2 * Copyright (C) 1995-2007 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 static ir_graph *outermost_ir_graph; /* The outermost graph the scc is computed
50 static ir_loop *current_loop; /* Current cfloop construction is working
52 static int loop_node_cnt = 0; /* Counts the number of allocated cfloop nodes.
53 Each cfloop node gets a unique number.
54 What for? ev. remove. @@@ */
55 static int current_dfn = 1; /* Counter to generate depth first numbering
58 static int max_loop_depth = 0;
60 void link_to_reg_end (ir_node *n, void *env);
62 /**********************************************************************/
63 /* Node attributes **/
64 /**********************************************************************/
66 /**********************************************************************/
67 /* Node attributes needed for the construction. **/
68 /**********************************************************************/
71 * The SCC info. Additional fields for an ir-node needed for the
74 typedef struct scc_info {
75 int in_stack; /**< Marks whether node is on the stack. */
76 int dfn; /**< Depth first search number. */
77 int uplink; /**< dfn number of ancestor. */
80 /** Allocate a new scc_info on the obstack of the outermost graph */
81 static INLINE scc_info *new_scc_info(void) {
82 scc_info *info = obstack_alloc (outermost_ir_graph->obst, sizeof (scc_info));
83 memset (info, 0, sizeof (scc_info));
88 * Marks the node n to be on the stack.
91 mark_irn_in_stack (ir_node *n) {
92 scc_info *info = get_irn_link(n);
97 * Marks the node n to be not on the stack.
100 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.
109 irn_is_in_stack (ir_node *n) {
110 scc_info *info = get_irn_link(n);
111 return info->in_stack;
115 * Sets node n uplink value.
118 set_irn_uplink (ir_node *n, int uplink) {
119 scc_info *info = get_irn_link(n);
120 info->uplink = uplink;
124 * Return node n uplink value.
127 get_irn_uplink (ir_node *n) {
128 scc_info *info = get_irn_link(n);
133 * Sets node n dfn value.
136 set_irn_dfn (ir_node *n, int dfn) {
137 scc_info *info = get_irn_link(n);
142 * Returns node n dfn value.
145 get_irn_dfn (ir_node *n) {
146 scc_info *info = get_irn_link(n);
150 /**********************************************************************/
152 /**********************************************************************/
154 static ir_node **stack = NULL; /**< An IR-node stack */
155 static int tos = 0; /**< The top (index) of the IR-node stack */
158 * Initializes the IR-node stack
160 static INLINE void init_stack(void) {
162 ARR_RESIZE(ir_node *, stack, 1000);
164 stack = NEW_ARR_F(ir_node *, 1000);
170 * Push a node n onto the IR-node stack.
175 if (tos == ARR_LEN(stack)) {
176 int nlen = ARR_LEN(stack) * 2;
177 ARR_RESIZE(ir_node *, stack, nlen);
180 mark_irn_in_stack(n);
184 * Pop a node from the IR-node stack and return it.
186 static INLINE ir_node *
189 ir_node *n = stack[--tos];
190 mark_irn_not_in_stack(n);
195 * The nodes from tos up to n belong to the current loop.
196 * Removes them from the stack and adds them to the current loop.
199 pop_scc_to_loop(ir_node *n)
207 set_irn_dfn(m, loop_node_cnt);
208 add_loop_node(current_loop, m);
209 set_irn_loop(m, current_loop);
210 /* if (m==n) break;*/
214 /* GL ??? my last son is my grandson??? Removes cfloops with no
215 ir_nodes in them. Such loops have only another loop as son. (Why
216 can't they have two loops as sons? Does it never get that far? ) */
217 static void close_loop (ir_loop *l)
219 int last = get_loop_n_elements(l) - 1;
220 loop_element lelement = get_loop_element(l, last);
221 ir_loop *last_son = lelement.son;
223 if (get_kind(last_son) == k_ir_loop &&
224 get_loop_n_elements(last_son) == 1) {
227 lelement = get_loop_element(last_son, 0);
229 if(get_kind(gson) == k_ir_loop) {
230 loop_element new_last_son;
232 gson -> outer_loop = l;
233 new_last_son.son = gson;
234 l -> children[last] = new_last_son;
242 * Removes and unmarks all nodes up to n from the stack.
243 * The nodes must be visited once more to assign them to a scc.
246 pop_scc_unmark_visit (ir_node *n)
252 set_irn_visited(m, 0);
256 /**********************************************************************/
257 /* The loop datastructure. **/
258 /**********************************************************************/
261 * Allocates a new loop as son of current_loop. Sets current_loop
262 * to the new loop and returns its father.
