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

[Alexander Monakov <amonakov@ispras.ru>]

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On Fri, 10 Nov 2023, Richard Biener wrote:

> 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 ...

Yeah, sel-sched invokes 'cfg_cleanup (0)' up front, and I suppose that
may be a preferable compromise for sched-rgn as well.

I'm afraid one does not simply remove all uses of no_real_insns_p from
sched-rgn, but would be happy to be wrong about that.

Alexander