3 * File name: ir/ana/irdom.c
4 * Purpose: Construct and access dominator / post dominator tree.
5 * Author: Goetz Lindenmaier
6 * Modified by: Michael Beck, Rubino Geiss
9 * Copyright: (c) 2002-2003 Universitaet Karlsruhe
10 * Licence: This file protected by GPL - GNU GENERAL PUBLIC LICENSE.
32 #include "irgraph_t.h" /* To access state field. */
39 #define get_dom_info(bl) (&(bl)->attr.block.dom)
40 #define get_pdom_info(bl) (&(bl)->attr.block.pdom)
42 /*--------------------------------------------------------------------*/
43 /** Accessing the dominator and post dominator data structures **/
44 /*--------------------------------------------------------------------*/
46 ir_node *get_Block_idom(const ir_node *bl) {
48 if (get_Block_dom_depth(bl) == -1) {
49 /* This block is not reachable from Start */
52 return get_dom_info(bl)->idom;
55 void set_Block_idom(ir_node *bl, ir_node *n) {
56 dom_info *bli = get_dom_info(bl);
58 assert(get_irn_op(bl) == op_Block);
60 /* Set the immediate dominator of bl to n */
64 * If we don't set the root of the dominator tree
65 * Append bl to the dominates queue of n.
68 dom_info *ni = get_dom_info(n);
70 bli->next = ni->first;
75 ir_node *get_Block_ipostdom(const ir_node *bl) {
77 if (get_Block_postdom_depth(bl) == -1) {
78 /* This block is not reachable from Start */
81 return get_pdom_info(bl)->idom;
84 void set_Block_ipostdom(ir_node *bl, ir_node *n) {
85 dom_info *bli = get_pdom_info(bl);
87 assert(get_irn_op(bl) == op_Block);
89 /* Set the immediate post dominator of bl to n */
93 * If we don't set the root of the post dominator tree
94 * Append bl to the post dominates queue of n.
97 dom_info *ni = get_pdom_info(n);
99 bli->next = ni->first;
104 int get_Block_dom_pre_num(const ir_node *bl) {
105 assert(get_irn_op(bl) == op_Block);
106 return get_dom_info(bl)->pre_num;
109 void set_Block_dom_pre_num(ir_node *bl, int num) {
110 assert(get_irn_op(bl) == op_Block);
111 get_dom_info(bl)->pre_num = num;
114 int get_Block_dom_depth(const ir_node *bl) {
115 assert(get_irn_op(bl) == op_Block);
116 return get_dom_info(bl)->dom_depth;
119 void set_Block_dom_depth(ir_node *bl, int depth) {
120 assert(get_irn_op(bl) == op_Block);
121 get_dom_info(bl)->dom_depth = depth;
125 int get_Block_postdom_pre_num(const ir_node *bl) {
126 assert(get_irn_op(bl) == op_Block);
127 return get_pdom_info(bl)->pre_num;
130 void set_Block_postdom_pre_num(ir_node *bl, int num) {
131 assert(get_irn_op(bl) == op_Block);
132 get_pdom_info(bl)->pre_num = num;
135 int get_Block_postdom_depth(const ir_node *bl) {
136 assert(get_irn_op(bl) == op_Block);
137 return get_pdom_info(bl)->dom_depth;
140 void set_Block_postdom_depth(ir_node *bl, int depth) {
141 assert(get_irn_op(bl) == op_Block);
142 get_pdom_info(bl)->dom_depth = depth;
145 unsigned get_Block_dom_tree_pre_num(const ir_node *bl)
147 assert(is_Block(bl));
148 return get_dom_info(bl)->tree_pre_num;
151 unsigned get_Block_dom_max_subtree_pre_num(const ir_node *bl)
153 assert(is_Block(bl));
154 return get_dom_info(bl)->max_subtree_pre_num;
157 unsigned get_Block_pdom_tree_pre_num(const ir_node *bl)
159 assert(is_Block(bl));
160 return get_pdom_info(bl)->tree_pre_num;
163 unsigned get_Block_pdom_max_subtree_pre_num(const ir_node *bl)
165 assert(is_Block(bl));
166 return get_pdom_info(bl)->max_subtree_pre_num;
169 /* Check, if a block dominates another block. */
170 int block_dominates(const ir_node *a, const ir_node *b)
172 const dom_info *ai, *bi;
174 if (is_Block(a) && is_Block(b)) {
175 ai = get_dom_info(a);
176 bi = get_dom_info(b);
177 return bi->tree_pre_num - ai->tree_pre_num
178 <= ai->max_subtree_pre_num - ai->tree_pre_num;
184 /* Returns the smallest common dominator block of two nodes. */
185 ir_node *node_smallest_common_dominator(ir_node *a, ir_node *b)
