Re: PING^1 [PATCH v3] sched: Change no_real_insns_p to no_real_nondebug_insns_p [PR108273]

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

On Fri, Nov 10, 2023 at 3:18 PM Alexander Monakov <amonakov@ispras.ru> wrote:
>
>
> On Fri, 10 Nov 2023, Richard Biener wrote:
>
> > > I'm afraid ignoring debug-only BBs goes contrary to overall var-tracking design:
> > > DEBUG_INSNs participate in dependency graph so that schedulers can remove or
> > > mutate them as needed when moving real insns across them.
> >
> > Note that debug-only BBs do not exist - the BB would be there even without debug
> > insns!
>
> Yep, sorry, I misspoke when I earlier said
>
> >> and cause divergence when passing through a debug-only BB which would not be
> >> present at all without -g.
>
> They are present in the region, but skipped via no_real_insns_p.
>
> > So instead you have to handle BBs with just debug insns the same you
> > handle a completely empty BB.
>
> Yeah. There would be no problem if the scheduler never used no_real_insns_p
> and handled empty and non-empty BBs the same way.

And I suppose it would be OK to do that.  Empty BBs are usually removed by
CFG cleanup so the situation should only happen in rare corner cases where
the fix would be to actually run CFG cleanup ...

Richard.

> Alexander