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
23 * backedge/loop datastructures.
24 * A variation on the Tarjan algorithm. See also [Trapp:99],
26 * @author Goetz Lindenmaier
37 #include "irgraph_t.h"
45 /* A variant of the loop tree that avoids loops without head.
46 This reduces the depth of the loop tree. */
47 #define NO_LOOPS_WITHOUT_HEAD 1
49 /** The outermost graph the scc is computed for. */
50 static ir_graph *outermost_ir_graph;
51 /** Current loop construction is working on. */
52 static ir_loop *current_loop;
53 /** Counts the number of allocated loop nodes.
54 * Each loop node gets a unique number.
55 * @todo What for? ev. remove.
57 static int loop_node_cnt = 0;
58 /** Counter to generate depth first numbering of visited nodes. */
59 static int current_dfn = 1;
61 static unsigned max_loop_depth = 0;
63 void link_to_reg_end(ir_node *n, void *env);
64 void set_projx_link(ir_node *cb_projx, ir_node *end_projx);
65 ir_node *get_projx_link(ir_node *cb_projx);
67 /**********************************************************************/
68 /* Node attributes **/
69 /**********************************************************************/
71 /**********************************************************************/
72 /* Node attributes needed for the construction. **/
73 /**********************************************************************/
75 typedef struct scc_info {
76 int in_stack; /**< Marks whether node is on the stack. */
77 int dfn; /**< Depth first search number. */
78 int uplink; /**< dfn number of ancestor. */
79 /* ir_loop *loop; *//* Refers to the containing loop. */
81 struct section *section;
88 * Allocates a new SCC info on the given obstack.
90 static inline scc_info *new_scc_info(struct obstack *obst)
92 return OALLOCZ(obst, scc_info);
96 * Mark node n being on the SCC stack.
98 static inline void mark_irn_in_stack(ir_node *n)
100 scc_info *scc = (scc_info*) get_irn_link(n);
106 * Mark node n NOT being on the SCC stack.
108 static inline void mark_irn_not_in_stack(ir_node *n)
110 scc_info *scc = (scc_info*) get_irn_link(n);
116 * Checks if a node is on the SCC stack.
118 static inline int irn_is_in_stack(ir_node *n)
120 scc_info *scc = (scc_info*) get_irn_link(n);
122 return scc->in_stack;
126 * Sets the uplink number for a node.
128 static inline void set_irn_uplink(ir_node *n, int uplink)
130 scc_info *scc = (scc_info*) get_irn_link(n);
132 scc->uplink = uplink;
136 * Returns the uplink number for a node.
138 static int get_irn_uplink(ir_node *n)
140 scc_info *scc = (scc_info*) get_irn_link(n);
146 * Sets the depth-first-search number for a node.
148 static inline void set_irn_dfn(ir_node *n, int dfn)
150 scc_info *scc = (scc_info*) get_irn_link(n);
156 * Returns the depth-first-search number of a node.
158 static int get_irn_dfn(ir_node *n)
160 scc_info *scc = (scc_info*) get_irn_link(n);
166 static ir_loop *find_nodes_loop(ir_node *n, ir_loop *l)
171 /* Test whether n is contained in this loop. */
172 for (i = 0; i < get_loop_n_nodes(l); i++)
173 if (n == get_loop_node(l, i)) return l;
175 /* Is this a leave in the loop tree? If so loop not found. */
176 if (get_loop_n_sons(l) == 0) return NULL;
178 /* Else descend in the loop tree. */
179 for (i = 0; i < get_loop_n_sons(l); i++) {
180 res = find_nodes_loop(n, get_loop_son(l, i));
186 /* @@@ temporary implementation, costly!!! */
187 ir_loop * get_irn_loop(ir_node *n)
189 ir_loop *l = get_irg_loop(current_ir_graph);
190 l = find_nodes_loop(n, l);
195 /**********************************************************************/
197 /**********************************************************************/
199 static ir_node **stack = NULL;
200 static size_t tos = 0; /* top of stack */
203 * initializes the stack
205 static inline void init_stack(void)
208 ARR_RESIZE(ir_node *, stack, 1000);
210 stack = NEW_ARR_F(ir_node *, 1000);
218 static void finish_stack(void)
225 * push a node onto the stack
227 * @param n The node to push
229 static inline void push(ir_node *n)
231 if (tos == ARR_LEN(stack)) {
232 size_t nlen = ARR_LEN(stack) * 2;
233 ARR_RESIZE(ir_node *, stack, nlen);
236 mark_irn_in_stack(n);
240 * pop a node from the stack
242 * @return The topmost node
244 static inline ir_node *pop(void)
250 mark_irn_not_in_stack(n);
255 * The nodes up to n belong to the current loop.
256 * Removes them from the stack and adds them to the current loop.
258 static inline void pop_scc_to_loop(ir_node *n)
266 set_irn_dfn(m, loop_node_cnt);
267 add_loop_node(current_loop, m);
268 set_irn_loop(m, current_loop);
272 /* GL ??? my last son is my grandson??? Removes loops with no
273 ir_nodes in them. Such loops have only another loop as son. (Why
274 can't they have two loops as sons? Does it never get that far? ) */
275 static void close_loop(ir_loop *l)
277 size_t last = get_loop_n_elements(l) - 1;
278 loop_element lelement = get_loop_element(l, last);
279 ir_loop *last_son = lelement.son;
281 if (get_kind(last_son) == k_ir_loop &&
282 get_loop_n_elements(last_son) == 1) {
285 lelement = get_loop_element(last_son, 0);
288 if (get_kind(gson) == k_ir_loop) {
289 loop_element new_last_son;
291 gson->outer_loop = l;
292 new_last_son.son = gson;
293 l->children[last] = new_last_son;
300 /* Removes and unmarks all nodes up to n from the stack.
301 The nodes must be visited once more to assign them to a scc. */
302 static inline void pop_scc_unmark_visit(ir_node *n)
308 set_irn_visited(m, 0);
312 /**********************************************************************/
313 /* The loop datastructure. **/
314 /**********************************************************************/
316 /* Allocates a new loop as son of current_loop. Sets current_loop
317 to the new loop and returns the father. */
318 static ir_loop *new_loop(void)
320 ir_loop *father = current_loop;
321 ir_loop *son = alloc_loop(father, get_irg_obstack(outermost_ir_graph));
323 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
328 /**********************************************************************/
329 /* Constructing and destructing the loop/backedge information. **/
330 /**********************************************************************/
332 /* Initialization steps. **********************************************/
334 static inline void init_node(ir_node *n, void *env)
336 struct obstack *obst = (struct obstack*) env;
337 set_irn_link(n, new_scc_info(obst));
341 static inline void init_scc_common(void)
348 static inline void init_scc(ir_graph *irg, struct obstack *obst)
351 irg_walk_graph(irg, init_node, NULL, obst);
353 irg_walk (irg, link_to_reg_end, NULL, NULL);
357 static inline void finish_scc(void)
363 * Check whether a given node represents the outermost Start
364 * block. In intra-procedural view this is the start block of the
365 * current graph, in interprocedural view it is the start block
366 * of the outer most graph.
368 * @param n the node to check
370 * This is the condition for breaking the scc recursion.
