aboutsummaryrefslogtreecommitdiff
path: root/gcc/cfgloop.c
blob: c0d9a4cacc2649b5d70287fe90f91b48c3be9d8f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
/* Natural loop discovery code for GNU compiler.
   Copyright (C) 2000, 2001, 2003, 2004, 2005, 2006, 2007, 2008
   Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "hard-reg-set.h"
#include "obstack.h"
#include "function.h"
#include "basic-block.h"
#include "toplev.h"
#include "cfgloop.h"
#include "flags.h"
#include "tree.h"
#include "tree-flow.h"
#include "pointer-set.h"
#include "output.h"
#include "ggc.h"

static void flow_loops_cfg_dump (FILE *);

/* Dump loop related CFG information.  */

static void
flow_loops_cfg_dump (FILE *file)
{
  basic_block bb;

  if (!file)
    return;

  FOR_EACH_BB (bb)
    {
      edge succ;
      edge_iterator ei;

      fprintf (file, ";; %d succs { ", bb->index);
      FOR_EACH_EDGE (succ, ei, bb->succs)
	fprintf (file, "%d ", succ->dest->index);
      fprintf (file, "}\n");
    }
}

/* Return nonzero if the nodes of LOOP are a subset of OUTER.  */

bool
flow_loop_nested_p (const struct loop *outer, const struct loop *loop)
{
  unsigned odepth = loop_depth (outer);

  return (loop_depth (loop) > odepth
	  && VEC_index (loop_p, loop->superloops, odepth) == outer);
}

/* Returns the loop such that LOOP is nested DEPTH (indexed from zero)
   loops within LOOP.  */

struct loop *
superloop_at_depth (struct loop *loop, unsigned depth)
{
  unsigned ldepth = loop_depth (loop);

  gcc_assert (depth <= ldepth);

  if (depth == ldepth)
    return loop;

  return VEC_index (loop_p, loop->superloops, depth);
}

/* Returns the list of the latch edges of LOOP.  */

static VEC (edge, heap) *
get_loop_latch_edges (const struct loop *loop)
{
  edge_iterator ei;
  edge e;
  VEC (edge, heap) *ret = NULL;

  FOR_EACH_EDGE (e, ei, loop->header->preds)
    {
      if (dominated_by_p (CDI_DOMINATORS, e->src, loop->header))
	VEC_safe_push (edge, heap, ret, e);
    }

  return ret;
}

/* Dump the loop information specified by LOOP to the stream FILE
   using auxiliary dump callback function LOOP_DUMP_AUX if non null.  */

void
flow_loop_dump (const struct loop *loop, FILE *file,
		void (*loop_dump_aux) (const struct loop *, FILE *, int),
		int verbose)
{
  basic_block *bbs;
  unsigned i;
  VEC (edge, heap) *latches;
  edge e;

  if (! loop || ! loop->header)
    return;

  fprintf (file, ";;\n;; Loop %d\n", loop->num);

  fprintf (file, ";;  header %d, ", loop->header->index);
  if (loop->latch)
    fprintf (file, "latch %d\n", loop->latch->index);
  else
    {
      fprintf (file, "multiple latches:");
      latches = get_loop_latch_edges (loop);
      for (i = 0; VEC_iterate (edge, latches, i, e); i++)
	fprintf (file, " %d", e->src->index);
      VEC_free (edge, heap, latches);
      fprintf (file, "\n");
    }

  fprintf (file, ";;  depth %d, outer %ld\n",
	   loop_depth (loop), (long) (loop_outer (loop)
				      ? loop_outer (loop)->num : -1));

  fprintf (file, ";;  nodes:");
  bbs = get_loop_body (loop);
  for (i = 0; i < loop->num_nodes; i++)
    fprintf (file, " %d", bbs[i]->index);
  free (bbs);
  fprintf (file, "\n");

  if (loop_dump_aux)
    loop_dump_aux (loop, file, verbose);
}

/* Dump the loop information about loops to the stream FILE,
   using auxiliary dump callback function LOOP_DUMP_AUX if non null.  */

void
flow_loops_dump (FILE *file, void (*loop_dump_aux) (const struct loop *, FILE *, int), int verbose)
{
  loop_iterator li;
  struct loop *loop;

  if (!current_loops || ! file)
    return;

  fprintf (file, ";; %d loops found\n", number_of_loops ());

  FOR_EACH_LOOP (li, loop, LI_INCLUDE_ROOT)
    {
      flow_loop_dump (loop, file, loop_dump_aux, verbose);
    }

  if (verbose)
    flow_loops_cfg_dump (file);
}

/* Free data allocated for LOOP.  */

void
flow_loop_free (struct loop *loop)
{
  struct loop_exit *exit, *next;

  VEC_free (loop_p, gc, loop->superloops);

  /* Break the list of the loop exit records.  They will be freed when the
     corresponding edge is rescanned or removed, and this avoids
     accessing the (already released) head of the list stored in the
     loop structure.  */
  for (exit = loop->exits->next; exit != loop->exits; exit = next)
    {
      next = exit->next;
      exit->next = exit;
      exit->prev = exit;
    }

  ggc_free (loop->exits);
  ggc_free (loop);
}

/* Free all the memory allocated for LOOPS.  */

void
flow_loops_free (struct loops *loops)
{
  if (loops->larray)
    {
      unsigned i;
      loop_p loop;

      /* Free the loop descriptors.  */
      for (i = 0; VEC_iterate (loop_p, loops->larray, i, loop); i++)
	{
	  if (!loop)
	    continue;

	  flow_loop_free (loop);
	}

      VEC_free (loop_p, gc, loops->larray);
    }
}

/* Find the nodes contained within the LOOP with header HEADER.
   Return the number of nodes within the loop.  */

int
flow_loop_nodes_find (basic_block header, struct loop *loop)
{
  VEC (basic_block, heap) *stack = NULL;
  int num_nodes = 1;
  edge latch;
  edge_iterator latch_ei;
  unsigned depth = loop_depth (loop);

  header->loop_father = loop;
  header->loop_depth = depth;

  FOR_EACH_EDGE (latch, latch_ei, loop->header->preds)
    {
      if (latch->src->loop_father == loop
	  || !dominated_by_p (CDI_DOMINATORS, latch->src, loop->header))
	continue;

      num_nodes++;
      VEC_safe_push (basic_block, heap, stack, latch->src);
      latch->src->loop_father = loop;
      latch->src->loop_depth = depth;

      while (!VEC_empty (basic_block, stack))
	{
	  basic_block node;
	  edge e;
	  edge_iterator ei;

	  node = VEC_pop (basic_block, stack);

	  FOR_EACH_EDGE (e, ei, node->preds)
	    {
	      basic_block ancestor = e->src;

	      if (ancestor->loop_father != loop)
		{
		  ancestor->loop_father = loop;
		  ancestor->loop_depth = depth;
		  num_nodes++;
		  VEC_safe_push (basic_block, heap, stack, ancestor);
		}
	    }
	}
    }
  VEC_free (basic_block, heap, stack);

  return num_nodes;
}

/* Records the vector of superloops of the loop LOOP, whose immediate
   superloop is FATHER.  */

static void
establish_preds (struct loop *loop, struct loop *father)
{
  loop_p ploop;
  unsigned depth = loop_depth (father) + 1;
  unsigned i;

  VEC_truncate (loop_p, loop->superloops, 0);
  VEC_reserve (loop_p, gc, loop->superloops, depth);
  for (i = 0; VEC_iterate (loop_p, father->superloops, i, ploop); i++)
    VEC_quick_push (loop_p, loop->superloops, ploop);
  VEC_quick_push (loop_p, loop->superloops, father);

  for (ploop = loop->inner; ploop; ploop = ploop->next)
    establish_preds (ploop, loop);
}

/* Add LOOP to the loop hierarchy tree where FATHER is father of the
   added loop.  If LOOP has some children, take care of that their
   pred field will be initialized correctly.  */

void
flow_loop_tree_node_add (struct loop *father, struct loop *loop)
{
  loop->next = father->inner;
  father->inner = loop;

  establish_preds (loop, father);
}

/* Remove LOOP from the loop hierarchy tree.  */

void
flow_loop_tree_node_remove (struct loop *loop)
{
  struct loop *prev, *father;

  father = loop_outer (loop);

  /* Remove loop from the list of sons.  */
  if (father->inner == loop)
    father->inner = loop->next;
  else
    {
      for (prev = father->inner; prev->next != loop; prev = prev->next)
	continue;
      prev->next = loop->next;
    }

  VEC_truncate (loop_p, loop->superloops, 0);
}

/* Allocates and returns new loop structure.  */

struct loop *
alloc_loop (void)
{
  struct loop *loop = ggc_alloc_cleared_loop ();

  loop->exits = ggc_alloc_cleared_loop_exit ();
  loop->exits->next = loop->exits->prev = loop->exits;
  loop->can_be_parallel = false;
  loop->single_iv = NULL_TREE;

  return loop;
}

/* Initializes loops structure LOOPS, reserving place for NUM_LOOPS loops
   (including the root of the loop tree).  */

static void
init_loops_structure (struct loops *loops, unsigned num_loops)
{
  struct loop *root;

  memset (loops, 0, sizeof *loops);
  loops->larray = VEC_alloc (loop_p, gc, num_loops);

  /* Dummy loop containing whole function.  */
  root = alloc_loop ();
  root->num_nodes = n_basic_blocks;
  root->latch = EXIT_BLOCK_PTR;
  root->header = ENTRY_BLOCK_PTR;
  ENTRY_BLOCK_PTR->loop_father = root;
  EXIT_BLOCK_PTR->loop_father = root;

  VEC_quick_push (loop_p, loops->larray, root);
  loops->tree_root = root;
}

/* Find all the natural loops in the function and save in LOOPS structure and
   recalculate loop_depth information in basic block structures.
   Return the number of natural loops found.  */

int
flow_loops_find (struct loops *loops)
{
  int b;
  int num_loops;
  edge e;
  sbitmap headers;
  int *dfs_order;
  int *rc_order;
  basic_block header;
  basic_block bb;

  /* Ensure that the dominators are computed.  */
  calculate_dominance_info (CDI_DOMINATORS);

  /* Taking care of this degenerate case makes the rest of
     this code simpler.  */
  if (n_basic_blocks == NUM_FIXED_BLOCKS)
    {
      init_loops_structure (loops, 1);
      return 1;
    }

  dfs_order = NULL;
  rc_order = NULL;

  /* Count the number of loop headers.  This should be the
     same as the number of natural loops.  */
  headers = sbitmap_alloc (last_basic_block);
  sbitmap_zero (headers);

  num_loops = 0;
  FOR_EACH_BB (header)
    {
      edge_iterator ei;

      header->loop_depth = 0;

      /* If we have an abnormal predecessor, do not consider the
	 loop (not worth the problems).  */
      FOR_EACH_EDGE (e, ei, header->preds)
	if (e->flags & EDGE_ABNORMAL)
	  break;
      if (e)
	continue;

      FOR_EACH_EDGE (e, ei, header->preds)
	{
	  basic_block latch = e->src;

	  gcc_assert (!(e->flags & EDGE_ABNORMAL));

	  /* Look for back edges where a predecessor is dominated
	     by this block.  A natural loop has a single entry
	     node (header) that dominates all the nodes in the
	     loop.  It also has single back edge to the header
	     from a latch node.  */
	  if (latch != ENTRY_BLOCK_PTR
	      && dominated_by_p (CDI_DOMINATORS, latch, header))
	    {
	      /* Shared headers should be eliminated by now.  */
	      SET_BIT (headers, header->index);
	      num_loops++;
	    }
	}
    }

  /* Allocate loop structures.  */
  init_loops_structure (loops, num_loops + 1);

  /* Find and record information about all the natural loops
     in the CFG.  */
  FOR_EACH_BB (bb)
    bb->loop_father = loops->tree_root;

  if (num_loops)
    {
      /* Compute depth first search order of the CFG so that outer
	 natural loops will be found before inner natural loops.  */
      dfs_order = XNEWVEC (int, n_basic_blocks);
      rc_order = XNEWVEC (int, n_basic_blocks);
      pre_and_rev_post_order_compute (dfs_order, rc_order, false);

      num_loops = 1;

      for (b = 0; b < n_basic_blocks - NUM_FIXED_BLOCKS; b++)
	{
	  struct loop *loop;
	  edge_iterator ei;

	  /* Search the nodes of the CFG in reverse completion order
	     so that we can find outer loops first.  */
	  if (!TEST_BIT (headers, rc_order[b]))
	    continue;

	  header = BASIC_BLOCK (rc_order[b]);

	  loop = alloc_loop ();
	  VEC_quick_push (loop_p, loops->larray, loop);

	  loop->header = header;
	  loop->num = num_loops;
	  num_loops++;

	  flow_loop_tree_node_add (header->loop_father, loop);
	  loop->num_nodes = flow_loop_nodes_find (loop->header, loop);

	  /* Look for the latch for this header block, if it has just a
	     single one.  */
	  FOR_EACH_EDGE (e, ei, header->preds)
	    {
	      basic_block latch = e->src;

	      if (flow_bb_inside_loop_p (loop, latch))
		{
		  if (loop->latch != NULL)
		    {
		      /* More than one latch edge.  */
		      loop->latch = NULL;
		      break;
		    }
		  loop->latch = latch;
		}
	    }
	}

      free (dfs_order);
      free (rc_order);
    }

  sbitmap_free (headers);

  loops->exits = NULL;
  return VEC_length (loop_p, loops->larray);
}

/* Ratio of frequencies of edges so that one of more latch edges is
   considered to belong to inner loop with same header.  */
#define HEAVY_EDGE_RATIO 8

/* Minimum number of samples for that we apply
   find_subloop_latch_edge_by_profile heuristics.  */
#define HEAVY_EDGE_MIN_SAMPLES 10

/* If the profile info is available, finds an edge in LATCHES that much more
   frequent than the remaining edges.  Returns such an edge, or NULL if we do
   not find one.

   We do not use guessed profile here, only the measured one.  The guessed
   profile is usually too flat and unreliable for this (and it is mostly based
   on the loop structure of the program, so it does not make much sense to
   derive the loop structure from it).  */

static edge
find_subloop_latch_edge_by_profile (VEC (edge, heap) *latches)
{
  unsigned i;
  edge e, me = NULL;
  gcov_type mcount = 0, tcount = 0;

  for (i = 0; VEC_iterate (edge, latches, i, e); i++)
    {
      if (e->count > mcount)
	{
	  me = e;
	  mcount = e->count;
	}
      tcount += e->count;
    }

  if (tcount < HEAVY_EDGE_MIN_SAMPLES
      || (tcount - mcount) * HEAVY_EDGE_RATIO > tcount)
    return NULL;

  if (dump_file)
    fprintf (dump_file,
	     "Found latch edge %d -> %d using profile information.\n",
	     me->src->index, me->dest->index);
  return me;
}

/* Among LATCHES, guesses a latch edge of LOOP corresponding to subloop, based
   on the structure of induction variables.  Returns this edge, or NULL if we
   do not find any.

   We are quite conservative, and look just for an obvious simple innermost
   loop (which is the case where we would lose the most performance by not
   disambiguating the loop).  More precisely, we look for the following
   situation: The source of the chosen latch edge dominates sources of all
   the other latch edges.  Additionally, the header does not contain a phi node
   such that the argument from the chosen edge is equal to the argument from
   another edge.  */

static edge
find_subloop_latch_edge_by_ivs (struct loop *loop ATTRIBUTE_UNUSED, VEC (edge, heap) *latches)
{
  edge e, latch = VEC_index (edge, latches, 0);
  unsigned i;
  gimple phi;
  gimple_stmt_iterator psi;
  tree lop;
  basic_block bb;

  /* Find the candidate for the latch edge.  */
  for (i = 1; VEC_iterate (edge, latches, i, e); i++)
    if (dominated_by_p (CDI_DOMINATORS, latch->src, e->src))
      latch = e;

  /* Verify that it dominates all the latch edges.  */
  for (i = 0; VEC_iterate (edge, latches, i, e); i++)
    if (!dominated_by_p (CDI_DOMINATORS, e->src, latch->src))
      return NULL;

  /* Check for a phi node that would deny that this is a latch edge of
     a subloop.  */
  for (psi = gsi_start_phis (loop->header); !gsi_end_p (psi); gsi_next (&psi))
    {
      phi = gsi_stmt (psi);
      lop = PHI_ARG_DEF_FROM_EDGE (phi, latch);

