summaryrefslogtreecommitdiff
path: root/lib/Target/Mips/MipsConstantIslandPass.cpp
blob: 8f607b057d209fb7bb8f0f5728db957bc1000726 (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
//===-- MipsConstantIslandPass.cpp - Emit Pc Relative loads----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//
// This pass is used to make Pc relative loads of constants.
// For now, only Mips16 will use this. 
//
// Loading constants inline is expensive on Mips16 and it's in general better
// to place the constant nearby in code space and then it can be loaded with a
// simple 16 bit load instruction.
//
// The constants can be not just numbers but addresses of functions and labels.
// This can be particularly helpful in static relocation mode for embedded
// non-linux targets.
//
//

#define DEBUG_TYPE "mips-constant-islands"

#include "Mips.h"
#include "MCTargetDesc/MipsBaseInfo.h"
#include "Mips16InstrInfo.h"
#include "MipsMachineFunction.h"
#include "MipsTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/InstIterator.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include <algorithm>

using namespace llvm;

STATISTIC(NumCPEs,       "Number of constpool entries");
STATISTIC(NumSplit,      "Number of uncond branches inserted");
STATISTIC(NumCBrFixed,   "Number of cond branches fixed");
STATISTIC(NumUBrFixed,   "Number of uncond branches fixed");

// FIXME: This option should be removed once it has received sufficient testing.
static cl::opt<bool>
AlignConstantIslands("mips-align-constant-islands", cl::Hidden, cl::init(true),
          cl::desc("Align constant islands in code"));


// Rather than do make check tests with huge amounts of code, we force
// the test to use this amount.
//
static cl::opt<int> ConstantIslandsSmallOffset(
  "mips-constant-islands-small-offset",
  cl::init(0),
  cl::desc("Make small offsets be this amount for testing purposes"),
  cl::Hidden);

//
// For testing purposes we tell it to not use relaxed load forms so that it
// will split blocks.
//
static cl::opt<bool> NoLoadRelaxation(
  "mips-constant-islands-no-load-relaxation",
  cl::init(false),
  cl::desc("Don't relax loads to long loads - for testing purposes"),
  cl::Hidden);

static unsigned int branchTargetOperand(MachineInstr *MI) {
  switch (MI->getOpcode()) {
  case Mips::Bimm16:
  case Mips::BimmX16:
  case Mips::Bteqz16:
  case Mips::BteqzX16:
  case Mips::Btnez16:
  case Mips::BtnezX16:
  case Mips::JalB16:
    return 0;
  case Mips::BeqzRxImm16:
  case Mips::BeqzRxImmX16:
  case Mips::BnezRxImm16:
  case Mips::BnezRxImmX16:
    return 1;
  }
  llvm_unreachable("Unknown branch type");
}

static bool isUnconditionalBranch(unsigned int Opcode) {
  switch (Opcode) {
  default: return false;
  case Mips::Bimm16:
  case Mips::BimmX16:
  case Mips::JalB16:
    return true;
  }
}

static unsigned int longformBranchOpcode(unsigned int Opcode) {
  switch (Opcode) {
  case Mips::Bimm16:
  case Mips::BimmX16:
    return Mips::BimmX16;
  case Mips::Bteqz16:
  case Mips::BteqzX16:
    return Mips::BteqzX16;
  case Mips::Btnez16:
  case Mips::BtnezX16:
    return Mips::BtnezX16;
  case Mips::JalB16:
    return Mips::JalB16;
  case Mips::BeqzRxImm16:
  case Mips::BeqzRxImmX16:
    return Mips::BeqzRxImmX16;
  case Mips::BnezRxImm16:
  case Mips::BnezRxImmX16:
    return Mips::BnezRxImmX16;
  }
  llvm_unreachable("Unknown branch type");
}

//
// FIXME: need to go through this whole constant islands port and check the math
// for branch ranges and clean this up and make some functions to calculate things
// that are done many times identically.
// Need to refactor some of the code to call this routine.
//
static unsigned int branchMaxOffsets(unsigned int Opcode) {
  unsigned Bits, Scale;
  switch (Opcode) {
    case Mips::Bimm16:
      Bits = 11;
      Scale = 2;
      break;
    case Mips::BimmX16:
      Bits = 16;
      Scale = 2;
      break;
    case Mips::BeqzRxImm16:
      Bits = 8;
      Scale = 2;
      break;
    case Mips::BeqzRxImmX16:
      Bits = 16;
      Scale = 2;
      break;
    case Mips::BnezRxImm16:
      Bits = 8;
      Scale = 2;
      break;
    case Mips::BnezRxImmX16:
      Bits = 16;
      Scale = 2;
      break;
    case Mips::Bteqz16:
      Bits = 8;
      Scale = 2;
      break;
    case Mips::BteqzX16:
      Bits = 16;
      Scale = 2;
      break;
    case Mips::Btnez16:
      Bits = 8;
      Scale = 2;
      break;
    case Mips::BtnezX16:
      Bits = 16;
      Scale = 2;
      break;
    default:
      llvm_unreachable("Unknown branch type");
  }
  unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
  return MaxOffs;
}

namespace {


  typedef MachineBasicBlock::iterator Iter;
  typedef MachineBasicBlock::reverse_iterator ReverseIter;

  /// MipsConstantIslands - Due to limited PC-relative displacements, Mips
  /// requires constant pool entries to be scattered among the instructions
  /// inside a function.  To do this, it completely ignores the normal LLVM
  /// constant pool; instead, it places constants wherever it feels like with
  /// special instructions.
  ///
  /// The terminology used in this pass includes:
  ///   Islands - Clumps of constants placed in the function.
  ///   Water   - Potential places where an island could be formed.
  ///   CPE     - A constant pool entry that has been placed somewhere, which
  ///             tracks a list of users.

  class MipsConstantIslands : public MachineFunctionPass {

    /// BasicBlockInfo - Information about the offset and size of a single
    /// basic block.
    struct BasicBlockInfo {
      /// Offset - Distance from the beginning of the function to the beginning
      /// of this basic block.
      ///
      /// Offsets are computed assuming worst case padding before an aligned
      /// block. This means that subtracting basic block offsets always gives a
      /// conservative estimate of the real distance which may be smaller.
      ///
      /// Because worst case padding is used, the computed offset of an aligned
      /// block may not actually be aligned.
      unsigned Offset;

      /// Size - Size of the basic block in bytes.  If the block contains
      /// inline assembly, this is a worst case estimate.
      ///
      /// The size does not include any alignment padding whether from the
      /// beginning of the block, or from an aligned jump table at the end.
      unsigned Size;

      // FIXME: ignore LogAlign for this patch
      //
      unsigned postOffset(unsigned LogAlign = 0) const {
        unsigned PO = Offset + Size;
        return PO;
      }

      BasicBlockInfo() : Offset(0), Size(0) {}

    };

    std::vector<BasicBlockInfo> BBInfo;

    /// WaterList - A sorted list of basic blocks where islands could be placed
    /// (i.e. blocks that don't fall through to the following block, due
    /// to a return, unreachable, or unconditional branch).
    std::vector<MachineBasicBlock*> WaterList;

    /// NewWaterList - The subset of WaterList that was created since the
    /// previous iteration by inserting unconditional branches.
    SmallSet<MachineBasicBlock*, 4> NewWaterList;

    typedef std::vector<MachineBasicBlock*>::iterator water_iterator;

    /// CPUser - One user of a constant pool, keeping the machine instruction
    /// pointer, the constant pool being referenced, and the max displacement
    /// allowed from the instruction to the CP.  The HighWaterMark records the
    /// highest basic block where a new CPEntry can be placed.  To ensure this
    /// pass terminates, the CP entries are initially placed at the end of the
    /// function and then move monotonically to lower addresses.  The
    /// exception to this rule is when the current CP entry for a particular
    /// CPUser is out of range, but there is another CP entry for the same
    /// constant value in range.  We want to use the existing in-range CP
    /// entry, but if it later moves out of range, the search for new water
    /// should resume where it left off.  The HighWaterMark is used to record
    /// that point.
    struct CPUser {
      MachineInstr *MI;
      MachineInstr *CPEMI;
      MachineBasicBlock *HighWaterMark;
    private:
      unsigned MaxDisp;
      unsigned LongFormMaxDisp; // mips16 has 16/32 bit instructions
                                // with different displacements
      unsigned LongFormOpcode;
    public:
      bool NegOk;
      CPUser(MachineInstr *mi, MachineInstr *cpemi, unsigned maxdisp,
             bool neg,
             unsigned longformmaxdisp, unsigned longformopcode)
        : MI(mi), CPEMI(cpemi), MaxDisp(maxdisp),
          LongFormMaxDisp(longformmaxdisp), LongFormOpcode(longformopcode),
          NegOk(neg){
        HighWaterMark = CPEMI->getParent();
      }
      /// getMaxDisp - Returns the maximum displacement supported by MI.
      unsigned getMaxDisp() const {
        unsigned xMaxDisp = ConstantIslandsSmallOffset?
                            ConstantIslandsSmallOffset: MaxDisp;
        return xMaxDisp;
      }
      void setMaxDisp(unsigned val) {
        MaxDisp = val;
      }
      unsigned getLongFormMaxDisp() const {
        return LongFormMaxDisp;
      }
      unsigned getLongFormOpcode() const {
          return LongFormOpcode;
      }
    };

