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1 /* Control flow graph analysis code for GNU compiler.
2 Copyright (C) 1987-2014 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 3, or (at your option) any later
9 version.
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
20 /* This file contains various simple utilities to analyze the CFG. */
22 #include "config.h"
23 #include "system.h"
24 #include "coretypes.h"
25 #include "predict.h"
26 #include "vec.h"
27 #include "hashtab.h"
28 #include "hash-set.h"
29 #include "machmode.h"
30 #include "tm.h"
31 #include "hard-reg-set.h"
32 #include "input.h"
33 #include "function.h"
34 #include "dominance.h"
35 #include "cfg.h"
36 #include "cfganal.h"
37 #include "basic-block.h"
38 #include "bitmap.h"
39 #include "sbitmap.h"
40 #include "timevar.h"
42 /* Store the data structures necessary for depth-first search. */
43 struct depth_first_search_dsS {
44 /* stack for backtracking during the algorithm */
45 basic_block *stack;
47 /* number of edges in the stack. That is, positions 0, ..., sp-1
48 have edges. */
49 unsigned int sp;
51 /* record of basic blocks already seen by depth-first search */
52 sbitmap visited_blocks;
54 typedef struct depth_first_search_dsS *depth_first_search_ds;
56 static void flow_dfs_compute_reverse_init (depth_first_search_ds);
57 static void flow_dfs_compute_reverse_add_bb (depth_first_search_ds,
58 basic_block);
59 static basic_block flow_dfs_compute_reverse_execute (depth_first_search_ds,
60 basic_block);
61 static void flow_dfs_compute_reverse_finish (depth_first_search_ds);
63 /* Mark the back edges in DFS traversal.
64 Return nonzero if a loop (natural or otherwise) is present.
65 Inspired by Depth_First_Search_PP described in:
67 Advanced Compiler Design and Implementation
68 Steven Muchnick
69 Morgan Kaufmann, 1997
71 and heavily borrowed from pre_and_rev_post_order_compute. */
73 bool
74 mark_dfs_back_edges (void)
76 edge_iterator *stack;
77 int *pre;
78 int *post;
79 int sp;
80 int prenum = 1;
81 int postnum = 1;
82 sbitmap visited;
83 bool found = false;
85 /* Allocate the preorder and postorder number arrays. */
86 pre = XCNEWVEC (int, last_basic_block_for_fn (cfun));
87 post = XCNEWVEC (int, last_basic_block_for_fn (cfun));
89 /* Allocate stack for back-tracking up CFG. */
90 stack = XNEWVEC (edge_iterator, n_basic_blocks_for_fn (cfun) + 1);
91 sp = 0;
93 /* Allocate bitmap to track nodes that have been visited. */
94 visited = sbitmap_alloc (last_basic_block_for_fn (cfun));
96 /* None of the nodes in the CFG have been visited yet. */
97 bitmap_clear (visited);
99 /* Push the first edge on to the stack. */
100 stack[sp++] = ei_start (ENTRY_BLOCK_PTR_FOR_FN (cfun)->succs);
102 while (sp)
104 edge_iterator ei;
105 basic_block src;
106 basic_block dest;
108 /* Look at the edge on the top of the stack. */
109 ei = stack[sp - 1];
110 src = ei_edge (ei)->src;
111 dest = ei_edge (ei)->dest;
112 ei_edge (ei)->flags &= ~EDGE_DFS_BACK;
114 /* Check if the edge destination has been visited yet. */
115 if (dest != EXIT_BLOCK_PTR_FOR_FN (cfun) && ! bitmap_bit_p (visited,
116 dest->index))
118 /* Mark that we have visited the destination. */
119 bitmap_set_bit (visited, dest->index);
121 pre[dest->index] = prenum++;
122 if (EDGE_COUNT (dest->succs) > 0)
124 /* Since the DEST node has been visited for the first
125 time, check its successors. */
126 stack[sp++] = ei_start (dest->succs);
128 else
129 post[dest->index] = postnum++;
131 else
133 if (dest != EXIT_BLOCK_PTR_FOR_FN (cfun)
134 && src != ENTRY_BLOCK_PTR_FOR_FN (cfun)
135 && pre[src->index] >= pre[dest->index]
136 && post[dest->index] == 0)
137 ei_edge (ei)->flags |= EDGE_DFS_BACK, found = true;
139 if (ei_one_before_end_p (ei)
140 && src != ENTRY_BLOCK_PTR_FOR_FN (cfun))
141 post[src->index] = postnum++;
143 if (!ei_one_before_end_p (ei))
144 ei_next (&stack[sp - 1]);
145 else
146 sp--;
150 free (pre);
151 free (post);
152 free (stack);
153 sbitmap_free (visited);
155 return found;
158 /* Find unreachable blocks. An unreachable block will have 0 in
159 the reachable bit in block->flags. A nonzero value indicates the
160 block is reachable. */
162 void
163 find_unreachable_blocks (void)
165 edge e;
166 edge_iterator ei;
167 basic_block *tos, *worklist, bb;
169 tos = worklist = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
171 /* Clear all the reachability flags. */
173 FOR_EACH_BB_FN (bb, cfun)
174 bb->flags &= ~BB_REACHABLE;
176 /* Add our starting points to the worklist. Almost always there will
177 be only one. It isn't inconceivable that we might one day directly
178 support Fortran alternate entry points. */
180 FOR_EACH_EDGE (e, ei, ENTRY_BLOCK_PTR_FOR_FN (cfun)->succs)
182 *tos++ = e->dest;
184 /* Mark the block reachable. */
185 e->dest->flags |= BB_REACHABLE;
188 /* Iterate: find everything reachable from what we've already seen. */
190 while (tos != worklist)
192 basic_block b = *--tos;
194 FOR_EACH_EDGE (e, ei, b->succs)
196 basic_block dest = e->dest;
198 if (!(dest->flags & BB_REACHABLE))
200 *tos++ = dest;
201 dest->flags |= BB_REACHABLE;
206 free (worklist);
209 /* Functions to access an edge list with a vector representation.
210 Enough data is kept such that given an index number, the
211 pred and succ that edge represents can be determined, or
212 given a pred and a succ, its index number can be returned.