      /* Ignore the values that are not changed inside the subloop.  */
      if (TREE_CODE (lop) != SSA_NAME
	  || SSA_NAME_DEF_STMT (lop) == phi)
	continue;
      bb = gimple_bb (SSA_NAME_DEF_STMT (lop));
      if (!bb || !flow_bb_inside_loop_p (loop, bb))
	continue;

      for (i = 0; VEC_iterate (edge, latches, i, e); i++)
	if (e != latch
	    && PHI_ARG_DEF_FROM_EDGE (phi, e) == lop)
	  return NULL;
    }

  if (dump_file)
    fprintf (dump_file,
	     "Found latch edge %d -> %d using iv structure.\n",
	     latch->src->index, latch->dest->index);
  return latch;
}

/* If we can determine that one of the several latch edges of LOOP behaves
   as a latch edge of a separate subloop, returns this edge.  Otherwise
   returns NULL.  */

static edge
find_subloop_latch_edge (struct loop *loop)
{
  VEC (edge, heap) *latches = get_loop_latch_edges (loop);
  edge latch = NULL;

  if (VEC_length (edge, latches) > 1)
    {
      latch = find_subloop_latch_edge_by_profile (latches);

      if (!latch
	  /* We consider ivs to guess the latch edge only in SSA.  Perhaps we
	     should use cfghook for this, but it is hard to imagine it would
	     be useful elsewhere.  */
	  && current_ir_type () == IR_GIMPLE)
	latch = find_subloop_latch_edge_by_ivs (loop, latches);
    }

  VEC_free (edge, heap, latches);
  return latch;
}

/* Callback for make_forwarder_block.  Returns true if the edge E is marked
   in the set MFB_REIS_SET.  */

static struct pointer_set_t *mfb_reis_set;
static bool
mfb_redirect_edges_in_set (edge e)
{
  return pointer_set_contains (mfb_reis_set, e);
}

/* Creates a subloop of LOOP with latch edge LATCH.  */

static void
form_subloop (struct loop *loop, edge latch)
{
  edge_iterator ei;
  edge e, new_entry;
  struct loop *new_loop;

  mfb_reis_set = pointer_set_create ();
  FOR_EACH_EDGE (e, ei, loop->header->preds)
    {
      if (e != latch)
	pointer_set_insert (mfb_reis_set, e);
    }
  new_entry = make_forwarder_block (loop->header, mfb_redirect_edges_in_set,
				    NULL);
  pointer_set_destroy (mfb_reis_set);

  loop->header = new_entry->src;

  /* Find the blocks and subloops that belong to the new loop, and add it to
     the appropriate place in the loop tree.  */
  new_loop = alloc_loop ();
  new_loop->header = new_entry->dest;
  new_loop->latch = latch->src;
  add_loop (new_loop, loop);
}

/* Make all the latch edges of LOOP to go to a single forwarder block --
   a new latch of LOOP.  */

static void
merge_latch_edges (struct loop *loop)
{
  VEC (edge, heap) *latches = get_loop_latch_edges (loop);
  edge latch, e;
  unsigned i;

  gcc_assert (VEC_length (edge, latches) > 0);

  if (VEC_length (edge, latches) == 1)
    loop->latch = VEC_index (edge, latches, 0)->src;
  else
    {
      if (dump_file)
	fprintf (dump_file, "Merged latch edges of loop %d\n", loop->num);

      mfb_reis_set = pointer_set_create ();
      for (i = 0; VEC_iterate (edge, latches, i, e); i++)
	pointer_set_insert (mfb_reis_set, e);
      latch = make_forwarder_block (loop->header, mfb_redirect_edges_in_set,
				    NULL);
      pointer_set_destroy (mfb_reis_set);

      loop->header = latch->dest;
      loop->latch = latch->src;
    }

  VEC_free (edge, heap, latches);
}

/* LOOP may have several latch edges.  Transform it into (possibly several)
   loops with single latch edge.  */

static void
disambiguate_multiple_latches (struct loop *loop)
{
  edge e;

  /* We eliminate the multiple latches by splitting the header to the forwarder
     block F and the rest R, and redirecting the edges.  There are two cases:

     1) If there is a latch edge E that corresponds to a subloop (we guess
        that based on profile -- if it is taken much more often than the
	remaining edges; and on trees, using the information about induction
	variables of the loops), we redirect E to R, all the remaining edges to
	F, then rescan the loops and try again for the outer loop.
     2) If there is no such edge, we redirect all latch edges to F, and the
        entry edges to R, thus making F the single latch of the loop.  */

  if (dump_file)
    fprintf (dump_file, "Disambiguating loop %d with multiple latches\n",
	     loop->num);

  /* During latch merging, we may need to redirect the entry edges to a new
     block.  This would cause problems if the entry edge was the one from the
     entry block.  To avoid having to handle this case specially, split
     such entry edge.  */
  e = find_edge (ENTRY_BLOCK_PTR, loop->header);
  if (e)
    split_edge (e);

  while (1)
    {
      e = find_subloop_latch_edge (loop);
      if (!e)
	break;

      form_subloop (loop, e);
    }

  merge_latch_edges (loop);
}

/* Split loops with multiple latch edges.  */

void
disambiguate_loops_with_multiple_latches (void)
{
  loop_iterator li;
  struct loop *loop;

  FOR_EACH_LOOP (li, loop, 0)
    {
      if (!loop->latch)
	disambiguate_multiple_latches (loop);
    }
}

/* Return nonzero if basic block BB belongs to LOOP.  */
bool
flow_bb_inside_loop_p (const struct loop *loop, const_basic_block bb)
{
  struct loop *source_loop;

  if (bb == ENTRY_BLOCK_PTR || bb == EXIT_BLOCK_PTR)
    return 0;

  source_loop = bb->loop_father;
  return loop == source_loop || flow_loop_nested_p (loop, source_loop);
}

