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

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

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'

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));