From: Richard Biener <richard.guenther@gmail.com>
To: Nathan Sidwell <nathan@acm.org>
Cc: Qing Zhao <qing.zhao@oracle.com>, GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: Where in C++ module streaming to handle a new bitfield added in "tree_decl_common"
Date: Mon, 15 Aug 2022 16:03:02 +0200 [thread overview]
Message-ID: <CAFiYyc16-qeVF1Z870-jeWjeFcPJA3saJVjc5c8fFYi=N986Mw@mail.gmail.com> (raw)
In-Reply-To: <65809051-2ecf-1f42-ec90-5d5b72935642@acm.org>
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
next prev parent reply other threads:[~2022-08-15 14:03 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-02 14:44 Qing Zhao
2022-08-15 13:28 ` Nathan Sidwell
2022-08-15 14:03 ` Richard Biener [this message]
2022-08-16 12:16 ` Nathan Sidwell
2022-08-16 12:37 ` Richard Biener
2022-08-16 13:50 ` Qing Zhao
2022-08-16 13:44 ` Qing Zhao
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