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
35 #include "irgraph_t.h"
42 #define NO_CFLOOPS_WITHOUT_HEAD 1
44 /** The outermost graph the scc is computed for */
45 static ir_graph *outermost_ir_graph;
46 /** Current cfloop construction is working on. */
47 static ir_loop *current_loop;
48 /** Counts the number of allocated cfloop nodes.
49 * Each cfloop node gets a unique number.
50 * @todo What for? ev. remove.
52 static int loop_node_cnt = 0;
53 /** Counter to generate depth first numbering of visited nodes. */
54 static int current_dfn = 1;
56 static int max_loop_depth = 0;
58 void link_to_reg_end(ir_node *n, void *env);
60 /**********************************************************************/
61 /* Node attributes **/
62 /**********************************************************************/
64 /**********************************************************************/
65 /* Node attributes needed for the construction. **/
66 /**********************************************************************/
69 * The SCC info. Additional fields for an ir-node needed for the
72 typedef struct scc_info {
73 int in_stack; /**< Marks whether node is on the stack. */
74 int dfn; /**< Depth first search number. */
75 int uplink; /**< dfn number of ancestor. */
78 /** Allocate a new scc_info on the given obstack */
79 static inline scc_info *new_scc_info(struct obstack *obst)
81 return OALLOCZ(obst, scc_info);
85 * Marks the node n to be on the stack.
87 static inline void mark_irn_in_stack(ir_node *n)
89 scc_info *info = get_irn_link(n);
94 * Marks the node n to be not on the stack.
96 static inline void mark_irn_not_in_stack(ir_node *n)
98 scc_info *info = get_irn_link(n);
103 * Returns whether node n is on the stack.
105 static inline int irn_is_in_stack(ir_node *n)
107 scc_info *info = get_irn_link(n);
108 return info->in_stack;
112 * Sets node n uplink value.
114 static inline void set_irn_uplink(ir_node *n, int uplink)
116 scc_info *info = get_irn_link(n);
117 info->uplink = uplink;
121 * Return node n uplink value.
123 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)
134 scc_info *info = get_irn_link(n);
139 * Returns node n dfn value.
141 static inline int get_irn_dfn(ir_node *n)
143 scc_info *info = get_irn_link(n);
147 /**********************************************************************/
149 /**********************************************************************/
151 /** An IR-node stack */
152 static ir_node **stack = NULL;
153 /** The top (index) of the IR-node stack */
157 * Initializes the IR-node stack
159 static inline void init_stack(void)
162 ARR_RESIZE(ir_node *, stack, 1000);
164 stack = NEW_ARR_F(ir_node *, 1000);
169 static void finish_stack(void)
176 * Push a node n onto the IR-node stack.
178 static inline void push(ir_node *n)
180 if (tos == ARR_LEN(stack)) {
181 int nlen = ARR_LEN(stack) * 2;
182 ARR_RESIZE(ir_node *, stack, nlen);
185 mark_irn_in_stack(n);
189 * Pop a node from the IR-node stack and return it.
191 static inline ir_node *pop(void)
193 ir_node *n = stack[--tos];
194 mark_irn_not_in_stack(n);
199 * The nodes from tos up to n belong to the current loop.
200 * Removes them from the stack and adds them to the current loop.
202 static inline void pop_scc_to_loop(ir_node *n)
209 set_irn_dfn(m, loop_node_cnt);
210 add_loop_node(current_loop, m);
211 set_irn_loop(m, current_loop);
215 /* GL ??? my last son is my grandson??? Removes cfloops with no
216 ir_nodes in them. Such loops have only another loop as son. (Why
217 can't they have two loops as sons? Does it never get that far? ) */
218 static void close_loop(ir_loop *l)
220 int last = get_loop_n_elements(l) - 1;
221 loop_element lelement = get_loop_element(l, last);
222 ir_loop *last_son = lelement.son;
224 if (get_kind(last_son) == k_ir_loop &&
225 get_loop_n_elements(last_son) == 1) {
228 lelement = get_loop_element(last_son, 0);
230 if (get_kind(gson) == k_ir_loop) {
231 loop_element new_last_son;
233 gson->outer_loop = l;
234 new_last_son.son = gson;
235 l->children[last] = new_last_son;
237 /* the loop last_son is dead now, recover at least some memory */
238 DEL_ARR_F(last_son->children);
246 * Removes and unmarks all nodes up to n from the stack.
