Hi all, hi Paul,
I started to implement the changes requested below, but I stumbled over an
oddity:
For a deferred length kind4 char array, the length of the string is stored
without multiplication by 4 in the length variable attached. So when we now
decide to store the length of the string in an unlimited polymorphic entity in
bytes in the component formerly called _len and the size of each character in
_vtype->_size then we have an inconsistency with the style deferred char
lengths are stored. IMHO we should store this consistently, i.e., both
'length'-variables store either the length of the string ('length' = array_len)
or the size of the memory needed ('length' = array_len * char_size). What do
you think?
Furthermore, think about debugging: When looking at an unlimited polymorphic
entity storing a kind-4-char-array of length 7, then having a 'length' component
set to 28 will lead to confusion. I humbly predict, that this will produce many
entries in the bugtracker, because people don't understand that 'length' stores
the product of elem_size times string_len, because all they see is an
assignment of a length-7 char array.
What do we do about it?
Regards,
Andre
On Thu, 8 Jan 2015 20:56:43 +0100
Paul Richard Thomas <paul.richard.tho...@gmail.com> wrote:
> Dear Andre,
>
> Thanks for the patch. As I have said to you, off list, I think that
> the _size field in the vtable should contain the kind information and
> that the _len field should carry the length of the string in bytes. I
> think that it is better to optimise array access this way than to
> avoid the division in evaluating LEN (). I am happy to accept contrary
> opinions from the others.
>
> I do not believe that the bind_c issue is an issue. Your patch
> correctly deals with it IMHO.
>
> Subject to the above change in the value of _len, I think that your
> patch is OK for trunk.
>
> With best regards
>
> Paul
>
> On 4 January 2015 at 13:40, Andre Vehreschild <ve...@gmx.de> wrote:
> > Hi Janus, hi Paul, hi Tobias,
> >
> > Janus: During code review, I found that I had the code in
> > gfc_get_len_component() duplicated. So I now reintroduced and documented the
> > routine making is more commonly usable and added more documentation. The
> > call sites are now simplify.c (gfc_simplify_len) and trans-expr.c
> > (gfc_trans_pointer_assignment). Attached is the reworked version of the
> > patch.
> >
> > Paul, Tobias: Can one of you have a look at line 253 of the patch? I need
> > some expertise on the bind_c behavior. My patch needs the check for
> > is_bind_c added in trans_expr.c (gfc_conv_expr) to prevent mistyping an
> > associated variable in a select type() during the conv. Background: This
> > code fragment taken from the testcase in the patch:
> >
> > MODULE m
> > contains
> > subroutine bar (arg, res)
> > class(*) :: arg
> > character(100) :: res
> > select type (w => arg)
> > type is (character(*))
> > write (res, '(I2)') len(w)
> > end select
> > end subroutine
> > END MODULE
> >
> > has the conditions required for line trans-expr.c:6630 of gfc_conv_expr when
> > the associate variable w is converted. This transforms the type of the
> > associate variable to something unexpected in the further processing
> > leading to some issues during fortraning. Janus told me, that the f90_type
> > has been abused for some other things (unlimited polymorphic treatment).
> > Although I believe that reading the comments above the if in question, the
> > check I had to enhance is treating bind_c stuff (see the threads content
> > for more). I would feel safer when one of you gfortran gurus can have a
> > look and given an opinion, whether the change is problematic. I couldn't
> > figure why w is resolved to meet the criteria (any ideas). Btw, all regtest
> > are ok reporting no issues at all.
> >
> > Bootstraps and regtests ok on x86_64-linux-gnu
> >
> > Regards,
> > Andre
> >
> >
> > On Sat, 3 Jan 2015 16:45:07 +0100
> > Janus Weil <ja...@gcc.gnu.org> wrote:
> >
> >> Hi Andre,
> >>
> >> >> >> For the
> >> >> >> second one (in gfc_conv_expr), I don't directly see how it's related
> >> >> >> to deferred char-len. Why is this change needed?
> >> >> >
> >> >> > That change is needed, because in some rare case where an associated
> >> >> > variable in a "select type ()" is used, then the type and f90_type
> >> >> > match the condition while them not really being in a bind_c context.
> >> >> > Therefore I have added the check for bind_c. Btw, I now have removed
> >> >> > the TODO, because that case is covered by the regression tests.
> >> >>
> >> >> I don't understand how f90_type can be BT_VOID without being in a
> >> >> BIND_C context, but I'm not really a ISO_C_BINDING expert. Which test
> >> >> case is the one that triggered this?
> >> >
> >> > This case is triggered by the test-case in the patch, where in the select
> >> > type (w => arg) in module m routine bar the w meets the criteria to make
> >> > the condition become true. The type of w is then "fixed" and gfortran
> >> > would terminate, because the type of w would be set be and BT_INTEGER. I
> >> > tried to backtrace where this is coming from, but to no success. In the
> >> > resolve () of the select type it looks all quite ok, but in the trans
> >> > stage the criteria are met. Most intriguing to me is, that in the
> >> > condition we are talking about the type of w and f90_type of the derived
> >> > class' ts (expr->ts.u.derived->ts.f90_type) of w is examined. But
> >> > expr->ts.u.derived->ts does not describe the type of w, but of the class
> >> > w is associate with __STAR...
> >> >
> >> > So I am not quite sure how to fix this, if this really needs fixing.
> >> > When I understand you right, then f90_type should only be set in a
> >> > bind_c context, so adding that check wouldn't hurt, right?
> >>
> >> Yes, in principle adding the check for attr.bind_c looks ok to me
> >> (alternatively one could also check for attr.unlimited_polymorphic). I
> >> think originally BT_VOID was indeed only used in a bind_c context, but
> >> recently it has also been 'hijacked' for unlimited polymorphism, e.g.
> >> for the STAR symbol and some of the components of the intrinsic vtabs.
> >>
> >> What I don't really understand is why these problems are triggered by
> >> your patch now and have not crept up earlier in other use-cases of
> >> CLASS(*).
> >>
> >>
> >> >> >> 3) The function 'gfc_get_len_component' that you're introducing is
> >> >> >> only called in a single place. Do you expect this to be useful in
> >> >> >> other places in the future, or could one remove the function and
> >> >> >> insert the code inline?
> >> >> >
> >> >> > In one of the first versions it was uses from two locations. But I
> >> >> > had to remove one call site again. I am currently not sure, if I will
> >> >> > be using it in the patch for allocatable components when deferred
> >> >> > char arrays are handled. So what I do I do now? Inline it and when
> >> >> > needed make it explicit again in a future patch?
> >> >>
> >> >> I leave that up to you. In principle I'm fine with keeping it as it
> >> >> is. The only problem I see is that the function name sounds rather
> >> >> general, but it apparently expects the expression to be an ASSOCIATE
> >> >> symbol.
> >> >
> >> > I am nearly finished with the patch on allocatable scalar components and
> >> > I don't need the code there. Therefore I have inlined the routine.
> >>
> >> Ok, good. Could you please post an updated patch?
> >>
> >>
> >> > So, what do we do about the bind_c issue above? Is some bind_c guru
> >> > available to have a look at this? It would be very much appreciated.
> >>
> >> From my non-guru POV, it can stay as is.
> >>
> >> It would be helpful if someone like Paul or Tobias could have a look
> >> at the patch before it goes to trunk. I think it's pretty close to
> >> being ready for prime-time. Thanks for your work!
> >>
> >> Cheers,
> >> Janus
> >
> >
> > --
> > Andre Vehreschild * Kreuzherrenstr. 8 * 52062 Aachen
> > Tel.: +49 241 9291018 * Email: ve...@gmx.de
>
>
>
--
Andre Vehreschild * Kreuzherrenstr. 8 * 52062 Aachen
Tel.: +49 241 9291018 * Email: ve...@gmx.de
