[Bug middle-end/41453] use INTENT(out) for optimization

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41453

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |anlauf at gcc dot gnu.org

--- Comment #8 from anlauf at gcc dot gnu.org ---
Sometimes we now generate a clobber for the wrong variable when a function
result is involved.  An example, derived from PR105012:

! compile with -fdump-tree-original

module m
contains

  SUBROUTINE Y (Z)
    real, intent(out) :: Z
    Z = 1.
  END SUBROUTINE Y

  FUNCTION X ()
    real :: X
    CALL Y (X)      ! direct use of function result, bad clobber
  END FUNCTION X

  FUNCTION F () result(res)
    real :: res
    CALL Y (res)    ! using explicit result variable, good clobber
  END FUNCTION F

end


With current trunk this produces:

__attribute__((fn spec (". ")))
real(kind=4) f ()
{
  real(kind=4) res;

  res = {CLOBBER};
  y (&res);
  return res;
}


__attribute__((fn spec (". ")))
real(kind=4) x ()
{
  real(kind=4) __result_x;

  x = {CLOBBER};
  y (&__result_x);
  return __result_x;
}


__attribute__((fn spec (". w ")))
void y (real(kind=4) & restrict z)
{
  *z = 1.0e+0;
}


For function X (without the result clause) we should have:

  __result_x = {CLOBBER};

instead.  We probably need to have a closer look here:

(gdb) l 9539,9548
9539          else if (add_clobber && expr->ref == NULL)
9540            {
9541              tree clobber;
9542              tree var;
9543              /* FIXME: This fails if var is passed by reference, see PR
9544                 41453.  */
9545              var = expr->symtree->n.sym->backend_decl;
9546              clobber = build_clobber (TREE_TYPE (var));
9547              gfc_add_modify (&se->pre, var, clobber);
9548            }