObject* maybe_obj =
-        backing_store->GetHeap()->AllocateFixedArray(len0 + extra);
-    if (!maybe_obj->To<FixedArray>(&result)) return maybe_obj;
+    MaybeObject* maybe_obj = from->GetHeap()->AllocateFixedArray(len0 + extra);
+    if (!maybe_obj->To(&result)) return maybe_obj;
 
     // Fill in the content
     {
       AssertNoAllocation no_gc;
       WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
       for (int i = 0; i < len0; i++) {
         Object* e = to->get(i);
         ASSERT(e->IsString() || e->IsNumber());
         result->set(i, e, mode);
       }
     }
     // Fill in the extra values.
     uint32_t index = 0;
     for (uint32_t y = 0; y < len1; y++) {
       uint32_t key =
-          ElementsAccessorSubclass::GetKeyForIndexImpl(backing_store, y);
+          ElementsAccessorSubclass::GetKeyForIndexImpl(from, y);
       if (ElementsAccessorSubclass::HasElementImpl(
-              receiver, holder, key, backing_store)) {
+              receiver, holder, key, from)) {
         MaybeObject* maybe_value =
-            ElementsAccessorSubclass::GetImpl(receiver, holder,
-                                              key, backing_store);
+            ElementsAccessorSubclass::GetImpl(receiver, holder, key, from);
         Object* value;
-        if (!maybe_value->ToObject(&value)) return maybe_value;
+        if (!maybe_value->To(&value)) return maybe_value;
         if (!value->IsTheHole() && !HasKey(to, value)) {
           result->set(len0 + index, value);
           index++;
         }
       }
     }
     ASSERT(extra == index);
     return result;
   }
 
  protected:
   static uint32_t GetCapacityImpl(FixedArrayBase* backing_store) {
     return backing_store->length();
   }
 
   virtual uint32_t GetCapacity(FixedArrayBase* backing_store) {
     return ElementsAccessorSubclass::GetCapacityImpl(backing_store);
   }
 
-  static uint32_t GetKeyForIndexImpl(BackingStore* backing_store,
+  static uint32_t GetKeyForIndexImpl(FixedArrayBase* backing_store,
                                      uint32_t index) {
     return index;
   }
 
   virtual uint32_t GetKeyForIndex(FixedArrayBase* backing_store,
                                   uint32_t index) {
-    return ElementsAccessorSubclass::GetKeyForIndexImpl(
-        BackingStore::cast(backing_store), index);
+    return ElementsAccessorSubclass::GetKeyForIndexImpl(backing_store, index);
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ElementsAccessorBase);
 };
 
 
 // Super class for all fast element arrays.
 template<typename FastElementsAccessorSubclass,
          typename KindTraits,
          int ElementSize>
 class FastElementsAccessor
     : public ElementsAccessorBase<FastElementsAccessorSubclass, KindTraits> {
  public:
   explicit FastElementsAccessor(const char* name)
       : ElementsAccessorBase<FastElementsAccessorSubclass,
                              KindTraits>(name) {}
  protected:
   friend class ElementsAccessorBase<FastElementsAccessorSubclass, KindTraits>;
   friend class NonStrictArgumentsElementsAccessor;
 
   typedef typename KindTraits::BackingStore BackingStore;
 
   // Adjusts the length of the fast backing store or returns the new length or
   // undefined in case conversion to a slow backing store should be performed.
-  static MaybeObject* SetLengthWithoutNormalize(BackingStore* backing_store,
+  static MaybeObject* SetLengthWithoutNormalize(FixedArrayBase* backing_store,
                                                 JSArray* array,
                                                 Object* length_object,
                                                 uint32_t length) {
     uint32_t old_capacity = backing_store->length();
     Object* old_length = array->length();
     bool same_or_smaller_size = old_length->IsSmi() &&
         static_cast<uint32_t>(Smi::cast(old_length)->value()) >= length;
     ElementsKind kind = array->GetElementsKind();
 
     if (!same_or_smaller_size && IsFastElementsKind(kind) &&
@@ skipping 17 matching lines @@
           backing_store->set_length(length);
           Address filler_start = backing_store->address() +
               BackingStore::OffsetOfElementAt(length);
           int filler_size = (old_capacity - length) * ElementSize;
           array->GetHeap()->CreateFillerObjectAt(filler_start, filler_size);
         }
       } else {
         // Otherwise, fill the unused tail with holes.
         int old_length = FastD2IChecked(array->length()->Number());
         for (int i = length; i < old_length; i++) {
-          backing_store->set_the_hole(i);
+          BackingStore::cast(backing_store)->set_the_hole(i);
         }
       }
       return length_object;
     }
 
