Implement tracking and optimizations of packed arrays.

src/runtime.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 190 matching lines @@
           if (!maybe_result->ToObject(&result)) return maybe_result;
         }
       }
     }
   }
 
   // Deep copy local elements.
   // Pixel elements cannot be created using an object literal.
   ASSERT(!copy->HasExternalArrayElements());
   switch (copy->GetElementsKind()) {
-    case FAST_SMI_ONLY_ELEMENTS:
-    case FAST_ELEMENTS: {
+    case FAST_SMI_ELEMENTS:
+    case FAST_ELEMENTS:
+    case FAST_HOLEY_SMI_ELEMENTS:
+    case FAST_HOLEY_ELEMENTS: {
       FixedArray* elements = FixedArray::cast(copy->elements());
       if (elements->map() == heap->fixed_cow_array_map()) {
         isolate->counters()->cow_arrays_created_runtime()->Increment();
 #ifdef DEBUG
         for (int i = 0; i < elements->length(); i++) {
           ASSERT(!elements->get(i)->IsJSObject());
         }
 #endif
       } else {
         for (int i = 0; i < elements->length(); i++) {
           Object* value = elements->get(i);
           ASSERT(value->IsSmi() ||
                  value->IsTheHole() ||
-                 (copy->GetElementsKind() == FAST_ELEMENTS));
+                 (IsFastObjectElementsKind(copy->GetElementsKind())));
           if (value->IsJSObject()) {
             JSObject* js_object = JSObject::cast(value);
             { MaybeObject* maybe_result = DeepCopyBoilerplate(isolate,
                                                               js_object);
               if (!maybe_result->ToObject(&result)) return maybe_result;
             }
             elements->set(i, result);
           }
         }
       }
@@ skipping 24 matching lines @@
     case EXTERNAL_PIXEL_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 FAST_DOUBLE_ELEMENTS:
+    case FAST_HOLEY_DOUBLE_ELEMENTS:
       // No contained objects, nothing to do.
       break;
   }
   return copy;
 }
 
 
 static Handle<Map> ComputeObjectLiteralMap(
     Handle<Context> context,
     Handle<FixedArray> constant_properties,
@@ skipping 164 matching lines @@
   if (Map::IsValidElementsTransition(from_kind, to_kind)) {
     Handle<Object> result = JSObject::TransitionElementsKind(
         Handle<JSObject>::cast(object), to_kind);
     if (result.is_null()) return isolate->ThrowIllegalOperation();
     return *result;
   }
   return isolate->ThrowIllegalOperation();
 }
 
 
-static const int kSmiOnlyLiteralMinimumLength = 1024;
+static const int kSmiLiteralMinimumLength = 1024;
 
 
 Handle<Object> Runtime::CreateArrayLiteralBoilerplate(
     Isolate* isolate,
     Handle<FixedArray> literals,
     Handle<FixedArray> elements) {
   // Create the JSArray.
   Handle<JSFunction> constructor(
       JSFunction::GlobalContextFromLiterals(*literals)->array_function());
   Handle<JSArray> object =
       Handle<JSArray>::cast(isolate->factory()->NewJSObject(constructor));
 
   ElementsKind constant_elements_kind =
       static_cast<ElementsKind>(Smi::cast(elements->get(0))->value());
   Handle<FixedArrayBase> constant_elements_values(
       FixedArrayBase::cast(elements->get(1)));
 
+  ASSERT(IsFastElementsKind(constant_elements_kind));
   Context* global_context = isolate->context()->global_context();
-  if (constant_elements_kind == FAST_SMI_ONLY_ELEMENTS) {
-    object->set_map(Map::cast(global_context->smi_js_array_map()));
-  } else if (constant_elements_kind == FAST_DOUBLE_ELEMENTS) {
-    object->set_map(Map::cast(global_context->double_js_array_map()));
-  } else {
-    object->set_map(Map::cast(global_context->object_js_array_map()));
-  }
+  Object* maybe_maps_array = global_context->js_array_maps();
+  ASSERT(!maybe_maps_array->IsUndefined());
+  Object* maybe_map = FixedArray::cast(maybe_maps_array)->get(
+      constant_elements_kind);
+  ASSERT(maybe_map->IsMap());
+  object->set_map(Map::cast(maybe_map));
 
   Handle<FixedArrayBase> copied_elements_values;
-  if (constant_elements_kind == FAST_DOUBLE_ELEMENTS) {
+  if (IsFastDoubleElementsKind(constant_elements_kind)) {
     ASSERT(FLAG_smi_only_arrays);
     copied_elements_values = isolate->factory()->CopyFixedDoubleArray(
         Handle<FixedDoubleArray>::cast(constant_elements_values));
   } else {
-    ASSERT(constant_elements_kind == FAST_SMI_ONLY_ELEMENTS ||
-           constant_elements_kind == FAST_ELEMENTS);
+    ASSERT(IsFastSmiOrObjectElementsKind(constant_elements_kind));
     const bool is_cow =
         (constant_elements_values->map() ==
          isolate->heap()->fixed_cow_array_map());
     if (is_cow) {
       copied_elements_values = constant_elements_values;
 #if DEBUG
       Handle<FixedArray> fixed_array_values =
           Handle<FixedArray>::cast(copied_elements_values);
       for (int i = 0; i < fixed_array_values->length(); i++) {
         ASSERT(!fixed_array_values->get(i)->IsFixedArray());
@@ skipping 15 matching lines @@
               CreateLiteralBoilerplate(isolate, literals, fa);
           if (result.is_null()) return result;
           fixed_array_values_copy->set(i, *result);
         }
       }
     }
   }
   object->set_elements(*copied_elements_values);
   object->set_length(Smi::FromInt(copied_elements_values->length()));
 
