Bug in GCC ?

He is the sample code I'm trying to compile:

with Ada.Containers.Hashed_Maps;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Strings.Unbounded.Hash;

package SCMAL.Tools.HashedMaps is

     package HashedStrStr is
         new Ada.Containers.Hashed_Maps(
         Key_Type => Unbounded_String,
         Element_Type => Unbounded_String,
         Hash => Ada.Strings.Unbounded.Hash,
         Equivalent_Keys => "=");

end SCMAL.Tools.HashedMaps;


At compile time:

$ gnatmake -Pgentest -cargs -gnatn
gcc-4.1 -c -gnat05 -g3 -O2 -gnatn -I- -gnatA 
/var/local/mscm/ada/tests/generic/scmal-tools-hashedmaps.ads
+===========================GNAT BUG
DETECTED==============================+
| 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu3) 
(i486-pc-linux-gnu) GCC error:|
| in referenced_var_lookup, at tree-dfa.c:578                             
|
| No source file position information available                           
|
| Please submit a bug re****t; see http://gcc.gnu.org/bugs.html.
          
|
| Use a subject line meaningful to you and us to track the bug.           
|
| Include the entire contents of this bug box in the re****t.              
|
| Include the exact gcc-4.1 or gnatmake command that you entered.         
|
| Also include sources listed below in gnatchop format                    
|
| (concatenated together with no headers between files).                  
|
+==========================================================================+

It works fine if I remove the -gnatn and -O2

Sebastien