http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53695
--- Comment #18 from rguenther at suse dot de <rguenther at suse dot de> 2012-08-23 09:22:54 UTC --- On Thu, 23 Aug 2012, rguenther at suse dot de wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53695 > > --- Comment #17 from rguenther at suse dot de <rguenther at suse dot de> > 2012-08-23 09:19:04 UTC --- > On Thu, 23 Aug 2012, steven at gcc dot gnu.org wrote: > > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53695 > > > > --- Comment #16 from Steven Bosscher <steven at gcc dot gnu.org> 2012-08-23 > > 08:53:04 UTC --- > > (In reply to comment #15) > > > Makes me wonder why the loop isn't recognized in the original test case... > > > > Ah, maybe because bb3 has an abnormal predecessor and is therefore ignored > > as a > > potential loop header? > > > > /* If we have an abnormal predecessor, do not consider the > > loop (not worth the problems). */ > > if (bb_has_abnormal_pred (header)) > > continue; > > > > Which brings things back to my question why this kind of loop header is > > rejected! :-) > > Because gimple_split_edge doesn't like to split abnormal edges, > called via force_single_succ_latches (). So we do definitely > not allow abnormal latch -> header edges. Still abnormal loop entries > should be fine. So, But we can't create pre-headers then, too. So optimizers that want pre-headers would be confused (well, or ICE). Why can we not split abnormal edges?
