[Bug fortran/47844] I/O: data transfer statement: Array stride ignored for pointer-valued function results

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47844

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pault at gcc dot gnu.org
            Summary|Pointer-valued function:    |I/O: data transfer
                   |Provide wrong result when   |statement: Array stride
                   |dereferenced automatically  |ignored for pointer-valued
                   |after list-write            |function results

--- Comment #2 from Tobias Burnus <burnus at gcc dot gnu.org> 2011-02-22 14:45:42 UTC ---
Paul, I added you as you are a tad more familiar with the scalarizer than I am.

 * * *

Slightly simplified test case:

  integer, target :: tgt(5) = [1,2,3,4,5]
  integer, pointer :: ptr(:)
  print *, f(tgt)
contains
  function f(x)
    integer, target :: x(:)
    integer, pointer :: f(:)
    f => x(::2)
  end function f
end

While "f" correctly sets the stride, it is ignored by the PRINT statement;
-fdump-tree-original shows:

      f (&atmp.8, D.1566);
[...]
              D.1579 = (*(integer(kind=4)[0:] * restrict) atmp.8.data)[S.9];
              _gfortran_transfer_integer_write (&dt_parm.5, &D.1579, 4);
            }
            S.9 = S.9 + 1;

The last line should be S.9 = S.9 + atmp.8.stride, which gets correctly set by
"f()".

Thus, one needs to teach the scalarizer that the stride does not have to be
always 1 for SS_FUNCTION, though the only case I currently can come up with are
array-valued pointer-returning functions. I think one should consider adding a
is_pointer_result:1 to gfc_ss, which could be set in gfc_walk_function_expr.

The scalarizers are set up via gfc_trans_transfer. The "1" setting seems to
happen in gfc_conv_ss_startstride:

        case GFC_SS_CONSTRUCTOR:
        case GFC_SS_FUNCTION:
          for (n = 0; n < ss->data.info.dimen; n++)
            {
              ss->data.info.start[n] = gfc_index_zero_node;
              ss->data.info.end[n] = gfc_index_zero_node;
              ss->data.info.stride[n] = gfc_index_one_node;
            }
          break;

At some point, it needs to be modified for array-pointer-returning functions; I
think that should happen in gfc_conv_loop_setup