Fast check undefined in EQUALS.

src/runtime.js

 // 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 60 matching lines @@
     } else if (IS_BOOLEAN(x)) {
       if (IS_BOOLEAN(y)) {
         return %_ObjectEquals(x, y) ? 0 : 1;
       }
       if (y == null) return 1;  // not equal
       return %NumberEquals(%ToNumber(x), %ToNumber(y));
     } else if (x == null) {
       // NOTE: This checks for both null and undefined.
       return (y == null) ? 0 : 1;
     } else {
+      // x is not a number, boolean, null or undefined.
+      if (IS_UNDEFINED(y)) return 1;  // not equal
+
       if (IS_OBJECT(y)) {
         return %_ObjectEquals(x, y) ? 0 : 1;
       }
       if (IS_FUNCTION(y)) {
         return %_ObjectEquals(x, y) ? 0 : 1;
       }
+
       x = %ToPrimitive(x, NO_HINT);
     }
   }
 }
 
 // ECMA-262, section 11.9.4, page 56.
 function STRICT_EQUALS(x) {
   if (IS_STRING(this)) {
     if (!IS_STRING(x)) return 1;  // not equal
     return %StringEquals(this, x);
@@ skipping 418 matching lines @@
   throw %MakeTypeError('cannot_convert_to_primitive', []);
 }
 
 
 // NOTE: Setting the prototype for Array must take place as early as
 // possible due to code generation for array literals.  When
 // generating code for a array literal a boilerplate array is created
 // that is cloned when running the code.  It is essiential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype($Array, new $Array(0));