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;
353 if (!is_outermost_StartBlock(n)) {
354 arity = get_Block_n_cfgpreds(n);
355 for (i = 0; i < arity; i++) {
356 ir_node *pred = get_Block_cfgpred_block(n, i);
357 /* ignore Bad control flow: it cannot happen */
360 if (is_backedge(n, i))
362 if (!irn_is_in_stack(pred)) {
365 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
370 return some_outof_loop & some_in_loop;
375 * Returns non-zero if n is possible loop head of an endless loop.
376 * I.e., it is a Block node and has only predecessors
379 * @param n the block node to check
380 * @param root only needed for assertion.
382 static int is_endless_head(ir_node *n, ir_node *root) {
384 int none_outof_loop = 1, some_in_loop = 0;
388 /* Test for legal loop header: Block, Phi, ... */
389 if (!is_outermost_StartBlock(n)) {
390 arity = get_Block_n_cfgpreds(n);
391 for (i = 0; i < arity; i++) {
392 ir_node *pred = get_Block_cfgpred_block(n, i);
393 /* ignore Bad control flow: it cannot happen */
396 if (is_backedge(n, i))
398 if (!irn_is_in_stack(pred)) {
401 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
406 return none_outof_loop && some_in_loop;
410 * Returns index of the predecessor with the smallest dfn number
411 * greater-equal than limit.
413 static int smallest_dfn_pred(ir_node *n, int limit) {
414 int i, index = -2, min = -1;
416 if (!is_outermost_StartBlock(n)) {
417 int arity = get_Block_n_cfgpreds(n);
418 for (i = 0; i < arity; i++) {
419 ir_node *pred = get_Block_cfgpred_block(n, i);
420 /* ignore Bad control flow: it cannot happen */
423 if (is_backedge(n, i) || !irn_is_in_stack(pred))
425 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
427 min = get_irn_dfn(pred);
435 * Returns index of the predecessor with the largest dfn number.
437 static int largest_dfn_pred(ir_node *n) {
438 int i, index = -2, max = -1;
440 if (!is_outermost_StartBlock(n)) {
441 int arity = get_Block_n_cfgpreds(n);
442 for (i = 0; i < arity; i++) {
443 ir_node *pred = get_Block_cfgpred_block(n, i);
444 /* ignore Bad control flow: it cannot happen */
447 if (is_backedge(n, i) || !irn_is_in_stack(pred))
449 if (get_irn_dfn(pred) > max) {
451 max = get_irn_dfn(pred);
459 * Searches the stack for possible loop heads. Tests these for backedges.
460 * If it finds a head with an unmarked backedge it marks this edge and
461 * returns the tail of the loop.
462 * If it finds no backedge returns NULL.
464 static ir_node *find_tail(ir_node *n) {
466 int i, res_index = -2;
468 m = stack[tos-1]; /* tos = top of stack */
470 res_index = smallest_dfn_pred(m, 0);
471 if ((res_index == -2) && /* no smallest dfn pred found. */
477 for (i = tos-2; i >= 0; --i) {
481 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
482 if (res_index == -2) /* no smallest dfn pred found. */
483 res_index = largest_dfn_pred(m);
485 if ((m == n) && (res_index == -2)) {
492 /* We should not walk past our selves on the stack: The upcoming nodes
493 are not in this loop. We assume a loop not reachable from Start. */
501 /* A dead loop not reachable from Start. */
502 for (i = tos-2; i >= 0; --i) {
504 if (is_endless_head(m, n)) {
505 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
506 if (res_index == -2) /* no smallest dfn pred found. */
507 res_index = largest_dfn_pred(m);
510 if (m == n) break; /* It's not an unreachable loop, either. */
512 //assert(0 && "no head found on stack");
515 assert(res_index > -2);
517 set_backedge(m, res_index);
518 return is_outermost_StartBlock(n) ? NULL : get_Block_cfgpred_block(m, res_index);
522 * returns non.zero if l is the outermost loop.
524 INLINE static int is_outermost_loop(ir_loop *l) {
525 return l == get_loop_outer_loop(l);
528 /*-----------------------------------------------------------*
529 * The core algorithm. *
530 *-----------------------------------------------------------*/
533 * Walks over all blocks of a graph
535 static void cfscc(ir_node *n) {
540 if (irn_visited_else_mark(n)) return;
542 /* Initialize the node */
543 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
544 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
545 set_irn_loop(n, NULL);
549 if (!is_outermost_StartBlock(n)) {
550 int arity = get_Block_n_cfgpreds(n);
552 for (i = 0; i < arity; i++) {
555 if (is_backedge(n, i))
557 m = get_Block_cfgpred_block(n, i);
558 /* ignore Bad control flow: it cannot happen */
563 if (irn_is_in_stack(m)) {
564 /* Uplink of m is smaller if n->m is a backedge.
565 Propagate the uplink to mark the cfloop. */
566 if (get_irn_uplink(m) < get_irn_uplink(n))
567 set_irn_uplink(n, get_irn_uplink(m));
572 if (get_irn_dfn(n) == get_irn_uplink(n)) {
573 /* This condition holds for
574 1) the node with the incoming backedge.
575 That is: We found a cfloop!
576 2) Straight line code, because no uplink has been propagated, so the
577 uplink still is the same as the dfn.
579 But n might not be a proper cfloop head for the analysis. Proper cfloop
580 heads are Block and Phi nodes. find_tail searches the stack for
581 Block's and Phi's and takes those nodes as cfloop heads for the current
582 cfloop instead and marks the incoming edge as backedge. */
584 ir_node *tail = find_tail(n);
586 /* We have a cfloop, that is no straight line code,
587 because we found a cfloop head!
588 Next actions: Open a new cfloop on the cfloop tree and
589 try to find inner cfloops */
591 #if NO_CFLOOPS_WITHOUT_HEAD
593 /* This is an adaption of the algorithm from fiasco / optscc to
594 * avoid cfloops without Block or Phi as first node. This should
595 * severely reduce the number of evaluations of nodes to detect
596 * a fixpoint in the heap analysis.
597 * Further it avoids cfloops without firm nodes that cause errors
598 * in the heap analyses. */
602 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
612 ir_loop *l = new_loop();
616 /* Remove the cfloop from the stack ... */
617 pop_scc_unmark_visit(n);
619 /* The current backedge has been marked, that is temporarily eliminated,
620 by find tail. Start the scc algorithm
621 anew on the subgraph thats left (the current cfloop without the backedge)
622 in order to find more inner cfloops. */
626 assert(irn_visited(n));
627 #if NO_CFLOOPS_WITHOUT_HEAD
632 /* AS: No cfloop head was found, that is we have straight line code.
633 Pop all nodes from the stack to the current cfloop. */
639 /* Constructs control flow backedge information for irg. */
640 int construct_cf_backedges(ir_graph *irg) {
641 ir_graph *rem = current_ir_graph;
643 ir_node *end = get_irg_end(irg);
647 assert(!get_interprocedural_view() &&
648 "use construct_ip_cf_backedges()");
651 current_ir_graph = irg;
652 outermost_ir_graph = irg;
655 init_scc(irg, &temp);
658 new_loop(); /* sets current_loop */
659 head_rem = current_loop; /* Just for assertion */
661 inc_irg_visited(irg);
663 /* walk over all blocks of the graph, including keep alives */
664 cfscc(get_irg_end_block(irg));
665 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
666 ir_node *el = get_End_keepalive(end, i);
671 obstack_free(&temp, NULL);
673 assert(head_rem == current_loop);
674 mature_loops(current_loop, irg->obst);
675 set_irg_loop(irg, current_loop);
676 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
677 assert(get_irg_loop(irg)->kind == k_ir_loop);
679 current_ir_graph = rem;
680 return max_loop_depth;
683 void assure_cf_loop(ir_graph *irg) {
