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1 /* Control flow graph analysis code for GNU compiler.
2 Copyright (C) 1987-2018 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 "backend.h"
26 #include "cfghooks.h"
27 #include "timevar.h"
28 #include "cfganal.h"
29 #include "cfgloop.h"
31 namespace {
32 /* Store the data structures necessary for depth-first search. */
33 class depth_first_search
35 public:
36 depth_first_search ();
38 basic_block execute (basic_block);
39 void add_bb (basic_block);
41 private:
42 /* stack for backtracking during the algorithm */
43 auto_vec<basic_block, 20> m_stack;
45 /* record of basic blocks already seen by depth-first search */
46 auto_sbitmap m_visited_blocks;
50 /* Mark the back edges in DFS traversal.
51 Return nonzero if a loop (natural or otherwise) is present.
52 Inspired by Depth_First_Search_PP described in:
54 Advanced Compiler Design and Implementation
55 Steven Muchnick
56 Morgan Kaufmann, 1997
58 and heavily borrowed from pre_and_rev_post_order_compute. */
60 bool
61 mark_dfs_back_edges (void)
63 int *pre;
64 int *post;
65 int prenum = 1;
66 int postnum = 1;
67 bool found = false;
69 /* Allocate the preorder and postorder number arrays. */
70 pre = XCNEWVEC (int, last_basic_block_for_fn (cfun));
71 post = XCNEWVEC (int, last_basic_block_for_fn (cfun));
73 /* Allocate stack for back-tracking up CFG. */
74 auto_vec<edge_iterator, 20> stack (n_basic_blocks_for_fn (cfun) + 1);
76 /* Allocate bitmap to track nodes that have been visited. */
77 auto_sbitmap visited (last_basic_block_for_fn (cfun));
79 /* None of the nodes in the CFG have been visited yet. */
80 bitmap_clear (visited);
82 /* Push the first edge on to the stack. */
83 stack.quick_push (ei_start (ENTRY_BLOCK_PTR_FOR_FN (cfun)->succs));
85 while (!stack.is_empty ())
87 basic_block src;
88 basic_block dest;
90 /* Look at the edge on the top of the stack. */
91 edge_iterator ei = stack.last ();
92 src = ei_edge (ei)->src;
93 dest = ei_edge (ei)->dest;
94 ei_edge (ei)->flags &= ~EDGE_DFS_BACK;
96 /* Check if the edge destination has been visited yet. */
97 if (dest != EXIT_BLOCK_PTR_FOR_FN (cfun) && ! bitmap_bit_p (visited,
98 dest->index))
100 /* Mark that we have visited the destination. */
101 bitmap_set_bit (visited, dest->index);
103 pre[dest->index] = prenum++;
104 if (EDGE_COUNT (dest->succs) > 0)
106 /* Since the DEST node has been visited for the first
107 time, check its successors. */
108 stack.quick_push (ei_start (dest->succs));
110 else
111 post[dest->index] = postnum++;
113 else
115 if (dest != EXIT_BLOCK_PTR_FOR_FN (cfun)
116 && src != ENTRY_BLOCK_PTR_FOR_FN (cfun)
117 && pre[src->index] >= pre[dest->index]
118 && post[dest->index] == 0)
119 ei_edge (ei)->flags |= EDGE_DFS_BACK, found = true;
121 if (ei_one_before_end_p (ei)
122 && src != ENTRY_BLOCK_PTR_FOR_FN (cfun))
123 post[src->index] = postnum++;
125 if (!ei_one_before_end_p (ei))
126 ei_next (&stack.last ());
127 else
128 stack.pop ();
132 free (pre);
133 free (post);
135 return found;
138 /* Find unreachable blocks. An unreachable block will have 0 in
139 the reachable bit in block->flags. A nonzero value indicates the
140 block is reachable. */
142 void
143 find_unreachable_blocks (void)
145 edge e;
146 edge_iterator ei;
147 basic_block *tos, *worklist, bb;
149 tos = worklist = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
151 /* Clear all the reachability flags. */
153 FOR_EACH_BB_FN (bb, cfun)
154 bb->flags &= ~BB_REACHABLE;
156 /* Add our starting points to the worklist. Almost always there will
157 be only one. It isn't inconceivable that we might one day directly
158 support Fortran alternate entry points. */
160 FOR_EACH_EDGE (e, ei, ENTRY_BLOCK_PTR_FOR_FN (cfun)->succs)
162 *tos++ = e->dest;
164 /* Mark the block reachable. */
165 e->dest->flags |= BB_REACHABLE;
168 /* Iterate: find everything reachable from what we've already seen. */
170 while (tos != worklist)
172 basic_block b = *--tos;
174 FOR_EACH_EDGE (e, ei, b->succs)
176 basic_block dest = e->dest;
178 if (!(dest->flags & BB_REACHABLE))
180 *tos++ = dest;
181 dest->flags |= BB_REACHABLE;
186 free (worklist);
189 /* Verify that there are no unreachable blocks in the current function. */
191 void
192 verify_no_unreachable_blocks (void)
194 find_unreachable_blocks ();
196 basic_block bb;
197 FOR_EACH_BB_FN (bb, cfun)
198 gcc_assert ((bb->flags & BB_REACHABLE) != 0);
202 /* Functions to access an edge list with a vector representation.
203 Enough data is kept such that given an index number, the
204 pred and succ that edge represents can be determined, or
205 given a pred and a succ, its index number can be returned.