/* Enumeration predicate for get_loop_body_with_size.  */
static bool
glb_enum_p (const_basic_block bb, const void *glb_loop)
{
  const struct loop *const loop = (const struct loop *) glb_loop;
  return (bb != loop->header
	  && dominated_by_p (CDI_DOMINATORS, bb, loop->header));
}

/* Gets basic blocks of a LOOP.  Header is the 0-th block, rest is in dfs
   order against direction of edges from latch.  Specially, if
   header != latch, latch is the 1-st block.  LOOP cannot be the fake
   loop tree root, and its size must be at most MAX_SIZE.  The blocks
   in the LOOP body are stored to BODY, and the size of the LOOP is
   returned.  */

unsigned
get_loop_body_with_size (const struct loop *loop, basic_block *body,
			 unsigned max_size)
{
  return dfs_enumerate_from (loop->header, 1, glb_enum_p,
			     body, max_size, loop);
}

/* Gets basic blocks of a LOOP.  Header is the 0-th block, rest is in dfs
   order against direction of edges from latch.  Specially, if
   header != latch, latch is the 1-st block.  */

basic_block *
get_loop_body (const struct loop *loop)
{
  basic_block *body, bb;
  unsigned tv = 0;

  gcc_assert (loop->num_nodes);

  body = XCNEWVEC (basic_block, loop->num_nodes);

  if (loop->latch == EXIT_BLOCK_PTR)
    {
      /* There may be blocks unreachable from EXIT_BLOCK, hence we need to
	 special-case the fake loop that contains the whole function.  */
      gcc_assert (loop->num_nodes == (unsigned) n_basic_blocks);
      body[tv++] = loop->header;
      body[tv++] = EXIT_BLOCK_PTR;
      FOR_EACH_BB (bb)
	body[tv++] = bb;
    }
  else
    tv = get_loop_body_with_size (loop, body, loop->num_nodes);

  gcc_assert (tv == loop->num_nodes);
  return body;
}

/* Fills dominance descendants inside LOOP of the basic block BB into
   array TOVISIT from index *TV.  */

static void
fill_sons_in_loop (const struct loop *loop, basic_block bb,
		   basic_block *tovisit, int *tv)
{
  basic_block son, postpone = NULL;

  tovisit[(*tv)++] = bb;
  for (son = first_dom_son (CDI_DOMINATORS, bb);
       son;
       son = next_dom_son (CDI_DOMINATORS, son))
    {
      if (!flow_bb_inside_loop_p (loop, son))
	continue;

      if (dominated_by_p (CDI_DOMINATORS, loop->latch, son))
	{
	  postpone = son;
	  continue;
	}
      fill_sons_in_loop (loop, son, tovisit, tv);
    }

  if (postpone)
    fill_sons_in_loop (loop, postpone, tovisit, tv);
}

/* Gets body of a LOOP (that must be different from the outermost loop)
   sorted by dominance relation.  Additionally, if a basic block s dominates
   the latch, then only blocks dominated by s are be after it.  */

basic_block *
get_loop_body_in_dom_order (const struct loop *loop)
{
  basic_block *tovisit;
  int tv;

  gcc_assert (loop->num_nodes);

  tovisit = XCNEWVEC (basic_block, loop->num_nodes);

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  tv = 0;
  fill_sons_in_loop (loop, loop->header, tovisit, &tv);

  gcc_assert (tv == (int) loop->num_nodes);

  return tovisit;
}

/* Gets body of a LOOP sorted via provided BB_COMPARATOR.  */

basic_block *
get_loop_body_in_custom_order (const struct loop *loop,
			       int (*bb_comparator) (const void *, const void *))
{
  basic_block *bbs = get_loop_body (loop);

  qsort (bbs, loop->num_nodes, sizeof (basic_block), bb_comparator);

  return bbs;
}

/* Get body of a LOOP in breadth first sort order.  */

basic_block *
get_loop_body_in_bfs_order (const struct loop *loop)
{
  basic_block *blocks;
  basic_block bb;
  bitmap visited;
  unsigned int i = 0;
  unsigned int vc = 1;

  gcc_assert (loop->num_nodes);
  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  blocks = XCNEWVEC (basic_block, loop->num_nodes);
  visited = BITMAP_ALLOC (NULL);

  bb = loop->header;
  while (i < loop->num_nodes)
    {
      edge e;
      edge_iterator ei;

      if (!bitmap_bit_p (visited, bb->index))
	{
	  /* This basic block is now visited */
	  bitmap_set_bit (visited, bb->index);
	  blocks[i++] = bb;
	}

      FOR_EACH_EDGE (e, ei, bb->succs)
	{
	  if (flow_bb_inside_loop_p (loop, e->dest))
	    {
	      if (!bitmap_bit_p (visited, e->dest->index))
		{
		  bitmap_set_bit (visited, e->dest->index);
		  blocks[i++] = e->dest;
		}
	    }
	}

      gcc_assert (i >= vc);

      bb = blocks[vc++];
    }

  BITMAP_FREE (visited);
  return blocks;
}

/* Hash function for struct loop_exit.  */

static hashval_t
loop_exit_hash (const void *ex)
{
  const struct loop_exit *const exit = (const struct loop_exit *) ex;

  return htab_hash_pointer (exit->e);
}

/* Equality function for struct loop_exit.  Compares with edge.  */

static int
loop_exit_eq (const void *ex, const void *e)
{
  const struct loop_exit *const exit = (const struct loop_exit *) ex;

  return exit->e == e;
}

/* Frees the list of loop exit descriptions EX.  */

static void
loop_exit_free (void *ex)
{
  struct loop_exit *exit = (struct loop_exit *) ex, *next;

  for (; exit; exit = next)
    {
      next = exit->next_e;

      exit->next->prev = exit->prev;
      exit->prev->next = exit->next;

      ggc_free (exit);
    }
}

/* Returns the list of records for E as an exit of a loop.  */

static struct loop_exit *
get_exit_descriptions (edge e)
{
  return (struct loop_exit *) htab_find_with_hash (current_loops->exits, e,
			                           htab_hash_pointer (e));
}