213 This allows algorithms which consume a lot of memory to
214 represent the normally full matrix of edge (pred,succ) with a
215 single indexed vector, edge (EDGE_INDEX (pred, succ)), with no
216 wasted space in the client code due to sparse flow graphs. */
218 /* This functions initializes the edge list. Basically the entire
219 flowgraph is processed, and all edges are assigned a number,
220 and the data structure is filled in. */
222 struct edge_list *
223 create_edge_list (void)
225 struct edge_list *elist;
226 edge e;
227 int num_edges;
228 basic_block bb;
229 edge_iterator ei;
231 /* Determine the number of edges in the flow graph by counting successor
232 edges on each basic block. */
233 num_edges = 0;
234 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
235 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
237 num_edges += EDGE_COUNT (bb->succs);
240 elist = XNEW (struct edge_list);
241 elist->num_edges = num_edges;
242 elist->index_to_edge = XNEWVEC (edge, num_edges);
244 num_edges = 0;
246 /* Follow successors of blocks, and register these edges. */
247 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
248 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
249 FOR_EACH_EDGE (e, ei, bb->succs)
250 elist->index_to_edge[num_edges++] = e;
252 return elist;
255 /* This function free's memory associated with an edge list. */
257 void
258 free_edge_list (struct edge_list *elist)
260 if (elist)
262 free (elist->index_to_edge);
263 free (elist);
267 /* This function provides debug output showing an edge list. */
269 DEBUG_FUNCTION void
270 print_edge_list (FILE *f, struct edge_list *elist)
272 int x;
274 fprintf (f, "Compressed edge list, %d BBs + entry & exit, and %d edges\n",
275 n_basic_blocks_for_fn (cfun), elist->num_edges);
277 for (x = 0; x < elist->num_edges; x++)
279 fprintf (f, " %-4d - edge(", x);
280 if (INDEX_EDGE_PRED_BB (elist, x) == ENTRY_BLOCK_PTR_FOR_FN (cfun))
281 fprintf (f, "entry,");
282 else
283 fprintf (f, "%d,", INDEX_EDGE_PRED_BB (elist, x)->index);
285 if (INDEX_EDGE_SUCC_BB (elist, x) == EXIT_BLOCK_PTR_FOR_FN (cfun))
286 fprintf (f, "exit)\n");
287 else
288 fprintf (f, "%d)\n", INDEX_EDGE_SUCC_BB (elist, x)->index);
292 /* This function provides an internal consistency check of an edge list,
293 verifying that all edges are present, and that there are no
294 extra edges. */
296 DEBUG_FUNCTION void
297 verify_edge_list (FILE *f, struct edge_list *elist)
299 int pred, succ, index;
300 edge e;
301 basic_block bb, p, s;
302 edge_iterator ei;
304 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
305 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
307 FOR_EACH_EDGE (e, ei, bb->succs)
309 pred = e->src->index;
310 succ = e->dest->index;
311 index = EDGE_INDEX (elist, e->src, e->dest);
312 if (index == EDGE_INDEX_NO_EDGE)
314 fprintf (f, "*p* No index for edge from %d to %d\n", pred, succ);
315 continue;
318 if (INDEX_EDGE_PRED_BB (elist, index)->index != pred)
319 fprintf (f, "*p* Pred for index %d should be %d not %d\n",
320 index, pred, INDEX_EDGE_PRED_BB (elist, index)->index);
321 if (INDEX_EDGE_SUCC_BB (elist, index)->index != succ)
322 fprintf (f, "*p* Succ for index %d should be %d not %d\n",
323 index, succ, INDEX_EDGE_SUCC_BB (elist, index)->index);
327 /* We've verified that all the edges are in the list, now lets make sure
328 there are no spurious edges in the list. This is an expensive check! */
330 FOR_BB_BETWEEN (p, ENTRY_BLOCK_PTR_FOR_FN (cfun),
331 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
332 FOR_BB_BETWEEN (s, ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb, NULL, next_bb)
334 int found_edge = 0;
336 FOR_EACH_EDGE (e, ei, p->succs)
337 if (e->dest == s)
339 found_edge = 1;
340 break;
343 FOR_EACH_EDGE (e, ei, s->preds)
344 if (e->src == p)
346 found_edge = 1;
347 break;
350 if (EDGE_INDEX (elist, p, s)
351 == EDGE_INDEX_NO_EDGE && found_edge != 0)
352 fprintf (f, "*** Edge (%d, %d) appears to not have an index\n",
353 p->index, s->index);
354 if (EDGE_INDEX (elist, p, s)
355 != EDGE_INDEX_NO_EDGE && found_edge == 0)
356 fprintf (f, "*** Edge (%d, %d) has index %d, but there is no edge\n",
357 p->index, s->index, EDGE_INDEX (elist, p, s));
362 /* Functions to compute control dependences. */
364 /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
365 void
366 control_dependences::set_control_dependence_map_bit (basic_block bb,
367 int edge_index)
369 if (bb == ENTRY_BLOCK_PTR_FOR_FN (cfun))
370 return;
371 gcc_assert (bb != EXIT_BLOCK_PTR_FOR_FN (cfun));
372 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
375 /* Clear all control dependences for block BB. */
376 void
377 control_dependences::clear_control_dependence_bitmap (basic_block bb)
379 bitmap_clear (control_dependence_map[bb->index]);
382 /* Find the immediate postdominator PDOM of the specified basic block BLOCK.
