2 * Copyright (C) 1995-2007 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 Compute the strongly connected regions and build backedge/cfloop
23 * datastructures. A variation on the Tarjan algorithm. See also
24 * [Trapp:99], Chapter 5.2.1.2.
25 * @author Goetz Lindenmaier
39 #include "irgraph_t.h"
46 #define NO_CFLOOPS_WITHOUT_HEAD 1
48 static ir_graph *outermost_ir_graph; /* The outermost graph the scc is computed
50 static ir_loop *current_loop; /* Current cfloop construction is working
52 static int loop_node_cnt = 0; /* Counts the number of allocated cfloop nodes.
53 Each cfloop node gets a unique number.
54 What for? ev. remove. @@@ */
55 static int current_dfn = 1; /* Counter to generate depth first numbering
58 static int max_loop_depth = 0;
60 void link_to_reg_end (ir_node *n, void *env);
62 /**********************************************************************/
63 /* Node attributes **/
64 /**********************************************************************/
66 /**********************************************************************/
67 /* Node attributes needed for the construction. **/
68 /**********************************************************************/
71 * The SCC info. Additional fields for an ir-node needed for the
74 typedef struct scc_info {
75 int in_stack; /**< Marks whether node is on the stack. */
76 int dfn; /**< Depth first search number. */
77 int uplink; /**< dfn number of ancestor. */
80 /** Allocate a new scc_info on the obstack of the outermost graph */
81 static INLINE scc_info *new_scc_info(void) {
82 scc_info *info = obstack_alloc (outermost_ir_graph->obst, sizeof (scc_info));
83 memset (info, 0, sizeof (scc_info));
88 * Marks the node n to be on the stack.
91 mark_irn_in_stack (ir_node *n) {
92 scc_info *info = get_irn_link(n);
97 * Marks the node n to be not on the stack.
100 mark_irn_not_in_stack (ir_node *n) {
101 scc_info *info = get_irn_link(n);
106 * Returns whether node n is on the stack.
109 irn_is_in_stack (ir_node *n) {
110 scc_info *info = get_irn_link(n);
111 return info->in_stack;
115 * Sets node n uplink value.
118 set_irn_uplink (ir_node *n, int uplink) {
119 scc_info *info = get_irn_link(n);
120 info->uplink = uplink;
124 * Return node n uplink value.
127 get_irn_uplink (ir_node *n) {
128 scc_info *info = get_irn_link(n);
133 * Sets node n dfn value.
136 set_irn_dfn (ir_node *n, int dfn) {
137 scc_info *info = get_irn_link(n);
142 * Returns node n dfn value.
145 get_irn_dfn (ir_node *n) {
146 scc_info *info = get_irn_link(n);
150 /**********************************************************************/
152 /**********************************************************************/
154 static ir_node **stack = NULL; /**< An IR-node stack */
155 static int tos = 0; /**< The top (index) of the IR-node stack */
158 * Initializes the IR-node stack
160 static INLINE void init_stack(void) {
162 ARR_RESIZE(ir_node *, stack, 1000);
164 stack = NEW_ARR_F(ir_node *, 1000);
170 * Push a node n onto the IR-node stack.
175 if (tos == ARR_LEN(stack)) {
176 int nlen = ARR_LEN(stack) * 2;
177 ARR_RESIZE(ir_node *, stack, nlen);
180 mark_irn_in_stack(n);
184 * Pop a node from the IR-node stack and return it.
186 static INLINE ir_node *
189 ir_node *n = stack[--tos];
190 mark_irn_not_in_stack(n);
195 * The nodes from tos up to n belong to the current loop.
196 * Removes them from the stack and adds them to the current loop.
199 pop_scc_to_loop(ir_node *n)
207 set_irn_dfn(m, loop_node_cnt);
208 add_loop_node(current_loop, m);
209 set_irn_loop(m, current_loop);
210 /* if (m==n) break;*/
214 /* GL ??? my last son is my grandson??? Removes cfloops with no
215 ir_nodes in them. Such loops have only another loop as son. (Why
216 can't they have two loops as sons? Does it never get that far? ) */
217 static void close_loop (ir_loop *l)
219 int last = get_loop_n_elements(l) - 1;
220 loop_element lelement = get_loop_element(l, last);
221 ir_loop *last_son = lelement.son;
223 if (get_kind(last_son) == k_ir_loop &&
224 get_loop_n_elements(last_son) == 1) {
227 lelement = get_loop_element(last_son, 0);
229 if(get_kind(gson) == k_ir_loop) {
230 loop_element new_last_son;
232 gson -> outer_loop = l;
233 new_last_son.son = gson;
234 l -> children[last] = new_last_son;
242 * Removes and unmarks all nodes up to n from the stack.