-  //  Ensure that the boilerplate object has FAST_ELEMENTS, unless the flag is
+  //  Ensure that the boilerplate object has FAST_*_ELEMENTS, unless the flag is
   //  on or the object is larger than the threshold.
   if (!FLAG_smi_only_arrays &&
-      constant_elements_values->length() < kSmiOnlyLiteralMinimumLength) {
-    if (object->GetElementsKind() != FAST_ELEMENTS) {
-      CHECK(!TransitionElements(object, FAST_ELEMENTS, isolate)->IsFailure());
+      constant_elements_values->length() < kSmiLiteralMinimumLength) {
+    ElementsKind elements_kind = object->GetElementsKind();
+    if (!IsFastObjectElementsKind(elements_kind)) {
+      if (IsFastHoleyElementsKind(elements_kind)) {
+        CHECK(!TransitionElements(object, FAST_HOLEY_ELEMENTS,
+                                  isolate)->IsFailure());
+      } else {
+        CHECK(!TransitionElements(object, FAST_ELEMENTS, isolate)->IsFailure());
+      }
     }
   }
 
   return object;
 }
 
 
 static Handle<Object> CreateLiteralBoilerplate(
     Isolate* isolate,
     Handle<FixedArray> literals,
@@ skipping 1182 matching lines @@
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpExec) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 4);
   CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, subject, 1);
   // Due to the way the JS calls are constructed this must be less than the
   // length of a string, i.e. it is always a Smi.  We check anyway for security.
   CONVERT_SMI_ARG_CHECKED(index, 2);
   CONVERT_ARG_HANDLE_CHECKED(JSArray, last_match_info, 3);
-  RUNTIME_ASSERT(last_match_info->HasFastElements());
+  RUNTIME_ASSERT(last_match_info->HasFastObjectElements());
   RUNTIME_ASSERT(index >= 0);
   RUNTIME_ASSERT(index <= subject->length());
   isolate->counters()->regexp_entry_runtime()->Increment();
   Handle<Object> result = RegExpImpl::Exec(regexp,
                                            subject,
                                            index,
                                            last_match_info);
   if (result.is_null()) return Failure::Exception();
   return *result;
 }
@@ skipping 1353 matching lines @@
 
   // Index of end of last match.
   int prev = 0;
 
   // Number of parts added by compiled replacement plus preceeding
   // string and possibly suffix after last match.  It is possible for
   // all components to use two elements when encoded as two smis.
   const int parts_added_per_loop = 2 * (compiled_replacement.parts() + 2);
   bool matched = true;
   do {
-    ASSERT(last_match_info_handle->HasFastElements());
+    ASSERT(last_match_info_handle->HasFastObjectElements());
     // Increase the capacity of the builder before entering local handle-scope,
     // so its internal buffer can safely allocate a new handle if it grows.
     builder.EnsureCapacity(parts_added_per_loop);
 
     HandleScope loop_scope(isolate);
     int start, end;
     {
       AssertNoAllocation match_info_array_is_not_in_a_handle;
       FixedArray* match_info_array =
           FixedArray::cast(last_match_info_handle->elements());
@@ skipping 76 matching lines @@
     }
   }
 
   Handle<Object> match = RegExpImpl::Exec(regexp_handle,
                                           subject_handle,
                                           0,
                                           last_match_info_handle);
   if (match.is_null()) return Failure::Exception();
   if (match->IsNull()) return *subject_handle;
 
-  ASSERT(last_match_info_handle->HasFastElements());
+  ASSERT(last_match_info_handle->HasFastObjectElements());
 
   int start, end;
   {
     AssertNoAllocation match_info_array_is_not_in_a_handle;
     FixedArray* match_info_array =
         FixedArray::cast(last_match_info_handle->elements());
 
     start = RegExpImpl::GetCapture(match_info_array, 0);
     end = RegExpImpl::GetCapture(match_info_array, 1);
   }
@@ skipping 53 matching lines @@
       next++;
       if (next > length) break;
     }
     match = RegExpImpl::Exec(regexp_handle,
                              subject_handle,
                              next,
                              last_match_info_handle);
     if (match.is_null()) return Failure::Exception();
     if (match->IsNull()) break;
 
-    ASSERT(last_match_info_handle->HasFastElements());
+    ASSERT(last_match_info_handle->HasFastObjectElements());
     HandleScope loop_scope(isolate);
     {
       AssertNoAllocation match_info_array_is_not_in_a_handle;
       FixedArray* match_info_array =
           FixedArray::cast(last_match_info_handle->elements());
       start = RegExpImpl::GetCapture(match_info_array, 0);
       end = RegExpImpl::GetCapture(match_info_array, 1);
     }
   } while (true);
 
