[Bug ada/42253] New: Wrong handling of null for fat pointers forced thin by size clause

[baldrick at free dot fr]

I see this nasty miscompilation with the latest gcc from subversion, as well
as with GNAT GPL 2009 and 2008 but not 2007.

$ gnatmake crash.adb
gcc -c crash.adb
gcc -c p64.adb
gnatbind -x crash.ali
gnatlink crash.ali
$ ./crash

raised STORAGE_ERROR : stack overflow (or erroneous memory access)

-- chop here --
package P64 is
   type SA is access String;
   for SA'Size use Standard'Address_Size;
   S : SA;
   function P return Character;
end;
package body P64 is
   function Q (S : access constant String) return Character is
   begin
      if S /= null and then S'Length > 0 then
         return S (S'First);
      end if;
      return '*';
   end;
   function P return Character is
   begin
      return Q (S);
   end P;
end;
with P64;
procedure Crash is
   C : Character;
begin
   C := P64.P;
   if C /= '*' then
      raise Program_Error;
   end if;
end;


-- 
           Summary: Wrong handling of null for fat pointers forced thin by
                    size clause
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: baldrick at free dot fr
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42253