Re: Where in C++ module streaming to handle a new bitfield added in "tree_decl_common"

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

> On Aug 16, 2022, at 8:37 AM, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Tue, Aug 16, 2022 at 2:16 PM Nathan Sidwell <nathan@acm.org> wrote:
>> 
>> On 8/15/22 10:03, Richard Biener wrote:
>>> On Mon, Aug 15, 2022 at 3:29 PM Nathan Sidwell via Gcc-patches
>>> <gcc-patches@gcc.gnu.org> wrote:
>>>> 
>>>> On 8/2/22 10:44, Qing Zhao wrote:
>>>>> Hi, Nathan,
>>>>> 
>>>>> I am adding a new bitfield “decl_not_flexarray” in “tree_decl_common”  (gcc/tree-core.h) for the new gcc feature -fstrict-flex-arrays.
>>>>> 
>>>>> ====
>>>>> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
>>>>> index ea9f281f1cc..458c6e6ceea 100644
>>>>> --- a/gcc/tree-core.h
>>>>> +++ b/gcc/tree-core.h
>>>>> @@ -1813,7 +1813,10 @@ struct GTY(()) tree_decl_common {
>>>>>       TYPE_WARN_IF_NOT_ALIGN.  */
>>>>>    unsigned int warn_if_not_align : 6;
>>>>> 
>>>>> -  /* 14 bits unused.  */
>>>>> +  /* In FIELD_DECL, this is DECL_NOT_FLEXARRAY.  */
>>>>> +  unsigned int decl_not_flexarray : 1;
>>>> 
>>>> Is it possible to invert the meaning here -- set the flag if it /IS/ a
>>>> flexible array? negated flags can be confusing, and I see your patch
>>>> sets it to '!is_flexible_array (...)' anyway?
>>> 
>>> The issue is it's consumed by the middle-end but set by a single (or two)
>>> frontends and the conservative setting is having the bit not set.  That works
>>> nicely together with touching just the frontends that want stricter behavior
>>> than currently ...
>> 
>> Makes sense, but is the comment incomplete?  I'm guessing this flag is
>> for FIELD_DECLs /of array type/, and not just any old FIELD_DECL?  After
>> all a field of type int is not a flexible array, but presumably doesn't
>> need this flag setting?
> 
> Yes, the docs should be more complete in tree.h on the actual DECL_NOT_FLEXARRAY
> definition.

Okay, will add more comments in tree.h to make the DECL_NOT_FLEXARRAY more complete.

thanks.

Qing
> 
> Richard.
> 
>> nathan
>> 
>> --
>> Nathan Sidwell