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 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
37 #include "irgraph_t.h"
44 #define NO_CFLOOPS_WITHOUT_HEAD 1
46 /** The outermost graph the scc is computed for */
47 static ir_graph *outermost_ir_graph;
48 /** Current cfloop construction is working on. */
49 static ir_loop *current_loop;
50 /** Counts the number of allocated cfloop nodes.
51 * Each cfloop node gets a unique number.
52 * @todo What for? ev. remove.
54 static int loop_node_cnt = 0;
55 /** Counter to generate depth first numbering of visited nodes. */
56 static int current_dfn = 1;
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 given obstack */
81 static inline scc_info *new_scc_info(struct obstack *obst) {
82 scc_info *info = obstack_alloc(obst, sizeof(*info));
83 memset(info, 0, sizeof(*info));
88 * Marks the node n to be on the stack.
90 static inline void mark_irn_in_stack(ir_node *n) {
91 scc_info *info = get_irn_link(n);
96 * Marks the node n to be not on the stack.
98 static inline void mark_irn_not_in_stack(ir_node *n) {
99 scc_info *info = get_irn_link(n);
104 * Returns whether node n is on the stack.
106 static inline int irn_is_in_stack(ir_node *n) {
107 scc_info *info = get_irn_link(n);
108 return info->in_stack;
112 * Sets node n uplink value.
114 static inline void set_irn_uplink(ir_node *n, int uplink) {
115 scc_info *info = get_irn_link(n);
116 info->uplink = uplink;
120 * Return node n uplink value.
122 static inline int get_irn_uplink(ir_node *n) {
123 scc_info *info = get_irn_link(n);
128 * Sets node n dfn value.
130 static inline void set_irn_dfn(ir_node *n, int dfn) {
131 scc_info *info = get_irn_link(n);
136 * Returns node n dfn value.
138 static inline int get_irn_dfn(ir_node *n) {
139 scc_info *info = get_irn_link(n);
143 /**********************************************************************/
145 /**********************************************************************/
147 /** An IR-node stack */
148 static ir_node **stack = NULL;
149 /** The top (index) of the IR-node stack */
153 * Initializes the IR-node stack
155 static inline void init_stack(void) {
157 ARR_RESIZE(ir_node *, stack, 1000);
159 stack = NEW_ARR_F(ir_node *, 1000);
164 static void finish_stack(void)
171 * Push a node n onto the IR-node stack.
173 static inline void push(ir_node *n) {
174 if (tos == ARR_LEN(stack)) {
175 int nlen = ARR_LEN(stack) * 2;
176 ARR_RESIZE(ir_node *, stack, nlen);
179 mark_irn_in_stack(n);
183 * Pop a node from the IR-node stack and return it.
185 static inline ir_node *pop(void) {
186 ir_node *n = stack[--tos];
187 mark_irn_not_in_stack(n);
192 * The nodes from tos up to n belong to the current loop.
193 * Removes them from the stack and adds them to the current loop.
195 static inline void pop_scc_to_loop(ir_node *n) {
201 set_irn_dfn(m, loop_node_cnt);
202 add_loop_node(current_loop, m);
203 set_irn_loop(m, current_loop);
207 /* GL ??? my last son is my grandson??? Removes cfloops with no
208 ir_nodes in them. Such loops have only another loop as son. (Why
209 can't they have two loops as sons? Does it never get that far? ) */
210 static void close_loop(ir_loop *l) {
211 int last = get_loop_n_elements(l) - 1;
212 loop_element lelement = get_loop_element(l, last);
213 ir_loop *last_son = lelement.son;
215 if (get_kind(last_son) == k_ir_loop &&
216 get_loop_n_elements(last_son) == 1) {
219 lelement = get_loop_element(last_son, 0);
221 if (get_kind(gson) == k_ir_loop) {
222 loop_element new_last_son;
224 gson->outer_loop = l;
225 new_last_son.son = gson;
226 l->children[last] = new_last_son;
228 /* the loop last_son is dead now, recover at least some memory */
229 DEL_ARR_F(last_son->children);
237 * Removes and unmarks all nodes up to n from the stack.
238 * The nodes must be visited once more to assign them to a scc.
240 static inline void pop_scc_unmark_visit(ir_node *n) {
245 set_irn_visited(m, 0);
249 /**********************************************************************/
250 /* The loop datastructure. **/
251 /**********************************************************************/
254 * Allocates a new loop as son of current_loop. Sets current_loop
255 * to the new loop and returns its father.
256 * The loop is allocated on the outermost_ir_graphs's obstack.