383 This function is necessary because some blocks have negative numbers. */
385 static inline basic_block
386 find_pdom (basic_block block)
388 gcc_assert (block != ENTRY_BLOCK_PTR_FOR_FN (cfun));
390 if (block == EXIT_BLOCK_PTR_FOR_FN (cfun))
391 return EXIT_BLOCK_PTR_FOR_FN (cfun);
392 else
394 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
395 if (! bb)
396 return EXIT_BLOCK_PTR_FOR_FN (cfun);
397 return bb;
401 /* Determine all blocks' control dependences on the given edge with edge_list
402 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
404 void
405 control_dependences::find_control_dependence (int edge_index)
407 basic_block current_block;
408 basic_block ending_block;
410 gcc_assert (INDEX_EDGE_PRED_BB (m_el, edge_index)
411 != EXIT_BLOCK_PTR_FOR_FN (cfun));
413 if (INDEX_EDGE_PRED_BB (m_el, edge_index) == ENTRY_BLOCK_PTR_FOR_FN (cfun))
414 ending_block = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
415 else
416 ending_block = find_pdom (INDEX_EDGE_PRED_BB (m_el, edge_index));
418 for (current_block = INDEX_EDGE_SUCC_BB (m_el, edge_index);
419 current_block != ending_block
420 && current_block != EXIT_BLOCK_PTR_FOR_FN (cfun);
421 current_block = find_pdom (current_block))
423 edge e = INDEX_EDGE (m_el, edge_index);
425 /* For abnormal edges, we don't make current_block control
426 dependent because instructions that throw are always necessary
427 anyway. */
428 if (e->flags & EDGE_ABNORMAL)
429 continue;
431 set_control_dependence_map_bit (current_block, edge_index);
435 /* Record all blocks' control dependences on all edges in the edge
436 list EL, ala Morgan, Section 3.6. */
438 control_dependences::control_dependences (struct edge_list *edges)
439 : m_el (edges)
441 timevar_push (TV_CONTROL_DEPENDENCES);
442 control_dependence_map.create (last_basic_block_for_fn (cfun));
443 for (int i = 0; i < last_basic_block_for_fn (cfun); ++i)
444 control_dependence_map.quick_push (BITMAP_ALLOC (NULL));
445 for (int i = 0; i < NUM_EDGES (m_el); ++i)
446 find_control_dependence (i);
447 timevar_pop (TV_CONTROL_DEPENDENCES);
450 /* Free control dependences and the associated edge list. */
452 control_dependences::~control_dependences ()
454 for (unsigned i = 0; i < control_dependence_map.length (); ++i)
455 BITMAP_FREE (control_dependence_map[i]);
456 control_dependence_map.release ();
457 free_edge_list (m_el);
460 /* Returns the bitmap of edges the basic-block I is dependent on. */
462 bitmap
463 control_dependences::get_edges_dependent_on (int i)
465 return control_dependence_map[i];
468 /* Returns the edge with index I from the edge list. */
470 edge
471 control_dependences::get_edge (int i)
473 return INDEX_EDGE (m_el, i);
477 /* Given PRED and SUCC blocks, return the edge which connects the blocks.
478 If no such edge exists, return NULL. */
480 edge
481 find_edge (basic_block pred, basic_block succ)
483 edge e;
484 edge_iterator ei;
486 if (EDGE_COUNT (pred->succs) <= EDGE_COUNT (succ->preds))
488 FOR_EACH_EDGE (e, ei, pred->succs)
489 if (e->dest == succ)
490 return e;
492 else
494 FOR_EACH_EDGE (e, ei, succ->preds)
495 if (e->src == pred)
496 return e;
499 return NULL;
502 /* This routine will determine what, if any, edge there is between
503 a specified predecessor and successor. */
506 find_edge_index (struct edge_list *edge_list, basic_block pred, basic_block succ)
508 int x;
510 for (x = 0; x < NUM_EDGES (edge_list); x++)
511 if (INDEX_EDGE_PRED_BB (edge_list, x) == pred
512 && INDEX_EDGE_SUCC_BB (edge_list, x) == succ)
513 return x;
515 return (EDGE_INDEX_NO_EDGE);
518 /* This routine will remove any fake predecessor edges for a basic block.
519 When the edge is removed, it is also removed from whatever successor
520 list it is in. */
522 static void
523 remove_fake_predecessors (basic_block bb)
525 edge e;
526 edge_iterator ei;
528 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
530 if ((e->flags & EDGE_FAKE) == EDGE_FAKE)
531 remove_edge (e);
532 else
533 ei_next (&ei);
537 /* This routine will remove all fake edges from the flow graph. If
538 we remove all fake successors, it will automatically remove all
539 fake predecessors. */
541 void
542 remove_fake_edges (void)
544 basic_block bb;
546 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb, NULL, next_bb)
547 remove_fake_predecessors (bb);
550 /* This routine will remove all fake edges to the EXIT_BLOCK. */
552 void
553 remove_fake_exit_edges (void)
555 remove_fake_predecessors (EXIT_BLOCK_PTR_FOR_FN (cfun));
559 /* This function will add a fake edge between any block which has no
560 successors, and the exit block. Some data flow equations require these
561 edges to exist. */
563 void
564 add_noreturn_fake_exit_edges (void)
566 basic_block bb;
568 FOR_EACH_BB_FN (bb, cfun)
569 if (EDGE_COUNT (bb->succs) == 0)
570 make_single_succ_edge (bb, EXIT_BLOCK_PTR_FOR_FN (cfun), EDGE_FAKE);
573 /* This function adds a fake edge between any infinite loops to the
574 exit block. Some optimizations require a path from each node to
575 the exit node.
