Make setting length on arrays faster.

src/ic.cc

 // Copyright 2006-2009 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 1030 matching lines @@
 
   // Check if the given name is an array index.
   uint32_t index;
   if (name->AsArrayIndex(&index)) {
     HandleScope scope;
     Handle<Object> result = SetElement(receiver, index, value);
     if (result.is_null()) return Failure::Exception();
     return *value;
   }
 
+
+  // Use specialized code for setting the length of arrays.
+  if (receiver->IsJSArray()
+      && name->Equals(Heap::length_symbol())
+      && receiver->AllowsSetElementsLength()) {
+#ifdef DEBUG
+    if (FLAG_trace_ic) PrintF("[StoreIC : +#length /array]\n");
+#endif
+    Code* target = Builtins::builtin(Builtins::StoreIC_ArrayLength);
+    set_target(target);
+    StubCache::Set(*name, HeapObject::cast(*object)->map(), target);
+    return receiver->SetProperty(*name, *value, NONE);
+  }
+
   // Lookup the property locally in the receiver.
   if (FLAG_use_ic && !receiver->IsJSGlobalProxy()) {
     LookupResult lookup;
     if (LookupForWrite(*receiver, *name, &lookup)) {
       UpdateCaches(&lookup, state, receiver, name, value);
     }
   }
 
   // Set the property.
   return receiver->SetProperty(*name, *value, NONE);
@@ skipping 275 matching lines @@
 Object* StoreIC_Miss(Arguments args) {
   NoHandleAllocation na;
   ASSERT(args.length() == 3);
   StoreIC ic;
   IC::State state = IC::StateFrom(ic.target(), args[0]);
   return ic.Store(state, args.at<Object>(0), args.at<String>(1),
                   args.at<Object>(2));
 }
 
 
+Object* StoreIC_ArrayLength(Arguments args) {
+  NoHandleAllocation nha;
+
+  ASSERT(args.length() == 2);
+  JSObject* receiver = JSObject::cast(args[0]);
+  Object* len = args[1];
+
+  return receiver->SetElementsLength(len);
+}
+
+
 // Extend storage is called in a store inline cache when
 // it is necessary to extend the properties array of a
 // JSObject.
 Object* SharedStoreIC_ExtendStorage(Arguments args) {
   NoHandleAllocation na;
   ASSERT(args.length() == 3);
 
   // Convert the parameters
   JSObject* object = JSObject::cast(args[0]);
   Map* transition = Map::cast(args[1]);
@@ skipping 39 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal