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
35 #include "irgraph_t.h"
42 #define NO_CFLOOPS_WITHOUT_HEAD 1
44 /** The outermost graph the scc is computed for */
45 static ir_graph *outermost_ir_graph;
46 /** Current cfloop construction is working on. */
47 static ir_loop *current_loop;
48 /** Counts the number of allocated cfloop nodes.
49 * Each cfloop node gets a unique number.
50 * @todo What for? ev. remove.
52 static int loop_node_cnt = 0;
53 /** Counter to generate depth first numbering of visited nodes. */
54 static int current_dfn = 1;
56 static int max_loop_depth = 0;
58 void link_to_reg_end(ir_node *n, void *env);
60 /**********************************************************************/
61 /* Node attributes **/
62 /**********************************************************************/
64 /**********************************************************************/
65 /* Node attributes needed for the construction. **/
66 /**********************************************************************/
69 * The SCC info. Additional fields for an ir-node needed for the
72 typedef struct scc_info {
73 int in_stack; /**< Marks whether node is on the stack. */
74 int dfn; /**< Depth first search number. */
75 int uplink; /**< dfn number of ancestor. */
78 /** Allocate a new scc_info on the given obstack */
79 static inline scc_info *new_scc_info(struct obstack *obst) {
80 return OALLOCZ(obst, scc_info);
84 * Marks the node n to be on the stack.
86 static inline void mark_irn_in_stack(ir_node *n) {
87 scc_info *info = get_irn_link(n);
92 * Marks the node n to be not on the stack.
94 static inline void mark_irn_not_in_stack(ir_node *n) {
95 scc_info *info = get_irn_link(n);
100 * Returns whether node n is on the stack.
102 static inline int irn_is_in_stack(ir_node *n) {
103 scc_info *info = get_irn_link(n);
104 return info->in_stack;
108 * Sets node n uplink value.
110 static inline void set_irn_uplink(ir_node *n, int uplink) {
111 scc_info *info = get_irn_link(n);
112 info->uplink = uplink;
116 * Return node n uplink value.
118 static inline int get_irn_uplink(ir_node *n) {
119 scc_info *info = get_irn_link(n);
124 * Sets node n dfn value.
126 static inline void set_irn_dfn(ir_node *n, int dfn) {
127 scc_info *info = get_irn_link(n);
132 * Returns node n dfn value.
134 static inline int get_irn_dfn(ir_node *n) {
135 scc_info *info = get_irn_link(n);
139 /**********************************************************************/
141 /**********************************************************************/
143 /** An IR-node stack */
144 static ir_node **stack = NULL;
145 /** The top (index) of the IR-node stack */
149 * Initializes the IR-node stack
151 static inline void init_stack(void) {
153 ARR_RESIZE(ir_node *, stack, 1000);
155 stack = NEW_ARR_F(ir_node *, 1000);
160 static void finish_stack(void)
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 static inline void finish_scc(void)
304 #ifdef INTERPROCEDURAL_VIEW
306 * Initializes the scc algorithm for the interprocedural case.
308 static inline void init_ip_scc(struct obstack *obst) {
310 cg_walk(init_node, NULL, obst);
312 #if EXPERIMENTAL_CFLOOP_TREE
313 cg_walk(link_to_reg_end, NULL, NULL);
319 * Condition for breaking the recursion: n is the block
320 * that gets the initial control flow from the Start node.
322 static int is_outermost_StartBlock(ir_node *n) {
323 /* Test whether this is the outermost Start node. If so
324 recursion must end. */
326 if (get_Block_n_cfgpreds(n) == 1 &&
327 is_Start(skip_Proj(get_Block_cfgpred(n, 0))) &&
328 get_Block_cfgpred_block(n, 0) == n) {
334 /** Returns non-zero if n is a loop header, i.e., it is a Block node
335 * and has predecessors within the cfloop and out of the cfloop.
337 * @param n the block node to check
338 * @param root only needed for assertion.
