https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47413
--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 26 Sep 2014, hubicka at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47413 > > Jan Hubicka <hubicka at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |hubicka at gcc dot gnu.org > > --- Comment #2 from Jan Hubicka <hubicka at gcc dot gnu.org> --- > Current mainline gets pretty close: > ;; Function int f1337(obj*) (_ZL5f1337P3obj, funcdef_no=19, decl_uid=3418, > cgraph_uid=19, symbol_order=19) > > int f1337(obj*) (struct obj * obj) > { > <bb 2>: > return 1337; > > } > > > > ;; Function int main() (main, funcdef_no=22, decl_uid=3427, cgraph_uid=22, > symbol_order=22) (executed once) > > Removing basic block 5 > int main() () > { > struct obj * obj; > int _1; > int _10; > > <bb 2>: > obj_7 = malloc (8); > if (obj_7 == 0B) > goto <bb 4>; > else > goto <bb 3>; > > <bb 3>: > obj_7->vtab = &vtab1337; > _10 = f1337 (obj_7); > printf ("%d\n", _10); > > <bb 4>: > # _1 = PHI <0(2), 1(3)> > return _1; > > } > > So we are down to one missing inline. After FRE we get: > > <bb 2>: > obj_13 = malloc (8); > if (obj_13 == 0B) > goto <bb 4>; > else > goto <bb 3>; > > <bb 3>: > obj_13->vtab = &vtab1337; > > <bb 4>: > # _14 = PHI <0B(2), obj_13(3)> > if (_14 == 0B) > goto <bb 6>; > else > goto <bb 5>; > > <bb 5>: > _4 = _14->vtab; > _15 = _4->f; > _16 = _15 (_14); > printf ("%d\n", _16); > > > So purely local problem. I suppose FRE could propagate through by knowing that > on the other path program with segfault? Not in the way value-numbering works (it value-numbers _14 as VARYING obviously). The above feels like a missed jump-threading opportunity to me. Eventually we could also help DOM/copyprop with replacing the test by _14 != ohj_13 ... In my view DOM should be able to figure out a value for _14 on the else edge as well (doesn't exactly fit DOM but certainly most easily implemented there)