206 This allows algorithms which consume a lot of memory to
207 represent the normally full matrix of edge (pred,succ) with a
208 single indexed vector, edge (EDGE_INDEX (pred, succ)), with no
209 wasted space in the client code due to sparse flow graphs. */
211 /* This functions initializes the edge list. Basically the entire
212 flowgraph is processed, and all edges are assigned a number,
213 and the data structure is filled in. */
215 struct edge_list *
216 create_edge_list (void)
218 struct edge_list *elist;
219 edge e;
220 int num_edges;
221 basic_block bb;
222 edge_iterator ei;
224 /* Determine the number of edges in the flow graph by counting successor
225 edges on each basic block. */
226 num_edges = 0;
227 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
228 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
230 num_edges += EDGE_COUNT (bb->succs);
233 elist = XNEW (struct edge_list);
234 elist->num_edges = num_edges;
235 elist->index_to_edge = XNEWVEC (edge, num_edges);
237 num_edges = 0;
239 /* Follow successors of blocks, and register these edges. */
240 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
241 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
242 FOR_EACH_EDGE (e, ei, bb->succs)
243 elist->index_to_edge[num_edges++] = e;
245 return elist;
248 /* This function free's memory associated with an edge list. */
250 void
251 free_edge_list (struct edge_list *elist)
253 if (elist)
255 free (elist->index_to_edge);
256 free (elist);
260 /* This function provides debug output showing an edge list. */
262 DEBUG_FUNCTION void
263 print_edge_list (FILE *f, struct edge_list *elist)
265 int x;
267 fprintf (f, "Compressed edge list, %d BBs + entry & exit, and %d edges\n",
268 n_basic_blocks_for_fn (cfun), elist->num_edges);
270 for (x = 0; x < elist->num_edges; x++)
272 fprintf (f, " %-4d - edge(", x);
273 if (INDEX_EDGE_PRED_BB (elist, x) == ENTRY_BLOCK_PTR_FOR_FN (cfun))
274 fprintf (f, "entry,");
275 else
276 fprintf (f, "%d,", INDEX_EDGE_PRED_BB (elist, x)->index);
278 if (INDEX_EDGE_SUCC_BB (elist, x) == EXIT_BLOCK_PTR_FOR_FN (cfun))
279 fprintf (f, "exit)\n");
280 else
281 fprintf (f, "%d)\n", INDEX_EDGE_SUCC_BB (elist, x)->index);
285 /* This function provides an internal consistency check of an edge list,
286 verifying that all edges are present, and that there are no
287 extra edges. */
289 DEBUG_FUNCTION void
290 verify_edge_list (FILE *f, struct edge_list *elist)
292 int pred, succ, index;
293 edge e;
294 basic_block bb, p, s;
295 edge_iterator ei;
297 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
298 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
300 FOR_EACH_EDGE (e, ei, bb->succs)
302 pred = e->src->index;
303 succ = e->dest->index;
304 index = EDGE_INDEX (elist, e->src, e->dest);
305 if (index == EDGE_INDEX_NO_EDGE)
307 fprintf (f, "*p* No index for edge from %d to %d\n", pred, succ);
308 continue;
311 if (INDEX_EDGE_PRED_BB (elist, index)->index != pred)
312 fprintf (f, "*p* Pred for index %d should be %d not %d\n",
313 index, pred, INDEX_EDGE_PRED_BB (elist, index)->index);
314 if (INDEX_EDGE_SUCC_BB (elist, index)->index != succ)
315 fprintf (f, "*p* Succ for index %d should be %d not %d\n",
316 index, succ, INDEX_EDGE_SUCC_BB (elist, index)->index);
320 /* We've verified that all the edges are in the list, now lets make sure
321 there are no spurious edges in the list. This is an expensive check! */
323 FOR_BB_BETWEEN (p, ENTRY_BLOCK_PTR_FOR_FN (cfun),
324 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
325 FOR_BB_BETWEEN (s, ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb, NULL, next_bb)
327 int found_edge = 0;
329 FOR_EACH_EDGE (e, ei, p->succs)
330 if (e->dest == s)
332 found_edge = 1;
333 break;
336 FOR_EACH_EDGE (e, ei, s->preds)
337 if (e->src == p)
339 found_edge = 1;
340 break;
343 if (EDGE_INDEX (elist, p, s)
344 == EDGE_INDEX_NO_EDGE && found_edge != 0)
345 fprintf (f, "*** Edge (%d, %d) appears to not have an index\n",
346 p->index, s->index);
347 if (EDGE_INDEX (elist, p, s)
348 != EDGE_INDEX_NO_EDGE && found_edge == 0)
349 fprintf (f, "*** Edge (%d, %d) has index %d, but there is no edge\n",
350 p->index, s->index, EDGE_INDEX (elist, p, s));
355 /* Functions to compute control dependences. */
357 /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
358 void
359 control_dependences::set_control_dependence_map_bit (basic_block bb,
360 int edge_index)
362 if (bb == ENTRY_BLOCK_PTR_FOR_FN (cfun))
363 return;
364 gcc_assert (bb != EXIT_BLOCK_PTR_FOR_FN (cfun));
365 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
368 /* Clear all control dependences for block BB. */
369 void
370 control_dependences::clear_control_dependence_bitmap (basic_block bb)
372 bitmap_clear (control_dependence_map[bb->index]);
375 /* Find the immediate postdominator PDOM of the specified basic block BLOCK.