340 static int is_head(ir_node *n, ir_node *root) {
342 int some_outof_loop = 0, some_in_loop = 0;
347 if (!is_outermost_StartBlock(n)) {
348 arity = get_Block_n_cfgpreds(n);
349 for (i = 0; i < arity; i++) {
350 ir_node *pred = get_Block_cfgpred_block(n, i);
351 /* ignore Bad control flow: it cannot happen */
354 if (is_backedge(n, i))
356 if (!irn_is_in_stack(pred)) {
359 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
364 return some_outof_loop & some_in_loop;
369 * Returns non-zero if n is possible loop head of an endless loop.
370 * I.e., it is a Block node and has only predecessors
373 * @param n the block node to check
374 * @param root only needed for assertion.
376 static int is_endless_head(ir_node *n, ir_node *root) {
378 int none_outof_loop = 1, some_in_loop = 0;
382 /* Test for legal loop header: Block, Phi, ... */
383 if (!is_outermost_StartBlock(n)) {
384 arity = get_Block_n_cfgpreds(n);
385 for (i = 0; i < arity; i++) {
386 ir_node *pred = get_Block_cfgpred_block(n, i);
387 /* ignore Bad control flow: it cannot happen */
390 if (is_backedge(n, i))
392 if (!irn_is_in_stack(pred)) {
395 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
400 return none_outof_loop && some_in_loop;
404 * Returns index of the predecessor with the smallest dfn number
405 * greater-equal than limit.
407 static int smallest_dfn_pred(ir_node *n, int limit) {
408 int i, index = -2, min = -1;
410 if (!is_outermost_StartBlock(n)) {
411 int arity = get_Block_n_cfgpreds(n);
412 for (i = 0; i < arity; i++) {
413 ir_node *pred = get_Block_cfgpred_block(n, i);
414 /* ignore Bad control flow: it cannot happen */
417 if (is_backedge(n, i) || !irn_is_in_stack(pred))
419 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
421 min = get_irn_dfn(pred);
429 * Returns index of the predecessor with the largest dfn number.
431 static int largest_dfn_pred(ir_node *n) {
432 int i, index = -2, max = -1;
434 if (!is_outermost_StartBlock(n)) {
435 int arity = get_Block_n_cfgpreds(n);
436 for (i = 0; i < arity; i++) {
437 ir_node *pred = get_Block_cfgpred_block(n, i);
438 /* ignore Bad control flow: it cannot happen */
441 if (is_backedge(n, i) || !irn_is_in_stack(pred))
443 if (get_irn_dfn(pred) > max) {
445 max = get_irn_dfn(pred);
453 * Searches the stack for possible loop heads. Tests these for backedges.
454 * If it finds a head with an unmarked backedge it marks this edge and
455 * returns the tail of the loop.
456 * If it finds no backedge returns NULL.
458 static ir_node *find_tail(ir_node *n) {
460 int i, res_index = -2;
462 m = stack[tos-1]; /* tos = top of stack */
464 res_index = smallest_dfn_pred(m, 0);
465 if ((res_index == -2) && /* no smallest dfn pred found. */
471 for (i = tos-2; i >= 0; --i) {
475 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
476 if (res_index == -2) /* no smallest dfn pred found. */
477 res_index = largest_dfn_pred(m);
479 if ((m == n) && (res_index == -2)) {
486 /* We should not walk past our selves on the stack: The upcoming nodes
487 are not in this loop. We assume a loop not reachable from Start. */
495 /* A dead loop not reachable from Start. */
496 for (i = tos-2; i >= 0; --i) {
498 if (is_endless_head(m, n)) {
499 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
500 if (res_index == -2) /* no smallest dfn pred found. */
501 res_index = largest_dfn_pred(m);
504 if (m == n) break; /* It's not an unreachable loop, either. */
506 //assert(0 && "no head found on stack");
509 assert(res_index > -2);
511 set_backedge(m, res_index);
512 return is_outermost_StartBlock(n) ? NULL : get_Block_cfgpred_block(m, res_index);
516 * returns non.zero if l is the outermost loop.
