2 * Copyright (C) 1995-2011 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
34 #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 unsigned 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 = (scc_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 = (scc_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 = (scc_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 = (scc_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 = (scc_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 = (scc_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 = (scc_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 */
154 static size_t tos = 0;
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 size_t 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 size_t 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, get_irg_obstack(outermost_ir_graph));
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 = (struct obstack*) 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 /** Returns non-zero if n is a loop header, i.e., it is a Block node
323 * and has predecessors within the cfloop and out of the cfloop.
325 * @param n the block node to check
326 * @param root only needed for assertion.
328 static int is_head(ir_node *n, ir_node *root)
330 int some_outof_loop = 0, some_in_loop = 0;
333 int const arity = get_Block_n_cfgpreds(n);
334 for (int i = 0; i < arity; i++) {
335 ir_node *pred = get_Block_cfgpred_block(n, i);
336 /* ignore Bad control flow: it cannot happen */
339 if (is_backedge(n, i))
341 if (!irn_is_in_stack(pred)) {
344 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
348 return some_outof_loop & some_in_loop;
353 * Returns non-zero if n is possible loop head of an endless loop.
354 * I.e., it is a Block node and has only predecessors
357 * @param n the block node to check
358 * @param root only needed for assertion.
360 static int is_endless_head(ir_node *n, ir_node *root)
362 int none_outof_loop = 1, some_in_loop = 0;
365 /* Test for legal loop header: Block, Phi, ... */
366 int const arity = get_Block_n_cfgpreds(n);
367 for (int i = 0; i < arity; i++) {
368 ir_node *pred = get_Block_cfgpred_block(n, i);
369 /* ignore Bad control flow: it cannot happen */
372 if (is_backedge(n, i))
374 if (!irn_is_in_stack(pred)) {
377 assert(get_irn_uplink(pred) >= get_irn_uplink(root));
381 return none_outof_loop && some_in_loop;
385 * Returns index of the predecessor with the smallest dfn number
386 * greater-equal than limit.
388 static int smallest_dfn_pred(ir_node *n, int limit)
390 int i, index = -2, min = -1;
392 int arity = get_Block_n_cfgpreds(n);
393 for (i = 0; i < arity; i++) {
394 ir_node *pred = get_Block_cfgpred_block(n, i);
395 /* ignore Bad control flow: it cannot happen */
398 if (is_backedge(n, i) || !irn_is_in_stack(pred))
400 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
402 min = get_irn_dfn(pred);
409 * Returns index of the predecessor with the largest dfn number.
411 static int largest_dfn_pred(ir_node *n)
413 int i, index = -2, max = -1;
415 int arity = get_Block_n_cfgpreds(n);
416 for (i = 0; i < arity; i++) {
417 ir_node *pred = get_Block_cfgpred_block(n, i);
418 /* ignore Bad control flow: it cannot happen */
421 if (is_backedge(n, i) || !irn_is_in_stack(pred))
423 if (get_irn_dfn(pred) > max) {
425 max = get_irn_dfn(pred);
432 * Searches the stack for possible loop heads. Tests these for backedges.
433 * If it finds a head with an unmarked backedge it marks this edge and
434 * returns the tail of the loop.
435 * If it finds no backedge returns NULL.
437 static ir_node *find_tail(ir_node *n)
443 m = stack[tos - 1]; /* tos = top of stack */
445 res_index = smallest_dfn_pred(m, 0);
446 if ((res_index == -2) && /* no smallest dfn pred found. */
452 for (i = tos - 1; i != 0;) {
455 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
456 if (res_index == -2) /* no smallest dfn pred found. */
457 res_index = largest_dfn_pred(m);
459 if ((m == n) && (res_index == -2)) {
466 /* We should not walk past our selves on the stack: The upcoming nodes
467 are not in this loop. We assume a loop not reachable from Start. */
474 if (i == (size_t)-1) {
475 /* A dead loop not reachable from Start. */
476 for (i = tos - 1; i != 0;) {
478 if (is_endless_head(m, n)) {
479 res_index = smallest_dfn_pred (m, get_irn_dfn(m) + 1);
480 if (res_index == -2) /* no smallest dfn pred found. */
481 res_index = largest_dfn_pred(m);
484 if (m == n) break; /* It's not an unreachable loop, either. */
486 //assert(0 && "no head found on stack");
489 assert(res_index > -2);
491 set_backedge(m, res_index);
492 return get_Block_cfgpred_block(m, res_index);
496 * returns non.zero if l is the outermost loop.