@@ skipping 49 matching lines @@
       if (!maybe_flat_replacement->ToObject(&flat_replacement)) {
         return maybe_flat_replacement;
       }
     }
     replacement = String::cast(flat_replacement);
   }
 
   CONVERT_ARG_CHECKED(JSRegExp, regexp, 1);
   CONVERT_ARG_CHECKED(JSArray, last_match_info, 3);
 
-  ASSERT(last_match_info->HasFastElements());
+  ASSERT(last_match_info->HasFastObjectElements());
 
   if (replacement->length() == 0) {
     if (subject->HasOnlyAsciiChars()) {
       return StringReplaceRegExpWithEmptyString<SeqAsciiString>(
           isolate, subject, regexp, last_match_info);
     } else {
       return StringReplaceRegExpWithEmptyString<SeqTwoByteString>(
           isolate, subject, regexp, last_match_info);
     }
   }
@@ skipping 644 matching lines @@
 RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpExecMultiple) {
   ASSERT(args.length() == 4);
   HandleScope handles(isolate);
 
   CONVERT_ARG_HANDLE_CHECKED(String, subject, 1);
   if (!subject->IsFlat()) FlattenString(subject);
   CONVERT_ARG_HANDLE_CHECKED(JSRegExp, regexp, 0);
   CONVERT_ARG_HANDLE_CHECKED(JSArray, last_match_info, 2);
   CONVERT_ARG_HANDLE_CHECKED(JSArray, result_array, 3);
 
-  ASSERT(last_match_info->HasFastElements());
+  ASSERT(last_match_info->HasFastObjectElements());
   ASSERT(regexp->GetFlags().is_global());
   Handle<FixedArray> result_elements;
-  if (result_array->HasFastElements()) {
+  if (result_array->HasFastObjectElements()) {
     result_elements =
         Handle<FixedArray>(FixedArray::cast(result_array->elements()));
   }
   if (result_elements.is_null() || result_elements->length() < 16) {
     result_elements = isolate->factory()->NewFixedArrayWithHoles(16);
   }
   FixedArrayBuilder builder(result_elements);
 
   if (regexp->TypeTag() == JSRegExp::ATOM) {
     Handle<String> pattern(
@@ skipping 281 matching lines @@
           if (!receiver->IsGlobalObject()) return value;
           value = JSGlobalPropertyCell::cast(value)->value();
           if (!value->IsTheHole()) return value;
           // If value is the hole do the general lookup.
         }
       }
     } else if (FLAG_smi_only_arrays && args.at<Object>(1)->IsSmi()) {
       // JSObject without a string key. If the key is a Smi, check for a
       // definite out-of-bounds access to elements, which is a strong indicator
       // that subsequent accesses will also call the runtime. Proactively
-      // transition elements to FAST_ELEMENTS to avoid excessive boxing of
+      // transition elements to FAST_*_ELEMENTS to avoid excessive boxing of
       // doubles for those future calls in the case that the elements would
       // become FAST_DOUBLE_ELEMENTS.
       Handle<JSObject> js_object(args.at<JSObject>(0));
       ElementsKind elements_kind = js_object->GetElementsKind();
-      if (elements_kind == FAST_SMI_ONLY_ELEMENTS ||
-          elements_kind == FAST_DOUBLE_ELEMENTS) {
+      if (IsFastSmiElementsKind(elements_kind)) {
         FixedArrayBase* elements = js_object->elements();
         if (args.at<Smi>(1)->value() >= elements->length()) {
+          elements_kind = FastSmiToObjectElementsKind(elements_kind);
           MaybeObject* maybe_object = TransitionElements(js_object,
-                                                         FAST_ELEMENTS,
+                                                         elements_kind,
                                                          isolate);
           if (maybe_object->IsFailure()) return maybe_object;
         }
       }
     }
   } else if (args[0]->IsString() && args[1]->IsSmi()) {
     // Fast case for string indexing using [] with a smi index.
     HandleScope scope(isolate);
     Handle<String> str = args.at<String>(0);
     int index = args.smi_at(1);
@@ skipping 149 matching lines @@
     // of a string using [] notation.  We need to support this too in
     // JavaScript.
     // In the case of a String object we just need to redirect the assignment to
     // the underlying string if the index is in range.  Since the underlying
     // string does nothing with the assignment then we can ignore such
     // assignments.
     if (js_object->IsStringObjectWithCharacterAt(index)) {
       return *value;
     }
 
