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 = current_loop;
256 ir_loop *son = alloc_loop(father, outermost_ir_graph->obst);
258 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
263 /**********************************************************************/
264 /* Constructing and destructing the loop/backedge information. **/
265 /**********************************************************************/
267 /* Initialization steps. **********************************************/
270 * Allocates a scc_info for every Block node n.
271 * Clear the backedges for all nodes.
272 * Called from a walker.
274 static INLINE void init_node(ir_node *n, void *env) {
275 struct obstack *obst = env;
277 set_irn_link(n, new_scc_info(obst));
282 * Initializes the common global settings for the scc algorithm
284 static INLINE void init_scc_common(void) {
291 * Initializes the scc algorithm for the intraprocedural case.
292 * Add scc info to every block node.
294 static INLINE void init_scc(ir_graph *irg, struct obstack *obst) {
296 irg_walk_graph(irg, init_node, NULL, obst);
299 #ifdef INTERPROCEDURAL_VIEW
301 * Initializes the scc algorithm for the interprocedural case.
303 static INLINE void init_ip_scc(struct obstack *obst) {
305 cg_walk(init_node, NULL, obst);
307 #if EXPERIMENTAL_CFLOOP_TREE
308 cg_walk(link_to_reg_end, NULL, NULL);
314 * Condition for breaking the recursion: n is the block
315 * that gets the initial control flow from the Start node.
317 static int is_outermost_StartBlock(ir_node *n) {
318 /* Test whether this is the outermost Start node. If so
319 recursion must end. */
321 if (get_Block_n_cfgpreds(n) == 1 &&
322 is_Start(skip_Proj(get_Block_cfgpred(n, 0))) &&
323 get_Block_cfgpred_block(n, 0) == n) {
329 /** Returns non-zero if n is a loop header, i.e., it is a Block node
330 * and has predecessors within the cfloop and out of the cfloop.
332 * @param n the block node to check
333 * @param root only needed for assertion.
335 static int is_head(ir_node *n, ir_node *root) {
337 int some_outof_loop = 0, some_in_loop = 0;
341 if (!is_outermost_StartBlock(n)) {
342 arity = get_irn_arity(n);
343 for (i = 0; i < arity; i++) {
344 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
345 if (is_backedge(n, i)) continue;
346 if (!irn_is_in_stack(pred)) {
349 if (get_irn_uplink(pred) < get_irn_uplink(root)) {
350 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
356 return some_outof_loop & some_in_loop;
361 * Returns non-zero if n is possible loop head of an endless loop.
362 * I.e., it is a Block, Phi or Filter node and has only predecessors
365 * @param n the block node to check
366 * @param root only needed for assertion.
368 static int is_endless_head(ir_node *n, ir_node *root) {
370 int some_outof_loop = 0, some_in_loop = 0;
373 /* Test for legal loop header: Block, Phi, ... */
374 if (!is_outermost_StartBlock(n)) {
375 arity = get_irn_arity(n);
376 for (i = 0; i < arity; i++) {
377 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
379 if (is_backedge(n, i))
381 if (!irn_is_in_stack(pred)) {
382 some_outof_loop = 1; //printf(" some out of loop ");
384 if (get_irn_uplink(pred) < get_irn_uplink(root)) {
385 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
391 return !some_outof_loop && some_in_loop;
395 * Returns index of the predecessor with the smallest dfn number
396 * greater-equal than limit.
398 static int smallest_dfn_pred(ir_node *n, int limit) {
399 int i, index = -2, min = -1;
401 if (!is_outermost_StartBlock(n)) {
402 int arity = get_irn_arity(n);
403 for (i = 0; i < arity; i++) {
404 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
405 if (is_backedge(n, i) || !irn_is_in_stack(pred))
407 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
409 min = get_irn_dfn(pred);
417 * Returns index of the predecessor with the largest dfn number.
419 static int largest_dfn_pred(ir_node *n) {
420 int i, index = -2, max = -1;
422 if (!is_outermost_StartBlock(n)) {
423 int arity = get_irn_arity(n);
424 for (i = 0; i < arity; i++) {
425 ir_node *pred = get_nodes_block(skip_Proj(get_irn_n(n, i)));
426 if (is_backedge(n, i) || !irn_is_in_stack(pred))
428 if (get_irn_dfn(pred) > max) {
430 max = get_irn_dfn(pred);
438 * Searches the stack for possible loop heads. Tests these for backedges.
439 * If it finds a head with an unmarked backedge it marks this edge and
440 * returns the tail of the loop.
441 * If it finds no backedge returns NULL.
