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
39 #include "irgraph_t.h"
46 #define NO_CFLOOPS_WITHOUT_HEAD 1
48 /** The outermost graph the scc is computed for */
49 static ir_graph *outermost_ir_graph;
50 /** Current cfloop construction is working on. */
51 static ir_loop *current_loop;
52 /** Counts the number of allocated cfloop nodes.
53 * Each cfloop node gets a unique number.
54 * @todo What for? ev. remove.
56 static int loop_node_cnt = 0;
57 /** Counter to generate depth first numbering of visited nodes. */
58 static int current_dfn = 1;
60 static int max_loop_depth = 0;
62 void link_to_reg_end(ir_node *n, void *env);
64 /**********************************************************************/
65 /* Node attributes **/
66 /**********************************************************************/
68 /**********************************************************************/
69 /* Node attributes needed for the construction. **/
70 /**********************************************************************/
73 * The SCC info. Additional fields for an ir-node needed for the
76 typedef struct scc_info {
77 int in_stack; /**< Marks whether node is on the stack. */
78 int dfn; /**< Depth first search number. */
79 int uplink; /**< dfn number of ancestor. */
82 /** Allocate a new scc_info on the given obstack */
83 static INLINE scc_info *new_scc_info(struct obstack *obst) {
84 scc_info *info = obstack_alloc(obst, sizeof(*info));
85 memset(info, 0, sizeof(*info));
90 * Marks the node n to be on the stack.
92 static INLINE void mark_irn_in_stack(ir_node *n) {
93 scc_info *info = get_irn_link(n);
98 * Marks the node n to be not on the stack.
100 static INLINE void 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.
108 static INLINE int irn_is_in_stack(ir_node *n) {
109 scc_info *info = get_irn_link(n);
110 return info->in_stack;
114 * Sets node n uplink value.
116 static INLINE void set_irn_uplink(ir_node *n, int uplink) {
117 scc_info *info = get_irn_link(n);
118 info->uplink = uplink;
122 * Return node n uplink value.
124 static INLINE int get_irn_uplink(ir_node *n) {
125 scc_info *info = get_irn_link(n);
130 * Sets node n dfn value.
132 static INLINE void set_irn_dfn(ir_node *n, int dfn) {
133 scc_info *info = get_irn_link(n);
138 * Returns node n dfn value.
140 static INLINE int get_irn_dfn(ir_node *n) {
141 scc_info *info = get_irn_link(n);
145 /**********************************************************************/
147 /**********************************************************************/
149 /** An IR-node stack */
150 static ir_node **stack = NULL;
151 /** The top (index) of the IR-node stack */
155 * Initializes the IR-node stack
157 static INLINE void init_stack(void) {
159 ARR_RESIZE(ir_node *, stack, 1000);
161 stack = NEW_ARR_F(ir_node *, 1000);
167 * Push a node n onto the IR-node stack.
169 static INLINE void push(ir_node *n) {
170 if (tos == ARR_LEN(stack)) {
171 int nlen = ARR_LEN(stack) * 2;
172 ARR_RESIZE(ir_node *, stack, nlen);
175 mark_irn_in_stack(n);
179 * Pop a node from the IR-node stack and return it.
181 static INLINE ir_node *pop(void) {
182 ir_node *n = stack[--tos];
183 mark_irn_not_in_stack(n);
188 * The nodes from tos up to n belong to the current loop.
189 * Removes them from the stack and adds them to the current loop.
191 static INLINE void pop_scc_to_loop(ir_node *n) {
197 set_irn_dfn(m, loop_node_cnt);
198 add_loop_node(current_loop, m);
199 set_irn_loop(m, current_loop);
203 /* GL ??? my last son is my grandson??? Removes cfloops with no
204 ir_nodes in them. Such loops have only another loop as son. (Why
205 can't they have two loops as sons? Does it never get that far? ) */
206 static void close_loop(ir_loop *l) {
207 int last = get_loop_n_elements(l) - 1;
208 loop_element lelement = get_loop_element(l, last);
209 ir_loop *last_son = lelement.son;
211 if (get_kind(last_son) == k_ir_loop &&
212 get_loop_n_elements(last_son) == 1) {
215 lelement = get_loop_element(last_son, 0);
217 if (get_kind(gson) == k_ir_loop) {
218 loop_element new_last_son;
220 gson->outer_loop = l;
221 new_last_son.son = gson;
222 l->children[last] = new_last_son;
224 /* the loop last_son is dead now, recover at least some memory */
225 DEL_ARR_F(last_son->children);
233 * Removes and unmarks all nodes up to n from the stack.
234 * The nodes must be visited once more to assign them to a scc.
