irg_block_walk_graph(chordal_env->irg, block_dims_walker, NULL, &env);
layout(&env, start_block, opts->x_margin);
set_y(&env, start_block, opts->y_margin);
irg_block_walk_graph(chordal_env->irg, block_dims_walker, NULL, &env);
layout(&env, start_block, opts->x_margin);
set_y(&env, start_block, opts->y_margin);