    /// CPUsers - Keep track of all of the machine instructions that use various
    /// constant pools and their max displacement.
    std::vector<CPUser> CPUsers;

  /// CPEntry - One per constant pool entry, keeping the machine instruction
  /// pointer, the constpool index, and the number of CPUser's which
  /// reference this entry.
  struct CPEntry {
    MachineInstr *CPEMI;
    unsigned CPI;
    unsigned RefCount;
    CPEntry(MachineInstr *cpemi, unsigned cpi, unsigned rc = 0)
      : CPEMI(cpemi), CPI(cpi), RefCount(rc) {}
  };

  /// CPEntries - Keep track of all of the constant pool entry machine
  /// instructions. For each original constpool index (i.e. those that
  /// existed upon entry to this pass), it keeps a vector of entries.
  /// Original elements are cloned as we go along; the clones are
  /// put in the vector of the original element, but have distinct CPIs.
  std::vector<std::vector<CPEntry> > CPEntries;

  /// ImmBranch - One per immediate branch, keeping the machine instruction
  /// pointer, conditional or unconditional, the max displacement,
  /// and (if isCond is true) the corresponding unconditional branch
  /// opcode.
  struct ImmBranch {
    MachineInstr *MI;
    unsigned MaxDisp : 31;
    bool isCond : 1;
    int UncondBr;
    ImmBranch(MachineInstr *mi, unsigned maxdisp, bool cond, int ubr)
      : MI(mi), MaxDisp(maxdisp), isCond(cond), UncondBr(ubr) {}
  };

  /// ImmBranches - Keep track of all the immediate branch instructions.
  ///
  std::vector<ImmBranch> ImmBranches;

  /// HasFarJump - True if any far jump instruction has been emitted during
  /// the branch fix up pass.
  bool HasFarJump;

  const TargetMachine &TM;
  bool IsPIC;
  unsigned ABI;
  const MipsSubtarget *STI;
  const Mips16InstrInfo *TII;
  MipsFunctionInfo *MFI;
  MachineFunction *MF;
  MachineConstantPool *MCP;

  unsigned PICLabelUId;
  bool PrescannedForConstants;

  void initPICLabelUId(unsigned UId) {
    PICLabelUId = UId;
  }


  unsigned createPICLabelUId() {
    return PICLabelUId++;
  }

  public:
    static char ID;
    MipsConstantIslands(TargetMachine &tm)
      : MachineFunctionPass(ID), TM(tm),
        IsPIC(TM.getRelocationModel() == Reloc::PIC_),
        ABI(TM.getSubtarget<MipsSubtarget>().getTargetABI()),
        STI(&TM.getSubtarget<MipsSubtarget>()), MF(0), MCP(0),
        PrescannedForConstants(false){}

    virtual const char *getPassName() const {
      return "Mips Constant Islands";
    }

    bool runOnMachineFunction(MachineFunction &F);

    void doInitialPlacement(std::vector<MachineInstr*> &CPEMIs);
    CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI);
    unsigned getCPELogAlign(const MachineInstr *CPEMI);
    void initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs);
    unsigned getOffsetOf(MachineInstr *MI) const;
    unsigned getUserOffset(CPUser&) const;
    void dumpBBs();
    void verify();

    bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
                         unsigned Disp, bool NegativeOK);
    bool isOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
                         const CPUser &U);

    bool isLongFormOffsetInRange(unsigned UserOffset, unsigned TrialOffset,
                                const CPUser &U);

    void computeBlockSize(MachineBasicBlock *MBB);
    MachineBasicBlock *splitBlockBeforeInstr(MachineInstr *MI);
    void updateForInsertedWaterBlock(MachineBasicBlock *NewBB);
    void adjustBBOffsetsAfter(MachineBasicBlock *BB);
    bool decrementCPEReferenceCount(unsigned CPI, MachineInstr* CPEMI);
    int findInRangeCPEntry(CPUser& U, unsigned UserOffset);
    int findLongFormInRangeCPEntry(CPUser& U, unsigned UserOffset);
    bool findAvailableWater(CPUser&U, unsigned UserOffset,
                            water_iterator &WaterIter);
    void createNewWater(unsigned CPUserIndex, unsigned UserOffset,
                        MachineBasicBlock *&NewMBB);
    bool handleConstantPoolUser(unsigned CPUserIndex);
    void removeDeadCPEMI(MachineInstr *CPEMI);
    bool removeUnusedCPEntries();
    bool isCPEntryInRange(MachineInstr *MI, unsigned UserOffset,
                          MachineInstr *CPEMI, unsigned Disp, bool NegOk,
                          bool DoDump = false);
    bool isWaterInRange(unsigned UserOffset, MachineBasicBlock *Water,
                        CPUser &U, unsigned &Growth);
    bool isBBInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);
    bool fixupImmediateBr(ImmBranch &Br);
    bool fixupConditionalBr(ImmBranch &Br);
    bool fixupUnconditionalBr(ImmBranch &Br);

    void prescanForConstants();

  private:

  };

  char MipsConstantIslands::ID = 0;
} // end of anonymous namespace


bool MipsConstantIslands::isLongFormOffsetInRange
  (unsigned UserOffset, unsigned TrialOffset,
   const CPUser &U) {
  return isOffsetInRange(UserOffset, TrialOffset,
                         U.getLongFormMaxDisp(), U.NegOk);
}

bool MipsConstantIslands::isOffsetInRange
  (unsigned UserOffset, unsigned TrialOffset,
   const CPUser &U) {
  return isOffsetInRange(UserOffset, TrialOffset,
                         U.getMaxDisp(), U.NegOk);
}
/// print block size and offset information - debugging
void MipsConstantIslands::dumpBBs() {
  DEBUG({
    for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) {
      const BasicBlockInfo &BBI = BBInfo[J];
      dbgs() << format("%08x BB#%u\t", BBI.Offset, J)
             << format(" size=%#x\n", BBInfo[J].Size);
    }
  });
}
/// createMipsLongBranchPass - Returns a pass that converts branches to long
/// branches.
FunctionPass *llvm::createMipsConstantIslandPass(MipsTargetMachine &tm) {
  return new MipsConstantIslands(tm);
}

bool MipsConstantIslands::runOnMachineFunction(MachineFunction &mf) {
  // The intention is for this to be a mips16 only pass for now
  // FIXME:
  MF = &mf;
  MCP = mf.getConstantPool();
  DEBUG(dbgs() << "constant island machine function " << "\n");
  if (!TM.getSubtarget<MipsSubtarget>().inMips16Mode() ||
      !MipsSubtarget::useConstantIslands()) {
    return false;
  }
  TII = (const Mips16InstrInfo*)MF->getTarget().getInstrInfo();
  MFI = MF->getInfo<MipsFunctionInfo>();
  DEBUG(dbgs() << "constant island processing " << "\n");
  //
  // will need to make predermination if there is any constants we need to
  // put in constant islands. TBD.
  //
  if (!PrescannedForConstants) prescanForConstants();

  HasFarJump = false;
  // This pass invalidates liveness information when it splits basic blocks.
  MF->getRegInfo().invalidateLiveness();

  // Renumber all of the machine basic blocks in the function, guaranteeing that
  // the numbers agree with the position of the block in the function.
  MF->RenumberBlocks();

  bool MadeChange = false;

  // Perform the initial placement of the constant pool entries.  To start with,
  // we put them all at the end of the function.
  std::vector<MachineInstr*> CPEMIs;
  if (!MCP->isEmpty())
    doInitialPlacement(CPEMIs);