243 * The nodes must be visited once more to assign them to a scc.
246 pop_scc_unmark_visit (ir_node *n)
252 set_irn_visited(m, 0);
256 /**********************************************************************/
257 /* The loop datastructure. **/
258 /**********************************************************************/
261 * Allocates a new loop as son of current_loop. Sets current_loop
262 * to the new loop and returns its father.
264 static ir_loop *new_loop (void) {
265 ir_loop *father, *son;
267 father = current_loop;
269 son = obstack_alloc(outermost_ir_graph->obst, sizeof(*son));
270 memset(son, 0, sizeof(*son));
271 son->kind = k_ir_loop;
272 son->children = NEW_ARR_F(loop_element, 0);
276 son->outer_loop = father;
277 add_loop_son(father, son);
278 son->depth = father->depth+1;
279 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
281 else { /* The root loop */
282 son->outer_loop = son;
287 son->loop_nr = get_irp_new_node_nr();
295 /**********************************************************************/
296 /* Constructing and destructing the loop/backedge information. **/
297 /**********************************************************************/
299 /* Initialization steps. **********************************************/
302 * Allocates a scc_info for every Block node n.
303 * Clear the backedges for all nodes.
304 * Called from a walker.
307 init_node (ir_node *n, void *env) {
309 set_irn_link (n, new_scc_info());
314 * Initializes the common global settings for the scc algorithm
317 init_scc_common (void) {
324 * Initializes the scc algorithm for the intraprocedural case.
325 * Add scc info to every block node.
328 init_scc (ir_graph *irg) {
330 irg_walk_graph(irg, init_node, NULL, NULL);
334 * Initializes the scc algorithm for the interprocedural case.
339 cg_walk (init_node, NULL, NULL);
341 #if EXPERIMENTAL_CFLOOP_TREE
342 cg_walk (link_to_reg_end, NULL, NULL);
347 * Condition for breaking the recursion: n is the block
348 * that gets the initial control flow from the Start node.
350 static int is_outermost_StartBlock(ir_node *n) {
351 /* Test whether this is the outermost Start node. If so
352 recursion must end. */
354 if ((get_Block_n_cfgpreds(n) == 1) &&
355 (get_irn_op(skip_Proj(get_Block_cfgpred(n, 0))) == op_Start) &&
356 (get_nodes_block(skip_Proj(get_Block_cfgpred(n, 0))) == n)) {
362 /** Returns non-zero if n is a loop header, i.e., it is a Block node
363 * and has predecessors within the cfloop and out of the cfloop.
365 * @param n the block node to check
366 * @param root only needed for assertion.
369 is_head (ir_node *n, ir_node *root)
372 int some_outof_loop = 0, some_in_loop = 0;
376 if (!is_outermost_StartBlock(n)) {
377 arity = get_irn_arity(n);
378 for (i = 0; i < arity; i++) {
379 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
380 if (is_backedge(n, i)) continue;
381 if (!irn_is_in_stack(pred)) {
384 if (get_irn_uplink(pred) < get_irn_uplink(root)) {
385 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
391 return some_outof_loop & some_in_loop;
396 * Returns non-zero if n is possible loop head of an endless loop.
397 * I.e., it is a Block, Phi or Filter node and has only predecessors
400 * @param n the block node to check
401 * @param root only needed for assertion.
404 is_endless_head (ir_node *n, ir_node *root)
407 int some_outof_loop = 0, some_in_loop = 0;
410 /* Test for legal loop header: Block, Phi, ... */
411 if (!is_outermost_StartBlock(n)) {
412 arity = get_irn_arity(n);
413 for (i = 0; i < arity; i++) {
414 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
416 if (is_backedge(n, i)) { continue; }
417 if (!irn_is_in_stack(pred)) {
418 some_outof_loop = 1; //printf(" some out of loop ");
420 if(get_irn_uplink(pred) < get_irn_uplink(root)) {
421 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
427 return !some_outof_loop && some_in_loop;
431 * Returns index of the predecessor with the smallest dfn number
432 * greater-equal than limit.
435 smallest_dfn_pred (ir_node *n, int limit)
437 int i, index = -2, min = -1;
439 if (!is_outermost_StartBlock(n)) {
440 int arity = get_irn_arity(n);
441 for (i = 0; i < arity; i++) {
442 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
443 if (is_backedge(n, i) || !irn_is_in_stack(pred))
445 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
447 min = get_irn_dfn(pred);
455 * Returns index of the predecessor with the largest dfn number.