372 static int is_outermost_Start(ir_node *n)
374 /* Test whether this is the outermost Start node. */
375 if (is_Block(n) && get_Block_n_cfgpreds(n) == 1) {
376 ir_node *pred = skip_Proj(get_Block_cfgpred(n, 0));
377 if (is_Start(pred) && get_nodes_block(pred) == n)
383 /* When to walk from nodes to blocks. Only for Control flow operations? */
384 static inline int get_start_index(ir_node *n)
386 #undef BLOCK_BEFORE_NODE
387 #define BLOCK_BEFORE_NODE 1
389 #if BLOCK_BEFORE_NODE
391 /* This version assures, that all nodes are ordered absolutely. This allows
392 to undef all nodes in the heap analysis if the block is false, which
394 I.e., with this code, the order on the loop tree is correct. But a
395 (single) test showed the loop tree is deeper. */
398 (get_irg_pinned(get_irn_irg(n)) == op_pin_state_floats &&
399 get_irn_pinned(n) == op_pin_state_floats))
400 // Here we could test for backedge at -1 which is illegal
407 /* This version causes deeper loop trees (at least we verified this
409 But it guarantees that Blocks are analysed before nodes contained in the
410 block. If so, we can set the value to undef if the block is not \
412 if (is_cfop(n) || is_fragile_op(n) || is_Start(n))
421 * Return non-zero if the given node is a legal loop header:
424 * @param n the node to check
426 static inline int is_possible_loop_head(ir_node *n)
428 return is_Block(n) || is_Phi(n);
432 * Returns non-zero if n is a loop header, i.e., it is a Block or Phi
433 * node and has predecessors within the loop and out of the loop.
435 * @param n the node to check
436 * @param root only needed for assertion.
438 static int is_head(ir_node *n, ir_node *root)
441 int some_outof_loop = 0, some_in_loop = 0;
443 /* Test for legal loop header: Block, Phi, ... */
444 if (!is_possible_loop_head(n))
447 if (!is_outermost_Start(n)) {
449 int uplink = get_irn_uplink(root);
453 arity = get_irn_arity(n);
454 for (i = get_start_index(n); i < arity; i++) {
456 if (is_backedge(n, i))
458 pred = get_irn_n(n, i);
459 if (! irn_is_in_stack(pred)) {
462 assert(get_irn_uplink(pred) >= uplink);
467 return some_outof_loop & some_in_loop;
471 * Returns non-zero if n is possible loop head of an endless loop.
472 * I.e., it is a Block or Phi node and has only predecessors
475 * @param n the node to check
476 * @param root only needed for assertion.
478 static int is_endless_head(ir_node *n, ir_node *root)
481 int none_outof_loop = 1, some_in_loop = 0;
483 /* Test for legal loop header: Block, Phi, ... */
484 if (!is_possible_loop_head(n))
487 if (!is_outermost_Start(n)) {
489 int uplink = get_irn_uplink(root);
493 arity = get_irn_arity(n);
494 for (i = get_start_index(n); i < arity; i++) {
496 if (is_backedge(n, i))
498 pred = get_irn_n(n, i);
499 if (!irn_is_in_stack(pred)) {
502 assert(get_irn_uplink(pred) >= uplink);
507 return none_outof_loop & some_in_loop;
510 /** Returns index of the predecessor with the smallest dfn number
511 greater-equal than limit. */
512 static int smallest_dfn_pred(ir_node *n, int limit)
514 int i, index = -2, min = -1;
516 if (!is_outermost_Start(n)) {
517 int arity = get_irn_arity(n);
518 for (i = get_start_index(n); i < arity; i++) {
519 ir_node *pred = get_irn_n(n, i);
520 if (is_backedge(n, i) || !irn_is_in_stack(pred))
522 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
524 min = get_irn_dfn(pred);
532 * Returns index of the predecessor with the largest dfn number.
534 static int largest_dfn_pred(ir_node *n)
536 int i, index = -2, max = -1;
538 if (!is_outermost_Start(n)) {
539 int arity = get_irn_arity(n);
540 for (i = get_start_index(n); i < arity; i++) {
541 ir_node *pred = get_irn_n(n, i);
542 if (is_backedge (n, i) || !irn_is_in_stack(pred))
544 if (get_irn_dfn(pred) > max) {
546 max = get_irn_dfn(pred);
554 * Searches the stack for possible loop heads. Tests these for backedges.
555 * If it finds a head with an unmarked backedge it marks this edge and
556 * returns the tail of the loop.
557 * If it finds no backedge returns NULL.
