Change IS_UNDEFINED to perform value comparison instead on typeof check.

src/macros.py

 # 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 79 matching lines @@
 # Native cache ids.
 const STRING_TO_REGEXP_CACHE_ID = 0;
 
 # Type query macros.
 #
 # Note: We have special support for typeof(foo) === 'bar' in the compiler.
 #       It will *not* generate a runtime typeof call for the most important
 #       values of 'bar'.
 macro IS_NULL(arg)              = (arg === null);
 macro IS_NULL_OR_UNDEFINED(arg) = (arg == null);
-macro IS_UNDEFINED(arg)         = (typeof(arg) === 'undefined');
+macro IS_UNDEFINED(arg)         = (arg === (void 0));
 macro IS_NUMBER(arg)            = (typeof(arg) === 'number');
 macro IS_STRING(arg)            = (typeof(arg) === 'string');
 macro IS_BOOLEAN(arg)           = (typeof(arg) === 'boolean');
 macro IS_SYMBOL(arg)            = (typeof(arg) === 'symbol');
 macro IS_OBJECT(arg)            = (%_IsObject(arg));
 macro IS_ARRAY(arg)             = (%_IsArray(arg));
 macro IS_FUNCTION(arg)          = (%_IsFunction(arg));
 macro IS_REGEXP(arg)            = (%_IsRegExp(arg));
 macro IS_SET(arg)               = (%_ClassOf(arg) === 'Set');
 macro IS_MAP(arg)               = (%_ClassOf(arg) === 'Map');
@@ skipping 154 matching lines @@
 const COMPILATION_TYPE_JSON = 2;
 
 # Matches Messages::kNoLineNumberInfo from v8.h
 const kNoLineNumberInfo = 0;
 
 # Matches PropertyAttributes from property-details.h
 const PROPERTY_ATTRIBUTES_NONE = 0;
 const PROPERTY_ATTRIBUTES_STRING = 8;
 const PROPERTY_ATTRIBUTES_SYMBOLIC = 16;
 const PROPERTY_ATTRIBUTES_PRIVATE_SYMBOL = 32;