458 largest_dfn_pred (ir_node *n)
460 int i, index = -2, max = -1;
462 if (!is_outermost_StartBlock(n)) {
463 int arity = get_irn_arity(n);
464 for (i = 0; i < arity; i++) {
465 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
466 if (is_backedge (n, i) || !irn_is_in_stack(pred))
468 if (get_irn_dfn(pred) > max) {
470 max = get_irn_dfn(pred);
478 * Searches the stack for possible loop heads. Tests these for backedges.
479 * If it finds a head with an unmarked backedge it marks this edge and
480 * returns the tail of the loop.
481 * If it finds no backedge returns NULL.
484 find_tail (ir_node *n) {
486 int i, res_index = -2;
488 m = stack[tos-1]; /* tos = top of stack */
490 res_index = smallest_dfn_pred(m, 0);
491 if ((res_index == -2) && /* no smallest dfn pred found. */
495 if (m == n) return NULL;
496 for (i = tos-2; i >= 0; --i) {
499 if (is_head (m, n)) {
500 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
501 if (res_index == -2) /* no smallest dfn pred found. */
502 res_index = largest_dfn_pred (m);
504 if ((m == n) && (res_index == -2)) {
511 /* We should not walk past our selves on the stack: The upcoming nodes
512 are not in this loop. We assume a loop not reachable from Start. */
520 /* A dead loop not reachable from Start. */
521 for (i = tos-2; i >= 0; --i) {
523 if (is_endless_head (m, n)) {
524 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
525 if (res_index == -2) /* no smallest dfn pred found. */
526 res_index = largest_dfn_pred (m);
529 if (m == n) break; /* It's not an unreachable loop, either. */
531 //assert(0 && "no head found on stack");
535 assert (res_index > -2);
537 set_backedge (m, res_index);
538 return is_outermost_StartBlock(n) ? NULL : get_nodes_block(skip_Proj(get_irn_n(m, res_index)));
542 * returns non.zero if l is the outermost loop.
545 is_outermost_loop(ir_loop *l) {
546 return l == get_loop_outer_loop(l);
549 /*-----------------------------------------------------------*
550 * The core algorithm. *
551 *-----------------------------------------------------------*/
554 * Walks over all blocks of a graph
556 static void cfscc (ir_node *n) {
561 if (irn_visited(n)) return;
564 /* Initialize the node */
565 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
566 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
567 set_irn_loop(n, NULL);
571 if (!is_outermost_StartBlock(n)) {
572 int arity = get_irn_arity(n);
574 for (i = 0; i < arity; i++) {
577 if (is_backedge(n, i))
579 m = get_nodes_block(skip_Proj(get_irn_n(n, i)));
582 if (irn_is_in_stack(m)) {
583 /* Uplink of m is smaller if n->m is a backedge.
584 Propagate the uplink to mark the cfloop. */
585 if (get_irn_uplink(m) < get_irn_uplink(n))
586 set_irn_uplink(n, get_irn_uplink(m));
591 if (get_irn_dfn(n) == get_irn_uplink(n)) {
592 /* This condition holds for
593 1) the node with the incoming backedge.
594 That is: We found a cfloop!
595 2) Straight line code, because no uplink has been propagated, so the
596 uplink still is the same as the dfn.
598 But n might not be a proper cfloop head for the analysis. Proper cfloop
599 heads are Block and Phi nodes. find_tail searches the stack for
600 Block's and Phi's and takes those nodes as cfloop heads for the current
601 cfloop instead and marks the incoming edge as backedge. */
603 ir_node *tail = find_tail(n);
605 /* We have a cfloop, that is no straight line code,
606 because we found a cfloop head!
607 Next actions: Open a new cfloop on the cfloop tree and
608 try to find inner cfloops */
610 #if NO_CFLOOPS_WITHOUT_HEAD
612 /* This is an adaption of the algorithm from fiasco / optscc to
613 * avoid cfloops without Block or Phi as first node. This should
614 * severely reduce the number of evaluations of nodes to detect
615 * a fixpoint in the heap analysis.
616 * Further it avoids cfloops without firm nodes that cause errors
617 * in the heap analyses. */
621 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
631 ir_loop *l = new_loop();
635 /* Remove the cfloop from the stack ... */
636 pop_scc_unmark_visit (n);
638 /* The current backedge has been marked, that is temporarily eliminated,
639 by find tail. Start the scc algorithm
640 anew on the subgraph thats left (the current cfloop without the backedge)
641 in order to find more inner cfloops. */
645 assert (irn_visited(n));
646 #if NO_CFLOOPS_WITHOUT_HEAD
652 /* AS: No cfloop head was found, that is we have straight line code.