443 static ir_node *find_tail(ir_node *n) {
445 int i, res_index = -2;
447 m = stack[tos-1]; /* tos = top of stack */
449 res_index = smallest_dfn_pred(m, 0);
450 if ((res_index == -2) && /* no smallest dfn pred found. */
456 for (i = tos-2; i >= 0; --i) {
460 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
461 if (res_index == -2) /* no smallest dfn pred found. */
462 res_index = largest_dfn_pred(m);
464 if ((m == n) && (res_index == -2)) {
471 /* We should not walk past our selves on the stack: The upcoming nodes
472 are not in this loop. We assume a loop not reachable from Start. */
480 /* A dead loop not reachable from Start. */
481 for (i = tos-2; i >= 0; --i) {
483 if (is_endless_head (m, n)) {
484 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
485 if (res_index == -2) /* no smallest dfn pred found. */
486 res_index = largest_dfn_pred (m);
489 if (m == n) break; /* It's not an unreachable loop, either. */
491 //assert(0 && "no head found on stack");
494 assert(res_index > -2);
496 set_backedge(m, res_index);
497 return is_outermost_StartBlock(n) ? NULL : get_nodes_block(skip_Proj(get_irn_n(m, res_index)));
501 * returns non.zero if l is the outermost loop.
503 INLINE static int is_outermost_loop(ir_loop *l) {
504 return l == get_loop_outer_loop(l);
507 /*-----------------------------------------------------------*
508 * The core algorithm. *
509 *-----------------------------------------------------------*/
512 * Walks over all blocks of a graph
514 static void cfscc(ir_node *n) {
519 if (irn_visited(n)) return;
522 /* Initialize the node */
523 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
524 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
525 set_irn_loop(n, NULL);
529 if (!is_outermost_StartBlock(n)) {
530 int arity = get_irn_arity(n);
532 for (i = 0; i < arity; i++) {
535 if (is_backedge(n, i))
537 m = get_nodes_block(skip_Proj(get_irn_n(n, i)));
540 if (irn_is_in_stack(m)) {
541 /* Uplink of m is smaller if n->m is a backedge.
542 Propagate the uplink to mark the cfloop. */
543 if (get_irn_uplink(m) < get_irn_uplink(n))
544 set_irn_uplink(n, get_irn_uplink(m));
549 if (get_irn_dfn(n) == get_irn_uplink(n)) {
550 /* This condition holds for
551 1) the node with the incoming backedge.
552 That is: We found a cfloop!
553 2) Straight line code, because no uplink has been propagated, so the
554 uplink still is the same as the dfn.
556 But n might not be a proper cfloop head for the analysis. Proper cfloop
557 heads are Block and Phi nodes. find_tail searches the stack for
558 Block's and Phi's and takes those nodes as cfloop heads for the current
559 cfloop instead and marks the incoming edge as backedge. */
561 ir_node *tail = find_tail(n);
563 /* We have a cfloop, that is no straight line code,
564 because we found a cfloop head!
565 Next actions: Open a new cfloop on the cfloop tree and
566 try to find inner cfloops */
568 #if NO_CFLOOPS_WITHOUT_HEAD
570 /* This is an adaption of the algorithm from fiasco / optscc to
571 * avoid cfloops without Block or Phi as first node. This should
572 * severely reduce the number of evaluations of nodes to detect
573 * a fixpoint in the heap analysis.
574 * Further it avoids cfloops without firm nodes that cause errors
575 * in the heap analyses. */
579 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
589 ir_loop *l = new_loop();
593 /* Remove the cfloop from the stack ... */
594 pop_scc_unmark_visit (n);
596 /* The current backedge has been marked, that is temporarily eliminated,
597 by find tail. Start the scc algorithm
598 anew on the subgraph thats left (the current cfloop without the backedge)
599 in order to find more inner cfloops. */
603 assert(irn_visited(n));
604 #if NO_CFLOOPS_WITHOUT_HEAD
609 /* AS: No cfloop head was found, that is we have straight line code.
610 Pop all nodes from the stack to the current cfloop. */
616 /* Constructs control flow backedge information for irg. */
617 int construct_cf_backedges(ir_graph *irg) {
618 ir_graph *rem = current_ir_graph;
620 ir_node *end = get_irg_end(irg);
624 assert(!get_interprocedural_view() &&
625 "use construct_ip_cf_backedges()");
628 current_ir_graph = irg;
629 outermost_ir_graph = irg;
632 init_scc(irg, &temp);
635 new_loop(); /* sets current_loop */
636 head_rem = current_loop; /* Just for assertion */
638 inc_irg_visited(irg);
640 /* walk over all blocks of the graph, including keep alives */
641 cfscc(get_irg_end_block(irg));
642 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
643 ir_node *el = get_End_keepalive(end, i);
648 assert(head_rem == current_loop);
649 mature_loops(current_loop, irg->obst);
650 set_irg_loop(irg, current_loop);
651 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
652 assert(get_irg_loop(irg)->kind == k_ir_loop);
654 obstack_free(&temp, NULL);
655 current_ir_graph = rem;
656 return max_loop_depth;
659 #ifdef INTERPROCEDURAL_VIEW
660 int construct_ip_cf_backedges (void) {
661 ir_graph *rem = current_ir_graph;
662 int rem_ipv = get_interprocedural_view();
666 assert(get_irp_ip_view_state() == ip_view_valid);
668 outermost_ir_graph = get_irp_main_irg();
674 new_loop(); /* sets current_loop */
675 set_interprocedural_view(1);
677 inc_max_irg_visited();
678 for (i = 0; i < get_irp_n_irgs(); i++)
679 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
681 /** We have to start the walk at the same nodes as cg_walk. **/
682 /* Walk starting at unreachable procedures. Only these
683 * have End blocks visible in interprocedural view. */
684 for (i = 0; i < get_irp_n_irgs(); i++) {
686 current_ir_graph = get_irp_irg(i);
688 sb = get_irg_start_block(current_ir_graph);
690 if ((get_Block_n_cfgpreds(sb) > 1) ||
691 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
693 cfscc(get_irg_end_block(current_ir_graph));
696 /* Check whether we walked all procedures: there could be procedures
697 with cyclic calls but no call from the outside. */
698 for (i = 0; i < get_irp_n_irgs(); i++) {
700 current_ir_graph = get_irp_irg(i);
702 /* Test start block: if inner procedure end and end block are not
703 * visible and therefore not marked. */
704 sb = get_irg_start_block(current_ir_graph);
705 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
708 /* Walk all endless cfloops in inner procedures.
709 * We recognize an inner procedure if the End node is not visited. */
710 for (i = 0; i < get_irp_n_irgs(); i++) {
712 current_ir_graph = get_irp_irg(i);
714 e = get_irg_end(current_ir_graph);
715 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
717 /* Don't visit the End node. */
718 for (j = 0; j < get_End_n_keepalives(e); j++) {
719 ir_node *el = get_End_keepalive(e, j);
720 if (is_Block(el)) cfscc(el);
725 set_irg_loop(outermost_ir_graph, current_loop);
726 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
727 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
729 obstack_free(&temp, NULL);
730 current_ir_graph = rem;
731 set_interprocedural_view(rem_ipv);
732 return max_loop_depth;
737 * Clear the intra- and the interprocedural
738 * backedge information pf a block.
740 static void reset_backedges(ir_node *block) {
743 assert(is_Block(block));
744 #ifdef INTERPROCEDURAL_VIEW
745 rem = get_interprocedural_view();
746 set_interprocedural_view(1);
747 clear_backedges(block);
748 set_interprocedural_view(0);
749 clear_backedges(block);
750 set_interprocedural_view(rem);
753 clear_backedges(block);
758 * Reset all backedges of the first block of
759 * a loop as well as all loop info for all nodes of this loop.
760 * Recurse into all nested loops.
762 static void loop_reset_backedges(ir_loop *l) {
764 reset_backedges(get_loop_node(l, 0));
765 for (i = 0; i < get_loop_n_nodes(l); ++i)
766 set_irn_loop(get_loop_node(l, i), NULL);
767 for (i = 0; i < get_loop_n_sons(l); ++i) {
768 loop_reset_backedges(get_loop_son(l, i));
772 /* Removes all cfloop information.
773 Resets all backedges */
774 void free_cfloop_information(ir_graph *irg) {
775 ir_loop *loop = get_irg_loop(irg);
777 loop_reset_backedges(loop);
778 set_irg_loop(irg, NULL);
780 set_irg_loopinfo_state(irg, loopinfo_none);
781 /* We cannot free the cfloop nodes, they are on the obstack. */
785 void free_all_cfloop_information(void) {
787 #ifdef INTERPROCEDURAL_VIEW
788 int rem = get_interprocedural_view();
789 set_interprocedural_view(1); /* To visit all filter nodes */
791 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
792 free_cfloop_information(get_irp_irg(i));
794 #ifdef INTERPROCEDURAL_VIEW
795 set_interprocedural_view(rem);