187 ir_node *bl_a = is_Block(a) ? a : get_nodes_block(a);
188 ir_node *bl_b = is_Block(b) ? b : get_nodes_block(b);
189 ir_node *dom_bl = NULL;
191 /* Check if block of a dominates block of b */
192 if (block_dominates(bl_a, bl_b))
194 /* Check if block of b dominates block of a */
195 else if (block_dominates(bl_b, bl_a))
198 /* walk up dominator tree and search for first block dominating a and b */
200 bl_a = get_Block_idom(bl_a);
202 assert(! is_Bad(bl_a) && "block is dead?");
204 if (block_dominates(bl_a, bl_b))
212 /* Returns the smallest common dominator block of all users of a node. */
213 ir_node *node_users_smallest_common_dominator(ir_node *irn, int handle_phi)
215 int n, j, i = 0, success;
216 ir_node **user_blocks, *dom_bl;
217 const ir_edge_t *edge;
219 assert(! is_Block(irn) && "WRONG USAGE of node_users_smallest_common_dominator");
220 assert(edges_activated(get_irn_irg(irn)) && "need edges activated");
222 n = get_irn_n_edges(irn);
224 /* get array to hold all block of the node users */
225 NEW_ARR_A(ir_node *, user_blocks, n);
226 foreach_out_edge(irn, edge) {
227 ir_node *src = get_edge_src_irn(edge);
229 if (is_Phi(src) && handle_phi) {
230 /* get the corresponding cfg predecessor block if phi handling requested */
231 j = get_edge_src_pos(edge);
232 assert(j >= 0 && "kaputt");
233 user_blocks[i++] = get_Block_cfgpred_block(get_nodes_block(src), j);
236 user_blocks[i++] = is_Block(src) ? src : get_nodes_block(src);
239 assert(i == n && "get_irn_n_edges probably broken");
241 /* in case of only one user: return the block of the user */
243 return user_blocks[0];
246 /* search the smallest block dominating all user blocks */
248 dom_bl = node_smallest_common_dominator(user_blocks[i], user_blocks[i + 1]);
251 /* check if this block dominates all remaining blocks as well */
252 for (j = i + 2; j < n; j++) {
253 if (! block_dominates(dom_bl, user_blocks[j]))
260 /* inherit the dominator block of the first (i + 1) users */
261 user_blocks[++i] = dom_bl;
264 assert(success && "no block found dominating all users");
270 /* Get the first node in the list of nodes dominated by a given block. */
271 ir_node *get_Block_dominated_first(const ir_node *bl)
273 assert(is_Block(bl));
274 return get_dom_info(bl)->first;
277 /* Get the next node in a list of nodes which are dominated by some
279 ir_node *get_Block_dominated_next(const ir_node *bl)
281 assert(is_Block(bl));
282 return get_dom_info(bl)->next;
285 /* Check, if a block post dominates another block. */
286 int block_postdominates(const ir_node *a, const ir_node *b)
288 const dom_info *ai, *bi;
290 if (is_Block(a) && is_Block(b)) {
291 ai = get_pdom_info(a);
292 bi = get_pdom_info(b);
293 return bi->tree_pre_num - ai->tree_pre_num
294 <= ai->max_subtree_pre_num - ai->tree_pre_num;
300 /* Get the first node in the list of nodes post dominated by a given block. */
301 ir_node *get_Block_postdominated_first(const ir_node *bl)
303 assert(is_Block(bl));
304 return get_pdom_info(bl)->first;
307 /* Get the next node in a list of nodes which are post dominated by some
309 ir_node *get_Block_postdominated_next(const ir_node *bl)
311 assert(is_Block(bl));
312 return get_pdom_info(bl)->next;
315 /* Visit all nodes in the dominator subtree of a given node. */
316 void dom_tree_walk(ir_node *bl, irg_walk_func *pre,
317 irg_walk_func *post, void *env)
324 dominates_for_each(bl, p) {
325 dom_tree_walk(p, pre, post, env);
332 /* Visit all nodes in the post dominator subtree of a given node. */
333 void postdom_tree_walk(ir_node *bl, irg_walk_func *pre,
334 irg_walk_func *post, void *env)
341 postdominates_for_each(bl, p) {
342 postdom_tree_walk(p, pre, post, env);
349 /* Walk over the dominator tree of an irg starting at the root. */
350 void dom_tree_walk_irg(ir_graph *irg, irg_walk_func *pre,