577 See also Morgan, Figure 3.10, pp. 82-83.
579 The current implementation is ugly, not attempting to minimize the
580 number of inserted fake edges. To reduce the number of fake edges
581 to insert, add fake edges from _innermost_ loops containing only
582 nodes not reachable from the exit block. */
584 void
585 connect_infinite_loops_to_exit (void)
587 basic_block unvisited_block = EXIT_BLOCK_PTR_FOR_FN (cfun);
588 basic_block deadend_block;
589 struct depth_first_search_dsS dfs_ds;
591 /* Perform depth-first search in the reverse graph to find nodes
592 reachable from the exit block. */
593 flow_dfs_compute_reverse_init (&dfs_ds);
594 flow_dfs_compute_reverse_add_bb (&dfs_ds, EXIT_BLOCK_PTR_FOR_FN (cfun));
596 /* Repeatedly add fake edges, updating the unreachable nodes. */
597 while (1)
599 unvisited_block = flow_dfs_compute_reverse_execute (&dfs_ds,
600 unvisited_block);
601 if (!unvisited_block)
602 break;
604 deadend_block = dfs_find_deadend (unvisited_block);
605 make_edge (deadend_block, EXIT_BLOCK_PTR_FOR_FN (cfun), EDGE_FAKE);
606 flow_dfs_compute_reverse_add_bb (&dfs_ds, deadend_block);
609 flow_dfs_compute_reverse_finish (&dfs_ds);
610 return;
613 /* Compute reverse top sort order. This is computing a post order
614 numbering of the graph. If INCLUDE_ENTRY_EXIT is true, then
615 ENTRY_BLOCK and EXIT_BLOCK are included. If DELETE_UNREACHABLE is
616 true, unreachable blocks are deleted. */
619 post_order_compute (int *post_order, bool include_entry_exit,
620 bool delete_unreachable)
622 edge_iterator *stack;
623 int sp;
624 int post_order_num = 0;
625 sbitmap visited;
626 int count;
628 if (include_entry_exit)
629 post_order[post_order_num++] = EXIT_BLOCK;
631 /* Allocate stack for back-tracking up CFG. */
632 stack = XNEWVEC (edge_iterator, n_basic_blocks_for_fn (cfun) + 1);
633 sp = 0;
635 /* Allocate bitmap to track nodes that have been visited. */
636 visited = sbitmap_alloc (last_basic_block_for_fn (cfun));
638 /* None of the nodes in the CFG have been visited yet. */
639 bitmap_clear (visited);
641 /* Push the first edge on to the stack. */
642 stack[sp++] = ei_start (ENTRY_BLOCK_PTR_FOR_FN (cfun)->succs);
644 while (sp)
646 edge_iterator ei;
647 basic_block src;
648 basic_block dest;
650 /* Look at the edge on the top of the stack. */
651 ei = stack[sp - 1];
652 src = ei_edge (ei)->src;
653 dest = ei_edge (ei)->dest;
655 /* Check if the edge destination has been visited yet. */
656 if (dest != EXIT_BLOCK_PTR_FOR_FN (cfun)
657 && ! bitmap_bit_p (visited, dest->index))
659 /* Mark that we have visited the destination. */
660 bitmap_set_bit (visited, dest->index);
662 if (EDGE_COUNT (dest->succs) > 0)
663 /* Since the DEST node has been visited for the first
664 time, check its successors. */
665 stack[sp++] = ei_start (dest->succs);
666 else
667 post_order[post_order_num++] = dest->index;
669 else
671 if (ei_one_before_end_p (ei)
672 && src != ENTRY_BLOCK_PTR_FOR_FN (cfun))
673 post_order[post_order_num++] = src->index;
675 if (!ei_one_before_end_p (ei))
676 ei_next (&stack[sp - 1]);
677 else
678 sp--;
682 if (include_entry_exit)
684 post_order[post_order_num++] = ENTRY_BLOCK;
685 count = post_order_num;
687 else
688 count = post_order_num + 2;
690 /* Delete the unreachable blocks if some were found and we are
691 supposed to do it. */
692 if (delete_unreachable && (count != n_basic_blocks_for_fn (cfun)))
694 basic_block b;
695 basic_block next_bb;
696 for (b = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb; b
697 != EXIT_BLOCK_PTR_FOR_FN (cfun); b = next_bb)
699 next_bb = b->next_bb;
701 if (!(bitmap_bit_p (visited, b->index)))
702 delete_basic_block (b);
705 tidy_fallthru_edges ();
708 free (stack);
709 sbitmap_free (visited);
710 return post_order_num;
714 /* Helper routine for inverted_post_order_compute
715 flow_dfs_compute_reverse_execute, and the reverse-CFG
716 deapth first search in dominance.c.
717 BB has to belong to a region of CFG
718 unreachable by inverted traversal from the exit.
719 i.e. there's no control flow path from ENTRY to EXIT
720 that contains this BB.
721 This can happen in two cases - if there's an infinite loop
722 or if there's a block that has no successor
723 (call to a function with no return).
724 Some RTL passes deal with this condition by
725 calling connect_infinite_loops_to_exit () and/or
726 add_noreturn_fake_exit_edges ().
727 However, those methods involve modifying the CFG itself
728 which may not be desirable.
729 Hence, we deal with the infinite loop/no return cases
730 by identifying a unique basic block that can reach all blocks
731 in such a region by inverted traversal.
732 This function returns a basic block that guarantees
733 that all blocks in the region are reachable
734 by starting an inverted traversal from the returned block. */
736 basic_block
737 dfs_find_deadend (basic_block bb)
739 bitmap visited = BITMAP_ALLOC (NULL);
741 for (;;)
743 if (EDGE_COUNT (bb->succs) == 0
744 || ! bitmap_set_bit (visited, bb->index))
746 BITMAP_FREE (visited);
747 return bb;
750 bb = EDGE_SUCC (bb, 0)->dest;
753 gcc_unreachable ();
757 /* Compute the reverse top sort order of the inverted CFG
758 i.e. starting from the exit block and following the edges backward
759 (from successors to predecessors).
760 This ordering can be used for forward dataflow problems among others.
762 This function assumes that all blocks in the CFG are reachable
763 from the ENTRY (but not necessarily from EXIT).
765 If there's an infinite loop,
766 a simple inverted traversal starting from the blocks
767 with no successors can't visit all blocks.
768 To solve this problem, we first do inverted traversal
769 starting from the blocks with no successor.
770 And if there's any block left that's not visited by the regular
771 inverted traversal from EXIT,
772 those blocks are in such problematic region.
773 Among those, we find one block that has
774 any visited predecessor (which is an entry into such a region),
775 and start looking for a "dead end" from that block
776 and do another inverted traversal from that block. */
779 inverted_post_order_compute (int *post_order)
781 basic_block bb;
782 edge_iterator *stack;
783 int sp;
784 int post_order_num = 0;
785 sbitmap visited;
787 /* Allocate stack for back-tracking up CFG. */
788 stack = XNEWVEC (edge_iterator, n_basic_blocks_for_fn (cfun) + 1);
789 sp = 0;
791 /* Allocate bitmap to track nodes that have been visited. */
792 visited = sbitmap_alloc (last_basic_block_for_fn (cfun));
794 /* None of the nodes in the CFG have been visited yet. */
795 bitmap_clear (visited);
797 /* Put all blocks that have no successor into the initial work list. */
798 FOR_ALL_BB_FN (bb, cfun)
799 if (EDGE_COUNT (bb->succs) == 0)
801 /* Push the initial edge on to the stack. */
802 if (EDGE_COUNT (bb->preds) > 0)
804 stack[sp++] = ei_start (bb->preds);
805 bitmap_set_bit (visited, bb->index);
811 bool has_unvisited_bb = false;
813 /* The inverted traversal loop. */
814 while (sp)
816 edge_iterator ei;
817 basic_block pred;
819 /* Look at the edge on the top of the stack. */
820 ei = stack[sp - 1];
821 bb = ei_edge (ei)->dest;
822 pred = ei_edge (ei)->src;
824 /* Check if the predecessor has been visited yet. */
825 if (! bitmap_bit_p (visited, pred->index))
827 /* Mark that we have visited the destination. */
828 bitmap_set_bit (visited, pred->index);
830 if (EDGE_COUNT (pred->preds) > 0)
831 /* Since the predecessor node has been visited for the first
832 time, check its predecessors. */
833 stack[sp++] = ei_start (pred->preds);
834 else
835 post_order[post_order_num++] = pred->index;
837 else
839 if (bb != EXIT_BLOCK_PTR_FOR_FN (cfun)
840 && ei_one_before_end_p (ei))
841 post_order[post_order_num++] = bb->index;
843 if (!ei_one_before_end_p (ei))
844 ei_next (&stack[sp - 1]);
845 else
846 sp--;
850 /* Detect any infinite loop and activate the kludge.
851 Note that this doesn't check EXIT_BLOCK itself
852 since EXIT_BLOCK is always added after the outer do-while loop. */
853 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
854 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
855 if (!bitmap_bit_p (visited, bb->index))
857 has_unvisited_bb = true;
859 if (EDGE_COUNT (bb->preds) > 0)
861 edge_iterator ei;
862 edge e;
863 basic_block visited_pred = NULL;
865 /* Find an already visited predecessor. */
866 FOR_EACH_EDGE (e, ei, bb->preds)
868 if (bitmap_bit_p (visited, e->src->index))
869 visited_pred = e->src;
872 if (visited_pred)
874 basic_block be = dfs_find_deadend (bb);
875 gcc_assert (be != NULL);
876 bitmap_set_bit (visited, be->index);
877 stack[sp++] = ei_start (be->preds);
878 break;
883 if (has_unvisited_bb && sp == 0)
885 /* No blocks are reachable from EXIT at all.
886 Find a dead-end from the ENTRY, and restart the iteration. */
887 basic_block be = dfs_find_deadend (ENTRY_BLOCK_PTR_FOR_FN (cfun));
888 gcc_assert (be != NULL);
889 bitmap_set_bit (visited, be->index);
890 stack[sp++] = ei_start (be->preds);
893 /* The only case the below while fires is
894 when there's an infinite loop. */
896 while (sp);
898 /* EXIT_BLOCK is always included. */
899 post_order[post_order_num++] = EXIT_BLOCK;
901 free (stack);
902 sbitmap_free (visited);
903 return post_order_num;
906 /* Compute the depth first search order of FN and store in the array
907 PRE_ORDER if nonzero. If REV_POST_ORDER is nonzero, return the
908 reverse completion number for each node. Returns the number of nodes
909 visited. A depth first search tries to get as far away from the starting
910 point as quickly as possible.
912 In case the function has unreachable blocks the number of nodes
913 visited does not include them.
915 pre_order is a really a preorder numbering of the graph.
916 rev_post_order is really a reverse postorder numbering of the graph. */
919 pre_and_rev_post_order_compute_fn (struct function *fn,
920 int *pre_order, int *rev_post_order,
921 bool include_entry_exit)
923 edge_iterator *stack;
924 int sp;
925 int pre_order_num = 0;
926 int rev_post_order_num = n_basic_blocks_for_fn (cfun) - 1;
927 sbitmap visited;
929 /* Allocate stack for back-tracking up CFG. */
930 stack = XNEWVEC (edge_iterator, n_basic_blocks_for_fn (cfun) + 1);
931 sp = 0;
933 if (include_entry_exit)
935 if (pre_order)
936 pre_order[pre_order_num] = ENTRY_BLOCK;
937 pre_order_num++;
938 if (rev_post_order)
939 rev_post_order[rev_post_order_num--] = ENTRY_BLOCK;
941 else
942 rev_post_order_num -= NUM_FIXED_BLOCKS;
944 /* Allocate bitmap to track nodes that have been visited. */
945 visited = sbitmap_alloc (last_basic_block_for_fn (cfun));
947 /* None of the nodes in the CFG have been visited yet. */
948 bitmap_clear (visited);
950 /* Push the first edge on to the stack. */
951 stack[sp++] = ei_start (ENTRY_BLOCK_PTR_FOR_FN (fn)->succs);
953 while (sp)
955 edge_iterator ei;
956 basic_block src;
957 basic_block dest;
959 /* Look at the edge on the top of the stack. */
960 ei = stack[sp - 1];
961 src = ei_edge (ei)->src;
962 dest = ei_edge (ei)->dest;
964 /* Check if the edge destination has been visited yet. */
965 if (dest != EXIT_BLOCK_PTR_FOR_FN (fn)
966 && ! bitmap_bit_p (visited, dest->index))
968 /* Mark that we have visited the destination. */
969 bitmap_set_bit (visited, dest->index);
971 if (pre_order)
972 pre_order[pre_order_num] = dest->index;
974 pre_order_num++;
976 if (EDGE_COUNT (dest->succs) > 0)
977 /* Since the DEST node has been visited for the first
978 time, check its successors. */
979 stack[sp++] = ei_start (dest->succs);
980 else if (rev_post_order)
981 /* There are no successors for the DEST node so assign
982 its reverse completion number. */
983 rev_post_order[rev_post_order_num--] = dest->index;
985 else
987 if (ei_one_before_end_p (ei)
988 && src != ENTRY_BLOCK_PTR_FOR_FN (fn)
989 && rev_post_order)
990 /* There are no more successors for the SRC node
991 so assign its reverse completion number. */
992 rev_post_order[rev_post_order_num--] = src->index;
994 if (!ei_one_before_end_p (ei))
995 ei_next (&stack[sp - 1]);
996 else
997 sp--;
1001 free (stack);
1002 sbitmap_free (visited);
1004 if (include_entry_exit)
1006 if (pre_order)
1007 pre_order[pre_order_num] = EXIT_BLOCK;
1008 pre_order_num++;
1009 if (rev_post_order)
1010 rev_post_order[rev_post_order_num--] = EXIT_BLOCK;
1013 return pre_order_num;
1016 /* Like pre_and_rev_post_order_compute_fn but operating on the
1017 current function and asserting that all nodes were visited. */
1020 pre_and_rev_post_order_compute (int *pre_order, int *rev_post_order,
1021 bool include_entry_exit)
1023 int pre_order_num
1024 = pre_and_rev_post_order_compute_fn (cfun, pre_order, rev_post_order,
1025 include_entry_exit);
1026 if (include_entry_exit)
1027 /* The number of nodes visited should be the number of blocks. */
1028 gcc_assert (pre_order_num == n_basic_blocks_for_fn (cfun));
1029 else
1030 /* The number of nodes visited should be the number of blocks minus
1031 the entry and exit blocks which are not visited here. */
1032 gcc_assert (pre_order_num
1033 == (n_basic_blocks_for_fn (cfun) - NUM_FIXED_BLOCKS));
1035 return pre_order_num;
1038 /* Compute the depth first search order on the _reverse_ graph and
1039 store in the array DFS_ORDER, marking the nodes visited in VISITED.
