> On Apr 11, 2024, at 02:02, Martin Uecker <[email protected]> wrote:
>
> Am Mittwoch, dem 10.04.2024 um 19:35 +0000 schrieb Qing Zhao:
>>
>>> On Apr 10, 2024, at 15:05, Martin Uecker <[email protected]> wrote:
>>>
>>> Am Mittwoch, dem 10.04.2024 um 20:25 +0200 schrieb Martin Uecker:
>>>> Am Mittwoch, dem 10.04.2024 um 17:35 +0000 schrieb Joseph Myers:
>>>>> On Fri, 29 Mar 2024, Qing Zhao wrote:
>>>>>
>>>>>> + /* Issue error when there is a counted_by attribute with a different
>>>>>> + field as the argument for the same flexible array member field. */
>>>>>
>>>>> There's another case of this to consider, though I'm not sure where best
>>>>> to check for it (Martin might have suggestions) - of course this case
>>>>> will
>>>>> need testcases as well.
>>>>>
>>>>> Suppose, as allowed in C23, a structure is defined twice in the same
>>>>> scope, but the two definitions of the structure use inconsistent
>>>>> counted_by attributes. I'd say that, when the declarations are in the
>>>>> same scope (thus required to be consistent), it should be an error for
>>>>> the
>>>>> two definitions of what is meant to be the same structure to use
>>>>> incompatible counted_by attributes (even though the member declarations
>>>>> are otherwise the same).
>>>>
>>>> I think the right place could be comp_types_attributes in
>>>> attributes.cc. It may be sufficient to set the
>>>> affects_type_identify flag.
>>>>
>>>> This should then give a redefinition error as it should do for
>>>> "packed".
>>>
>>> Thinking about this a bit more, this will not work here, because
>>> the counted_by attribute is not applied to the struct type but
>>> one of the members.
>>>
>>> So probably there should be a check added directly
>>> to tagged_types_tu_compatible_p
>>
>>
>> There are two cases we will check:
>>
>> A. Both definitions are in the same scope;
>> Then if the 2nd definition has a counted-by attribute different from
>> the 1st definition, the 2nd definition will be given a redefinition error;
>>
>> B. These two definitions are in different scope;
>> When these two definitions are used in a way need to be compatible, an
>> incompatible error need to be issued at that
>> Point;
>>
>>
>> My question is, Will the routine “tagged_types_tu_compatible_p” can handle
>> both A and B?
>
> Yes, changing this function should address both cases if I am
> not missing something.
>
Thanks for the help.
Will study this routine in more details and update the patch.
Qing
> Martin
>
>>
>> Thanks.
>>
>> Qing
>>>
>>> Martin
>>>
>>>>
>>>>>
>>>>> In C23 structures defined with the same tag in different scopes are
>>>>> compatible given requirements including compatible types for
>>>>> corresponding
>>>>> elements. It would seem most appropriate to me for such structures with
>>>>> incompatible counted_by attributes to be considered *not* compatible
>>>>> types
>>>>> (but it would be valid to define structures with the same tag, different
>>>>> scopes, and elements the same except for counted_by - just not to use
>>>>> them
>>>>> in any way requiring them to be compatible).
>>>>
>>>> Another option might be to warn about the case when those types
>>>> are then used together in a way where they are required to
>>>> be compatible. Then comp_types_attributes would have to return 2.
>>>>
>>>>
>>>> Martin
>>>>
>>>>>
>>>>>> +The @code{counted_by} attribute may be attached to the C99 flexible
>>>>>> array
>>>>>> +member of a structure. It indicates that the number of the elements of
>>>>>> the
>>>>>> +array is given by the field "@var{count}" in the same structure as the
>>>>>
>>>>> As noted previously, the "" quotes should be removed there (or replaced
>>>>> by
>>>>> ``'' quotes).
>>>>>
>>>>
>>>
>>
>