498 inline static int is_outermost_loop(ir_loop *l)
500 return l == get_loop_outer_loop(l);
503 /*-----------------------------------------------------------*
504 * The core algorithm. *
505 *-----------------------------------------------------------*/
508 * Walks over all blocks of a graph
510 static void cfscc(ir_node *n)
517 if (irn_visited_else_mark(n)) return;
519 /* Initialize the node */
520 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
521 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
522 set_irn_loop(n, NULL);
526 arity = get_Block_n_cfgpreds(n);
528 for (i = 0; i < arity; i++) {
531 if (is_backedge(n, i))
533 m = get_Block_cfgpred_block(n, i);
534 /* ignore Bad control flow: it cannot happen */
539 if (irn_is_in_stack(m)) {
540 /* Uplink of m is smaller if n->m is a backedge.
541 Propagate the uplink to mark the cfloop. */
542 if (get_irn_uplink(m) < get_irn_uplink(n))
543 set_irn_uplink(n, get_irn_uplink(m));
547 if (get_irn_dfn(n) == get_irn_uplink(n)) {
548 /* This condition holds for
549 1) the node with the incoming backedge.
550 That is: We found a cfloop!
551 2) Straight line code, because no uplink has been propagated, so the
552 uplink still is the same as the dfn.
554 But n might not be a proper cfloop head for the analysis. Proper cfloop
555 heads are Block and Phi nodes. find_tail searches the stack for
556 Block's and Phi's and takes those nodes as cfloop heads for the current
557 cfloop instead and marks the incoming edge as backedge. */
559 ir_node *tail = find_tail(n);
561 /* We have a cfloop, that is no straight line code,
562 because we found a cfloop head!
563 Next actions: Open a new cfloop on the cfloop tree and
564 try to find inner cfloops */
566 #if NO_CFLOOPS_WITHOUT_HEAD
568 /* This is an adaption of the algorithm from fiasco / optscc to
569 * avoid cfloops without Block or Phi as first node. This should
570 * severely reduce the number of evaluations of nodes to detect
571 * a fixpoint in the heap analysis.
572 * Further it avoids cfloops without firm nodes that cause errors
573 * in the heap analyses. */
577 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
587 ir_loop *l = new_loop();
591 /* Remove the cfloop from the stack ... */
592 pop_scc_unmark_visit(n);
594 /* The current backedge has been marked, that is temporarily eliminated,
595 by find tail. Start the scc algorithm
596 anew on the subgraph thats left (the current cfloop without the backedge)
597 in order to find more inner cfloops. */
601 assert(irn_visited(n));
602 #if NO_CFLOOPS_WITHOUT_HEAD
607 /* AS: No cfloop head was found, that is we have straight line code.
608 Pop all nodes from the stack to the current cfloop. */
614 int construct_cf_backedges(ir_graph *irg)
617 ir_node *end = get_irg_end(irg);
623 outermost_ir_graph = irg;
626 init_scc(irg, &temp);
629 new_loop(); /* sets current_loop */
630 head_rem = current_loop; /* Just for assertion */
632 inc_irg_visited(irg);
634 /* walk over all blocks of the graph, including keep alives */
635 cfscc(get_irg_end_block(irg));
636 for (i = get_End_n_keepalives(end) - 1; i >= 0; --i) {
637 ir_node *el = get_End_keepalive(end, i);
642 obstack_free(&temp, NULL);
644 assert(head_rem == current_loop);
645 mature_loops(current_loop, get_irg_obstack(irg));
646 set_irg_loop(irg, current_loop);
647 add_irg_properties(irg, IR_GRAPH_PROPERTY_CONSISTENT_LOOPINFO);
649 return max_loop_depth;
652 void assure_loopinfo(ir_graph *irg)
654 if (irg_has_properties(irg, IR_GRAPH_PROPERTY_CONSISTENT_LOOPINFO))
656 construct_cf_backedges(irg);