518 inline static int is_outermost_loop(ir_loop *l) {
519 return l == get_loop_outer_loop(l);
522 /*-----------------------------------------------------------*
523 * The core algorithm. *
524 *-----------------------------------------------------------*/
527 * Walks over all blocks of a graph
529 static void cfscc(ir_node *n) {
534 if (irn_visited_else_mark(n)) return;
536 /* Initialize the node */
537 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
538 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
539 set_irn_loop(n, NULL);
543 if (!is_outermost_StartBlock(n)) {
544 int arity = get_Block_n_cfgpreds(n);
546 for (i = 0; i < arity; i++) {
549 if (is_backedge(n, i))
551 m = get_Block_cfgpred_block(n, i);
552 /* ignore Bad control flow: it cannot happen */
557 if (irn_is_in_stack(m)) {
558 /* Uplink of m is smaller if n->m is a backedge.
559 Propagate the uplink to mark the cfloop. */
560 if (get_irn_uplink(m) < get_irn_uplink(n))
561 set_irn_uplink(n, get_irn_uplink(m));
566 if (get_irn_dfn(n) == get_irn_uplink(n)) {
567 /* This condition holds for
568 1) the node with the incoming backedge.
569 That is: We found a cfloop!
570 2) Straight line code, because no uplink has been propagated, so the
571 uplink still is the same as the dfn.
573 But n might not be a proper cfloop head for the analysis. Proper cfloop
574 heads are Block and Phi nodes. find_tail searches the stack for
575 Block's and Phi's and takes those nodes as cfloop heads for the current
576 cfloop instead and marks the incoming edge as backedge. */
578 ir_node *tail = find_tail(n);
580 /* We have a cfloop, that is no straight line code,
581 because we found a cfloop head!
582 Next actions: Open a new cfloop on the cfloop tree and
583 try to find inner cfloops */
585 #if NO_CFLOOPS_WITHOUT_HEAD
587 /* This is an adaption of the algorithm from fiasco / optscc to
588 * avoid cfloops without Block or Phi as first node. This should
589 * severely reduce the number of evaluations of nodes to detect
590 * a fixpoint in the heap analysis.
591 * Further it avoids cfloops without firm nodes that cause errors
592 * in the heap analyses. */
596 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
606 ir_loop *l = new_loop();
610 /* Remove the cfloop from the stack ... */
611 pop_scc_unmark_visit(n);
613 /* The current backedge has been marked, that is temporarily eliminated,
614 by find tail. Start the scc algorithm
615 anew on the subgraph thats left (the current cfloop without the backedge)
616 in order to find more inner cfloops. */
620 assert(irn_visited(n));
621 #if NO_CFLOOPS_WITHOUT_HEAD
626 /* AS: No cfloop head was found, that is we have straight line code.
627 Pop all nodes from the stack to the current cfloop. */
633 /* Constructs control flow backedge information for irg. */
634 int construct_cf_backedges(ir_graph *irg) {
635 ir_graph *rem = current_ir_graph;
637 ir_node *end = get_irg_end(irg);
641 assert(!get_interprocedural_view() &&
642 "use construct_ip_cf_backedges()");
645 current_ir_graph = irg;
646 outermost_ir_graph = irg;
649 init_scc(irg, &temp);
652 new_loop(); /* sets current_loop */
653 head_rem = current_loop; /* Just for assertion */
655 inc_irg_visited(irg);
657 /* walk over all blocks of the graph, including keep alives */
658 cfscc(get_irg_end_block(irg));
659 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
660 ir_node *el = get_End_keepalive(end, i);
665 obstack_free(&temp, NULL);
667 assert(head_rem == current_loop);
668 mature_loops(current_loop, irg->obst);
669 set_irg_loop(irg, current_loop);
670 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
671 assert(get_irg_loop(irg)->kind == k_ir_loop);
673 current_ir_graph = rem;
674 return max_loop_depth;
677 void assure_cf_loop(ir_graph *irg) {
