Re: [PATCH] sched1: Fix -fcompare-debug issue in schedule_region [PR105586]

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

On Tue, Sep 20, 2022 at 9:18 AM Surya Kumari Jangala via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi Jeff, Richard,
> Thank you for reviewing the patch!
> I have committed the patch to the gcc repo.
> Can I backport this patch to prior versions of gcc, as this is an easy patch to backport and the issue exists in prior versions too?

It doesn't seem to be a regression so I'd error on the safe side here.

Richard.

> Regards,
> Surya
>
>
> On 31/08/22 9:09 pm, Jeff Law via Gcc-patches wrote:
> >
> >
> > On 8/23/2022 5:49 AM, Surya Kumari Jangala via Gcc-patches wrote:
> >> sched1: Fix -fcompare-debug issue in schedule_region [PR105586]
> >>
> >> In schedule_region(), a basic block that does not contain any real insns
> >> is not scheduled and the dfa state at the entry of the bb is not copied
> >> to the fallthru basic block. However a DEBUG insn is treated as a real
> >> insn, and if a bb contains non-real insns and a DEBUG insn, it's dfa
> >> state is copied to the fallthru bb. This was resulting in
> >> -fcompare-debug failure as the incoming dfa state of the fallthru block
> >> is different with -g. We should always copy the dfa state of a bb to
> >> it's fallthru bb even if the bb does not contain real insns.
> >>
> >> 2022-08-22  Surya Kumari Jangala  <jskumari@linux.ibm.com>
> >>
> >> gcc/
> >>     PR rtl-optimization/105586
> >>     * sched-rgn.cc (schedule_region): Always copy dfa state to
> >>     fallthru block.
> >>
> >> gcc/testsuite/
> >>     PR rtl-optimization/105586
> >>     * gcc.target/powerpc/pr105586.c: New test.
> > Interesting.    We may have stumbled over this bug internally a little while ago -- not from a compare-debug standpoint, but from a "why isn't the processor state copied to the fallthru block" point of view.   I had it on my to investigate list, but hadn't gotten around to it yet.
> >
> > I think there were requests for ChangeLog updates and a function comment for save_state_for_fallthru_edge.  OK with those updates.
> >
> > jeff
> >