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, *son;
257 father = current_loop;
259 son = obstack_alloc(outermost_ir_graph->obst, sizeof(*son));
260 memset(son, 0, sizeof(*son));
261 son->kind = k_ir_loop;
262 son->children = NEW_ARR_F(loop_element, 0);
266 son->outer_loop = father;
267 add_loop_son(father, son);
268 son->depth = father->depth+1;
269 if (son->depth > max_loop_depth)
270 max_loop_depth = son->depth;
271 } else { /* The root loop */
272 son->outer_loop = son;
277 son->loop_nr = get_irp_new_node_nr();
285 /**********************************************************************/
286 /* Constructing and destructing the loop/backedge information. **/
287 /**********************************************************************/
289 /* Initialization steps. **********************************************/
292 * Allocates a scc_info for every Block node n.
293 * Clear the backedges for all nodes.
294 * Called from a walker.
296 static INLINE void init_node(ir_node *n, void *env) {
297 struct obstack *obst = env;
299 set_irn_link(n, new_scc_info(obst));
304 * Initializes the common global settings for the scc algorithm
306 static INLINE void init_scc_common(void) {
313 * Initializes the scc algorithm for the intraprocedural case.
314 * Add scc info to every block node.
316 static INLINE void init_scc(ir_graph *irg, struct obstack *obst) {
318 irg_walk_graph(irg, init_node, NULL, obst);
321 #ifdef INTERPROCEDURAL_VIEW
323 * Initializes the scc algorithm for the interprocedural case.
325 static INLINE void init_ip_scc(struct obstack *obst) {
327 cg_walk(init_node, NULL, obst);
329 #if EXPERIMENTAL_CFLOOP_TREE
330 cg_walk(link_to_reg_end, NULL, NULL);
336 * Condition for breaking the recursion: n is the block
337 * that gets the initial control flow from the Start node.
339 static int is_outermost_StartBlock(ir_node *n) {
340 /* Test whether this is the outermost Start node. If so
341 recursion must end. */
343 if (get_Block_n_cfgpreds(n) == 1 &&
344 is_Start(skip_Proj(get_Block_cfgpred(n, 0))) &&
345 get_Block_cfgpred_block(n, 0) == n) {
351 /** Returns non-zero if n is a loop header, i.e., it is a Block node
352 * and has predecessors within the cfloop and out of the cfloop.
354 * @param n the block node to check
355 * @param root only needed for assertion.
357 static int is_head(ir_node *n, ir_node *root) {
359 int some_outof_loop = 0, some_in_loop = 0;
363 if (!is_outermost_StartBlock(n)) {
364 arity = get_irn_arity(n);
365 for (i = 0; i < arity; i++) {
366 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
367 if (is_backedge(n, i)) continue;
368 if (!irn_is_in_stack(pred)) {
371 if (get_irn_uplink(pred) < get_irn_uplink(root)) {
372 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
378 return some_outof_loop & some_in_loop;
383 * Returns non-zero if n is possible loop head of an endless loop.
384 * I.e., it is a Block, Phi or Filter node and has only predecessors
387 * @param n the block node to check
388 * @param root only needed for assertion.
390 static int is_endless_head(ir_node *n, ir_node *root) {
392 int some_outof_loop = 0, some_in_loop = 0;
395 /* Test for legal loop header: Block, Phi, ... */
396 if (!is_outermost_StartBlock(n)) {
397 arity = get_irn_arity(n);
398 for (i = 0; i < arity; i++) {
399 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
401 if (is_backedge(n, i))
403 if (!irn_is_in_stack(pred)) {
404 some_outof_loop = 1; //printf(" some out of loop ");
406 if (get_irn_uplink(pred) < get_irn_uplink(root)) {
407 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
413 return !some_outof_loop && some_in_loop;
417 * Returns index of the predecessor with the smallest dfn number
418 * greater-equal than limit.
420 static int smallest_dfn_pred(ir_node *n, int limit) {
421 int i, index = -2, min = -1;
423 if (!is_outermost_StartBlock(n)) {
424 int arity = get_irn_arity(n);
425 for (i = 0; i < arity; i++) {
426 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
427 if (is_backedge(n, i) || !irn_is_in_stack(pred))
429 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
431 min = get_irn_dfn(pred);
439 * Returns index of the predecessor with the largest dfn number.
441 static int largest_dfn_pred(ir_node *n) {
442 int i, index = -2, max = -1;
444 if (!is_outermost_StartBlock(n)) {
445 int arity = get_irn_arity(n);
446 for (i = 0; i < arity; i++) {
447 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
448 if (is_backedge(n, i) || !irn_is_in_stack(pred))
450 if (get_irn_dfn(pred) > max) {
452 max = get_irn_dfn(pred);
460 * Searches the stack for possible loop heads. Tests these for backedges.
461 * If it finds a head with an unmarked backedge it marks this edge and
462 * returns the tail of the loop.
463 * If it finds no backedge returns NULL.
465 static ir_node *find_tail(ir_node *n) {
467 int i, res_index = -2;
469 m = stack[tos-1]; /* tos = top of stack */
471 res_index = smallest_dfn_pred(m, 0);
472 if ((res_index == -2) && /* no smallest dfn pred found. */
478 for (i = tos-2; i >= 0; --i) {
482 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
483 if (res_index == -2) /* no smallest dfn pred found. */
484 res_index = largest_dfn_pred(m);
486 if ((m == n) && (res_index == -2)) {
493 /* We should not walk past our selves on the stack: The upcoming nodes
494 are not in this loop. We assume a loop not reachable from Start. */
502 /* A dead loop not reachable from Start. */
503 for (i = tos-2; i >= 0; --i) {
505 if (is_endless_head (m, n)) {
506 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
507 if (res_index == -2) /* no smallest dfn pred found. */
508 res_index = largest_dfn_pred (m);
511 if (m == n) break; /* It's not an unreachable loop, either. */
513 //assert(0 && "no head found on stack");
516 assert(res_index > -2);
518 set_backedge(m, res_index);
519 return is_outermost_StartBlock(n) ? NULL : get_nodes_block(skip_Proj(get_irn_n(m, res_index)));
523 * returns non.zero if l is the outermost loop.
525 INLINE static int is_outermost_loop(ir_loop *l) {
526 return l == get_loop_outer_loop(l);
529 /*-----------------------------------------------------------*
530 * The core algorithm. *
531 *-----------------------------------------------------------*/
534 * Walks over all blocks of a graph
536 static void cfscc(ir_node *n) {
541 if (irn_visited(n)) return;
544 /* Initialize the node */
545 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
546 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
547 set_irn_loop(n, NULL);
551 if (!is_outermost_StartBlock(n)) {
552 int arity = get_irn_arity(n);
554 for (i = 0; i < arity; i++) {
557 if (is_backedge(n, i))
559 m = get_nodes_block(skip_Proj(get_irn_n(n, i)));
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. */
639 * Mature all loops by removing the flexible arrays of a loop.
641 static void mature_loops(ir_loop *loop) {
642 loop_element *new_children = DUP_ARR_D(loop_element, outermost_ir_graph->obst, loop->children);
643 DEL_ARR_F(loop->children);
644 loop->children = new_children;
646 if (loop->n_sons > 0) {
647 /* we have child loops, mature them */
650 for (i = ARR_LEN(new_children) - 1; i >= 0; --i) {
651 loop_element child = new_children[i];
653 if (*child.kind == k_ir_loop) {
654 mature_loops(child.son);
660 /* Constructs control flow backedge information for irg. */
661 int construct_cf_backedges(ir_graph *irg) {
662 ir_graph *rem = current_ir_graph;
664 ir_node *end = get_irg_end(irg);
668 assert(!get_interprocedural_view() &&
669 "use construct_ip_cf_backedges()");
672 current_ir_graph = irg;
673 outermost_ir_graph = irg;
676 init_scc(irg, &temp);
679 new_loop(); /* sets current_loop */
680 head_rem = current_loop; /* Just for assertion */
682 inc_irg_visited(irg);
684 /* walk over all blocks of the graph, including keep alives */
685 cfscc(get_irg_end_block(irg));
686 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
687 ir_node *el = get_End_keepalive(end, i);
692 assert(head_rem == current_loop);
693 mature_loops(current_loop);
694 set_irg_loop(irg, current_loop);