  /// The next UID to take is the first unused one.
  initPICLabelUId(CPEMIs.size());

  // Do the initial scan of the function, building up information about the
  // sizes of each block, the location of all the water, and finding all of the
  // constant pool users.
  initializeFunctionInfo(CPEMIs);
  CPEMIs.clear();
  DEBUG(dumpBBs());

  /// Remove dead constant pool entries.
  MadeChange |= removeUnusedCPEntries();

  // Iteratively place constant pool entries and fix up branches until there
  // is no change.
  unsigned NoCPIters = 0, NoBRIters = 0;
  (void)NoBRIters;
  while (true) {
    DEBUG(dbgs() << "Beginning CP iteration #" << NoCPIters << '\n');
    bool CPChange = false;
    for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)
      CPChange |= handleConstantPoolUser(i);
    if (CPChange && ++NoCPIters > 30)
      report_fatal_error("Constant Island pass failed to converge!");
    DEBUG(dumpBBs());

    // Clear NewWaterList now.  If we split a block for branches, it should
    // appear as "new water" for the next iteration of constant pool placement.
    NewWaterList.clear();

    DEBUG(dbgs() << "Beginning BR iteration #" << NoBRIters << '\n');
    bool BRChange = false;
    for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
      BRChange |= fixupImmediateBr(ImmBranches[i]);
    if (BRChange && ++NoBRIters > 30)
      report_fatal_error("Branch Fix Up pass failed to converge!");
    DEBUG(dumpBBs());
    if (!CPChange && !BRChange)
      break;
    MadeChange = true;
  }

  DEBUG(dbgs() << '\n'; dumpBBs());

  BBInfo.clear();
  WaterList.clear();
  CPUsers.clear();
  CPEntries.clear();
  ImmBranches.clear();
  return MadeChange;
}

/// doInitialPlacement - Perform the initial placement of the constant pool
/// entries.  To start with, we put them all at the end of the function.
void
MipsConstantIslands::doInitialPlacement(std::vector<MachineInstr*> &CPEMIs) {
  // Create the basic block to hold the CPE's.
  MachineBasicBlock *BB = MF->CreateMachineBasicBlock();
  MF->push_back(BB);


  // MachineConstantPool measures alignment in bytes. We measure in log2(bytes).
  unsigned MaxAlign = Log2_32(MCP->getConstantPoolAlignment());

  // Mark the basic block as required by the const-pool.
  // If AlignConstantIslands isn't set, use 4-byte alignment for everything.
  BB->setAlignment(AlignConstantIslands ? MaxAlign : 2);

  // The function needs to be as aligned as the basic blocks. The linker may
  // move functions around based on their alignment.
  MF->ensureAlignment(BB->getAlignment());

  // Order the entries in BB by descending alignment.  That ensures correct
  // alignment of all entries as long as BB is sufficiently aligned.  Keep
  // track of the insertion point for each alignment.  We are going to bucket
  // sort the entries as they are created.
  SmallVector<MachineBasicBlock::iterator, 8> InsPoint(MaxAlign + 1, BB->end());

  // Add all of the constants from the constant pool to the end block, use an
  // identity mapping of CPI's to CPE's.
  const std::vector<MachineConstantPoolEntry> &CPs = MCP->getConstants();

  const DataLayout &TD = *MF->getTarget().getDataLayout();
  for (unsigned i = 0, e = CPs.size(); i != e; ++i) {
    unsigned Size = TD.getTypeAllocSize(CPs[i].getType());
    assert(Size >= 4 && "Too small constant pool entry");
    unsigned Align = CPs[i].getAlignment();
    assert(isPowerOf2_32(Align) && "Invalid alignment");
    // Verify that all constant pool entries are a multiple of their alignment.
    // If not, we would have to pad them out so that instructions stay aligned.
    assert((Size % Align) == 0 && "CP Entry not multiple of 4 bytes!");

    // Insert CONSTPOOL_ENTRY before entries with a smaller alignment.
    unsigned LogAlign = Log2_32(Align);
    MachineBasicBlock::iterator InsAt = InsPoint[LogAlign];

    MachineInstr *CPEMI =
      BuildMI(*BB, InsAt, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY))
        .addImm(i).addConstantPoolIndex(i).addImm(Size);

    CPEMIs.push_back(CPEMI);

    // Ensure that future entries with higher alignment get inserted before
    // CPEMI. This is bucket sort with iterators.
    for (unsigned a = LogAlign + 1; a <= MaxAlign; ++a)
      if (InsPoint[a] == InsAt)
        InsPoint[a] = CPEMI;
    // Add a new CPEntry, but no corresponding CPUser yet.
    std::vector<CPEntry> CPEs;
    CPEs.push_back(CPEntry(CPEMI, i));
    CPEntries.push_back(CPEs);
    ++NumCPEs;
    DEBUG(dbgs() << "Moved CPI#" << i << " to end of function, size = "
                 << Size << ", align = " << Align <<'\n');
  }
  DEBUG(BB->dump());
}

/// BBHasFallthrough - Return true if the specified basic block can fallthrough
/// into the block immediately after it.
static bool BBHasFallthrough(MachineBasicBlock *MBB) {
  // Get the next machine basic block in the function.
  MachineFunction::iterator MBBI = MBB;
  // Can't fall off end of function.
  if (llvm::next(MBBI) == MBB->getParent()->end())
    return false;

  MachineBasicBlock *NextBB = llvm::next(MBBI);
  for (MachineBasicBlock::succ_iterator I = MBB->succ_begin(),
       E = MBB->succ_end(); I != E; ++I)
    if (*I == NextBB)
      return true;

  return false;
}

/// findConstPoolEntry - Given the constpool index and CONSTPOOL_ENTRY MI,
/// look up the corresponding CPEntry.
MipsConstantIslands::CPEntry
*MipsConstantIslands::findConstPoolEntry(unsigned CPI,
                                        const MachineInstr *CPEMI) {
  std::vector<CPEntry> &CPEs = CPEntries[CPI];
  // Number of entries per constpool index should be small, just do a
  // linear search.
  for (unsigned i = 0, e = CPEs.size(); i != e; ++i) {
    if (CPEs[i].CPEMI == CPEMI)
      return &CPEs[i];
  }
  return NULL;
}

/// getCPELogAlign - Returns the required alignment of the constant pool entry
/// represented by CPEMI.  Alignment is measured in log2(bytes) units.
unsigned MipsConstantIslands::getCPELogAlign(const MachineInstr *CPEMI) {
  assert(CPEMI && CPEMI->getOpcode() == Mips::CONSTPOOL_ENTRY);

  // Everything is 4-byte aligned unless AlignConstantIslands is set.
  if (!AlignConstantIslands)
    return 2;

  unsigned CPI = CPEMI->getOperand(1).getIndex();
  assert(CPI < MCP->getConstants().size() && "Invalid constant pool index.");
  unsigned Align = MCP->getConstants()[CPI].getAlignment();
  assert(isPowerOf2_32(Align) && "Invalid CPE alignment");
  return Log2_32(Align);
}

/// initializeFunctionInfo - Do the initial scan of the function, building up
/// information about the sizes of each block, the location of all the water,
/// and finding all of the constant pool users.
void MipsConstantIslands::
initializeFunctionInfo(const std::vector<MachineInstr*> &CPEMIs) {
  BBInfo.clear();
  BBInfo.resize(MF->getNumBlockIDs());

  // First thing, compute the size of all basic blocks, and see if the function
  // has any inline assembly in it. If so, we have to be conservative about
  // alignment assumptions, as we don't know for sure the size of any
  // instructions in the inline assembly.
  for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I)
    computeBlockSize(I);


  // Compute block offsets.
  adjustBBOffsetsAfter(MF->begin());

  // Now go back through the instructions and build up our data structures.
  for (MachineFunction::iterator MBBI = MF->begin(), E = MF->end();
       MBBI != E; ++MBBI) {
    MachineBasicBlock &MBB = *MBBI;

    // If this block doesn't fall through into the next MBB, then this is
    // 'water' that a constant pool island could be placed.
    if (!BBHasFallthrough(&MBB))
      WaterList.push_back(&MBB);
    for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
         I != E; ++I) {
      if (I->isDebugValue())
        continue;

      int Opc = I->getOpcode();
      if (I->isBranch()) {
        bool isCond = false;
        unsigned Bits = 0;
        unsigned Scale = 1;
        int UOpc = Opc;
        switch (Opc) {
        default:
          continue;  // Ignore other branches for now
        case Mips::Bimm16:
          Bits = 11;
          Scale = 2;
          isCond = false;
          break;
        case Mips::BimmX16:
          Bits = 16;
          Scale = 2;
          isCond = false;
          break;
        case Mips::BeqzRxImm16:
          UOpc=Mips::Bimm16;
          Bits = 8;
          Scale = 2;
          isCond = true;
          break;
        case Mips::BeqzRxImmX16:
          UOpc=Mips::Bimm16;
          Bits = 16;
          Scale = 2;
          isCond = true;
          break;
        case Mips::BnezRxImm16:
          UOpc=Mips::Bimm16;
          Bits = 8;
          Scale = 2;
          isCond = true;
          break;
        case Mips::BnezRxImmX16:
          UOpc=Mips::Bimm16;
          Bits = 16;
          Scale = 2;
          isCond = true;
          break;
        case Mips::Bteqz16:
          UOpc=Mips::Bimm16;
          Bits = 8;
          Scale = 2;
          isCond = true;
          break;
        case Mips::BteqzX16:
          UOpc=Mips::Bimm16;
          Bits = 16;
          Scale = 2;
          isCond = true;
          break;
        case Mips::Btnez16:
          UOpc=Mips::Bimm16;
          Bits = 8;
          Scale = 2;
          isCond = true;
          break;
        case Mips::BtnezX16:
          UOpc=Mips::Bimm16;
          Bits = 16;
          Scale = 2;
          isCond = true;
          break;
        }
        // Record this immediate branch.
        unsigned MaxOffs = ((1 << (Bits-1))-1) * Scale;
        ImmBranches.push_back(ImmBranch(I, MaxOffs, isCond, UOpc));
      }

      if (Opc == Mips::CONSTPOOL_ENTRY)
        continue;


      // Scan the instructions for constant pool operands.
      for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
        if (I->getOperand(op).isCPI()) {

          // We found one.  The addressing mode tells us the max displacement
          // from the PC that this instruction permits.

          // Basic size info comes from the TSFlags field.
          unsigned Bits = 0;
          unsigned Scale = 1;
          bool NegOk = false;
          unsigned LongFormBits = 0;
          unsigned LongFormScale = 0;
          unsigned LongFormOpcode = 0;
          switch (Opc) {
          default:
            llvm_unreachable("Unknown addressing mode for CP reference!");
          case Mips::LwRxPcTcp16:
            Bits = 8;
            Scale = 4;
            LongFormOpcode = Mips::LwRxPcTcpX16;
            LongFormBits = 14;
            LongFormScale = 1;
            break;
          case Mips::LwRxPcTcpX16:
            Bits = 14;
            Scale = 1;
            NegOk = true;
            break;
          }
          // Remember that this is a user of a CP entry.
          unsigned CPI = I->getOperand(op).getIndex();
          MachineInstr *CPEMI = CPEMIs[CPI];
          unsigned MaxOffs = ((1 << Bits)-1) * Scale;
          unsigned LongFormMaxOffs = ((1 << LongFormBits)-1) * LongFormScale;
          CPUsers.push_back(CPUser(I, CPEMI, MaxOffs, NegOk,
                                   LongFormMaxOffs, LongFormOpcode));

          // Increment corresponding CPEntry reference count.
          CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
          assert(CPE && "Cannot find a corresponding CPEntry!");
          CPE->RefCount++;

          // Instructions can only use one CP entry, don't bother scanning the
          // rest of the operands.
          break;

        }

    }
  }

}

/// computeBlockSize - Compute the size and some alignment information for MBB.
/// This function updates BBInfo directly.
void MipsConstantIslands::computeBlockSize(MachineBasicBlock *MBB) {
  BasicBlockInfo &BBI = BBInfo[MBB->getNumber()];
  BBI.Size = 0;

  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
       ++I)
    BBI.Size += TII->GetInstSizeInBytes(I);

}

/// getOffsetOf - Return the current offset of the specified machine instruction
/// from the start of the function.  This offset changes as stuff is moved
/// around inside the function.
unsigned MipsConstantIslands::getOffsetOf(MachineInstr *MI) const {
  MachineBasicBlock *MBB = MI->getParent();

  // The offset is composed of two things: the sum of the sizes of all MBB's
  // before this instruction's block, and the offset from the start of the block
  // it is in.
  unsigned Offset = BBInfo[MBB->getNumber()].Offset;

  // Sum instructions before MI in MBB.
  for (MachineBasicBlock::iterator I = MBB->begin(); &*I != MI; ++I) {
    assert(I != MBB->end() && "Didn't find MI in its own basic block?");
    Offset += TII->GetInstSizeInBytes(I);
  }
  return Offset;
}

/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB
/// ID.
static bool CompareMBBNumbers(const MachineBasicBlock *LHS,
                              const MachineBasicBlock *RHS) {
  return LHS->getNumber() < RHS->getNumber();
}

/// updateForInsertedWaterBlock - When a block is newly inserted into the
/// machine function, it upsets all of the block numbers.  Renumber the blocks
/// and update the arrays that parallel this numbering.
void MipsConstantIslands::updateForInsertedWaterBlock
  (MachineBasicBlock *NewBB) {
  // Renumber the MBB's to keep them consecutive.
  NewBB->getParent()->RenumberBlocks(NewBB);

  // Insert an entry into BBInfo to align it properly with the (newly
  // renumbered) block numbers.
  BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());

  // Next, update WaterList.  Specifically, we need to add NewMBB as having
  // available water after it.
  water_iterator IP =
    std::lower_bound(WaterList.begin(), WaterList.end(), NewBB,
                     CompareMBBNumbers);
  WaterList.insert(IP, NewBB);
}

unsigned MipsConstantIslands::getUserOffset(CPUser &U) const {
  return getOffsetOf(U.MI);
}

/// Split the basic block containing MI into two blocks, which are joined by
/// an unconditional branch.  Update data structures and renumber blocks to
/// account for this change and returns the newly created block.
MachineBasicBlock *MipsConstantIslands::splitBlockBeforeInstr
  (MachineInstr *MI) {
  MachineBasicBlock *OrigBB = MI->getParent();

  // Create a new MBB for the code after the OrigBB.
  MachineBasicBlock *NewBB =
    MF->CreateMachineBasicBlock(OrigBB->getBasicBlock());
  MachineFunction::iterator MBBI = OrigBB; ++MBBI;
  MF->insert(MBBI, NewBB);

  // Splice the instructions starting with MI over to NewBB.
  NewBB->splice(NewBB->end(), OrigBB, MI, OrigBB->end());

  // Add an unconditional branch from OrigBB to NewBB.
  // Note the new unconditional branch is not being recorded.
  // There doesn't seem to be meaningful DebugInfo available; this doesn't
  // correspond to anything in the source.
  BuildMI(OrigBB, DebugLoc(), TII->get(Mips::Bimm16)).addMBB(NewBB);
  ++NumSplit;

  // Update the CFG.  All succs of OrigBB are now succs of NewBB.
  NewBB->transferSuccessors(OrigBB);

  // OrigBB branches to NewBB.
  OrigBB->addSuccessor(NewBB);

  // Update internal data structures to account for the newly inserted MBB.
  // This is almost the same as updateForInsertedWaterBlock, except that
  // the Water goes after OrigBB, not NewBB.
  MF->RenumberBlocks(NewBB);

  // Insert an entry into BBInfo to align it properly with the (newly
  // renumbered) block numbers.
  BBInfo.insert(BBInfo.begin() + NewBB->getNumber(), BasicBlockInfo());

  // Next, update WaterList.  Specifically, we need to add OrigMBB as having
  // available water after it (but not if it's already there, which happens
  // when splitting before a conditional branch that is followed by an
  // unconditional branch - in that case we want to insert NewBB).
  water_iterator IP =
    std::lower_bound(WaterList.begin(), WaterList.end(), OrigBB,
                     CompareMBBNumbers);
  MachineBasicBlock* WaterBB = *IP;
  if (WaterBB == OrigBB)
    WaterList.insert(llvm::next(IP), NewBB);
  else
    WaterList.insert(IP, OrigBB);
  NewWaterList.insert(OrigBB);