247 * The nodes must be visited once more to assign them to a scc.
249 static inline void pop_scc_unmark_visit(ir_node *n)
255 set_irn_visited(m, 0);
259 /**********************************************************************/
260 /* The loop datastructure. **/
261 /**********************************************************************/
264 * Allocates a new loop as son of current_loop. Sets current_loop
265 * to the new loop and returns its father.
266 * The loop is allocated on the outermost_ir_graphs's obstack.
268 static ir_loop *new_loop(void)
270 ir_loop *father = current_loop;
271 ir_loop *son = alloc_loop(father, outermost_ir_graph->obst);
273 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
278 /**********************************************************************/
279 /* Constructing and destructing the loop/backedge information. **/
280 /**********************************************************************/
282 /* Initialization steps. **********************************************/
285 * Allocates a scc_info for every Block node n.
286 * Clear the backedges for all nodes.
287 * Called from a walker.
289 static inline void init_node(ir_node *n, void *env)
291 struct obstack *obst = env;
293 set_irn_link(n, new_scc_info(obst));
298 * Initializes the common global settings for the scc algorithm
300 static inline void init_scc_common(void)
308 * Initializes the scc algorithm for the intraprocedural case.
309 * Add scc info to every block node.
311 static inline void init_scc(ir_graph *irg, struct obstack *obst)
314 irg_walk_graph(irg, init_node, NULL, obst);
317 static inline void finish_scc(void)
322 #ifdef INTERPROCEDURAL_VIEW
324 * Initializes the scc algorithm for the interprocedural case.
326 static inline void init_ip_scc(struct obstack *obst)
329 cg_walk(init_node, NULL, obst);
331 #if EXPERIMENTAL_CFLOOP_TREE
332 cg_walk(link_to_reg_end, NULL, NULL);
338 * Condition for breaking the recursion: n is the block
339 * that gets the initial control flow from the Start node.
341 static int is_outermost_StartBlock(ir_node *n)
343 /* Test whether this is the outermost Start node. If so
344 recursion must end. */
346 if (get_Block_n_cfgpreds(n) == 1 &&
347 is_Start(skip_Proj(get_Block_cfgpred(n, 0))) &&
348 get_Block_cfgpred_block(n, 0) == n) {
354 /** Returns non-zero if n is a loop header, i.e., it is a Block node
355 * and has predecessors within the cfloop and out of the cfloop.
357 * @param n the block node to check
358 * @param root only needed for assertion.
360 static int is_head(ir_node *n, ir_node *root)
363 int some_outof_loop = 0, some_in_loop = 0;
368 if (!is_outermost_StartBlock(n)) {
369 arity = get_Block_n_cfgpreds(n);
370 for (i = 0; i < arity; i++) {
371 ir_node *pred = get_Block_cfgpred_block(n, i);
372 /* ignore Bad control flow: it cannot happen */
375 if (is_backedge(n, i))
377 if (!irn_is_in_stack(pred)) {
380 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
385 return some_outof_loop & some_in_loop;
390 * Returns non-zero if n is possible loop head of an endless loop.
391 * I.e., it is a Block node and has only predecessors
394 * @param n the block node to check
395 * @param root only needed for assertion.
