get_implied_strlen
get_implied_strlen(arg, &rl);
int get_implied_strlen(struct expression *expr, struct range_list **rl);
if (get_implied_strlen(str, rl) && sval_is_positive(rl_min(*rl))) {
if (!get_implied_strlen(expr, &rl))
if (!get_implied_strlen(arg, &rl))
if (!get_implied_strlen(expr->right, &rl))