On Thu, Oct 21, 2021 at 12:20 PM Richard Biener <richard.guent...@gmail.com> wrote: > > On Wed, Oct 20, 2021 at 10:58 PM Jeff Law <jeffreya...@gmail.com> wrote: > > > > > > > > On 10/18/2021 2:17 AM, Aldy Hernandez wrote: > > > > > > > > > On 10/18/21 12:52 AM, Jeff Law wrote: > > >> > > >> > > >> On 10/8/2021 9:12 AM, Aldy Hernandez via Gcc-patches wrote: > > >>> The following patch converts the strlen pass from evrp to ranger, > > >>> leaving DOM as the last remaining user. > > >> So is there any reason why we can't convert DOM as well? DOM's use > > >> of EVRP is pretty limited. You've mentioned FP bits before, but my > > >> recollection is those are not part of the EVRP analysis DOM uses. > > >> Hell, give me a little guidance and I'll do the work... > > > > > > Not only will I take you up on that offer, but I can provide 90% of > > > the work. Here be dragons, though (well, for me, maybe not for you ;-)). > > > > > > DOM is actually an evrp pass at -O1 in disguise. The reason it really > > > is a covert evrp pass is because: > > > > > > a) It calls extract_range_from_stmt on each statement. > > > > > > b) It folds conditionals with simplify_using_ranges. > > > > > > c) But most importantly, it exports discovered ranges when it's done > > > (evrp_range_analyzer(true)). > > > > > > If you look at the evrp pass, you'll notice that that's basically what > > > it does, albeit with the substitute and fold engine, which also calls > > > gimple fold plus other goodies. > > > > > > But I could argue that we've made DOM into an evrp pass without > > > noticing. The last item (c) is particularly invasive because these > > > exported ranges show up in other passes unexpectedly. For instance, I > > > saw an RTL pass at -O1 miss an optimization because it was dependent > > > on some global range being set. IMO, DOM should not export global > > > ranges it discovered during its walk (do one thing and do it well), > > > but I leave it to you experts to pontificate. > > All true. But I don't think we've got many, if any, hard dependencies > > on those behaviors. > > > > > > > > The attached patch is rather trivial. It's mostly deleting state. It > > > seems DOM spends a lot of time massaging the IL so that it can fold > > > conditionals or thread paths. None of this is needed, because the > > > ranger can do all of this. Well, except floats, but... > > Massaging the IL should only take two forms IIRC. > > > > First, if we have a simplification we can do. That could be const/copy > > propagation, replacing an expression with an SSA_NAME or constant and > > the like. It doesn't massage the IL just to massage the IL. > > > > Second, we do temporarily copy propagate the current known values of an > > SSA name into use points and then see if that allows us to determine if > > a statement is already in the hash tables. But we undo that so that > > nobody should see that temporary change in state. > > Are you sure we still do that? I can't find it at least.
I couldn't either, but perhaps what Jeff is referring to is the ad-hoc copy propagation that happens in the DOM's use of the threader: /* Make a copy of the uses & vuses into USES_COPY, then cprop into the operands. */ FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES) { tree tmp = NULL; tree use = USE_FROM_PTR (use_p); copy[i++] = use; if (TREE_CODE (use) == SSA_NAME) tmp = SSA_NAME_VALUE (use); if (tmp) SET_USE (use_p, tmp); } cached_lhs = simplifier->simplify (stmt, stmt, bb, this); /* Restore the statement's original uses/defs. */ i = 0; FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES) SET_USE (use_p, copy[i++]); Aldy