236 static INLINE void pop_scc_unmark_visit(ir_node *n) {
241 set_irn_visited(m, 0);
245 /**********************************************************************/
246 /* The loop datastructure. **/
247 /**********************************************************************/
250 * Allocates a new loop as son of current_loop. Sets current_loop
251 * to the new loop and returns its father.
252 * The loop is allocated on the outermost_ir_graphs's obstack.
254 static ir_loop *new_loop(void) {
255 ir_loop *father = current_loop;
256 ir_loop *son = alloc_loop(father, outermost_ir_graph->obst);
258 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
263 /**********************************************************************/
264 /* Constructing and destructing the loop/backedge information. **/
265 /**********************************************************************/
267 /* Initialization steps. **********************************************/
270 * Allocates a scc_info for every Block node n.
271 * Clear the backedges for all nodes.
272 * Called from a walker.
274 static INLINE void init_node(ir_node *n, void *env) {
275 struct obstack *obst = env;
277 set_irn_link(n, new_scc_info(obst));
282 * Initializes the common global settings for the scc algorithm
284 static INLINE void init_scc_common(void) {
291 * Initializes the scc algorithm for the intraprocedural case.
292 * Add scc info to every block node.
294 static INLINE void init_scc(ir_graph *irg, struct obstack *obst) {
296 irg_walk_graph(irg, init_node, NULL, obst);
299 #ifdef INTERPROCEDURAL_VIEW
301 * Initializes the scc algorithm for the interprocedural case.
303 static INLINE void init_ip_scc(struct obstack *obst) {
305 cg_walk(init_node, NULL, obst);
307 #if EXPERIMENTAL_CFLOOP_TREE
308 cg_walk(link_to_reg_end, NULL, NULL);
314 * Condition for breaking the recursion: n is the block
315 * that gets the initial control flow from the Start node.
317 static int is_outermost_StartBlock(ir_node *n) {
318 /* Test whether this is the outermost Start node. If so
319 recursion must end. */
321 if (get_Block_n_cfgpreds(n) == 1 &&
322 is_Start(skip_Proj(get_Block_cfgpred(n, 0))) &&
323 get_Block_cfgpred_block(n, 0) == n) {
329 /** Returns non-zero if n is a loop header, i.e., it is a Block node
330 * and has predecessors within the cfloop and out of the cfloop.
332 * @param n the block node to check
333 * @param root only needed for assertion.
335 static int is_head(ir_node *n, ir_node *root) {
337 int some_outof_loop = 0, some_in_loop = 0;
341 if (!is_outermost_StartBlock(n)) {
342 arity = get_Block_n_cfgpreds(n);
343 for (i = 0; i < arity; i++) {
344 ir_node *pred = get_Block_cfgpred_block(n, i);
345 if (is_backedge(n, i)) continue;
346 if (!irn_is_in_stack(pred)) {
349 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
354 return some_outof_loop & some_in_loop;
359 * Returns non-zero if n is possible loop head of an endless loop.
360 * I.e., it is a Block and has only predecessors
363 * @param n the block node to check
364 * @param root only needed for assertion.
366 static int is_endless_head(ir_node *n, ir_node *root) {
368 int some_outof_loop = 0, some_in_loop = 0;
371 /* Test for legal loop header: Block, Phi, ... */
372 if (!is_outermost_StartBlock(n)) {
373 arity = get_Block_n_cfgpreds(n);
374 for (i = 0; i < arity; i++) {
375 ir_node *pred = get_Block_cfgpred_block(n, i);
376 if (is_backedge(n, i))
378 if (!irn_is_in_stack(pred)) {
381 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
386 return !some_outof_loop && some_in_loop;
390 * Returns index of the predecessor with the smallest dfn number
391 * greater-equal than limit.
393 static int smallest_dfn_pred(ir_node *n, int limit) {
394 int i, index = -2, min = -1;
396 if (!is_outermost_StartBlock(n)) {
397 int arity = get_Block_n_cfgpreds(n);
398 for (i = 0; i < arity; i++) {
399 ir_node *pred = get_Block_cfgpred_block(n, i);
400 if (is_backedge(n, i) || !irn_is_in_stack(pred))
402 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
404 min = get_irn_dfn(pred);
412 * Returns index of the predecessor with the largest dfn number.
414 static int largest_dfn_pred(ir_node *n) {
415 int i, index = -2, max = -1;
417 if (!is_outermost_StartBlock(n)) {
418 int arity = get_Block_n_cfgpreds(n);
419 for (i = 0; i < arity; i++) {
420 ir_node *pred = get_Block_cfgpred_block(n, i);
421 if (is_backedge(n, i) || !irn_is_in_stack(pred))
423 if (get_irn_dfn(pred) > max) {
425 max = get_irn_dfn(pred);
433 * Searches the stack for possible loop heads. Tests these for backedges.
