Undefined is not a literal.

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 964f5bc76e2ea88b9b0f16fac9f167ed3d5bd927..6317e50b8b0365c19273f96ba8443dcd5cefcf82 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -72,7 +72,13 @@ bool Expression::IsNullLiteral() {
 
 
 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.

 }