376 This function is necessary because some blocks have negative numbers. */
378 static inline basic_block
379 find_pdom (basic_block block)
381 gcc_assert (block != ENTRY_BLOCK_PTR_FOR_FN (cfun));
383 if (block == EXIT_BLOCK_PTR_FOR_FN (cfun))
384 return EXIT_BLOCK_PTR_FOR_FN (cfun);
385 else
387 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
388 if (! bb)
389 return EXIT_BLOCK_PTR_FOR_FN (cfun);
390 return bb;
394 /* Determine all blocks' control dependences on the given edge with edge_list
395 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
397 void
398 control_dependences::find_control_dependence (int edge_index)
400 basic_block current_block;
401 basic_block ending_block;
403 gcc_assert (get_edge_src (edge_index) != EXIT_BLOCK_PTR_FOR_FN (cfun));
405 /* For abnormal edges, we don't make current_block control
406 dependent because instructions that throw are always necessary
407 anyway. */
408 edge e = find_edge (get_edge_src (edge_index), get_edge_dest (edge_index));
409 if (e->flags & EDGE_ABNORMAL)
410 return;
412 if (get_edge_src (edge_index) == ENTRY_BLOCK_PTR_FOR_FN (cfun))
413 ending_block = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
414 else
415 ending_block = find_pdom (get_edge_src (edge_index));
417 for (current_block = get_edge_dest (edge_index);
418 current_block != ending_block
419 && current_block != EXIT_BLOCK_PTR_FOR_FN (cfun);
420 current_block = find_pdom (current_block))
421 set_control_dependence_map_bit (current_block, edge_index);
424 /* Record all blocks' control dependences on all edges in the edge
425 list EL, ala Morgan, Section 3.6. */
427 control_dependences::control_dependences ()
429 timevar_push (TV_CONTROL_DEPENDENCES);
431 /* Initialize the edge list. */
432 int num_edges = 0;
433 basic_block bb;
434 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
435 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
436 num_edges += EDGE_COUNT (bb->succs);
437 m_el.create (num_edges);
438 edge e;
439 edge_iterator ei;
440 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
441 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
442 FOR_EACH_EDGE (e, ei, bb->succs)
443 m_el.quick_push (std::make_pair (e->src->index, e->dest->index));
445 control_dependence_map.create (last_basic_block_for_fn (cfun));
446 for (int i = 0; i < last_basic_block_for_fn (cfun); ++i)
447 control_dependence_map.quick_push (BITMAP_ALLOC (NULL));
448 for (int i = 0; i < num_edges; ++i)
449 find_control_dependence (i);
451 timevar_pop (TV_CONTROL_DEPENDENCES);
454 /* Free control dependences and the associated edge list. */
456 control_dependences::~control_dependences ()
458 for (unsigned i = 0; i < control_dependence_map.length (); ++i)
459 BITMAP_FREE (control_dependence_map[i]);
460 control_dependence_map.release ();
461 m_el.release ();
464 /* Returns the bitmap of edges the basic-block I is dependent on. */
466 bitmap
467 control_dependences::get_edges_dependent_on (int i)
469 return control_dependence_map[i];
472 /* Returns the edge source with index I from the edge list. */
474 basic_block
475 control_dependences::get_edge_src (int i)
477 return BASIC_BLOCK_FOR_FN (cfun, m_el[i].first);
480 /* Returns the edge destination with index I from the edge list. */
482 basic_block
483 control_dependences::get_edge_dest (int i)
485 return BASIC_BLOCK_FOR_FN (cfun, m_el[i].second);
489 /* Given PRED and SUCC blocks, return the edge which connects the blocks.
490 If no such edge exists, return NULL. */
492 edge
493 find_edge (basic_block pred, basic_block succ)
495 edge e;
496 edge_iterator ei;
498 if (EDGE_COUNT (pred->succs) <= EDGE_COUNT (succ->preds))
500 FOR_EACH_EDGE (e, ei, pred->succs)
501 if (e->dest == succ)
502 return e;
504 else
506 FOR_EACH_EDGE (e, ei, succ->preds)
507 if (e->src == pred)
508 return e;
511 return NULL;
514 /* This routine will determine what, if any, edge there is between
515 a specified predecessor and successor. */
518 find_edge_index (struct edge_list *edge_list, basic_block pred, basic_block succ)
520 int x;
522 for (x = 0; x < NUM_EDGES (edge_list); x++)
523 if (INDEX_EDGE_PRED_BB (edge_list, x) == pred
524 && INDEX_EDGE_SUCC_BB (edge_list, x) == succ)
525 return x;
527 return (EDGE_INDEX_NO_EDGE);
530 /* This routine will remove any fake predecessor edges for a basic block.
531 When the edge is removed, it is also removed from whatever successor
532 list it is in. */
534 static void
535 remove_fake_predecessors (basic_block bb)
537 edge e;
538 edge_iterator ei;
540 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
542 if ((e->flags & EDGE_FAKE) == EDGE_FAKE)
543 remove_edge (e);
544 else
545 ei_next (&ei);
549 /* This routine will remove all fake edges from the flow graph. If
550 we remove all fake successors, it will automatically remove all
551 fake predecessors. */
553 void
554 remove_fake_edges (void)
556 basic_block bb;
558 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb, NULL, next_bb)
559 remove_fake_predecessors (bb);
562 /* This routine will remove all fake edges to the EXIT_BLOCK. */
564 void
565 remove_fake_exit_edges (void)
567 remove_fake_predecessors (EXIT_BLOCK_PTR_FOR_FN (cfun));
571 /* This function will add a fake edge between any block which has no
572 successors, and the exit block. Some data flow equations require these
573 edges to exist. */
575 void
576 add_noreturn_fake_exit_edges (void)
578 basic_block bb;
580 FOR_EACH_BB_FN (bb, cfun)
581 if (EDGE_COUNT (bb->succs) == 0)
582 make_single_succ_edge (bb, EXIT_BLOCK_PTR_FOR_FN (cfun), EDGE_FAKE);
585 /* This function adds a fake edge between any infinite loops to the
586 exit block. Some optimizations require a path from each node to
587 the exit node.
