3 * File name: ir/ana/irscc.c
4 * Purpose: Compute the strongly connected regions and build
5 * backedge/cfloop datastructures.
6 * A variation on the Tarjan algorithm. See also [Trapp:99],
8 * Author: Goetz Lindenmaier
12 * Copyright: (c) 2002-2003 Universität Karlsruhe
13 * Licence: This file protected by GPL - GNU GENERAL PUBLIC LICENSE.
26 #include "irgraph_t.h"
33 #define NO_CFLOOPS_WITHOUT_HEAD 1
35 static ir_graph *outermost_ir_graph; /* The outermost graph the scc is computed
37 static ir_loop *current_loop; /* Current cfloop construction is working
39 static int loop_node_cnt = 0; /* Counts the number of allocated cfloop nodes.
40 Each cfloop node gets a unique number.
41 What for? ev. remove. @@@ */
42 static int current_dfn = 1; /* Counter to generate depth first numbering
45 static int max_loop_depth = 0;
47 void link_to_reg_end (ir_node *n, void *env);
49 /**********************************************************************/
50 /* Node attributes **/
51 /**********************************************************************/
53 /**********************************************************************/
54 /* Node attributes needed for the construction. **/
55 /**********************************************************************/
58 * The SCC info. Additional fields for an ir-node needed for the
61 typedef struct scc_info {
62 bool in_stack; /**< Marks whether node is on the stack. */
63 int dfn; /**< Depth first search number. */
64 int uplink; /**< dfn number of ancestor. */
67 /** Allocate a new scc_info on the obstack of the outermost graph */
68 static INLINE scc_info *new_scc_info(void) {
69 scc_info *info = obstack_alloc (outermost_ir_graph->obst, sizeof (scc_info));
70 memset (info, 0, sizeof (scc_info));
75 * Marks the node n to be on the stack.
78 mark_irn_in_stack (ir_node *n) {
79 scc_info *info = get_irn_link(n);
80 info->in_stack = true;
84 * Marks the node n to be not on the stack.
87 mark_irn_not_in_stack (ir_node *n) {
88 scc_info *info = get_irn_link(n);
89 info->in_stack = false;
93 * Returns whether node n is on the stack.
96 irn_is_in_stack (ir_node *n) {
97 scc_info *info = get_irn_link(n);
98 return info->in_stack;
102 * Sets node n uplink value.
105 set_irn_uplink (ir_node *n, int uplink) {
106 scc_info *info = get_irn_link(n);
107 info->uplink = uplink;
111 * Return node n uplink value.
114 get_irn_uplink (ir_node *n) {
115 scc_info *info = get_irn_link(n);
120 * Sets node n dfn value.
123 set_irn_dfn (ir_node *n, int dfn) {
124 scc_info *info = get_irn_link(n);
129 * Returns node n dfn value.
132 get_irn_dfn (ir_node *n) {
133 scc_info *info = get_irn_link(n);
137 /**********************************************************************/
139 /**********************************************************************/
141 static ir_node **stack = NULL; /**< An IR-node stack */
142 static int tos = 0; /**< The top (index) of the IR-node stack */
145 * Initializes the IR-node stack
147 static INLINE void init_stack(void) {
149 ARR_RESIZE(ir_node *, stack, 1000);
151 stack = NEW_ARR_F(ir_node *, 1000);
157 * Push a node n onto the IR-node stack.
162 if (tos == ARR_LEN(stack)) {
163 int nlen = ARR_LEN(stack) * 2;
164 ARR_RESIZE(ir_node *, stack, nlen);
167 mark_irn_in_stack(n);
171 * Pop a node from the IR-node stack and return it.
173 static INLINE ir_node *
176 ir_node *n = stack[--tos];
177 mark_irn_not_in_stack(n);
182 * The nodes from tos up to n belong to the current loop.
183 * Removes them from the stack and adds them to the current loop.
186 pop_scc_to_loop(ir_node *n)
194 set_irn_dfn(m, loop_node_cnt);
195 add_loop_node(current_loop, m);
196 set_irn_loop(m, current_loop);
197 /* if (m==n) break;*/
201 /* GL ??? my last son is my grandson??? Removes cfloops with no
202 ir_nodes in them. Such loops have only another loop as son. (Why
203 can't they have two loops as sons? Does it never get that far? ) */
204 static void close_loop (ir_loop *l)
206 int last = get_loop_n_elements(l) - 1;
207 loop_element lelement = get_loop_element(l, last);
208 ir_loop *last_son = lelement.son;
210 if (get_kind(last_son) == k_ir_loop &&
211 get_loop_n_elements(last_son) == 1) {
214 lelement = get_loop_element(last_son, 0);
216 if(get_kind(gson) == k_ir_loop) {
217 loop_element new_last_son;
219 gson -> outer_loop = l;
220 new_last_son.son = gson;
221 l -> children[last] = new_last_son;
229 * Removes and unmarks all nodes up to n from the stack.