684 irg_loopinfo_state state = get_irg_loopinfo_state(irg);
686 if (state != loopinfo_cf_consistent)
687 construct_cf_backedges(irg);
690 #ifdef INTERPROCEDURAL_VIEW
691 int construct_ip_cf_backedges (void) {
692 ir_graph *rem = current_ir_graph;
693 int rem_ipv = get_interprocedural_view();
697 assert(get_irp_ip_view_state() == ip_view_valid);
699 outermost_ir_graph = get_irp_main_irg();
705 new_loop(); /* sets current_loop */
706 set_interprocedural_view(1);
708 inc_max_irg_visited();
709 for (i = 0; i < get_irp_n_irgs(); i++)
710 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
712 /** We have to start the walk at the same nodes as cg_walk. **/
713 /* Walk starting at unreachable procedures. Only these
714 * have End blocks visible in interprocedural view. */
715 for (i = 0; i < get_irp_n_irgs(); i++) {
717 current_ir_graph = get_irp_irg(i);
719 sb = get_irg_start_block(current_ir_graph);
721 if ((get_Block_n_cfgpreds(sb) > 1) ||
722 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
724 cfscc(get_irg_end_block(current_ir_graph));
727 /* Check whether we walked all procedures: there could be procedures
728 with cyclic calls but no call from the outside. */
729 for (i = 0; i < get_irp_n_irgs(); i++) {
731 current_ir_graph = get_irp_irg(i);
733 /* Test start block: if inner procedure end and end block are not
734 * visible and therefore not marked. */
735 sb = get_irg_start_block(current_ir_graph);
736 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
739 /* Walk all endless cfloops in inner procedures.
740 * We recognize an inner procedure if the End node is not visited. */
741 for (i = 0; i < get_irp_n_irgs(); i++) {
743 current_ir_graph = get_irp_irg(i);
745 e = get_irg_end(current_ir_graph);
746 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
748 /* Don't visit the End node. */
749 for (j = 0; j < get_End_n_keepalives(e); j++) {
750 ir_node *el = get_End_keepalive(e, j);
751 if (is_Block(el)) cfscc(el);
756 set_irg_loop(outermost_ir_graph, current_loop);
757 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
758 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
760 obstack_free(&temp, NULL);
761 current_ir_graph = rem;
762 set_interprocedural_view(rem_ipv);
763 return max_loop_depth;
768 * Clear the intra- and the interprocedural
769 * backedge information pf a block.
771 static void reset_backedges(ir_node *block) {
774 assert(is_Block(block));
775 #ifdef INTERPROCEDURAL_VIEW
776 rem = get_interprocedural_view();
777 set_interprocedural_view(1);
778 clear_backedges(block);
779 set_interprocedural_view(0);
780 clear_backedges(block);
781 set_interprocedural_view(rem);
784 clear_backedges(block);
789 * Reset all backedges of the first block of
790 * a loop as well as all loop info for all nodes of this loop.
791 * Recurse into all nested loops.
793 static void loop_reset_backedges(ir_loop *l) {
795 reset_backedges(get_loop_node(l, 0));
796 for (i = 0; i < get_loop_n_nodes(l); ++i)
797 set_irn_loop(get_loop_node(l, i), NULL);
798 for (i = 0; i < get_loop_n_sons(l); ++i) {
799 loop_reset_backedges(get_loop_son(l, i));
803 /* Removes all cfloop information.
804 Resets all backedges */
805 void free_cfloop_information(ir_graph *irg) {
806 ir_loop *loop = get_irg_loop(irg);
808 loop_reset_backedges(loop);
809 set_irg_loop(irg, NULL);
811 set_irg_loopinfo_state(irg, loopinfo_none);
812 /* We cannot free the cfloop nodes, they are on the obstack. */
816 void free_all_cfloop_information(void) {
818 #ifdef INTERPROCEDURAL_VIEW
819 int rem = get_interprocedural_view();
820 set_interprocedural_view(1); /* To visit all filter nodes */
822 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
823 free_cfloop_information(get_irp_irg(i));
825 #ifdef INTERPROCEDURAL_VIEW
826 set_interprocedural_view(rem);