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);
166 static void finish_stack(void)
173 * Push a node n onto the IR-node stack.
175 static INLINE void push(ir_node *n) {
176 if (tos == ARR_LEN(stack)) {
177 int nlen = ARR_LEN(stack) * 2;
178 ARR_RESIZE(ir_node *, stack, nlen);
181 mark_irn_in_stack(n);
185 * Pop a node from the IR-node stack and return it.
187 static INLINE ir_node *pop(void) {
188 ir_node *n = stack[--tos];
189 mark_irn_not_in_stack(n);
194 * The nodes from tos up to n belong to the current loop.
195 * Removes them from the stack and adds them to the current loop.
197 static INLINE void pop_scc_to_loop(ir_node *n) {
203 set_irn_dfn(m, loop_node_cnt);
204 add_loop_node(current_loop, m);
205 set_irn_loop(m, current_loop);
209 /* GL ??? my last son is my grandson??? Removes cfloops with no
210 ir_nodes in them. Such loops have only another loop as son. (Why
211 can't they have two loops as sons? Does it never get that far? ) */
212 static void close_loop(ir_loop *l) {
213 int last = get_loop_n_elements(l) - 1;
214 loop_element lelement = get_loop_element(l, last);
215 ir_loop *last_son = lelement.son;
217 if (get_kind(last_son) == k_ir_loop &&
218 get_loop_n_elements(last_son) == 1) {
221 lelement = get_loop_element(last_son, 0);
223 if (get_kind(gson) == k_ir_loop) {
224 loop_element new_last_son;
226 gson->outer_loop = l;
227 new_last_son.son = gson;
228 l->children[last] = new_last_son;
230 /* the loop last_son is dead now, recover at least some memory */
231 DEL_ARR_F(last_son->children);
239 * Removes and unmarks all nodes up to n from the stack.
240 * The nodes must be visited once more to assign them to a scc.
242 static INLINE void pop_scc_unmark_visit(ir_node *n) {
247 set_irn_visited(m, 0);
251 /**********************************************************************/
252 /* The loop datastructure. **/
253 /**********************************************************************/
256 * Allocates a new loop as son of current_loop. Sets current_loop
257 * to the new loop and returns its father.
258 * The loop is allocated on the outermost_ir_graphs's obstack.
260 static ir_loop *new_loop(void) {
261 ir_loop *father = current_loop;
262 ir_loop *son = alloc_loop(father, outermost_ir_graph->obst);
264 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
269 /**********************************************************************/
270 /* Constructing and destructing the loop/backedge information. **/
271 /**********************************************************************/
273 /* Initialization steps. **********************************************/
276 * Allocates a scc_info for every Block node n.
277 * Clear the backedges for all nodes.
278 * Called from a walker.
280 static INLINE void init_node(ir_node *n, void *env) {
281 struct obstack *obst = env;
283 set_irn_link(n, new_scc_info(obst));
288 * Initializes the common global settings for the scc algorithm
290 static INLINE void init_scc_common(void) {
297 * Initializes the scc algorithm for the intraprocedural case.
298 * Add scc info to every block node.
300 static INLINE void init_scc(ir_graph *irg, struct obstack *obst) {
302 irg_walk_graph(irg, init_node, NULL, obst);
305 static INLINE void finish_scc(void)
310 #ifdef INTERPROCEDURAL_VIEW
312 * Initializes the scc algorithm for the interprocedural case.
314 static INLINE void init_ip_scc(struct obstack *obst) {
316 cg_walk(init_node, NULL, obst);
318 #if EXPERIMENTAL_CFLOOP_TREE
319 cg_walk(link_to_reg_end, NULL, NULL);
325 * Condition for breaking the recursion: n is the block
326 * that gets the initial control flow from the Start node.
328 static int is_outermost_StartBlock(ir_node *n) {
329 /* Test whether this is the outermost Start node. If so
330 recursion must end. */
332 if (get_Block_n_cfgpreds(n) == 1 &&
333 is_Start(skip_Proj(get_Block_cfgpred(n, 0))) &&
334 get_Block_cfgpred_block(n, 0) == n) {
340 /** Returns non-zero if n is a loop header, i.e., it is a Block node
341 * and has predecessors within the cfloop and out of the cfloop.
343 * @param n the block node to check
344 * @param root only needed for assertion.
