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
38 #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 int 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, outermost_ir_graph->obst);
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 weather a given node represents the outer most 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. */
396 if (get_irn_op(n) == op_Phi ||
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 ir_op *op = get_irn_op(n);
429 return ((op == op_Block) ||
434 * Returns non-zero if n is a loop header, i.e., it is a Block or Phi
435 * node and has predecessors within the loop and out of the loop.
437 * @param n the node to check
438 * @param root only needed for assertion.
440 static int is_head(ir_node *n, ir_node *root)
443 int some_outof_loop = 0, some_in_loop = 0;
445 /* Test for legal loop header: Block, Phi, ... */
446 if (!is_possible_loop_head(n))
449 if (!is_outermost_Start(n)) {
451 int uplink = get_irn_uplink(root);
455 arity = get_irn_arity(n);
456 for (i = get_start_index(n); i < arity; i++) {
458 if (is_backedge(n, i))
460 pred = get_irn_n(n, i);
461 if (! irn_is_in_stack(pred)) {
464 assert(get_irn_uplink(pred) >= uplink);
469 return some_outof_loop & some_in_loop;
473 * Returns non-zero if n is possible loop head of an endless loop.
474 * I.e., it is a Block or Phi node and has only predecessors
477 * @param n the node to check
478 * @param root only needed for assertion.
480 static int is_endless_head(ir_node *n, ir_node *root)
483 int none_outof_loop = 1, some_in_loop = 0;
485 /* Test for legal loop header: Block, Phi, ... */
486 if (!is_possible_loop_head(n))
489 if (!is_outermost_Start(n)) {
491 int uplink = get_irn_uplink(root);
495 arity = get_irn_arity(n);
496 for (i = get_start_index(n); i < arity; i++) {
498 if (is_backedge(n, i))
500 pred = get_irn_n(n, i);
501 if (!irn_is_in_stack(pred)) {
504 assert(get_irn_uplink(pred) >= uplink);
509 return none_outof_loop & some_in_loop;
512 /** Returns index of the predecessor with the smallest dfn number
513 greater-equal than limit. */
514 static int smallest_dfn_pred(ir_node *n, int limit)
516 int i, index = -2, min = -1;
518 if (!is_outermost_Start(n)) {
519 int arity = get_irn_arity(n);
520 for (i = get_start_index(n); i < arity; i++) {
521 ir_node *pred = get_irn_n(n, i);
522 if (is_backedge(n, i) || !irn_is_in_stack(pred))
524 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
526 min = get_irn_dfn(pred);
534 * Returns index of the predecessor with the largest dfn number.
536 static int largest_dfn_pred(ir_node *n)
538 int i, index = -2, max = -1;
540 if (!is_outermost_Start(n)) {
541 int arity = get_irn_arity(n);
542 for (i = get_start_index(n); i < arity; i++) {
543 ir_node *pred = get_irn_n(n, i);
544 if (is_backedge (n, i) || !irn_is_in_stack(pred))
546 if (get_irn_dfn(pred) > max) {
548 max = get_irn_dfn(pred);
556 * Searches the stack for possible loop heads. Tests these for backedges.
557 * If it finds a head with an unmarked backedge it marks this edge and
558 * returns the tail of the loop.
559 * If it finds no backedge returns NULL.
560 * ("disable_backedge" in fiasco)
562 * @param n A node where uplink == dfn.
564 static ir_node *find_tail(ir_node *n)
567 int i, res_index = -2;
570 if (!icfg && rm_cyclic_phis && remove_cyclic_phis (n)) return NULL;
572 m = stack[tos-1]; /* tos = top of stack */
574 res_index = smallest_dfn_pred(m, 0);
575 if ((res_index == -2) && /* no smallest dfn pred found. */
579 if (m == n) return NULL; // Is this to catch Phi - self loops?
580 for (i = tos-2; i >= 0; --i) {
584 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
585 if (res_index == -2) /* no smallest dfn pred found. */
586 res_index = largest_dfn_pred(m);
588 if ((m == n) && (res_index == -2)) { /* don't walk past loop head. */
594 /* We should not walk past our selves on the stack: The upcoming nodes
595 are not in this loop. We assume a loop not reachable from Start. */
603 /* A dead loop not reachable from Start. */
604 for (i = tos-2; i >= 0; --i) {
606 if (is_endless_head(m, n)) {
607 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
608 if (res_index == -2) /* no smallest dfn pred found. */
609 res_index = largest_dfn_pred (m);
612 if (m == n) { break; } /* 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 int arity = get_irn_arity(n);
623 ir_node *bad = get_irg_bad(get_irn_irg(n));
624 for (i = -1; i < arity; ++i) {
625 set_irn_n(n, i, bad);
629 assert(res_index > -2);
631 set_backedge(m, res_index);
632 return is_outermost_Start(n) ? NULL : get_irn_n(m, res_index);
635 static inline int is_outermost_loop(ir_loop *l)
637 return l == get_loop_outer_loop(l);
640 /*-----------------------------------------------------------*
641 * The core algorithm. *
642 *-----------------------------------------------------------*/
645 * The core algorithm: Find strongly coupled components.
647 * @param n node to start
649 static void scc(ir_node *n)
651 if (irn_visited_else_mark(n))
654 /* Initialize the node */
655 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
656 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
657 set_irn_loop(n, NULL);
661 /* AS: get_start_index might return -1 for Control Flow Nodes, and thus a negative
662 array index would be passed to is_backedge(). But CFG Nodes dont't have a backedge array,
663 so is_backedge does not access array[-1] but correctly returns false! */
665 if (!is_outermost_Start(n)) {
666 int i, arity = get_irn_arity(n);
668 for (i = get_start_index(n); i < arity; ++i) {
670 if (is_backedge(n, i))
674 if (irn_is_in_stack(m)) {
675 /* Uplink of m is smaller if n->m is a backedge.
676 Propagate the uplink to mark the loop. */
677 if (get_irn_uplink(m) < get_irn_uplink(n))
678 set_irn_uplink(n, get_irn_uplink(m));
683 if (get_irn_dfn(n) == get_irn_uplink(n)) {
684 /* This condition holds for
685 1) the node with the incoming backedge.
686 That is: We found a loop!
687 2) Straight line code, because no uplink has been propagated, so the
688 uplink still is the same as the dfn.
690 But n might not be a proper loop head for the analysis. Proper loop
691 heads are Block and Phi nodes. find_tail() searches the stack for
692 Block's and Phi's and takes those nodes as loop heads for the current
693 loop instead and marks the incoming edge as backedge. */
695 ir_node *tail = find_tail(n);
697 /* We have a loop, that is no straight line code,
698 because we found a loop head!
699 Next actions: Open a new loop on the loop tree and
700 try to find inner loops */
702 #if NO_LOOPS_WITHOUT_HEAD
703 /* This is an adaption of the algorithm from fiasco / optscc to
704 * avoid loops without Block or Phi as first node. This should
705 * severely reduce the number of evaluations of nodes to detect
706 * a fixpoint in the heap analysis.
707 * Further it avoids loops without firm nodes that cause errors
708 * in the heap analyses.
709 * But attention: don't do it for the outermost loop: This loop
710 * is not iterated. A first block can be a loop head in case of
711 * an endless recursion. */
715 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
723 ir_loop *l = new_loop();
726 /* Remove the loop from the stack ... */
727 pop_scc_unmark_visit(n);
729 /* The current backedge has been marked, that is temporarily eliminated,
730 by find tail. Start the scc algorithm
731 again on the subgraph that is left (the current loop without the backedge)
732 in order to find more inner loops. */
735 assert(irn_visited(n));
736 #if NO_LOOPS_WITHOUT_HEAD
741 /* No loop head was found, that is we have straight line code.
742 Pop all nodes from the stack to the current loop. */
748 /* Constructs backedge information for irg. In interprocedural view constructs
749 backedges for all methods called by irg, too. */
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, irg->obst);
776 set_irg_loop(irg, current_loop);
777 set_irg_loopinfo_state(irg, loopinfo_consistent);
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 /** Removes all loop information.
811 Resets all backedges */
812 void free_loop_information(ir_graph *irg)
814 /* We can not use this recursion, as the loop might contain
815 illegal nodes by now. Why else would we throw away the
817 if (get_irg_loop(irg)) loop_reset_backedges(get_irg_loop(irg));
819 irg_walk_graph(irg, loop_reset_node, NULL, NULL);
820 set_irg_loop(irg, NULL);
821 set_irg_loopinfo_state(current_ir_graph, loopinfo_none);
822 /* We cannot free the loop nodes, they are on the obstack. */
825 void free_all_loop_information(void)
828 for (i = 0; i < get_irp_n_irgs(); i++) {
829 free_loop_information(get_irp_irg(i));
833 /* ------------------------------------------------------------------- */
834 /* Simple analyses based on the loop information */
835 /* ------------------------------------------------------------------- */
837 static int is_loop_variant(ir_loop *l, ir_loop *b)
841 if (l == b) return 1;
843 n_elems = get_loop_n_elements(l);
844 for (i = 0; i < n_elems; ++i) {
845 loop_element e = get_loop_element(l, i);
846 if (is_ir_loop(e.kind))
847 if (is_loop_variant(e.son, b))
854 /* Test whether a value is loop invariant.
856 * @param n The node to be tested.
857 * @param block A block node. We pass the block, not the loop as we must
858 * start off with a block loop to find all proper uses.
860 * Returns non-zero, if the node n is not changed in the loop block
861 * belongs to or in inner loops of this blocks loop. */
862 int is_loop_invariant(const ir_node *n, const ir_node *block)
864 ir_loop *l = get_irn_loop(block);
865 const ir_node *b = is_Block(n) ? n : get_nodes_block(n);
866 return !is_loop_variant(l, get_irn_loop(b));