[PATCH, v2] Fortran: fix invalid rank error in ASSOCIATED when rank is remapped [PR77652]

[Harald Anlauf]

Hi Mikael, all,

I've just reverted commit 0110cfd5449bae3a772f45ea2e4c5dab5b7a8ccd.
As it seems that commit ca170ed9f8a086ca7e1eec841882b6bed9ec1a3a did
not update bugzilla, I'll add a note to the PR and close it as invalid.

Thanks,
Harald


Am 04.08.22 um 14:03 schrieb Mikael Morin:
> Le 30/07/2022 à 12:03, Mikael Morin a écrit :
>> Le 28/07/2022 à 22:19, Mikael Morin a écrit :
>>> I propose to prepare something tomorrow.
>>>
>>
>> Here you go.
>
> I posted the message the other day.
> The mailing list archive are not automatic, so there is no link to the
> message (yet?), nor to the thread that follows it.
> So I attach below the answer from Malcolm Cohen.
> Long story short, he confirms the interpretation from Steve Lionel, and
> that the text in the standard needs fixing.
> I’m afraid we’ll have to revert.
>
>
> -------- Message transféré --------
> Sujet : [SC22WG5.6416] RE: [ukfortran] Request for interpretation of
> compile-time restrictions on ASSOCIATED
> Date : Thu, 4 Aug 2022 11:43:16 +0900
> De : Malcolm Cohen <malcolm@nag-j.co.jp>
> Pour : 'Mikael Morin' <morin-mikael@orange.fr>, sc22wg5@open-std.org
> Copie à : 'Harald Anlauf' <anlauf@gmx.de>
>
> Dear Mikael,
>
> Thank you for your query.
>
> I would agree with Steve Lionel that the ranks must be the same (when
> POINTER is not assumed-rank), for two reasons.
>
> (1) The result of ASSOCIATED is unambiguously .FALSE. when the shapes of
> POINTER and TARGET differ. As the shapes cannot be the same when the ranks
> differ seeing as how the number of elements in the shape are not the same,
> that means it would always be .FALSE. when the ranks differ. The Fortran
> language does not need an extra way to produce the LOGICAL constant .FALSE.
>
> Note that this means that even in the case where POINTER is dimension (2,1)
> and TARGET is dimension (1,2), and they both refer to the same elements in
> array element order, ASSOCIATED will return .FALSE. because the shapes are
> not the same. ASSOCIATED is a much stronger test than mere address
> comparison.
>
> (2) This text arises from an attempted, but failed, simplification of what
> we had before. Unfortunately, it is completely and utterly broken, as it
> forbids the use of ASSOCIATED when POINTER is assumed-rank, has INTENT(IN),
> is PROTECTED (outside of its module), or is a pointer function reference.
> That is because there are no pointer assignment statements where the
> pointer
> object is permitted to be any of those, and thus the conditions for TARGET
> cannot ever be satisfied.
>
> However, the processor is not *required* to report an error when the ranks
> differ, as this is not a "Constraint" in the standard. I would expect a
> high
> quality implementation to do so, but maybe I just have high expectations...
>
> It could also be a deliberate extension, with different semantics provided
> by the processor. In that case, the processor would be required to have the
> capability to report the use of the extension (but this need not be the
> default).
>
> Finally, I note that we are not accepting interpretation requests on
> Fortran
> 2018 at this time, as we are in the process of replacing it with a new
> revision (Fortran 2023). However, we will certainly consider whether we can
> make any correction to Fortran 2023 before publication (expected next
> year);
> if there is consensus on how to fix the clearly-incorrect requirements on
> TARGET, we can do so. Otherwise, we will need to wait until after Fortran
> 2023 is published before we can restart the Defect Processing process.
>
> I will undertake to write a meeting paper addressing this issue before this
> year's October meeting. If no paper has appeared by mid-September, please
> feel free to remind me to do that!
>
> Cheers,