     // Check whether the backing store should be expanded.
     uint32_t min = JSObject::NewElementsCapacity(old_capacity);
     uint32_t new_capacity = length > min ? length : min;
     if (!array->ShouldConvertToSlowElements(new_capacity)) {
       MaybeObject* result = FastElementsAccessorSubclass::
@@ skipping 16 matching lines @@
     Heap* heap = obj->GetHeap();
     Object* elements = obj->elements();
     if (elements == heap->empty_fixed_array()) {
       return heap->true_value();
     }
     typename KindTraits::BackingStore* backing_store =
         KindTraits::BackingStore::cast(elements);
     bool is_non_strict_arguments_elements_map =
         backing_store->map() == heap->non_strict_arguments_elements_map();
     if (is_non_strict_arguments_elements_map) {
-      backing_store =
-          KindTraits::BackingStore::cast(
-              FixedArray::cast(backing_store)->get(1));
+      backing_store = KindTraits::BackingStore::cast(
+          FixedArray::cast(backing_store)->get(1));
     }
     uint32_t length = static_cast<uint32_t>(
         obj->IsJSArray()
         ? Smi::cast(JSArray::cast(obj)->length())->value()
         : backing_store->length());
     if (key < length) {
       if (!is_non_strict_arguments_elements_map) {
         ElementsKind kind = KindTraits::Kind;
         if (IsFastPackedElementsKind(kind)) {
           MaybeObject* transitioned =
@@ skipping 35 matching lines @@
   virtual MaybeObject* Delete(JSObject* obj,
                               uint32_t key,
                               JSReceiver::DeleteMode mode) {
     return DeleteCommon(obj, key, mode);
   }
 
   static bool HasElementImpl(
       Object* receiver,
       JSObject* holder,
       uint32_t key,
-      typename KindTraits::BackingStore* backing_store) {
+      FixedArrayBase* backing_store) {
     if (key >= static_cast<uint32_t>(backing_store->length())) {
       return false;
     }
-    return !backing_store->is_the_hole(key);
+    return !BackingStore::cast(backing_store)->is_the_hole(key);
   }
 
   static void ValidateContents(JSObject* holder, int length) {
 #if DEBUG
     FixedArrayBase* elements = holder->elements();
     Heap* heap = elements->GetHeap();
     Map* map = elements->map();
     ASSERT((IsFastSmiOrObjectElementsKind(KindTraits::Kind) &&
             (map == heap->fixed_array_map() ||
              map == heap->fixed_cow_array_map())) ||
            (IsFastDoubleElementsKind(KindTraits::Kind) ==
             ((map == heap->fixed_array_map() && length == 0) ||
              map == heap->fixed_double_array_map())));
     for (int i = 0; i < length; i++) {
       typename KindTraits::BackingStore* backing_store =
           KindTraits::BackingStore::cast(elements);
       ASSERT((!IsFastSmiElementsKind(KindTraits::Kind) ||
               static_cast<Object*>(backing_store->get(i))->IsSmi()) ||
              (IsFastHoleyElementsKind(KindTraits::Kind) ==
               backing_store->is_the_hole(i)));
     }
 #endif
   }
 };
 
