[runtime] Avoid @@isConcatSpreadable lookup for fast path Array.prototype.concat

src/isolate.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/isolate.h"
 
 #include <stdlib.h>
 
 #include <fstream>  // NOLINT(readability/streams)
 #include <sstream>
@@ skipping 2415 matching lines @@
 }
 
 
 bool Isolate::use_crankshaft() const {
   return FLAG_crankshaft &&
          !serializer_enabled_ &&
          CpuFeatures::SupportsCrankshaft();
 }
 
 
+Context* Isolate::ContextForArrayOrObjectPrototype(Handle<JSObject> object) {
+  Object* context = heap()->native_contexts_list();
+  while (!context->IsUndefined()) {
+    Context* current_context = Context::cast(context);
+    if (current_context->initial_object_prototype() == *object ||
+        current_context->initial_array_prototype() == *object) {
+      return current_context;
+    }
+    context = current_context->get(Context::NEXT_CONTEXT_LINK);
+  }
+  return NULL;
+}
+
+
+bool Isolate::IsArrayIsConcatSpreadableSet() {
+  PropertyCell* is_concat_spreadable_cell =
+      heap()->array_is_concat_spreadable_protector();
+  bool is_concat_spreadable_set =
+      is_concat_spreadable_cell->value()->IsSmi() &&
+      Smi::cast(is_concat_spreadable_cell->value())->value() ==
+          kArrayIsConcatSpreadableProtectorInvalid;
+
+#ifdef DEBUG
+  Map* root_array_map = get_initial_js_array_map(GetInitialFastElementsKind());
+  if (root_array_map == NULL) {
+    //
+    return is_concat_spreadable_set;
+  }
+
+  Handle<Object> array_prototype(array_function()->prototype(), this);
+  Handle<Symbol> key(factory()->is_concat_spreadable_symbol());
+  Handle<Object> value;
+  MaybeHandle<Object> maybeValue =
+      i::Runtime::GetObjectProperty(this, array_prototype, key);
+  if (maybeValue.ToHandle(&value) && !value->IsUndefined()) {

[Toon Verwaest, 2015/11/02 12:32:45]

Plus o[@@isConcatSpreadable] = undefined

[Camillo Bruni, 2015/11/03 14:49:25]

?

+    // TODO(cbruni): Currently we do not revert if we unset the
+    // isConcatSpreadable property on Array.prototype or Object.prototype hence
+    // the reverse implication doesn't hold.
+    DCHECK(is_concat_spreadable_set);
+    return true;
+  }
+#endif  // DEBUG
+
+  return is_concat_spreadable_set;
+}
+
+
+void Isolate::UpdateArrayIsConcatSpreadableProtectorOnAddProperty(
+    Handle<JSObject> object, Handle<Name> name) {
+  // The invalidate the is_concat_spreadable_protector invalidation is a one-way
+  // action.
+  if (IsArrayIsConcatSpreadableSet()) return;
+  if (!object->map()->is_prototype_map()) return;
+  Handle<Name> key(factory()->is_concat_spreadable_symbol());

[Toon Verwaest, 2015/11/02 12:32:45]

key = factory()->is_concat_spreadable_symbol();

[Camillo Bruni, 2015/11/03 14:49:25]

right

+  if (!Name::Equals(name, key)) return;
+  Context* context = ContextForArrayOrObjectPrototype(object);
+  if (context == NULL) return;
+  PropertyCell::SetValueWithInvalidation(
+      factory()->array_is_concat_spreadable_protector(),
+      handle(Smi::FromInt(kArrayElementsProtectorInvalid), this));
+}
+
+
 bool Isolate::IsFastArrayConstructorPrototypeChainIntact() {
-  PropertyCell* no_elements_cell = heap()->array_protector();
-  bool cell_reports_intact =
-      no_elements_cell->value()->IsSmi() &&
-      Smi::cast(no_elements_cell->value())->value() == kArrayProtectorValid;
+  PropertyCell* no_elements_cell = heap()->array_elements_protector();
+  bool cell_reports_intact = no_elements_cell->value()->IsSmi() &&
+                             Smi::cast(no_elements_cell->value())->value() ==
+                                 kArrayElementsProtectorValid;
 