264 static ir_loop *new_loop (void) {
265 ir_loop *father, *son;
267 father = current_loop;
269 son = obstack_alloc(outermost_ir_graph->obst, sizeof(*son));
270 memset(son, 0, sizeof(*son));
271 son->kind = k_ir_loop;
272 son->children = NEW_ARR_F(loop_element, 0);
276 son->outer_loop = father;
277 add_loop_son(father, son);
278 son->depth = father->depth+1;
279 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
281 else { /* The root loop */
282 son->outer_loop = son;
287 son->loop_nr = get_irp_new_node_nr();
295 /**********************************************************************/
296 /* Constructing and destructing the loop/backedge information. **/
297 /**********************************************************************/
299 /* Initialization steps. **********************************************/
302 * Allocates a scc_info for every Block node n.
303 * Clear the backedges for all nodes.
304 * Called from a walker.
307 init_node (ir_node *n, void *env)
311 set_irn_link (n, new_scc_info());
316 * Initializes the common global settings for the scc algorithm
319 init_scc_common (void) {
326 * Initializes the scc algorithm for the intraprocedural case.
327 * Add scc info to every block node.
330 init_scc (ir_graph *irg) {
332 irg_walk_graph(irg, init_node, NULL, NULL);
335 #ifdef INTERPROCEDURAL_VIEW
337 * Initializes the scc algorithm for the interprocedural case.
342 cg_walk (init_node, NULL, NULL);
344 #if EXPERIMENTAL_CFLOOP_TREE
345 cg_walk (link_to_reg_end, NULL, NULL);
351 * Condition for breaking the recursion: n is the block
352 * that gets the initial control flow from the Start node.
354 static int is_outermost_StartBlock(ir_node *n) {
355 /* Test whether this is the outermost Start node. If so
356 recursion must end. */
358 if ((get_Block_n_cfgpreds(n) == 1) &&
359 (get_irn_op(skip_Proj(get_Block_cfgpred(n, 0))) == op_Start) &&
360 (get_nodes_block(skip_Proj(get_Block_cfgpred(n, 0))) == n)) {
366 /** Returns non-zero if n is a loop header, i.e., it is a Block node
367 * and has predecessors within the cfloop and out of the cfloop.
369 * @param n the block node to check
370 * @param root only needed for assertion.
373 is_head (ir_node *n, ir_node *root)
376 int some_outof_loop = 0, some_in_loop = 0;
380 if (!is_outermost_StartBlock(n)) {
381 arity = get_irn_arity(n);
382 for (i = 0; i < arity; i++) {
383 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
384 if (is_backedge(n, i)) continue;
385 if (!irn_is_in_stack(pred)) {
388 if (get_irn_uplink(pred) < get_irn_uplink(root)) {
389 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
395 return some_outof_loop & some_in_loop;
400 * Returns non-zero if n is possible loop head of an endless loop.
401 * I.e., it is a Block, Phi or Filter node and has only predecessors
404 * @param n the block node to check
405 * @param root only needed for assertion.
408 is_endless_head (ir_node *n, ir_node *root)
411 int some_outof_loop = 0, some_in_loop = 0;
414 /* Test for legal loop header: Block, Phi, ... */
415 if (!is_outermost_StartBlock(n)) {
416 arity = get_irn_arity(n);
417 for (i = 0; i < arity; i++) {
418 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
420 if (is_backedge(n, i)) { continue; }
421 if (!irn_is_in_stack(pred)) {
422 some_outof_loop = 1; //printf(" some out of loop ");
424 if(get_irn_uplink(pred) < get_irn_uplink(root)) {
425 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
431 return !some_outof_loop && some_in_loop;
435 * Returns index of the predecessor with the smallest dfn number
436 * greater-equal than limit.
439 smallest_dfn_pred (ir_node *n, int limit)
441 int i, index = -2, min = -1;
443 if (!is_outermost_StartBlock(n)) {
444 int arity = get_irn_arity(n);
445 for (i = 0; i < arity; i++) {
446 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
447 if (is_backedge(n, i) || !irn_is_in_stack(pred))
449 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
451 min = get_irn_dfn(pred);
459 * Returns index of the predecessor with the largest dfn number.
462 largest_dfn_pred (ir_node *n)
464 int i, index = -2, max = -1;
466 if (!is_outermost_StartBlock(n)) {
467 int arity = get_irn_arity(n);
468 for (i = 0; i < arity; i++) {
469 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
470 if (is_backedge (n, i) || !irn_is_in_stack(pred))
472 if (get_irn_dfn(pred) > max) {
474 max = get_irn_dfn(pred);
482 * Searches the stack for possible loop heads. Tests these for backedges.
