2 * Copyright (C) 1995-2008 University of Karlsruhe. All right reserved.
4 * This file is part of libFirm.
6 * This file may be distributed and/or modified under the terms of the
7 * GNU General Public License version 2 as published by the Free Software
8 * Foundation and appearing in the file LICENSE.GPL included in the
9 * packaging of this file.
11 * Licensees holding valid libFirm Professional Edition licenses may use
12 * this file in accordance with the libFirm Commercial License.
13 * Agreement provided with the Software.
15 * This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
16 * WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * @brief Construct and access dominator / post dominator tree.
23 * @author Goetz Lindenmaier, Michael Beck, Rubino Geiss
40 #include "irgraph_t.h" /* To access state field. */
47 #define get_dom_info(bl) (&(bl)->attr.block.dom)
48 #define get_pdom_info(bl) (&(bl)->attr.block.pdom)
50 /*--------------------------------------------------------------------*/
51 /** Accessing the dominator and post dominator data structures **/
52 /*--------------------------------------------------------------------*/
54 ir_node *get_Block_idom(const ir_node *bl) {
56 if (get_Block_dom_depth(bl) == -1) {
57 /* This block is not reachable from Start */
60 return get_dom_info(bl)->idom;
63 void set_Block_idom(ir_node *bl, ir_node *n) {
64 ir_dom_info *bli = get_dom_info(bl);
68 /* Set the immediate dominator of bl to n */
72 * If we don't set the root of the dominator tree
73 * Append bl to the dominates queue of n.
76 ir_dom_info *ni = get_dom_info(n);
78 bli->next = ni->first;
83 ir_node *get_Block_ipostdom(const ir_node *bl) {
85 if (get_Block_postdom_depth(bl) == -1) {
86 /* This block is not reachable from Start */
89 return get_pdom_info(bl)->idom;
92 void set_Block_ipostdom(ir_node *bl, ir_node *n) {
93 ir_dom_info *bli = get_pdom_info(bl);
97 /* Set the immediate post dominator of bl to n */
101 * If we don't set the root of the post dominator tree
102 * Append bl to the post dominates queue of n.
105 ir_dom_info *ni = get_pdom_info(n);
107 bli->next = ni->first;
112 int get_Block_dom_pre_num(const ir_node *bl) {
113 assert(is_Block(bl));
114 return get_dom_info(bl)->pre_num;
117 void set_Block_dom_pre_num(ir_node *bl, int num) {
118 assert(is_Block(bl));
119 get_dom_info(bl)->pre_num = num;
122 int get_Block_dom_depth(const ir_node *bl) {
123 assert(is_Block(bl));
124 return get_dom_info(bl)->dom_depth;
127 void set_Block_dom_depth(ir_node *bl, int depth) {
128 assert(is_Block(bl));
129 get_dom_info(bl)->dom_depth = depth;
133 int get_Block_postdom_pre_num(const ir_node *bl) {
134 assert(is_Block(bl));
135 return get_pdom_info(bl)->pre_num;
138 void set_Block_postdom_pre_num(ir_node *bl, int num) {
139 assert(is_Block(bl));
140 get_pdom_info(bl)->pre_num = num;
143 int get_Block_postdom_depth(const ir_node *bl) {
144 assert(is_Block(bl));
145 return get_pdom_info(bl)->dom_depth;
148 void set_Block_postdom_depth(ir_node *bl, int depth) {
149 assert(is_Block(bl));
150 get_pdom_info(bl)->dom_depth = depth;
153 unsigned get_Block_dom_tree_pre_num(const ir_node *bl) {
154 assert(is_Block(bl));
155 return get_dom_info(bl)->tree_pre_num;
158 unsigned get_Block_dom_max_subtree_pre_num(const ir_node *bl) {
159 assert(is_Block(bl));
160 return get_dom_info(bl)->max_subtree_pre_num;
163 unsigned get_Block_pdom_tree_pre_num(const ir_node *bl) {
164 assert(is_Block(bl));
165 return get_pdom_info(bl)->tree_pre_num;
168 unsigned get_Block_pdom_max_subtree_pre_num(const ir_node *bl) {
169 assert(is_Block(bl));
170 return get_pdom_info(bl)->max_subtree_pre_num;
173 /* Check, if a block dominates another block. */
174 int block_dominates(const ir_node *a, const ir_node *b) {
175 const ir_dom_info *ai, *bi;
177 if (is_Block(a) && is_Block(b)) {
178 ai = get_dom_info(a);
179 bi = get_dom_info(b);
180 return bi->tree_pre_num - ai->tree_pre_num
181 <= ai->max_subtree_pre_num - ai->tree_pre_num;
187 /* Check, if a block strictly dominates another block. */
