[Bug fortran/55990] New: Absent optional: gfortran.dg/class_optional_2.f90: Conditional jump depends on uninitialised value

["burnus at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55990

             Bug #: 55990
           Summary: Absent optional: gfortran.dg/class_optional_2.f90:
                    Conditional jump depends on uninitialised value
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org


Note: gfortran.dg/class_optional_2.f90 has been added for PR 50981 / PR 54618.
It uses nullified pointers and absent optionals.


http://gcc.gnu.org/ml/gcc-testresults/2013-01/msg01524.html shows:

Running target unix/-m32 on x86_64-unknown-linux-gnu
FAIL: gfortran.dg/class_optional_2.f90  -O2  execution test


If one uses valgrind on the examples, one finds many failure of the form:
==15916== Conditional jump or move depends on uninitialised value(s)
==15916==    at 0x41103BD: _gfortran_internal_pack (in_pack_generic.c:53)

which is called, respectively, in the lines:
==15916==    by 0x80489A9: MAIN__ (class_optional_2.f90:39)
==15916==    by 0x80489C5: MAIN__ (class_optional_2.f90:40)

Those contain the calls:
   type(t), optional :: z(4)  ! Absent actual argument
   type(t), pointer :: y(:)   ! nullified pointer
   y => null()
...
   call a4t(y) ! line 39
   call a4t(z) ! line 40

Hereby, a4t is:

 subroutine a4t(x)
   type(t), intent(in), optional :: x(4)