Re: [GCC 13][PATCH] PR101836: Add a new option -fstrict-flex-array[=n] and use it in __builtin_object_size

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Jun 28, 2022 at 06:15:58PM +0000, Qing Zhao wrote:
> > Because the flag just tells whether some array shouldn't be treated as (poor man's)
> > flexible array member.  We still need to find out if some FIELD_DECL is to
> > be treated like a flexible array member, which is a minority of
> > COMPONENT_REFs.
> > struct S { int a; char b[0]; int c; } s;
> > struct T { int d; char e[]; };
> > struct U { int f; struct T g; int h; } u;
> > Neither s.b nor u.g.e is to be treated like flexible array member,
> > no matter what -fstrict-flex-array= option is used.
> 
> Then, to resolve this issue, we might need a opposite  flag DECL_IS_FLEXARRAY in FIELD_DECL?
> 
> The default is FALSE for all FIELD_DECL.

Doesn't matter whether it is positive or negative, you still need to analyze
it.  See the above example.  If you have struct T t; and test t.e, then it
is flexarray.  But u.g.e is not, even when the COMPONENT_REF refers to the
same FIELD_DECL.  In the t.e case e is the very last field, in the latter
case u.g.e is the last field in struct T, but struct U has the h field after
it.

	Jakub