589 See also Morgan, Figure 3.10, pp. 82-83.
591 The current implementation is ugly, not attempting to minimize the
592 number of inserted fake edges. To reduce the number of fake edges
593 to insert, add fake edges from _innermost_ loops containing only
594 nodes not reachable from the exit block. */
596 void
597 connect_infinite_loops_to_exit (void)
599 /* Perform depth-first search in the reverse graph to find nodes
600 reachable from the exit block. */
601 depth_first_search dfs;
602 dfs.add_bb (EXIT_BLOCK_PTR_FOR_FN (cfun));
604 /* Repeatedly add fake edges, updating the unreachable nodes. */
605 basic_block unvisited_block = EXIT_BLOCK_PTR_FOR_FN (cfun);
606 while (1)
608 unvisited_block = dfs.execute (unvisited_block);
609 if (!unvisited_block)
610 break;
612 basic_block deadend_block = dfs_find_deadend (unvisited_block);
613 edge e = make_edge (deadend_block, EXIT_BLOCK_PTR_FOR_FN (cfun),
614 EDGE_FAKE);
615 e->probability = profile_probability::never ();
616 dfs.add_bb (deadend_block);
620 /* Compute reverse top sort order. This is computing a post order
621 numbering of the graph. If INCLUDE_ENTRY_EXIT is true, then
622 ENTRY_BLOCK and EXIT_BLOCK are included. If DELETE_UNREACHABLE is
623 true, unreachable blocks are deleted. */
626 post_order_compute (int *post_order, bool include_entry_exit,
627 bool delete_unreachable)
629 int post_order_num = 0;
630 int count;
632 if (include_entry_exit)
633 post_order[post_order_num++] = EXIT_BLOCK;
635 /* Allocate stack for back-tracking up CFG. */
636 auto_vec<edge_iterator, 20> stack (n_basic_blocks_for_fn (cfun) + 1);
638 /* Allocate bitmap to track nodes that have been visited. */
639 auto_sbitmap visited (last_basic_block_for_fn (cfun));
641 /* None of the nodes in the CFG have been visited yet. */
642 bitmap_clear (visited);
644 /* Push the first edge on to the stack. */
645 stack.quick_push (ei_start (ENTRY_BLOCK_PTR_FOR_FN (cfun)->succs));
647 while (!stack.is_empty ())
649 basic_block src;
650 basic_block dest;
652 /* Look at the edge on the top of the stack. */
653 edge_iterator ei = stack.last ();
654 src = ei_edge (ei)->src;
655 dest = ei_edge (ei)->dest;
657 /* Check if the edge destination has been visited yet. */
658 if (dest != EXIT_BLOCK_PTR_FOR_FN (cfun)
659 && ! bitmap_bit_p (visited, dest->index))
661 /* Mark that we have visited the destination. */
662 bitmap_set_bit (visited, dest->index);
664 if (EDGE_COUNT (dest->succs) > 0)
665 /* Since the DEST node has been visited for the first
666 time, check its successors. */
667 stack.quick_push (ei_start (dest->succs));
668 else
669 post_order[post_order_num++] = dest->index;
671 else
673 if (ei_one_before_end_p (ei)
674 && src != ENTRY_BLOCK_PTR_FOR_FN (cfun))
675 post_order[post_order_num++] = src->index;
677 if (!ei_one_before_end_p (ei))
678 ei_next (&stack.last ());
679 else
680 stack.pop ();
684 if (include_entry_exit)
686 post_order[post_order_num++] = ENTRY_BLOCK;
687 count = post_order_num;
689 else
690 count = post_order_num + 2;
692 /* Delete the unreachable blocks if some were found and we are
693 supposed to do it. */
694 if (delete_unreachable && (count != n_basic_blocks_for_fn (cfun)))
696 basic_block b;
697 basic_block next_bb;
698 for (b = ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb; b
699 != EXIT_BLOCK_PTR_FOR_FN (cfun); b = next_bb)
701 next_bb = b->next_bb;
703 if (!(bitmap_bit_p (visited, b->index)))
704 delete_basic_block (b);
707 tidy_fallthru_edges ();
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 auto_bitmap visited;
740 basic_block next = bb;
742 for (;;)
744 if (EDGE_COUNT (next->succs) == 0)
745 return next;
747 if (! bitmap_set_bit (visited, next->index))
748 return bb;
750 bb = next;
751 /* If we are in an analyzed cycle make sure to try exiting it.
752 Note this is a heuristic only and expected to work when loop
753 fixup is needed as well. */
754 if (! bb->loop_father
755 || ! loop_outer (bb->loop_father))
756 next = EDGE_SUCC (bb, 0)->dest;
757 else
759 edge_iterator ei;
760 edge e;
761 FOR_EACH_EDGE (e, ei, bb->succs)
762 if (loop_exit_edge_p (bb->loop_father, e))
763 break;
764 next = e ? e->dest : EDGE_SUCC (bb, 0)->dest;
768 gcc_unreachable ();
772 /* Compute the reverse top sort order of the inverted CFG
773 i.e. starting from the exit block and following the edges backward
774 (from successors to predecessors).
775 This ordering can be used for forward dataflow problems among others.
777 Optionally if START_POINTS is specified, start from exit block and all
778 basic blocks in START_POINTS. This is used by CD-DCE.
780 This function assumes that all blocks in the CFG are reachable
781 from the ENTRY (but not necessarily from EXIT).
783 If there's an infinite loop,
784 a simple inverted traversal starting from the blocks
785 with no successors can't visit all blocks.
786 To solve this problem, we first do inverted traversal
787 starting from the blocks with no successor.
788 And if there's any block left that's not visited by the regular
789 inverted traversal from EXIT,
790 those blocks are in such problematic region.