351 irg_walk_func *post, void *env)
353 /* The root of the dominator tree should be the Start block. */
354 ir_node *root = get_irg_start_block(irg);
356 assert(irg->dom_state == dom_consistent
357 && "The dominators of the irg must be consistent");
358 assert(root && "The start block of the graph is NULL?");
359 assert(get_dom_info(root)->idom == NULL
360 && "The start node in the graph must be the root of the dominator tree");
361 dom_tree_walk(root, pre, post, env);
364 /* Walk over the post dominator tree of an irg starting at the root. */
365 void postdom_tree_walk_irg(ir_graph *irg, irg_walk_func *pre,
366 irg_walk_func *post, void *env)
368 /* The root of the dominator tree should be the End block. */
369 ir_node *root = get_irg_end_block(irg);
371 assert(irg->pdom_state == dom_consistent
372 && "The dominators of the irg must be consistent");
373 assert(root && "The end block of the graph is NULL?");
374 assert(get_pdom_info(root)->idom == NULL
375 && "The End block node in the graph must be the root of the post dominator tree");
376 postdom_tree_walk(root, pre, post, env);
380 static void assign_tree_dom_pre_order(ir_node *bl, void *data)
382 unsigned *num = data;
383 dom_info *bi = get_dom_info(bl);
385 bi->tree_pre_num = (*num)++;
388 static void assign_tree_dom_pre_order_max(ir_node *bl, void *data)
390 dom_info *bi = get_dom_info(bl);
393 unsigned children = 0;
395 for(p = bi->first; p; p = get_dom_info(p)->next) {
396 unsigned max_p = get_dom_info(p)->max_subtree_pre_num;
397 max = max > max_p ? max : max_p;
401 bi->max_subtree_pre_num = children > 0 ? max : bi->tree_pre_num;
402 assert(bi->max_subtree_pre_num >= bi->tree_pre_num);
405 static void assign_tree_postdom_pre_order(ir_node *bl, void *data)
407 unsigned *num = data;
408 dom_info *bi = get_pdom_info(bl);
410 bi->tree_pre_num = (*num)++;
413 static void assign_tree_postdom_pre_order_max(ir_node *bl, void *data)
415 dom_info *bi = get_pdom_info(bl);
418 unsigned children = 0;
420 for(p = bi->first; p; p = get_pdom_info(p)->next) {
421 unsigned max_p = get_pdom_info(p)->max_subtree_pre_num;
422 max = max > max_p ? max : max_p;
426 bi->max_subtree_pre_num = children > 0 ? max : bi->tree_pre_num;
427 assert(bi->max_subtree_pre_num >= bi->tree_pre_num);
430 /*--------------------------------------------------------------------*/
431 /* Building and Removing the dominator data structure */
432 /*--------------------------------------------------------------------*/
435 * count the number of blocks and clears the post dominance info
437 static void count_and_init_blocks_pdom(ir_node *bl, void *env) {
438 int *n_blocks = (int *) env;
441 memset(get_pdom_info(bl), 0, sizeof(dom_info));
442 set_Block_ipostdom(bl, NULL);
443 set_Block_postdom_pre_num(bl, -1);
444 set_Block_postdom_depth(bl, -1);
447 /** temporary type used while constructing the dominator / post dominator tree. */
448 typedef struct tmp_dom_info {
449 ir_node *block; /**< backlink */
451 struct tmp_dom_info *semi; /**< semidominator */
452 struct tmp_dom_info *parent;
453 struct tmp_dom_info *label; /**< used for LINK and EVAL */
454 struct tmp_dom_info *ancestor;/**< used for LINK and EVAL */
455 struct tmp_dom_info *dom; /**< After step 3, if the semidominator of w is
456 its immediate dominator, then w->dom is the
457 immediate dominator of w. Otherwise w->dom
458 is a vertex v whose number is smaller than
459 w and whose immediate dominator is also w's
460 immediate dominator. After step 4, w->dom
461 is the immediate dominator of w. */
462 struct tmp_dom_info *bucket; /**< set of vertices with same semidominator */
465 /** Struct to pass info through walker. */
473 * Walks Blocks along the out data structure. If recursion started with
474 * Start block misses control dead blocks.
476 static void init_tmp_dom_info(ir_node *bl, tmp_dom_info *parent,
477 tmp_dom_info *tdi_list, int *used) {
481 assert(is_Block(bl));
482 if (get_irg_block_visited(current_ir_graph) == get_Block_block_visited(bl))
484 mark_Block_block_visited(bl);
485 set_Block_dom_pre_num(bl, *used);
487 tdi = &tdi_list[*used];
492 tdi->ancestor = NULL;
494 tdi->parent = parent;
498 for (i = get_Block_n_cfg_outs_ka(bl) - 1; i >= 0; --i) {
499 ir_node *pred = get_Block_cfg_out_ka(bl, i);
500 assert(is_Block(pred));
501 init_tmp_dom_info(pred, tdi, tdi_list, used);
506 * Walks Blocks along the control flow. If recursion started with
507 * End block misses blocks in endless loops.
509 static void init_tmp_pdom_info(ir_node *bl, tmp_dom_info *parent,
510 tmp_dom_info *tdi_list, int* used) {
514 assert(is_Block(bl));
515 if (get_irg_block_visited(current_ir_graph) == get_Block_block_visited(bl))
517 mark_Block_block_visited(bl);
518 set_Block_postdom_pre_num(bl, *used);
520 tdi = &tdi_list[*used];
525 tdi->ancestor = NULL;
527 tdi->parent = parent;
531 for (i = get_Block_n_cfgpreds(bl) - 1; i >= 0; --i) {
532 ir_node *pred = get_Block_cfgpred_block(bl, i);
535 assert(is_Block(pred));
536 init_tmp_pdom_info(pred, tdi, tdi_list, used);
539 /* Handle keep-alives. Note that the preprocessing
540 in init_construction() had already killed all
541 phantom keep-alive edges. All remaining block keep-alives
542 are really edges to endless loops.
544 if (bl == get_irg_end_block(current_ir_graph)) {
545 ir_node *end = get_irg_end(current_ir_graph);
547 for (i = get_irn_arity(end) - 1; i >= 0; --i) {
548 ir_node *pred = get_irn_n(end, i);
551 init_tmp_pdom_info(pred, tdi, tdi_list, used);
556 static void dom_compress(tmp_dom_info *v)
558 assert (v->ancestor);
559 if (v->ancestor->ancestor) {
560 dom_compress (v->ancestor);
561 if (v->ancestor->label->semi < v->label->semi) {
562 v->label = v->ancestor->label;
564 v->ancestor = v->ancestor->ancestor;
569 * if V is a root, return v, else return the vertex u, not being the
570 * root, with minimum u->semi on the path from v to its root.
572 INLINE static tmp_dom_info *dom_eval (tmp_dom_info *v)
574 if (!v->ancestor) return v;
579 /** make V W's ancestor */
580 INLINE static void dom_link(tmp_dom_info *v, tmp_dom_info *w)
586 * Walker: count the number of blocks and clears the dominance info
588 static void count_and_init_blocks_dom(ir_node *bl, void *env) {
589 int *n_blocks = (int *) env;
592 memset(get_dom_info(bl), 0, sizeof(dom_info));
593 set_Block_idom(bl, NULL);
594 set_Block_dom_pre_num(bl, -1);
595 set_Block_dom_depth(bl, -1);
599 * Initialize the dominance/postdominance construction:
601 * - count the number of blocks
602 * - clear the dominance info
603 * - remove Block-keepalives of live blocks to reduce
604 * the number of "phantom" block edges
606 * @param irg the graph
607 * @param pre a walker function that will be called for every block in the graph
609 static int init_construction(ir_graph *irg, irg_walk_func *pre) {
610 ir_graph *rem = current_ir_graph;
615 current_ir_graph = irg;
617 /* this visits only the reachable blocks */
618 irg_block_walk(get_irg_end_block(irg), pre, NULL, &n_blocks);
620 /* now visit the unreachable (from End) Blocks and remove unnecessary keep-alives */
621 end = get_irg_end(irg);
622 arity = get_End_n_keepalives(end);
623 if (arity) { /* we have keep-alives */
627 NEW_ARR_A(ir_node *, in, arity);
628 for (i = j = 0; i < arity; i++) {
629 ir_node *pred = get_End_keepalive(end, i);
631 if (get_irn_op(pred) == op_Block) {
632 if (Block_not_block_visited(pred)) {
633 /* we found a endless loop */
634 dec_irg_block_visited(irg);
635 irg_block_walk(pred, pre, NULL, &n_blocks);
643 /* we kill some Block keep-alives */
644 set_End_keepalives(end, j, in);
645 set_irg_outs_inconsistent(irg);
649 current_ir_graph = rem;
654 /* Computes the dominator trees. Sets a flag in irg to "dom_consistent".