230 * The nodes must be visited once more to assign them to a scc.
233 pop_scc_unmark_visit (ir_node *n)
239 set_irn_visited(m, 0);
243 /**********************************************************************/
244 /* The loop datastructure. **/
245 /**********************************************************************/
248 * Allocates a new loop as son of current_loop. Sets current_loop
249 * to the new loop and returns its father.
251 static ir_loop *new_loop (void) {
252 ir_loop *father, *son;
254 father = current_loop;
256 son = obstack_alloc(outermost_ir_graph->obst, sizeof(*son));
257 memset(son, 0, sizeof(*son));
258 son->kind = k_ir_loop;
259 son->children = NEW_ARR_F(loop_element, 0);
263 son->outer_loop = father;
264 add_loop_son(father, son);
265 son->depth = father->depth+1;
266 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
268 else { /* The root loop */
269 son->outer_loop = son;
274 son->loop_nr = get_irp_new_node_nr();
282 /**********************************************************************/
283 /* Constructing and destructing the loop/backedge information. **/
284 /**********************************************************************/
286 /* Initialization steps. **********************************************/
289 * Allocates a scc_info for every Block node n.
290 * Clear the backedges for all nodes.
291 * Called from a walker.
294 init_node (ir_node *n, void *env) {
296 set_irn_link (n, new_scc_info());
301 * Initializes the common global settings for the scc algorthm
304 init_scc_common (void) {
311 * Initializes the scc algorithm for the intraprocedural case.
314 init_scc (ir_graph *irg) {
316 irg_walk_graph(irg, init_node, NULL, NULL);
320 * Initializes the scc algorithm for the interprocedural case.
325 cg_walk (init_node, NULL, NULL);
327 #if EXPERIMENTAL_CFLOOP_TREE
328 cg_walk (link_to_reg_end, NULL, NULL);
333 * Condition for breaking the recursion: n is the block
334 * that gets the initial control flow from the Start node.
336 static bool is_outermost_StartBlock(ir_node *n) {
337 /* Test whether this is the outermost Start node. If so
338 recursion must end. */
340 if ((get_Block_n_cfgpreds(n) == 1) &&
341 (get_irn_op(skip_Proj(get_Block_cfgpred(n, 0))) == op_Start) &&
342 (get_nodes_block(skip_Proj(get_Block_cfgpred(n, 0))) == n)) {
348 /** Returns true if n is a loop header, i.e., it is a Block node
349 * and has predecessors within the cfloop and out of the cfloop.
351 * @param root only needed for assertion.
354 is_head (ir_node *n, ir_node *root)
357 int some_outof_loop = 0, some_in_loop = 0;
361 if (!is_outermost_StartBlock(n)) {
362 arity = get_irn_arity(n);
363 for (i = 0; i < arity; i++) {
364 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
365 if (is_backedge(n, i)) continue;
366 if (!irn_is_in_stack(pred)) {
369 if (get_irn_uplink(pred) < get_irn_uplink(root)) {
370 DDMN(pred); DDMN(root);
371 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
377 return some_outof_loop & some_in_loop;
382 * Returns true if n is possible loop head of an endless loop.
383 * I.e., it is a Block, Phi or Filter node and has only predecessors
385 * @arg root: only needed for assertion.
388 is_endless_head (ir_node *n, ir_node *root)
391 int some_outof_loop = 0, some_in_loop = 0;
394 /* Test for legal loop header: Block, Phi, ... */
395 if (!is_outermost_StartBlock(n)) {
396 arity = get_irn_arity(n);
397 for (i = 0; i < arity; i++) {
398 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
400 if (is_backedge(n, i)) { continue; }
401 if (!irn_is_in_stack(pred)) {
402 some_outof_loop = 1; //printf(" some out of loop ");
404 if(get_irn_uplink(pred) < get_irn_uplink(root)) {
405 DDMN(pred); DDMN(root);
406 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
412 return !some_outof_loop && some_in_loop;
416 * Returns index of the predecessor with the smallest dfn number
417 * greater-equal than limit.
420 smallest_dfn_pred (ir_node *n, int limit)
422 int i, index = -2, min = -1;
424 if (!is_outermost_StartBlock(n)) {
425 int arity = get_irn_arity(n);
426 for (i = 0; i < arity; i++) {
427 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
428 if (is_backedge(n, i) || !irn_is_in_stack(pred))
430 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
432 min = get_irn_dfn(pred);
440 * Returns index of the predecessor with the largest dfn number.