+#if DEBUG
+    js_object->ValidateElements();
+#endif
     Handle<Object> result = JSObject::SetElement(
         js_object, index, value, attr, strict_mode, set_mode);
+#if DEBUG
+    js_object->ValidateElements();
+#endif
     if (result.is_null()) return Failure::Exception();
     return *value;
   }
 
   if (key->IsString()) {
     Handle<Object> result;
     if (Handle<String>::cast(key)->AsArrayIndex(&index)) {
       result = JSObject::SetElement(
           js_object, index, value, attr, strict_mode, set_mode);
     } else {
@@ skipping 137 matching lines @@
                                     value,
                                     attributes,
                                     strict_mode);
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsSmiToDouble) {
   NoHandleAllocation ha;
   RUNTIME_ASSERT(args.length() == 1);
   Handle<Object> object = args.at<Object>(0);
-  return TransitionElements(object, FAST_DOUBLE_ELEMENTS, isolate);
+  if (object->IsJSObject()) {
+    Handle<JSObject> js_object(Handle<JSObject>::cast(object));
+    ElementsKind new_kind = js_object->HasFastHoleyElements()
+        ? FAST_HOLEY_DOUBLE_ELEMENTS
+        : FAST_DOUBLE_ELEMENTS;
+    return TransitionElements(object, new_kind, isolate);
+  } else {
+    return *object;
+  }
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_TransitionElementsDoubleToObject) {
   NoHandleAllocation ha;
   RUNTIME_ASSERT(args.length() == 1);
   Handle<Object> object = args.at<Object>(0);
-  return TransitionElements(object, FAST_ELEMENTS, isolate);
+  if (object->IsJSObject()) {
+    Handle<JSObject> js_object(Handle<JSObject>::cast(object));
+    ElementsKind new_kind = js_object->HasFastHoleyElements()
+        ? FAST_HOLEY_ELEMENTS
+        : FAST_ELEMENTS;
+    return TransitionElements(object, new_kind, isolate);
+  } else {
+    return *object;
+  }
 }
 
 
 // Set the native flag on the function.
 // This is used to decide if we should transform null and undefined
 // into the global object when doing call and apply.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetNativeFlag) {
   NoHandleAllocation ha;
   RUNTIME_ASSERT(args.length() == 1);
 
@@ skipping 10 matching lines @@
 RUNTIME_FUNCTION(MaybeObject*, Runtime_StoreArrayLiteralElement) {
   RUNTIME_ASSERT(args.length() == 5);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
   CONVERT_SMI_ARG_CHECKED(store_index, 1);
   Handle<Object> value = args.at<Object>(2);
   CONVERT_ARG_HANDLE_CHECKED(FixedArray, literals, 3);
   CONVERT_SMI_ARG_CHECKED(literal_index, 4);
   HandleScope scope;
 
   Object* raw_boilerplate_object = literals->get(literal_index);
-  Handle<JSArray> boilerplate(JSArray::cast(raw_boilerplate_object));
-#if DEBUG
+  Handle<JSArray> boilerplate_object(JSArray::cast(raw_boilerplate_object));
   ElementsKind elements_kind = object->GetElementsKind();
-#endif
-  ASSERT(elements_kind <= FAST_DOUBLE_ELEMENTS);
+  ASSERT(IsFastElementsKind(elements_kind));
   // Smis should never trigger transitions.
   ASSERT(!value->IsSmi());
 
   if (value->IsNumber()) {
-    ASSERT(elements_kind == FAST_SMI_ONLY_ELEMENTS);
-    JSObject::TransitionElementsKind(object, FAST_DOUBLE_ELEMENTS);
-    if (IsMoreGeneralElementsKindTransition(boilerplate->GetElementsKind(),
-                                            FAST_DOUBLE_ELEMENTS)) {
-      JSObject::TransitionElementsKind(boilerplate, FAST_DOUBLE_ELEMENTS);
+    ASSERT(IsFastSmiElementsKind(elements_kind));
+    ElementsKind transitioned_kind = IsFastHoleyElementsKind(elements_kind)
+        ? FAST_HOLEY_DOUBLE_ELEMENTS
+        : FAST_DOUBLE_ELEMENTS;
+    if (IsMoreGeneralElementsKindTransition(
+            boilerplate_object->GetElementsKind(),
+            transitioned_kind)) {
+      JSObject::TransitionElementsKind(boilerplate_object, transitioned_kind);
     }
-    ASSERT(object->GetElementsKind() == FAST_DOUBLE_ELEMENTS);
-    FixedDoubleArray* double_array = FixedDoubleArray::cast(object->elements());
+    JSObject::TransitionElementsKind(object, transitioned_kind);
+    ASSERT(IsFastDoubleElementsKind(object->GetElementsKind()));
+    FixedDoubleArray* double_array =
+        FixedDoubleArray::cast(object->elements());
     HeapNumber* number = HeapNumber::cast(*value);
     double_array->set(store_index, number->Number());
   } else {
-    ASSERT(elements_kind == FAST_SMI_ONLY_ELEMENTS ||
-           elements_kind == FAST_DOUBLE_ELEMENTS);
-    JSObject::TransitionElementsKind(object, FAST_ELEMENTS);
-    if (IsMoreGeneralElementsKindTransition(boilerplate->GetElementsKind(),
-                                            FAST_ELEMENTS)) {
-      JSObject::TransitionElementsKind(boilerplate, FAST_ELEMENTS);
+    ASSERT(IsFastSmiElementsKind(elements_kind) ||
+           IsFastDoubleElementsKind(elements_kind));
+    ElementsKind transitioned_kind = IsFastHoleyElementsKind(elements_kind)
+        ? FAST_HOLEY_ELEMENTS
+        : FAST_ELEMENTS;
+    JSObject::TransitionElementsKind(object, transitioned_kind);
+    if (IsMoreGeneralElementsKindTransition(
+            boilerplate_object->GetElementsKind(),
+            transitioned_kind)) {
+      JSObject::TransitionElementsKind(boilerplate_object, transitioned_kind);
     }
-    FixedArray* object_array = FixedArray::cast(object->elements());
+    FixedArray* object_array =
+        FixedArray::cast(object->elements());
     object_array->set(store_index, *value);
   }
   return *object;
 }
 