/* Updates the lists of loop exits in that E appears.
   If REMOVED is true, E is being removed, and we
   just remove it from the lists of exits.
   If NEW_EDGE is true and E is not a loop exit, we
   do not try to remove it from loop exit lists.  */

void
rescan_loop_exit (edge e, bool new_edge, bool removed)
{
  void **slot;
  struct loop_exit *exits = NULL, *exit;
  struct loop *aloop, *cloop;

  if (!loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    return;

  if (!removed
      && e->src->loop_father != NULL
      && e->dest->loop_father != NULL
      && !flow_bb_inside_loop_p (e->src->loop_father, e->dest))
    {
      cloop = find_common_loop (e->src->loop_father, e->dest->loop_father);
      for (aloop = e->src->loop_father;
	   aloop != cloop;
	   aloop = loop_outer (aloop))
	{
	  exit = ggc_alloc_loop_exit ();
	  exit->e = e;

	  exit->next = aloop->exits->next;
	  exit->prev = aloop->exits;
	  exit->next->prev = exit;
	  exit->prev->next = exit;

	  exit->next_e = exits;
	  exits = exit;
	}
    }

  if (!exits && new_edge)
    return;

  slot = htab_find_slot_with_hash (current_loops->exits, e,
				   htab_hash_pointer (e),
				   exits ? INSERT : NO_INSERT);
  if (!slot)
    return;

  if (exits)
    {
      if (*slot)
	loop_exit_free (*slot);
      *slot = exits;
    }
  else
    htab_clear_slot (current_loops->exits, slot);
}

/* For each loop, record list of exit edges, and start maintaining these
   lists.  */

void
record_loop_exits (void)
{
  basic_block bb;
  edge_iterator ei;
  edge e;

  if (!current_loops)
    return;

  if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    return;
  loops_state_set (LOOPS_HAVE_RECORDED_EXITS);

  gcc_assert (current_loops->exits == NULL);
  current_loops->exits = htab_create_ggc (2 * number_of_loops (),
					  loop_exit_hash, loop_exit_eq,
					  loop_exit_free);

  FOR_EACH_BB (bb)
    {
      FOR_EACH_EDGE (e, ei, bb->succs)
	{
	  rescan_loop_exit (e, true, false);
	}
    }
}

/* Dumps information about the exit in *SLOT to FILE.
   Callback for htab_traverse.  */

static int
dump_recorded_exit (void **slot, void *file)
{
  struct loop_exit *exit = (struct loop_exit *) *slot;
  unsigned n = 0;
  edge e = exit->e;

  for (; exit != NULL; exit = exit->next_e)
    n++;

  fprintf ((FILE*) file, "Edge %d->%d exits %u loops\n",
	   e->src->index, e->dest->index, n);

  return 1;
}

/* Dumps the recorded exits of loops to FILE.  */

extern void dump_recorded_exits (FILE *);
void
dump_recorded_exits (FILE *file)
{
  if (!current_loops->exits)
    return;
  htab_traverse (current_loops->exits, dump_recorded_exit, file);
}

/* Releases lists of loop exits.  */

void
release_recorded_exits (void)
{
  gcc_assert (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS));
  htab_delete (current_loops->exits);
  current_loops->exits = NULL;
  loops_state_clear (LOOPS_HAVE_RECORDED_EXITS);
}

/* Returns the list of the exit edges of a LOOP.  */

VEC (edge, heap) *
get_loop_exit_edges (const struct loop *loop)
{
  VEC (edge, heap) *edges = NULL;
  edge e;
  unsigned i;
  basic_block *body;
  edge_iterator ei;
  struct loop_exit *exit;

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  /* If we maintain the lists of exits, use them.  Otherwise we must
     scan the body of the loop.  */
  if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    {
      for (exit = loop->exits->next; exit->e; exit = exit->next)
	VEC_safe_push (edge, heap, edges, exit->e);
    }
  else
    {
      body = get_loop_body (loop);
      for (i = 0; i < loop->num_nodes; i++)
	FOR_EACH_EDGE (e, ei, body[i]->succs)
	  {
	    if (!flow_bb_inside_loop_p (loop, e->dest))
	      VEC_safe_push (edge, heap, edges, e);
	  }
      free (body);
    }

  return edges;
}

/* Counts the number of conditional branches inside LOOP.  */

unsigned
num_loop_branches (const struct loop *loop)
{
  unsigned i, n;
  basic_block * body;

  gcc_assert (loop->latch != EXIT_BLOCK_PTR);

  body = get_loop_body (loop);
  n = 0;
  for (i = 0; i < loop->num_nodes; i++)
    if (EDGE_COUNT (body[i]->succs) >= 2)
      n++;
  free (body);

  return n;
}

/* Adds basic block BB to LOOP.  */
void
add_bb_to_loop (basic_block bb, struct loop *loop)
{
  unsigned i;
  loop_p ploop;
  edge_iterator ei;
  edge e;

  gcc_assert (bb->loop_father == NULL);
  bb->loop_father = loop;
  bb->loop_depth = loop_depth (loop);
  loop->num_nodes++;
  for (i = 0; VEC_iterate (loop_p, loop->superloops, i, ploop); i++)
    ploop->num_nodes++;

  FOR_EACH_EDGE (e, ei, bb->succs)
    {
      rescan_loop_exit (e, true, false);
    }
  FOR_EACH_EDGE (e, ei, bb->preds)
    {
      rescan_loop_exit (e, true, false);
    }
}