188 int block_strictly_dominates(const ir_node *a, const ir_node *b) {
189 return (a != b) && block_dominates(a, b);
192 /* Returns the smallest common dominator block of two nodes. */
193 ir_node *node_smallest_common_dominator(ir_node *a, ir_node *b) {
194 ir_node *bl_a = is_Block(a) ? a : get_nodes_block(a);
195 ir_node *bl_b = is_Block(b) ? b : get_nodes_block(b);
196 ir_node *dom_bl = NULL;
198 /* Check if block of a dominates block of b */
199 if (block_dominates(bl_a, bl_b))
201 /* Check if block of b dominates block of a */
202 else if (block_dominates(bl_b, bl_a))
205 /* walk up dominator tree and search for first block dominating a and b */
207 bl_a = get_Block_idom(bl_a);
209 assert(! is_Bad(bl_a) && "block is dead?");
211 if (block_dominates(bl_a, bl_b))
219 /* Returns the smallest common dominator block of all users of a node. */
220 ir_node *node_users_smallest_common_dominator(ir_node *irn, int handle_phi) {
221 int n, j, i = 0, success;
222 ir_node **user_blocks, *dom_bl;
223 const ir_edge_t *edge;
225 assert(! is_Block(irn) && "WRONG USAGE of node_users_smallest_common_dominator");
226 assert(edges_activated(get_irn_irg(irn)) && "need edges activated");
228 n = get_irn_n_edges(irn);
230 /* get array to hold all block of the node users */
231 NEW_ARR_A(ir_node *, user_blocks, n);
232 foreach_out_edge(irn, edge) {
233 ir_node *src = get_edge_src_irn(edge);
235 if (is_Phi(src) && handle_phi) {
236 /* get the corresponding cfg predecessor block if phi handling requested */
237 j = get_edge_src_pos(edge);
238 assert(j >= 0 && "kaputt");
239 user_blocks[i++] = get_Block_cfgpred_block(get_nodes_block(src), j);
242 user_blocks[i++] = is_Block(src) ? src : get_nodes_block(src);
245 assert(i == n && "get_irn_n_edges probably broken");
247 /* in case of only one user: return the block of the user */
249 return user_blocks[0];
252 /* search the smallest block dominating all user blocks */
254 dom_bl = node_smallest_common_dominator(user_blocks[i], user_blocks[i + 1]);
257 /* check if this block dominates all remaining blocks as well */
258 for (j = i + 2; j < n; j++) {
259 if (! block_dominates(dom_bl, user_blocks[j]))
266 /* inherit the dominator block of the first (i + 1) users */
267 user_blocks[++i] = dom_bl;
270 assert(success && "no block found dominating all users");
276 /* Get the first node in the list of nodes dominated by a given block. */
277 ir_node *get_Block_dominated_first(const ir_node *bl) {
278 assert(is_Block(bl));
279 return get_dom_info(bl)->first;
282 /* Get the next node in a list of nodes which are dominated by some
284 ir_node *get_Block_dominated_next(const ir_node *bl) {
285 assert(is_Block(bl));
286 return get_dom_info(bl)->next;
289 /* Check, if a block post dominates another block. */
290 int block_postdominates(const ir_node *a, const ir_node *b) {
291 const ir_dom_info *ai, *bi;
293 if (is_Block(a) && is_Block(b)) {
294 ai = get_pdom_info(a);
295 bi = get_pdom_info(b);
296 return bi->tree_pre_num - ai->tree_pre_num
297 <= ai->max_subtree_pre_num - ai->tree_pre_num;
303 /* Check, if a block strictly dominates another block. */
304 int block_strictly_postdominates(const ir_node *a, const ir_node *b) {
305 return (a != b) && block_postdominates(a, b);
309 /* Get the first node in the list of nodes post dominated by a given block. */
310 ir_node *get_Block_postdominated_first(const ir_node *bl) {
311 assert(is_Block(bl));
312 return get_pdom_info(bl)->first;
315 /* Get the next node in a list of nodes which are post dominated by some
317 ir_node *get_Block_postdominated_next(const ir_node *bl) {
318 assert(is_Block(bl));
319 return get_pdom_info(bl)->next;
322 /* Visit all nodes in the dominator subtree of a given node. */
323 void dom_tree_walk(ir_node *bl, irg_walk_func *pre,
324 irg_walk_func *post, void *env)
331 dominates_for_each(bl, p) {
332 dom_tree_walk(p, pre, post, env);
339 /* Visit all nodes in the post dominator subtree of a given node. */
340 void postdom_tree_walk(ir_node *bl, irg_walk_func *pre,