443 largest_dfn_pred (ir_node *n)
445 int i, index = -2, max = -1;
447 if (!is_outermost_StartBlock(n)) {
448 int arity = get_irn_arity(n);
449 for (i = 0; i < arity; i++) {
450 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
451 if (is_backedge (n, i) || !irn_is_in_stack(pred))
453 if (get_irn_dfn(pred) > max) {
455 max = get_irn_dfn(pred);
463 * Searches the stack for possible loop heads. Tests these for backedges.
464 * If it finds a head with an unmarked backedge it marks this edge and
465 * returns the tail of the loop.
466 * If it finds no backedge returns NULL.
469 find_tail (ir_node *n) {
471 int i, res_index = -2;
473 m = stack[tos-1]; /* tos = top of stack */
475 res_index = smallest_dfn_pred(m, 0);
476 if ((res_index == -2) && /* no smallest dfn pred found. */
480 if (m == n) return NULL;
481 for (i = tos-2; i >= 0; --i) {
484 if (is_head (m, n)) {
485 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
486 if (res_index == -2) /* no smallest dfn pred found. */
487 res_index = largest_dfn_pred (m);
489 if ((m == n) && (res_index == -2)) {
496 /* We should not walk past our selves on the stack: The upcoming nodes
497 are not in this loop. We assume a loop not reachable from Start. */
505 /* A dead loop not reachable from Start. */
506 for (i = tos-2; i >= 0; --i) {
508 if (is_endless_head (m, n)) {
509 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
510 if (res_index == -2) /* no smallest dfn pred found. */
511 res_index = largest_dfn_pred (m);
514 if (m == n) break; /* It's not an unreachable loop, either. */
516 //assert(0 && "no head found on stack");
520 assert (res_index > -2);
522 set_backedge (m, res_index);
523 return is_outermost_StartBlock(n) ? NULL : get_nodes_block(skip_Proj(get_irn_n(m, res_index)));
527 * returns non.zero if l is the outermost loop.
530 is_outermost_loop(ir_loop *l) {
531 return l == get_loop_outer_loop(l);
534 /*-----------------------------------------------------------*
535 * The core algorithm. *
536 *-----------------------------------------------------------*/
539 * Walks over all blocks of a graph
541 static void cfscc (ir_node *n) {
546 if (irn_visited(n)) return;
549 /* Initialize the node */
550 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
551 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
552 set_irn_loop(n, NULL);
556 if (!is_outermost_StartBlock(n)) {
557 int arity = get_irn_arity(n);
559 for (i = 0; i < arity; i++) {
562 if (is_backedge(n, i))
564 m = get_nodes_block(skip_Proj(get_irn_n(n, i)));
567 if (irn_is_in_stack(m)) {
568 /* Uplink of m is smaller if n->m is a backedge.
569 Propagate the uplink to mark the cfloop. */
570 if (get_irn_uplink(m) < get_irn_uplink(n))
571 set_irn_uplink(n, get_irn_uplink(m));
576 if (get_irn_dfn(n) == get_irn_uplink(n)) {
577 /* This condition holds for
578 1) the node with the incoming backedge.
579 That is: We found a cfloop!
580 2) Straight line code, because no uplink has been propagated, so the
581 uplink still is the same as the dfn.
583 But n might not be a proper cfloop head for the analysis. Proper cfloop
584 heads are Block and Phi nodes. find_tail searches the stack for
585 Block's and Phi's and takes those nodes as cfloop heads for the current
586 cfloop instead and marks the incoming edge as backedge. */
588 ir_node *tail = find_tail(n);
590 /* We have a cfloop, that is no straight line code,
591 because we found a cfloop head!
592 Next actions: Open a new cfloop on the cfloop tree and
593 try to find inner cfloops */
595 #if NO_CFLOOPS_WITHOUT_HEAD
597 /* This is an adaption of the algorithm from fiasco / optscc to
598 * avoid cfloops without Block or Phi as first node. This should
599 * severely reduce the number of evaluations of nodes to detect
600 * a fixpoint in the heap analysis.
601 * Further it avoids cfloops without firm nodes that cause errors
602 * in the heap analyses. */
606 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
616 ir_loop *l = new_loop();
620 /* Remove the cfloop from the stack ... */
621 pop_scc_unmark_visit (n);
623 /* The current backedge has been marked, that is temporarily eliminated,
624 by find tail. Start the scc algorithm
625 anew on the subgraph thats left (the current cfloop without the backedge)
626 in order to find more inner cfloops. */
630 assert (irn_visited(n));
631 #if NO_CFLOOPS_WITHOUT_HEAD
637 /* AS: No cfloop head was found, that is we have straight line code.
