[Bug fortran/53692] New: OPTIONAL: Scalarizing over the wrong array

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53692

             Bug #: 53692
           Summary: OPTIONAL: Scalarizing over the wrong array
    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
                CC: mikael@gcc.gnu.org
            Blocks: 50981


The following program of Daniel C Chen fails due to invalid OPTIONAL handling:
The scalarizer uses the first array instead of the first array belonging to a
nonoptional argument.

Cf. http://j3-fortran.org/pipermail/j3/2012-June/005356.html

See also: 12.5.2.12p3(6), 
  "An optional dummy argument that is not present is subject to the 
   following restrictions.
   ...
  "(6) If it is an array, it shall not be supplied as an actual argument to 
   an elemental procedure unless an array of the same rank is supplied as an 
   actual argument corresponding to a nonoptional dummy argument of that 
   elemental procedure."


Untested draft patch. I think one might need to have a fall back if there is no
actual argument (which is an array) belonging to a nonoptional dummy. In that
case (cf. above) one can assume that the first array in the list has to be
present.

--- a/gcc/fortran/trans-array.c
+++ b/gcc/fortran/trans-array.c
@@ -4356,3 +4356,4 @@ set_loop_bounds (gfc_loopinfo *loop)
              || ss_type == GFC_SS_TEMP
-             || ss_type == GFC_SS_REFERENCE)
+             || ss_type == GFC_SS_REFERENCE
+             || ss->info->can_be_null_ref)
            continue;



Program main
  implicit none
  integer :: arr(2)

  arr = [ 1, 2 ]
  call sub1(arg2=arr)
contains
   subroutine sub1(arg1,arg2)
      integer, optional :: arg1(:)
      integer :: arg2(:)
      print *,fun1 (arg1, arg2)
      if (size (fun1 (arg1, arg2)) /= 2) call abort()
      if (any (fun1 (arg1, arg2) /= [1,2])) call abort()
   end subroutine

   elemental function fun1(arg1,arg2)
      integer,intent(in), optional :: arg1
      integer,intent(in)          :: arg2
      integer                     :: fun1
      fun1 = arg2
   end function
end program