341 irg_walk_func *post, void *env)
348 postdominates_for_each(bl, p) {
349 postdom_tree_walk(p, pre, post, env);
356 /* Walk over the dominator tree of an irg starting at the root. */
357 void dom_tree_walk_irg(ir_graph *irg, irg_walk_func *pre,
358 irg_walk_func *post, void *env)
360 /* The root of the dominator tree should be the Start block. */
361 ir_node *root = get_irg_start_block(irg);
363 assert(irg->dom_state == dom_consistent
364 && "The dominators of the irg must be consistent");
365 assert(root && "The start block of the graph is NULL?");
366 assert(get_dom_info(root)->idom == NULL
367 && "The start node in the graph must be the root of the dominator tree");
368 dom_tree_walk(root, pre, post, env);
371 /* Walk over the post dominator tree of an irg starting at the root. */
372 void postdom_tree_walk_irg(ir_graph *irg, irg_walk_func *pre,
373 irg_walk_func *post, void *env)
375 /* The root of the dominator tree should be the End block. */
376 ir_node *root = get_irg_end_block(irg);
378 assert(irg->pdom_state == dom_consistent
379 && "The dominators of the irg must be consistent");
380 assert(root && "The end block of the graph is NULL?");
381 assert(get_pdom_info(root)->idom == NULL
382 && "The End block node in the graph must be the root of the post dominator tree");
383 postdom_tree_walk(root, pre, post, env);
387 static void assign_tree_dom_pre_order(ir_node *bl, void *data)
389 unsigned *num = data;
390 ir_dom_info *bi = get_dom_info(bl);
392 bi->tree_pre_num = (*num)++;
395 static void assign_tree_dom_pre_order_max(ir_node *bl, void *data)
397 ir_dom_info *bi = get_dom_info(bl);
400 unsigned children = 0;
403 for(p = bi->first; p; p = get_dom_info(p)->next) {
404 unsigned max_p = get_dom_info(p)->max_subtree_pre_num;
405 max = max > max_p ? max : max_p;
409 bi->max_subtree_pre_num = children > 0 ? max : bi->tree_pre_num;
410 assert(bi->max_subtree_pre_num >= bi->tree_pre_num);
413 static void assign_tree_postdom_pre_order(ir_node *bl, void *data)
415 unsigned *num = data;
416 ir_dom_info *bi = get_pdom_info(bl);
418 bi->tree_pre_num = (*num)++;
421 static void assign_tree_postdom_pre_order_max(ir_node *bl, void *data)
423 ir_dom_info *bi = get_pdom_info(bl);
426 unsigned children = 0;
429 for(p = bi->first; p; p = get_pdom_info(p)->next) {
430 unsigned max_p = get_pdom_info(p)->max_subtree_pre_num;
431 max = max > max_p ? max : max_p;
435 bi->max_subtree_pre_num = children > 0 ? max : bi->tree_pre_num;
436 assert(bi->max_subtree_pre_num >= bi->tree_pre_num);
439 /*--------------------------------------------------------------------*/
440 /* Building and Removing the dominator data structure */
441 /*--------------------------------------------------------------------*/
444 * count the number of blocks and clears the post dominance info
446 static void count_and_init_blocks_pdom(ir_node *bl, void *env) {
448 int *n_blocks = (int *) env;
451 memset(get_pdom_info(bl), 0, sizeof(ir_dom_info));
452 set_Block_ipostdom(bl, NULL);
453 set_Block_postdom_pre_num(bl, -1);
454 set_Block_postdom_depth(bl, -1);
458 /** temporary type used while constructing the dominator / post dominator tree. */
459 typedef struct tmp_dom_info {
460 ir_node *block; /**< backlink */
462 struct tmp_dom_info *semi; /**< semidominator */
463 struct tmp_dom_info *parent;
464 struct tmp_dom_info *label; /**< used for LINK and EVAL */
465 struct tmp_dom_info *ancestor;/**< used for LINK and EVAL */
466 struct tmp_dom_info *dom; /**< After step 3, if the semidominator of w is
467 its immediate dominator, then w->dom is the
468 immediate dominator of w. Otherwise w->dom
469 is a vertex v whose number is smaller than
470 w and whose immediate dominator is also w's
471 immediate dominator. After step 4, w->dom
472 is the immediate dominator of w. */
473 struct tmp_dom_info *bucket; /**< set of vertices with same semidominator */
476 /** Struct to pass info through walker. */
484 * Walks Blocks along the out data structure. If recursion started with
485 * Start block misses control dead blocks.
