Reapplying r5147 (caching maps for slow case objects).

r5147 wrongly assumed that a code cache for a slow case map is always empty.
This patch solves this: whenever we attempt to add a stub to a map's code cache 
we check that this map is cached. If it is we give the object its own copy
of the map and only then modify the map.

Review URL: http://codereview.chromium.org/3134027

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5342 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/bootstrapper.cc

@@ -232,6 +232,7 @@ class Genesis BASE_EMBEDDED {
   bool InstallNatives();
   void InstallCustomCallGenerators();
   void InstallJSFunctionResultCaches();
+  void InitializeNormalizedMapCaches();
   // Used both for deserialized and from-scratch contexts to add the extensions
   // provided.
   static bool InstallExtensions(Handle<Context> global_context,
@@ -1400,6 +1401,13 @@ void Genesis::InstallJSFunctionResultCaches() {
 }
 
 
+void Genesis::InitializeNormalizedMapCaches() {
+  Handle<FixedArray> array(
+      Factory::NewFixedArray(NormalizedMapCache::kEntries, TENURED));
+  global_context()->set_normalized_map_cache(NormalizedMapCache::cast(*array));
+}
+
+
 int BootstrapperActive::nesting_ = 0;
 
 
@@ -1768,6 +1776,7 @@ Genesis::Genesis(Handle<Object> global_object,
     HookUpGlobalProxy(inner_global, global_proxy);
     InitializeGlobal(inner_global, empty_function);
     InstallJSFunctionResultCaches();
+    InitializeNormalizedMapCaches();
     if (!InstallNatives()) return;
 
     MakeFunctionInstancePrototypeWritable();

src/contexts.h

@@ -86,6 +86,7 @@ enum ContextLookupFlags {
   V(CONFIGURE_GLOBAL_INDEX, JSFunction, configure_global_fun) \
   V(FUNCTION_CACHE_INDEX, JSObject, function_cache) \
   V(JSFUNCTION_RESULT_CACHES_INDEX, FixedArray, jsfunction_result_caches) \
+  V(NORMALIZED_MAP_CACHE_INDEX, NormalizedMapCache, normalized_map_cache) \
   V(RUNTIME_CONTEXT_INDEX, Context, runtime_context) \
   V(CALL_AS_FUNCTION_DELEGATE_INDEX, JSFunction, call_as_function_delegate) \
   V(CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, JSFunction, \
@@ -211,6 +212,7 @@ class Context: public FixedArray {
     CONFIGURE_GLOBAL_INDEX,
     FUNCTION_CACHE_INDEX,
     JSFUNCTION_RESULT_CACHES_INDEX,
+    NORMALIZED_MAP_CACHE_INDEX,
     RUNTIME_CONTEXT_INDEX,
     CALL_AS_FUNCTION_DELEGATE_INDEX,
     CALL_AS_CONSTRUCTOR_DELEGATE_INDEX,

src/heap.cc

@@ -571,6 +571,22 @@ void Heap::ClearJSFunctionResultCaches() {
 }
 
 
+class ClearThreadNormalizedMapCachesVisitor: public ThreadVisitor {
+  virtual void VisitThread(ThreadLocalTop* top) {
+    Context* context = top->context_;
+    if (context == NULL) return;
+    context->global()->global_context()->normalized_map_cache()->Clear();
+  }
+};
+
+
+void Heap::ClearNormalizedMapCaches() {
+  if (Bootstrapper::IsActive()) return;
+  ClearThreadNormalizedMapCachesVisitor visitor;
+  ThreadManager::IterateArchivedThreads(&visitor);
+}
+
+
 #ifdef DEBUG
 
 enum PageWatermarkValidity {
@@ -755,6 +771,8 @@ void Heap::MarkCompactPrologue(bool is_compacting) {
   CompletelyClearInstanceofCache();
 
   if (is_compacting) FlushNumberStringCache();
+
+  ClearNormalizedMapCaches();
 }
 
 

src/heap.h

@@ -1021,6 +1021,8 @@ class Heap : public AllStatic {
 
   static void ClearJSFunctionResultCaches();
 
+  static void ClearNormalizedMapCaches();
+
   static GCTracer* tracer() { return tracer_; }
 
  private:

src/ic-inl.h

@@ -108,10 +108,10 @@ InlineCacheHolderFlag IC::GetCodeCacheForObject(JSObject* object,
 }
 
 
-Map* IC::GetCodeCacheMap(Object* object, InlineCacheHolderFlag holder) {
+JSObject* IC::GetCodeCacheHolder(Object* object, InlineCacheHolderFlag holder) {
   Object* map_owner = (holder == OWN_MAP ? object : object->GetPrototype());
   ASSERT(map_owner->IsJSObject());
-  return JSObject::cast(map_owner)->map();
+  return JSObject::cast(map_owner);
 }
 
