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 int 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);
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);
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 algorithm
304 init_scc_common (void) {
311 * Initializes the scc algorithm for the intraprocedural case.
312 * Add scc info to every block node.
315 init_scc (ir_graph *irg) {
317 irg_walk_graph(irg, init_node, NULL, NULL);
321 * Initializes the scc algorithm for the interprocedural case.
326 cg_walk (init_node, NULL, NULL);
328 #if EXPERIMENTAL_CFLOOP_TREE
329 cg_walk (link_to_reg_end, NULL, NULL);
334 * Condition for breaking the recursion: n is the block
335 * that gets the initial control flow from the Start node.
337 static int is_outermost_StartBlock(ir_node *n) {
338 /* Test whether this is the outermost Start node. If so
339 recursion must end. */
341 if ((get_Block_n_cfgpreds(n) == 1) &&
342 (get_irn_op(skip_Proj(get_Block_cfgpred(n, 0))) == op_Start) &&
343 (get_nodes_block(skip_Proj(get_Block_cfgpred(n, 0))) == n)) {
349 /** Returns non-zero if n is a loop header, i.e., it is a Block node
350 * and has predecessors within the cfloop and out of the cfloop.
352 * @param n the block node to check
353 * @param root only needed for assertion.
356 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 DDMN(pred); DDMN(root);
373 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
379 return some_outof_loop & some_in_loop;
384 * Returns non-zero if n is possible loop head of an endless loop.
385 * I.e., it is a Block, Phi or Filter node and has only predecessors
388 * @param n the block node to check
389 * @param root only needed for assertion.
392 is_endless_head (ir_node *n, ir_node *root)
395 int some_outof_loop = 0, some_in_loop = 0;
398 /* Test for legal loop header: Block, Phi, ... */
399 if (!is_outermost_StartBlock(n)) {
400 arity = get_irn_arity(n);
401 for (i = 0; i < arity; i++) {
402 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
404 if (is_backedge(n, i)) { continue; }
405 if (!irn_is_in_stack(pred)) {
406 some_outof_loop = 1; //printf(" some out of loop ");
408 if(get_irn_uplink(pred) < get_irn_uplink(root)) {
409 DDMN(pred); DDMN(root);
410 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
416 return !some_outof_loop && some_in_loop;
420 * Returns index of the predecessor with the smallest dfn number
421 * greater-equal than limit.
424 smallest_dfn_pred (ir_node *n, int limit)
426 int i, index = -2, min = -1;
428 if (!is_outermost_StartBlock(n)) {
429 int arity = get_irn_arity(n);
430 for (i = 0; i < arity; i++) {
431 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
432 if (is_backedge(n, i) || !irn_is_in_stack(pred))
434 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
436 min = get_irn_dfn(pred);
444 * Returns index of the predecessor with the largest dfn number.
447 largest_dfn_pred (ir_node *n)
449 int i, index = -2, max = -1;
451 if (!is_outermost_StartBlock(n)) {
452 int arity = get_irn_arity(n);
453 for (i = 0; i < arity; i++) {
454 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
455 if (is_backedge (n, i) || !irn_is_in_stack(pred))
457 if (get_irn_dfn(pred) > max) {
459 max = get_irn_dfn(pred);
467 * Searches the stack for possible loop heads. Tests these for backedges.
468 * If it finds a head with an unmarked backedge it marks this edge and
469 * returns the tail of the loop.
470 * If it finds no backedge returns NULL.
473 find_tail (ir_node *n) {
475 int i, res_index = -2;
477 m = stack[tos-1]; /* tos = top of stack */
479 res_index = smallest_dfn_pred(m, 0);
480 if ((res_index == -2) && /* no smallest dfn pred found. */
484 if (m == n) return NULL;
485 for (i = tos-2; i >= 0; --i) {
488 if (is_head (m, n)) {
489 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
490 if (res_index == -2) /* no smallest dfn pred found. */
491 res_index = largest_dfn_pred (m);
493 if ((m == n) && (res_index == -2)) {
500 /* We should not walk past our selves on the stack: The upcoming nodes
501 are not in this loop. We assume a loop not reachable from Start. */
509 /* A dead loop not reachable from Start. */
510 for (i = tos-2; i >= 0; --i) {
512 if (is_endless_head (m, n)) {
513 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
514 if (res_index == -2) /* no smallest dfn pred found. */
515 res_index = largest_dfn_pred (m);
518 if (m == n) break; /* It's not an unreachable loop, either. */
520 //assert(0 && "no head found on stack");
524 assert (res_index > -2);
526 set_backedge (m, res_index);
527 return is_outermost_StartBlock(n) ? NULL : get_nodes_block(skip_Proj(get_irn_n(m, res_index)));
531 * returns non.zero if l is the outermost loop.
534 is_outermost_loop(ir_loop *l) {
535 return l == get_loop_outer_loop(l);
538 /*-----------------------------------------------------------*
539 * The core algorithm. *
540 *-----------------------------------------------------------*/
543 * Walks over all blocks of a graph
545 static void cfscc (ir_node *n) {
550 if (irn_visited(n)) return;
553 /* Initialize the node */
554 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
555 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
556 set_irn_loop(n, NULL);
560 if (!is_outermost_StartBlock(n)) {
561 int arity = get_irn_arity(n);
563 for (i = 0; i < arity; i++) {
566 if (is_backedge(n, i))
568 m = get_nodes_block(skip_Proj(get_irn_n(n, i)));
571 if (irn_is_in_stack(m)) {
572 /* Uplink of m is smaller if n->m is a backedge.