397 static int is_endless_head(ir_node *n, ir_node *root)
400 int none_outof_loop = 1, some_in_loop = 0;
404 /* Test for legal loop header: Block, Phi, ... */
405 if (!is_outermost_StartBlock(n)) {
406 arity = get_Block_n_cfgpreds(n);
407 for (i = 0; i < arity; i++) {
408 ir_node *pred = get_Block_cfgpred_block(n, i);
409 /* ignore Bad control flow: it cannot happen */
412 if (is_backedge(n, i))
414 if (!irn_is_in_stack(pred)) {
417 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
422 return none_outof_loop && some_in_loop;
426 * Returns index of the predecessor with the smallest dfn number
427 * greater-equal than limit.
429 static int smallest_dfn_pred(ir_node *n, int limit)
431 int i, index = -2, min = -1;
433 if (!is_outermost_StartBlock(n)) {
434 int arity = get_Block_n_cfgpreds(n);
435 for (i = 0; i < arity; i++) {
436 ir_node *pred = get_Block_cfgpred_block(n, i);
437 /* ignore Bad control flow: it cannot happen */
440 if (is_backedge(n, i) || !irn_is_in_stack(pred))
442 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
444 min = get_irn_dfn(pred);
452 * Returns index of the predecessor with the largest dfn number.
454 static int largest_dfn_pred(ir_node *n)
456 int i, index = -2, max = -1;
458 if (!is_outermost_StartBlock(n)) {
459 int arity = get_Block_n_cfgpreds(n);
460 for (i = 0; i < arity; i++) {
461 ir_node *pred = get_Block_cfgpred_block(n, i);
462 /* ignore Bad control flow: it cannot happen */
465 if (is_backedge(n, i) || !irn_is_in_stack(pred))
467 if (get_irn_dfn(pred) > max) {
469 max = get_irn_dfn(pred);
477 * Searches the stack for possible loop heads. Tests these for backedges.
478 * If it finds a head with an unmarked backedge it marks this edge and
479 * returns the tail of the loop.
480 * If it finds no backedge returns NULL.
482 static ir_node *find_tail(ir_node *n)
485 int i, res_index = -2;
487 m = stack[tos-1]; /* tos = top of stack */
489 res_index = smallest_dfn_pred(m, 0);
490 if ((res_index == -2) && /* no smallest dfn pred found. */
496 for (i = tos-2; i >= 0; --i) {
500 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
501 if (res_index == -2) /* no smallest dfn pred found. */
502 res_index = largest_dfn_pred(m);
504 if ((m == n) && (res_index == -2)) {
511 /* We should not walk past our selves on the stack: The upcoming nodes
512 are not in this loop. We assume a loop not reachable from Start. */
520 /* A dead loop not reachable from Start. */
521 for (i = tos-2; i >= 0; --i) {
523 if (is_endless_head(m, n)) {
524 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
525 if (res_index == -2) /* no smallest dfn pred found. */
526 res_index = largest_dfn_pred(m);
529 if (m == n) break; /* It's not an unreachable loop, either. */
531 //assert(0 && "no head found on stack");
534 assert(res_index > -2);
536 set_backedge(m, res_index);
537 return is_outermost_StartBlock(n) ? NULL : get_Block_cfgpred_block(m, res_index);
541 * returns non.zero if l is the outermost loop.
543 inline static int is_outermost_loop(ir_loop *l)
545 return l == get_loop_outer_loop(l);
548 /*-----------------------------------------------------------*
549 * The core algorithm. *
550 *-----------------------------------------------------------*/
553 * Walks over all blocks of a graph
555 static void cfscc(ir_node *n)
561 if (irn_visited_else_mark(n)) return;
563 /* Initialize the node */
564 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
565 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
566 set_irn_loop(n, NULL);
570 if (!is_outermost_StartBlock(n)) {
571 int arity = get_Block_n_cfgpreds(n);
573 for (i = 0; i < arity; i++) {
576 if (is_backedge(n, i))
578 m = get_Block_cfgpred_block(n, i);
579 /* ignore Bad control flow: it cannot happen */
584 if (irn_is_in_stack(m)) {
585 /* Uplink of m is smaller if n->m is a backedge.
