Re: [PATCH 1/2] Handle component_ref to a structre/union field including flexible array member [PR101832]

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

> On Feb 9, 2023, at 5:35 AM, Richard Biener <rguenther@suse.de> wrote:
> 
> On Wed, 8 Feb 2023, Qing Zhao wrote:
> 
>> 
>> 
>>> On Feb 7, 2023, at 6:37 PM, Joseph Myers <joseph@codesourcery.com> wrote:
>>> 
>>> On Tue, 7 Feb 2023, Qing Zhao via Gcc-patches wrote:
>>> 
>>>> Then, this routine (flexible_array_type_p) is mainly for diagnostic purpose.
>>>> It cannot be used to determine whether the structure/union type recursively
>>>> include a flexible array member at the end.
>>>> 
>>>> Is my understanding correct?
>>> 
>>> My comments were about basic principles of what gets diagnosed, and the 
>>> need for different predicates in different contexts; I wasn't trying to 
>>> assert anything about how that maps onto what functions should be used in 
>>> what contexts.
>> Okay. 
>> 
>> But I noticed that “flexible_array_type_p” later was moved from FE to
>> middle-end and put into tree.cc, tree.h as a general utility routine, and to 
>> 
>> /* Determine whether TYPE is a structure with a flexible array member,
>>   or a union containing such a structure (possibly recursively).  */
>> 
>> However, since this routine does not cover the cases when the structure 
>> with flexible array member was recursively embedded into structures, (which we 
>> agreed that it should be considered as a flexible sized type). 
>> 
>> Therefore, I feel that It might not be proper to include this routine in middle end 
>> (and actually no other places In middle end use this routine so far).
>> 
>> That’s the reason I asked the previous question. 
>> 
>> It might be better to move the routine “flexible_array_type_p” back from middle-end to
>> FE for the diagnosis purpose only. 
> 
> It's always dangerous to move functions with such a descriptive name to
> a place where it suggests wider use is applicable.  Also since
> objc/objc-act.cc has a function with the same name (if that had same
> content before r10-5097-g4569f8b3652ae1 then the function should
> have been moved to c-family/ instead).
The routine “flexible_array_type_p” in objc/objc-act.cc is a little different from the one in middle-end:

It includes the ARRAY_TYPE in addition to RECORD_TYPE and UNION_TYPE.
> 
> The only "middle-end" use, btw., is in ./config/nios2/nios2.cc,
> intoduced by said revision and your points probably mean this change
> was misguided and flexible_array_type_p isn't the thing to fix here.

Yes, I guess so. 

Qing
> flexible-size _objects_ are clearly denoted by DECL_SIZE being
> non-constant - though the case of .sdata is quite odd and the issue
> fixed is probably running into a bug elsewhere ...
> 
> Sandra?
> 
> Thanks,
> Richard.