/* Remove basic block BB from loops.  */
void
remove_bb_from_loops (basic_block bb)
{
  int i;
  struct loop *loop = bb->loop_father;
  loop_p ploop;
  edge_iterator ei;
  edge e;

  gcc_assert (loop != NULL);
  loop->num_nodes--;
  for (i = 0; VEC_iterate (loop_p, loop->superloops, i, ploop); i++)
    ploop->num_nodes--;
  bb->loop_father = NULL;
  bb->loop_depth = 0;

  FOR_EACH_EDGE (e, ei, bb->succs)
    {
      rescan_loop_exit (e, false, true);
    }
  FOR_EACH_EDGE (e, ei, bb->preds)
    {
      rescan_loop_exit (e, false, true);
    }
}

/* Finds nearest common ancestor in loop tree for given loops.  */
struct loop *
find_common_loop (struct loop *loop_s, struct loop *loop_d)
{
  unsigned sdepth, ddepth;

  if (!loop_s) return loop_d;
  if (!loop_d) return loop_s;

  sdepth = loop_depth (loop_s);
  ddepth = loop_depth (loop_d);

  if (sdepth < ddepth)
    loop_d = VEC_index (loop_p, loop_d->superloops, sdepth);
  else if (sdepth > ddepth)
    loop_s = VEC_index (loop_p, loop_s->superloops, ddepth);

  while (loop_s != loop_d)
    {
      loop_s = loop_outer (loop_s);
      loop_d = loop_outer (loop_d);
    }
  return loop_s;
}

/* Removes LOOP from structures and frees its data.  */

void
delete_loop (struct loop *loop)
{
  /* Remove the loop from structure.  */
  flow_loop_tree_node_remove (loop);

  /* Remove loop from loops array.  */
  VEC_replace (loop_p, current_loops->larray, loop->num, NULL);

  /* Free loop data.  */
  flow_loop_free (loop);
}

/* Cancels the LOOP; it must be innermost one.  */

static void
cancel_loop (struct loop *loop)
{
  basic_block *bbs;
  unsigned i;
  struct loop *outer = loop_outer (loop);

  gcc_assert (!loop->inner);

  /* Move blocks up one level (they should be removed as soon as possible).  */
  bbs = get_loop_body (loop);
  for (i = 0; i < loop->num_nodes; i++)
    bbs[i]->loop_father = outer;

  delete_loop (loop);
}

/* Cancels LOOP and all its subloops.  */
void
cancel_loop_tree (struct loop *loop)
{
  while (loop->inner)
    cancel_loop_tree (loop->inner);
  cancel_loop (loop);
}

/* Checks that information about loops is correct
     -- sizes of loops are all right
     -- results of get_loop_body really belong to the loop
     -- loop header have just single entry edge and single latch edge
     -- loop latches have only single successor that is header of their loop
     -- irreducible loops are correctly marked
  */
DEBUG_FUNCTION void
verify_loop_structure (void)
{
  unsigned *sizes, i, j;
  sbitmap irreds;
  basic_block *bbs, bb;
  struct loop *loop;
  int err = 0;
  edge e;
  unsigned num = number_of_loops ();
  loop_iterator li;
  struct loop_exit *exit, *mexit;

  /* Check sizes.  */
  sizes = XCNEWVEC (unsigned, num);
  sizes[0] = 2;

  FOR_EACH_BB (bb)
    for (loop = bb->loop_father; loop; loop = loop_outer (loop))
      sizes[loop->num]++;

  FOR_EACH_LOOP (li, loop, LI_INCLUDE_ROOT)
    {
      i = loop->num;

      if (loop->num_nodes != sizes[i])
	{
	  error ("size of loop %d should be %d, not %d",
		   i, sizes[i], loop->num_nodes);
	  err = 1;
	}
    }

  /* Check get_loop_body.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      bbs = get_loop_body (loop);

      for (j = 0; j < loop->num_nodes; j++)
	if (!flow_bb_inside_loop_p (loop, bbs[j]))
	  {
	    error ("bb %d do not belong to loop %d",
		    bbs[j]->index, loop->num);
	    err = 1;
	  }
      free (bbs);
    }

  /* Check headers and latches.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      i = loop->num;

      if (loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS)
	  && EDGE_COUNT (loop->header->preds) != 2)
	{
	  error ("loop %d's header does not have exactly 2 entries", i);
	  err = 1;
	}
      if (loops_state_satisfies_p (LOOPS_HAVE_SIMPLE_LATCHES))
	{
	  if (!single_succ_p (loop->latch))
	    {
	      error ("loop %d's latch does not have exactly 1 successor", i);
	      err = 1;
	    }
	  if (single_succ (loop->latch) != loop->header)
	    {
	      error ("loop %d's latch does not have header as successor", i);
	      err = 1;
	    }
	  if (loop->latch->loop_father != loop)
	    {
	      error ("loop %d's latch does not belong directly to it", i);
	      err = 1;
	    }
	}
      if (loop->header->loop_father != loop)
	{
	  error ("loop %d's header does not belong directly to it", i);
	  err = 1;
	}
      if (loops_state_satisfies_p (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS)
	  && (loop_latch_edge (loop)->flags & EDGE_IRREDUCIBLE_LOOP))
	{
	  error ("loop %d's latch is marked as part of irreducible region", i);
	  err = 1;
	}
    }

  /* Check irreducible loops.  */
  if (loops_state_satisfies_p (LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS))
    {
      /* Record old info.  */
      irreds = sbitmap_alloc (last_basic_block);
      FOR_EACH_BB (bb)
	{
	  edge_iterator ei;
	  if (bb->flags & BB_IRREDUCIBLE_LOOP)
	    SET_BIT (irreds, bb->index);
	  else
	    RESET_BIT (irreds, bb->index);
	  FOR_EACH_EDGE (e, ei, bb->succs)
	    if (e->flags & EDGE_IRREDUCIBLE_LOOP)
	      e->flags |= EDGE_ALL_FLAGS + 1;
	}