483 * If it finds a head with an unmarked backedge it marks this edge and
484 * returns the tail of the loop.
485 * If it finds no backedge returns NULL.
488 find_tail (ir_node *n) {
490 int i, res_index = -2;
492 m = stack[tos-1]; /* tos = top of stack */
494 res_index = smallest_dfn_pred(m, 0);
495 if ((res_index == -2) && /* no smallest dfn pred found. */
499 if (m == n) return NULL;
500 for (i = tos-2; i >= 0; --i) {
503 if (is_head (m, n)) {
504 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
505 if (res_index == -2) /* no smallest dfn pred found. */
506 res_index = largest_dfn_pred (m);
508 if ((m == n) && (res_index == -2)) {
515 /* We should not walk past our selves on the stack: The upcoming nodes
516 are not in this loop. We assume a loop not reachable from Start. */
524 /* A dead loop not reachable from Start. */
525 for (i = tos-2; i >= 0; --i) {
527 if (is_endless_head (m, n)) {
528 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
529 if (res_index == -2) /* no smallest dfn pred found. */
530 res_index = largest_dfn_pred (m);
533 if (m == n) break; /* It's not an unreachable loop, either. */
535 //assert(0 && "no head found on stack");
539 assert (res_index > -2);
541 set_backedge (m, res_index);
542 return is_outermost_StartBlock(n) ? NULL : get_nodes_block(skip_Proj(get_irn_n(m, res_index)));
546 * returns non.zero if l is the outermost loop.
549 is_outermost_loop(ir_loop *l) {
550 return l == get_loop_outer_loop(l);
553 /*-----------------------------------------------------------*
554 * The core algorithm. *
555 *-----------------------------------------------------------*/
558 * Walks over all blocks of a graph
560 static void cfscc (ir_node *n) {
565 if (irn_visited(n)) return;
568 /* Initialize the node */
569 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
570 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
571 set_irn_loop(n, NULL);
575 if (!is_outermost_StartBlock(n)) {
576 int arity = get_irn_arity(n);
578 for (i = 0; i < arity; i++) {
581 if (is_backedge(n, i))
583 m = get_nodes_block(skip_Proj(get_irn_n(n, i)));
586 if (irn_is_in_stack(m)) {
587 /* Uplink of m is smaller if n->m is a backedge.
588 Propagate the uplink to mark the cfloop. */
589 if (get_irn_uplink(m) < get_irn_uplink(n))
590 set_irn_uplink(n, get_irn_uplink(m));
595 if (get_irn_dfn(n) == get_irn_uplink(n)) {
596 /* This condition holds for
597 1) the node with the incoming backedge.
598 That is: We found a cfloop!
599 2) Straight line code, because no uplink has been propagated, so the
600 uplink still is the same as the dfn.
602 But n might not be a proper cfloop head for the analysis. Proper cfloop
603 heads are Block and Phi nodes. find_tail searches the stack for
604 Block's and Phi's and takes those nodes as cfloop heads for the current
605 cfloop instead and marks the incoming edge as backedge. */
607 ir_node *tail = find_tail(n);
609 /* We have a cfloop, that is no straight line code,
610 because we found a cfloop head!
611 Next actions: Open a new cfloop on the cfloop tree and
612 try to find inner cfloops */
614 #if NO_CFLOOPS_WITHOUT_HEAD
616 /* This is an adaption of the algorithm from fiasco / optscc to
617 * avoid cfloops without Block or Phi as first node. This should
618 * severely reduce the number of evaluations of nodes to detect
619 * a fixpoint in the heap analysis.
620 * Further it avoids cfloops without firm nodes that cause errors
621 * in the heap analyses. */
625 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
635 ir_loop *l = new_loop();
639 /* Remove the cfloop from the stack ... */
640 pop_scc_unmark_visit (n);
642 /* The current backedge has been marked, that is temporarily eliminated,
643 by find tail. Start the scc algorithm
644 anew on the subgraph thats left (the current cfloop without the backedge)
645 in order to find more inner cfloops. */
649 assert (irn_visited(n));
650 #if NO_CFLOOPS_WITHOUT_HEAD
656 /* AS: No cfloop head was found, that is we have straight line code.