791 Among those, we find one block that has
792 any visited predecessor (which is an entry into such a region),
793 and start looking for a "dead end" from that block
794 and do another inverted traversal from that block. */
796 void
797 inverted_post_order_compute (vec<int> *post_order,
798 sbitmap *start_points)
800 basic_block bb;
801 post_order->reserve_exact (n_basic_blocks_for_fn (cfun));
803 if (flag_checking)
804 verify_no_unreachable_blocks ();
806 /* Allocate stack for back-tracking up CFG. */
807 auto_vec<edge_iterator, 20> stack (n_basic_blocks_for_fn (cfun) + 1);
809 /* Allocate bitmap to track nodes that have been visited. */
810 auto_sbitmap visited (last_basic_block_for_fn (cfun));
812 /* None of the nodes in the CFG have been visited yet. */
813 bitmap_clear (visited);
815 if (start_points)
817 FOR_ALL_BB_FN (bb, cfun)
818 if (bitmap_bit_p (*start_points, bb->index)
819 && EDGE_COUNT (bb->preds) > 0)
821 stack.quick_push (ei_start (bb->preds));
822 bitmap_set_bit (visited, bb->index);
824 if (EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (cfun)->preds))
826 stack.quick_push (ei_start (EXIT_BLOCK_PTR_FOR_FN (cfun)->preds));
827 bitmap_set_bit (visited, EXIT_BLOCK_PTR_FOR_FN (cfun)->index);
830 else
831 /* Put all blocks that have no successor into the initial work list. */
832 FOR_ALL_BB_FN (bb, cfun)
833 if (EDGE_COUNT (bb->succs) == 0)
835 /* Push the initial edge on to the stack. */
836 if (EDGE_COUNT (bb->preds) > 0)
838 stack.quick_push (ei_start (bb->preds));
839 bitmap_set_bit (visited, bb->index);
845 bool has_unvisited_bb = false;
847 /* The inverted traversal loop. */
848 while (!stack.is_empty ())
850 edge_iterator ei;
851 basic_block pred;
853 /* Look at the edge on the top of the stack. */
854 ei = stack.last ();
855 bb = ei_edge (ei)->dest;
856 pred = ei_edge (ei)->src;
858 /* Check if the predecessor has been visited yet. */
859 if (! bitmap_bit_p (visited, pred->index))
861 /* Mark that we have visited the destination. */
862 bitmap_set_bit (visited, pred->index);
864 if (EDGE_COUNT (pred->preds) > 0)
865 /* Since the predecessor node has been visited for the first
866 time, check its predecessors. */
867 stack.quick_push (ei_start (pred->preds));
868 else
869 post_order->quick_push (pred->index);
871 else
873 if (bb != EXIT_BLOCK_PTR_FOR_FN (cfun)
874 && ei_one_before_end_p (ei))
875 post_order->quick_push (bb->index);
877 if (!ei_one_before_end_p (ei))
878 ei_next (&stack.last ());
879 else
880 stack.pop ();
884 /* Detect any infinite loop and activate the kludge.
885 Note that this doesn't check EXIT_BLOCK itself
886 since EXIT_BLOCK is always added after the outer do-while loop. */
887 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR_FOR_FN (cfun),
888 EXIT_BLOCK_PTR_FOR_FN (cfun), next_bb)
889 if (!bitmap_bit_p (visited, bb->index))
891 has_unvisited_bb = true;
893 if (EDGE_COUNT (bb->preds) > 0)
895 edge_iterator ei;
896 edge e;
897 basic_block visited_pred = NULL;
899 /* Find an already visited predecessor. */
900 FOR_EACH_EDGE (e, ei, bb->preds)
902 if (bitmap_bit_p (visited, e->src->index))
903 visited_pred = e->src;
906 if (visited_pred)
908 basic_block be = dfs_find_deadend (bb);
909 gcc_assert (be != NULL);
910 bitmap_set_bit (visited, be->index);
911 stack.quick_push (ei_start (be->preds));
912 break;
917 if (has_unvisited_bb && stack.is_empty ())
919 /* No blocks are reachable from EXIT at all.
920 Find a dead-end from the ENTRY, and restart the iteration. */
921 basic_block be = dfs_find_deadend (ENTRY_BLOCK_PTR_FOR_FN (cfun));
922 gcc_assert (be != NULL);
923 bitmap_set_bit (visited, be->index);
924 stack.quick_push (ei_start (be->preds));
927 /* The only case the below while fires is
928 when there's an infinite loop. */
930 while (!stack.is_empty ());
932 /* EXIT_BLOCK is always included. */
933 post_order->quick_push (EXIT_BLOCK);
936 /* Compute the depth first search order of FN and store in the array
937 PRE_ORDER if nonzero. If REV_POST_ORDER is nonzero, return the
938 reverse completion number for each node. Returns the number of nodes
939 visited. A depth first search tries to get as far away from the starting
940 point as quickly as possible.
942 In case the function has unreachable blocks the number of nodes
943 visited does not include them.
945 pre_order is a really a preorder numbering of the graph.
946 rev_post_order is really a reverse postorder numbering of the graph. */
949 pre_and_rev_post_order_compute_fn (struct function *fn,
950 int *pre_order, int *rev_post_order,
951 bool include_entry_exit)
953 int pre_order_num = 0;
954 int rev_post_order_num = n_basic_blocks_for_fn (cfun) - 1;
956 /* Allocate stack for back-tracking up CFG. */
957 auto_vec<edge_iterator, 20> stack (n_basic_blocks_for_fn (cfun) + 1);
959 if (include_entry_exit)
961 if (pre_order)
962 pre_order[pre_order_num] = ENTRY_BLOCK;
963 pre_order_num++;
964 if (rev_post_order)
965 rev_post_order[rev_post_order_num--] = EXIT_BLOCK;
967 else
968 rev_post_order_num -= NUM_FIXED_BLOCKS;
970 /* Allocate bitmap to track nodes that have been visited. */
971 auto_sbitmap visited (last_basic_block_for_fn (cfun));
973 /* None of the nodes in the CFG have been visited yet. */
974 bitmap_clear (visited);
976 /* Push the first edge on to the stack. */
977 stack.quick_push (ei_start (ENTRY_BLOCK_PTR_FOR_FN (fn)->succs));
979 while (!stack.is_empty ())
981 basic_block src;
982 basic_block dest;
984 /* Look at the edge on the top of the stack. */
985 edge_iterator ei = stack.last ();
986 src = ei_edge (ei)->src;
987 dest = ei_edge (ei)->dest;
989 /* Check if the edge destination has been visited yet. */
990 if (dest != EXIT_BLOCK_PTR_FOR_FN (fn)
991 && ! bitmap_bit_p (visited, dest->index))
993 /* Mark that we have visited the destination. */
994 bitmap_set_bit (visited, dest->index);
996 if (pre_order)
997 pre_order[pre_order_num] = dest->index;
999 pre_order_num++;
1001 if (EDGE_COUNT (dest->succs) > 0)
1002 /* Since the DEST node has been visited for the first
1003 time, check its successors. */
1004 stack.quick_push (ei_start (dest->succs));
1005 else if (rev_post_order)
1006 /* There are no successors for the DEST node so assign
1007 its reverse completion number. */
1008 rev_post_order[rev_post_order_num--] = dest->index;
1010 else
1012 if (ei_one_before_end_p (ei)
1013 && src != ENTRY_BLOCK_PTR_FOR_FN (fn)
1014 && rev_post_order)
1015 /* There are no more successors for the SRC node
1016 so assign its reverse completion number. */
1017 rev_post_order[rev_post_order_num--] = src->index;
1019 if (!ei_one_before_end_p (ei))
1020 ei_next (&stack.last ());
1021 else
1022 stack.pop ();
1026 if (include_entry_exit)
1028 if (pre_order)
1029 pre_order[pre_order_num] = EXIT_BLOCK;
1030 pre_order_num++;
1031 if (rev_post_order)
1032 rev_post_order[rev_post_order_num--] = ENTRY_BLOCK;
1035 return pre_order_num;
1038 /* Like pre_and_rev_post_order_compute_fn but operating on the
1039 current function and asserting that all nodes were visited. */
1042 pre_and_rev_post_order_compute (int *pre_order, int *rev_post_order,
1043 bool include_entry_exit)
1045 int pre_order_num
1046 = pre_and_rev_post_order_compute_fn (cfun, pre_order, rev_post_order,
1047 include_entry_exit);
1048 if (include_entry_exit)
1049 /* The number of nodes visited should be the number of blocks. */
1050 gcc_assert (pre_order_num == n_basic_blocks_for_fn (cfun));
1051 else
1052 /* The number of nodes visited should be the number of blocks minus
1053 the entry and exit blocks which are not visited here. */
1054 gcc_assert (pre_order_num
1055 == (n_basic_blocks_for_fn (cfun) - NUM_FIXED_BLOCKS));
1057 return pre_order_num;
1060 /* Compute the depth first search order on the _reverse_ graph and
1061 store in the array DFS_ORDER, marking the nodes visited in VISITED.
