Patch by Vitaly Repeshko. Improve performance of internal fields...

src/objects-inl.h

 // Copyright 2006-2008 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 1057 matching lines @@
 
 
 void JSGlobalPropertyCell::set_value(Object* val, WriteBarrierMode ignored) {
   // The write barrier is not used for global property cells.
   ASSERT(!val->IsJSGlobalPropertyCell());
   WRITE_FIELD(this, kValueOffset, val);
 }
 
 
 int JSObject::GetHeaderSize() {
-  switch (map()->instance_type()) {
+  InstanceType type = map()->instance_type();
+  // Check for the most common kind of JavaScript object before
+  // falling into the generic switch. This speeds up the internal
+  // field operations considerably on average.
+  if (type == JS_OBJECT_TYPE) return JSObject::kHeaderSize;
+  switch (type) {
     case JS_GLOBAL_PROXY_TYPE:
       return JSGlobalProxy::kSize;
     case JS_GLOBAL_OBJECT_TYPE:
       return JSGlobalObject::kSize;
     case JS_BUILTINS_OBJECT_TYPE:
       return JSBuiltinsObject::kSize;
     case JS_FUNCTION_TYPE:
       return JSFunction::kSize;
     case JS_VALUE_TYPE:
       return JSValue::kSize;
     case JS_ARRAY_TYPE:
       return JSValue::kSize;
     case JS_REGEXP_TYPE:
       return JSValue::kSize;
-    case JS_OBJECT_TYPE:
     case JS_CONTEXT_EXTENSION_OBJECT_TYPE:
       return JSObject::kHeaderSize;
     default:
       UNREACHABLE();
       return 0;
   }
 }
 
 
 int JSObject::GetInternalFieldCount() {
@@ skipping 1661 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_