 
+static ElementsKind ElementsKindForArray(FixedArrayBase* array) {
+  switch (array->map()->instance_type()) {
+    case FIXED_ARRAY_TYPE:
+      if (array->IsDictionary()) {
+        return DICTIONARY_ELEMENTS;
+      } else {
+        return FAST_HOLEY_ELEMENTS;
+      }
+    case FIXED_DOUBLE_ARRAY_TYPE:
+      return FAST_HOLEY_DOUBLE_ELEMENTS;
+    case EXTERNAL_BYTE_ARRAY_TYPE:
+      return EXTERNAL_BYTE_ELEMENTS;
+    case EXTERNAL_UNSIGNED_BYTE_ARRAY_TYPE:
+      return EXTERNAL_UNSIGNED_BYTE_ELEMENTS;
+    case EXTERNAL_SHORT_ARRAY_TYPE:
+      return EXTERNAL_SHORT_ELEMENTS;
+    case EXTERNAL_UNSIGNED_SHORT_ARRAY_TYPE:
+      return EXTERNAL_UNSIGNED_SHORT_ELEMENTS;
+    case EXTERNAL_INT_ARRAY_TYPE:
+      return EXTERNAL_INT_ELEMENTS;
+    case EXTERNAL_UNSIGNED_INT_ARRAY_TYPE:
+      return EXTERNAL_UNSIGNED_INT_ELEMENTS;
+    case EXTERNAL_FLOAT_ARRAY_TYPE:
+      return EXTERNAL_FLOAT_ELEMENTS;
+    case EXTERNAL_DOUBLE_ARRAY_TYPE:
+      return EXTERNAL_DOUBLE_ELEMENTS;
+    case EXTERNAL_PIXEL_ARRAY_TYPE:
+      return EXTERNAL_PIXEL_ELEMENTS;
+    default:
+      UNREACHABLE();
+  }
+  return FAST_HOLEY_ELEMENTS;
+}
+
+
 template<typename FastElementsAccessorSubclass,
          typename KindTraits>
 class FastSmiOrObjectElementsAccessor
     : public FastElementsAccessor<FastElementsAccessorSubclass,
                                   KindTraits,
                                   kPointerSize> {
  public:
   explicit FastSmiOrObjectElementsAccessor(const char* name)
       : FastElementsAccessor<FastElementsAccessorSubclass,
                              KindTraits,
                              kPointerSize>(name) {}
 
   static MaybeObject* CopyElementsImpl(FixedArrayBase* from,
                                        uint32_t from_start,
                                        FixedArrayBase* to,
-                                       ElementsKind to_kind,
+                                       ElementsKind from_kind,
                                        uint32_t to_start,
                                        int packed_size,
                                        int copy_size) {
-    if (IsFastSmiOrObjectElementsKind(to_kind)) {
-      CopyObjectToObjectElements(
-          FixedArray::cast(from), KindTraits::Kind, from_start,
-          FixedArray::cast(to), to_kind, to_start, copy_size);
-    } else if (IsFastDoubleElementsKind(to_kind)) {
-      if (IsFastSmiElementsKind(KindTraits::Kind)) {
-        if (IsFastPackedElementsKind(KindTraits::Kind) &&
-            packed_size != kPackedSizeNotKnown) {
-          CopyPackedSmiToDoubleElements(
-              FixedArray::cast(from), from_start,
-              FixedDoubleArray::castOrEmptyFixedArray(to), to_start,
-              packed_size, copy_size);
-        } else {
-          CopySmiToDoubleElements(
-              FixedArray::cast(from), from_start,
-              FixedDoubleArray::castOrEmptyFixedArray(to), to_start, copy_size);
-        }
-      } else {
-        CopyObjectToDoubleElements(
-            FixedArray::cast(from), from_start,
-            FixedDoubleArray::castOrEmptyFixedArray(to), to_start, copy_size);
+    ElementsKind to_kind = KindTraits::Kind;
+    switch (from_kind) {
+      case FAST_SMI_ELEMENTS:
+      case FAST_HOLEY_SMI_ELEMENTS:
+      case FAST_ELEMENTS:
+      case FAST_HOLEY_ELEMENTS:
+        CopyObjectToObjectElements(
+            from, from_kind, from_start, to, to_kind, to_start, copy_size);
+        return to->GetHeap()->undefined_value();
+      case FAST_DOUBLE_ELEMENTS:
+      case FAST_HOLEY_DOUBLE_ELEMENTS:
+        return CopyDoubleToObjectElements(
+            from, from_start, to, to_kind, to_start, copy_size);
+      case DICTIONARY_ELEMENTS:
+        CopyDictionaryToObjectElements(
+            from, from_start, to, to_kind, to_start, copy_size);
+        return to->GetHeap()->undefined_value();
+      case NON_STRICT_ARGUMENTS_ELEMENTS: {
+        // TODO(verwaest): This is a temporary hack to support extending
+        // NON_STRICT_ARGUMENTS_ELEMENTS in SetFastElementsCapacityAndLength.
+        // This case should be UNREACHABLE().
+        FixedArray* parameter_map = FixedArray::cast(from);
+        FixedArrayBase* arguments = FixedArrayBase::cast(parameter_map->get(1));
+        ElementsKind from_kind = ElementsKindForArray(arguments);
+        return CopyElementsImpl(arguments, from_start, to, from_kind,
+                                to_start, packed_size, copy_size);
       }
-    } else {
-      UNREACHABLE();
+      case EXTERNAL_BYTE_ELEMENTS:
+      case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
+      case EXTERNAL_SHORT_ELEMENTS:
+      case EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
+      case EXTERNAL_INT_ELEMENTS:
+      case EXTERNAL_UNSIGNED_INT_ELEMENTS:
+      case EXTERNAL_FLOAT_ELEMENTS:
+      case EXTERNAL_DOUBLE_ELEMENTS:
+      case EXTERNAL_PIXEL_ELEMENTS:
+        UNREACHABLE();
     }
-    return to->GetHeap()->undefined_value();
+    return NULL;
   }
 