 #ifdef DEBUG
   Map* root_array_map =
       get_initial_js_array_map(GetInitialFastElementsKind());
   Context* native_context = context()->native_context();
-  JSObject* initial_array_proto = JSObject::cast(
-      native_context->get(Context::INITIAL_ARRAY_PROTOTYPE_INDEX));
-  JSObject* initial_object_proto = JSObject::cast(
-      native_context->get(Context::INITIAL_OBJECT_PROTOTYPE_INDEX));
+  JSObject* initial_array_proto =
+      JSObject::cast(native_context->initial_array_prototype());
+  JSObject* initial_object_proto =
+      JSObject::cast(native_context->initial_object_prototype());
 
   if (root_array_map == NULL || initial_array_proto == initial_object_proto) {
     // We are in the bootstrapping process, and the entire check sequence
     // shouldn't be performed.
     return cell_reports_intact;
   }
 
   // Check that the array prototype hasn't been altered WRT empty elements.
   if (root_array_map->prototype() != initial_array_proto) {
     DCHECK_EQ(false, cell_reports_intact);
-    return cell_reports_intact;
+    return false;
   }
 
   FixedArrayBase* elements = initial_array_proto->elements();
   if (elements != heap()->empty_fixed_array() &&
       elements != heap()->empty_slow_element_dictionary()) {
     DCHECK_EQ(false, cell_reports_intact);
-    return cell_reports_intact;
+    return false;
   }
 
   // Check that the object prototype hasn't been altered WRT empty elements.
   PrototypeIterator iter(this, initial_array_proto);
   if (iter.IsAtEnd() || iter.GetCurrent() != initial_object_proto) {
     DCHECK_EQ(false, cell_reports_intact);
-    return cell_reports_intact;
+    return false;
   }
 
   elements = initial_object_proto->elements();
   if (elements != heap()->empty_fixed_array() &&
       elements != heap()->empty_slow_element_dictionary()) {
     DCHECK_EQ(false, cell_reports_intact);
-    return cell_reports_intact;
+    return false;
   }
 
   iter.Advance();
   if (!iter.IsAtEnd()) {
     DCHECK_EQ(false, cell_reports_intact);
-    return cell_reports_intact;
+    return false;
   }
 
 #endif
 
   return cell_reports_intact;
 }
 
 
 void Isolate::UpdateArrayProtectorOnSetElement(Handle<JSObject> object) {
-  if (IsFastArrayConstructorPrototypeChainIntact() &&
-      object->map()->is_prototype_map()) {
-    Object* context = heap()->native_contexts_list();
-    while (!context->IsUndefined()) {
-      Context* current_context = Context::cast(context);
-      if (current_context->get(Context::INITIAL_OBJECT_PROTOTYPE_INDEX) ==
-              *object ||
-          current_context->get(Context::INITIAL_ARRAY_PROTOTYPE_INDEX) ==
-              *object) {
-        PropertyCell::SetValueWithInvalidation(
-            factory()->array_protector(),
-            handle(Smi::FromInt(kArrayProtectorInvalid), this));
-        break;
-      }
-      context = current_context->get(Context::NEXT_CONTEXT_LINK);
-    }
-  }
+  if (!IsFastArrayConstructorPrototypeChainIntact()) return;
+  if (!object->map()->is_prototype_map()) return;
+  Context* context = ContextForArrayOrObjectPrototype(object);
+  if (context == NULL) return;
+  PropertyCell::SetValueWithInvalidation(
+      factory()->array_elements_protector(),
+      handle(Smi::FromInt(kArrayElementsProtectorInvalid), this));
 }
 
 
 bool Isolate::IsAnyInitialArrayPrototype(Handle<JSArray> array) {
-  if (array->map()->is_prototype_map()) {
-    Object* context = heap()->native_contexts_list();
-    while (!context->IsUndefined()) {
-      Context* current_context = Context::cast(context);
-      if (current_context->get(Context::INITIAL_ARRAY_PROTOTYPE_INDEX) ==
-          *array) {
-        return true;
-      }
-      context = current_context->get(Context::NEXT_CONTEXT_LINK);
+  if (!array->map()->is_prototype_map()) return false;
+  Object* context = heap()->native_contexts_list();
+  while (!context->IsUndefined()) {
+    Context* current_context = Context::cast(context);
+    if (current_context->initial_array_prototype() == *array) {
+      return true;
     }
+    context = current_context->get(Context::NEXT_CONTEXT_LINK);
   }
   return false;
 }
 
 
 CallInterfaceDescriptorData* Isolate::call_descriptor_data(int index) {
   DCHECK(0 <= index && index < CallDescriptors::NUMBER_OF_DESCRIPTORS);
   return &call_descriptor_data_[index];
 }
 
@@ skipping 311 matching lines @@
   // Then check whether this scope intercepts.
   if ((flag & intercept_mask_)) {
     intercepted_flags_ |= flag;
     return true;
   }
   return false;
 }
 
 }  // namespace internal
 }  // namespace v8