      /* Recount it.  */
      mark_irreducible_loops ();

      /* Compare.  */
      FOR_EACH_BB (bb)
	{
	  edge_iterator ei;

	  if ((bb->flags & BB_IRREDUCIBLE_LOOP)
	      && !TEST_BIT (irreds, bb->index))
	    {
	      error ("basic block %d should be marked irreducible", bb->index);
	      err = 1;
	    }
	  else if (!(bb->flags & BB_IRREDUCIBLE_LOOP)
	      && TEST_BIT (irreds, bb->index))
	    {
	      error ("basic block %d should not be marked irreducible", bb->index);
	      err = 1;
	    }
	  FOR_EACH_EDGE (e, ei, bb->succs)
	    {
	      if ((e->flags & EDGE_IRREDUCIBLE_LOOP)
		  && !(e->flags & (EDGE_ALL_FLAGS + 1)))
		{
		  error ("edge from %d to %d should be marked irreducible",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	      else if (!(e->flags & EDGE_IRREDUCIBLE_LOOP)
		       && (e->flags & (EDGE_ALL_FLAGS + 1)))
		{
		  error ("edge from %d to %d should not be marked irreducible",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	      e->flags &= ~(EDGE_ALL_FLAGS + 1);
	    }
	}
      free (irreds);
    }

  /* Check the recorded loop exits.  */
  FOR_EACH_LOOP (li, loop, 0)
    {
      if (!loop->exits || loop->exits->e != NULL)
	{
	  error ("corrupted head of the exits list of loop %d",
		 loop->num);
	  err = 1;
	}
      else
	{
	  /* Check that the list forms a cycle, and all elements except
	     for the head are nonnull.  */
	  for (mexit = loop->exits, exit = mexit->next, i = 0;
	       exit->e && exit != mexit;
	       exit = exit->next)
	    {
	      if (i++ & 1)
		mexit = mexit->next;
	    }

	  if (exit != loop->exits)
	    {
	      error ("corrupted exits list of loop %d", loop->num);
	      err = 1;
	    }
	}

      if (!loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
	{
	  if (loop->exits->next != loop->exits)
	    {
	      error ("nonempty exits list of loop %d, but exits are not recorded",
		     loop->num);
	      err = 1;
	    }
	}
    }

  if (loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    {
      unsigned n_exits = 0, eloops;

      memset (sizes, 0, sizeof (unsigned) * num);
      FOR_EACH_BB (bb)
	{
	  edge_iterator ei;
	  if (bb->loop_father == current_loops->tree_root)
	    continue;
	  FOR_EACH_EDGE (e, ei, bb->succs)
	    {
	      if (flow_bb_inside_loop_p (bb->loop_father, e->dest))
		continue;

	      n_exits++;
	      exit = get_exit_descriptions (e);
	      if (!exit)
		{
		  error ("Exit %d->%d not recorded",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	      eloops = 0;
	      for (; exit; exit = exit->next_e)
		eloops++;

	      for (loop = bb->loop_father;
		   loop != e->dest->loop_father;
		   loop = loop_outer (loop))
		{
		  eloops--;
		  sizes[loop->num]++;
		}

	      if (eloops != 0)
		{
		  error ("Wrong list of exited loops for edge  %d->%d",
			 e->src->index, e->dest->index);
		  err = 1;
		}
	    }
	}

      if (n_exits != htab_elements (current_loops->exits))
	{
	  error ("Too many loop exits recorded");
	  err = 1;
	}

      FOR_EACH_LOOP (li, loop, 0)
	{
	  eloops = 0;
	  for (exit = loop->exits->next; exit->e; exit = exit->next)
	    eloops++;
	  if (eloops != sizes[loop->num])
	    {
	      error ("%d exits recorded for loop %d (having %d exits)",
		     eloops, loop->num, sizes[loop->num]);
	      err = 1;
	    }
	}
    }

  gcc_assert (!err);

  free (sizes);
}

/* Returns latch edge of LOOP.  */
edge
loop_latch_edge (const struct loop *loop)
{
  return find_edge (loop->latch, loop->header);
}

/* Returns preheader edge of LOOP.  */
edge
loop_preheader_edge (const struct loop *loop)
{
  edge e;
  edge_iterator ei;

  gcc_assert (loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS));

  FOR_EACH_EDGE (e, ei, loop->header->preds)
    if (e->src != loop->latch)
      break;

  return e;
}

/* Returns true if E is an exit of LOOP.  */

bool
loop_exit_edge_p (const struct loop *loop, const_edge e)
{
  return (flow_bb_inside_loop_p (loop, e->src)
	  && !flow_bb_inside_loop_p (loop, e->dest));
}

/* Returns the single exit edge of LOOP, or NULL if LOOP has either no exit
   or more than one exit.  If loops do not have the exits recorded, NULL
   is returned always.  */

edge
single_exit (const struct loop *loop)
{
  struct loop_exit *exit = loop->exits->next;

  if (!loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
    return NULL;

  if (exit->e && exit->next == loop->exits)
    return exit->e;
  else
    return NULL;
}

/* Returns true when BB has an edge exiting LOOP.  */

bool
is_loop_exit (struct loop *loop, basic_block bb)
{
  edge e;
  edge_iterator ei;

  FOR_EACH_EDGE (e, ei, bb->preds)
    if (loop_exit_edge_p (loop, e))
      return true;

  return false;
}