 
   static MaybeObject* SetFastElementsCapacityAndLength(JSObject* obj,
                                                        uint32_t capacity,
                                                        uint32_t length) {
     JSObject::SetFastElementsCapacitySmiMode set_capacity_mode =
         obj->HasFastSmiElements()
             ? JSObject::kAllowSmiElements
             : JSObject::kDontAllowSmiElements;
@@ skipping 68 matching lines @@
                                                        uint32_t capacity,
                                                        uint32_t length) {
     return obj->SetFastDoubleElementsCapacityAndLength(capacity,
                                                        length);
   }
 
  protected:
   static MaybeObject* CopyElementsImpl(FixedArrayBase* from,
                                        uint32_t from_start,
                                        FixedArrayBase* to,
-                                       ElementsKind to_kind,
+                                       ElementsKind from_kind,
                                        uint32_t to_start,
                                        int packed_size,
                                        int copy_size) {
-    switch (to_kind) {
+    switch (from_kind) {
       case FAST_SMI_ELEMENTS:
-      case FAST_ELEMENTS:
+        CopyPackedSmiToDoubleElements(
+            from, from_start, to, to_start, packed_size, copy_size);
+        break;
       case FAST_HOLEY_SMI_ELEMENTS:
-      case FAST_HOLEY_ELEMENTS:
-        return CopyDoubleToObjectElements(
-            FixedDoubleArray::castOrEmptyFixedArray(from), from_start,
-            FixedArray::cast(to), to_kind, to_start, copy_size);
+        CopySmiToDoubleElements(from, from_start, to, to_start, copy_size);
+        break;
       case FAST_DOUBLE_ELEMENTS:
       case FAST_HOLEY_DOUBLE_ELEMENTS:
-        CopyDoubleToDoubleElements(
-            FixedDoubleArray::castOrEmptyFixedArray(from), from_start,
-            FixedDoubleArray::castOrEmptyFixedArray(to), to_start, copy_size);
-        return from;
-      default:
+        CopyDoubleToDoubleElements(from, from_start, to, to_start, copy_size);
+        break;
+      case FAST_ELEMENTS:
+      case FAST_HOLEY_ELEMENTS:
+        CopyObjectToDoubleElements(from, from_start, to, to_start, copy_size);
+        break;
+      case DICTIONARY_ELEMENTS:
+        CopyDictionaryToDoubleElements(
+            from, from_start, to, to_start, copy_size);
+        break;
+      case NON_STRICT_ARGUMENTS_ELEMENTS:
+      case EXTERNAL_BYTE_ELEMENTS:
+      case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
+      case EXTERNAL_SHORT_ELEMENTS:
+      case EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
+      case EXTERNAL_INT_ELEMENTS:
+      case EXTERNAL_UNSIGNED_INT_ELEMENTS:
+      case EXTERNAL_FLOAT_ELEMENTS:
+      case EXTERNAL_DOUBLE_ELEMENTS:
+      case EXTERNAL_PIXEL_ELEMENTS:
         UNREACHABLE();
     }
     return to->GetHeap()->undefined_value();
   }
 };
 
 
 class FastPackedDoubleElementsAccessor
     : public FastDoubleElementsAccessor<
         FastPackedDoubleElementsAccessor,
@@ skipping 36 matching lines @@
 
  protected:
   typedef typename ElementsKindTraits<Kind>::BackingStore BackingStore;
 
   friend class ElementsAccessorBase<ExternalElementsAccessorSubclass,
                                     ElementsKindTraits<Kind> >;
 
   MUST_USE_RESULT static MaybeObject* GetImpl(Object* receiver,
                                               JSObject* obj,
                                               uint32_t key,
-                                              BackingStore* backing_store) {
+                                              FixedArrayBase* backing_store) {
     return
         key < ExternalElementsAccessorSubclass::GetCapacityImpl(backing_store)
-        ? backing_store->get(key)
+        ? BackingStore::cast(backing_store)->get(key)
         : backing_store->GetHeap()->undefined_value();
   }
 
