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 ...
> > +
> > + /* 13 bits unused. */
> >
> > /* UID for points-to sets, stable over copying from inlining. */
> > unsigned int pt_uid;
> > ====
> >
> > (Please refer to the following for details:
> >
> > https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598556.html
> > https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598965.html
>
>
>
> > )
> >
> > Richard mentioned the following:
> >
> > "I've not seen it so you are probably missing it - the bit has to be
> > streamed in tree-streamer-{in,out}.cc to be usable from LTO. Possibly
> > C++ module streaming also needs to handle it.”
> >
> > I have figured out that where to add the handling of the bit in
> > “tree-streamer-{in, out}.cc,
> > However, it’s quite difficult for me to locate where should I add the
> > handling of this new bit in
> > C++ module streaming, could you please help me on this?
> >
>
>
> add it in to trees_{in,out}::core_bools. You could elide streaming for
> non-FIELD_DECL decls.
>
> Hope that helps.
>
> nathan
>
>
>
> > Thanks a lot for your help.
> >
> > Qing
>
>
> --
> Nathan Sidwell