487 static void init_tmp_dom_info(ir_node *bl, tmp_dom_info *parent,
488 tmp_dom_info *tdi_list, int *used, int n_blocks) {
492 assert(is_Block(bl));
493 if (get_irg_block_visited(current_ir_graph) == get_Block_block_visited(bl))
495 mark_Block_block_visited(bl);
496 set_Block_dom_pre_num(bl, *used);
498 assert(*used < n_blocks);
499 tdi = &tdi_list[*used];
504 tdi->ancestor = NULL;
506 tdi->parent = parent;
510 for (i = get_Block_n_cfg_outs_ka(bl) - 1; i >= 0; --i) {
511 ir_node *pred = get_Block_cfg_out_ka(bl, i);
512 assert(is_Block(pred));
513 init_tmp_dom_info(pred, tdi, tdi_list, used, n_blocks);
518 * Walks Blocks along the control flow. If recursion started with
519 * End block misses blocks in endless loops.
521 static void init_tmp_pdom_info(ir_node *bl, tmp_dom_info *parent,
522 tmp_dom_info *tdi_list, int* used, int n_blocks) {
526 assert(is_Block(bl));
527 if (get_irg_block_visited(current_ir_graph) == get_Block_block_visited(bl))
529 mark_Block_block_visited(bl);
530 set_Block_postdom_pre_num(bl, *used);
532 assert(*used < n_blocks);
533 tdi = &tdi_list[*used];
538 tdi->ancestor = NULL;
540 tdi->parent = parent;
544 for (i = get_Block_n_cfgpreds(bl) - 1; i >= 0; --i) {
545 ir_node *pred = get_Block_cfgpred_block(bl, i);
548 assert(is_Block(pred));
549 init_tmp_pdom_info(pred, tdi, tdi_list, used, n_blocks);
552 /* Handle keep-alives. Note that the preprocessing
553 in init_construction() had already killed all
554 phantom keep-alive edges. All remaining block keep-alives
555 are really edges to endless loops.
557 if (bl == get_irg_end_block(current_ir_graph)) {
558 ir_node *end = get_irg_end(current_ir_graph);
560 for (i = get_irn_arity(end) - 1; i >= 0; --i) {
561 ir_node *pred = get_irn_n(end, i);
564 init_tmp_pdom_info(pred, tdi, tdi_list, used, n_blocks);
569 static void dom_compress(tmp_dom_info *v) {
570 assert (v->ancestor);
571 if (v->ancestor->ancestor) {
572 dom_compress (v->ancestor);
573 if (v->ancestor->label->semi < v->label->semi) {
574 v->label = v->ancestor->label;
576 v->ancestor = v->ancestor->ancestor;
581 * if V is a root, return v, else return the vertex u, not being the
582 * root, with minimum u->semi on the path from v to its root.