 
 // Check whether debugger and is about to step into the callback that is passed
 // to a built-in function such as Array.forEach.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugCallbackSupportsStepping) {
   if (!isolate->IsDebuggerActive()) return isolate->heap()->false_value();
@@ skipping 1190 matching lines @@
           new_string, final_length);
   return new_string;
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_QuoteJSONStringArray) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 1);
   CONVERT_ARG_CHECKED(JSArray, array, 0);
 
-  if (!array->HasFastElements()) return isolate->heap()->undefined_value();
+  if (!array->HasFastObjectElements()) {
+    return isolate->heap()->undefined_value();
+  }
   FixedArray* elements = FixedArray::cast(array->elements());
   int n = elements->length();
   bool ascii = true;
   int total_length = 0;
 
   for (int i = 0; i < n; i++) {
     Object* elt = elements->get(i);
     if (!elt->IsString()) return isolate->heap()->undefined_value();
     String* element = String::cast(elt);
     if (!element->IsFlat()) return isolate->heap()->undefined_value();
@@ skipping 422 matching lines @@
   // The list indices now contains the end of each part to create.
 
   // Create JSArray of substrings separated by separator.
   int part_count = indices.length();
 
   Handle<JSArray> result = isolate->factory()->NewJSArray(part_count);
   MaybeObject* maybe_result = result->EnsureCanContainHeapObjectElements();
   if (maybe_result->IsFailure()) return maybe_result;
   result->set_length(Smi::FromInt(part_count));
 
-  ASSERT(result->HasFastElements());
+  ASSERT(result->HasFastObjectElements());
 
   if (part_count == 1 && indices.at(0) == subject_length) {
     FixedArray::cast(result->elements())->set(0, *subject);
     return *result;
   }
 
   Handle<FixedArray> elements(FixedArray::cast(result->elements()));
   int part_start = 0;
   for (int i = 0; i < part_count; i++) {
     HandleScope local_loop_handle;
     int part_end = indices.at(i);
     Handle<String> substring =
         isolate->factory()->NewProperSubString(subject, part_start, part_end);
     elements->set(i, *substring);
     part_start = part_end + pattern_length;
   }
 
   if (limit == 0xffffffffu) {
-    if (result->HasFastElements()) {
+    if (result->HasFastObjectElements()) {
       StringSplitCache::Enter(isolate->heap(),
                               isolate->heap()->string_split_cache(),
                               *subject,
                               *pattern,
                               *elements);
     }
   }
 
   return *result;
 }
@@ skipping 336 matching lines @@
   int array_length = args.smi_at(1);
   CONVERT_ARG_CHECKED(String, special, 2);
 
   // This assumption is used by the slice encoding in one or two smis.
   ASSERT(Smi::kMaxValue >= String::kMaxLength);
 
   MaybeObject* maybe_result = array->EnsureCanContainHeapObjectElements();
   if (maybe_result->IsFailure()) return maybe_result;
 
   int special_length = special->length();
-  if (!array->HasFastElements()) {
+  if (!array->HasFastObjectElements()) {
     return isolate->Throw(isolate->heap()->illegal_argument_symbol());
   }
   FixedArray* fixed_array = FixedArray::cast(array->elements());
   if (fixed_array->length() < array_length) {
     array_length = fixed_array->length();
   }
 
   if (array_length == 0) {
     return isolate->heap()->empty_string();
   } else if (array_length == 1) {
@@ skipping 89 matching lines @@
   NoHandleAllocation ha;
   ASSERT(args.length() == 3);
   CONVERT_ARG_CHECKED(JSArray, array, 0);
   if (!args[1]->IsSmi()) {
     isolate->context()->mark_out_of_memory();
     return Failure::OutOfMemoryException();
   }
   int array_length = args.smi_at(1);
   CONVERT_ARG_CHECKED(String, separator, 2);
 
-  if (!array->HasFastElements()) {
+  if (!array->HasFastObjectElements()) {
     return isolate->Throw(isolate->heap()->illegal_argument_symbol());
   }
   FixedArray* fixed_array = FixedArray::cast(array->elements());
   if (fixed_array->length() < array_length) {
     array_length = fixed_array->length();
   }
 
   if (array_length == 0) {
     return isolate->heap()->empty_string();
   } else if (array_length == 1) {
@@ skipping 96 matching lines @@
     }
   }
   ASSERT(cursor <= buffer.length());
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SparseJoinWithSeparator) {
   NoHandleAllocation ha;
   ASSERT(args.length() == 3);
   CONVERT_ARG_CHECKED(JSArray, elements_array, 0);
-  RUNTIME_ASSERT(elements_array->HasFastElements() ||
-                 elements_array->HasFastSmiOnlyElements());
+  RUNTIME_ASSERT(elements_array->HasFastObjectElements() ||
+                 elements_array->HasFastSmiElements());
   CONVERT_NUMBER_CHECKED(uint32_t, array_length, Uint32, args[1]);
   CONVERT_ARG_CHECKED(String, separator, 2);
   // elements_array is fast-mode JSarray of alternating positions
   // (increasing order) and strings.
   // array_length is length of original array (used to add separators);
   // separator is string to put between elements. Assumed to be non-empty.
 