  // Figure out how large the OrigBB is.  As the first half of the original
  // block, it cannot contain a tablejump.  The size includes
  // the new jump we added.  (It should be possible to do this without
  // recounting everything, but it's very confusing, and this is rarely
  // executed.)
  computeBlockSize(OrigBB);

  // Figure out how large the NewMBB is.  As the second half of the original
  // block, it may contain a tablejump.
  computeBlockSize(NewBB);

  // All BBOffsets following these blocks must be modified.
  adjustBBOffsetsAfter(OrigBB);

  return NewBB;
}



/// isOffsetInRange - Checks whether UserOffset (the location of a constant pool
/// reference) is within MaxDisp of TrialOffset (a proposed location of a
/// constant pool entry).
bool MipsConstantIslands::isOffsetInRange(unsigned UserOffset,
                                         unsigned TrialOffset, unsigned MaxDisp,
                                         bool NegativeOK) {
  if (UserOffset <= TrialOffset) {
    // User before the Trial.
    if (TrialOffset - UserOffset <= MaxDisp)
      return true;
  } else if (NegativeOK) {
    if (UserOffset - TrialOffset <= MaxDisp)
      return true;
  }
  return false;
}

/// isWaterInRange - Returns true if a CPE placed after the specified
/// Water (a basic block) will be in range for the specific MI.
///
/// Compute how much the function will grow by inserting a CPE after Water.
bool MipsConstantIslands::isWaterInRange(unsigned UserOffset,
                                        MachineBasicBlock* Water, CPUser &U,
                                        unsigned &Growth) {
  unsigned CPELogAlign = getCPELogAlign(U.CPEMI);
  unsigned CPEOffset = BBInfo[Water->getNumber()].postOffset(CPELogAlign);
  unsigned NextBlockOffset, NextBlockAlignment;
  MachineFunction::const_iterator NextBlock = Water;
  if (++NextBlock == MF->end()) {
    NextBlockOffset = BBInfo[Water->getNumber()].postOffset();
    NextBlockAlignment = 0;
  } else {
    NextBlockOffset = BBInfo[NextBlock->getNumber()].Offset;
    NextBlockAlignment = NextBlock->getAlignment();
  }
  unsigned Size = U.CPEMI->getOperand(2).getImm();
  unsigned CPEEnd = CPEOffset + Size;

  // The CPE may be able to hide in the alignment padding before the next
  // block. It may also cause more padding to be required if it is more aligned
  // that the next block.
  if (CPEEnd > NextBlockOffset) {
    Growth = CPEEnd - NextBlockOffset;
    // Compute the padding that would go at the end of the CPE to align the next
    // block.
    Growth += OffsetToAlignment(CPEEnd, 1u << NextBlockAlignment);

    // If the CPE is to be inserted before the instruction, that will raise
    // the offset of the instruction. Also account for unknown alignment padding
    // in blocks between CPE and the user.
    if (CPEOffset < UserOffset)
      UserOffset += Growth;
  } else
    // CPE fits in existing padding.
    Growth = 0;

  return isOffsetInRange(UserOffset, CPEOffset, U);
}

/// isCPEntryInRange - Returns true if the distance between specific MI and
/// specific ConstPool entry instruction can fit in MI's displacement field.
bool MipsConstantIslands::isCPEntryInRange
  (MachineInstr *MI, unsigned UserOffset,
   MachineInstr *CPEMI, unsigned MaxDisp,
   bool NegOk, bool DoDump) {
  unsigned CPEOffset  = getOffsetOf(CPEMI);

  if (DoDump) {
    DEBUG({
      unsigned Block = MI->getParent()->getNumber();
      const BasicBlockInfo &BBI = BBInfo[Block];
      dbgs() << "User of CPE#" << CPEMI->getOperand(0).getImm()
             << " max delta=" << MaxDisp
             << format(" insn address=%#x", UserOffset)
             << " in BB#" << Block << ": "
             << format("%#x-%x\t", BBI.Offset, BBI.postOffset()) << *MI
             << format("CPE address=%#x offset=%+d: ", CPEOffset,
                       int(CPEOffset-UserOffset));
    });
  }

  return isOffsetInRange(UserOffset, CPEOffset, MaxDisp, NegOk);
}

#ifndef NDEBUG
/// BBIsJumpedOver - Return true of the specified basic block's only predecessor
/// unconditionally branches to its only successor.
static bool BBIsJumpedOver(MachineBasicBlock *MBB) {
  if (MBB->pred_size() != 1 || MBB->succ_size() != 1)
    return false;
  MachineBasicBlock *Succ = *MBB->succ_begin();
  MachineBasicBlock *Pred = *MBB->pred_begin();
  MachineInstr *PredMI = &Pred->back();
  if (PredMI->getOpcode() == Mips::Bimm16)
    return PredMI->getOperand(0).getMBB() == Succ;
  return false;
}
#endif

void MipsConstantIslands::adjustBBOffsetsAfter(MachineBasicBlock *BB) {
  unsigned BBNum = BB->getNumber();
  for(unsigned i = BBNum + 1, e = MF->getNumBlockIDs(); i < e; ++i) {
    // Get the offset and known bits at the end of the layout predecessor.
    // Include the alignment of the current block.
    unsigned Offset = BBInfo[i - 1].Offset + BBInfo[i - 1].Size;
    BBInfo[i].Offset = Offset;
  }
}

/// decrementCPEReferenceCount - find the constant pool entry with index CPI
/// and instruction CPEMI, and decrement its refcount.  If the refcount
/// becomes 0 remove the entry and instruction.  Returns true if we removed
/// the entry, false if we didn't.

bool MipsConstantIslands::decrementCPEReferenceCount(unsigned CPI,
                                                    MachineInstr *CPEMI) {
  // Find the old entry. Eliminate it if it is no longer used.
  CPEntry *CPE = findConstPoolEntry(CPI, CPEMI);
  assert(CPE && "Unexpected!");
  if (--CPE->RefCount == 0) {
    removeDeadCPEMI(CPEMI);
    CPE->CPEMI = NULL;
    --NumCPEs;
    return true;
  }
  return false;
}

/// LookForCPEntryInRange - see if the currently referenced CPE is in range;
/// if not, see if an in-range clone of the CPE is in range, and if so,
/// change the data structures so the user references the clone.  Returns:
/// 0 = no existing entry found
/// 1 = entry found, and there were no code insertions or deletions
/// 2 = entry found, and there were code insertions or deletions
int MipsConstantIslands::findInRangeCPEntry(CPUser& U, unsigned UserOffset)
{
  MachineInstr *UserMI = U.MI;
  MachineInstr *CPEMI  = U.CPEMI;

  // Check to see if the CPE is already in-range.
  if (isCPEntryInRange(UserMI, UserOffset, CPEMI, U.getMaxDisp(), U.NegOk,
                       true)) {
    DEBUG(dbgs() << "In range\n");
    return 1;
  }

  // No.  Look for previously created clones of the CPE that are in range.
  unsigned CPI = CPEMI->getOperand(1).getIndex();
  std::vector<CPEntry> &CPEs = CPEntries[CPI];
  for (unsigned i = 0, e = CPEs.size(); i != e; ++i) {
    // We already tried this one
    if (CPEs[i].CPEMI == CPEMI)
      continue;
    // Removing CPEs can leave empty entries, skip
    if (CPEs[i].CPEMI == NULL)
      continue;
    if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI, U.getMaxDisp(),
                     U.NegOk)) {
      DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#"
                   << CPEs[i].CPI << "\n");
      // Point the CPUser node to the replacement
      U.CPEMI = CPEs[i].CPEMI;
      // Change the CPI in the instruction operand to refer to the clone.
      for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j)
        if (UserMI->getOperand(j).isCPI()) {
          UserMI->getOperand(j).setIndex(CPEs[i].CPI);
          break;
        }
      // Adjust the refcount of the clone...
      CPEs[i].RefCount++;
      // ...and the original.  If we didn't remove the old entry, none of the
      // addresses changed, so we don't need another pass.
      return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1;
    }
  }
  return 0;
}

/// LookForCPEntryInRange - see if the currently referenced CPE is in range;
/// This version checks if the longer form of the instruction can be used to
/// to satisfy things.
/// if not, see if an in-range clone of the CPE is in range, and if so,
/// change the data structures so the user references the clone.  Returns:
/// 0 = no existing entry found
/// 1 = entry found, and there were no code insertions or deletions
/// 2 = entry found, and there were code insertions or deletions
int MipsConstantIslands::findLongFormInRangeCPEntry
  (CPUser& U, unsigned UserOffset)
{
  MachineInstr *UserMI = U.MI;
  MachineInstr *CPEMI  = U.CPEMI;