434 * If it finds a head with an unmarked backedge it marks this edge and
435 * returns the tail of the loop.
436 * If it finds no backedge returns NULL.
438 static ir_node *find_tail(ir_node *n) {
440 int i, res_index = -2;
442 m = stack[tos-1]; /* tos = top of stack */
444 res_index = smallest_dfn_pred(m, 0);
445 if ((res_index == -2) && /* no smallest dfn pred found. */
451 for (i = tos-2; i >= 0; --i) {
455 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
456 if (res_index == -2) /* no smallest dfn pred found. */
457 res_index = largest_dfn_pred(m);
459 if ((m == n) && (res_index == -2)) {
466 /* We should not walk past our selves on the stack: The upcoming nodes
467 are not in this loop. We assume a loop not reachable from Start. */
475 /* A dead loop not reachable from Start. */
476 for (i = tos-2; i >= 0; --i) {
478 if (is_endless_head (m, n)) {
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);
484 if (m == n) break; /* It's not an unreachable loop, either. */
486 //assert(0 && "no head found on stack");
489 assert(res_index > -2);
491 set_backedge(m, res_index);
492 return is_outermost_StartBlock(n) ? NULL : get_Block_cfgpred_block(m, res_index);
496 * returns non.zero if l is the outermost loop.
498 INLINE static int is_outermost_loop(ir_loop *l) {
499 return l == get_loop_outer_loop(l);
502 /*-----------------------------------------------------------*
503 * The core algorithm. *
504 *-----------------------------------------------------------*/
507 * Walks over all blocks of a graph
509 static void cfscc(ir_node *n) {
514 if (irn_visited(n)) return;
517 /* Initialize the node */
518 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
519 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
520 set_irn_loop(n, NULL);
524 if (!is_outermost_StartBlock(n)) {
525 int arity = get_irn_arity(n);
527 for (i = 0; i < arity; i++) {
530 if (is_backedge(n, i))
532 m = get_nodes_block(skip_Proj(get_irn_n(n, i)));
535 if (irn_is_in_stack(m)) {
536 /* Uplink of m is smaller if n->m is a backedge.
537 Propagate the uplink to mark the cfloop. */
538 if (get_irn_uplink(m) < get_irn_uplink(n))
539 set_irn_uplink(n, get_irn_uplink(m));
544 if (get_irn_dfn(n) == get_irn_uplink(n)) {
545 /* This condition holds for
546 1) the node with the incoming backedge.
547 That is: We found a cfloop!
548 2) Straight line code, because no uplink has been propagated, so the
549 uplink still is the same as the dfn.
551 But n might not be a proper cfloop head for the analysis. Proper cfloop
552 heads are Block and Phi nodes. find_tail searches the stack for
553 Block's and Phi's and takes those nodes as cfloop heads for the current
554 cfloop instead and marks the incoming edge as backedge. */
556 ir_node *tail = find_tail(n);
558 /* We have a cfloop, that is no straight line code,
559 because we found a cfloop head!
560 Next actions: Open a new cfloop on the cfloop tree and
561 try to find inner cfloops */
563 #if NO_CFLOOPS_WITHOUT_HEAD
565 /* This is an adaption of the algorithm from fiasco / optscc to
566 * avoid cfloops without Block or Phi as first node. This should
567 * severely reduce the number of evaluations of nodes to detect
568 * a fixpoint in the heap analysis.
569 * Further it avoids cfloops without firm nodes that cause errors
570 * in the heap analyses. */
574 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
584 ir_loop *l = new_loop();
588 /* Remove the cfloop from the stack ... */
589 pop_scc_unmark_visit (n);
591 /* The current backedge has been marked, that is temporarily eliminated,
592 by find tail. Start the scc algorithm
593 anew on the subgraph thats left (the current cfloop without the backedge)
594 in order to find more inner cfloops. */
598 assert(irn_visited(n));
599 #if NO_CFLOOPS_WITHOUT_HEAD
604 /* AS: No cfloop head was found, that is we have straight line code.