1040 Returns the number of nodes visited.
1042 The computation is split into three pieces:
1044 flow_dfs_compute_reverse_init () creates the necessary data
1045 structures.
1047 flow_dfs_compute_reverse_add_bb () adds a basic block to the data
1048 structures. The block will start the search.
1050 flow_dfs_compute_reverse_execute () continues (or starts) the
1051 search using the block on the top of the stack, stopping when the
1052 stack is empty.
1054 flow_dfs_compute_reverse_finish () destroys the necessary data
1055 structures.
1057 Thus, the user will probably call ..._init(), call ..._add_bb() to
1058 add a beginning basic block to the stack, call ..._execute(),
1059 possibly add another bb to the stack and again call ..._execute(),
1060 ..., and finally call _finish(). */
1062 /* Initialize the data structures used for depth-first search on the
1063 reverse graph. If INITIALIZE_STACK is nonzero, the exit block is
1064 added to the basic block stack. DATA is the current depth-first
1065 search context. If INITIALIZE_STACK is nonzero, there is an
1066 element on the stack. */
1068 static void
1069 flow_dfs_compute_reverse_init (depth_first_search_ds data)
1071 /* Allocate stack for back-tracking up CFG. */
1072 data->stack = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
1073 data->sp = 0;
1075 /* Allocate bitmap to track nodes that have been visited. */
1076 data->visited_blocks = sbitmap_alloc (last_basic_block_for_fn (cfun));
1078 /* None of the nodes in the CFG have been visited yet. */
1079 bitmap_clear (data->visited_blocks);
1081 return;
1084 /* Add the specified basic block to the top of the dfs data
1085 structures. When the search continues, it will start at the
1086 block. */
1088 static void
1089 flow_dfs_compute_reverse_add_bb (depth_first_search_ds data, basic_block bb)
1091 data->stack[data->sp++] = bb;
1092 bitmap_set_bit (data->visited_blocks, bb->index);
1095 /* Continue the depth-first search through the reverse graph starting with the
1096 block at the stack's top and ending when the stack is empty. Visited nodes
1097 are marked. Returns an unvisited basic block, or NULL if there is none
1098 available. */
1100 static basic_block
1101 flow_dfs_compute_reverse_execute (depth_first_search_ds data,
1102 basic_block last_unvisited)
1104 basic_block bb;
1105 edge e;
1106 edge_iterator ei;
1108 while (data->sp > 0)
1110 bb = data->stack[--data->sp];
1112 /* Perform depth-first search on adjacent vertices. */
1113 FOR_EACH_EDGE (e, ei, bb->preds)
1114 if (!bitmap_bit_p (data->visited_blocks, e->src->index))
1115 flow_dfs_compute_reverse_add_bb (data, e->src);
1118 /* Determine if there are unvisited basic blocks. */
1119 FOR_BB_BETWEEN (bb, last_unvisited, NULL, prev_bb)
1120 if (!bitmap_bit_p (data->visited_blocks, bb->index))
1121 return bb;
1123 return NULL;
1126 /* Destroy the data structures needed for depth-first search on the
1127 reverse graph. */
1129 static void
1130 flow_dfs_compute_reverse_finish (depth_first_search_ds data)
1132 free (data->stack);
1133 sbitmap_free (data->visited_blocks);
1136 /* Performs dfs search from BB over vertices satisfying PREDICATE;
1137 if REVERSE, go against direction of edges. Returns number of blocks
1138 found and their list in RSLT. RSLT can contain at most RSLT_MAX items. */
1140 dfs_enumerate_from (basic_block bb, int reverse,
1141 bool (*predicate) (const_basic_block, const void *),
1142 basic_block *rslt, int rslt_max, const void *data)
1144 basic_block *st, lbb;
1145 int sp = 0, tv = 0;
1146 unsigned size;
1148 /* A bitmap to keep track of visited blocks. Allocating it each time
1149 this function is called is not possible, since dfs_enumerate_from
1150 is often used on small (almost) disjoint parts of cfg (bodies of
1151 loops), and allocating a large sbitmap would lead to quadratic
1152 behavior. */
1153 static sbitmap visited;
1154 static unsigned v_size;
1156 #define MARK_VISITED(BB) (bitmap_set_bit (visited, (BB)->index))
1157 #define UNMARK_VISITED(BB) (bitmap_clear_bit (visited, (BB)->index))
1158 #define VISITED_P(BB) (bitmap_bit_p (visited, (BB)->index))
1160 /* Resize the VISITED sbitmap if necessary. */
1161 size = last_basic_block_for_fn (cfun);
1162 if (size < 10)
1163 size = 10;
1165 if (!visited)
1168 visited = sbitmap_alloc (size);
1169 bitmap_clear (visited);
1170 v_size = size;
1172 else if (v_size < size)
1174 /* Ensure that we increase the size of the sbitmap exponentially. */
1175 if (2 * v_size > size)
1176 size = 2 * v_size;
1178 visited = sbitmap_resize (visited, size, 0);
1179 v_size = size;
1182 st = XNEWVEC (basic_block, rslt_max);
1183 rslt[tv++] = st[sp++] = bb;
1184 MARK_VISITED (bb);
1185 while (sp)
1187 edge e;
1188 edge_iterator ei;
1189 lbb = st[--sp];
1190 if (reverse)
1192 FOR_EACH_EDGE (e, ei, lbb->preds)
1193 if (!VISITED_P (e->src) && predicate (e->src, data))
1195 gcc_assert (tv != rslt_max);
1196 rslt[tv++] = st[sp++] = e->src;
1197 MARK_VISITED (e->src);
1200 else
1202 FOR_EACH_EDGE (e, ei, lbb->succs)
1203 if (!VISITED_P (e->dest) && predicate (e->dest, data))
1205 gcc_assert (tv != rslt_max);
1206 rslt[tv++] = st[sp++] = e->dest;
1207 MARK_VISITED (e->dest);
1211 free (st);
1212 for (sp = 0; sp < tv; sp++)
1213 UNMARK_VISITED (rslt[sp]);
1214 return tv;
1215 #undef MARK_VISITED
1216 #undef UNMARK_VISITED
1217 #undef VISITED_P
1221 /* Compute dominance frontiers, ala Harvey, Ferrante, et al.