  // Check to see if the CPE is already in-range.
  if (isCPEntryInRange(UserMI, UserOffset, CPEMI,
                       U.getLongFormMaxDisp(), U.NegOk,
                       true)) {
    DEBUG(dbgs() << "In range\n");
    UserMI->setDesc(TII->get(U.getLongFormOpcode()));
    U.setMaxDisp(U.getLongFormMaxDisp());
    return 2;  // instruction is longer length now
  }

  // No.  Look for previously created clones of the CPE that are in range.
  unsigned CPI = CPEMI->getOperand(1).getIndex();
  std::vector<CPEntry> &CPEs = CPEntries[CPI];
  for (unsigned i = 0, e = CPEs.size(); i != e; ++i) {
    // We already tried this one
    if (CPEs[i].CPEMI == CPEMI)
      continue;
    // Removing CPEs can leave empty entries, skip
    if (CPEs[i].CPEMI == NULL)
      continue;
    if (isCPEntryInRange(UserMI, UserOffset, CPEs[i].CPEMI,
                         U.getLongFormMaxDisp(), U.NegOk)) {
      DEBUG(dbgs() << "Replacing CPE#" << CPI << " with CPE#"
                   << CPEs[i].CPI << "\n");
      // Point the CPUser node to the replacement
      U.CPEMI = CPEs[i].CPEMI;
      // Change the CPI in the instruction operand to refer to the clone.
      for (unsigned j = 0, e = UserMI->getNumOperands(); j != e; ++j)
        if (UserMI->getOperand(j).isCPI()) {
          UserMI->getOperand(j).setIndex(CPEs[i].CPI);
          break;
        }
      // Adjust the refcount of the clone...
      CPEs[i].RefCount++;
      // ...and the original.  If we didn't remove the old entry, none of the
      // addresses changed, so we don't need another pass.
      return decrementCPEReferenceCount(CPI, CPEMI) ? 2 : 1;
    }
  }
  return 0;
}

/// getUnconditionalBrDisp - Returns the maximum displacement that can fit in
/// the specific unconditional branch instruction.
static inline unsigned getUnconditionalBrDisp(int Opc) {
  switch (Opc) {
  case Mips::Bimm16:
    return ((1<<10)-1)*2;
  case Mips::BimmX16:
    return ((1<<16)-1)*2;
  default:
    break;
  }
  return ((1<<16)-1)*2;
}

/// findAvailableWater - Look for an existing entry in the WaterList in which
/// we can place the CPE referenced from U so it's within range of U's MI.
/// Returns true if found, false if not.  If it returns true, WaterIter
/// is set to the WaterList entry.  
/// To ensure that this pass
/// terminates, the CPE location for a particular CPUser is only allowed to
/// move to a lower address, so search backward from the end of the list and
/// prefer the first water that is in range.
bool MipsConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset,
                                      water_iterator &WaterIter) {
  if (WaterList.empty())
    return false;

  unsigned BestGrowth = ~0u;
  for (water_iterator IP = prior(WaterList.end()), B = WaterList.begin();;
       --IP) {
    MachineBasicBlock* WaterBB = *IP;
    // Check if water is in range and is either at a lower address than the
    // current "high water mark" or a new water block that was created since
    // the previous iteration by inserting an unconditional branch.  In the
    // latter case, we want to allow resetting the high water mark back to
    // this new water since we haven't seen it before.  Inserting branches
    // should be relatively uncommon and when it does happen, we want to be
    // sure to take advantage of it for all the CPEs near that block, so that
    // we don't insert more branches than necessary.
    unsigned Growth;
    if (isWaterInRange(UserOffset, WaterBB, U, Growth) &&
        (WaterBB->getNumber() < U.HighWaterMark->getNumber() ||
         NewWaterList.count(WaterBB)) && Growth < BestGrowth) {
      // This is the least amount of required padding seen so far.
      BestGrowth = Growth;
      WaterIter = IP;
      DEBUG(dbgs() << "Found water after BB#" << WaterBB->getNumber()
                   << " Growth=" << Growth << '\n');

      // Keep looking unless it is perfect.
      if (BestGrowth == 0)
        return true;
    }
    if (IP == B)
      break;
  }
  return BestGrowth != ~0u;
}

/// createNewWater - No existing WaterList entry will work for
/// CPUsers[CPUserIndex], so create a place to put the CPE.  The end of the
/// block is used if in range, and the conditional branch munged so control
/// flow is correct.  Otherwise the block is split to create a hole with an
/// unconditional branch around it.  In either case NewMBB is set to a
/// block following which the new island can be inserted (the WaterList
/// is not adjusted).
void MipsConstantIslands::createNewWater(unsigned CPUserIndex,
                                        unsigned UserOffset,
                                        MachineBasicBlock *&NewMBB) {
  CPUser &U = CPUsers[CPUserIndex];
  MachineInstr *UserMI = U.MI;
  MachineInstr *CPEMI  = U.CPEMI;
  unsigned CPELogAlign = getCPELogAlign(CPEMI);
  MachineBasicBlock *UserMBB = UserMI->getParent();
  const BasicBlockInfo &UserBBI = BBInfo[UserMBB->getNumber()];

  // If the block does not end in an unconditional branch already, and if the
  // end of the block is within range, make new water there.  
  if (BBHasFallthrough(UserMBB)) {
    // Size of branch to insert.
    unsigned Delta = 2;
    // Compute the offset where the CPE will begin.
    unsigned CPEOffset = UserBBI.postOffset(CPELogAlign) + Delta;

    if (isOffsetInRange(UserOffset, CPEOffset, U)) {
      DEBUG(dbgs() << "Split at end of BB#" << UserMBB->getNumber()
            << format(", expected CPE offset %#x\n", CPEOffset));
      NewMBB = llvm::next(MachineFunction::iterator(UserMBB));
      // Add an unconditional branch from UserMBB to fallthrough block.  Record
      // it for branch lengthening; this new branch will not get out of range,
      // but if the preceding conditional branch is out of range, the targets
      // will be exchanged, and the altered branch may be out of range, so the
      // machinery has to know about it.
      int UncondBr = Mips::Bimm16;
      BuildMI(UserMBB, DebugLoc(), TII->get(UncondBr)).addMBB(NewMBB);
      unsigned MaxDisp = getUnconditionalBrDisp(UncondBr);
      ImmBranches.push_back(ImmBranch(&UserMBB->back(),
                                      MaxDisp, false, UncondBr));
      BBInfo[UserMBB->getNumber()].Size += Delta;
      adjustBBOffsetsAfter(UserMBB);
      return;
    }
  }

  // What a big block.  Find a place within the block to split it.  

  // Try to split the block so it's fully aligned.  Compute the latest split
  // point where we can add a 4-byte branch instruction, and then align to
  // LogAlign which is the largest possible alignment in the function.
  unsigned LogAlign = MF->getAlignment();
  assert(LogAlign >= CPELogAlign && "Over-aligned constant pool entry");
  unsigned BaseInsertOffset = UserOffset + U.getMaxDisp();
  DEBUG(dbgs() << format("Split in middle of big block before %#x",
                         BaseInsertOffset));

  // The 4 in the following is for the unconditional branch we'll be inserting
  // Alignment of the island is handled
  // inside isOffsetInRange.
  BaseInsertOffset -= 4;

  DEBUG(dbgs() << format(", adjusted to %#x", BaseInsertOffset)
               << " la=" << LogAlign << '\n');

