aboutsummaryrefslogtreecommitdiffstats
path: root/gcc-4.9/gcc/tree-ssa-tail-merge.c
blob: 6efe02ed4957ec5b62a4c5788f3c3d62cac0c870 (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
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
/* Tail merging for gimple.
   Copyright (C) 2011-2014 Free Software Foundation, Inc.
   Contributed by Tom de Vries (tom@codesourcery.com)

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/>.  */

/* Pass overview.


   MOTIVATIONAL EXAMPLE

   gimple representation of gcc/testsuite/gcc.dg/pr43864.c at

   hprofStartupp (charD.1 * outputFileNameD.2600, charD.1 * ctxD.2601)
   {
     struct FILED.1638 * fpD.2605;
     charD.1 fileNameD.2604[1000];
     intD.0 D.3915;
     const charD.1 * restrict outputFileName.0D.3914;

     # BLOCK 2 freq:10000
     # PRED: ENTRY [100.0%]  (fallthru,exec)
     # PT = nonlocal { D.3926 } (restr)
     outputFileName.0D.3914_3
       = (const charD.1 * restrict) outputFileNameD.2600_2(D);
     # .MEMD.3923_13 = VDEF <.MEMD.3923_12(D)>
     # USE = nonlocal null { fileNameD.2604 D.3926 } (restr)
     # CLB = nonlocal null { fileNameD.2604 D.3926 } (restr)
     sprintfD.759 (&fileNameD.2604, outputFileName.0D.3914_3);
     # .MEMD.3923_14 = VDEF <.MEMD.3923_13>
     # USE = nonlocal null { fileNameD.2604 D.3926 } (restr)
     # CLB = nonlocal null { fileNameD.2604 D.3926 } (restr)
     D.3915_4 = accessD.2606 (&fileNameD.2604, 1);
     if (D.3915_4 == 0)
       goto <bb 3>;
     else
       goto <bb 4>;
     # SUCC: 3 [10.0%]  (true,exec) 4 [90.0%]  (false,exec)

     # BLOCK 3 freq:1000
     # PRED: 2 [10.0%]  (true,exec)
     # .MEMD.3923_15 = VDEF <.MEMD.3923_14>
     # USE = nonlocal null { fileNameD.2604 D.3926 } (restr)
     # CLB = nonlocal null { fileNameD.2604 D.3926 } (restr)
     freeD.898 (ctxD.2601_5(D));
     goto <bb 7>;
     # SUCC: 7 [100.0%]  (fallthru,exec)

     # BLOCK 4 freq:9000
     # PRED: 2 [90.0%]  (false,exec)
     # .MEMD.3923_16 = VDEF <.MEMD.3923_14>
     # PT = nonlocal escaped
     # USE = nonlocal null { fileNameD.2604 D.3926 } (restr)
     # CLB = nonlocal null { fileNameD.2604 D.3926 } (restr)
     fpD.2605_8 = fopenD.1805 (&fileNameD.2604[0], 0B);
     if (fpD.2605_8 == 0B)
       goto <bb 5>;
     else
       goto <bb 6>;
     # SUCC: 5 [1.9%]  (true,exec) 6 [98.1%]  (false,exec)

     # BLOCK 5 freq:173
     # PRED: 4 [1.9%]  (true,exec)
     # .MEMD.3923_17 = VDEF <.MEMD.3923_16>
     # USE = nonlocal null { fileNameD.2604 D.3926 } (restr)
     # CLB = nonlocal null { fileNameD.2604 D.3926 } (restr)
     freeD.898 (ctxD.2601_5(D));
     goto <bb 7>;
     # SUCC: 7 [100.0%]  (fallthru,exec)

     # BLOCK 6 freq:8827
     # PRED: 4 [98.1%]  (false,exec)
     # .MEMD.3923_18 = VDEF <.MEMD.3923_16>
     # USE = nonlocal null { fileNameD.2604 D.3926 } (restr)
     # CLB = nonlocal null { fileNameD.2604 D.3926 } (restr)
     fooD.2599 (outputFileNameD.2600_2(D), fpD.2605_8);
     # SUCC: 7 [100.0%]  (fallthru,exec)

     # BLOCK 7 freq:10000
     # PRED: 3 [100.0%]  (fallthru,exec) 5 [100.0%]  (fallthru,exec)
             6 [100.0%]  (fallthru,exec)
     # PT = nonlocal null

     # ctxD.2601_1 = PHI <0B(3), 0B(5), ctxD.2601_5(D)(6)>
     # .MEMD.3923_11 = PHI <.MEMD.3923_15(3), .MEMD.3923_17(5),
                            .MEMD.3923_18(6)>
     # VUSE <.MEMD.3923_11>
     return ctxD.2601_1;
     # SUCC: EXIT [100.0%]
   }

   bb 3 and bb 5 can be merged.  The blocks have different predecessors, but the
   same successors, and the same operations.


   CONTEXT

   A technique called tail merging (or cross jumping) can fix the example
   above.  For a block, we look for common code at the end (the tail) of the
   predecessor blocks, and insert jumps from one block to the other.
   The example is a special case for tail merging, in that 2 whole blocks
   can be merged, rather than just the end parts of it.
   We currently only focus on whole block merging, so in that sense
   calling this pass tail merge is a bit of a misnomer.

   We distinguish 2 kinds of situations in which blocks can be merged:
   - same operations, same predecessors.  The successor edges coming from one
     block are redirected to come from the other block.
   - same operations, same successors.  The predecessor edges entering one block
     are redirected to enter the other block.  Note that this operation might
     involve introducing phi operations.

   For efficient implementation, we would like to value numbers the blocks, and
   have a comparison operator that tells us whether the blocks are equal.
   Besides being runtime efficient, block value numbering should also abstract
   from irrelevant differences in order of operations, much like normal value
   numbering abstracts from irrelevant order of operations.

   For the first situation (same_operations, same predecessors), normal value
   numbering fits well.  We can calculate a block value number based on the
   value numbers of the defs and vdefs.

   For the second situation (same operations, same successors), this approach
   doesn't work so well.  We can illustrate this using the example.  The calls
   to free use different vdefs: MEMD.3923_16 and MEMD.3923_14, and these will
   remain different in value numbering, since they represent different memory
   states.  So the resulting vdefs of the frees will be different in value
   numbering, so the block value numbers will be different.

   The reason why we call the blocks equal is not because they define the same
   values, but because uses in the blocks use (possibly different) defs in the
   same way.  To be able to detect this efficiently, we need to do some kind of
   reverse value numbering, meaning number the uses rather than the defs, and
   calculate a block value number based on the value number of the uses.
   Ideally, a block comparison operator will also indicate which phis are needed
   to merge the blocks.

   For the moment, we don't do block value numbering, but we do insn-by-insn
   matching, using scc value numbers to match operations with results, and
   structural comparison otherwise, while ignoring vop mismatches.


   IMPLEMENTATION

   1. The pass first determines all groups of blocks with the same successor
      blocks.
   2. Within each group, it tries to determine clusters of equal basic blocks.
   3. The clusters are applied.
   4. The same successor groups are updated.
   5. This process is repeated from 2 onwards, until no more changes.


