Re: [PATCH v8 1/5] Provide counted_by attribute to flexible array member field (PR108896)

[Qing Zhao <qing.zhao@oracle.com>]

Thanks for the comments.

> On Apr 10, 2024, at 13:35, Joseph Myers <josmyers@redhat.com> wrote:
> 
> 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.

Looks like this additional case relates to the new C23 feature, where is the
documentation on this new feature, I need to study a little bit on this, thanks.

> 
> Suppose, as allowed in C23, a structure is defined twice in the same 
> scope,

A stupid question first, the same scope means the same file? (Or same function)

Is there a testing case for this feature in current GCC source tree I can take a look? (and
Then I can use it to construct the new testing case for the counted-by attribute).

> but the two definitions of the structure use inconsistent 
> counted_by attributes.

Where in the current C FE to handle the same structure is defined twice in the same scope? Which routine
In the C FE?

>  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).

Agreed. Wil add such checking. 

> 
> In C23 structures defined with the same tag in different scopes are 
> compatible given requirements including compatible types for corresponding 
> elements.
Again, which routine in the C FE handle such case? I’d like to take a look at the current
Handling and how to update it for the counted-by attribute. 


>  It would seem most appropriate to me for such structures with 
> incompatible counted_by attributes to be considered *not* compatible types

Is there a utility routine for checking “compatible type”? 


> (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).

Updating that routine (checking compatible type) with the new “counted-by” attribute
Might be enough for this purpose, I guess. 
> 
>> +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).

Okay, will update this.

thanks.

Qing
> 
> -- 
> Joseph S. Myers
> josmyers@redhat.com
>