https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122664
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- >Maybe the key piece of information that GCC uses to vectorize this is that the >loop in `v2_helper()` always finishes? Right called countable loops. Which is why I pointed to the patch set which was posted 2 days ago about uncountable loops :).