586 Propagate the uplink to mark the cfloop. */
587 if (get_irn_uplink(m) < get_irn_uplink(n))
588 set_irn_uplink(n, get_irn_uplink(m));
593 if (get_irn_dfn(n) == get_irn_uplink(n)) {
594 /* This condition holds for
595 1) the node with the incoming backedge.
596 That is: We found a cfloop!
597 2) Straight line code, because no uplink has been propagated, so the
598 uplink still is the same as the dfn.
600 But n might not be a proper cfloop head for the analysis. Proper cfloop
601 heads are Block and Phi nodes. find_tail searches the stack for
602 Block's and Phi's and takes those nodes as cfloop heads for the current
603 cfloop instead and marks the incoming edge as backedge. */
605 ir_node *tail = find_tail(n);
607 /* We have a cfloop, that is no straight line code,
608 because we found a cfloop head!
609 Next actions: Open a new cfloop on the cfloop tree and
610 try to find inner cfloops */
612 #if NO_CFLOOPS_WITHOUT_HEAD
614 /* This is an adaption of the algorithm from fiasco / optscc to
615 * avoid cfloops without Block or Phi as first node. This should
616 * severely reduce the number of evaluations of nodes to detect
617 * a fixpoint in the heap analysis.
618 * Further it avoids cfloops without firm nodes that cause errors
619 * in the heap analyses. */
623 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
633 ir_loop *l = new_loop();
637 /* Remove the cfloop from the stack ... */
638 pop_scc_unmark_visit(n);
640 /* The current backedge has been marked, that is temporarily eliminated,
641 by find tail. Start the scc algorithm
642 anew on the subgraph thats left (the current cfloop without the backedge)
643 in order to find more inner cfloops. */
647 assert(irn_visited(n));
648 #if NO_CFLOOPS_WITHOUT_HEAD
653 /* AS: No cfloop head was found, that is we have straight line code.
654 Pop all nodes from the stack to the current cfloop. */
660 /* Constructs control flow backedge information for irg. */
661 int construct_cf_backedges(ir_graph *irg)
663 ir_graph *rem = current_ir_graph;
665 ir_node *end = get_irg_end(irg);
669 #ifdef INTERPROCEDURAL_VIEW
670 assert(!get_interprocedural_view() &&
671 "use construct_ip_cf_backedges()");
675 current_ir_graph = irg;
676 outermost_ir_graph = irg;
679 init_scc(irg, &temp);
682 new_loop(); /* sets current_loop */
683 head_rem = current_loop; /* Just for assertion */
685 inc_irg_visited(irg);
687 /* walk over all blocks of the graph, including keep alives */
688 cfscc(get_irg_end_block(irg));
689 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
690 ir_node *el = get_End_keepalive(end, i);
695 obstack_free(&temp, NULL);
697 assert(head_rem == current_loop);
698 mature_loops(current_loop, irg->obst);
699 set_irg_loop(irg, current_loop);
700 set_irg_loopinfo_state(irg, loopinfo_cf_consistent);
701 assert(get_irg_loop(irg)->kind == k_ir_loop);
703 current_ir_graph = rem;
704 return max_loop_depth;
707 void assure_cf_loop(ir_graph *irg)
709 irg_loopinfo_state state = get_irg_loopinfo_state(irg);
711 if (state != loopinfo_cf_consistent)
712 construct_cf_backedges(irg);
715 #ifdef INTERPROCEDURAL_VIEW
716 int construct_ip_cf_backedges (void)
718 ir_graph *rem = current_ir_graph;
719 int rem_ipv = get_interprocedural_view();
723 assert(get_irp_ip_view_state() == ip_view_valid);
725 outermost_ir_graph = get_irp_main_irg();
731 new_loop(); /* sets current_loop */
732 set_interprocedural_view(1);
734 inc_max_irg_visited();
735 for (i = 0; i < get_irp_n_irgs(); i++)
736 set_irg_visited(get_irp_irg(i), get_max_irg_visited());
738 /** We have to start the walk at the same nodes as cg_walk. **/
739 /* Walk starting at unreachable procedures. Only these
740 * have End blocks visible in interprocedural view. */
741 for (i = 0; i < get_irp_n_irgs(); i++) {
743 current_ir_graph = get_irp_irg(i);
745 sb = get_irg_start_block(current_ir_graph);
747 if ((get_Block_n_cfgpreds(sb) > 1) ||
748 (get_nodes_block(get_Block_cfgpred(sb, 0)) != sb)) continue;
750 cfscc(get_irg_end_block(current_ir_graph));
753 /* Check whether we walked all procedures: there could be procedures
754 with cyclic calls but no call from the outside. */
755 for (i = 0; i < get_irp_n_irgs(); i++) {
757 current_ir_graph = get_irp_irg(i);
759 /* Test start block: if inner procedure end and end block are not
760 * visible and therefore not marked. */
761 sb = get_irg_start_block(current_ir_graph);
762 if (get_irn_visited(sb) < get_irg_visited(current_ir_graph)) cfscc(sb);
765 /* Walk all endless cfloops in inner procedures.