605 Pop all nodes from the stack to the current cfloop. */
611 /* Constructs control flow backedge information for irg. */
612 int construct_cf_backedges(ir_graph *irg) {
613 ir_graph *rem = current_ir_graph;
615 ir_node *end = get_irg_end(irg);
619 assert(!get_interprocedural_view() &&
620 "use construct_ip_cf_backedges()");
623 current_ir_graph = irg;
624 outermost_ir_graph = irg;
627 init_scc(irg, &temp);
630 new_loop(); /* sets current_loop */
631 head_rem = current_loop; /* Just for assertion */
633 inc_irg_visited(irg);
635 /* walk over all blocks of the graph, including keep alives */
636 cfscc(get_irg_end_block(irg));
637 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
638 ir_node *el = get_End_keepalive(end, i);
642 obstack_free(&temp, NULL);
644 assert(head_rem == current_loop);
645 mature_loops(current_loop, irg->obst);
646 set_irg_loop(irg, current_loop);
647 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
648 assert(get_irg_loop(irg)->kind == k_ir_loop);
650 current_ir_graph = rem;
651 return max_loop_depth;
654 void assure_cf_loop(ir_graph *irg) {
655 irg_loopinfo_state state = get_irg_loopinfo_state(irg);
657 if (state != loopinfo_cf_consistent)
658 construct_cf_backedges(irg);
661 #ifdef INTERPROCEDURAL_VIEW
662 int construct_ip_cf_backedges (void) {
663 ir_graph *rem = current_ir_graph;
664 int rem_ipv = get_interprocedural_view();
668 assert(get_irp_ip_view_state() == ip_view_valid);
670 outermost_ir_graph = get_irp_main_irg();
676 new_loop(); /* sets current_loop */
677 set_interprocedural_view(1);
679 inc_max_irg_visited();
680 for (i = 0; i < get_irp_n_irgs(); i++)
681 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
683 /** We have to start the walk at the same nodes as cg_walk. **/
684 /* Walk starting at unreachable procedures. Only these
685 * have End blocks visible in interprocedural view. */
686 for (i = 0; i < get_irp_n_irgs(); i++) {
688 current_ir_graph = get_irp_irg(i);
690 sb = get_irg_start_block(current_ir_graph);
692 if ((get_Block_n_cfgpreds(sb) > 1) ||
693 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
695 cfscc(get_irg_end_block(current_ir_graph));
698 /* Check whether we walked all procedures: there could be procedures
699 with cyclic calls but no call from the outside. */
700 for (i = 0; i < get_irp_n_irgs(); i++) {
702 current_ir_graph = get_irp_irg(i);
704 /* Test start block: if inner procedure end and end block are not
705 * visible and therefore not marked. */
706 sb = get_irg_start_block(current_ir_graph);
707 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
710 /* Walk all endless cfloops in inner procedures.
711 * We recognize an inner procedure if the End node is not visited. */
712 for (i = 0; i < get_irp_n_irgs(); i++) {
714 current_ir_graph = get_irp_irg(i);
716 e = get_irg_end(current_ir_graph);
717 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
719 /* Don't visit the End node. */
720 for (j = 0; j < get_End_n_keepalives(e); j++) {
721 ir_node *el = get_End_keepalive(e, j);
722 if (is_Block(el)) cfscc(el);
727 set_irg_loop(outermost_ir_graph, current_loop);
728 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
729 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
731 obstack_free(&temp, NULL);
732 current_ir_graph = rem;
733 set_interprocedural_view(rem_ipv);
734 return max_loop_depth;
739 * Clear the intra- and the interprocedural
740 * backedge information pf a block.
742 static void reset_backedges(ir_node *block) {
745 assert(is_Block(block));
746 #ifdef INTERPROCEDURAL_VIEW
747 rem = get_interprocedural_view();
748 set_interprocedural_view(1);
749 clear_backedges(block);
750 set_interprocedural_view(0);
751 clear_backedges(block);
752 set_interprocedural_view(rem);
755 clear_backedges(block);
760 * Reset all backedges of the first block of
761 * a loop as well as all loop info for all nodes of this loop.
762 * Recurse into all nested loops.
764 static void loop_reset_backedges(ir_loop *l) {
766 reset_backedges(get_loop_node(l, 0));
767 for (i = 0; i < get_loop_n_nodes(l); ++i)
768 set_irn_loop(get_loop_node(l, i), NULL);
769 for (i = 0; i < get_loop_n_sons(l); ++i) {
770 loop_reset_backedges(get_loop_son(l, i));
774 /* Removes all cfloop information.
775 Resets all backedges */
776 void free_cfloop_information(ir_graph *irg) {
777 ir_loop *loop = get_irg_loop(irg);
779 loop_reset_backedges(loop);
780 set_irg_loop(irg, NULL);
782 set_irg_loopinfo_state(irg, loopinfo_none);
783 /* We cannot free the cfloop nodes, they are on the obstack. */
787 void free_all_cfloop_information(void) {
789 #ifdef INTERPROCEDURAL_VIEW
790 int rem = get_interprocedural_view();
791 set_interprocedural_view(1); /* To visit all filter nodes */
793 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
794 free_cfloop_information(get_irp_irg(i));
796 #ifdef INTERPROCEDURAL_VIEW
797 set_interprocedural_view(rem);