1062 Returns the number of nodes visited.
1064 The computation is split into three pieces:
1066 flow_dfs_compute_reverse_init () creates the necessary data
1067 structures.
1069 flow_dfs_compute_reverse_add_bb () adds a basic block to the data
1070 structures. The block will start the search.
1072 flow_dfs_compute_reverse_execute () continues (or starts) the
1073 search using the block on the top of the stack, stopping when the
1074 stack is empty.
1076 flow_dfs_compute_reverse_finish () destroys the necessary data
1077 structures.
1079 Thus, the user will probably call ..._init(), call ..._add_bb() to
1080 add a beginning basic block to the stack, call ..._execute(),
1081 possibly add another bb to the stack and again call ..._execute(),
1082 ..., and finally call _finish(). */
1084 /* Initialize the data structures used for depth-first search on the
1085 reverse graph. If INITIALIZE_STACK is nonzero, the exit block is
1086 added to the basic block stack. DATA is the current depth-first
1087 search context. If INITIALIZE_STACK is nonzero, there is an
1088 element on the stack. */
1090 depth_first_search::depth_first_search () :
1091 m_stack (n_basic_blocks_for_fn (cfun)),
1092 m_visited_blocks (last_basic_block_for_fn (cfun))
1094 bitmap_clear (m_visited_blocks);
1097 /* Add the specified basic block to the top of the dfs data
1098 structures. When the search continues, it will start at the
1099 block. */
1101 void
1102 depth_first_search::add_bb (basic_block bb)
1104 m_stack.quick_push (bb);
1105 bitmap_set_bit (m_visited_blocks, bb->index);
1108 /* Continue the depth-first search through the reverse graph starting with the
1109 block at the stack's top and ending when the stack is empty. Visited nodes
1110 are marked. Returns an unvisited basic block, or NULL if there is none
1111 available. */
1113 basic_block
1114 depth_first_search::execute (basic_block last_unvisited)
1116 basic_block bb;
1117 edge e;
1118 edge_iterator ei;
1120 while (!m_stack.is_empty ())
1122 bb = m_stack.pop ();
1124 /* Perform depth-first search on adjacent vertices. */
1125 FOR_EACH_EDGE (e, ei, bb->preds)
1126 if (!bitmap_bit_p (m_visited_blocks, e->src->index))
1127 add_bb (e->src);
1130 /* Determine if there are unvisited basic blocks. */
1131 FOR_BB_BETWEEN (bb, last_unvisited, NULL, prev_bb)
1132 if (!bitmap_bit_p (m_visited_blocks, bb->index))
1133 return bb;
1135 return NULL;
1138 /* Performs dfs search from BB over vertices satisfying PREDICATE;
1139 if REVERSE, go against direction of edges. Returns number of blocks
1140 found and their list in RSLT. RSLT can contain at most RSLT_MAX items. */
1142 dfs_enumerate_from (basic_block bb, int reverse,
1143 bool (*predicate) (const_basic_block, const void *),
1144 basic_block *rslt, int rslt_max, const void *data)
1146 basic_block *st, lbb;
1147 int sp = 0, tv = 0;
1148 unsigned size;
1150 /* A bitmap to keep track of visited blocks. Allocating it each time
1151 this function is called is not possible, since dfs_enumerate_from
1152 is often used on small (almost) disjoint parts of cfg (bodies of
1153 loops), and allocating a large sbitmap would lead to quadratic
1154 behavior. */
1155 static sbitmap visited;
1156 static unsigned v_size;
1158 #define MARK_VISITED(BB) (bitmap_set_bit (visited, (BB)->index))
1159 #define UNMARK_VISITED(BB) (bitmap_clear_bit (visited, (BB)->index))
1160 #define VISITED_P(BB) (bitmap_bit_p (visited, (BB)->index))
1162 /* Resize the VISITED sbitmap if necessary. */
1163 size = last_basic_block_for_fn (cfun);
1164 if (size < 10)
1165 size = 10;
1167 if (!visited)
1170 visited = sbitmap_alloc (size);
1171 bitmap_clear (visited);
1172 v_size = size;
1174 else if (v_size < size)
1176 /* Ensure that we increase the size of the sbitmap exponentially. */
1177 if (2 * v_size > size)
1178 size = 2 * v_size;
1180 visited = sbitmap_resize (visited, size, 0);
1181 v_size = size;
1184 st = XNEWVEC (basic_block, rslt_max);
1185 rslt[tv++] = st[sp++] = bb;
1186 MARK_VISITED (bb);
1187 while (sp)
1189 edge e;
1190 edge_iterator ei;
1191 lbb = st[--sp];
1192 if (reverse)
1194 FOR_EACH_EDGE (e, ei, lbb->preds)
1195 if (!VISITED_P (e->src) && predicate (e->src, data))
1197 gcc_assert (tv != rslt_max);
1198 rslt[tv++] = st[sp++] = e->src;
1199 MARK_VISITED (e->src);
1202 else
1204 FOR_EACH_EDGE (e, ei, lbb->succs)
1205 if (!VISITED_P (e->dest) && predicate (e->dest, data))
1207 gcc_assert (tv != rslt_max);
1208 rslt[tv++] = st[sp++] = e->dest;
1209 MARK_VISITED (e->dest);
1213 free (st);
1214 for (sp = 0; sp < tv; sp++)
1215 UNMARK_VISITED (rslt[sp]);
1216 return tv;
1217 #undef MARK_VISITED
1218 #undef UNMARK_VISITED
1219 #undef VISITED_P
1223 /* Compute dominance frontiers, ala Harvey, Ferrante, et al.