653 Pop all nodes from the stack to the current cfloop. */
659 /* Constructs control flow backedge information for irg. */
660 int construct_cf_backedges(ir_graph *irg) {
661 ir_graph *rem = current_ir_graph;
663 ir_node *end = get_irg_end(irg);
666 assert(!get_interprocedural_view() &&
667 "use construct_ip_cf_backedges()");
670 current_ir_graph = irg;
671 outermost_ir_graph = irg;
673 init_scc(current_ir_graph);
676 new_loop(); /* sets current_loop */
677 head_rem = current_loop; /* Just for assertion */
679 inc_irg_visited(current_ir_graph);
681 /* walk over all blocks of the graph, including keep alives */
682 cfscc(get_irg_end_block(current_ir_graph));
683 for (i = 0; i < get_End_n_keepalives(end); i++) {
684 ir_node *el = get_End_keepalive(end, i);
685 if (is_Block(el)) cfscc(el);
688 assert(head_rem == current_loop);
689 set_irg_loop(current_ir_graph, current_loop);
690 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_consistent);
691 assert(get_irg_loop(current_ir_graph)->kind == k_ir_loop);
693 current_ir_graph = rem;
694 return max_loop_depth;
698 int construct_ip_cf_backedges (void) {
699 ir_graph *rem = current_ir_graph;
700 int rem_ipv = get_interprocedural_view();
703 assert(get_irp_ip_view_state() == ip_view_valid);
705 outermost_ir_graph = get_irp_main_irg();
710 new_loop(); /* sets current_loop */
711 set_interprocedural_view(1);
713 inc_max_irg_visited();
714 for (i = 0; i < get_irp_n_irgs(); i++)
715 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
717 /** We have to start the walk at the same nodes as cg_walk. **/
718 /* Walk starting at unreachable procedures. Only these
719 * have End blocks visible in interprocedural view. */
720 for (i = 0; i < get_irp_n_irgs(); i++) {
722 current_ir_graph = get_irp_irg(i);
724 sb = get_irg_start_block(current_ir_graph);
726 if ((get_Block_n_cfgpreds(sb) > 1) ||
727 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
729 cfscc(get_irg_end_block(current_ir_graph));
732 /* Check whether we walked all procedures: there could be procedures
733 with cyclic calls but no call from the outside. */
734 for (i = 0; i < get_irp_n_irgs(); i++) {
736 current_ir_graph = get_irp_irg(i);
738 /* Test start block: if inner procedure end and end block are not
739 * visible and therefore not marked. */
740 sb = get_irg_start_block(current_ir_graph);
741 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
744 /* Walk all endless cfloops in inner procedures.
745 * We recognize an inner procedure if the End node is not visited. */
746 for (i = 0; i < get_irp_n_irgs(); i++) {
748 current_ir_graph = get_irp_irg(i);
750 e = get_irg_end(current_ir_graph);
751 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
753 /* Don't visit the End node. */
754 for (j = 0; j < get_End_n_keepalives(e); j++) {
755 ir_node *el = get_End_keepalive(e, j);
756 if (is_Block(el)) cfscc(el);
761 set_irg_loop(outermost_ir_graph, current_loop);
762 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
763 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
765 current_ir_graph = rem;
766 set_interprocedural_view(rem_ipv);
767 return max_loop_depth;
771 * Clear the intra- and the interprocedural
772 * backedge information pf a block.
774 static void reset_backedges(ir_node *block) {
775 int rem = get_interprocedural_view();
777 assert(is_Block(block));
778 set_interprocedural_view(1);
779 clear_backedges(block);
780 set_interprocedural_view(0);
781 clear_backedges(block);
782 set_interprocedural_view(rem);
786 * Reset all backedges of the first block of
787 * a loop as well as all loop info for all nodes of this loop.
788 * Recurse into all nested loops.
790 static void loop_reset_backedges(ir_loop *l) {
792 reset_backedges(get_loop_node(l, 0));
793 for (i = 0; i < get_loop_n_nodes(l); ++i)
794 set_irn_loop(get_loop_node(l, i), NULL);
795 for (i = 0; i < get_loop_n_sons(l); ++i) {
796 loop_reset_backedges(get_loop_son(l, i));
800 /* Removes all cfloop information.
801 Resets all backedges */
802 void free_cfloop_information(ir_graph *irg) {
803 if (get_irg_loop(irg))
804 loop_reset_backedges(get_irg_loop(irg));
805 set_irg_loop(irg, NULL);
806 set_irg_loopinfo_state(irg, loopinfo_none);
807 /* We cannot free the cfloop nodes, they are on the obstack. */
811 void free_all_cfloop_information (void) {
813 int rem = get_interprocedural_view();
814 set_interprocedural_view(1); /* To visit all filter nodes */
815 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
816 free_cfloop_information(get_irp_irg(i));
818 set_interprocedural_view(rem);