   LIMITATIONS/TODO

   - block only
   - handles only 'same operations, same successors'.
     It handles same predecessors as a special subcase though.
   - does not implement the reverse value numbering and block value numbering.
   - improve memory allocation: use garbage collected memory, obstacks,
     allocpools where appropriate.
   - no insertion of gimple_reg phis,  We only introduce vop-phis.
   - handle blocks with gimple_reg phi_nodes.


   PASS PLACEMENT
   This 'pass' is not a stand-alone gimple pass, but runs as part of
   pass_pre, in order to share the value numbering.


   SWITCHES

   - ftree-tail-merge.  On at -O2.  We may have to enable it only at -Os.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "stor-layout.h"
#include "trans-mem.h"
#include "tm_p.h"
#include "basic-block.h"
#include "flags.h"
#include "function.h"
#include "hash-table.h"
#include "tree-ssa-alias.h"
#include "internal-fn.h"
#include "tree-eh.h"
#include "gimple-expr.h"
#include "is-a.h"
#include "gimple.h"
#include "gimple-iterator.h"
#include "gimple-ssa.h"
#include "tree-cfg.h"
#include "tree-phinodes.h"
#include "ssa-iterators.h"
#include "tree-into-ssa.h"
#include "params.h"
#include "gimple-pretty-print.h"
#include "tree-ssa-sccvn.h"
#include "tree-dump.h"
#include "cfgloop.h"
#include "tree-pass.h"
#include "trans-mem.h"

/* Describes a group of bbs with the same successors.  The successor bbs are
   cached in succs, and the successor edge flags are cached in succ_flags.
   If a bb has the EDGE_TRUE/VALSE_VALUE flags swapped compared to succ_flags,
   it's marked in inverse.
   Additionally, the hash value for the struct is cached in hashval, and
   in_worklist indicates whether it's currently part of worklist.  */

struct same_succ_def
{
  /* The bbs that have the same successor bbs.  */
  bitmap bbs;
  /* The successor bbs.  */
  bitmap succs;
  /* Indicates whether the EDGE_TRUE/FALSE_VALUEs of succ_flags are swapped for
     bb.  */
  bitmap inverse;
  /* The edge flags for each of the successor bbs.  */
  vec<int> succ_flags;
  /* Indicates whether the struct is currently in the worklist.  */
  bool in_worklist;
  /* The hash value of the struct.  */
  hashval_t hashval;

  /* hash_table support.  */
  typedef same_succ_def value_type;
  typedef same_succ_def compare_type;
  static inline hashval_t hash (const value_type *);
  static int equal (const value_type *, const compare_type *);
  static void remove (value_type *);
};
typedef struct same_succ_def *same_succ;
typedef const struct same_succ_def *const_same_succ;

/* hash routine for hash_table support, returns hashval of E.  */

inline hashval_t
same_succ_def::hash (const value_type *e)
{
  return e->hashval;
}

/* A group of bbs where 1 bb from bbs can replace the other bbs.  */

struct bb_cluster_def
{
  /* The bbs in the cluster.  */
  bitmap bbs;
  /* The preds of the bbs in the cluster.  */
  bitmap preds;
  /* Index in all_clusters vector.  */
  int index;
  /* The bb to replace the cluster with.  */
  basic_block rep_bb;
};
typedef struct bb_cluster_def *bb_cluster;
typedef const struct bb_cluster_def *const_bb_cluster;

/* Per bb-info.  */

struct aux_bb_info
{
  /* The number of non-debug statements in the bb.  */
  int size;
  /* The same_succ that this bb is a member of.  */
  same_succ bb_same_succ;
  /* The cluster that this bb is a member of.  */
  bb_cluster cluster;
  /* The vop state at the exit of a bb.  This is shortlived data, used to
     communicate data between update_block_by and update_vuses.  */
  tree vop_at_exit;
  /* The bb that either contains or is dominated by the dependencies of the
     bb.  */
  basic_block dep_bb;
};

/* Macros to access the fields of struct aux_bb_info.  */

#define BB_SIZE(bb) (((struct aux_bb_info *)bb->aux)->size)
#define BB_SAME_SUCC(bb) (((struct aux_bb_info *)bb->aux)->bb_same_succ)
#define BB_CLUSTER(bb) (((struct aux_bb_info *)bb->aux)->cluster)
#define BB_VOP_AT_EXIT(bb) (((struct aux_bb_info *)bb->aux)->vop_at_exit)
#define BB_DEP_BB(bb) (((struct aux_bb_info *)bb->aux)->dep_bb)

/* Returns true if the only effect a statement STMT has, is to define locally
   used SSA_NAMEs.  */

static bool
stmt_local_def (gimple stmt)
{
  basic_block bb, def_bb;
  imm_use_iterator iter;
  use_operand_p use_p;
  tree val;
  def_operand_p def_p;

  if (gimple_vdef (stmt) != NULL_TREE
      || gimple_has_side_effects (stmt)
      || gimple_could_trap_p_1 (stmt, false, false)
      || gimple_vuse (stmt) != NULL_TREE)
    return false;

  def_p = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_DEF);
  if (def_p == NULL)
    return false;

  val = DEF_FROM_PTR (def_p);
  if (val == NULL_TREE || TREE_CODE (val) != SSA_NAME)
    return false;

  def_bb = gimple_bb (stmt);

  FOR_EACH_IMM_USE_FAST (use_p, iter, val)
    {
      if (is_gimple_debug (USE_STMT (use_p)))
	continue;
      bb = gimple_bb (USE_STMT (use_p));
      if (bb == def_bb)
	continue;

      if (gimple_code (USE_STMT (use_p)) == GIMPLE_PHI
	  && EDGE_PRED (bb, PHI_ARG_INDEX_FROM_USE (use_p))->src == def_bb)
	continue;

      return false;
    }

  return true;
}

/* Let GSI skip forwards over local defs.  */

static void
gsi_advance_fw_nondebug_nonlocal (gimple_stmt_iterator *gsi)
{
  gimple stmt;

  while (true)
    {
      if (gsi_end_p (*gsi))
	return;
      stmt = gsi_stmt (*gsi);
      if (!stmt_local_def (stmt))
	return;
	gsi_next_nondebug (gsi);
    }
}

/* VAL1 and VAL2 are either:
   - uses in BB1 and BB2, or
   - phi alternatives for BB1 and BB2.
   Return true if the uses have the same gvn value.  */

static bool
gvn_uses_equal (tree val1, tree val2)
{
  gcc_checking_assert (val1 != NULL_TREE && val2 != NULL_TREE);

  if (val1 == val2)
    return true;

  if (vn_valueize (val1) != vn_valueize (val2))
    return false;

  return ((TREE_CODE (val1) == SSA_NAME || CONSTANT_CLASS_P (val1))
	  && (TREE_CODE (val2) == SSA_NAME || CONSTANT_CLASS_P (val2)));
}

