Promoting elements transitions to their own field.

src/heap.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 3648 matching lines @@
   // different context.
   JSFunction* object_function =
       function->context()->global_context()->object_function();
 
   // Each function prototype gets a copy of the object function map.
   // This avoid unwanted sharing of maps between prototypes of different
   // constructors.
   Map* new_map;
   ASSERT(object_function->has_initial_map());
   { MaybeObject* maybe_map =
-        object_function->initial_map()->CopyDropTransitions();
+        object_function->initial_map()->CopyDropTransitions(
+            DescriptorArray::MAY_BE_SHARED);
     if (!maybe_map->To<Map>(&new_map)) return maybe_map;
   }
   Object* prototype;
   { MaybeObject* maybe_prototype = AllocateJSObjectFromMap(new_map);
     if (!maybe_prototype->ToObject(&prototype)) return maybe_prototype;
   }
   // When creating the prototype for the function we must set its
   // constructor to the function.
   Object* result;
   { MaybeObject* maybe_result =
@@ skipping 127 matching lines @@
   // the inline_new flag so we only change the map if we generate a
   // specialized construct stub.
   ASSERT(in_object_properties <= Map::kMaxPreAllocatedPropertyFields);
   if (fun->shared()->CanGenerateInlineConstructor(prototype)) {
     int count = fun->shared()->this_property_assignments_count();
     if (count > in_object_properties) {
       // Inline constructor can only handle inobject properties.
       fun->shared()->ForbidInlineConstructor();
     } else {
       DescriptorArray* descriptors;
-      { MaybeObject* maybe_descriptors_obj = DescriptorArray::Allocate(count);
+      { MaybeObject* maybe_descriptors_obj =
+            DescriptorArray::Allocate(count, DescriptorArray::MAY_BE_SHARED);
         if (!maybe_descriptors_obj->To<DescriptorArray>(&descriptors)) {
           return maybe_descriptors_obj;
         }
       }
       DescriptorArray::WhitenessWitness witness(descriptors);
       for (int i = 0; i < count; i++) {
         String* name = fun->shared()->GetThisPropertyAssignmentName(i);
         ASSERT(name->IsSymbol());
         FieldDescriptor field(name, i, NONE);
         field.SetEnumerationIndex(i);
@@ skipping 3317 matching lines @@
   } else {
     p ^= 0x1d1ed & (Page::kPageSize - 1);  // I died.
   }
   remembered_unmapped_pages_[remembered_unmapped_pages_index_] =
       reinterpret_cast<Address>(p);
   remembered_unmapped_pages_index_++;
   remembered_unmapped_pages_index_ %= kRememberedUnmappedPages;
 }
 
 } }  // namespace v8::internal