1225 This algorithm can be found in Timothy Harvey's PhD thesis, at
1226 http://www.cs.rice.edu/~harv/dissertation.pdf in the section on iterative
1227 dominance algorithms.
1229 First, we identify each join point, j (any node with more than one
1230 incoming edge is a join point).
1232 We then examine each predecessor, p, of j and walk up the dominator tree
1233 starting at p.
1235 We stop the walk when we reach j's immediate dominator - j is in the
1236 dominance frontier of each of the nodes in the walk, except for j's
1237 immediate dominator. Intuitively, all of the rest of j's dominators are
1238 shared by j's predecessors as well.
1239 Since they dominate j, they will not have j in their dominance frontiers.
1241 The number of nodes touched by this algorithm is equal to the size
1242 of the dominance frontiers, no more, no less.
1246 static void
1247 compute_dominance_frontiers_1 (bitmap_head *frontiers)
1249 edge p;
1250 edge_iterator ei;
1251 basic_block b;
1252 FOR_EACH_BB_FN (b, cfun)
1254 if (EDGE_COUNT (b->preds) >= 2)
1256 FOR_EACH_EDGE (p, ei, b->preds)
1258 basic_block runner = p->src;
1259 basic_block domsb;
1260 if (runner == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1261 continue;
1263 domsb = get_immediate_dominator (CDI_DOMINATORS, b);
1264 while (runner != domsb)
1266 if (!bitmap_set_bit (&frontiers[runner->index],
1267 b->index))
1268 break;
1269 runner = get_immediate_dominator (CDI_DOMINATORS,
1270 runner);
1278 void
1279 compute_dominance_frontiers (bitmap_head *frontiers)
1281 timevar_push (TV_DOM_FRONTIERS);
1283 compute_dominance_frontiers_1 (frontiers);
1285 timevar_pop (TV_DOM_FRONTIERS);
1288 /* Given a set of blocks with variable definitions (DEF_BLOCKS),
1289 return a bitmap with all the blocks in the iterated dominance
1290 frontier of the blocks in DEF_BLOCKS. DFS contains dominance
1291 frontier information as returned by compute_dominance_frontiers.
1293 The resulting set of blocks are the potential sites where PHI nodes
1294 are needed. The caller is responsible for freeing the memory
1295 allocated for the return value. */
1297 bitmap
1298 compute_idf (bitmap def_blocks, bitmap_head *dfs)
1300 bitmap_iterator bi;
1301 unsigned bb_index, i;
1302 bitmap phi_insertion_points;
1304 /* Each block can appear at most twice on the work-stack. */
1305 auto_vec<int> work_stack (2 * n_basic_blocks_for_fn (cfun));
1306 phi_insertion_points = BITMAP_ALLOC (NULL);
1308 /* Seed the work list with all the blocks in DEF_BLOCKS. We use
1309 vec::quick_push here for speed. This is safe because we know that
1310 the number of definition blocks is no greater than the number of
1311 basic blocks, which is the initial capacity of WORK_STACK. */
1312 EXECUTE_IF_SET_IN_BITMAP (def_blocks, 0, bb_index, bi)
1313 work_stack.quick_push (bb_index);
1315 /* Pop a block off the worklist, add every block that appears in
1316 the original block's DF that we have not already processed to
1317 the worklist. Iterate until the worklist is empty. Blocks
1318 which are added to the worklist are potential sites for
1319 PHI nodes. */
1320 while (work_stack.length () > 0)
1322 bb_index = work_stack.pop ();
1324 /* Since the registration of NEW -> OLD name mappings is done
1325 separately from the call to update_ssa, when updating the SSA
1326 form, the basic blocks where new and/or old names are defined
1327 may have disappeared by CFG cleanup calls. In this case,
1328 we may pull a non-existing block from the work stack. */
1329 gcc_checking_assert (bb_index
1330 < (unsigned) last_basic_block_for_fn (cfun));
1332 EXECUTE_IF_AND_COMPL_IN_BITMAP (&dfs[bb_index], phi_insertion_points,
1333 0, i, bi)
1335 work_stack.quick_push (i);
1336 bitmap_set_bit (phi_insertion_points, i);
1340 return phi_insertion_points;
1343 /* Intersection and union of preds/succs for sbitmap based data flow
1344 solvers. All four functions defined below take the same arguments:
1345 B is the basic block to perform the operation for. DST is the
1346 target sbitmap, i.e. the result. SRC is an sbitmap vector of size
1347 last_basic_block so that it can be indexed with basic block indices.