584 INLINE static tmp_dom_info *dom_eval(tmp_dom_info *v) {
585 if (!v->ancestor) return v;
590 /** make V W's ancestor */
591 INLINE static void dom_link(tmp_dom_info *v, tmp_dom_info *w) {
596 * Walker: count the number of blocks and clears the dominance info
598 static void count_and_init_blocks_dom(ir_node *bl, void *env) {
600 int *n_blocks = (int *) env;
603 memset(get_dom_info(bl), 0, sizeof(ir_dom_info));
604 set_Block_idom(bl, NULL);
605 set_Block_dom_pre_num(bl, -1);
606 set_Block_dom_depth(bl, -1);
611 * Initialize the dominance/postdominance construction:
613 * - count the number of blocks
614 * - clear the dominance info
616 * @param irg the graph
617 * @param pre a walker function that will be called for every block in the graph
619 static int init_construction(ir_graph *irg, irg_walk_func *pre) {
623 * Normally one would use irg_block_walk_graph() here, however, this does NOT
624 * guarantee that all UNREACHABLE blocks are visited.
625 * This could led to wrong dominance info in those blocks, causing
626 * the verifier to crash for instance.
627 * So, we visit EVERY node to ensure the info is updated.
629 irg_walk_graph(irg, pre, NULL, &n_blocks);
634 /* Computes the dominator trees. Sets a flag in irg to "dom_consistent".
635 If the control flow of the graph is changed this flag must be set to
636 "dom_inconsistent". */
637 void compute_doms(ir_graph *irg) {
638 ir_graph *rem = current_ir_graph;
639 int n_blocks, used, i, j;
640 tmp_dom_info *tdi_list; /* Ein Golf? */
642 current_ir_graph = irg;
644 /* Update graph state */
645 assert(get_irg_phase_state(irg) != phase_building);
646 irg->dom_state = dom_consistent;
648 /* Count the number of blocks in the graph. */
649 n_blocks = init_construction(irg, count_and_init_blocks_dom);
651 /* Memory for temporary information. */
652 tdi_list = XMALLOCNZ(tmp_dom_info, n_blocks);
654 /* We need the out data structure. */
655 assure_irg_outs(irg);
657 /* this with a standard walker as passing the parent to the sons isn't
660 inc_irg_block_visited(irg);
661 init_tmp_dom_info(get_irg_start_block(irg), NULL, tdi_list, &used, n_blocks);
662 /* If not all blocks are reachable from Start by out edges this assertion
664 assert(used == n_blocks && "Precondition for dom construction violated"); */
665 assert(used <= n_blocks && "Precondition for dom construction violated");
669 for (i = n_blocks-1; i > 0; i--) { /* Don't iterate the root, it's done. */
671 tmp_dom_info *w = &tdi_list[i];
675 irn_arity = get_irn_arity(w->block);
676 for (j = 0; j < irn_arity; j++) {
677 ir_node *pred = get_Block_cfgpred_block(w->block, j);
680 if (is_Bad(pred) || (get_Block_dom_pre_num (pred) == -1))
681 continue; /* control-dead */
683 u = dom_eval (&tdi_list[get_Block_dom_pre_num(pred)]);
684 if (u->semi < w->semi) w->semi = u->semi;
687 /* handle keep-alives if we are at the end block */
688 if (w->block == get_irg_end_block(irg)) {
689 ir_node *end = get_irg_end(irg);
691 irn_arity = get_irn_arity(end);
692 for (j = 0; j < irn_arity; j++) {
693 ir_node *pred = get_irn_n(end, j);
696 if (is_no_Block(pred) || get_Block_dom_pre_num(pred) == -1)
697 continue; /* control-dead */
699 u = dom_eval (&tdi_list[get_Block_dom_pre_num(pred)]);
700 if (u->semi < w->semi) w->semi = u->semi;
704 /* Add w to w->semi's bucket. w is in exactly one bucket, so
705 buckets can been implemented as linked lists. */
706 w->bucket = w->semi->bucket;
709 dom_link (w->parent, w);
712 while (w->parent->bucket) {
714 v = w->parent->bucket;
715 /* remove v from w->parent->bucket */
716 w->parent->bucket = v->bucket;
720 if (u->semi < v->semi)
727 tdi_list[0].dom = NULL;
728 set_Block_idom(tdi_list[0].block, NULL);
729 set_Block_dom_depth(tdi_list[0].block, 1);
730 for (i = 1; i < n_blocks; i++) {
731 tmp_dom_info *w = &tdi_list[i];
735 continue; /* control dead */
737 if (w->dom != w->semi) w->dom = w->dom->dom;
738 set_Block_idom(w->block, w->dom->block);
740 /* blocks dominated by dead one's are still dead */
741 depth = get_Block_dom_depth(w->dom->block);
744 set_Block_dom_depth(w->block, depth);
750 /* Do a walk over the tree and assign the tree pre orders. */
752 unsigned tree_pre_order = 0;
753 dom_tree_walk_irg(irg, assign_tree_dom_pre_order,
754 assign_tree_dom_pre_order_max, &tree_pre_order);
756 current_ir_graph = rem;
759 void assure_doms(ir_graph *irg) {
760 if (get_irg_dom_state(irg) != dom_consistent)
764 void free_dom(ir_graph *irg) {
765 /* Update graph state */
766 assert(get_irg_phase_state(irg) != phase_building);
767 irg->dom_state = dom_none;
769 /* With the implementation right now there is nothing to free,
770 but better call it anyways... */
773 /* Computes the post dominator trees. Sets a flag in irg to "dom_consistent".