   MUST_USE_RESULT static PropertyAttributes GetAttributesImpl(
       Object* receiver,
       JSObject* obj,
       uint32_t key,
       FixedArrayBase* backing_store) {
     return
         key < ExternalElementsAccessorSubclass::GetCapacityImpl(backing_store)
           ? NONE : ABSENT;
   }
 
   MUST_USE_RESULT static PropertyType GetTypeImpl(
       Object* receiver,
       JSObject* obj,
       uint32_t key,
-      BackingStore* backing_store) {
+      FixedArrayBase* backing_store) {
     return
         key < ExternalElementsAccessorSubclass::GetCapacityImpl(backing_store)
           ? FIELD : NONEXISTENT;
   }
 
   MUST_USE_RESULT static MaybeObject* SetLengthImpl(
       JSObject* obj,
       Object* length,
-      BackingStore* backing_store) {
+      FixedArrayBase* backing_store) {
     // External arrays do not support changing their length.
     UNREACHABLE();
     return obj;
   }
 
   MUST_USE_RESULT virtual MaybeObject* Delete(JSObject* obj,
                                               uint32_t key,
                                               JSReceiver::DeleteMode mode) {
     // External arrays always ignore deletes.
     return obj->GetHeap()->true_value();
   }
 
   static bool HasElementImpl(Object* receiver,
                              JSObject* holder,
                              uint32_t key,
-                             BackingStore* backing_store) {
+                             FixedArrayBase* backing_store) {
     uint32_t capacity =
         ExternalElementsAccessorSubclass::GetCapacityImpl(backing_store);
     return key < capacity;
   }
 };
 
 
 class ExternalByteElementsAccessor
     : public ExternalElementsAccessor<ExternalByteElementsAccessor,
                                       EXTERNAL_BYTE_ELEMENTS> {
@@ skipping 88 matching lines @@
     : public ElementsAccessorBase<DictionaryElementsAccessor,
                                   ElementsKindTraits<DICTIONARY_ELEMENTS> > {
  public:
   explicit DictionaryElementsAccessor(const char* name)
       : ElementsAccessorBase<DictionaryElementsAccessor,
                              ElementsKindTraits<DICTIONARY_ELEMENTS> >(name) {}
 
   // Adjusts the length of the dictionary backing store and returns the new
   // length according to ES5 section 15.4.5.2 behavior.
   MUST_USE_RESULT static MaybeObject* SetLengthWithoutNormalize(
-      SeededNumberDictionary* dict,
+      FixedArrayBase* store,
       JSArray* array,
       Object* length_object,
       uint32_t length) {
+    SeededNumberDictionary* dict = SeededNumberDictionary::cast(store);
     Heap* heap = array->GetHeap();
     int capacity = dict->Capacity();
     uint32_t new_length = length;
     uint32_t old_length = static_cast<uint32_t>(array->length()->Number());
     if (new_length < old_length) {
       // Find last non-deletable element in range of elements to be
       // deleted and adjust range accordingly.
       for (int i = 0; i < capacity; i++) {
         Object* key = dict->KeyAt(i);
         if (key->IsNumber()) {
@@ skipping 79 matching lines @@
       } else {
         obj->set_elements(new_elements);
       }
     }
     return heap->true_value();
   }
 
   MUST_USE_RESULT static MaybeObject* CopyElementsImpl(FixedArrayBase* from,
                                                        uint32_t from_start,
                                                        FixedArrayBase* to,
-                                                       ElementsKind to_kind,
+                                                       ElementsKind from_kind,
                                                        uint32_t to_start,
                                                        int packed_size,
                                                        int copy_size) {
-    switch (to_kind) {
-      case FAST_SMI_ELEMENTS:
-      case FAST_ELEMENTS:
-      case FAST_HOLEY_SMI_ELEMENTS:
-      case FAST_HOLEY_ELEMENTS:
-        CopyDictionaryToObjectElements(
-            SeededNumberDictionary::cast(from), from_start,
-            FixedArray::cast(to), to_kind, to_start, copy_size);
-        return from;
-      case FAST_DOUBLE_ELEMENTS:
-      case FAST_HOLEY_DOUBLE_ELEMENTS:
-        CopyDictionaryToDoubleElements(
-            SeededNumberDictionary::cast(from), from_start,
-            FixedDoubleArray::castOrEmptyFixedArray(to), to_start,
-            copy_size);
-        return from;
-      default:
-        UNREACHABLE();
-    }
-    return to->GetHeap()->undefined_value();
+    UNREACHABLE();
+    return NULL;
   }
 
 
  protected:
   friend class ElementsAccessorBase<DictionaryElementsAccessor,
                                     ElementsKindTraits<DICTIONARY_ELEMENTS> >;
 
