http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55529
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-11-29 13:06:21 UTC --- This kind of warning is diagnosed even for code that isn't always executed (after all, in most cases you don't know whether a function will be ever executed from main or not), unless the compiler can prove it is never executed early enough not to warn. I think in this case the warning is very much desirable, if you know rcu_num_lvls will be always 0, why to have the loop at all?