346 static int is_head(ir_node *n, ir_node *root) {
348 int some_outof_loop = 0, some_in_loop = 0;
352 if (!is_outermost_StartBlock(n)) {
353 arity = get_Block_n_cfgpreds(n);
354 for (i = 0; i < arity; i++) {
355 ir_node *pred = get_Block_cfgpred_block(n, i);
356 /* ignore Bad control flow: it cannot happen */
359 if (is_backedge(n, i))
361 if (!irn_is_in_stack(pred)) {
364 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
369 return some_outof_loop & some_in_loop;
374 * Returns non-zero if n is possible loop head of an endless loop.
375 * I.e., it is a Block node and has only predecessors
378 * @param n the block node to check
379 * @param root only needed for assertion.
381 static int is_endless_head(ir_node *n, ir_node *root) {
383 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(n)) return;
541 /* Initialize the node */
542 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
543 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
544 set_irn_loop(n, NULL);
548 if (!is_outermost_StartBlock(n)) {
549 int arity = get_Block_n_cfgpreds(n);
551 for (i = 0; i < arity; i++) {
554 if (is_backedge(n, i))
556 m = get_Block_cfgpred_block(n, i);
557 /* ignore Bad control flow: it cannot happen */
562 if (irn_is_in_stack(m)) {
563 /* Uplink of m is smaller if n->m is a backedge.
564 Propagate the uplink to mark the cfloop. */
565 if (get_irn_uplink(m) < get_irn_uplink(n))
566 set_irn_uplink(n, get_irn_uplink(m));
571 if (get_irn_dfn(n) == get_irn_uplink(n)) {
572 /* This condition holds for
573 1) the node with the incoming backedge.
574 That is: We found a cfloop!
575 2) Straight line code, because no uplink has been propagated, so the
576 uplink still is the same as the dfn.
578 But n might not be a proper cfloop head for the analysis. Proper cfloop
579 heads are Block and Phi nodes. find_tail searches the stack for
580 Block's and Phi's and takes those nodes as cfloop heads for the current
581 cfloop instead and marks the incoming edge as backedge. */
583 ir_node *tail = find_tail(n);
585 /* We have a cfloop, that is no straight line code,
586 because we found a cfloop head!
587 Next actions: Open a new cfloop on the cfloop tree and
588 try to find inner cfloops */
590 #if NO_CFLOOPS_WITHOUT_HEAD
592 /* This is an adaption of the algorithm from fiasco / optscc to
593 * avoid cfloops without Block or Phi as first node. This should
594 * severely reduce the number of evaluations of nodes to detect
595 * a fixpoint in the heap analysis.
596 * Further it avoids cfloops without firm nodes that cause errors
597 * in the heap analyses. */
601 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
611 ir_loop *l = new_loop();
615 /* Remove the cfloop from the stack ... */
616 pop_scc_unmark_visit(n);
618 /* The current backedge has been marked, that is temporarily eliminated,
619 by find tail. Start the scc algorithm
620 anew on the subgraph thats left (the current cfloop without the backedge)
621 in order to find more inner cfloops. */
625 assert(irn_visited(n));
626 #if NO_CFLOOPS_WITHOUT_HEAD
631 /* AS: No cfloop head was found, that is we have straight line code.
