Re: [PATCH, fortran] PR fortran/60255 Deferred character length

[Paul Richard Thomas <paul dot richard dot thomas at gmail dot com>]

Cancel that - It should be multiplies by kind, shouldn't it ? :-) OK,
string length it is. We will probably have to set _len = 1 for other
dynamic types, though, so that the pointer arising from an array
reference is base_address + _len*vptr->size*index

Cheers

Paul

On 17 January 2015 at 13:44, Paul Richard Thomas
<paul.richard.thomas@gmail.com> wrote:
> Dear Andre,
>
> I am open to either - what do the others think?
>
> The reason why I am for differentiating between unlimited_polymorphic
> objects and the deferred length character arrays is because of the
> difference in the way in which arrays are accessed. The former uses
> pointer arithmetic and the latter array references. I was trying to
> avoid divisions by KIND within scalarization loops. Also, I found that
> in developing your patch, that allocating with unlimited polymorphic
> sources looks neatest when the _len contains the memory size of the
> elements of any dynamic type, since a priori it is not known at
> compile time whether it is a character or not. Of course, one could
> interrogate the _hash field of the vtable, at the expense of more
> runtime code.
>
> Cheers
>
> Paul
>
> PS I have your patches for PR60357 and 61275 regtesting right now.
> Both look OK to me. At the risk of making potential regressions more
> complicated to unravel, to save my time I intend to commit both at
> once, unless anybody objects.
>
>
>
> On 17 January 2015 at 13:10, Andre Vehreschild <vehre@gmx.de> wrote:
>> Hi Paul,
>>
>> I am open on what to call the new component.
>>
>> Have you thought about my findings, that for deferred length char arrays the
>> length is stored in characters and not in bytes, I.e., for a
>> character(kind=4, Len=:) the length is stored in number of characters and
>> not in bytes needed, which would be Len*4. IMHO both concepts should be
>> changed, or none. I favor to keep storing the string length of both concepts
>> (deferred char arrays and chararrays in unlimited polymorphic entities)
>> interchangeable w/o computation.
>>
>> What's your opinion?
>>
>> Regards, Andre
>>
>> Andre Vehreschild * Kreuzherrenstr. 8 * 52062 Aachen
>> Tel. +49 241.9291018 * vehre@gmx.de
>>
>>
>> Paul Richard Thomas <paul.richard.thomas@gmail.com> schrieb:
>>
>>
>> Dear Andre,
>>
>> Perhaps, rather than calling the new component _len, we should call it
>> _mem_size or some such?
>>
>> Cheers
>>
>> Paul
>>
>> On 9 January 2015 at 11:52, Andre Vehreschild <vehre@gmx.de> wrote:
>>> 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.thomas@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 <vehre@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 <janus@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: vehre@gmx.de
>>>>
>>>>
>>>>
>>>
>>>
>>> --
>>> Andre Vehreschild * Kreuzherrenstr. 8 * 52062 Aachen
>>> Tel.: +49 241 9291018 * Email: vehre@gmx.de
>>
>>
>>
>> --
>> Outside of a dog, a book is a man's best friend. Inside of a dog it's
>> too dark to read.
>>
>> Groucho Marx
>
>
>
> --
> Outside of a dog, a book is a man's best friend. Inside of a dog it's
> too dark to read.
>
> Groucho Marx



-- 
Outside of a dog, a book is a man's best friend. Inside of a dog it's
too dark to read.

Groucho Marx