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Date: Wed, 26 Apr 2023 12:30:30 +0200
From: Jan Hubicka <hubicka@ucw.cz>
To: Richard Biener <rguenther@suse.de>
Cc: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>,
	Jan Hubicka via Gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: Unloop no longer looping loops in loop-ch
Message-ID: <ZEj9RhxSm5mVZY3w@kam.mff.cuni.cz>
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> > -      if (precise)
> > +      if (precise
> > +	  && get_max_loop_iterations_int (loop) == 1)
> > +	{
> > +	  if (dump_file && (dump_flags & TDF_DETAILS))
> > +	    fprintf (dump_file, "Loop %d no longer loops.\n", loop->num);
> 
> but max loop iterations is 1 ...?

I first check for loops with 0 iterations, push them to unlooping list
and avoid any header copying (it is useless).
At this patch we already did header duplication and verified that the
maximal number of iterations will drop by 1 since there is no way loop
can terminate except for the header tests we peeled out.

So 1 would turn to 0 in the loop info update and it seems useless to do
it.
> 
> > +	  loops_to_unloop.safe_push (loop);
> > +	  loops_to_unloop_nunroll.safe_push (0);
> > +	}
> > +      else if (precise)
> >  	{
> >  	  if (dump_file && (dump_flags & TDF_DETAILS))
> >  	    fprintf (dump_file,
> > @@ -688,6 +699,12 @@ ch_base::copy_headers (function *fun)
> >  	  BITMAP_FREE (exit_bbs);
> >  	}
> >      }
> > +  if (loops_to_unloop.length())
> 
>   !loops_to_unloop.is_empty ()
I updated that in my copy of the patch.
> 
> > +    {
> > +      bool irred_invalidated;
> > +      unloop_loops (loops_to_unloop, loops_to_unloop_nunroll, NULL, &irred_invalidated);
> > +      changed = true;
> > +    }
> >    free (bbs);
> >    free (copied_bbs);
> 
> 
> Since we run VN on the header copies I wonder if, since you remove
> edges, we need to run CFG cleanup before this and updating SSA form?
> For safety we usually let CFG cleanup do the actual CFG manipulation
> and just change cond jumps to if (0) or if (1)?

I do unlooping only after the VN so I think I am safe here.

Honza