Unify monomorphic and polymorphic cases in IC::PatchCache.

src/ic.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 606 matching lines @@
 }
 
 
 bool IC::UpdatePolymorphicIC(Handle<HeapType> type,
                              Handle<String> name,
                              Handle<Code> code) {
   if (!code->is_handler()) return false;
   TypeHandleList types;
   CodeHandleList handlers;
 
-  int number_of_valid_types;
-  int handler_to_overwrite = -1;
-
   target()->FindAllTypes(&types);
   int number_of_types = types.length();
-  number_of_valid_types = number_of_types;
+  int deprecated_types = 0;
+  int handler_to_overwrite = -1;
 
   for (int i = 0; i < number_of_types; i++) {
     Handle<HeapType> current_type = types.at(i);
-    // Filter out deprecated maps to ensure their instances get migrated.
     if (current_type->IsClass() && current_type->AsClass()->is_deprecated()) {
-      number_of_valid_types--;
-    // If the receiver type is already in the polymorphic IC, this indicates
-    // there was a prototoype chain failure. In that case, just overwrite the
-    // handler.
+      // Filter out deprecated maps to ensure their instances get migrated.
+      ++deprecated_types;
     } else if (type->IsCurrently(current_type)) {
-      ASSERT(handler_to_overwrite == -1);
-      number_of_valid_types--;
+      // If the receiver type is already in the polymorphic IC, this indicates
+      // there was a prototoype chain failure. In that case, just overwrite the
+      // handler.
+      handler_to_overwrite = i;
+    } else if (handler_to_overwrite == -1 &&
+               current_type->IsClass() &&
+               type->IsClass() &&
+               IsTransitionOfMonomorphicTarget(*current_type->AsClass(),
+                                               *type->AsClass())) {
       handler_to_overwrite = i;
     }
   }
 
+  int number_of_valid_types =
+    number_of_types - deprecated_types - (handler_to_overwrite != -1);
+
   if (number_of_valid_types >= 4) return false;
   if (number_of_types == 0) return false;
   if (!target()->FindHandlers(&handlers, types.length())) return false;
 
   number_of_valid_types++;
   if (handler_to_overwrite >= 0) {
     handlers.Set(handler_to_overwrite, code);
+    if (!type->IsCurrently(types.at(handler_to_overwrite))) {
+      types.Set(handler_to_overwrite, type);
+    }
   } else {
     types.Add(type);
     handlers.Add(code);
   }
 
   Handle<Code> ic = isolate()->stub_cache()->ComputePolymorphicIC(
       kind(), &types, &handlers, number_of_valid_types, name, extra_ic_state());
   set_target(*ic);
   return true;
 }
@@ skipping 54 matching lines @@
   TypeHandleList types;
   CodeHandleList handlers;
   target()->FindAllTypes(&types);
   if (!target()->FindHandlers(&handlers, types.length())) return;
   for (int i = 0; i < types.length(); i++) {
     UpdateMegamorphicCache(*types.at(i), *name, *handlers.at(i));
   }
 }
 
 
-bool IC::IsTransitionOfMonomorphicTarget(Handle<HeapType> type) {
-  if (!type->IsClass()) return false;
-  Map* receiver_map = *type->AsClass();
-  Map* current_map = target()->FindFirstMap();
-  ElementsKind receiver_elements_kind = receiver_map->elements_kind();
+bool IC::IsTransitionOfMonomorphicTarget(Map* source_map, Map* target_map) {
+  if (source_map == NULL) return true;
+  if (target_map == NULL) return false;
+  ElementsKind target_elements_kind = target_map->elements_kind();
   bool more_general_transition =
       IsMoreGeneralElementsKindTransition(
-        current_map->elements_kind(), receiver_elements_kind);
+        source_map->elements_kind(), target_elements_kind);
   Map* transitioned_map = more_general_transition
-      ? current_map->LookupElementsTransitionMap(receiver_elements_kind)
+      ? source_map->LookupElementsTransitionMap(target_elements_kind)
       : NULL;
 
-  return transitioned_map == receiver_map;
+  return transitioned_map == target_map;
 }
 
 
 void IC::PatchCache(Handle<HeapType> type,
                     Handle<String> name,
                     Handle<Code> code) {
   switch (state()) {
     case UNINITIALIZED:
     case PREMONOMORPHIC:
     case MONOMORPHIC_PROTOTYPE_FAILURE:
       UpdateMonomorphicIC(type, code, name);
       break;
-    case MONOMORPHIC: {
-      // For now, call stubs are allowed to rewrite to the same stub. This
-      // happens e.g., when the field does not contain a function.
-      ASSERT(!target().is_identical_to(code));
-      Code* old_handler = target()->FindFirstHandler();
-      if (old_handler == *code && IsTransitionOfMonomorphicTarget(type)) {
-        UpdateMonomorphicIC(type, code, name);
-        break;
-      }
-      // Fall through.
-    }
+    case MONOMORPHIC:  // Fall through.
     case POLYMORPHIC:
       if (!target()->is_keyed_stub()) {
         if (UpdatePolymorphicIC(type, name, code)) break;
         CopyICToMegamorphicCache(name);
       }
       set_target(*megamorphic_stub());
       // Fall through.
     case MEGAMORPHIC:
       UpdateMegamorphicCache(*type, *name, *code);
       break;
@@ skipping 674 matching lines @@
   KeyedAccessStoreMode old_store_mode =
       KeyedStoreIC::GetKeyedAccessStoreMode(target()->extra_ic_state());
   Handle<Map> previous_receiver_map = target_receiver_maps.at(0);
   if (state() == MONOMORPHIC) {
     Handle<Map> transitioned_receiver_map = receiver_map;
     if (IsTransitionStoreMode(store_mode)) {
       transitioned_receiver_map = ComputeTransitionedMap(receiver, store_mode);
     }
     if ((receiver_map.is_identical_to(previous_receiver_map) &&
          IsTransitionStoreMode(store_mode)) ||
-        IsTransitionOfMonomorphicTarget(
-            MapToType<HeapType>(transitioned_receiver_map, isolate()))) {
+        IsTransitionOfMonomorphicTarget(*previous_receiver_map,
+                                        *transitioned_receiver_map)) {
       // If the "old" and "new" maps are in the same elements map family, or
       // if they at least come from the same origin for a transitioning store,
       // stay MONOMORPHIC and use the map for the most generic ElementsKind.
       store_mode = GetNonTransitioningStoreMode(store_mode);
       return isolate()->stub_cache()->ComputeKeyedStoreElement(
           transitioned_receiver_map, strict_mode(), store_mode);
     } else if (*previous_receiver_map == receiver->map() &&
                old_store_mode == STANDARD_STORE &&
                (store_mode == STORE_AND_GROW_NO_TRANSITION ||
                 store_mode == STORE_NO_TRANSITION_IGNORE_OUT_OF_BOUNDS ||
@@ skipping 1365 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal