Cache maps when normalizing properties....

src/objects.cc

Index: src/objects.cc
===================================================================
--- src/objects.cc	(revision 5120)
+++ src/objects.cc	(working copy)
@@ -2114,6 +2114,84 @@
 }
 
 
+class NormalizedMapCache {

[Mads Ager (chromium), 2010/07/23 09:07:32]

: public AllStatic ?

Also, please have public: section before private:.

+  static bool IsMatchFor(Map* slow, Map* fast, PropertyNormalizationMode mode);
+
+ public:
+  static int Hash(Map* fast, PropertyNormalizationMode mode);
+
+  static Object* Get(Map* fast, int hash, PropertyNormalizationMode mode);
+
+  static void Set(int hash, Map* slow);
+};
+
+
+int NormalizedMapCache::Hash(Map* fast, PropertyNormalizationMode mode) {
+  // XOR bytes in every fields that will be copied to the normalized fast_map.
+  // Ignoring:
+  //   instance_size (determined by instance_type and inobject_properties)
+  //   scavenger (determined by instance_type and instance_size)
+  //   pre_allocated_property_fields (always 0)
+  //   unused_property_fields (always 0)
+  //   code_cache (always empty)
+  //   instance_descriptors (always empty)
+
+  int index =
+    (static_cast<uint32_t>(
+        reinterpret_cast<uintptr_t>(fast->constructor())) >> 2) ^
+    (static_cast<uint32_t>(
+        reinterpret_cast<uintptr_t>(fast->prototype())) >> 2);
+
+  index ^= (index >> 16);
+  index ^= (index >> 8);
+
+  index ^=
+      ((mode == CLEAR_INOBJECT_PROPERTIES) ? 0 : fast->inobject_properties());
+  index ^= fast->instance_type();
+  index ^= fast->bit_field();
+  index ^= fast->bit_field2();
+
+  return index & 0xFF;

[Mads Ager (chromium), 2010/07/23 09:07:32]

Why do you return only 8 bits?

+}
+
+
+bool NormalizedMapCache::IsMatchFor(Map* slow,
+                                    Map* fast,
+                                    PropertyNormalizationMode mode) {
+  ASSERT(slow->pre_allocated_property_fields() == 0);
+  ASSERT(slow->unused_property_fields() == 0);
+
+  return
+    slow->constructor() == fast->constructor() &&
+    slow->prototype() == fast->prototype() &&
+    slow->inobject_properties() == ((mode == CLEAR_INOBJECT_PROPERTIES) ?
+                                    0 :
+                                    fast->inobject_properties()) &&
+    slow->instance_type() == fast->instance_type() &&
+    slow->bit_field() == fast->bit_field() &&
+    slow->bit_field2() == fast->bit_field2();
+}
+
+
+Object* NormalizedMapCache::Get(Map* fast,
+                                int hash,
+                                PropertyNormalizationMode mode) {
+  Object* cached = Top::slow_map_cache()->get(hash);
+  if (!cached->IsMap()) return cached;  // Cache miss.
+
+  Map* slow = Map::cast(cached);
+  if (IsMatchFor(slow, fast, mode)) return cached;  // Found the right map.
+
+  // Hash collision. Pretend there was a miss, the entry will be overwritten.
+  return Heap::undefined_value();
+}
+
+
+void NormalizedMapCache::Set(int hash, Map* map) {
+  Top::slow_map_cache()->set(hash, map);
+}
+
+
 Object* JSObject::NormalizeProperties(PropertyNormalizationMode mode,
                                       int expected_additional_properties) {
   if (!HasFastProperties()) return this;
@@ -2178,30 +2256,46 @@
   int index = map()->instance_descriptors()->NextEnumerationIndex();
   dictionary->SetNextEnumerationIndex(index);
 
-  // Allocate new map.
-  obj = map()->CopyDropDescriptors();
-  if (obj->IsFailure()) return obj;
-  Map* new_map = Map::cast(obj);
+  int hash = NormalizedMapCache::Hash(map(), mode);
+  obj = NormalizedMapCache::Get(map(), hash, mode);
+  if (obj->IsMap()) {
+    Map* new_map = Map::cast(obj);
+    int new_instance_size = new_map->instance_size();
+    int instance_size_delta = map()->instance_size() - new_instance_size;
+    if (instance_size_delta != 0) {
+      Heap::CreateFillerObjectAt(this->address() + new_instance_size,
+                                 instance_size_delta);
+    }
+    set_map(new_map);
+  } else {
+    // Allocate new map.
+    obj = map()->CopyDropDescriptors();
+    if (obj->IsFailure()) return obj;
+    Map* new_map = Map::cast(obj);
 
-  // Clear inobject properties if needed by adjusting the instance size and
-  // putting in a filler object instead of the inobject properties.
-  if (mode == CLEAR_INOBJECT_PROPERTIES && map()->inobject_properties() > 0) {
-    int instance_size_delta = map()->inobject_properties() * kPointerSize;
-    int new_instance_size = map()->instance_size() - instance_size_delta;
-    new_map->set_inobject_properties(0);
-    new_map->set_instance_size(new_instance_size);
-    new_map->set_scavenger(Heap::GetScavenger(new_map->instance_type(),
-                                              new_map->instance_size()));
-    Heap::CreateFillerObjectAt(this->address() + new_instance_size,
-                               instance_size_delta);
+    // Clear inobject properties if needed by adjusting the instance size and
+    // putting in a filler object instead of the inobject properties.
+    if (mode == CLEAR_INOBJECT_PROPERTIES && map()->inobject_properties() > 0) {
+      int instance_size_delta = map()->inobject_properties() * kPointerSize;
+      int new_instance_size = map()->instance_size() - instance_size_delta;
+      new_map->set_inobject_properties(0);
+      new_map->set_instance_size(new_instance_size);
+      new_map->set_scavenger(Heap::GetScavenger(new_map->instance_type(),
+                                                new_map->instance_size()));
+      Heap::CreateFillerObjectAt(this->address() + new_instance_size,
+                                 instance_size_delta);
+    }
+    new_map->set_unused_property_fields(0);
+    new_map->set_pre_allocated_property_fields(0);
+
+    // We have now successfully allocated all the necessary objects.
+    // Changes can now be made with the guarantee that all of them take effect.
+    set_map(new_map);
+    map()->set_instance_descriptors(Heap::empty_descriptor_array());
+    NormalizedMapCache::Set(hash, new_map);
+    Counters::normalized_maps.Increment();
   }
-  new_map->set_unused_property_fields(0);
 
-  // We have now successfully allocated all the necessary objects.
-  // Changes can now be made with the guarantee that all of them take effect.
-  set_map(new_map);
-  map()->set_instance_descriptors(Heap::empty_descriptor_array());
-
   set_properties(dictionary);
 
   Counters::props_to_dictionary.Increment();