On Tue, 27 Mar 2018, Richard Biener wrote: > > > so this is kind-of global regs being live across all BBs? This sounds > > > a bit stupid to me, but well ... IMHO those refs should be at > > > specific insns like calls. > > > > > > So maybe, with a big fat comment, it is OK to ignore artificial > > > refs in this loop... > > > > Yeah, I'd like someone else's opinion too, as I know even less about > > real artificial uses (as opposed to my incorrect mention in my first > > post). :-) > > If they only appear in the exit/entry block ignoring them should be safe. > > But who knows...
Roman and I discussed a related problem a few weeks ago, so here's my 2c. As I don't have any special DF knowledge, this is merely my understanding. (apropos i: SMS uses sched-deps for intra-loop deps, and then separately uses DF for cross-iteration deps, which means that it should be ready for surprises when the two scanners are not 100% in sync) (apropos ii: given the flexibility of RTL, it would have been really nice if there were no implicit cc0-like uses that need to be special-cased in DF, sched-deps and other scanners) In this case I believe it's fine to skip processing of r_use when the associated BB is not the loop BB (i.e. 'if (DF_REF_BB (r_use->ref) != g->bb)' as Richard suggested), but I'm concerned that skipping it when the artificial's use BB corresponds to loop BB goes from ICE to wrong-code. It should be detected earlier, in sms_schedule (see the comment starting with "Don't handle BBs with calls or barriers"). Alexander