 

src/ic.cc

@@ -165,14 +165,14 @@ IC::State IC::StateFrom(Code* target, Object* receiver, Object* name) {
 
   if (cache_holder == OWN_MAP && !receiver->IsJSObject()) {
     // The stub was generated for JSObject but called for non-JSObject.
-    // IC::GetCodeCacheMap is not applicable.
+    // IC::GetCodeCacheHolder is not applicable.
     return MONOMORPHIC;
   } else if (cache_holder == PROTOTYPE_MAP &&
              receiver->GetPrototype()->IsNull()) {
-    // IC::GetCodeCacheMap is not applicable.
+    // IC::GetCodeCacheHolder is not applicable.
     return MONOMORPHIC;
   }
-  Map* map = IC::GetCodeCacheMap(receiver, cache_holder);
+  Map* map = IC::GetCodeCacheHolder(receiver, cache_holder)->map();
 
   // Decide whether the inline cache failed because of changes to the
   // receiver itself or changes to one of its prototypes.

src/ic.h

@@ -123,8 +123,8 @@ class IC {
                                                             JSObject* holder);
   static inline InlineCacheHolderFlag GetCodeCacheForObject(JSObject* object,
                                                             JSObject* holder);
-  static inline Map* GetCodeCacheMap(Object* object,
-                                     InlineCacheHolderFlag holder);
+  static inline JSObject* GetCodeCacheHolder(Object* object,
+                                             InlineCacheHolderFlag holder);
 
  protected:
   Address fp() const { return fp_; }

src/objects-debug.cc

@@ -30,6 +30,7 @@
 #include "disassembler.h"
 #include "disasm.h"
 #include "jsregexp.h"
+#include "objects-visiting.h"
 
 namespace v8 {
 namespace internal {
@@ -648,6 +649,17 @@ void Map::MapVerify() {
 }
 
 
+void Map::NormalizedMapVerify() {
+  MapVerify();
+  ASSERT_EQ(Heap::empty_descriptor_array(), instance_descriptors());
+  ASSERT_EQ(Heap::empty_fixed_array(), code_cache());
+  ASSERT_EQ(0, pre_allocated_property_fields());
+  ASSERT_EQ(0, unused_property_fields());
+  ASSERT_EQ(StaticVisitorBase::GetVisitorId(instance_type(), instance_size()),
+      visitor_id());
+}
+
+
 void CodeCache::CodeCachePrint() {
   HeapObject::PrintHeader("CodeCache");
   PrintF("\n - default_cache: ");
@@ -1363,6 +1375,21 @@ void JSFunctionResultCache::JSFunctionResultCacheVerify() {
 }
 
 
+void NormalizedMapCache::NormalizedMapCacheVerify() {
+  FixedArray::cast(this)->Verify();
+  if (FLAG_enable_slow_asserts) {
+    for (int i = 0; i < length(); i++) {
+      Object* e = get(i);
+      if (e->IsMap()) {
+        Map::cast(e)->NormalizedMapVerify();
+      } else {
+        ASSERT(e->IsUndefined());
+      }
+    }
+  }
+}
+
+
 #endif  // DEBUG
 
 } }  // namespace v8::internal

src/objects-inl.h

@@ -575,6 +575,18 @@ bool Object::IsJSFunctionResultCache() {
 }
 
 
+bool Object::IsNormalizedMapCache() {
+  if (!IsFixedArray()) return false;
+  if (FixedArray::cast(this)->length() != NormalizedMapCache::kEntries) {
+    return false;
+  }
+#ifdef DEBUG
+  reinterpret_cast<NormalizedMapCache*>(this)->NormalizedMapCacheVerify();
+#endif
+  return true;
+}
+
+
 bool Object::IsCompilationCacheTable() {
   return IsHashTable();
 }
@@ -1660,6 +1672,7 @@ CAST_ACCESSOR(FixedArray)
 CAST_ACCESSOR(DescriptorArray)
 CAST_ACCESSOR(SymbolTable)
 CAST_ACCESSOR(JSFunctionResultCache)
+CAST_ACCESSOR(NormalizedMapCache)
 CAST_ACCESSOR(CompilationCacheTable)
 CAST_ACCESSOR(CodeCacheHashTable)
 CAST_ACCESSOR(MapCache)

src/objects.cc

@@ -2098,6 +2098,124 @@ PropertyAttributes JSObject::GetLocalPropertyAttribute(String* name) {
 }
 