/* Prints E to FILE.  */

static void
same_succ_print (FILE *file, const same_succ e)
{
  unsigned int i;
  bitmap_print (file, e->bbs, "bbs:", "\n");
  bitmap_print (file, e->succs, "succs:", "\n");
  bitmap_print (file, e->inverse, "inverse:", "\n");
  fprintf (file, "flags:");
  for (i = 0; i < e->succ_flags.length (); ++i)
    fprintf (file, " %x", e->succ_flags[i]);
  fprintf (file, "\n");
}

/* Prints same_succ VE to VFILE.  */

inline int
ssa_same_succ_print_traverse (same_succ *pe, FILE *file)
{
  const same_succ e = *pe;
  same_succ_print (file, e);
  return 1;
}

/* Update BB_DEP_BB (USE_BB), given a use of VAL in USE_BB.  */

static void
update_dep_bb (basic_block use_bb, tree val)
{
  basic_block dep_bb;

  /* Not a dep.  */
  if (TREE_CODE (val) != SSA_NAME)
    return;

  /* Skip use of global def.  */
  if (SSA_NAME_IS_DEFAULT_DEF (val))
    return;

  /* Skip use of local def.  */
  dep_bb = gimple_bb (SSA_NAME_DEF_STMT (val));
  if (dep_bb == use_bb)
    return;

  if (BB_DEP_BB (use_bb) == NULL
      || dominated_by_p (CDI_DOMINATORS, dep_bb, BB_DEP_BB (use_bb)))
    BB_DEP_BB (use_bb) = dep_bb;
}

/* Update BB_DEP_BB, given the dependencies in STMT.  */

static void
stmt_update_dep_bb (gimple stmt)
{
  ssa_op_iter iter;
  use_operand_p use;

  FOR_EACH_SSA_USE_OPERAND (use, stmt, iter, SSA_OP_USE)
    update_dep_bb (gimple_bb (stmt), USE_FROM_PTR (use));
}

/* Calculates hash value for same_succ VE.  */

static hashval_t
same_succ_hash (const_same_succ e)
{
  hashval_t hashval = bitmap_hash (e->succs);
  int flags;
  unsigned int i;
  unsigned int first = bitmap_first_set_bit (e->bbs);
  basic_block bb = BASIC_BLOCK_FOR_FN (cfun, first);
  int size = 0;
  gimple_stmt_iterator gsi;
  gimple stmt;
  tree arg;
  unsigned int s;
  bitmap_iterator bs;

  for (gsi = gsi_start_nondebug_bb (bb);
       !gsi_end_p (gsi); gsi_next_nondebug (&gsi))
    {
      stmt = gsi_stmt (gsi);
      stmt_update_dep_bb (stmt);
      if (stmt_local_def (stmt))
	continue;
      size++;

      hashval = iterative_hash_hashval_t (gimple_code (stmt), hashval);
      if (is_gimple_assign (stmt))
	hashval = iterative_hash_hashval_t (gimple_assign_rhs_code (stmt),
					    hashval);
      if (!is_gimple_call (stmt))
	continue;
      if (gimple_call_internal_p (stmt))
	hashval = iterative_hash_hashval_t
	  ((hashval_t) gimple_call_internal_fn (stmt), hashval);
      else
	{
	  hashval = iterative_hash_expr (gimple_call_fn (stmt), hashval);
	  if (gimple_call_chain (stmt))
	    hashval = iterative_hash_expr (gimple_call_chain (stmt), hashval);
	}
      for (i = 0; i < gimple_call_num_args (stmt); i++)
	{
	  arg = gimple_call_arg (stmt, i);
	  arg = vn_valueize (arg);
	  hashval = iterative_hash_expr (arg, hashval);
	}
    }

  hashval = iterative_hash_hashval_t (size, hashval);
  BB_SIZE (bb) = size;

  for (i = 0; i < e->succ_flags.length (); ++i)
    {
      flags = e->succ_flags[i];
      flags = flags & ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
      hashval = iterative_hash_hashval_t (flags, hashval);
    }

  EXECUTE_IF_SET_IN_BITMAP (e->succs, 0, s, bs)
    {
      int n = find_edge (bb, BASIC_BLOCK_FOR_FN (cfun, s))->dest_idx;
      for (gsi = gsi_start_phis (BASIC_BLOCK_FOR_FN (cfun, s)); !gsi_end_p (gsi);
	   gsi_next (&gsi))
	{
	  gimple phi = gsi_stmt (gsi);
	  tree lhs = gimple_phi_result (phi);
	  tree val = gimple_phi_arg_def (phi, n);

	  if (virtual_operand_p (lhs))
	    continue;
	  update_dep_bb (bb, val);
	}
    }

  return hashval;
}

/* Returns true if E1 and E2 have 2 successors, and if the successor flags
   are inverse for the EDGE_TRUE_VALUE and EDGE_FALSE_VALUE flags, and equal for
   the other edge flags.  */

static bool
inverse_flags (const_same_succ e1, const_same_succ e2)
{
  int f1a, f1b, f2a, f2b;
  int mask = ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);

  if (e1->succ_flags.length () != 2)
    return false;

  f1a = e1->succ_flags[0];
  f1b = e1->succ_flags[1];
  f2a = e2->succ_flags[0];
  f2b = e2->succ_flags[1];

  if (f1a == f2a && f1b == f2b)
    return false;

  return (f1a & mask) == (f2a & mask) && (f1b & mask) == (f2b & mask);
}

/* Compares SAME_SUCCs E1 and E2.  */

int
same_succ_def::equal (const value_type *e1, const compare_type *e2)
{
  unsigned int i, first1, first2;
  gimple_stmt_iterator gsi1, gsi2;
  gimple s1, s2;
  basic_block bb1, bb2;

  if (e1->hashval != e2->hashval)
    return 0;

  if (e1->succ_flags.length () != e2->succ_flags.length ())
    return 0;

  if (!bitmap_equal_p (e1->succs, e2->succs))
    return 0;

  if (!inverse_flags (e1, e2))
    {
      for (i = 0; i < e1->succ_flags.length (); ++i)
	if (e1->succ_flags[i] != e1->succ_flags[i])
	  return 0;
    }

  first1 = bitmap_first_set_bit (e1->bbs);
  first2 = bitmap_first_set_bit (e2->bbs);

  bb1 = BASIC_BLOCK_FOR_FN (cfun, first1);
  bb2 = BASIC_BLOCK_FOR_FN (cfun, first2);

  if (BB_SIZE (bb1) != BB_SIZE (bb2))
    return 0;

  gsi1 = gsi_start_nondebug_bb (bb1);
  gsi2 = gsi_start_nondebug_bb (bb2);
  gsi_advance_fw_nondebug_nonlocal (&gsi1);
  gsi_advance_fw_nondebug_nonlocal (&gsi2);
  while (!(gsi_end_p (gsi1) || gsi_end_p (gsi2)))
    {
      s1 = gsi_stmt (gsi1);
      s2 = gsi_stmt (gsi2);
      if (gimple_code (s1) != gimple_code (s2))
	return 0;
      if (is_gimple_call (s1) && !gimple_call_same_target_p (s1, s2))
	return 0;
      gsi_next_nondebug (&gsi1);
      gsi_next_nondebug (&gsi2);
      gsi_advance_fw_nondebug_nonlocal (&gsi1);
      gsi_advance_fw_nondebug_nonlocal (&gsi2);
    }

  return 1;
}

/* Alloc and init a new SAME_SUCC.  */

static same_succ
same_succ_alloc (void)
{
  same_succ same = XNEW (struct same_succ_def);

  same->bbs = BITMAP_ALLOC (NULL);
  same->succs = BITMAP_ALLOC (NULL);
  same->inverse = BITMAP_ALLOC (NULL);
  same->succ_flags.create (10);
  same->in_worklist = false;

  return same;
}

/* Delete same_succ E.  */

void
same_succ_def::remove (same_succ e)
{
  BITMAP_FREE (e->bbs);
  BITMAP_FREE (e->succs);
  BITMAP_FREE (e->inverse);
  e->succ_flags.release ();