632 Pop all nodes from the stack to the current cfloop. */
638 /* Constructs control flow backedge information for irg. */
639 int construct_cf_backedges(ir_graph *irg) {
640 ir_graph *rem = current_ir_graph;
642 ir_node *end = get_irg_end(irg);
646 assert(!get_interprocedural_view() &&
647 "use construct_ip_cf_backedges()");
650 current_ir_graph = irg;
651 outermost_ir_graph = irg;
654 init_scc(irg, &temp);
657 new_loop(); /* sets current_loop */
658 head_rem = current_loop; /* Just for assertion */
660 inc_irg_visited(irg);
662 /* walk over all blocks of the graph, including keep alives */
663 cfscc(get_irg_end_block(irg));
664 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
665 ir_node *el = get_End_keepalive(end, i);
670 obstack_free(&temp, NULL);
672 assert(head_rem == current_loop);
673 mature_loops(current_loop, irg->obst);
674 set_irg_loop(irg, current_loop);
675 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
676 assert(get_irg_loop(irg)->kind == k_ir_loop);
678 current_ir_graph = rem;
679 return max_loop_depth;
682 void assure_cf_loop(ir_graph *irg) {
683 irg_loopinfo_state state = get_irg_loopinfo_state(irg);
685 if (state != loopinfo_cf_consistent)
686 construct_cf_backedges(irg);
689 #ifdef INTERPROCEDURAL_VIEW
690 int construct_ip_cf_backedges (void) {
691 ir_graph *rem = current_ir_graph;
692 int rem_ipv = get_interprocedural_view();
696 assert(get_irp_ip_view_state() == ip_view_valid);
698 outermost_ir_graph = get_irp_main_irg();
704 new_loop(); /* sets current_loop */
705 set_interprocedural_view(1);
707 inc_max_irg_visited();
708 for (i = 0; i < get_irp_n_irgs(); i++)
709 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
711 /** We have to start the walk at the same nodes as cg_walk. **/
712 /* Walk starting at unreachable procedures. Only these
713 * have End blocks visible in interprocedural view. */
714 for (i = 0; i < get_irp_n_irgs(); i++) {
716 current_ir_graph = get_irp_irg(i);
718 sb = get_irg_start_block(current_ir_graph);
720 if ((get_Block_n_cfgpreds(sb) > 1) ||
721 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
723 cfscc(get_irg_end_block(current_ir_graph));
726 /* Check whether we walked all procedures: there could be procedures
727 with cyclic calls but no call from the outside. */
728 for (i = 0; i < get_irp_n_irgs(); i++) {
730 current_ir_graph = get_irp_irg(i);
732 /* Test start block: if inner procedure end and end block are not
733 * visible and therefore not marked. */
734 sb = get_irg_start_block(current_ir_graph);
735 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
738 /* Walk all endless cfloops in inner procedures.
739 * We recognize an inner procedure if the End node is not visited. */
740 for (i = 0; i < get_irp_n_irgs(); i++) {
742 current_ir_graph = get_irp_irg(i);
744 e = get_irg_end(current_ir_graph);
745 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
747 /* Don't visit the End node. */
748 for (j = 0; j < get_End_n_keepalives(e); j++) {
749 ir_node *el = get_End_keepalive(e, j);
750 if (is_Block(el)) cfscc(el);
755 set_irg_loop(outermost_ir_graph, current_loop);
756 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
757 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
759 obstack_free(&temp, NULL);
760 current_ir_graph = rem;
761 set_interprocedural_view(rem_ipv);
762 return max_loop_depth;
767 * Clear the intra- and the interprocedural
768 * backedge information pf a block.
770 static void reset_backedges(ir_node *block) {
773 assert(is_Block(block));
774 #ifdef INTERPROCEDURAL_VIEW
775 rem = get_interprocedural_view();
776 set_interprocedural_view(1);
777 clear_backedges(block);
778 set_interprocedural_view(0);
779 clear_backedges(block);
780 set_interprocedural_view(rem);
783 clear_backedges(block);
788 * Reset all backedges of the first block of
789 * a loop as well as all loop info for all nodes of this loop.
790 * Recurse into all nested loops.
792 static void loop_reset_backedges(ir_loop *l) {
794 reset_backedges(get_loop_node(l, 0));
795 for (i = 0; i < get_loop_n_nodes(l); ++i)
796 set_irn_loop(get_loop_node(l, i), NULL);
797 for (i = 0; i < get_loop_n_sons(l); ++i) {
798 loop_reset_backedges(get_loop_son(l, i));
802 /* Removes all cfloop information.
803 Resets all backedges */
804 void free_cfloop_information(ir_graph *irg) {
805 ir_loop *loop = get_irg_loop(irg);
807 loop_reset_backedges(loop);
808 set_irg_loop(irg, NULL);
810 set_irg_loopinfo_state(irg, loopinfo_none);
811 /* We cannot free the cfloop nodes, they are on the obstack. */
815 void free_all_cfloop_information(void) {
817 #ifdef INTERPROCEDURAL_VIEW
818 int rem = get_interprocedural_view();
819 set_interprocedural_view(1); /* To visit all filter nodes */
821 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
822 free_cfloop_information(get_irp_irg(i));
824 #ifdef INTERPROCEDURAL_VIEW
825 set_interprocedural_view(rem);