655 If the control flow of the graph is changed this flag must be set to
656 "dom_inconsistent". */
657 void compute_doms(ir_graph *irg) {
658 ir_graph *rem = current_ir_graph;
659 int n_blocks, used, i, j;
660 tmp_dom_info *tdi_list; /* Ein Golf? */
662 current_ir_graph = irg;
664 /* Update graph state */
665 assert(get_irg_phase_state(irg) != phase_building);
666 irg->dom_state = dom_consistent;
668 /* Count the number of blocks in the graph. */
669 n_blocks = init_construction(irg, count_and_init_blocks_dom);
671 /* Memory for temporary information. */
672 tdi_list = xcalloc(n_blocks, sizeof(tdi_list[0]));
674 /* We need the out data structure. */
675 assure_irg_outs(irg);
677 /* this with a standard walker as passing the parent to the sons isn't
680 inc_irg_block_visited(irg);
681 init_tmp_dom_info(get_irg_start_block(irg), NULL, tdi_list, &used);
682 /* If not all blocks are reachable from Start by out edges this assertion
684 assert(used == n_blocks && "Precondition for dom construction violated"); */
685 assert(used <= n_blocks && "Precondition for dom construction violated");
689 for (i = n_blocks-1; i > 0; i--) { /* Don't iterate the root, it's done. */
691 tmp_dom_info *w = &tdi_list[i];
695 irn_arity = get_irn_arity(w->block);
696 for (j = 0; j < irn_arity; j++) {
697 ir_node *pred = get_Block_cfgpred_block(w->block, j);
700 if (is_Bad(pred) || (get_Block_dom_pre_num (pred) == -1))
701 continue; /* control-dead */
703 u = dom_eval (&tdi_list[get_Block_dom_pre_num(pred)]);
704 if (u->semi < w->semi) w->semi = u->semi;
707 /* handle keep-alives if we are at the end block */
708 if (w->block == get_irg_end_block(irg)) {
709 ir_node *end = get_irg_end(irg);
711 irn_arity = get_irn_arity(end);
712 for (j = 0; j < irn_arity; j++) {
713 ir_node *pred = get_irn_n(end, j);
716 if (is_no_Block(pred) || get_Block_dom_pre_num(pred) == -1)
717 continue; /* control-dead */
719 u = dom_eval (&tdi_list[get_Block_dom_pre_num(pred)]);
720 if (u->semi < w->semi) w->semi = u->semi;
724 /* Add w to w->semi's bucket. w is in exactly one bucket, so
725 buckets can been implemented as linked lists. */
726 w->bucket = w->semi->bucket;
729 dom_link (w->parent, w);
732 while (w->parent->bucket) {
734 v = w->parent->bucket;
735 /* remove v from w->parent->bucket */
736 w->parent->bucket = v->bucket;
740 if (u->semi < v->semi)
747 tdi_list[0].dom = NULL;
748 set_Block_idom(tdi_list[0].block, NULL);
749 set_Block_dom_depth(tdi_list[0].block, 1);
750 for (i = 1; i < n_blocks; i++) {
751 tmp_dom_info *w = &tdi_list[i];
755 continue; /* control dead */
757 if (w->dom != w->semi) w->dom = w->dom->dom;
758 set_Block_idom(w->block, w->dom->block);
760 /* blocks dominated by dead one's are still dead */
761 depth = get_Block_dom_depth(w->dom->block);
764 set_Block_dom_depth(w->block, depth);
770 /* Do a walk over the tree and assign the tree pre orders. */
772 unsigned tree_pre_order = 0;
773 dom_tree_walk_irg(irg, assign_tree_dom_pre_order,
774 assign_tree_dom_pre_order_max, &tree_pre_order);
776 current_ir_graph = rem;
779 void assure_doms(ir_graph *irg) {
780 if (get_irg_dom_state(irg) != dom_consistent)
784 void free_dom(ir_graph *irg) {
785 /* Update graph state */
786 assert(get_irg_phase_state(current_ir_graph) != phase_building);
787 current_ir_graph->dom_state = dom_none;
789 /* With the implementation right now there is nothing to free,
790 but better call it anyways... */
793 /* Computes the post dominator trees. Sets a flag in irg to "dom_consistent".
