Undefined is not a literal.

src/ast.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 54 matching lines @@
   return AsLiteral() != NULL && AsLiteral()->value()->IsString();
 }
 
 
 bool Expression::IsNullLiteral() {
   return AsLiteral() != NULL && AsLiteral()->value()->IsNull();
 }
 
 
 bool Expression::IsUndefinedLiteral() {
-  return AsLiteral() != NULL && AsLiteral()->value()->IsUndefined();
+  if (!IsVariableProxy()) return false;
+  VariableProxy* var_proxy = static_cast<VariableProxy*>(this);

[rossberg, 2013/07/12 13:40:32]

Instead of these two lines, use AsVariableProxy() and return false if it's NULL.

+  Variable* var = var_proxy->var();
+  // The global identifier "undefined" is immutable. Everything
+  // else could be reassigned.
+  return var != NULL && var->location() == Variable::UNALLOCATED &&
+         strncmp(*var_proxy->name()->ToCString(), "undefined", 10) == 0;

[rossberg, 2013/07/12 13:40:32]

You should be able to say

  var->name()->Equals(isolate()->heap()->undefined_string())

especially since that will take advantage of the string internalization the
parser performs.

 }
 
 
 VariableProxy::VariableProxy(Isolate* isolate, Variable* var)
     : Expression(isolate),
       name_(var->name()),
       var_(NULL),  // Will be set by the call to BindTo.
       is_this_(var->is_this()),
       is_trivial_(false),
       is_lvalue_(false),
@@ skipping 1101 matching lines @@
     OS::SNPrintF(buffer, "%d", Smi::cast(*value_)->value());
     str = arr;
   } else {
     str = DoubleToCString(value_->Number(), buffer);
   }
   return factory->NewStringFromAscii(CStrVector(str));
 }
 
 
 } }  // namespace v8::internal