$ gcc -c p-c.adb
+===========================GNAT BUG DETECTED==============================+
| 4.4.0 20080630 (experimental) (x86_64-unknown-linux-gnu) Storage_Error heap exhausted|
| Error detected at p-c.adb:1:1                                            |
| Please submit a bug report; 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 report.               |
| Include the exact gcc or gnatmake command that you entered.              |
| Also include sources listed below in gnatchop format                     |
| (concatenated together with no headers between files).                   |
+==========================================================================+

Please include these source files with error report
Note that list may not be accurate in some cases,
so please double check that the problem can still
be reproduced with the set of files listed.

p-c.adb
p-c.ads
p.ads
f.ads
g.ads

compilation abandoned

$ gcc -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc.fsf.master/configure --prefix=/usr/local/gnat-fsf --enable-languages=ada,c,c++ --disable-bootstrap --disable-multilib --enable-checking
Thread model: posix
gcc version 4.4.0 20080630 (experimental) (GCC)

gcc built from svn as of this morning.

-- chop here --
with G;
generic
   type T is private;
package F is
   type R (<>) is tagged private;
   function C return R;
private
   package GI is new G (T);
   type R is new GI.R with null record;
end;
generic
  type T is private;
package G is
   type R is tagged null record;
   procedure P (X : R; Y : T);
end;
package P is end;
with F;
package P.C is
private
   type New_Integer is new Integer;
   package FI is new F (New_Integer);
   type R is new FI.R with null record;
   function C return R;
end;
package body P.C is end;