573 Propagate the uplink to mark the cfloop. */
574 if (get_irn_uplink(m) < get_irn_uplink(n))
575 set_irn_uplink(n, get_irn_uplink(m));
580 if (get_irn_dfn(n) == get_irn_uplink(n)) {
581 /* This condition holds for
582 1) the node with the incoming backedge.
583 That is: We found a cfloop!
584 2) Straight line code, because no uplink has been propagated, so the
585 uplink still is the same as the dfn.
587 But n might not be a proper cfloop head for the analysis. Proper cfloop
588 heads are Block and Phi nodes. find_tail searches the stack for
589 Block's and Phi's and takes those nodes as cfloop heads for the current
590 cfloop instead and marks the incoming edge as backedge. */
592 ir_node *tail = find_tail(n);
594 /* We have a cfloop, that is no straight line code,
595 because we found a cfloop head!
596 Next actions: Open a new cfloop on the cfloop tree and
597 try to find inner cfloops */
599 #if NO_CFLOOPS_WITHOUT_HEAD
601 /* This is an adaption of the algorithm from fiasco / optscc to
602 * avoid cfloops without Block or Phi as first node. This should
603 * severely reduce the number of evaluations of nodes to detect
604 * a fixpoint in the heap analysis.
605 * Further it avoids cfloops without firm nodes that cause errors
606 * in the heap analyses. */
610 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
620 ir_loop *l = new_loop();
624 /* Remove the cfloop from the stack ... */
625 pop_scc_unmark_visit (n);
627 /* The current backedge has been marked, that is temporarily eliminated,
628 by find tail. Start the scc algorithm
629 anew on the subgraph thats left (the current cfloop without the backedge)
630 in order to find more inner cfloops. */
634 assert (irn_visited(n));
635 #if NO_CFLOOPS_WITHOUT_HEAD
641 /* AS: No cfloop head was found, that is we have straight line code.
642 Pop all nodes from the stack to the current cfloop. */
648 /* Constructs control flow backedge information for irg. */
649 int construct_cf_backedges(ir_graph *irg) {
650 ir_graph *rem = current_ir_graph;
652 ir_node *end = get_irg_end(irg);
655 assert(!get_interprocedural_view() &&
656 "use construct_ip_cf_backedges()");
659 current_ir_graph = irg;
660 outermost_ir_graph = irg;
662 init_scc(current_ir_graph);
665 new_loop(); /* sets current_loop */
666 head_rem = current_loop; /* Just for assertion */
668 inc_irg_visited(current_ir_graph);
670 /* walk over all blocks of the graph, including keep alives */
671 cfscc(get_irg_end_block(current_ir_graph));
672 for (i = 0; i < get_End_n_keepalives(end); i++) {
673 ir_node *el = get_End_keepalive(end, i);
674 if (is_Block(el)) cfscc(el);
677 assert(head_rem == current_loop);
678 set_irg_loop(current_ir_graph, current_loop);
679 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_consistent);
680 assert(get_irg_loop(current_ir_graph)->kind == k_ir_loop);
682 current_ir_graph = rem;
683 return max_loop_depth;
687 int construct_ip_cf_backedges (void) {
688 ir_graph *rem = current_ir_graph;
689 int rem_ipv = get_interprocedural_view();
692 assert(get_irp_ip_view_state() == ip_view_valid);
694 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 current_ir_graph = rem;
755 set_interprocedural_view(rem_ipv);
756 return max_loop_depth;
760 * Clear the intra- and the interprocedural
761 * backedge information pf a block.
763 static void reset_backedges(ir_node *block) {
764 int rem = get_interprocedural_view();
766 assert(is_Block(block));
767 set_interprocedural_view(1);
768 clear_backedges(block);
769 set_interprocedural_view(0);
770 clear_backedges(block);
771 set_interprocedural_view(rem);
775 * Reset all backedges of the first block of
776 * a loop as well as all loop info for all nodes of this loop.
777 * Recurse into all nested loops.
779 static void loop_reset_backedges(ir_loop *l) {
781 reset_backedges(get_loop_node(l, 0));
782 for (i = 0; i < get_loop_n_nodes(l); ++i)
783 set_irn_loop(get_loop_node(l, i), NULL);
784 for (i = 0; i < get_loop_n_sons(l); ++i) {
785 loop_reset_backedges(get_loop_son(l, i));
789 /* Removes all cfloop information.
790 Resets all backedges */
791 void free_cfloop_information(ir_graph *irg) {
792 if (get_irg_loop(irg))
793 loop_reset_backedges(get_irg_loop(irg));
794 set_irg_loop(irg, NULL);
795 set_irg_loopinfo_state(current_ir_graph, loopinfo_none);
796 /* We cannot free the cfloop nodes, they are on the obstack. */
800 void free_all_cfloop_information (void) {
802 int rem = get_interprocedural_view();
803 set_interprocedural_view(1); /* To visit all filter nodes */
804 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
805 free_cfloop_information(get_irp_irg(i));
807 set_interprocedural_view(rem);