766 * We recognize an inner procedure if the End node is not visited. */
767 for (i = 0; i < get_irp_n_irgs(); i++) {
769 current_ir_graph = get_irp_irg(i);
771 e = get_irg_end(current_ir_graph);
772 if (get_irn_visited(e) < get_irg_visited(current_ir_graph)) {
774 /* Don't visit the End node. */
775 for (j = 0; j < get_End_n_keepalives(e); j++) {
776 ir_node *el = get_End_keepalive(e, j);
777 if (is_Block(el)) cfscc(el);
782 set_irg_loop(outermost_ir_graph, current_loop);
783 set_irg_loopinfo_state(current_ir_graph, loopinfo_cf_ip_consistent);
784 assert(get_irg_loop(outermost_ir_graph)->kind == k_ir_loop);
786 obstack_free(&temp, NULL);
787 current_ir_graph = rem;
788 set_interprocedural_view(rem_ipv);
789 return max_loop_depth;
795 * Clear the intra- and the interprocedural
796 * backedge information pf a block.
798 static void reset_backedges(ir_node *block)
802 assert(is_Block(block));
803 #ifdef INTERPROCEDURAL_VIEW
804 rem = get_interprocedural_view();
805 set_interprocedural_view(1);
806 clear_backedges(block);
807 set_interprocedural_view(0);
808 clear_backedges(block);
809 set_interprocedural_view(rem);
812 clear_backedges(block);
817 * Reset all backedges of the first block of
818 * a loop as well as all loop info for all nodes of this loop.
819 * Recurse into all nested loops.
821 static void loop_reset_backedges(ir_loop *l)
824 reset_backedges(get_loop_node(l, 0));
825 for (i = 0; i < get_loop_n_nodes(l); ++i)
826 set_irn_loop(get_loop_node(l, i), NULL);
827 for (i = 0; i < get_loop_n_sons(l); ++i) {
828 loop_reset_backedges(get_loop_son(l, i));
832 /* Removes all cfloop information.
833 Resets all backedges */
834 static void free_cfloop_information(ir_graph *irg)
836 ir_loop *loop = get_irg_loop(irg);
838 loop_reset_backedges(loop);
839 set_irg_loop(irg, NULL);
841 set_irg_loopinfo_state(irg, loopinfo_none);
842 /* We cannot free the cfloop nodes, they are on the obstack. */
846 void free_all_cfloop_information(void)
849 #ifdef INTERPROCEDURAL_VIEW
850 int rem = get_interprocedural_view();
851 set_interprocedural_view(1); /* To visit all filter nodes */
853 for (i = get_irp_n_irgs() - 1; i >= 0; --i) {
854 free_cfloop_information(get_irp_irg(i));
856 #ifdef INTERPROCEDURAL_VIEW
857 set_interprocedural_view(rem);