Re: [Fortran] PR37336 - FIINAL patch [1/n]: Implement the finalization wrapper subroutine

[Mikael Morin <mikael.morin@sfr.fr>]

On 25/08/2012 22:06, Tobias Burnus wrote:
>>>> If comp has finalizable subcomponents, it has a finalization
>>>> wrapper, which is (or should be) caught above, so this branch
>>>> is (or should be) unreachable.
>>> I probably miss something, but I don't see why this branch should
>>> be unreachable. One has:
>>> 
>>> if (component is allocatable) call DEALLOCATE(comp) ! which might
>>> invoke finalizers else if (component itself has a finalizer) call
>>> FINAL_WRAPPER else for all nonpointer subcomponents which are
>>> allocatables, have finalizers or have allocatable/finalizable
>>> components, call finalize_component. end if
>> I expected something like: if (allocatable) call deallocate (comp) 
>> else if (finalizer or subcomponents have a finalizer) call
>> FINAL_WRAPPER
> 
> Well, the question is whether one wants to call a finalize wrapper
> for a simple "comp%alloctable_int(10)" or not. In the current scheme,
> I tried to avoid calling a finalizer wrapper for simple allocatable
> components.
> 
> Thus, one has the choice: a) Directly call DEALLOCATE for alloctable
> components of subcomponents b) Always call the finalizer wrapper –
> also for nonalloctable TYPEs (with finalizable/allocatable
> components)
> 
> (a) is more direct and possibly a bit faster while (b) makes the
> wrapper function a tad smaller.
OK, this is a deliberate choice of implementation to avoid call
overhead. I slightly prefer (b), but we can keep (a).
I'm fine with (a) if the code walking the components is shared - which
avoids c vs. comp issues by the way ;-) .

> * * *
> 
> Regarding the flag or nonflag final_comp, I have to admit that I
> still do not completely understand how you would implement it.
> 
> One option would be something like the following
> 
> bool has_final_comp(derived) { for (comp = derived->components; comp;
> comp = comp->next) { if (comp->attr.pointer) continue; if
> (comp->f2k_derived->finalizers || comp->ts.type == BT_CLASS) return
> true; if (comp->ts.type == BT_DERIVED &&
> has_final_comp(comp->ts.u.derived)) return true; } return false }
This was my initial proposition. The benefit is it is very clear how it
works compared to manual setting the flag here and there.
As you raised a performance issue, I proposed something like this:

bool has_final_comp(derived) {
  bool retval = false;

  if (derived->cache.final_comp_set)
    return derived->cache.final_comp;

  for (comp = derived->components; comp; comp = comp->next)
  {
   if (comp->attr.pointer)
     continue;
    if (comp->f2k_derived->finalizers || comp->ts.type == BT_CLASS)
      {
        retval = true;
        break;
      }
    if (comp->ts.type == BT_DERIVED
        && has_final_comp(comp->ts.u.derived))
      {
        retval = true;
        break;
      }
  }
  derived->cache.final_comp_set = 1;
  derived->cache.final_comp = retval;
  return retval;
}

It's no big deal anyway.
I dream of a compiler where all the non-standard symbol attribute flags,
expression rank and typespec, etc, would be implemented like this... No
need for resolution, etc; it would just work everywhere.
I know the story, patches welcome; they may come, one day...

Mikael