   MUST_USE_RESULT virtual MaybeObject* Delete(JSObject* obj,
                                               uint32_t key,
                                               JSReceiver::DeleteMode mode) {
     return DeleteCommon(obj, key, mode);
   }
 
   MUST_USE_RESULT static MaybeObject* GetImpl(
       Object* receiver,
       JSObject* obj,
       uint32_t key,
-      SeededNumberDictionary* backing_store) {
+      FixedArrayBase* store) {
+    SeededNumberDictionary* backing_store = SeededNumberDictionary::cast(store);
     int entry = backing_store->FindEntry(key);
     if (entry != SeededNumberDictionary::kNotFound) {
       Object* element = backing_store->ValueAt(entry);
       PropertyDetails details = backing_store->DetailsAt(entry);
       if (details.type() == CALLBACKS) {
         return obj->GetElementWithCallback(receiver,
                                            element,
                                            key,
                                            obj);
       } else {
@@ skipping 14 matching lines @@
     if (entry != SeededNumberDictionary::kNotFound) {
       return dictionary->DetailsAt(entry).attributes();
     }
     return ABSENT;
   }
 
   MUST_USE_RESULT static PropertyType GetTypeImpl(
       Object* receiver,
       JSObject* obj,
       uint32_t key,
-      SeededNumberDictionary* backing_store) {
+      FixedArrayBase* store) {
+    SeededNumberDictionary* backing_store = SeededNumberDictionary::cast(store);
     int entry = backing_store->FindEntry(key);
     if (entry != SeededNumberDictionary::kNotFound) {
       return backing_store->DetailsAt(entry).type();
     }
     return NONEXISTENT;
   }
 
   MUST_USE_RESULT static AccessorPair* GetAccessorPairImpl(
       Object* receiver,
       JSObject* obj,
       uint32_t key,
-      BackingStore* backing_store) {
+      FixedArrayBase* store) {
+    SeededNumberDictionary* backing_store = SeededNumberDictionary::cast(store);
     int entry = backing_store->FindEntry(key);
     if (entry != SeededNumberDictionary::kNotFound &&
         backing_store->DetailsAt(entry).type() == CALLBACKS &&
         backing_store->ValueAt(entry)->IsAccessorPair()) {
       return AccessorPair::cast(backing_store->ValueAt(entry));
     }
     return NULL;
   }
 
   static bool HasElementImpl(Object* receiver,
                              JSObject* holder,
                              uint32_t key,
-                             SeededNumberDictionary* backing_store) {
-    return backing_store->FindEntry(key) !=
+                             FixedArrayBase* backing_store) {
+    return SeededNumberDictionary::cast(backing_store)->FindEntry(key) !=
         SeededNumberDictionary::kNotFound;
   }
 
-  static uint32_t GetKeyForIndexImpl(SeededNumberDictionary* dict,
+  static uint32_t GetKeyForIndexImpl(FixedArrayBase* store,
                                      uint32_t index) {
+    SeededNumberDictionary* dict = SeededNumberDictionary::cast(store);
     Object* key = dict->KeyAt(index);
     return Smi::cast(key)->value();
   }
 };
 
 
 class NonStrictArgumentsElementsAccessor : public ElementsAccessorBase<
     NonStrictArgumentsElementsAccessor,
     ElementsKindTraits<NON_STRICT_ARGUMENTS_ELEMENTS> > {
  public:
   explicit NonStrictArgumentsElementsAccessor(const char* name)
       : ElementsAccessorBase<
           NonStrictArgumentsElementsAccessor,
           ElementsKindTraits<NON_STRICT_ARGUMENTS_ELEMENTS> >(name) {}
  protected:
   friend class ElementsAccessorBase<
       NonStrictArgumentsElementsAccessor,
       ElementsKindTraits<NON_STRICT_ARGUMENTS_ELEMENTS> >;
 