258 static ir_loop *new_loop(void) {
259 ir_loop *father = current_loop;
260 ir_loop *son = alloc_loop(father, outermost_ir_graph->obst);
262 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
267 /**********************************************************************/
268 /* Constructing and destructing the loop/backedge information. **/
269 /**********************************************************************/
271 /* Initialization steps. **********************************************/
274 * Allocates a scc_info for every Block node n.
275 * Clear the backedges for all nodes.
276 * Called from a walker.
278 static inline void init_node(ir_node *n, void *env) {
279 struct obstack *obst = env;
281 set_irn_link(n, new_scc_info(obst));
286 * Initializes the common global settings for the scc algorithm
288 static inline void init_scc_common(void) {
295 * Initializes the scc algorithm for the intraprocedural case.
296 * Add scc info to every block node.
298 static inline void init_scc(ir_graph *irg, struct obstack *obst) {
300 irg_walk_graph(irg, init_node, NULL, obst);
303 static inline void finish_scc(void)
308 #ifdef INTERPROCEDURAL_VIEW
310 * Initializes the scc algorithm for the interprocedural case.
312 static inline void init_ip_scc(struct obstack *obst) {
314 cg_walk(init_node, NULL, obst);
316 #if EXPERIMENTAL_CFLOOP_TREE
317 cg_walk(link_to_reg_end, NULL, NULL);
323 * Condition for breaking the recursion: n is the block
324 * that gets the initial control flow from the Start node.
326 static int is_outermost_StartBlock(ir_node *n) {
327 /* Test whether this is the outermost Start node. If so
328 recursion must end. */
330 if (get_Block_n_cfgpreds(n) == 1 &&
331 is_Start(skip_Proj(get_Block_cfgpred(n, 0))) &&
332 get_Block_cfgpred_block(n, 0) == n) {
338 /** Returns non-zero if n is a loop header, i.e., it is a Block node
339 * and has predecessors within the cfloop and out of the cfloop.
341 * @param n the block node to check
342 * @param root only needed for assertion.
344 static int is_head(ir_node *n, ir_node *root) {
346 int some_outof_loop = 0, some_in_loop = 0;
351 if (!is_outermost_StartBlock(n)) {
352 arity = get_Block_n_cfgpreds(n);
353 for (i = 0; i < arity; i++) {
354 ir_node *pred = get_Block_cfgpred_block(n, i);
355 /* ignore Bad control flow: it cannot happen */
358 if (is_backedge(n, i))
360 if (!irn_is_in_stack(pred)) {
363 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
368 return some_outof_loop & some_in_loop;
373 * Returns non-zero if n is possible loop head of an endless loop.
374 * I.e., it is a Block node and has only predecessors
377 * @param n the block node to check
378 * @param root only needed for assertion.
380 static int is_endless_head(ir_node *n, ir_node *root) {
382 int none_outof_loop = 1, some_in_loop = 0;
386 /* Test for legal loop header: Block, Phi, ... */
387 if (!is_outermost_StartBlock(n)) {
388 arity = get_Block_n_cfgpreds(n);
389 for (i = 0; i < arity; i++) {
390 ir_node *pred = get_Block_cfgpred_block(n, i);
391 /* ignore Bad control flow: it cannot happen */
394 if (is_backedge(n, i))
396 if (!irn_is_in_stack(pred)) {
399 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
404 return none_outof_loop && some_in_loop;
408 * Returns index of the predecessor with the smallest dfn number
409 * greater-equal than limit.
411 static int smallest_dfn_pred(ir_node *n, int limit) {
412 int i, index = -2, min = -1;
414 if (!is_outermost_StartBlock(n)) {
415 int arity = get_Block_n_cfgpreds(n);
416 for (i = 0; i < arity; i++) {
417 ir_node *pred = get_Block_cfgpred_block(n, i);
418 /* ignore Bad control flow: it cannot happen */
421 if (is_backedge(n, i) || !irn_is_in_stack(pred))
423 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
425 min = get_irn_dfn(pred);
433 * Returns index of the predecessor with the largest dfn number.
435 static int largest_dfn_pred(ir_node *n) {
436 int i, index = -2, max = -1;
438 if (!is_outermost_StartBlock(n)) {
439 int arity = get_Block_n_cfgpreds(n);
440 for (i = 0; i < arity; i++) {
441 ir_node *pred = get_Block_cfgpred_block(n, i);
442 /* ignore Bad control flow: it cannot happen */
445 if (is_backedge(n, i) || !irn_is_in_stack(pred))
447 if (get_irn_dfn(pred) > max) {
449 max = get_irn_dfn(pred);
457 * Searches the stack for possible loop heads. Tests these for backedges.
458 * If it finds a head with an unmarked backedge it marks this edge and
459 * returns the tail of the loop.
460 * If it finds no backedge returns NULL.