774 If the control flow of the graph is changed this flag must be set to
775 "dom_inconsistent". */
776 void compute_postdoms(ir_graph *irg) {
777 ir_graph *rem = current_ir_graph;
778 int n_blocks, used, i, j;
779 tmp_dom_info *tdi_list;
781 current_ir_graph = irg;
783 /* Update graph state */
784 assert(get_irg_phase_state(irg) != phase_building);
785 irg->pdom_state = dom_consistent;
787 /* Count the number of blocks in the graph. */
788 n_blocks = init_construction(irg, count_and_init_blocks_pdom);
790 /* Memory for temporary information. */
791 tdi_list = XMALLOCNZ(tmp_dom_info, n_blocks);
793 /* We need the out data structure. */
794 assure_irg_outs(irg);
796 /* this with a standard walker as passing the parent to the sons isn't
799 inc_irg_block_visited(irg);
800 init_tmp_pdom_info(get_irg_end_block(irg), NULL, tdi_list, &used, n_blocks);
801 /* If not all blocks are reachable from End by cfg edges this assertion
803 assert(used == n_blocks && "Precondition for dom construction violated"); */
807 for (i = n_blocks-1; i > 0; i--) { /* Don't iterate the root, it's done. */
809 tmp_dom_info *w = &tdi_list[i];
813 irn_arity = get_Block_n_cfg_outs_ka(w->block);
814 for (j = 0; j < irn_arity; j++) {
815 ir_node *succ = get_Block_cfg_out_ka(w->block, j);
818 if (get_Block_postdom_pre_num (succ) == -1)
819 continue; /* endless-loop */
821 u = dom_eval (&tdi_list[get_Block_postdom_pre_num(succ)]);
822 if (u->semi < w->semi) w->semi = u->semi;
824 /* Add w to w->semi's bucket. w is in exactly one bucket, so
825 buckets can be implemented as linked lists. */
826 w->bucket = w->semi->bucket;
829 dom_link (w->parent, w);
832 while (w->parent->bucket) {
834 v = w->parent->bucket;
835 /* remove v from w->parent->bucket */
836 w->parent->bucket = v->bucket;
840 if (u->semi < v->semi)
847 tdi_list[0].dom = NULL;
848 set_Block_ipostdom(tdi_list[0].block, NULL);
849 set_Block_postdom_depth(tdi_list[0].block, 1);
850 for (i = 1; i < n_blocks; i++) {
851 tmp_dom_info *w = &tdi_list[i];
853 if (w->dom != w->semi) w->dom = w->dom->dom;
854 set_Block_ipostdom(w->block, w->dom->block);
855 set_Block_postdom_depth(w->block, get_Block_postdom_depth(w->dom->block) + 1);
861 /* Do a walk over the tree and assign the tree pre orders. */
863 unsigned tree_pre_order = 0;
864 postdom_tree_walk_irg(irg, assign_tree_postdom_pre_order,
865 assign_tree_postdom_pre_order_max, &tree_pre_order);
867 current_ir_graph = rem;
870 void assure_postdoms(ir_graph *irg) {
871 if (get_irg_postdom_state(irg) != dom_consistent)
872 compute_postdoms(irg);
875 void free_postdom(ir_graph *irg) {
876 /* Update graph state */
877 assert(get_irg_phase_state(irg) != phase_building);
878 irg->pdom_state = dom_none;
880 /* With the implementation right now there is nothing to free,
881 but better call it anyways... */