Basic support for tracking smi-only arrays on ia32.

src/heap.cc

 // Copyright 2011 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 1682 matching lines @@
         StaticVisitorBase::GetVisitorId(instance_type, instance_size));
   reinterpret_cast<Map*>(result)->set_inobject_properties(0);
   reinterpret_cast<Map*>(result)->set_pre_allocated_property_fields(0);
   reinterpret_cast<Map*>(result)->set_unused_property_fields(0);
   reinterpret_cast<Map*>(result)->set_bit_field(0);
   reinterpret_cast<Map*>(result)->set_bit_field2(0);
   return result;
 }
 
 
-MaybeObject* Heap::AllocateMap(InstanceType instance_type, int instance_size) {
+MaybeObject* Heap::AllocateMap(InstanceType instance_type,
+                               int instance_size,
+                               ElementsKind elements_kind) {
   Object* result;
   { MaybeObject* maybe_result = AllocateRawMap();
     if (!maybe_result->ToObject(&result)) return maybe_result;
   }
 
   Map* map = reinterpret_cast<Map*>(result);
   map->set_map(meta_map());
   map->set_instance_type(instance_type);
   map->set_visitor_id(
       StaticVisitorBase::GetVisitorId(instance_type, instance_size));
   map->set_prototype(null_value());
   map->set_constructor(null_value());
   map->set_instance_size(instance_size);
   map->set_inobject_properties(0);
   map->set_pre_allocated_property_fields(0);
   map->init_instance_descriptors();
   map->set_code_cache(empty_fixed_array());
   map->set_prototype_transitions(empty_fixed_array());
   map->set_unused_property_fields(0);
   map->set_bit_field(0);
   map->set_bit_field2(1 << Map::kIsExtensible);
-  map->set_elements_kind(FAST_ELEMENTS);
+  map->set_elements_kind(elements_kind);
 
   // If the map object is aligned fill the padding area with Smi 0 objects.
   if (Map::kPadStart < Map::kSize) {
     memset(reinterpret_cast<byte*>(map) + Map::kPadStart - kHeapObjectTag,
            0,
            Map::kSize - Map::kPadStart);
   }
   return map;
 }
 
@@ skipping 369 matching lines @@
   return Oddball::cast(result)->Initialize(to_string, to_number, kind);
 }
 
 
 bool Heap::CreateApiObjects() {
   Object* obj;
 
   { MaybeObject* maybe_obj = AllocateMap(JS_OBJECT_TYPE, JSObject::kHeaderSize);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
-  set_neander_map(Map::cast(obj));
+  // Don't use Smi-only elements optimizations for objects with the neander
+  // map. There are too many cases where element values are set directly with a
+  // bottleneck to trap the Smi-only -> fast elements transition, and there
+  // appears to be no benefit for optimize this case.
+  Map* new_neander_map = Map::cast(obj);
+  new_neander_map->set_elements_kind(FAST_ELEMENTS);
+  set_neander_map(new_neander_map);
 
   { MaybeObject* maybe_obj = AllocateJSObjectFromMap(neander_map());
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   Object* elements;
   { MaybeObject* maybe_elements = AllocateFixedArray(2);
     if (!maybe_elements->ToObject(&elements)) return false;
   }
   FixedArray::cast(elements)->set(0, Smi::FromInt(0));
   JSObject::cast(obj)->set_elements(FixedArray::cast(elements));
@@ skipping 1361 matching lines @@
   if (map->instance_size() > MaxObjectSizeInPagedSpace()) space = LO_SPACE;
   Object* obj;
   { MaybeObject* maybe_obj = Allocate(map, space);
     if (!maybe_obj->ToObject(&obj)) return maybe_obj;
   }
 
   // Initialize the JSObject.
   InitializeJSObjectFromMap(JSObject::cast(obj),
                             FixedArray::cast(properties),
                             map);
-  ASSERT(JSObject::cast(obj)->HasFastElements());
+  ASSERT(JSObject::cast(obj)->HasFastSmiOnlyElements() ||
+         JSObject::cast(obj)->HasFastElements());
   return obj;
 }
 
 
 MaybeObject* Heap::AllocateJSObject(JSFunction* constructor,
                                     PretenureFlag pretenure) {
   // Allocate the initial map if absent.
   if (!constructor->has_initial_map()) {
     Object* initial_map;
     { MaybeObject* maybe_initial_map = AllocateInitialMap(constructor);
@@ skipping 161 matching lines @@
       if (!maybe_clone->ToObject(&clone)) return maybe_clone;
     }
     ASSERT(InNewSpace(clone));
     // Since we know the clone is allocated in new space, we can copy
     // the contents without worrying about updating the write barrier.
     CopyBlock(HeapObject::cast(clone)->address(),
               source->address(),
               object_size);
   }
 
+  ASSERT(JSObject::cast(clone)->GetElementsKind() == source->GetElementsKind());
   FixedArrayBase* elements = FixedArrayBase::cast(source->elements());
   FixedArray* properties = FixedArray::cast(source->properties());
   // Update elements if necessary.
   if (elements->length() > 0) {
     Object* elem;
     { MaybeObject* maybe_elem;
       if (elements->map() == fixed_cow_array_map()) {
         maybe_elem = FixedArray::cast(elements);
       } else if (source->HasFastDoubleElements()) {
         maybe_elem = CopyFixedDoubleArray(FixedDoubleArray::cast(elements));
@@ skipping 2658 matching lines @@
   }
   isolate_->heap()->store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
   for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
     next = chunk->next_chunk();
     isolate_->memory_allocator()->Free(chunk);
   }
   chunks_queued_for_free_ = NULL;
 }
 
 } }  // namespace v8::internal