Re: [PATCH] ipa-fnsummary: Remove inconsistent bp_pack_value

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Sep 17, 2021 at 12:03 PM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Fri, Sep 17, 2021 at 11:43 AM Kewen.Lin <linkw@linux.ibm.com> wrote:
> >
> > Hi,
> >
> > When changing target_info with bitfield, I happened to find this
> > inconsistent streaming in and out.  We have the streaming in:
> >
> >           bp_pack_value (&bp, info->inlinable, 1);
> >           bp_pack_value (&bp, false, 1);
> >           bp_pack_value (&bp, info->fp_expressions, 1);
> >
> > while the streaming out:
> >
> >           info->inlinable = bp_unpack_value (&bp, 1);
> >           info->fp_expressions = bp_unpack_value (&bp, 1)
> >
> > The cleanup of Cilk Plus support seemed to miss to remove the bit
> > streaming out but change with streaming false.
> >
> > By hacking fp_expression_p to return true always, I can see it
> > reads the wrong fp_expressions value (false) out in wpa dumping.
> >
> > Bootstrapped and regress-tested on powerpc64le-linux-gnu Power9.
> >
> > Is it ok for trunk?
>
> OK for trunk and all affected branches (note we need to bump the
> LTO minor version there).  The issue comes from the removal
> of cilk+ in r8-4956 which removed the bp_unpack but replaced
> the bp_pack ...
>
> It's a correctness issue as we'll read fp_expressions as always 'false'

Btw, on branches we could also simply unpack a dummy bit to avoid
changing the format.

> Thanks,
> Richard.
>
> >
> > BR,
> > Kewen
> > -----
> > gcc/ChangeLog:
> >
> >         * ipa-fnsummary.c (ipa_fn_summary_write): Remove inconsistent
> >         bitfield streaming out.
> >
> > diff --git a/gcc/ipa-fnsummary.c b/gcc/ipa-fnsummary.c
> > index 2470937460f..31199919405 100644
> > --- a/gcc/ipa-fnsummary.c
> > +++ b/gcc/ipa-fnsummary.c
> > @@ -4652,7 +4652,6 @@ ipa_fn_summary_write (void)
> >            info->time.stream_out (ob);
> >            bp = bitpack_create (ob->main_stream);
> >            bp_pack_value (&bp, info->inlinable, 1);
> > -          bp_pack_value (&bp, false, 1);
> >            bp_pack_value (&bp, info->fp_expressions, 1);
> >            streamer_write_bitpack (&bp);
> >            streamer_write_uhwi (ob, vec_safe_length (info->conds));