462 static ir_node *find_tail(ir_node *n) {
464 int i, res_index = -2;
466 m = stack[tos-1]; /* tos = top of stack */
468 res_index = smallest_dfn_pred(m, 0);
469 if ((res_index == -2) && /* no smallest dfn pred found. */
475 for (i = tos-2; i >= 0; --i) {
479 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
480 if (res_index == -2) /* no smallest dfn pred found. */
481 res_index = largest_dfn_pred(m);
483 if ((m == n) && (res_index == -2)) {
490 /* We should not walk past our selves on the stack: The upcoming nodes
491 are not in this loop. We assume a loop not reachable from Start. */
499 /* A dead loop not reachable from Start. */
500 for (i = tos-2; i >= 0; --i) {
502 if (is_endless_head(m, n)) {
503 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
504 if (res_index == -2) /* no smallest dfn pred found. */
505 res_index = largest_dfn_pred(m);
508 if (m == n) break; /* It's not an unreachable loop, either. */
510 //assert(0 && "no head found on stack");
513 assert(res_index > -2);
515 set_backedge(m, res_index);
516 return is_outermost_StartBlock(n) ? NULL : get_Block_cfgpred_block(m, res_index);
520 * returns non.zero if l is the outermost loop.
522 inline static int is_outermost_loop(ir_loop *l) {
523 return l == get_loop_outer_loop(l);
526 /*-----------------------------------------------------------*
527 * The core algorithm. *
528 *-----------------------------------------------------------*/
531 * Walks over all blocks of a graph
533 static void cfscc(ir_node *n) {
538 if (irn_visited_else_mark(n)) return;
540 /* Initialize the node */
541 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
542 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
543 set_irn_loop(n, NULL);
547 if (!is_outermost_StartBlock(n)) {
548 int arity = get_Block_n_cfgpreds(n);
550 for (i = 0; i < arity; i++) {
553 if (is_backedge(n, i))
555 m = get_Block_cfgpred_block(n, i);
556 /* ignore Bad control flow: it cannot happen */
561 if (irn_is_in_stack(m)) {
562 /* Uplink of m is smaller if n->m is a backedge.
563 Propagate the uplink to mark the cfloop. */
564 if (get_irn_uplink(m) < get_irn_uplink(n))
565 set_irn_uplink(n, get_irn_uplink(m));
570 if (get_irn_dfn(n) == get_irn_uplink(n)) {
571 /* This condition holds for
572 1) the node with the incoming backedge.
573 That is: We found a cfloop!
574 2) Straight line code, because no uplink has been propagated, so the
575 uplink still is the same as the dfn.
577 But n might not be a proper cfloop head for the analysis. Proper cfloop
578 heads are Block and Phi nodes. find_tail searches the stack for
579 Block's and Phi's and takes those nodes as cfloop heads for the current
580 cfloop instead and marks the incoming edge as backedge. */
582 ir_node *tail = find_tail(n);
584 /* We have a cfloop, that is no straight line code,
585 because we found a cfloop head!
586 Next actions: Open a new cfloop on the cfloop tree and
587 try to find inner cfloops */
589 #if NO_CFLOOPS_WITHOUT_HEAD
591 /* This is an adaption of the algorithm from fiasco / optscc to
592 * avoid cfloops without Block or Phi as first node. This should
593 * severely reduce the number of evaluations of nodes to detect
594 * a fixpoint in the heap analysis.
595 * Further it avoids cfloops without firm nodes that cause errors
596 * in the heap analyses. */
600 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
610 ir_loop *l = new_loop();
614 /* Remove the cfloop from the stack ... */
615 pop_scc_unmark_visit(n);
617 /* The current backedge has been marked, that is temporarily eliminated,
618 by find tail. Start the scc algorithm
619 anew on the subgraph thats left (the current cfloop without the backedge)
620 in order to find more inner cfloops. */
624 assert(irn_visited(n));
625 #if NO_CFLOOPS_WITHOUT_HEAD
630 /* AS: No cfloop head was found, that is we have straight line code.
