https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88771
--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to rguent...@suse.de from comment #12) > On Fri, 11 Jan 2019, msebor at gcc dot gnu.org wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88771 > > > > --- Comment #11 from Martin Sebor <msebor at gcc dot gnu.org> --- > > I understand what jump threading does but I don't know enough about how it > > works to have a clear idea how viable marking up the created statements > > would > > be. > > Jump threading just makes existing paths explicit, thus path sensitive > analysis would come up with similar answers. There may be cases where > we could prove such paths are unreachable and fail to do so, but the > cases where the path ends up in this kind of "undefined" builtin call > do not count IMHO because it is exactly those cases we want to warn > about - so we cannot really reason they cannot happen because of that. Sure, but the warnings we are talking about typically don't warn about calls (etc.) that can overflow, but nothing is known about the value ranges of those arguments. Because then we'd need to warn about void foo (char *x, char *y, unsigned long z) { __builtin_strncpy (x, y, z); } which indeed can overflow if user passes wrong arguments. We'd just warn all the time about that though and the warning wouldn't be useful at all.