1223 This algorithm can be found in Timothy Harvey's PhD thesis, at
1224 http://www.cs.rice.edu/~harv/dissertation.pdf in the section on iterative
1225 dominance algorithms.
1227 First, we identify each join point, j (any node with more than one
1228 incoming edge is a join point).
1230 We then examine each predecessor, p, of j and walk up the dominator tree
1231 starting at p.
1233 We stop the walk when we reach j's immediate dominator - j is in the
1234 dominance frontier of each of the nodes in the walk, except for j's
1235 immediate dominator. Intuitively, all of the rest of j's dominators are
1236 shared by j's predecessors as well.
1237 Since they dominate j, they will not have j in their dominance frontiers.
1239 The number of nodes touched by this algorithm is equal to the size
1240 of the dominance frontiers, no more, no less.
1244 static void
1245 compute_dominance_frontiers_1 (bitmap_head *frontiers)
1247 edge p;
1248 edge_iterator ei;
1249 basic_block b;
1250 FOR_EACH_BB_FN (b, cfun)
1252 if (EDGE_COUNT (b->preds) >= 2)
1254 FOR_EACH_EDGE (p, ei, b->preds)
1256 basic_block runner = p->src;
1257 basic_block domsb;
1258 if (runner == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1259 continue;
1261 domsb = get_immediate_dominator (CDI_DOMINATORS, b);
1262 while (runner != domsb)
1264 if (!bitmap_set_bit (&frontiers[runner->index],
1265 b->index))
1266 break;
1267 runner = get_immediate_dominator (CDI_DOMINATORS,
1268 runner);
1276 void
1277 compute_dominance_frontiers (bitmap_head *frontiers)
1279 timevar_push (TV_DOM_FRONTIERS);
1281 compute_dominance_frontiers_1 (frontiers);
1283 timevar_pop (TV_DOM_FRONTIERS);
1286 /* Given a set of blocks with variable definitions (DEF_BLOCKS),
1287 return a bitmap with all the blocks in the iterated dominance
1288 frontier of the blocks in DEF_BLOCKS. DFS contains dominance
1289 frontier information as returned by compute_dominance_frontiers.
1291 The resulting set of blocks are the potential sites where PHI nodes
1292 are needed. The caller is responsible for freeing the memory
1293 allocated for the return value. */
1295 bitmap
1296 compute_idf (bitmap def_blocks, bitmap_head *dfs)
1298 bitmap_iterator bi;
1299 unsigned bb_index, i;
1300 bitmap phi_insertion_points;
1302 /* Each block can appear at most twice on the work-stack. */
1303 auto_vec<int> work_stack (2 * n_basic_blocks_for_fn (cfun));
1304 phi_insertion_points = BITMAP_ALLOC (NULL);
1306 /* Seed the work list with all the blocks in DEF_BLOCKS. We use
1307 vec::quick_push here for speed. This is safe because we know that
1308 the number of definition blocks is no greater than the number of
1309 basic blocks, which is the initial capacity of WORK_STACK. */
1310 EXECUTE_IF_SET_IN_BITMAP (def_blocks, 0, bb_index, bi)
1311 work_stack.quick_push (bb_index);
1313 /* Pop a block off the worklist, add every block that appears in
1314 the original block's DF that we have not already processed to
1315 the worklist. Iterate until the worklist is empty. Blocks
1316 which are added to the worklist are potential sites for
1317 PHI nodes. */
1318 while (work_stack.length () > 0)
1320 bb_index = work_stack.pop ();
1322 /* Since the registration of NEW -> OLD name mappings is done
1323 separately from the call to update_ssa, when updating the SSA
1324 form, the basic blocks where new and/or old names are defined
1325 may have disappeared by CFG cleanup calls. In this case,
1326 we may pull a non-existing block from the work stack. */
1327 gcc_checking_assert (bb_index
1328 < (unsigned) last_basic_block_for_fn (cfun));
1330 EXECUTE_IF_AND_COMPL_IN_BITMAP (&dfs[bb_index], phi_insertion_points,
1331 0, i, bi)
1333 work_stack.quick_push (i);
1334 bitmap_set_bit (phi_insertion_points, i);
1338 return phi_insertion_points;
1341 /* Intersection and union of preds/succs for sbitmap based data flow
1342 solvers. All four functions defined below take the same arguments:
1343 B is the basic block to perform the operation for. DST is the
1344 target sbitmap, i.e. the result. SRC is an sbitmap vector of size
1345 last_basic_block so that it can be indexed with basic block indices.