657 Pop all nodes from the stack to the current cfloop. */
663 /* Constructs control flow backedge information for irg. */
664 int construct_cf_backedges(ir_graph *irg) {
665 ir_graph *rem = current_ir_graph;
667 ir_node *end = get_irg_end(irg);
670 assert(!get_interprocedural_view() &&
671 "use construct_ip_cf_backedges()");
674 current_ir_graph = irg;
675 outermost_ir_graph = irg;
677 init_scc(current_ir_graph);
680 new_loop(); /* sets current_loop */
681 head_rem = current_loop; /* Just for assertion */
683 inc_irg_visited(current_ir_graph);
685 /* walk over all blocks of the graph, including keep alives */
686 cfscc(get_irg_end_block(current_ir_graph));
687 for (i = 0; i < get_End_n_keepalives(end); i++) {
688 ir_node *el = get_End_keepalive(end, i);
689 if (is_Block(el)) cfscc(el);
692 assert(head_rem == current_loop);
693 set_irg_loop(current_ir_graph, current_loop);
694 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_consistent);
695 assert(get_irg_loop(current_ir_graph)->kind == k_ir_loop);
697 current_ir_graph = rem;
698 return max_loop_depth;
701 #ifdef INTERPROCEDURAL_VIEW
702 int construct_ip_cf_backedges (void) {
703 ir_graph *rem = current_ir_graph;
704 int rem_ipv = get_interprocedural_view();
707 assert(get_irp_ip_view_state() == ip_view_valid);
709 outermost_ir_graph = get_irp_main_irg();
714 new_loop(); /* sets current_loop */
715 set_interprocedural_view(1);
717 inc_max_irg_visited();
718 for (i = 0; i < get_irp_n_irgs(); i++)
719 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
721 /** We have to start the walk at the same nodes as cg_walk. **/
722 /* Walk starting at unreachable procedures. Only these
723 * have End blocks visible in interprocedural view. */
724 for (i = 0; i < get_irp_n_irgs(); i++) {
726 current_ir_graph = get_irp_irg(i);
728 sb = get_irg_start_block(current_ir_graph);
730 if ((get_Block_n_cfgpreds(sb) > 1) ||
731 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
733 cfscc(get_irg_end_block(current_ir_graph));
736 /* Check whether we walked all procedures: there could be procedures
737 with cyclic calls but no call from the outside. */
738 for (i = 0; i < get_irp_n_irgs(); i++) {
740 current_ir_graph = get_irp_irg(i);
742 /* Test start block: if inner procedure end and end block are not
743 * visible and therefore not marked. */
744 sb = get_irg_start_block(current_ir_graph);
745 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
748 /* Walk all endless cfloops in inner procedures.
749 * We recognize an inner procedure if the End node is not visited. */
750 for (i = 0; i < get_irp_n_irgs(); i++) {
752 current_ir_graph = get_irp_irg(i);
754 e = get_irg_end(current_ir_graph);
755 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
757 /* Don't visit the End node. */
758 for (j = 0; j < get_End_n_keepalives(e); j++) {
759 ir_node *el = get_End_keepalive(e, j);
760 if (is_Block(el)) cfscc(el);
765 set_irg_loop(outermost_ir_graph, current_loop);
766 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
767 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
769 current_ir_graph = rem;
770 set_interprocedural_view(rem_ipv);
771 return max_loop_depth;
776 * Clear the intra- and the interprocedural
777 * backedge information pf a block.
779 static void reset_backedges(ir_node *block) {
782 assert(is_Block(block));
783 #ifdef INTERPROCEDURAL_VIEW
784 rem = get_interprocedural_view();
785 set_interprocedural_view(1);
786 clear_backedges(block);
787 set_interprocedural_view(0);
788 clear_backedges(block);
789 set_interprocedural_view(rem);
792 clear_backedges(block);
797 * Reset all backedges of the first block of
798 * a loop as well as all loop info for all nodes of this loop.
799 * Recurse into all nested loops.
801 static void loop_reset_backedges(ir_loop *l) {
803 reset_backedges(get_loop_node(l, 0));
804 for (i = 0; i < get_loop_n_nodes(l); ++i)
805 set_irn_loop(get_loop_node(l, i), NULL);
806 for (i = 0; i < get_loop_n_sons(l); ++i) {
807 loop_reset_backedges(get_loop_son(l, i));
811 /* Removes all cfloop information.
812 Resets all backedges */
813 void free_cfloop_information(ir_graph *irg) {
814 if (get_irg_loop(irg))
815 loop_reset_backedges(get_irg_loop(irg));
816 set_irg_loop(irg, NULL);
817 set_irg_loopinfo_state(irg, loopinfo_none);
818 /* We cannot free the cfloop nodes, they are on the obstack. */
822 void free_all_cfloop_information (void) {
824 #ifdef INTERPROCEDURAL_VIEW
825 int rem = get_interprocedural_view();
826 set_interprocedural_view(1); /* To visit all filter nodes */
828 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
829 free_cfloop_information(get_irp_irg(i));
831 #ifdef INTERPROCEDURAL_VIEW
832 set_interprocedural_view(rem);