695 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
696 assert(get_irg_loop(irg)->kind == k_ir_loop);
698 obstack_free(&temp, NULL);
699 current_ir_graph = rem;
700 return max_loop_depth;
703 #ifdef INTERPROCEDURAL_VIEW
704 int construct_ip_cf_backedges (void) {
705 ir_graph *rem = current_ir_graph;
706 int rem_ipv = get_interprocedural_view();
710 assert(get_irp_ip_view_state() == ip_view_valid);
712 outermost_ir_graph = get_irp_main_irg();
718 new_loop(); /* sets current_loop */
719 set_interprocedural_view(1);
721 inc_max_irg_visited();
722 for (i = 0; i < get_irp_n_irgs(); i++)
723 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
725 /** We have to start the walk at the same nodes as cg_walk. **/
726 /* Walk starting at unreachable procedures. Only these
727 * have End blocks visible in interprocedural view. */
728 for (i = 0; i < get_irp_n_irgs(); i++) {
730 current_ir_graph = get_irp_irg(i);
732 sb = get_irg_start_block(current_ir_graph);
734 if ((get_Block_n_cfgpreds(sb) > 1) ||
735 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
737 cfscc(get_irg_end_block(current_ir_graph));
740 /* Check whether we walked all procedures: there could be procedures
741 with cyclic calls but no call from the outside. */
742 for (i = 0; i < get_irp_n_irgs(); i++) {
744 current_ir_graph = get_irp_irg(i);
746 /* Test start block: if inner procedure end and end block are not
747 * visible and therefore not marked. */
748 sb = get_irg_start_block(current_ir_graph);
749 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
752 /* Walk all endless cfloops in inner procedures.
753 * We recognize an inner procedure if the End node is not visited. */
754 for (i = 0; i < get_irp_n_irgs(); i++) {
756 current_ir_graph = get_irp_irg(i);
758 e = get_irg_end(current_ir_graph);
759 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
761 /* Don't visit the End node. */
762 for (j = 0; j < get_End_n_keepalives(e); j++) {
763 ir_node *el = get_End_keepalive(e, j);
764 if (is_Block(el)) cfscc(el);
769 set_irg_loop(outermost_ir_graph, current_loop);
770 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
771 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
773 obstack_free(&temp, NULL);
774 current_ir_graph = rem;
775 set_interprocedural_view(rem_ipv);
776 return max_loop_depth;
781 * Clear the intra- and the interprocedural
782 * backedge information pf a block.
784 static void reset_backedges(ir_node *block) {
787 assert(is_Block(block));
788 #ifdef INTERPROCEDURAL_VIEW
789 rem = get_interprocedural_view();
790 set_interprocedural_view(1);
791 clear_backedges(block);
792 set_interprocedural_view(0);
793 clear_backedges(block);
794 set_interprocedural_view(rem);
797 clear_backedges(block);
802 * Reset all backedges of the first block of
803 * a loop as well as all loop info for all nodes of this loop.
804 * Recurse into all nested loops.
806 static void loop_reset_backedges(ir_loop *l) {
808 reset_backedges(get_loop_node(l, 0));
809 for (i = 0; i < get_loop_n_nodes(l); ++i)
810 set_irn_loop(get_loop_node(l, i), NULL);
811 for (i = 0; i < get_loop_n_sons(l); ++i) {
812 loop_reset_backedges(get_loop_son(l, i));
816 /* Removes all cfloop information.
817 Resets all backedges */
818 void free_cfloop_information(ir_graph *irg) {
819 ir_loop *loop = get_irg_loop(irg);
821 loop_reset_backedges(loop);
822 set_irg_loop(irg, NULL);
824 set_irg_loopinfo_state(irg, loopinfo_none);
825 /* We cannot free the cfloop nodes, they are on the obstack. */
829 void free_all_cfloop_information(void) {
831 #ifdef INTERPROCEDURAL_VIEW
832 int rem = get_interprocedural_view();
833 set_interprocedural_view(1); /* To visit all filter nodes */
835 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
836 free_cfloop_information(get_irp_irg(i));
838 #ifdef INTERPROCEDURAL_VIEW
839 set_interprocedural_view(rem);