1346 DST may be (but does not have to be) SRC[B->index]. */
1348 /* Set the bitmap DST to the intersection of SRC of successors of
1349 basic block B. */
1351 void
1352 bitmap_intersection_of_succs (sbitmap dst, sbitmap *src, basic_block b)
1354 unsigned int set_size = dst->size;
1355 edge e;
1356 unsigned ix;
1358 gcc_assert (!dst->popcount);
1360 for (e = NULL, ix = 0; ix < EDGE_COUNT (b->succs); ix++)
1362 e = EDGE_SUCC (b, ix);
1363 if (e->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
1364 continue;
1366 bitmap_copy (dst, src[e->dest->index]);
1367 break;
1370 if (e == 0)
1371 bitmap_ones (dst);
1372 else
1373 for (++ix; ix < EDGE_COUNT (b->succs); ix++)
1375 unsigned int i;
1376 SBITMAP_ELT_TYPE *p, *r;
1378 e = EDGE_SUCC (b, ix);
1379 if (e->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
1380 continue;
1382 p = src[e->dest->index]->elms;
1383 r = dst->elms;
1384 for (i = 0; i < set_size; i++)
1385 *r++ &= *p++;
1389 /* Set the bitmap DST to the intersection of SRC of predecessors of
1390 basic block B. */
1392 void
1393 bitmap_intersection_of_preds (sbitmap dst, sbitmap *src, basic_block b)
1395 unsigned int set_size = dst->size;
1396 edge e;
1397 unsigned ix;
1399 gcc_assert (!dst->popcount);
1401 for (e = NULL, ix = 0; ix < EDGE_COUNT (b->preds); ix++)
1403 e = EDGE_PRED (b, ix);
1404 if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1405 continue;
1407 bitmap_copy (dst, src[e->src->index]);
1408 break;
1411 if (e == 0)
1412 bitmap_ones (dst);
1413 else
1414 for (++ix; ix < EDGE_COUNT (b->preds); ix++)
1416 unsigned int i;
1417 SBITMAP_ELT_TYPE *p, *r;
1419 e = EDGE_PRED (b, ix);
1420 if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1421 continue;
1423 p = src[e->src->index]->elms;
1424 r = dst->elms;
1425 for (i = 0; i < set_size; i++)
1426 *r++ &= *p++;
1430 /* Set the bitmap DST to the union of SRC of successors of
1431 basic block B. */
1433 void
1434 bitmap_union_of_succs (sbitmap dst, sbitmap *src, basic_block b)
1436 unsigned int set_size = dst->size;
1437 edge e;
1438 unsigned ix;
1440 gcc_assert (!dst->popcount);
1442 for (ix = 0; ix < EDGE_COUNT (b->succs); ix++)
1444 e = EDGE_SUCC (b, ix);
1445 if (e->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
1446 continue;
1448 bitmap_copy (dst, src[e->dest->index]);
1449 break;
1452 if (ix == EDGE_COUNT (b->succs))
1453 bitmap_clear (dst);
1454 else
1455 for (ix++; ix < EDGE_COUNT (b->succs); ix++)
1457 unsigned int i;
1458 SBITMAP_ELT_TYPE *p, *r;
1460 e = EDGE_SUCC (b, ix);
1461 if (e->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
1462 continue;
1464 p = src[e->dest->index]->elms;
1465 r = dst->elms;
1466 for (i = 0; i < set_size; i++)
1467 *r++ |= *p++;
1471 /* Set the bitmap DST to the union of SRC of predecessors of
1472 basic block B. */
1474 void
1475 bitmap_union_of_preds (sbitmap dst, sbitmap *src, basic_block b)
1477 unsigned int set_size = dst->size;
1478 edge e;
1479 unsigned ix;
1481 gcc_assert (!dst->popcount);
1483 for (ix = 0; ix < EDGE_COUNT (b->preds); ix++)
1485 e = EDGE_PRED (b, ix);
1486 if (e->src== ENTRY_BLOCK_PTR_FOR_FN (cfun))
1487 continue;
1489 bitmap_copy (dst, src[e->src->index]);
1490 break;
1493 if (ix == EDGE_COUNT (b->preds))
1494 bitmap_clear (dst);
1495 else
1496 for (ix++; ix < EDGE_COUNT (b->preds); ix++)
1498 unsigned int i;
1499 SBITMAP_ELT_TYPE *p, *r;
1501 e = EDGE_PRED (b, ix);
1502 if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1503 continue;
1505 p = src[e->src->index]->elms;
1506 r = dst->elms;
1507 for (i = 0; i < set_size; i++)
1508 *r++ |= *p++;
1512 /* Returns the list of basic blocks in the function in an order that guarantees
1513 that if a block X has just a single predecessor Y, then Y is after X in the
1514 ordering. */
1516 basic_block *
1517 single_pred_before_succ_order (void)
1519 basic_block x, y;
1520 basic_block *order = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
1521 unsigned n = n_basic_blocks_for_fn (cfun) - NUM_FIXED_BLOCKS;
1522 unsigned np, i;
1523 sbitmap visited = sbitmap_alloc (last_basic_block_for_fn (cfun));
1525 #define MARK_VISITED(BB) (bitmap_set_bit (visited, (BB)->index))
1526 #define VISITED_P(BB) (bitmap_bit_p (visited, (BB)->index))
1528 bitmap_clear (visited);
1530 MARK_VISITED (ENTRY_BLOCK_PTR_FOR_FN (cfun));
1531 FOR_EACH_BB_FN (x, cfun)
1533 if (VISITED_P (x))
1534 continue;
1536 /* Walk the predecessors of x as long as they have precisely one
1537 predecessor and add them to the list, so that they get stored
1538 after x. */
1539 for (y = x, np = 1;
1540 single_pred_p (y) && !VISITED_P (single_pred (y));
1541 y = single_pred (y))
1542 np++;
1543 for (y = x, i = n - np;
1544 single_pred_p (y) && !VISITED_P (single_pred (y));
1545 y = single_pred (y), i++)
1547 order[i] = y;
1548 MARK_VISITED (y);
1550 order[i] = y;
1551 MARK_VISITED (y);
1553 gcc_assert (i == n - 1);
1554 n -= np;
1557 sbitmap_free (visited);
1558 gcc_assert (n == 0);
1559 return order;
1561 #undef MARK_VISITED
1562 #undef VISITED_P