1348 DST may be (but does not have to be) SRC[B->index]. */
1350 /* Set the bitmap DST to the intersection of SRC of successors of
1351 basic block B. */
1353 void
1354 bitmap_intersection_of_succs (sbitmap dst, sbitmap *src, basic_block b)
1356 unsigned int set_size = dst->size;
1357 edge e;
1358 unsigned ix;
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 for (e = NULL, ix = 0; ix < EDGE_COUNT (b->preds); ix++)
1401 e = EDGE_PRED (b, ix);
1402 if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1403 continue;
1405 bitmap_copy (dst, src[e->src->index]);
1406 break;
1409 if (e == 0)
1410 bitmap_ones (dst);
1411 else
1412 for (++ix; ix < EDGE_COUNT (b->preds); ix++)
1414 unsigned int i;
1415 SBITMAP_ELT_TYPE *p, *r;
1417 e = EDGE_PRED (b, ix);
1418 if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1419 continue;
1421 p = src[e->src->index]->elms;
1422 r = dst->elms;
1423 for (i = 0; i < set_size; i++)
1424 *r++ &= *p++;
1428 /* Set the bitmap DST to the union of SRC of successors of
1429 basic block B. */
1431 void
1432 bitmap_union_of_succs (sbitmap dst, sbitmap *src, basic_block b)
1434 unsigned int set_size = dst->size;
1435 edge e;
1436 unsigned ix;
1438 for (ix = 0; ix < EDGE_COUNT (b->succs); ix++)
1440 e = EDGE_SUCC (b, ix);
1441 if (e->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
1442 continue;
1444 bitmap_copy (dst, src[e->dest->index]);
1445 break;
1448 if (ix == EDGE_COUNT (b->succs))
1449 bitmap_clear (dst);
1450 else
1451 for (ix++; ix < EDGE_COUNT (b->succs); ix++)
1453 unsigned int i;
1454 SBITMAP_ELT_TYPE *p, *r;
1456 e = EDGE_SUCC (b, ix);
1457 if (e->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
1458 continue;
1460 p = src[e->dest->index]->elms;
1461 r = dst->elms;
1462 for (i = 0; i < set_size; i++)
1463 *r++ |= *p++;
1467 /* Set the bitmap DST to the union of SRC of predecessors of
1468 basic block B. */
1470 void
1471 bitmap_union_of_preds (sbitmap dst, sbitmap *src, basic_block b)
1473 unsigned int set_size = dst->size;
1474 edge e;
1475 unsigned ix;
1477 for (ix = 0; ix < EDGE_COUNT (b->preds); ix++)
1479 e = EDGE_PRED (b, ix);
1480 if (e->src== ENTRY_BLOCK_PTR_FOR_FN (cfun))
1481 continue;
1483 bitmap_copy (dst, src[e->src->index]);
1484 break;
1487 if (ix == EDGE_COUNT (b->preds))
1488 bitmap_clear (dst);
1489 else
1490 for (ix++; ix < EDGE_COUNT (b->preds); ix++)
1492 unsigned int i;
1493 SBITMAP_ELT_TYPE *p, *r;
1495 e = EDGE_PRED (b, ix);
1496 if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun))
1497 continue;
1499 p = src[e->src->index]->elms;
1500 r = dst->elms;
1501 for (i = 0; i < set_size; i++)
1502 *r++ |= *p++;
1506 /* Returns the list of basic blocks in the function in an order that guarantees
1507 that if a block X has just a single predecessor Y, then Y is after X in the
1508 ordering. */
1510 basic_block *
1511 single_pred_before_succ_order (void)
1513 basic_block x, y;
1514 basic_block *order = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
1515 unsigned n = n_basic_blocks_for_fn (cfun) - NUM_FIXED_BLOCKS;
1516 unsigned np, i;
1517 auto_sbitmap visited (last_basic_block_for_fn (cfun));
1519 #define MARK_VISITED(BB) (bitmap_set_bit (visited, (BB)->index))
1520 #define VISITED_P(BB) (bitmap_bit_p (visited, (BB)->index))
1522 bitmap_clear (visited);
1524 MARK_VISITED (ENTRY_BLOCK_PTR_FOR_FN (cfun));
1525 FOR_EACH_BB_FN (x, cfun)
1527 if (VISITED_P (x))
1528 continue;
1530 /* Walk the predecessors of x as long as they have precisely one
1531 predecessor and add them to the list, so that they get stored
1532 after x. */
1533 for (y = x, np = 1;
1534 single_pred_p (y) && !VISITED_P (single_pred (y));
1535 y = single_pred (y))
1536 np++;
1537 for (y = x, i = n - np;
1538 single_pred_p (y) && !VISITED_P (single_pred (y));
1539 y = single_pred (y), i++)
1541 order[i] = y;
1542 MARK_VISITED (y);
1544 order[i] = y;
1545 MARK_VISITED (y);
1547 gcc_assert (i == n - 1);
1548 n -= np;
1551 gcc_assert (n == 0);
1552 return order;
1554 #undef MARK_VISITED
1555 #undef VISITED_P
1558 /* Ignoring loop backedges, if BB has precisely one incoming edge then
1559 return that edge. Otherwise return NULL.
1561 When IGNORE_NOT_EXECUTABLE is true, also ignore edges that are not marked
1562 as executable. */
1564 edge
1565 single_pred_edge_ignoring_loop_edges (basic_block bb,
1566 bool ignore_not_executable)
1568 edge retval = NULL;
1569 edge e;
1570 edge_iterator ei;
1572 FOR_EACH_EDGE (e, ei, bb->preds)
1574 /* A loop back edge can be identified by the destination of
1575 the edge dominating the source of the edge. */
1576 if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest))
1577 continue;
1579 /* We can safely ignore edges that are not executable. */
1580 if (ignore_not_executable
1581 && (e->flags & EDGE_EXECUTABLE) == 0)
1582 continue;
1584 /* If we have already seen a non-loop edge, then we must have
1585 multiple incoming non-loop edges and thus we return NULL. */
1586 if (retval)
1587 return NULL;
1589 /* This is the first non-loop incoming edge we have found. Record
1590 it. */
1591 retval = e;
1594 return retval;