   // Find total length of join result.
   int string_length = 0;
   bool is_ascii = separator->IsAsciiRepresentation();
@@ skipping 2124 matching lines @@
   ASSERT(args.length() == 2);
 
   CONVERT_ARG_HANDLE_CHECKED(String, str, 0);
   FlattenString(str);
 
   CONVERT_ARG_HANDLE_CHECKED(JSArray, output, 1);
 
   MaybeObject* maybe_result_array =
       output->EnsureCanContainHeapObjectElements();
   if (maybe_result_array->IsFailure()) return maybe_result_array;
-  RUNTIME_ASSERT(output->HasFastElements());
+  RUNTIME_ASSERT(output->HasFastObjectElements());
 
   AssertNoAllocation no_allocation;
 
   FixedArray* output_array = FixedArray::cast(output->elements());
   RUNTIME_ASSERT(output_array->length() >= DateParser::OUTPUT_SIZE);
   bool result;
   String::FlatContent str_content = str->GetFlatContent();
   if (str_content.IsAscii()) {
     result = DateParser::Parse(str_content.ToAsciiVector(),
                                output_array,
@@ skipping 211 matching lines @@
 }
 
 
 // Push an object unto an array of objects if it is not already in the
 // array.  Returns true if the element was pushed on the stack and
 // false otherwise.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_PushIfAbsent) {
   ASSERT(args.length() == 2);
   CONVERT_ARG_CHECKED(JSArray, array, 0);
   CONVERT_ARG_CHECKED(JSObject, element, 1);
-  RUNTIME_ASSERT(array->HasFastElements() || array->HasFastSmiOnlyElements());
+  RUNTIME_ASSERT(array->HasFastSmiOrObjectElements());
   int length = Smi::cast(array->length())->value();
   FixedArray* elements = FixedArray::cast(array->elements());
   for (int i = 0; i < length; i++) {
     if (elements->get(i) == element) return isolate->heap()->false_value();
   }
   Object* obj;
   // Strict not needed. Used for cycle detection in Array join implementation.
   { MaybeObject* maybe_obj =
         array->SetFastElement(length, element, kNonStrictMode, true);
     if (!maybe_obj->ToObject(&obj)) return maybe_obj;
@@ skipping 64 matching lines @@
     }
   }
 
   Handle<JSArray> ToArray() {
     Handle<JSArray> array = isolate_->factory()->NewJSArray(0);
     Handle<Object> length =
         isolate_->factory()->NewNumber(static_cast<double>(index_offset_));
     Handle<Map> map;
     if (fast_elements_) {
       map = isolate_->factory()->GetElementsTransitionMap(array,
-                                                          FAST_ELEMENTS);
+                                                          FAST_HOLEY_ELEMENTS);
     } else {
       map = isolate_->factory()->GetElementsTransitionMap(array,
                                                           DICTIONARY_ELEMENTS);
     }
     array->set_map(*map);
     array->set_length(*length);
     array->set_elements(*storage_);
     return array;
   }
 
@@ skipping 38 matching lines @@
   // JSObject::kMaxElementCount.
   uint32_t index_offset_;
   bool fast_elements_;
 };
 
 
 static uint32_t EstimateElementCount(Handle<JSArray> array) {
   uint32_t length = static_cast<uint32_t>(array->length()->Number());
   int element_count = 0;
   switch (array->GetElementsKind()) {
-    case FAST_SMI_ONLY_ELEMENTS:
-    case FAST_ELEMENTS: {
+    case FAST_SMI_ELEMENTS:
+    case FAST_HOLEY_SMI_ELEMENTS:
+    case FAST_ELEMENTS:
+    case FAST_HOLEY_ELEMENTS: {
       // Fast elements can't have lengths that are not representable by
       // a 32-bit signed integer.
       ASSERT(static_cast<int32_t>(FixedArray::kMaxLength) >= 0);
       int fast_length = static_cast<int>(length);
       Handle<FixedArray> elements(FixedArray::cast(array->elements()));
       for (int i = 0; i < fast_length; i++) {
         if (!elements->get(i)->IsTheHole()) element_count++;
       }
       break;
     }
     case FAST_DOUBLE_ELEMENTS:
+    case FAST_HOLEY_DOUBLE_ELEMENTS:
       // TODO(1810): Decide if it's worthwhile to implement this.
       UNREACHABLE();
       break;
     case DICTIONARY_ELEMENTS: {
       Handle<SeededNumberDictionary> dictionary(
           SeededNumberDictionary::cast(array->elements()));
       int capacity = dictionary->Capacity();
       for (int i = 0; i < capacity; i++) {
         Handle<Object> key(dictionary->KeyAt(i));
         if (dictionary->IsKey(*key)) {
@@ skipping 70 matching lines @@
   uint32_t b = *bp;
   return (a == b) ? 0 : (a < b) ? -1 : 1;
 }
 