558 * ("disable_backedge" in fiasco)
560 * @param n A node where uplink == dfn.
562 static ir_node *find_tail(ir_node *n)
565 int i, res_index = -2;
568 if (!icfg && rm_cyclic_phis && remove_cyclic_phis (n)) return NULL;
570 m = stack[tos-1]; /* tos = top of stack */
572 res_index = smallest_dfn_pred(m, 0);
573 if ((res_index == -2) && /* no smallest dfn pred found. */
577 if (m == n) return NULL; // Is this to catch Phi - self loops?
578 for (i = tos-2; i >= 0; --i) {
582 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
583 if (res_index == -2) /* no smallest dfn pred found. */
584 res_index = largest_dfn_pred(m);
586 if ((m == n) && (res_index == -2)) { /* don't walk past loop head. */
592 /* We should not walk past our selves on the stack: The upcoming nodes
593 are not in this loop. We assume a loop not reachable from Start. */
601 /* A dead loop not reachable from Start. */
602 for (i = tos-2; i >= 0; --i) {
604 if (is_endless_head(m, n)) {
605 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
606 if (res_index == -2) /* no smallest dfn pred found. */
607 res_index = largest_dfn_pred (m);
610 /* It's not an unreachable loop, either. */
614 //assert(0 && "no head found on stack");
618 if (res_index <= -2) {
619 /* It's a completely bad loop: without Phi/Block nodes that can
620 be a head. I.e., the code is "dying". We break the loop by
621 setting Bad nodes. */
622 ir_graph *irg = get_irn_irg(n);
623 ir_mode *mode = get_irn_mode(n);
624 ir_node *bad = new_r_Bad(irg, mode);
625 int arity = get_irn_arity(n);
626 for (i = -1; i < arity; ++i) {
627 set_irn_n(n, i, bad);
631 assert(res_index > -2);
633 set_backedge(m, res_index);
634 return is_outermost_Start(n) ? NULL : get_irn_n(m, res_index);
637 static inline int is_outermost_loop(ir_loop *l)
639 return l == get_loop_outer_loop(l);
642 /*-----------------------------------------------------------*
643 * The core algorithm. *
644 *-----------------------------------------------------------*/
647 * The core algorithm: Find strongly coupled components.
649 * @param n node to start
651 static void scc(ir_node *n)
653 if (irn_visited_else_mark(n))
656 /* Initialize the node */
657 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
658 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
659 set_irn_loop(n, NULL);
663 /* AS: get_start_index might return -1 for Control Flow Nodes, and thus a negative
664 array index would be passed to is_backedge(). But CFG Nodes dont't have a backedge array,
665 so is_backedge does not access array[-1] but correctly returns false! */
667 if (!is_outermost_Start(n)) {
668 int i, arity = get_irn_arity(n);
670 for (i = get_start_index(n); i < arity; ++i) {
672 if (is_backedge(n, i))
676 if (irn_is_in_stack(m)) {
677 /* Uplink of m is smaller if n->m is a backedge.
678 Propagate the uplink to mark the loop. */
679 if (get_irn_uplink(m) < get_irn_uplink(n))
680 set_irn_uplink(n, get_irn_uplink(m));
685 if (get_irn_dfn(n) == get_irn_uplink(n)) {
686 /* This condition holds for
687 1) the node with the incoming backedge.
688 That is: We found a loop!
689 2) Straight line code, because no uplink has been propagated, so the
690 uplink still is the same as the dfn.
692 But n might not be a proper loop head for the analysis. Proper loop
693 heads are Block and Phi nodes. find_tail() searches the stack for
694 Block's and Phi's and takes those nodes as loop heads for the current
695 loop instead and marks the incoming edge as backedge. */
697 ir_node *tail = find_tail(n);
699 /* We have a loop, that is no straight line code,
700 because we found a loop head!
701 Next actions: Open a new loop on the loop tree and
702 try to find inner loops */
704 #if NO_LOOPS_WITHOUT_HEAD
705 /* This is an adaption of the algorithm from fiasco / optscc to
706 * avoid loops without Block or Phi as first node. This should
707 * severely reduce the number of evaluations of nodes to detect
708 * a fixpoint in the heap analysis.
709 * Further it avoids loops without firm nodes that cause errors
710 * in the heap analyses.
711 * But attention: don't do it for the outermost loop: This loop
712 * is not iterated. A first block can be a loop head in case of
713 * an endless recursion. */
717 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
725 ir_loop *l = new_loop();
728 /* Remove the loop from the stack ... */
729 pop_scc_unmark_visit(n);
731 /* The current backedge has been marked, that is temporarily eliminated,
732 by find tail. Start the scc algorithm
733 again on the subgraph that is left (the current loop without the backedge)
734 in order to find more inner loops. */
737 assert(irn_visited(n));
738 #if NO_LOOPS_WITHOUT_HEAD
743 /* No loop head was found, that is we have straight line code.
744 Pop all nodes from the stack to the current loop. */
750 int construct_backedges(ir_graph *irg)
752 ir_graph *rem = current_ir_graph;
757 current_ir_graph = irg;
758 outermost_ir_graph = irg;
761 init_scc(irg, &temp);
764 new_loop(); /* sets current_loop */
765 head_rem = current_loop; /* Just for assertion */
767 inc_irg_visited(irg);
769 scc(get_irg_end(irg));
772 obstack_free(&temp, NULL);
774 assert(head_rem == current_loop);
775 mature_loops(current_loop, get_irg_obstack(irg));
776 set_irg_loop(irg, current_loop);
777 add_irg_properties(irg, IR_GRAPH_PROPERTY_CONSISTENT_LOOPINFO);
778 assert(get_irg_loop(irg)->kind == k_ir_loop);
779 current_ir_graph = rem;
780 return max_loop_depth;
783 static void reset_backedges(ir_node *n)
785 if (is_possible_loop_head(n)) {
791 static void loop_reset_backedges(ir_loop *l)
794 reset_backedges(get_loop_node(l, 0));
795 for (i = 0; i < get_loop_n_nodes(l); ++i)
796 set_irn_loop(get_loop_node(l, i), NULL);
797 for (i = 0; i < get_loop_n_sons(l); ++i) {
798 loop_reset_backedges(get_loop_son(l, i));
803 static void loop_reset_node(ir_node *n, void *env)
806 set_irn_loop(n, NULL);
810 void free_loop_information(ir_graph *irg)
812 /* We can not use this recursion, as the loop might contain
813 illegal nodes by now. Why else would we throw away the
815 if (get_irg_loop(irg)) loop_reset_backedges(get_irg_loop(irg));
817 irg_walk_graph(irg, loop_reset_node, NULL, NULL);
818 set_irg_loop(irg, NULL);
819 clear_irg_properties(current_ir_graph, IR_GRAPH_PROPERTY_CONSISTENT_LOOPINFO);
820 /* We cannot free the loop nodes, they are on the obstack. */
823 void free_all_loop_information(void)
826 for (i = 0; i < get_irp_n_irgs(); i++) {
827 free_loop_information(get_irp_irg(i));
831 /* ------------------------------------------------------------------- */
832 /* Simple analyses based on the loop information */
833 /* ------------------------------------------------------------------- */
835 static int is_loop_variant(ir_loop *l, ir_loop *b)
839 if (l == b) return 1;
841 n_elems = get_loop_n_elements(l);
842 for (i = 0; i < n_elems; ++i) {
843 loop_element e = get_loop_element(l, i);
844 if (is_ir_loop(e.kind))
845 if (is_loop_variant(e.son, b))
852 int is_loop_invariant(const ir_node *n, const ir_node *block)
854 ir_loop *l = get_irn_loop(block);
855 const ir_node *b = is_Block(n) ? n : get_nodes_block(n);
856 return !is_loop_variant(l, get_irn_loop(b));