678 irg_loopinfo_state state = get_irg_loopinfo_state(irg);
680 if (state != loopinfo_cf_consistent)
681 construct_cf_backedges(irg);
684 #ifdef INTERPROCEDURAL_VIEW
685 int construct_ip_cf_backedges (void) {
686 ir_graph *rem = current_ir_graph;
687 int rem_ipv = get_interprocedural_view();
691 assert(get_irp_ip_view_state() == ip_view_valid);
693 outermost_ir_graph = get_irp_main_irg();
699 new_loop(); /* sets current_loop */
700 set_interprocedural_view(1);
702 inc_max_irg_visited();
703 for (i = 0; i < get_irp_n_irgs(); i++)
704 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
706 /** We have to start the walk at the same nodes as cg_walk. **/
707 /* Walk starting at unreachable procedures. Only these
708 * have End blocks visible in interprocedural view. */
709 for (i = 0; i < get_irp_n_irgs(); i++) {
711 current_ir_graph = get_irp_irg(i);
713 sb = get_irg_start_block(current_ir_graph);
715 if ((get_Block_n_cfgpreds(sb) > 1) ||
716 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
718 cfscc(get_irg_end_block(current_ir_graph));
721 /* Check whether we walked all procedures: there could be procedures
722 with cyclic calls but no call from the outside. */
723 for (i = 0; i < get_irp_n_irgs(); i++) {
725 current_ir_graph = get_irp_irg(i);
727 /* Test start block: if inner procedure end and end block are not
728 * visible and therefore not marked. */
729 sb = get_irg_start_block(current_ir_graph);
730 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
733 /* Walk all endless cfloops in inner procedures.
734 * We recognize an inner procedure if the End node is not visited. */
735 for (i = 0; i < get_irp_n_irgs(); i++) {
737 current_ir_graph = get_irp_irg(i);
739 e = get_irg_end(current_ir_graph);
740 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
742 /* Don't visit the End node. */
743 for (j = 0; j < get_End_n_keepalives(e); j++) {
744 ir_node *el = get_End_keepalive(e, j);
745 if (is_Block(el)) cfscc(el);
750 set_irg_loop(outermost_ir_graph, current_loop);
751 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
752 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
754 obstack_free(&temp, NULL);
755 current_ir_graph = rem;
756 set_interprocedural_view(rem_ipv);
757 return max_loop_depth;
762 * Clear the intra- and the interprocedural
763 * backedge information pf a block.
765 static void reset_backedges(ir_node *block) {
768 assert(is_Block(block));
769 #ifdef INTERPROCEDURAL_VIEW
770 rem = get_interprocedural_view();
771 set_interprocedural_view(1);
772 clear_backedges(block);
773 set_interprocedural_view(0);
774 clear_backedges(block);
775 set_interprocedural_view(rem);
778 clear_backedges(block);
783 * Reset all backedges of the first block of
784 * a loop as well as all loop info for all nodes of this loop.
785 * Recurse into all nested loops.
787 static void loop_reset_backedges(ir_loop *l) {
789 reset_backedges(get_loop_node(l, 0));
790 for (i = 0; i < get_loop_n_nodes(l); ++i)
791 set_irn_loop(get_loop_node(l, i), NULL);
792 for (i = 0; i < get_loop_n_sons(l); ++i) {
793 loop_reset_backedges(get_loop_son(l, i));
797 /* Removes all cfloop information.
798 Resets all backedges */
799 void free_cfloop_information(ir_graph *irg) {
800 ir_loop *loop = get_irg_loop(irg);
802 loop_reset_backedges(loop);
803 set_irg_loop(irg, NULL);
805 set_irg_loopinfo_state(irg, loopinfo_none);
806 /* We cannot free the cfloop nodes, they are on the obstack. */
810 void free_all_cfloop_information(void) {
812 #ifdef INTERPROCEDURAL_VIEW
813 int rem = get_interprocedural_view();
814 set_interprocedural_view(1); /* To visit all filter nodes */
816 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
817 free_cfloop_information(get_irp_irg(i));
819 #ifdef INTERPROCEDURAL_VIEW
820 set_interprocedural_view(rem);