 
+bool NormalizedMapCache::IsCacheable(JSObject* object) {
+  // Caching for global objects is not worth it (there are too few of them).
+  return !object->IsGlobalObject();
+}
+
+
+Object* NormalizedMapCache::Get(JSObject* obj, PropertyNormalizationMode mode) {
+  Object* result;
+
+  Map* fast = obj->map();
+  if (!IsCacheable(obj)) {
+    result = fast->CopyNormalized(mode);
+    if (result->IsFailure()) return result;
+  } else {
+    int index = Hash(fast) % kEntries;
+    result = get(index);
+
+    if (result->IsMap() && CheckHit(Map::cast(result), fast, mode)) {
+#ifdef DEBUG
+      if (FLAG_enable_slow_asserts) {
+        // Make sure that the new slow map has exactly the same hash as the
+        // original fast map. This way we can use hash to check if a slow map
+        // is already in the hash (see Contains method).
+        ASSERT(Hash(fast) == Hash(Map::cast(result)));
+        // The cached map should match newly created normalized map bit-by-bit.
+        Object* fresh = fast->CopyNormalized(mode);
+        if (!fresh->IsFailure()) {
+          // Copy the unused byte so that the assertion below works.
+          Map::cast(fresh)->address()[Map::kUnusedOffset] =
+              Map::cast(result)->address()[Map::kUnusedOffset];
+          ASSERT(memcmp(Map::cast(fresh)->address(),
+                        Map::cast(result)->address(),
+                        Map::kSize) == 0);
+        }
+      }
+#endif
+      return result;
+    }
+
+    result = fast->CopyNormalized(mode);
+    if (result->IsFailure()) return result;
+    set(index, result);
+  }
+  Counters::normalized_maps.Increment();
+
+  return result;
+}
+
+
+bool NormalizedMapCache::Contains(Map* map) {
+  // If the map is present in the cache it can only be at one place:
+  // at the index calculated from the hash. We assume that a slow map has the
+  // same hash as a fast map it has been generated from.
+  int index = Hash(map) % kEntries;
+  return get(index) == map;
+}
+
+
+void NormalizedMapCache::Clear() {
+  int entries = length();
+  for (int i = 0; i != entries; i++) {
+    set_undefined(i);
+  }
+}
+
+
+int NormalizedMapCache::Hash(Map* fast) {
+  // For performance reasons we only hash the 3 most variable fields of a map:
+  // constructor, prototype and bit_field2.
+
+  // Shift away the tag.
+  int hash = (static_cast<uint32_t>(
+        reinterpret_cast<uintptr_t>(fast->constructor())) >> 2);
+
+  // XOR-ing the prototype and constructor directly yields too many zero bits
+  // when the two pointers are close (which is fairly common).
+  // To avoid this we shift the prototype 4 bits relatively to the constructor.
+  hash ^= (static_cast<uint32_t>(
+        reinterpret_cast<uintptr_t>(fast->prototype())) << 2);
+
+  return hash ^ (hash >> 16) ^ fast->bit_field2();
+}
+
+
+bool NormalizedMapCache::CheckHit(Map* slow,
+                                  Map* fast,
+                                  PropertyNormalizationMode mode) {
+#ifdef DEBUG
+  slow->NormalizedMapVerify();
+#endif
+  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* JSObject::UpdateMapCodeCache(String* name, Code* code) {
+  if (!HasFastProperties() &&
+      NormalizedMapCache::IsCacheable(this) &&
+      Top::context()->global_context()->normalized_map_cache()->
+          Contains(map())) {
+    // Replace the map with the identical copy that can be safely modified.
+    Object* obj = map()->CopyNormalized(KEEP_INOBJECT_PROPERTIES);
+    if (obj->IsFailure()) return obj;
+    Counters::normalized_maps.Increment();
+
+    set_map(Map::cast(obj));
+  }
+  return map()->UpdateCodeCache(name, code);
+}
+
+
 Object* JSObject::NormalizeProperties(PropertyNormalizationMode mode,
                                       int expected_additional_properties) {
   if (!HasFastProperties()) return this;
@@ -2162,28 +2280,22 @@ Object* JSObject::NormalizeProperties(PropertyNormalizationMode mode,
   int index = map()->instance_descriptors()->NextEnumerationIndex();
   dictionary->SetNextEnumerationIndex(index);
 
-  // Allocate new map.
-  obj = map()->CopyDropDescriptors();
+  obj = Top::context()->global_context()->
+      normalized_map_cache()->Get(this, mode);
   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_visitor_id(StaticVisitorBase::GetVisitorId(new_map));
-    Heap::CreateFillerObjectAt(this->address() + new_instance_size,
-                               instance_size_delta);
-  }
-  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.
+
+  // Resize the object in the heap if necessary.
+  int new_instance_size = new_map->instance_size();
+  int instance_size_delta = map()->instance_size() - new_instance_size;
+  ASSERT(instance_size_delta >= 0);
+  Heap::CreateFillerObjectAt(this->address() + new_instance_size,
+                             instance_size_delta);
+
   set_map(new_map);
-  map()->set_instance_descriptors(Heap::empty_descriptor_array());
 
   set_properties(dictionary);
 