  XDELETE (e);
}

/* Reset same_succ SAME.  */

static void
same_succ_reset (same_succ same)
{
  bitmap_clear (same->bbs);
  bitmap_clear (same->succs);
  bitmap_clear (same->inverse);
  same->succ_flags.truncate (0);
}

static hash_table <same_succ_def> same_succ_htab;

/* Array that is used to store the edge flags for a successor.  */

static int *same_succ_edge_flags;

/* Bitmap that is used to mark bbs that are recently deleted.  */

static bitmap deleted_bbs;

/* Bitmap that is used to mark predecessors of bbs that are
   deleted.  */

static bitmap deleted_bb_preds;

/* Prints same_succ_htab to stderr.  */

extern void debug_same_succ (void);
DEBUG_FUNCTION void
debug_same_succ ( void)
{
  same_succ_htab.traverse <FILE *, ssa_same_succ_print_traverse> (stderr);
}


/* Vector of bbs to process.  */

static vec<same_succ> worklist;

/* Prints worklist to FILE.  */

static void
print_worklist (FILE *file)
{
  unsigned int i;
  for (i = 0; i < worklist.length (); ++i)
    same_succ_print (file, worklist[i]);
}

/* Adds SAME to worklist.  */

static void
add_to_worklist (same_succ same)
{
  if (same->in_worklist)
    return;

  if (bitmap_count_bits (same->bbs) < 2)
    return;

  same->in_worklist = true;
  worklist.safe_push (same);
}

/* Add BB to same_succ_htab.  */

static void
find_same_succ_bb (basic_block bb, same_succ *same_p)
{
  unsigned int j;
  bitmap_iterator bj;
  same_succ same = *same_p;
  same_succ *slot;
  edge_iterator ei;
  edge e;

  if (bb == NULL
      /* Be conservative with loop structure.  It's not evident that this test
	 is sufficient.  Before tail-merge, we've just called
	 loop_optimizer_finalize, and LOOPS_MAY_HAVE_MULTIPLE_LATCHES is now
	 set, so there's no guarantee that the loop->latch value is still valid.
	 But we assume that, since we've forced LOOPS_HAVE_SIMPLE_LATCHES at the
	 start of pre, we've kept that property intact throughout pre, and are
	 keeping it throughout tail-merge using this test.  */
      || bb->loop_father->latch == bb)
    return;
  bitmap_set_bit (same->bbs, bb->index);
  FOR_EACH_EDGE (e, ei, bb->succs)
    {
      int index = e->dest->index;
      bitmap_set_bit (same->succs, index);
      same_succ_edge_flags[index] = e->flags;
    }
  EXECUTE_IF_SET_IN_BITMAP (same->succs, 0, j, bj)
    same->succ_flags.safe_push (same_succ_edge_flags[j]);

  same->hashval = same_succ_hash (same);

  slot = same_succ_htab.find_slot_with_hash (same, same->hashval, INSERT);
  if (*slot == NULL)
    {
      *slot = same;
      BB_SAME_SUCC (bb) = same;
      add_to_worklist (same);
      *same_p = NULL;
    }
  else
    {
      bitmap_set_bit ((*slot)->bbs, bb->index);
      BB_SAME_SUCC (bb) = *slot;
      add_to_worklist (*slot);
      if (inverse_flags (same, *slot))
	bitmap_set_bit ((*slot)->inverse, bb->index);
      same_succ_reset (same);
    }
}

/* Find bbs with same successors.  */

static void
find_same_succ (void)
{
  same_succ same = same_succ_alloc ();
  basic_block bb;

  FOR_EACH_BB_FN (bb, cfun)
    {
      find_same_succ_bb (bb, &same);
      if (same == NULL)
	same = same_succ_alloc ();
    }

  same_succ_def::remove (same);
}

/* Initializes worklist administration.  */

static void
init_worklist (void)
{
  alloc_aux_for_blocks (sizeof (struct aux_bb_info));
  same_succ_htab.create (n_basic_blocks_for_fn (cfun));
  same_succ_edge_flags = XCNEWVEC (int, last_basic_block_for_fn (cfun));
  deleted_bbs = BITMAP_ALLOC (NULL);
  deleted_bb_preds = BITMAP_ALLOC (NULL);
  worklist.create (n_basic_blocks_for_fn (cfun));
  find_same_succ ();

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "initial worklist:\n");
      print_worklist (dump_file);
    }
}

/* Deletes worklist administration.  */

static void
delete_worklist (void)
{
  free_aux_for_blocks ();
  same_succ_htab.dispose ();
  XDELETEVEC (same_succ_edge_flags);
  same_succ_edge_flags = NULL;
  BITMAP_FREE (deleted_bbs);
  BITMAP_FREE (deleted_bb_preds);
  worklist.release ();
}

/* Mark BB as deleted, and mark its predecessors.  */

static void
mark_basic_block_deleted (basic_block bb)
{
  edge e;
  edge_iterator ei;

  bitmap_set_bit (deleted_bbs, bb->index);

  FOR_EACH_EDGE (e, ei, bb->preds)
    bitmap_set_bit (deleted_bb_preds, e->src->index);
}

/* Removes BB from its corresponding same_succ.  */

static void
same_succ_flush_bb (basic_block bb)
{
  same_succ same = BB_SAME_SUCC (bb);
  BB_SAME_SUCC (bb) = NULL;
  if (bitmap_single_bit_set_p (same->bbs))
    same_succ_htab.remove_elt_with_hash (same, same->hashval);
  else
    bitmap_clear_bit (same->bbs, bb->index);
}

/* Removes all bbs in BBS from their corresponding same_succ.  */

static void
same_succ_flush_bbs (bitmap bbs)
{
  unsigned int i;
  bitmap_iterator bi;

  EXECUTE_IF_SET_IN_BITMAP (bbs, 0, i, bi)
    same_succ_flush_bb (BASIC_BLOCK_FOR_FN (cfun, i));
}