794 If the control flow of the graph is changed this flag must be set to
795 "dom_inconsistent". */
796 void compute_postdoms(ir_graph *irg) {
797 ir_graph *rem = current_ir_graph;
798 int n_blocks, used, i, j;
799 tmp_dom_info *tdi_list;
801 current_ir_graph = irg;
803 /* Update graph state */
804 assert(get_irg_phase_state(irg) != phase_building);
805 irg->pdom_state = dom_consistent;
807 /* Count the number of blocks in the graph. */
808 n_blocks = init_construction(irg, count_and_init_blocks_pdom);
810 /* Memory for temporary information. */
811 tdi_list = xcalloc(n_blocks, sizeof(tdi_list[0]));
813 /* We need the out data structure. */
814 assure_irg_outs(irg);
816 /* this with a standard walker as passing the parent to the sons isn't
819 inc_irg_block_visited(irg);
820 init_tmp_pdom_info(get_irg_end_block(irg), NULL, tdi_list, &used);
821 /* If not all blocks are reachable from End by cfg edges this assertion
823 assert(used == n_blocks && "Precondition for dom construction violated"); */
827 for (i = n_blocks-1; i > 0; i--) { /* Don't iterate the root, it's done. */
829 tmp_dom_info *w = &tdi_list[i];
833 irn_arity = get_Block_n_cfg_outs_ka(w->block);
834 for (j = 0; j < irn_arity; j++) {
835 ir_node *succ = get_Block_cfg_out_ka(w->block, j);
838 if (get_Block_postdom_pre_num (succ) == -1)
839 continue; /* endless-loop */
841 u = dom_eval (&tdi_list[get_Block_postdom_pre_num(succ)]);
842 if (u->semi < w->semi) w->semi = u->semi;
844 /* Add w to w->semi's bucket. w is in exactly one bucket, so
845 buckets can be implemented as linked lists. */
846 w->bucket = w->semi->bucket;
849 dom_link (w->parent, w);
852 while (w->parent->bucket) {
854 v = w->parent->bucket;
855 /* remove v from w->parent->bucket */
856 w->parent->bucket = v->bucket;
860 if (u->semi < v->semi)
867 tdi_list[0].dom = NULL;
868 set_Block_ipostdom(tdi_list[0].block, NULL);
869 set_Block_postdom_depth(tdi_list[0].block, 1);
870 for (i = 1; i < n_blocks; i++) {
871 tmp_dom_info *w = &tdi_list[i];
873 if (w->dom != w->semi) w->dom = w->dom->dom;
874 set_Block_ipostdom(w->block, w->dom->block);
875 set_Block_postdom_depth(w->block, get_Block_postdom_depth(w->dom->block) + 1);
881 /* Do a walk over the tree and assign the tree pre orders. */
883 unsigned tree_pre_order = 0;
884 postdom_tree_walk_irg(irg, assign_tree_postdom_pre_order,
885 assign_tree_postdom_pre_order_max, &tree_pre_order);
887 current_ir_graph = rem;
890 void assure_postdoms(ir_graph *irg) {
891 if (get_irg_postdom_state(irg) != dom_consistent)
892 compute_postdoms(irg);
895 void free_postdom(ir_graph *irg) {
896 /* Update graph state */
897 assert(get_irg_phase_state(current_ir_graph) != phase_building);
898 current_ir_graph->pdom_state = dom_none;
900 /* With the implementation right now there is nothing to free,
901 but better call it anyways... */