 
 static void CollectElementIndices(Handle<JSObject> object,
                                   uint32_t range,
                                   List<uint32_t>* indices) {
   ElementsKind kind = object->GetElementsKind();
   switch (kind) {
-    case FAST_SMI_ONLY_ELEMENTS:
-    case FAST_ELEMENTS: {
+    case FAST_SMI_ELEMENTS:
+    case FAST_ELEMENTS:
+    case FAST_HOLEY_SMI_ELEMENTS:
+    case FAST_HOLEY_ELEMENTS: {
       Handle<FixedArray> elements(FixedArray::cast(object->elements()));
       uint32_t length = static_cast<uint32_t>(elements->length());
       if (range < length) length = range;
       for (uint32_t i = 0; i < length; i++) {
         if (!elements->get(i)->IsTheHole()) {
           indices->Add(i);
         }
       }
       break;
     }
+    case FAST_HOLEY_DOUBLE_ELEMENTS:
     case FAST_DOUBLE_ELEMENTS: {
       // TODO(1810): Decide if it's worthwhile to implement this.
       UNREACHABLE();
       break;
     }
     case DICTIONARY_ELEMENTS: {
       Handle<SeededNumberDictionary> dict(
           SeededNumberDictionary::cast(object->elements()));
       uint32_t capacity = dict->Capacity();
       for (uint32_t j = 0; j < capacity; j++) {
@@ skipping 94 matching lines @@
  * with the element index and the element's value.
  * Afterwards it increments the base-index of the visitor by the array
  * length.
  * Returns false if any access threw an exception, otherwise true.
  */
 static bool IterateElements(Isolate* isolate,
                             Handle<JSArray> receiver,
                             ArrayConcatVisitor* visitor) {
   uint32_t length = static_cast<uint32_t>(receiver->length()->Number());
   switch (receiver->GetElementsKind()) {
-    case FAST_SMI_ONLY_ELEMENTS:
-    case FAST_ELEMENTS: {
+    case FAST_SMI_ELEMENTS:
+    case FAST_ELEMENTS:
+    case FAST_HOLEY_SMI_ELEMENTS:
+    case FAST_HOLEY_ELEMENTS: {
       // Run through the elements FixedArray and use HasElement and GetElement
       // to check the prototype for missing elements.
       Handle<FixedArray> elements(FixedArray::cast(receiver->elements()));
       int fast_length = static_cast<int>(length);
       ASSERT(fast_length <= elements->length());
       for (int j = 0; j < fast_length; j++) {
         HandleScope loop_scope(isolate);
         Handle<Object> element_value(elements->get(j), isolate);
         if (!element_value->IsTheHole()) {
           visitor->visit(j, element_value);
         } else if (receiver->HasElement(j)) {
           // Call GetElement on receiver, not its prototype, or getters won't
           // have the correct receiver.
           element_value = Object::GetElement(receiver, j);
           RETURN_IF_EMPTY_HANDLE_VALUE(isolate, element_value, false);
           visitor->visit(j, element_value);
         }
       }
       break;
     }
+    case FAST_HOLEY_DOUBLE_ELEMENTS:
     case FAST_DOUBLE_ELEMENTS: {
       // TODO(1810): Decide if it's worthwhile to implement this.
       UNREACHABLE();
       break;
     }
     case DICTIONARY_ELEMENTS: {
       Handle<SeededNumberDictionary> dict(receiver->element_dictionary());
       List<uint32_t> indices(dict->Capacity() / 2);
       // Collect all indices in the object and the prototypes less
       // than length. This might introduce duplicates in the indices list.
@@ skipping 77 matching lines @@
  * See ECMAScript 262, 15.4.4.4.
  * TODO(581): Fix non-compliance for very large concatenations and update to
  * following the ECMAScript 5 specification.
  */
 RUNTIME_FUNCTION(MaybeObject*, Runtime_ArrayConcat) {
   ASSERT(args.length() == 1);
   HandleScope handle_scope(isolate);
 
   CONVERT_ARG_HANDLE_CHECKED(JSArray, arguments, 0);
   int argument_count = static_cast<int>(arguments->length()->Number());
-  RUNTIME_ASSERT(arguments->HasFastElements());
+  RUNTIME_ASSERT(arguments->HasFastObjectElements());
   Handle<FixedArray> elements(FixedArray::cast(arguments->elements()));
 
   // Pass 1: estimate the length and number of elements of the result.
   // The actual length can be larger if any of the arguments have getters
   // that mutate other arguments (but will otherwise be precise).
   // The number of elements is precise if there are no inherited elements.
 