   MUST_USE_RESULT static MaybeObject* GetImpl(Object* receiver,
                                               JSObject* obj,
                                               uint32_t key,
-                                              FixedArray* parameter_map) {
+                                              FixedArrayBase* parameters) {
+    FixedArray* parameter_map = FixedArray::cast(parameters);
     Object* probe = GetParameterMapArg(obj, parameter_map, key);
     if (!probe->IsTheHole()) {
       Context* context = Context::cast(parameter_map->get(0));
       int context_index = Smi::cast(probe)->value();
       ASSERT(!context->get(context_index)->IsTheHole());
       return context->get(context_index);
     } else {
       // Object is not mapped, defer to the arguments.
       FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
       MaybeObject* maybe_result = ElementsAccessor::ForArray(arguments)->Get(
@@ skipping 27 matching lines @@
       FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
       return ElementsAccessor::ForArray(arguments)->GetAttributes(
           receiver, obj, key, arguments);
     }
   }
 
   MUST_USE_RESULT static PropertyType GetTypeImpl(
       Object* receiver,
       JSObject* obj,
       uint32_t key,
-      FixedArray* parameter_map) {
+      FixedArrayBase* parameters) {
+    FixedArray* parameter_map = FixedArray::cast(parameters);
     Object* probe = GetParameterMapArg(obj, parameter_map, key);
     if (!probe->IsTheHole()) {
       return FIELD;
     } else {
       // If not aliased, check the arguments.
       FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
       return ElementsAccessor::ForArray(arguments)->GetType(
           receiver, obj, key, arguments);
     }
   }
 
   MUST_USE_RESULT static AccessorPair* GetAccessorPairImpl(
       Object* receiver,
       JSObject* obj,
       uint32_t key,
-      FixedArray* parameter_map) {
+      FixedArrayBase* parameters) {
+    FixedArray* parameter_map = FixedArray::cast(parameters);
     Object* probe = GetParameterMapArg(obj, parameter_map, key);
     if (!probe->IsTheHole()) {
       return NULL;
     } else {
       // If not aliased, check the arguments.
       FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
       return ElementsAccessor::ForArray(arguments)->GetAccessorPair(
           receiver, obj, key, arguments);
     }
   }
 
   MUST_USE_RESULT static MaybeObject* SetLengthImpl(
       JSObject* obj,
       Object* length,
-      FixedArray* parameter_map) {
+      FixedArrayBase* parameter_map) {
     // TODO(mstarzinger): This was never implemented but will be used once we
     // correctly implement [[DefineOwnProperty]] on arrays.
     UNIMPLEMENTED();
     return obj;
   }
 
   MUST_USE_RESULT virtual MaybeObject* Delete(JSObject* obj,
                                               uint32_t key,
                                               JSReceiver::DeleteMode mode) {
     FixedArray* parameter_map = FixedArray::cast(obj->elements());
@@ skipping 13 matching lines @@
         // the class for the most generalized ElementsKind subclass.
         return FastHoleyObjectElementsAccessor::DeleteCommon(obj, key, mode);
       }
     }
     return obj->GetHeap()->true_value();
   }
 
   MUST_USE_RESULT static MaybeObject* CopyElementsImpl(FixedArrayBase* from,
                                                        uint32_t from_start,
                                                        FixedArrayBase* to,
-                                                       ElementsKind to_kind,
+                                                       ElementsKind from_kind,
                                                        uint32_t to_start,
                                                        int packed_size,
                                                        int copy_size) {
-    FixedArray* parameter_map = FixedArray::cast(from);
-    FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
-    ElementsAccessor* accessor = ElementsAccessor::ForArray(arguments);
-    return accessor->CopyElements(NULL, from_start, to, to_kind,
-                                  to_start, copy_size, arguments);
+    UNREACHABLE();
+    return NULL;
   }
 
   static uint32_t GetCapacityImpl(FixedArrayBase* backing_store) {
     FixedArray* parameter_map = FixedArray::cast(backing_store);
     FixedArrayBase* arguments = FixedArrayBase::cast(parameter_map->get(1));
     return Max(static_cast<uint32_t>(parameter_map->length() - 2),
                ForArray(arguments)->GetCapacity(arguments));
   }
 