  // This could point off the end of the block if we've already got constant
  // pool entries following this block; only the last one is in the water list.
  // Back past any possible branches (allow for a conditional and a maximally
  // long unconditional).
  if (BaseInsertOffset + 8 >= UserBBI.postOffset()) {
    BaseInsertOffset = UserBBI.postOffset() - 8;
    DEBUG(dbgs() << format("Move inside block: %#x\n", BaseInsertOffset));
  }
  unsigned EndInsertOffset = BaseInsertOffset + 4 +
    CPEMI->getOperand(2).getImm();
  MachineBasicBlock::iterator MI = UserMI;
  ++MI;
  unsigned CPUIndex = CPUserIndex+1;
  unsigned NumCPUsers = CPUsers.size();
  //MachineInstr *LastIT = 0;
  for (unsigned Offset = UserOffset+TII->GetInstSizeInBytes(UserMI);
       Offset < BaseInsertOffset;
       Offset += TII->GetInstSizeInBytes(MI),
       MI = llvm::next(MI)) {
    assert(MI != UserMBB->end() && "Fell off end of block");
    if (CPUIndex < NumCPUsers && CPUsers[CPUIndex].MI == MI) {
      CPUser &U = CPUsers[CPUIndex];
      if (!isOffsetInRange(Offset, EndInsertOffset, U)) {
        // Shift intertion point by one unit of alignment so it is within reach.
        BaseInsertOffset -= 1u << LogAlign;
        EndInsertOffset  -= 1u << LogAlign;
      }
      // This is overly conservative, as we don't account for CPEMIs being
      // reused within the block, but it doesn't matter much.  Also assume CPEs
      // are added in order with alignment padding.  We may eventually be able
      // to pack the aligned CPEs better.
      EndInsertOffset += U.CPEMI->getOperand(2).getImm();
      CPUIndex++;
    }
  }

  --MI;
  NewMBB = splitBlockBeforeInstr(MI);
}

/// handleConstantPoolUser - Analyze the specified user, checking to see if it
/// is out-of-range.  If so, pick up the constant pool value and move it some
/// place in-range.  Return true if we changed any addresses (thus must run
/// another pass of branch lengthening), false otherwise.
bool MipsConstantIslands::handleConstantPoolUser(unsigned CPUserIndex) {
  CPUser &U = CPUsers[CPUserIndex];
  MachineInstr *UserMI = U.MI;
  MachineInstr *CPEMI  = U.CPEMI;
  unsigned CPI = CPEMI->getOperand(1).getIndex();
  unsigned Size = CPEMI->getOperand(2).getImm();
  // Compute this only once, it's expensive.
  unsigned UserOffset = getUserOffset(U);

  // See if the current entry is within range, or there is a clone of it
  // in range.
  int result = findInRangeCPEntry(U, UserOffset);
  if (result==1) return false;
  else if (result==2) return true;


  // Look for water where we can place this CPE.
  MachineBasicBlock *NewIsland = MF->CreateMachineBasicBlock();
  MachineBasicBlock *NewMBB;
  water_iterator IP;
  if (findAvailableWater(U, UserOffset, IP)) {
    DEBUG(dbgs() << "Found water in range\n");
    MachineBasicBlock *WaterBB = *IP;

    // If the original WaterList entry was "new water" on this iteration,
    // propagate that to the new island.  This is just keeping NewWaterList
    // updated to match the WaterList, which will be updated below.
    if (NewWaterList.erase(WaterBB))
      NewWaterList.insert(NewIsland);

    // The new CPE goes before the following block (NewMBB).
    NewMBB = llvm::next(MachineFunction::iterator(WaterBB));

  } else {
    // No water found.
    // we first see if a longer form of the instrucion could have reached
    // the constant. in that case we won't bother to split
    if (!NoLoadRelaxation) {
      result = findLongFormInRangeCPEntry(U, UserOffset);
      if (result != 0) return true;
    }
    DEBUG(dbgs() << "No water found\n");
    createNewWater(CPUserIndex, UserOffset, NewMBB);

    // splitBlockBeforeInstr adds to WaterList, which is important when it is
    // called while handling branches so that the water will be seen on the
    // next iteration for constant pools, but in this context, we don't want
    // it.  Check for this so it will be removed from the WaterList.
    // Also remove any entry from NewWaterList.
    MachineBasicBlock *WaterBB = prior(MachineFunction::iterator(NewMBB));
    IP = std::find(WaterList.begin(), WaterList.end(), WaterBB);
    if (IP != WaterList.end())
      NewWaterList.erase(WaterBB);

    // We are adding new water.  Update NewWaterList.
    NewWaterList.insert(NewIsland);
  }

  // Remove the original WaterList entry; we want subsequent insertions in
  // this vicinity to go after the one we're about to insert.  This
  // considerably reduces the number of times we have to move the same CPE
  // more than once and is also important to ensure the algorithm terminates.
  if (IP != WaterList.end())
    WaterList.erase(IP);

  // Okay, we know we can put an island before NewMBB now, do it!
  MF->insert(NewMBB, NewIsland);

  // Update internal data structures to account for the newly inserted MBB.
  updateForInsertedWaterBlock(NewIsland);

  // Decrement the old entry, and remove it if refcount becomes 0.
  decrementCPEReferenceCount(CPI, CPEMI);

  // No existing clone of this CPE is within range.
  // We will be generating a new clone.  Get a UID for it.
  unsigned ID = createPICLabelUId();

  // Now that we have an island to add the CPE to, clone the original CPE and
  // add it to the island.
  U.HighWaterMark = NewIsland;
  U.CPEMI = BuildMI(NewIsland, DebugLoc(), TII->get(Mips::CONSTPOOL_ENTRY))
                .addImm(ID).addConstantPoolIndex(CPI).addImm(Size);
  CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1));
  ++NumCPEs;

  // Mark the basic block as aligned as required by the const-pool entry.
  NewIsland->setAlignment(getCPELogAlign(U.CPEMI));

  // Increase the size of the island block to account for the new entry.
  BBInfo[NewIsland->getNumber()].Size += Size;
  adjustBBOffsetsAfter(llvm::prior(MachineFunction::iterator(NewIsland)));



  // Finally, change the CPI in the instruction operand to be ID.
  for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i)
    if (UserMI->getOperand(i).isCPI()) {
      UserMI->getOperand(i).setIndex(ID);
      break;
    }

  DEBUG(dbgs() << "  Moved CPE to #" << ID << " CPI=" << CPI
        << format(" offset=%#x\n", BBInfo[NewIsland->getNumber()].Offset));

  return true;
}

/// removeDeadCPEMI - Remove a dead constant pool entry instruction. Update
/// sizes and offsets of impacted basic blocks.
void MipsConstantIslands::removeDeadCPEMI(MachineInstr *CPEMI) {
  MachineBasicBlock *CPEBB = CPEMI->getParent();
  unsigned Size = CPEMI->getOperand(2).getImm();
  CPEMI->eraseFromParent();
  BBInfo[CPEBB->getNumber()].Size -= Size;
  // All succeeding offsets have the current size value added in, fix this.
  if (CPEBB->empty()) {
    BBInfo[CPEBB->getNumber()].Size = 0;

    // This block no longer needs to be aligned.
    CPEBB->setAlignment(0);
  } else
    // Entries are sorted by descending alignment, so realign from the front.
    CPEBB->setAlignment(getCPELogAlign(CPEBB->begin()));

  adjustBBOffsetsAfter(CPEBB);
  // An island has only one predecessor BB and one successor BB. Check if
  // this BB's predecessor jumps directly to this BB's successor. This
  // shouldn't happen currently.
  assert(!BBIsJumpedOver(CPEBB) && "How did this happen?");
  // FIXME: remove the empty blocks after all the work is done?
}

/// removeUnusedCPEntries - Remove constant pool entries whose refcounts
/// are zero.
bool MipsConstantIslands::removeUnusedCPEntries() {
  unsigned MadeChange = false;
  for (unsigned i = 0, e = CPEntries.size(); i != e; ++i) {
      std::vector<CPEntry> &CPEs = CPEntries[i];
      for (unsigned j = 0, ee = CPEs.size(); j != ee; ++j) {
        if (CPEs[j].RefCount == 0 && CPEs[j].CPEMI) {
          removeDeadCPEMI(CPEs[j].CPEMI);
          CPEs[j].CPEMI = NULL;
          MadeChange = true;
        }
      }
  }
  return MadeChange;
}

/// isBBInRange - Returns true if the distance between specific MI and
/// specific BB can fit in MI's displacement field.
bool MipsConstantIslands::isBBInRange
  (MachineInstr *MI,MachineBasicBlock *DestBB, unsigned MaxDisp) {

unsigned PCAdj = 4;

  unsigned BrOffset   = getOffsetOf(MI) + PCAdj;
  unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;

  DEBUG(dbgs() << "Branch of destination BB#" << DestBB->getNumber()
               << " from BB#" << MI->getParent()->getNumber()
               << " max delta=" << MaxDisp
               << " from " << getOffsetOf(MI) << " to " << DestOffset
               << " offset " << int(DestOffset-BrOffset) << "\t" << *MI);

  if (BrOffset <= DestOffset) {
    // Branch before the Dest.
    if (DestOffset-BrOffset <= MaxDisp)
      return true;
  } else {
    if (BrOffset-DestOffset <= MaxDisp)
      return true;
  }
  return false;
}

/// fixupImmediateBr - Fix up an immediate branch whose destination is too far
/// away to fit in its displacement field.
bool MipsConstantIslands::fixupImmediateBr(ImmBranch &Br) {
  MachineInstr *MI = Br.MI;
  unsigned TargetOperand = branchTargetOperand(MI);
  MachineBasicBlock *DestBB = MI->getOperand(TargetOperand).getMBB();

  // Check to see if the DestBB is already in-range.
  if (isBBInRange(MI, DestBB, Br.MaxDisp))
    return false;

  if (!Br.isCond)
    return fixupUnconditionalBr(Br);
  return fixupConditionalBr(Br);
}

/// fixupUnconditionalBr - Fix up an unconditional branch whose destination is
/// too far away to fit in its displacement field. If the LR register has been
/// spilled in the epilogue, then we can use BL to implement a far jump.
/// Otherwise, add an intermediate branch instruction to a branch.
bool
MipsConstantIslands::fixupUnconditionalBr(ImmBranch &Br) {
  MachineInstr *MI = Br.MI;
  MachineBasicBlock *MBB = MI->getParent();
  MachineBasicBlock *DestBB = MI->getOperand(0).getMBB();
  // Use BL to implement far jump.
  unsigned BimmX16MaxDisp = ((1 << 16)-1) * 2;
  if (isBBInRange(MI, DestBB, BimmX16MaxDisp)) {
    Br.MaxDisp = BimmX16MaxDisp;
    MI->setDesc(TII->get(Mips::BimmX16));
  }
  else {
    // need to give the math a more careful look here
    // this is really a segment address and not
    // a PC relative address. FIXME. But I think that
    // just reducing the bits by 1 as I've done is correct.
    // The basic block we are branching too much be longword aligned.
    // we know that RA is saved because we always save it right now.
    // this requirement will be relaxed later but we also have an alternate
    // way to implement this that I will implement that does not need jal.
    // We should have a way to back out this alignment restriction if we "can" later.
    // but it is not harmful.
    //
    DestBB->setAlignment(2);
    Br.MaxDisp = ((1<<24)-1) * 2;
    MI->setDesc(TII->get(Mips::JalB16));
  }
  BBInfo[MBB->getNumber()].Size += 2;
  adjustBBOffsetsAfter(MBB);
  HasFarJump = true;
  ++NumUBrFixed;

  DEBUG(dbgs() << "  Changed B to long jump " << *MI);

  return true;
}


/// fixupConditionalBr - Fix up a conditional branch whose destination is too
/// far away to fit in its displacement field. It is converted to an inverse
/// conditional branch + an unconditional branch to the destination.
bool
MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) {
  MachineInstr *MI = Br.MI;
  unsigned TargetOperand = branchTargetOperand(MI);
  MachineBasicBlock *DestBB = MI->getOperand(TargetOperand).getMBB();
  unsigned Opcode = MI->getOpcode();
  unsigned LongFormOpcode = longformBranchOpcode(Opcode);
  unsigned LongFormMaxOff = branchMaxOffsets(LongFormOpcode);

  // Check to see if the DestBB is already in-range.
  if (isBBInRange(MI, DestBB, LongFormMaxOff)) {
    Br.MaxDisp = LongFormMaxOff;
    MI->setDesc(TII->get(LongFormOpcode));
    return true;
  }

  // Add an unconditional branch to the destination and invert the branch
  // condition to jump over it:
  // bteqz L1
  // =>
  // bnez L2
  // b   L1
  // L2:

  // If the branch is at the end of its MBB and that has a fall-through block,
  // direct the updated conditional branch to the fall-through block. Otherwise,
  // split the MBB before the next instruction.
  MachineBasicBlock *MBB = MI->getParent();
  MachineInstr *BMI = &MBB->back();
  bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB);
  unsigned OppositeBranchOpcode = TII->getOppositeBranchOpc(Opcode);
 
  ++NumCBrFixed;
  if (BMI != MI) {
    if (llvm::next(MachineBasicBlock::iterator(MI)) == prior(MBB->end()) &&
        isUnconditionalBranch(BMI->getOpcode())) {
      // Last MI in the BB is an unconditional branch. Can we simply invert the
      // condition and swap destinations:
      // beqz L1
      // b   L2
      // =>
      // bnez L2
      // b   L1
      unsigned BMITargetOperand = branchTargetOperand(BMI);
      MachineBasicBlock *NewDest = 
        BMI->getOperand(BMITargetOperand).getMBB();
      if (isBBInRange(MI, NewDest, Br.MaxDisp)) {
        DEBUG(dbgs() << "  Invert Bcc condition and swap its destination with "
                     << *BMI);
        MI->setDesc(TII->get(OppositeBranchOpcode));
        BMI->getOperand(BMITargetOperand).setMBB(DestBB);
        MI->getOperand(TargetOperand).setMBB(NewDest);
        return true;
      }
    }
  }


  if (NeedSplit) {
    splitBlockBeforeInstr(MI);
    // No need for the branch to the next block. We're adding an unconditional
    // branch to the destination.
    int delta = TII->GetInstSizeInBytes(&MBB->back());
    BBInfo[MBB->getNumber()].Size -= delta;
    MBB->back().eraseFromParent();
    // BBInfo[SplitBB].Offset is wrong temporarily, fixed below
  }
  MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB));

  DEBUG(dbgs() << "  Insert B to BB#" << DestBB->getNumber()
               << " also invert condition and change dest. to BB#"
               << NextBB->getNumber() << "\n");

  // Insert a new conditional branch and a new unconditional branch.
  // Also update the ImmBranch as well as adding a new entry for the new branch.
  if (MI->getNumExplicitOperands() == 2) {
    BuildMI(MBB, DebugLoc(), TII->get(OppositeBranchOpcode))
           .addReg(MI->getOperand(0).getReg())
           .addMBB(NextBB);
  } else {
    BuildMI(MBB, DebugLoc(), TII->get(OppositeBranchOpcode))
           .addMBB(NextBB);
  }
  Br.MI = &MBB->back();
  BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back());
  BuildMI(MBB, DebugLoc(), TII->get(Br.UncondBr)).addMBB(DestBB);
  BBInfo[MBB->getNumber()].Size += TII->GetInstSizeInBytes(&MBB->back());
  unsigned MaxDisp = getUnconditionalBrDisp(Br.UncondBr);
  ImmBranches.push_back(ImmBranch(&MBB->back(), MaxDisp, false, Br.UncondBr));

  // Remove the old conditional branch.  It may or may not still be in MBB.
  BBInfo[MI->getParent()->getNumber()].Size -= TII->GetInstSizeInBytes(MI);
  MI->eraseFromParent();
  adjustBBOffsetsAfter(MBB);
  return true;
}


void MipsConstantIslands::prescanForConstants() {
  unsigned J = 0;
  (void)J;
  for (MachineFunction::iterator B =
         MF->begin(), E = MF->end(); B != E; ++B) {
    for (MachineBasicBlock::instr_iterator I =
        B->instr_begin(), EB = B->instr_end(); I != EB; ++I) {
      switch(I->getDesc().getOpcode()) {
        case Mips::LwConstant32: {
          PrescannedForConstants = true;
          DEBUG(dbgs() << "constant island constant " << *I << "\n");
          J = I->getNumOperands();
          DEBUG(dbgs() << "num operands " << J  << "\n");
          MachineOperand& Literal = I->getOperand(1);
          if (Literal.isImm()) {
            int64_t V = Literal.getImm();
            DEBUG(dbgs() << "literal " << V  << "\n");
            Type *Int32Ty =
              Type::getInt32Ty(MF->getFunction()->getContext());
            const Constant *C = ConstantInt::get(Int32Ty, V);
            unsigned index = MCP->getConstantPoolIndex(C, 4);
            I->getOperand(2).ChangeToImmediate(index);
            DEBUG(dbgs() << "constant island constant " << *I << "\n");
            I->setDesc(TII->get(Mips::LwRxPcTcp16));
            I->RemoveOperand(1);
            I->RemoveOperand(1);
            I->addOperand(MachineOperand::CreateCPI(index, 0));
            I->addOperand(MachineOperand::CreateImm(4));
          }
          break;
        }
        default:
          break;
      }
    }
  }
}