@@ -3083,6 +3195,33 @@ Object* Map::CopyDropDescriptors() {
 }
 
 
+Object* Map::CopyNormalized(PropertyNormalizationMode mode) {
+  int new_instance_size = instance_size();
+  if (mode == CLEAR_INOBJECT_PROPERTIES) {
+    new_instance_size -= inobject_properties() * kPointerSize;
+  }
+
+  Object* result = Heap::AllocateMap(instance_type(), new_instance_size);
+  if (result->IsFailure()) return result;
+
+  if (mode != CLEAR_INOBJECT_PROPERTIES) {
+    Map::cast(result)->set_inobject_properties(inobject_properties());
+  }
+
+  Map::cast(result)->set_prototype(prototype());
+  Map::cast(result)->set_constructor(constructor());
+
+  Map::cast(result)->set_bit_field(bit_field());
+  Map::cast(result)->set_bit_field2(bit_field2());
+
+#ifdef DEBUG
+  Map::cast(result)->NormalizedMapVerify();
+#endif
+
+  return result;
+}
+
+
 Object* Map::CopyDropTransitions() {
   Object* new_map = CopyDropDescriptors();
   if (new_map->IsFailure()) return new_map;

src/objects.h

@@ -638,6 +638,7 @@ class Object BASE_EMBEDDED {
   inline bool IsDictionary();
   inline bool IsSymbolTable();
   inline bool IsJSFunctionResultCache();
+  inline bool IsNormalizedMapCache();
   inline bool IsCompilationCacheTable();
   inline bool IsCodeCacheHashTable();
   inline bool IsMapCache();
@@ -1551,6 +1552,8 @@ class JSObject: public HeapObject {
                               int expected_additional_properties);
   Object* NormalizeElements();
 
+  Object* UpdateMapCodeCache(String* name, Code* code);
+
   // Transform slow named properties to fast variants.
   // Returns failure if allocation failed.
   Object* TransformToFastProperties(int unused_property_fields);
@@ -2465,6 +2468,35 @@ class JSFunctionResultCache: public FixedArray {
 };
 
 
+// The cache for maps used by normalized (dictionary mode) objects.
+// Such maps do not have property descriptors, so a typical program
+// needs very limited number of distinct normalized maps.
+class NormalizedMapCache: public FixedArray {
+ public:
+  static const int kEntries = 64;
+
+  static bool IsCacheable(JSObject* object);
+
+  Object* Get(JSObject* object, PropertyNormalizationMode mode);
+
+  bool Contains(Map* map);
+
+  void Clear();
+
+  // Casting
+  static inline NormalizedMapCache* cast(Object* obj);
+
+#ifdef DEBUG
+  void NormalizedMapCacheVerify();
+#endif
+
+ private:
+  static int Hash(Map* fast);
+
+  static bool CheckHit(Map* slow, Map* fast, PropertyNormalizationMode mode);
+};
+
+
 // ByteArray represents fixed sized byte arrays.  Used by the outside world,
 // such as PCRE, and also by the memory allocator and garbage collector to
 // fill in free blocks in the heap.
@@ -3123,6 +3155,8 @@ class Map: public HeapObject {
 
   Object* CopyDropDescriptors();
 
+  Object* CopyNormalized(PropertyNormalizationMode mode);
+
   // Returns a copy of the map, with all transitions dropped from the
   // instance descriptors.
   Object* CopyDropTransitions();
@@ -3185,6 +3219,7 @@ class Map: public HeapObject {
 #ifdef DEBUG
   void MapPrint();
   void MapVerify();
+  void NormalizedMapVerify();
 #endif
 
   inline int visitor_id();
@@ -3219,6 +3254,8 @@ class Map: public HeapObject {
   static const int kPreAllocatedPropertyFieldsOffset =
       kInstanceSizesOffset + kPreAllocatedPropertyFieldsByte;
   // The byte at position 3 is not in use at the moment.
+  static const int kUnusedByte = 3;
+  static const int kUnusedOffset = kInstanceSizesOffset + kUnusedByte;
 
   // Byte offsets within kInstanceAttributesOffset attributes.
   static const int kInstanceTypeOffset = kInstanceAttributesOffset + 0;

src/v8-counters.h

@@ -67,6 +67,7 @@ namespace internal {
   SC(pcre_mallocs, V8.PcreMallocCount)                                \
   /* OS Memory allocated */                                           \
   SC(memory_allocated, V8.OsMemoryAllocated)                          \
+  SC(normalized_maps, V8.NormalizedMaps)                              \
   SC(props_to_dictionary, V8.ObjectPropertiesToDictionary)            \
   SC(elements_to_dictionary, V8.ObjectElementsToDictionary)           \
   SC(alive_after_last_gc, V8.AliveAfterLastGC)                        \