-  static uint32_t GetKeyForIndexImpl(FixedArray* dict,
+  static uint32_t GetKeyForIndexImpl(FixedArrayBase* dict,
                                      uint32_t index) {
     return index;
   }
 
   static bool HasElementImpl(Object* receiver,
                              JSObject* holder,
                              uint32_t key,
-                             FixedArray* parameter_map) {
+                             FixedArrayBase* parameters) {
+    FixedArray* parameter_map = FixedArray::cast(parameters);
     Object* probe = GetParameterMapArg(holder, parameter_map, key);
     if (!probe->IsTheHole()) {
       return true;
     } else {
-      FixedArrayBase* arguments = FixedArrayBase::cast(parameter_map->get(1));
+      FixedArrayBase* arguments =
+          FixedArrayBase::cast(FixedArray::cast(parameter_map)->get(1));
       ElementsAccessor* accessor = ElementsAccessor::ForArray(arguments);
       return !accessor->Get(receiver, holder, key, arguments)->IsTheHole();
     }
   }
 
  private:
   static Object* GetParameterMapArg(JSObject* holder,
                                     FixedArray* parameter_map,
                                     uint32_t key) {
     uint32_t length = holder->IsJSArray()
         ? Smi::cast(JSArray::cast(holder)->length())->value()
         : parameter_map->length();
-    return key < (length - 2 )
+    return key < (length - 2)
         ? parameter_map->get(key + 2)
         : parameter_map->GetHeap()->the_hole_value();
   }
 };
 
 
 ElementsAccessor* ElementsAccessor::ForArray(FixedArrayBase* array) {
-  switch (array->map()->instance_type()) {
-    case FIXED_ARRAY_TYPE:
-      if (array->IsDictionary()) {
-        return elements_accessors_[DICTIONARY_ELEMENTS];
-      } else {
-        return elements_accessors_[FAST_HOLEY_ELEMENTS];
-      }
-    case EXTERNAL_BYTE_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_BYTE_ELEMENTS];
-    case EXTERNAL_UNSIGNED_BYTE_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_UNSIGNED_BYTE_ELEMENTS];
-    case EXTERNAL_SHORT_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_SHORT_ELEMENTS];
-    case EXTERNAL_UNSIGNED_SHORT_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_UNSIGNED_SHORT_ELEMENTS];
-    case EXTERNAL_INT_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_INT_ELEMENTS];
-    case EXTERNAL_UNSIGNED_INT_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_UNSIGNED_INT_ELEMENTS];
-    case EXTERNAL_FLOAT_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_FLOAT_ELEMENTS];
-    case EXTERNAL_DOUBLE_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_DOUBLE_ELEMENTS];
-    case EXTERNAL_PIXEL_ARRAY_TYPE:
-      return elements_accessors_[EXTERNAL_PIXEL_ELEMENTS];
-    default:
-      UNREACHABLE();
-      return NULL;
-  }
+  return elements_accessors_[ElementsKindForArray(array)];
 }
 
 
 void ElementsAccessor::InitializeOncePerProcess() {
   static ElementsAccessor* accessor_array[] = {
 #define ACCESSOR_ARRAY(Class, Kind, Store) new Class(#Kind),
     ELEMENTS_LIST(ACCESSOR_ARRAY)
 #undef ACCESSOR_ARRAY
   };
 
@@ skipping 10 matching lines @@
 #undef ACCESSOR_DELETE
   elements_accessors_ = NULL;
 }
 
 
 template <typename ElementsAccessorSubclass, typename ElementsKindTraits>
 MUST_USE_RESULT MaybeObject* ElementsAccessorBase<ElementsAccessorSubclass,
                                                   ElementsKindTraits>::
     SetLengthImpl(JSObject* obj,
                   Object* length,
-                  typename ElementsKindTraits::BackingStore* backing_store) {
+                  FixedArrayBase* backing_store) {
   JSArray* array = JSArray::cast(obj);
 
   // Fast case: The new length fits into a Smi.
   MaybeObject* maybe_smi_length = length->ToSmi();
   Object* smi_length = Smi::FromInt(0);
   if (maybe_smi_length->ToObject(&smi_length) && smi_length->IsSmi()) {
     const int value = Smi::cast(smi_length)->value();
     if (value >= 0) {
       Object* new_length;
       MaybeObject* result = ElementsAccessorSubclass::
@@ skipping 36 matching lines @@
   if (!maybe_obj->To(&new_backing_store)) return maybe_obj;
   new_backing_store->set(0, length);
   { MaybeObject* result = array->SetContent(new_backing_store);
     if (result->IsFailure()) return result;
   }
   return array;
 }
 
 
 } }  // namespace v8::internal