https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107608
--- Comment #9 from Aldy Hernandez <aldyh at gcc dot gnu.org> --- (In reply to Richard Biener from comment #8) > (In reply to Aldy Hernandez from comment #7) > > (In reply to Richard Biener from comment #6) > > > (In reply to Jakub Jelinek from comment #0) > > > > ... but then > > > > comes dom2 and happily replaces > > > > _1 = 3.4028234663852885981170418348451692544e+38 * 2.0e+0; > > > > return _1; > > > > with > > > > _1 = 3.4028234663852885981170418348451692544e+38 * 2.0e+0; > > > > return Inf; > > > > (I think this is still correct) > > > > > > Note this is also a pessimization code-generation wise since if we > > > preserve the multiplication the result is readily available in a > > > register but as optimized we have another constant pool entry and load. > > > > > > So we might want to consider not propagating constants generated by > > > operations > > > we cannot eliminate. If the only consumer is a compare-and-branch we > > > can of course still end up with a seemingly dead stmt, so this would be > > > only > > > for the missed optimization. > > > > Up to y'all if this is the way to go, but here are some thoughts... > > > > Off the top of my head, we have VRP and DOM propagating constants. > > Technically also simplify_using_ranges, but it's only called from VRP/DOM, > > and it currently only works with integers, so we should be ok here. > > > > I think we could limit propagation in may_propagate_copy() which both VRP > > and DOM gate on. VRP uses it through its use of substitute_and_fold_engine > > and DOM uses it directly. Would this work? > > I don't think may_propagate_copy is the correct vehicle. Instead the > substitute_and_fold_engine could only substitute from defs with no > side-effects - IIRC it already refrains from propagating _into_ defs > that will be removed after the propagation. So where do you suggest we clamp this? The uses I can think of are VRP (various places in tree-ssa-propagate.cc) and DOM (cprop_operand).
