https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66129
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- Oops... Index: tree-vect-slp.c =================================================================== --- tree-vect-slp.c (revision 223119) +++ tree-vect-slp.c (working copy) @@ -3459,7 +3459,7 @@ vect_schedule_slp_instance (slp_tree nod tree *melts = XALLOCAVEC (tree, TYPE_VECTOR_SUBPARTS (vectype)); for (l = 0; l < TYPE_VECTOR_SUBPARTS (vectype); ++l) { - if (k > group_size) + if (k >= group_size) k = 0; melts[l] = build_int_cst (meltype, mask[k++] * TYPE_VECTOR_SUBPARTS (vectype) + l);