https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65930
--- Comment #16 from Richard Biener <rguenth at gcc dot gnu.org> --- So to outline the desired approach again the idea is to make the SCC finding (the DFS walk) in check_reduction_path the first-class operation of vect_is_simple_reduction, not passing in the reduction code but instead computing it (the reduction code eventually used in the lane reduction of the epilogue).
