http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39326
--- Comment #28 from rguenther at suse dot de <rguenther at suse dot de> 2013-03-07 08:44:28 UTC --- On Wed, 6 Mar 2013, steven at gcc dot gnu.org wrote: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39326 > > Steven Bosscher <steven at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |steven at gcc dot gnu.org > > --- Comment #24 from Steven Bosscher <steven at gcc dot gnu.org> 2013-03-06 > 23:39:27 UTC --- > (In reply to comment #22) > > 4.8.0 -O2 (terminated after 9 minutes waiting, LIM being the offender, I > > suspect domwalk ...) >2.5GB > > > > applying domwalk fix ... > > It is LIM, for sure. I've been watching in GDB for a while at some > back traces, and it's spent minutes already in this DOM walk: > > #5 0x0000000000b841e1 in walk_dominator_tree (walk_data=0x7fffffffdd60, > bb=0x7fffef033958) at ../../trunk/gcc/domwalk.c:187 > #6 0x0000000000c02d73 in determine_invariantness () at > ../../trunk/gcc/tree-ssa-loop-im.c:1189 > #7 tree_ssa_lim () at ../../trunk/gcc/tree-ssa-loop-im.c:2632 > #8 0x000000000075bcd7 in execute_one_pass (pass=0x12323e0 <pass_lim>) at > ../../trunk/gcc/passes.c:2330 > #9 0x000000000075c0f5 in execute_pass_list (pass=0x12323e0 <pass_lim>) at > ../../trunk/gcc/passes.c:2378 > > This is supposed to be cheap. Is this a known bottle-neck? > > Pathetic... Yes, it's known - and there are several known (to me ...) ways to make constant factor compile-time and memory-usage improvements... (I _think_ we have a bug for LIMs slowness, if you can't find it quickly you can create one and assign me - I have some TLC patches locally queued for 4.9, but they don't help the slowness very much)