   uint32_t estimate_result_length = 0;
   uint32_t estimate_nof_elements = 0;
   {
     for (int i = 0; i < argument_count; i++) {
       HandleScope loop_scope;
       Handle<Object> obj(elements->get(i));
       uint32_t length_estimate;
       uint32_t element_estimate;
       if (obj->IsJSArray()) {
         Handle<JSArray> array(Handle<JSArray>::cast(obj));
         // TODO(1810): Find out if it's worthwhile to properly support
         // arbitrary ElementsKinds. For now, pessimistically transition to
-        // FAST_ELEMENTS.
+        // FAST_*_ELEMENTS.
         if (array->HasFastDoubleElements()) {
+          ElementsKind to_kind = FAST_ELEMENTS;
+          if (array->HasFastHoleyElements()) {
+            to_kind = FAST_HOLEY_ELEMENTS;
+          }
           array = Handle<JSArray>::cast(
               JSObject::TransitionElementsKind(array, FAST_ELEMENTS));
         }
         length_estimate =
             static_cast<uint32_t>(array->length()->Number());
         element_estimate =
             EstimateElementCount(array);
       } else {
         length_estimate = 1;
         element_estimate = 1;
@@ skipping 78 matching lines @@
   CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[1]);
   return object->PrepareElementsForSort(limit);
 }
 
 
 // Move contents of argument 0 (an array) to argument 1 (an array)
 RUNTIME_FUNCTION(MaybeObject*, Runtime_MoveArrayContents) {
   ASSERT(args.length() == 2);
   CONVERT_ARG_CHECKED(JSArray, from, 0);
   CONVERT_ARG_CHECKED(JSArray, to, 1);
+#if DEBUG
+  from->ValidateElements();
+  to->ValidateElements();
+#endif
   FixedArrayBase* new_elements = from->elements();
+  ElementsKind from_kind = from->GetElementsKind();
   MaybeObject* maybe_new_map;
-  ElementsKind elements_kind;
-  if (new_elements->map() == isolate->heap()->fixed_array_map() ||
-      new_elements->map() == isolate->heap()->fixed_cow_array_map()) {
-    elements_kind = FAST_ELEMENTS;
-  } else if (new_elements->map() ==
-             isolate->heap()->fixed_double_array_map()) {
-    elements_kind = FAST_DOUBLE_ELEMENTS;
-  } else {
-    elements_kind = DICTIONARY_ELEMENTS;
-  }
-  maybe_new_map = to->GetElementsTransitionMap(isolate, elements_kind);
+  maybe_new_map = to->GetElementsTransitionMap(isolate, from_kind);
   Object* new_map;
   if (!maybe_new_map->ToObject(&new_map)) return maybe_new_map;
-  to->set_map(Map::cast(new_map));
-  to->set_elements(new_elements);
+  to->set_map_and_elements(Map::cast(new_map), new_elements);
   to->set_length(from->length());
   Object* obj;
   { MaybeObject* maybe_obj = from->ResetElements();
     if (!maybe_obj->ToObject(&obj)) return maybe_obj;
   }
   from->set_length(Smi::FromInt(0));
+#if DEBUG
+  to->ValidateElements();
+#endif
   return to;
 }
 
 
 // How many elements does this object/array have?
 RUNTIME_FUNCTION(MaybeObject*, Runtime_EstimateNumberOfElements) {
   ASSERT(args.length() == 1);
   CONVERT_ARG_CHECKED(JSObject, object, 0);
   HeapObject* elements = object->elements();
   if (elements->IsDictionary()) {
@@ skipping 59 matching lines @@
     for (int i = 0; i < keys_length; i++) {
       Object* key = keys->get(i);
       uint32_t index = 0;
       if (!key->ToArrayIndex(&index) || index >= length) {
         // Zap invalid keys.
         keys->set_undefined(i);
       }
     }
     return *isolate->factory()->NewJSArrayWithElements(keys);
   } else {
-    ASSERT(array->HasFastElements() ||
-           array->HasFastSmiOnlyElements() ||
+    ASSERT(array->HasFastSmiOrObjectElements() ||
            array->HasFastDoubleElements());
     Handle<FixedArray> single_interval = isolate->factory()->NewFixedArray(2);
     // -1 means start of array.
     single_interval->set(0, Smi::FromInt(-1));
     FixedArrayBase* elements = FixedArrayBase::cast(array->elements());
     uint32_t actual_length =
         static_cast<uint32_t>(elements->length());
     uint32_t min_length = actual_length < length ? actual_length : length;
     Handle<Object> length_object =
         isolate->factory()->NewNumber(static_cast<double>(min_length));
@@ skipping 3238 matching lines @@
   return NULL;
 }
 
 
 #define ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(Name)        \
   RUNTIME_FUNCTION(MaybeObject*, Runtime_Has##Name) {     \
     CONVERT_ARG_CHECKED(JSObject, obj, 0);              \
     return isolate->heap()->ToBoolean(obj->Has##Name());  \
   }
 
-ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastSmiOnlyElements)
-ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastElements)
+ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastSmiElements)
+ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastObjectElements)
+ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastSmiOrObjectElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastDoubleElements)
+ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(FastHoleyElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(DictionaryElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalPixelElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalArrayElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalByteElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalUnsignedByteElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalShortElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalUnsignedShortElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalIntElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalUnsignedIntElements)
 ELEMENTS_KIND_CHECK_RUNTIME_FUNCTION(ExternalFloatElements)
@@ skipping 88 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal