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
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 int 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 = 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 = 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 = 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 = 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 = 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 = 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 = 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 int 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 int 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)
246 ir_node *n = stack[--tos];
247 mark_irn_not_in_stack(n);
252 * The nodes up to n belong to the current loop.
253 * Removes them from the stack and adds them to the current loop.
255 static inline void pop_scc_to_loop(ir_node *n)
263 set_irn_dfn(m, loop_node_cnt);
264 add_loop_node(current_loop, m);
265 set_irn_loop(m, current_loop);
269 /* GL ??? my last son is my grandson??? Removes loops with no
270 ir_nodes in them. Such loops have only another loop as son. (Why
271 can't they have two loops as sons? Does it never get that far? ) */
272 static void close_loop(ir_loop *l)
274 int last = get_loop_n_elements(l) - 1;
275 loop_element lelement = get_loop_element(l, last);
276 ir_loop *last_son = lelement.son;
278 if (get_kind(last_son) == k_ir_loop &&
279 get_loop_n_elements(last_son) == 1) {
282 lelement = get_loop_element(last_son, 0);
285 if (get_kind(gson) == k_ir_loop) {
286 loop_element new_last_son;
288 gson->outer_loop = l;
289 new_last_son.son = gson;
290 l->children[last] = new_last_son;
297 /* Removes and unmarks all nodes up to n from the stack.
298 The nodes must be visited once more to assign them to a scc. */
299 static inline void pop_scc_unmark_visit(ir_node *n)
305 set_irn_visited(m, 0);
309 /**********************************************************************/
310 /* The loop datastructure. **/
311 /**********************************************************************/
313 /* Allocates a new loop as son of current_loop. Sets current_loop
314 to the new loop and returns the father. */
315 static ir_loop *new_loop(void)
317 ir_loop *father = current_loop;
318 ir_loop *son = alloc_loop(father, outermost_ir_graph->obst);
320 if (son->depth > max_loop_depth) max_loop_depth = son->depth;
325 /**********************************************************************/
326 /* Constructing and destructing the loop/backedge information. **/
327 /**********************************************************************/
329 /* Initialization steps. **********************************************/
331 static inline void init_node(ir_node *n, void *env)
333 struct obstack *obst = env;
334 set_irn_link(n, new_scc_info(obst));
338 static inline void init_scc_common(void)
345 static inline void init_scc(ir_graph *irg, struct obstack *obst)
348 irg_walk_graph(irg, init_node, NULL, obst);
350 irg_walk (irg, link_to_reg_end, NULL, NULL);
354 static inline void finish_scc(void)
360 * Check weather a given node represents the outer most Start
361 * block. In intra-procedural view this is the start block of the
362 * current graph, in interprocedural view it is the start block
363 * of the outer most graph.
365 * @param n the node to check
367 * This is the condition for breaking the scc recursion.
369 static int is_outermost_Start(ir_node *n)
371 /* Test whether this is the outermost Start node. */
372 if (is_Block(n) && get_Block_n_cfgpreds(n) == 1) {
373 ir_node *pred = skip_Proj(get_Block_cfgpred(n, 0));
374 if (is_Start(pred) && get_nodes_block(pred) == n)
380 /* When to walk from nodes to blocks. Only for Control flow operations? */
381 static inline int get_start_index(ir_node *n)
383 #undef BLOCK_BEFORE_NODE
384 #define BLOCK_BEFORE_NODE 1
386 #if BLOCK_BEFORE_NODE
388 /* This version assures, that all nodes are ordered absolutely. This allows
389 to undef all nodes in the heap analysis if the block is false, which
391 I.e., with this code, the order on the loop tree is correct. But a
392 (single) test showed the loop tree is deeper. */
393 if (get_irn_op(n) == op_Phi ||
395 (get_irg_pinned(get_irn_irg(n)) == op_pin_state_floats &&
396 get_irn_pinned(n) == op_pin_state_floats))
397 // Here we could test for backedge at -1 which is illegal
404 /* This version causes deeper loop trees (at least we verified this
406 But it guarantees that Blocks are analysed before nodes contained in the
407 block. If so, we can set the value to undef if the block is not \
409 if (is_cfop(n) || is_fragile_op(n) || is_Start(n))
418 * Return non-zero if the given node is a legal loop header:
421 * @param n the node to check
423 static inline int is_possible_loop_head(ir_node *n)
425 ir_op *op = get_irn_op(n);
426 return ((op == op_Block) ||
431 * Returns non-zero if n is a loop header, i.e., it is a Block or Phi
432 * node and has predecessors within the loop and out of the loop.
434 * @param n the node to check
435 * @param root only needed for assertion.
437 static int is_head(ir_node *n, ir_node *root)
440 int some_outof_loop = 0, some_in_loop = 0;
442 /* Test for legal loop header: Block, Phi, ... */
443 if (!is_possible_loop_head(n))
446 if (!is_outermost_Start(n)) {
448 int uplink = get_irn_uplink(root);
452 arity = get_irn_arity(n);
453 for (i = get_start_index(n); i < arity; i++) {
455 if (is_backedge(n, i))
457 pred = get_irn_n(n, i);
458 if (! irn_is_in_stack(pred)) {
461 assert(get_irn_uplink(pred) >= uplink);
466 return some_outof_loop & some_in_loop;
470 * Returns non-zero if n is possible loop head of an endless loop.
471 * I.e., it is a Block or Phi node and has only predecessors
474 * @param n the node to check
475 * @param root only needed for assertion.
477 static int is_endless_head(ir_node *n, ir_node *root)
480 int none_outof_loop = 1, some_in_loop = 0;
482 /* Test for legal loop header: Block, Phi, ... */
483 if (!is_possible_loop_head(n))
486 if (!is_outermost_Start(n)) {
488 int uplink = get_irn_uplink(root);
492 arity = get_irn_arity(n);
493 for (i = get_start_index(n); i < arity; i++) {
495 if (is_backedge(n, i))
497 pred = get_irn_n(n, i);
498 if (!irn_is_in_stack(pred)) {
501 assert(get_irn_uplink(pred) >= uplink);
506 return none_outof_loop & some_in_loop;
509 /** Returns index of the predecessor with the smallest dfn number
510 greater-equal than limit. */
511 static int smallest_dfn_pred(ir_node *n, int limit)
513 int i, index = -2, min = -1;
515 if (!is_outermost_Start(n)) {
516 int arity = get_irn_arity(n);
517 for (i = get_start_index(n); i < arity; i++) {
518 ir_node *pred = get_irn_n(n, i);
519 if (is_backedge(n, i) || !irn_is_in_stack(pred))
521 if (get_irn_dfn(pred) >= limit && (min == -1 || get_irn_dfn(pred) < min)) {
523 min = get_irn_dfn(pred);
531 * Returns index of the predecessor with the largest dfn number.
533 static int largest_dfn_pred(ir_node *n)
535 int i, index = -2, max = -1;
537 if (!is_outermost_Start(n)) {
538 int arity = get_irn_arity(n);
539 for (i = get_start_index(n); i < arity; i++) {
540 ir_node *pred = get_irn_n(n, i);
541 if (is_backedge (n, i) || !irn_is_in_stack(pred))
543 if (get_irn_dfn(pred) > max) {
545 max = get_irn_dfn(pred);
553 * Searches the stack for possible loop heads. Tests these for backedges.
554 * If it finds a head with an unmarked backedge it marks this edge and
555 * returns the tail of the loop.
556 * If it finds no backedge returns NULL.
557 * ("disable_backedge" in fiasco)
559 * @param n A node where uplink == dfn.
561 static ir_node *find_tail(ir_node *n)
564 int i, res_index = -2;
567 if (!icfg && rm_cyclic_phis && remove_cyclic_phis (n)) return NULL;
569 m = stack[tos-1]; /* tos = top of stack */
571 res_index = smallest_dfn_pred(m, 0);
572 if ((res_index == -2) && /* no smallest dfn pred found. */
576 if (m == n) return NULL; // Is this to catch Phi - self loops?
577 for (i = tos-2; i >= 0; --i) {
581 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
582 if (res_index == -2) /* no smallest dfn pred found. */
583 res_index = largest_dfn_pred(m);
585 if ((m == n) && (res_index == -2)) { /* don't walk past loop head. */
591 /* We should not walk past our selves on the stack: The upcoming nodes
592 are not in this loop. We assume a loop not reachable from Start. */
600 /* A dead loop not reachable from Start. */
601 for (i = tos-2; i >= 0; --i) {
603 if (is_endless_head(m, n)) {
604 res_index = smallest_dfn_pred(m, get_irn_dfn(m) + 1);
605 if (res_index == -2) /* no smallest dfn pred found. */
606 res_index = largest_dfn_pred (m);
609 if (m == n) { break; } /* It's not an unreachable loop, either. */
611 //assert(0 && "no head found on stack");
615 if (res_index <= -2) {
616 /* It's a completely bad loop: without Phi/Block nodes that can
617 be a head. I.e., the code is "dying". We break the loop by
618 setting Bad nodes. */
619 int arity = get_irn_arity(n);
620 ir_node *bad = get_irg_bad(get_irn_irg(n));
621 for (i = -1; i < arity; ++i) {
622 set_irn_n(n, i, bad);
626 assert(res_index > -2);
628 set_backedge(m, res_index);
629 return is_outermost_Start(n) ? NULL : get_irn_n(m, res_index);
632 static inline int is_outermost_loop(ir_loop *l)
634 return l == get_loop_outer_loop(l);
637 /*-----------------------------------------------------------*
638 * The core algorithm. *
639 *-----------------------------------------------------------*/
642 * The core algorithm: Find strongly coupled components.
644 * @param n node to start
646 static void scc(ir_node *n)
648 if (irn_visited_else_mark(n))
651 /* Initialize the node */
652 set_irn_dfn(n, current_dfn); /* Depth first number for this node */
653 set_irn_uplink(n, current_dfn); /* ... is default uplink. */
654 set_irn_loop(n, NULL);
658 /* AS: get_start_index might return -1 for Control Flow Nodes, and thus a negative
659 array index would be passed to is_backedge(). But CFG Nodes dont't have a backedge array,
660 so is_backedge does not access array[-1] but correctly returns false! */
662 if (!is_outermost_Start(n)) {
663 int i, arity = get_irn_arity(n);
665 for (i = get_start_index(n); i < arity; ++i) {
667 if (is_backedge(n, i))
671 if (irn_is_in_stack(m)) {
672 /* Uplink of m is smaller if n->m is a backedge.
673 Propagate the uplink to mark the loop. */
674 if (get_irn_uplink(m) < get_irn_uplink(n))
675 set_irn_uplink(n, get_irn_uplink(m));
680 if (get_irn_dfn(n) == get_irn_uplink(n)) {
681 /* This condition holds for
682 1) the node with the incoming backedge.
683 That is: We found a loop!
684 2) Straight line code, because no uplink has been propagated, so the
685 uplink still is the same as the dfn.
687 But n might not be a proper loop head for the analysis. Proper loop
688 heads are Block and Phi nodes. find_tail() searches the stack for
689 Block's and Phi's and takes those nodes as loop heads for the current
690 loop instead and marks the incoming edge as backedge. */
692 ir_node *tail = find_tail(n);
694 /* We have a loop, that is no straight line code,
695 because we found a loop head!
696 Next actions: Open a new loop on the loop tree and
697 try to find inner loops */
699 #if NO_LOOPS_WITHOUT_HEAD
700 /* This is an adaption of the algorithm from fiasco / optscc to
701 * avoid loops without Block or Phi as first node. This should
702 * severely reduce the number of evaluations of nodes to detect
703 * a fixpoint in the heap analysis.
704 * Further it avoids loops without firm nodes that cause errors
705 * in the heap analyses.
706 * But attention: don't do it for the outermost loop: This loop
707 * is not iterated. A first block can be a loop head in case of
708 * an endless recursion. */
712 if ((get_loop_n_elements(current_loop) > 0) || (is_outermost_loop(current_loop))) {
720 ir_loop *l = new_loop();
723 /* Remove the loop from the stack ... */
724 pop_scc_unmark_visit(n);
726 /* The current backedge has been marked, that is temporarily eliminated,
727 by find tail. Start the scc algorithm
728 again on the subgraph that is left (the current loop without the backedge)
729 in order to find more inner loops. */
732 assert(irn_visited(n));
733 #if NO_LOOPS_WITHOUT_HEAD
738 /* No loop head was found, that is we have straight line code.
739 Pop all nodes from the stack to the current loop. */
745 /* Constructs backedge information for irg. In interprocedural view constructs
746 backedges for all methods called by irg, too. */
747 int construct_backedges(ir_graph *irg)
749 ir_graph *rem = current_ir_graph;
754 current_ir_graph = irg;
755 outermost_ir_graph = irg;
758 init_scc(irg, &temp);
761 new_loop(); /* sets current_loop */
762 head_rem = current_loop; /* Just for assertion */
764 inc_irg_visited(irg);
766 scc(get_irg_end(irg));
769 obstack_free(&temp, NULL);
771 assert(head_rem == current_loop);
772 mature_loops(current_loop, irg->obst);
773 set_irg_loop(irg, current_loop);
774 set_irg_loopinfo_state(irg, loopinfo_consistent);
775 assert(get_irg_loop(irg)->kind == k_ir_loop);
776 current_ir_graph = rem;
777 return max_loop_depth;
780 static void reset_backedges(ir_node *n)
782 if (is_possible_loop_head(n)) {
788 static void loop_reset_backedges(ir_loop *l)
791 reset_backedges(get_loop_node(l, 0));
792 for (i = 0; i < get_loop_n_nodes(l); ++i)
793 set_irn_loop(get_loop_node(l, i), NULL);
794 for (i = 0; i < get_loop_n_sons(l); ++i) {
795 loop_reset_backedges(get_loop_son(l, i));
800 static void loop_reset_node(ir_node *n, void *env)
803 set_irn_loop(n, NULL);
807 /** Removes all loop information.
808 Resets all backedges */
809 void free_loop_information(ir_graph *irg)
811 /* We can not use this recursion, as the loop might contain
812 illegal nodes by now. Why else would we throw away the
814 if (get_irg_loop(irg)) loop_reset_backedges(get_irg_loop(irg));
816 irg_walk_graph(irg, loop_reset_node, NULL, NULL);
817 set_irg_loop(irg, NULL);
818 set_irg_loopinfo_state(current_ir_graph, loopinfo_none);
819 /* We cannot free the loop nodes, they are on the obstack. */
822 void free_all_loop_information(void)
825 for (i = 0; i < get_irp_n_irgs(); i++) {
826 free_loop_information(get_irp_irg(i));
830 /* ------------------------------------------------------------------- */
831 /* Simple analyses based on the loop information */
832 /* ------------------------------------------------------------------- */
834 static int is_loop_variant(ir_loop *l, ir_loop *b)
838 if (l == b) return 1;
840 n_elems = get_loop_n_elements(l);
841 for (i = 0; i < n_elems; ++i) {
842 loop_element e = get_loop_element(l, i);
843 if (is_ir_loop(e.kind))
844 if (is_loop_variant(e.son, b))
851 /* Test whether a value is loop invariant.
853 * @param n The node to be tested.
854 * @param block A block node. We pass the block, not the loop as we must
855 * start off with a block loop to find all proper uses.
857 * Returns non-zero, if the node n is not changed in the loop block
858 * belongs to or in inner loops of this blocks loop. */
859 int is_loop_invariant(const ir_node *n, const ir_node *block)
861 ir_loop *l = get_irn_loop(block);
862 const ir_node *b = is_Block(n) ? n : get_nodes_block(n);
863 return !is_loop_variant(l, get_irn_loop(b));