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

[Nathan Sidwell <nathan@acm.org>]

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?

nathan

-- 
Nathan Sidwell