rl_filter
nonnull_rl = rl_filter(rl, rl_zero());
nonzero_rl = rl_filter(rl, rl_zero());
rl_after = rl_filter(rl_before, filter);
struct range_list *rl_filter(struct range_list *rl, struct range_list *filter);
*left_false_rl = rl_filter(left_orig, right_orig);
rl = rl_filter(estate_rl(state), valid_ptr_rl);
rl = rl_filter(rl, filter);