/* Release the last vdef in BB, either normal or phi result.  */

static void
release_last_vdef (basic_block bb)
{
  gimple_stmt_iterator i;

  for (i = gsi_last_bb (bb); !gsi_end_p (i); gsi_prev_nondebug (&i))
    {
      gimple stmt = gsi_stmt (i);
      if (gimple_vdef (stmt) == NULL_TREE)
	continue;

      mark_virtual_operand_for_renaming (gimple_vdef (stmt));
      return;
    }

  for (i = gsi_start_phis (bb); !gsi_end_p (i); gsi_next (&i))
    {
      gimple phi = gsi_stmt (i);
      tree res = gimple_phi_result (phi);

      if (!virtual_operand_p (res))
	continue;

      mark_virtual_phi_result_for_renaming (phi);
      return;
    }
  
}

/* For deleted_bb_preds, find bbs with same successors.  */

static void
update_worklist (void)
{
  unsigned int i;
  bitmap_iterator bi;
  basic_block bb;
  same_succ same;

  bitmap_and_compl_into (deleted_bb_preds, deleted_bbs);
  bitmap_clear (deleted_bbs);

  bitmap_clear_bit (deleted_bb_preds, ENTRY_BLOCK);
  same_succ_flush_bbs (deleted_bb_preds);

  same = same_succ_alloc ();
  EXECUTE_IF_SET_IN_BITMAP (deleted_bb_preds, 0, i, bi)
    {
      bb = BASIC_BLOCK_FOR_FN (cfun, i);
      gcc_assert (bb != NULL);
      find_same_succ_bb (bb, &same);
      if (same == NULL)
	same = same_succ_alloc ();
    }
  same_succ_def::remove (same);
  bitmap_clear (deleted_bb_preds);
}

/* Prints cluster C to FILE.  */

static void
print_cluster (FILE *file, bb_cluster c)
{
  if (c == NULL)
    return;
  bitmap_print (file, c->bbs, "bbs:", "\n");
  bitmap_print (file, c->preds, "preds:", "\n");
}

/* Prints cluster C to stderr.  */

extern void debug_cluster (bb_cluster);
DEBUG_FUNCTION void
debug_cluster (bb_cluster c)
{
  print_cluster (stderr, c);
}

/* Update C->rep_bb, given that BB is added to the cluster.  */

static void
update_rep_bb (bb_cluster c, basic_block bb)
{
  /* Initial.  */
  if (c->rep_bb == NULL)
    {
      c->rep_bb = bb;
      return;
    }

  /* Current needs no deps, keep it.  */
  if (BB_DEP_BB (c->rep_bb) == NULL)
    return;

  /* Bb needs no deps, change rep_bb.  */
  if (BB_DEP_BB (bb) == NULL)
    {
      c->rep_bb = bb;
      return;
    }

  /* Bb needs last deps earlier than current, change rep_bb.  A potential
     problem with this, is that the first deps might also be earlier, which
     would mean we prefer longer lifetimes for the deps.  To be able to check
     for this, we would have to trace BB_FIRST_DEP_BB as well, besides
     BB_DEP_BB, which is really BB_LAST_DEP_BB.
     The benefit of choosing the bb with last deps earlier, is that it can
     potentially be used as replacement for more bbs.  */
  if (dominated_by_p (CDI_DOMINATORS, BB_DEP_BB (c->rep_bb), BB_DEP_BB (bb)))
    c->rep_bb = bb;
}

/* Add BB to cluster C.  Sets BB in C->bbs, and preds of BB in C->preds.  */

static void
add_bb_to_cluster (bb_cluster c, basic_block bb)
{
  edge e;
  edge_iterator ei;

  bitmap_set_bit (c->bbs, bb->index);

  FOR_EACH_EDGE (e, ei, bb->preds)
    bitmap_set_bit (c->preds, e->src->index);

  update_rep_bb (c, bb);
}

/* Allocate and init new cluster.  */

static bb_cluster
new_cluster (void)
{
  bb_cluster c;
  c = XCNEW (struct bb_cluster_def);
  c->bbs = BITMAP_ALLOC (NULL);
  c->preds = BITMAP_ALLOC (NULL);
  c->rep_bb = NULL;
  return c;
}

/* Delete clusters.  */

static void
delete_cluster (bb_cluster c)
{
  if (c == NULL)
    return;
  BITMAP_FREE (c->bbs);
  BITMAP_FREE (c->preds);
  XDELETE (c);
}


/* Array that contains all clusters.  */

static vec<bb_cluster> all_clusters;

/* Allocate all cluster vectors.  */

static void
alloc_cluster_vectors (void)
{
  all_clusters.create (n_basic_blocks_for_fn (cfun));
}

/* Reset all cluster vectors.  */

static void
reset_cluster_vectors (void)
{
  unsigned int i;
  basic_block bb;
  for (i = 0; i < all_clusters.length (); ++i)
    delete_cluster (all_clusters[i]);
  all_clusters.truncate (0);
  FOR_EACH_BB_FN (bb, cfun)
    BB_CLUSTER (bb) = NULL;
}

/* Delete all cluster vectors.  */

static void
delete_cluster_vectors (void)
{
  unsigned int i;
  for (i = 0; i < all_clusters.length (); ++i)
    delete_cluster (all_clusters[i]);
  all_clusters.release ();
}

/* Merge cluster C2 into C1.  */

static void
merge_clusters (bb_cluster c1, bb_cluster c2)
{
  bitmap_ior_into (c1->bbs, c2->bbs);
  bitmap_ior_into (c1->preds, c2->preds);
}

/* Register equivalence of BB1 and BB2 (members of cluster C).  Store c in
   all_clusters, or merge c with existing cluster.  */

static void
set_cluster (basic_block bb1, basic_block bb2)
{
  basic_block merge_bb, other_bb;
  bb_cluster merge, old, c;

  if (BB_CLUSTER (bb1) == NULL && BB_CLUSTER (bb2) == NULL)
    {
      c = new_cluster ();
      add_bb_to_cluster (c, bb1);
      add_bb_to_cluster (c, bb2);
      BB_CLUSTER (bb1) = c;
      BB_CLUSTER (bb2) = c;
      c->index = all_clusters.length ();
      all_clusters.safe_push (c);
    }
  else if (BB_CLUSTER (bb1) == NULL || BB_CLUSTER (bb2) == NULL)
    {
      merge_bb = BB_CLUSTER (bb1) == NULL ? bb2 : bb1;
      other_bb = BB_CLUSTER (bb1) == NULL ? bb1 : bb2;
      merge = BB_CLUSTER (merge_bb);
      add_bb_to_cluster (merge, other_bb);
      BB_CLUSTER (other_bb) = merge;
    }
  else if (BB_CLUSTER (bb1) != BB_CLUSTER (bb2))
    {
      unsigned int i;
      bitmap_iterator bi;

      old = BB_CLUSTER (bb2);
      merge = BB_CLUSTER (bb1);
      merge_clusters (merge, old);
      EXECUTE_IF_SET_IN_BITMAP (old->bbs, 0, i, bi)
	BB_CLUSTER (BASIC_BLOCK_FOR_FN (cfun, i)) = merge;
      all_clusters[old->index] = NULL;
      update_rep_bb (merge, old->rep_bb);
      delete_cluster (old);
    }
  else
    gcc_unreachable ();
}