631 Pop all nodes from the stack to the current cfloop. */
637 /* Constructs control flow backedge information for irg. */
638 int construct_cf_backedges(ir_graph *irg) {
639 ir_graph *rem = current_ir_graph;
641 ir_node *end = get_irg_end(irg);
645 assert(!get_interprocedural_view() &&
646 "use construct_ip_cf_backedges()");
649 current_ir_graph = irg;
650 outermost_ir_graph = irg;
653 init_scc(irg, &temp);
656 new_loop(); /* sets current_loop */
657 head_rem = current_loop; /* Just for assertion */
659 inc_irg_visited(irg);
661 /* walk over all blocks of the graph, including keep alives */
662 cfscc(get_irg_end_block(irg));
663 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
664 ir_node *el = get_End_keepalive(end, i);
669 obstack_free(&temp, NULL);
671 assert(head_rem == current_loop);
672 mature_loops(current_loop, irg->obst);
673 set_irg_loop(irg, current_loop);
674 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
675 assert(get_irg_loop(irg)->kind == k_ir_loop);
677 current_ir_graph = rem;
678 return max_loop_depth;
681 void assure_cf_loop(ir_graph *irg) {
682 irg_loopinfo_state state = get_irg_loopinfo_state(irg);
684 if (state != loopinfo_cf_consistent)
685 construct_cf_backedges(irg);
688 #ifdef INTERPROCEDURAL_VIEW
689 int construct_ip_cf_backedges (void) {
690 ir_graph *rem = current_ir_graph;
691 int rem_ipv = get_interprocedural_view();
695 assert(get_irp_ip_view_state() == ip_view_valid);
697 outermost_ir_graph = get_irp_main_irg();
703 new_loop(); /* sets current_loop */
704 set_interprocedural_view(1);
706 inc_max_irg_visited();
707 for (i = 0; i < get_irp_n_irgs(); i++)
708 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
710 /** We have to start the walk at the same nodes as cg_walk. **/
711 /* Walk starting at unreachable procedures. Only these
712 * have End blocks visible in interprocedural view. */
713 for (i = 0; i < get_irp_n_irgs(); i++) {
715 current_ir_graph = get_irp_irg(i);
717 sb = get_irg_start_block(current_ir_graph);
719 if ((get_Block_n_cfgpreds(sb) > 1) ||
720 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
722 cfscc(get_irg_end_block(current_ir_graph));
725 /* Check whether we walked all procedures: there could be procedures
726 with cyclic calls but no call from the outside. */
727 for (i = 0; i < get_irp_n_irgs(); i++) {
729 current_ir_graph = get_irp_irg(i);
731 /* Test start block: if inner procedure end and end block are not
732 * visible and therefore not marked. */
733 sb = get_irg_start_block(current_ir_graph);
734 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
737 /* Walk all endless cfloops in inner procedures.
738 * We recognize an inner procedure if the End node is not visited. */
739 for (i = 0; i < get_irp_n_irgs(); i++) {
741 current_ir_graph = get_irp_irg(i);
743 e = get_irg_end(current_ir_graph);
744 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
746 /* Don't visit the End node. */
747 for (j = 0; j < get_End_n_keepalives(e); j++) {
748 ir_node *el = get_End_keepalive(e, j);
749 if (is_Block(el)) cfscc(el);
754 set_irg_loop(outermost_ir_graph, current_loop);
755 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
756 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
758 obstack_free(&temp, NULL);
759 current_ir_graph = rem;
760 set_interprocedural_view(rem_ipv);
761 return max_loop_depth;
766 * Clear the intra- and the interprocedural
767 * backedge information pf a block.
769 static void reset_backedges(ir_node *block) {
772 assert(is_Block(block));
773 #ifdef INTERPROCEDURAL_VIEW
774 rem = get_interprocedural_view();
775 set_interprocedural_view(1);
776 clear_backedges(block);
777 set_interprocedural_view(0);
778 clear_backedges(block);
779 set_interprocedural_view(rem);
782 clear_backedges(block);
787 * Reset all backedges of the first block of
788 * a loop as well as all loop info for all nodes of this loop.
789 * Recurse into all nested loops.
791 static void loop_reset_backedges(ir_loop *l) {
793 reset_backedges(get_loop_node(l, 0));
794 for (i = 0; i < get_loop_n_nodes(l); ++i)
795 set_irn_loop(get_loop_node(l, i), NULL);
796 for (i = 0; i < get_loop_n_sons(l); ++i) {
797 loop_reset_backedges(get_loop_son(l, i));
801 /* Removes all cfloop information.
802 Resets all backedges */
803 void free_cfloop_information(ir_graph *irg) {
804 ir_loop *loop = get_irg_loop(irg);
806 loop_reset_backedges(loop);
807 set_irg_loop(irg, NULL);
809 set_irg_loopinfo_state(irg, loopinfo_none);
810 /* We cannot free the cfloop nodes, they are on the obstack. */
814 void free_all_cfloop_information(void) {
816 #ifdef INTERPROCEDURAL_VIEW
817 int rem = get_interprocedural_view();
818 set_interprocedural_view(1); /* To visit all filter nodes */
820 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
821 free_cfloop_information(get_irp_irg(i));
823 #ifdef INTERPROCEDURAL_VIEW
824 set_interprocedural_view(rem);