638 Pop all nodes from the stack to the current cfloop. */
644 /* Constructs control flow backedge information for irg. */
645 int construct_cf_backedges(ir_graph *irg) {
646 ir_graph *rem = current_ir_graph;
648 ir_node *end = get_irg_end(irg);
651 assert(!get_interprocedural_view() &&
652 "use construct_ip_cf_backedges()");
655 current_ir_graph = irg;
656 outermost_ir_graph = irg;
658 init_scc(current_ir_graph);
661 new_loop(); /* sets current_loop */
662 head_rem = current_loop; /* Just for assertion */
664 inc_irg_visited(current_ir_graph);
666 /* walk over all blocks of the graph, including keep alives */
667 cfscc(get_irg_end_block(current_ir_graph));
668 for (i = 0; i < get_End_n_keepalives(end); i++) {
669 ir_node *el = get_End_keepalive(end, i);
670 if (is_Block(el)) cfscc(el);
673 assert(head_rem == current_loop);
674 set_irg_loop(current_ir_graph, current_loop);
675 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_consistent);
676 assert(get_irg_loop(current_ir_graph)->kind == k_ir_loop);
678 current_ir_graph = rem;
679 return max_loop_depth;
683 int construct_ip_cf_backedges (void) {
684 ir_graph *rem = current_ir_graph;
685 int rem_ipv = get_interprocedural_view();
688 assert(get_irp_ip_view_state() == ip_view_valid);
690 outermost_ir_graph = get_irp_main_irg();
695 new_loop(); /* sets current_loop */
696 set_interprocedural_view(true);
698 inc_max_irg_visited();
699 for (i = 0; i < get_irp_n_irgs(); i++)
700 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
702 /** We have to start the walk at the same nodes as cg_walk. **/
703 /* Walk starting at unreachable procedures. Only these
704 * have End blocks visible in interprocedural view. */
705 for (i = 0; i < get_irp_n_irgs(); i++) {
707 current_ir_graph = get_irp_irg(i);
709 sb = get_irg_start_block(current_ir_graph);
711 if ((get_Block_n_cfgpreds(sb) > 1) ||
712 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
714 cfscc(get_irg_end_block(current_ir_graph));
717 /* Check whether we walked all procedures: there could be procedures
718 with cyclic calls but no call from the outside. */
719 for (i = 0; i < get_irp_n_irgs(); i++) {
721 current_ir_graph = get_irp_irg(i);
723 /* Test start block: if inner procedure end and end block are not
724 * visible and therefore not marked. */
725 sb = get_irg_start_block(current_ir_graph);
726 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
729 /* Walk all endless cfloops in inner procedures.
730 * We recognize an inner procedure if the End node is not visited. */
731 for (i = 0; i < get_irp_n_irgs(); i++) {
733 current_ir_graph = get_irp_irg(i);
735 e = get_irg_end(current_ir_graph);
736 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
738 /* Don't visit the End node. */
739 for (j = 0; j < get_End_n_keepalives(e); j++) {
740 ir_node *el = get_End_keepalive(e, j);
741 if (is_Block(el)) cfscc(el);
746 set_irg_loop(outermost_ir_graph, current_loop);
747 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
748 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
750 current_ir_graph = rem;
751 set_interprocedural_view(rem_ipv);
752 return max_loop_depth;
756 * Clear the intra- and the interprocedural
757 * backedge information pf a block.
759 static void reset_backedges(ir_node *block) {
760 int rem = get_interprocedural_view();
762 assert(is_Block(block));
763 set_interprocedural_view(true);
764 clear_backedges(block);
765 set_interprocedural_view(false);
766 clear_backedges(block);
767 set_interprocedural_view(rem);
771 * Reset all backedges of the first block of
772 * a loop as well as all loop info for all nodes of this loop.
773 * Recurse into all nested loops.
775 static void loop_reset_backedges(ir_loop *l) {
777 reset_backedges(get_loop_node(l, 0));
778 for (i = 0; i < get_loop_n_nodes(l); ++i)
779 set_irn_loop(get_loop_node(l, i), NULL);
780 for (i = 0; i < get_loop_n_sons(l); ++i) {
781 loop_reset_backedges(get_loop_son(l, i));
785 /* Removes all cfloop information.
786 Resets all backedges */
787 void free_cfloop_information(ir_graph *irg) {
788 if (get_irg_loop(irg))
789 loop_reset_backedges(get_irg_loop(irg));
790 set_irg_loop(irg, NULL);
791 set_irg_loopinfo_state(current_ir_graph, loopinfo_none);
792 /* We cannot free the cfloop nodes, they are on the obstack. */
796 void free_all_cfloop_information (void) {
798 int rem = get_interprocedural_view();
799 set_interprocedural_view(true); /* To visit all filter nodes */
800 for (i = 0; i < get_irp_n_irgs(); i++) {
801 free_cfloop_information(get_irp_irg(i));
803 set_interprocedural_view(rem);