/* Return true if gimple operands T1 and T2 have the same value.  */

static bool
gimple_operand_equal_value_p (tree t1, tree t2)
{
  if (t1 == t2)
    return true;

  if (t1 == NULL_TREE
      || t2 == NULL_TREE)
    return false;

  if (operand_equal_p (t1, t2, 0))
    return true;

  return gvn_uses_equal (t1, t2);
}

/* Return true if gimple statements S1 and S2 are equal.  Gimple_bb (s1) and
   gimple_bb (s2) are members of SAME_SUCC.  */

static bool
gimple_equal_p (same_succ same_succ, gimple s1, gimple s2)
{
  unsigned int i;
  tree lhs1, lhs2;
  basic_block bb1 = gimple_bb (s1), bb2 = gimple_bb (s2);
  tree t1, t2;
  bool inv_cond;
  enum tree_code code1, code2;

  if (gimple_code (s1) != gimple_code (s2))
    return false;

  switch (gimple_code (s1))
    {
    case GIMPLE_CALL:
      if (!gimple_call_same_target_p (s1, s2))
        return false;

      t1 = gimple_call_chain (s1);
      t2 = gimple_call_chain (s2);
      if (!gimple_operand_equal_value_p (t1, t2))
	return false;

      if (gimple_call_num_args (s1) != gimple_call_num_args (s2))
	return false;

      for (i = 0; i < gimple_call_num_args (s1); ++i)
	{
	  t1 = gimple_call_arg (s1, i);
	  t2 = gimple_call_arg (s2, i);
	  if (!gimple_operand_equal_value_p (t1, t2))
	    return false;
	}

      lhs1 = gimple_get_lhs (s1);
      lhs2 = gimple_get_lhs (s2);
      if (lhs1 == NULL_TREE && lhs2 == NULL_TREE)
	return true;
      if (lhs1 == NULL_TREE || lhs2 == NULL_TREE)
	return false;
      if (TREE_CODE (lhs1) == SSA_NAME && TREE_CODE (lhs2) == SSA_NAME)
	return vn_valueize (lhs1) == vn_valueize (lhs2);
      return operand_equal_p (lhs1, lhs2, 0);

    case GIMPLE_ASSIGN:
      lhs1 = gimple_get_lhs (s1);
      lhs2 = gimple_get_lhs (s2);
      if (TREE_CODE (lhs1) != SSA_NAME
	  && TREE_CODE (lhs2) != SSA_NAME)
	return (operand_equal_p (lhs1, lhs2, 0)
		&& gimple_operand_equal_value_p (gimple_assign_rhs1 (s1),
						 gimple_assign_rhs1 (s2)));
      else if (TREE_CODE (lhs1) == SSA_NAME
	       && TREE_CODE (lhs2) == SSA_NAME)
	return operand_equal_p (gimple_assign_rhs1 (s1),
				gimple_assign_rhs1 (s2), 0);
      return false;

    case GIMPLE_COND:
      t1 = gimple_cond_lhs (s1);
      t2 = gimple_cond_lhs (s2);
      if (!gimple_operand_equal_value_p (t1, t2))
	return false;

      t1 = gimple_cond_rhs (s1);
      t2 = gimple_cond_rhs (s2);
      if (!gimple_operand_equal_value_p (t1, t2))
	return false;

      code1 = gimple_expr_code (s1);
      code2 = gimple_expr_code (s2);
      inv_cond = (bitmap_bit_p (same_succ->inverse, bb1->index)
		  != bitmap_bit_p (same_succ->inverse, bb2->index));
      if (inv_cond)
	{
	  bool honor_nans
	    = HONOR_NANS (TYPE_MODE (TREE_TYPE (gimple_cond_lhs (s1))));
	  code2 = invert_tree_comparison (code2, honor_nans);
	}
      return code1 == code2;

    default:
      return false;
    }
}

/* Let GSI skip backwards over local defs.  Return the earliest vuse in VUSE.
   Return true in VUSE_ESCAPED if the vuse influenced a SSA_OP_DEF of one of the
   processed statements.  */

static void
gsi_advance_bw_nondebug_nonlocal (gimple_stmt_iterator *gsi, tree *vuse,
				  bool *vuse_escaped)
{
  gimple stmt;
  tree lvuse;

  while (true)
    {
      if (gsi_end_p (*gsi))
	return;
      stmt = gsi_stmt (*gsi);

      lvuse = gimple_vuse (stmt);
      if (lvuse != NULL_TREE)
	{
	  *vuse = lvuse;
	  if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_DEF))
	    *vuse_escaped = true;
	}

      if (!stmt_local_def (stmt))
	return;
      gsi_prev_nondebug (gsi);
    }
}

/* Determines whether BB1 and BB2 (members of same_succ) are duplicates.  If so,
   clusters them.  */

static void
find_duplicate (same_succ same_succ, basic_block bb1, basic_block bb2)
{
  gimple_stmt_iterator gsi1 = gsi_last_nondebug_bb (bb1);
  gimple_stmt_iterator gsi2 = gsi_last_nondebug_bb (bb2);
  tree vuse1 = NULL_TREE, vuse2 = NULL_TREE;
  bool vuse_escaped = false;

  gsi_advance_bw_nondebug_nonlocal (&gsi1, &vuse1, &vuse_escaped);
  gsi_advance_bw_nondebug_nonlocal (&gsi2, &vuse2, &vuse_escaped);

  while (!gsi_end_p (gsi1) && !gsi_end_p (gsi2))
    {
      gimple stmt1 = gsi_stmt (gsi1);
      gimple stmt2 = gsi_stmt (gsi2);

      /* What could be better than to this this here is to blacklist the bb
	 containing the stmt, when encountering the stmt f.i. in
	 same_succ_hash.  */
      if (is_tm_ending (stmt1)
	  || is_tm_ending (stmt2))
	return;

      if (!gimple_equal_p (same_succ, stmt1, stmt2))
	return;

      gsi_prev_nondebug (&gsi1);
      gsi_prev_nondebug (&gsi2);
      gsi_advance_bw_nondebug_nonlocal (&gsi1, &vuse1, &vuse_escaped);
      gsi_advance_bw_nondebug_nonlocal (&gsi2, &vuse2, &vuse_escaped);
    }

  if (!(gsi_end_p (gsi1) && gsi_end_p (gsi2)))
    return;

  /* If the incoming vuses are not the same, and the vuse escaped into an
     SSA_OP_DEF, then merging the 2 blocks will change the value of the def,
     which potentially means the semantics of one of the blocks will be changed.
     TODO: make this check more precise.  */
  if (vuse_escaped && vuse1 != vuse2)
    return;

  if (dump_file)
    fprintf (dump_file, "find_duplicates: <bb %d> duplicate of <bb %d>\n",
	     bb1->index, bb2->index);

  set_cluster (bb1, bb2);
}

/* Returns whether for all phis in DEST the phi alternatives for E1 and
   E2 are equal.  */

static bool
same_phi_alternatives_1 (basic_block dest, edge e1, edge e2)
{
  int n1 = e1->dest_idx, n2 = e2->dest_idx;
  gimple_stmt_iterator gsi;

  for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
    {
      gimple phi = gsi_stmt (gsi);
      tree lhs = gimple_phi_result (phi);
      tree val1 = gimple_phi_arg_def (phi, n1);
      tree val2 = gimple_phi_arg_def (phi, n2);

      if (virtual_operand_p (lhs))
	continue;

      if (operand_equal_for_phi_arg_p (val1, val2))
        continue;
      if (gvn_uses_equal (val1, val2))
	continue;

      return false;
    }

  return true;
}

/* Returns whether for all successors of BB1 and BB2 (members of SAME_SUCC), the
   phi alternatives for BB1 and BB2 are equal.  */

static bool
same_phi_alternatives (same_succ same_succ, basic_block bb1, basic_block bb2)
{
  unsigned int s;
  bitmap_iterator bs;
  edge e1, e2;
  basic_block succ;

  EXECUTE_IF_SET_IN_BITMAP (same_succ->succs, 0, s, bs)
    {
      succ = BASIC_BLOCK_FOR_FN (cfun, s);
      e1 = find_edge (bb1, succ);
      e2 = find_edge (bb2, succ);
      if (e1->flags & EDGE_COMPLEX
	  || e2->flags & EDGE_COMPLEX)
	return false;

      /* For all phis in bb, the phi alternatives for e1 and e2 need to have
	 the same value.  */
      if (!same_phi_alternatives_1 (succ, e1, e2))
	return false;
    }

  return true;
}

/* Return true if BB has non-vop phis.  */

static bool
bb_has_non_vop_phi (basic_block bb)
{
  gimple_seq phis = phi_nodes (bb);
  gimple phi;

  if (phis == NULL)
    return false;

  if (!gimple_seq_singleton_p (phis))
    return true;

  phi = gimple_seq_first_stmt (phis);
  return !virtual_operand_p (gimple_phi_result (phi));
}

/* Returns true if redirecting the incoming edges of FROM to TO maintains the
   invariant that uses in FROM are dominates by their defs.  */

static bool
deps_ok_for_redirect_from_bb_to_bb (basic_block from, basic_block to)
{
  basic_block cd, dep_bb = BB_DEP_BB (to);
  edge_iterator ei;
  edge e;
  bitmap from_preds = BITMAP_ALLOC (NULL);

  if (dep_bb == NULL)
    return true;

  FOR_EACH_EDGE (e, ei, from->preds)
    bitmap_set_bit (from_preds, e->src->index);
  cd = nearest_common_dominator_for_set (CDI_DOMINATORS, from_preds);
  BITMAP_FREE (from_preds);

  return dominated_by_p (CDI_DOMINATORS, dep_bb, cd);
}

/* Returns true if replacing BB1 (or its replacement bb) by BB2 (or its
   replacement bb) and vice versa maintains the invariant that uses in the
   replacement are dominates by their defs.  */

static bool
deps_ok_for_redirect (basic_block bb1, basic_block bb2)
{
  if (BB_CLUSTER (bb1) != NULL)
    bb1 = BB_CLUSTER (bb1)->rep_bb;

  if (BB_CLUSTER (bb2) != NULL)
    bb2 = BB_CLUSTER (bb2)->rep_bb;

  return (deps_ok_for_redirect_from_bb_to_bb (bb1, bb2)
	  && deps_ok_for_redirect_from_bb_to_bb (bb2, bb1));
}

/* Within SAME_SUCC->bbs, find clusters of bbs which can be merged.  */

static void
find_clusters_1 (same_succ same_succ)
{
  basic_block bb1, bb2;
  unsigned int i, j;
  bitmap_iterator bi, bj;
  int nr_comparisons;
  int max_comparisons = PARAM_VALUE (PARAM_MAX_TAIL_MERGE_COMPARISONS);

  EXECUTE_IF_SET_IN_BITMAP (same_succ->bbs, 0, i, bi)
    {
      bb1 = BASIC_BLOCK_FOR_FN (cfun, i);

      /* TODO: handle blocks with phi-nodes.  We'll have to find corresponding
	 phi-nodes in bb1 and bb2, with the same alternatives for the same
	 preds.  */
      if (bb_has_non_vop_phi (bb1))
	continue;

      nr_comparisons = 0;
      EXECUTE_IF_SET_IN_BITMAP (same_succ->bbs, i + 1, j, bj)
	{
	  bb2 = BASIC_BLOCK_FOR_FN (cfun, j);

	  if (bb_has_non_vop_phi (bb2))
	    continue;

	  if (BB_CLUSTER (bb1) != NULL && BB_CLUSTER (bb1) == BB_CLUSTER (bb2))
	    continue;

	  /* Limit quadratic behaviour.  */
	  nr_comparisons++;
	  if (nr_comparisons > max_comparisons)
	    break;

	  /* This is a conservative dependency check.  We could test more
	     precise for allowed replacement direction.  */
	  if (!deps_ok_for_redirect (bb1, bb2))
	    continue;

	  if (!(same_phi_alternatives (same_succ, bb1, bb2)))
	    continue;

	  find_duplicate (same_succ, bb1, bb2);
        }
    }
}

/* Find clusters of bbs which can be merged.  */

static void
find_clusters (void)
{
  same_succ same;

  while (!worklist.is_empty ())
    {
      same = worklist.pop ();
      same->in_worklist = false;
      if (dump_file && (dump_flags & TDF_DETAILS))
	{
	  fprintf (dump_file, "processing worklist entry\n");
	  same_succ_print (dump_file, same);
	}
      find_clusters_1 (same);
    }
}

/* Returns the vop phi of BB, if any.  */

static gimple
vop_phi (basic_block bb)
{
  gimple stmt;
  gimple_stmt_iterator gsi;
  for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
    {
      stmt = gsi_stmt (gsi);
      if (! virtual_operand_p (gimple_phi_result (stmt)))
	continue;
      return stmt;
    }
  return NULL;
}

/* Redirect all edges from BB1 to BB2, removes BB1 and marks it as removed.  */

static void
replace_block_by (basic_block bb1, basic_block bb2)
{
  edge pred_edge;
  edge e1, e2;
  edge_iterator ei;
  unsigned int i;
  gimple bb2_phi;

  bb2_phi = vop_phi (bb2);

  /* Mark the basic block as deleted.  */
  mark_basic_block_deleted (bb1);

  /* Redirect the incoming edges of bb1 to bb2.  */
  for (i = EDGE_COUNT (bb1->preds); i > 0 ; --i)
    {
      pred_edge = EDGE_PRED (bb1, i - 1);
      pred_edge = redirect_edge_and_branch (pred_edge, bb2);
      gcc_assert (pred_edge != NULL);

      if (bb2_phi == NULL)
	continue;

      /* The phi might have run out of capacity when the redirect added an
	 argument, which means it could have been replaced.  Refresh it.  */
      bb2_phi = vop_phi (bb2);

      add_phi_arg (bb2_phi, SSA_NAME_VAR (gimple_phi_result (bb2_phi)),
		   pred_edge, UNKNOWN_LOCATION);
    }

  bb2->frequency += bb1->frequency;
  if (bb2->frequency > BB_FREQ_MAX)
    bb2->frequency = BB_FREQ_MAX;

  bb2->count += bb1->count;

  /* Merge the outgoing edge counts from bb1 onto bb2.  */
  gcov_type out_sum = 0;
  FOR_EACH_EDGE (e1, ei, bb1->succs)
    {
      e2 = find_edge (bb2, e1->dest);
      gcc_assert (e2);
      e2->count += e1->count;
      out_sum += e2->count;
    }
  /* Recompute the edge probabilities from the new merged edge count.
     Use the sum of the new merged edge counts computed above instead
     of bb2's merged count, in case there are profile count insanities
     making the bb count inconsistent with the edge weights.  */
  FOR_EACH_EDGE (e2, ei, bb2->succs)
    {
      e2->probability = GCOV_COMPUTE_SCALE (e2->count, out_sum);
    }

  /* Do updates that use bb1, before deleting bb1.  */
  release_last_vdef (bb1);
  same_succ_flush_bb (bb1);

  delete_basic_block (bb1);
}

/* Bbs for which update_debug_stmt need to be called.  */

static bitmap update_bbs;

/* For each cluster in all_clusters, merge all cluster->bbs.  Returns
   number of bbs removed.  */

static int
apply_clusters (void)
{
  basic_block bb1, bb2;
  bb_cluster c;
  unsigned int i, j;
  bitmap_iterator bj;
  int nr_bbs_removed = 0;

  for (i = 0; i < all_clusters.length (); ++i)
    {
      c = all_clusters[i];
      if (c == NULL)
	continue;

      bb2 = c->rep_bb;
      bitmap_set_bit (update_bbs, bb2->index);

      bitmap_clear_bit (c->bbs, bb2->index);
      EXECUTE_IF_SET_IN_BITMAP (c->bbs, 0, j, bj)
	{
	  bb1 = BASIC_BLOCK_FOR_FN (cfun, j);
	  bitmap_clear_bit (update_bbs, bb1->index);

	  replace_block_by (bb1, bb2);
	  nr_bbs_removed++;
	}
    }

  return nr_bbs_removed;
}

/* Resets debug statement STMT if it has uses that are not dominated by their
   defs.  */

static void
update_debug_stmt (gimple stmt)
{
  use_operand_p use_p;
  ssa_op_iter oi;
  basic_block bbdef, bbuse;
  gimple def_stmt;
  tree name;

  if (!gimple_debug_bind_p (stmt))
    return;

  bbuse = gimple_bb (stmt);
  FOR_EACH_PHI_OR_STMT_USE (use_p, stmt, oi, SSA_OP_USE)
    {
      name = USE_FROM_PTR (use_p);
      gcc_assert (TREE_CODE (name) == SSA_NAME);

      def_stmt = SSA_NAME_DEF_STMT (name);
      gcc_assert (def_stmt != NULL);

      bbdef = gimple_bb (def_stmt);
      if (bbdef == NULL || bbuse == bbdef
	  || dominated_by_p (CDI_DOMINATORS, bbuse, bbdef))
	continue;

      gimple_debug_bind_reset_value (stmt);
      update_stmt (stmt);
    }
}

/* Resets all debug statements that have uses that are not
   dominated by their defs.  */

static void
update_debug_stmts (void)
{
  basic_block bb;
  bitmap_iterator bi;
  unsigned int i;

  EXECUTE_IF_SET_IN_BITMAP (update_bbs, 0, i, bi)
    {
      gimple stmt;
      gimple_stmt_iterator gsi;

      bb = BASIC_BLOCK_FOR_FN (cfun, i);
      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
	{
	  stmt = gsi_stmt (gsi);
	  if (!is_gimple_debug (stmt))
	    continue;
	  update_debug_stmt (stmt);
	}
    }
}

/* Runs tail merge optimization.  */

unsigned int
tail_merge_optimize (unsigned int todo)
{
  int nr_bbs_removed_total = 0;
  int nr_bbs_removed;
  bool loop_entered = false;
  int iteration_nr = 0;
  int max_iterations = PARAM_VALUE (PARAM_MAX_TAIL_MERGE_ITERATIONS);

  if (!flag_tree_tail_merge
      || max_iterations == 0
      /* We try to be conservative with respect to loop structure, since:
	 - the cases where tail-merging could both affect loop structure and be
	   beneficial are rare,
	 - it prevents us from having to fixup the loops using
	   loops_state_set (LOOPS_NEED_FIXUP), and
	 - keeping loop structure may allow us to simplify the pass.
	 In order to be conservative, we need loop information.	 In rare cases
	 (about 7 test-cases in the g++ testsuite) there is none (because
	 loop_optimizer_finalize has been called before tail-merge, and
	 PROP_loops is not set), so we bail out.  */
      || current_loops == NULL)
    return 0;

  timevar_push (TV_TREE_TAIL_MERGE);

  if (!dom_info_available_p (CDI_DOMINATORS))
    {
      /* PRE can leave us with unreachable blocks, remove them now.  */
      delete_unreachable_blocks ();
      calculate_dominance_info (CDI_DOMINATORS);
    }
  init_worklist ();

  while (!worklist.is_empty ())
    {
      if (!loop_entered)
	{
	  loop_entered = true;
	  alloc_cluster_vectors ();
	  update_bbs = BITMAP_ALLOC (NULL);
	}
      else
	reset_cluster_vectors ();

      iteration_nr++;
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file, "worklist iteration #%d\n", iteration_nr);

      find_clusters ();
      gcc_assert (worklist.is_empty ());
      if (all_clusters.is_empty ())
	break;

      nr_bbs_removed = apply_clusters ();
      nr_bbs_removed_total += nr_bbs_removed;
      if (nr_bbs_removed == 0)
	break;

      free_dominance_info (CDI_DOMINATORS);

      if (iteration_nr == max_iterations)
	break;

      calculate_dominance_info (CDI_DOMINATORS);
      update_worklist ();
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "htab collision / search: %f\n",
	     same_succ_htab.collisions ());

  if (nr_bbs_removed_total > 0)
    {
      if (MAY_HAVE_DEBUG_STMTS)
	{
	  calculate_dominance_info (CDI_DOMINATORS);
	  update_debug_stmts ();
	}

      if (dump_file && (dump_flags & TDF_DETAILS))
	{
	  fprintf (dump_file, "Before TODOs.\n");
	  dump_function_to_file (current_function_decl, dump_file, dump_flags);
	}

      todo |= (TODO_verify_ssa | TODO_verify_stmts | TODO_verify_flow);
      mark_virtual_operands_for_renaming (cfun);
    }

  delete_worklist ();
  if (loop_entered)
    {
      delete_cluster_vectors ();
      BITMAP_FREE (update_bbs);
    }

  timevar_pop (TV_TREE_TAIL_MERGE);

  return todo;
}