summaryrefslogtreecommitdiffstats
path: root/lib/Transforms/Scalar/SCCP.cpp
blob: 4701d2f740564217f3f7a29686d1ff8765fdd892 (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
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
//===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements sparse conditional constant propagation and merging:
//
// Specifically, this:
//   * Assumes values are constant unless proven otherwise
//   * Assumes BasicBlocks are dead unless proven otherwise
//   * Proves values to be constant, and replaces them with constants
//   * Proves conditional branches to be unconditional
//
// Notice that:
//   * This pass has a habit of making definitions be dead.  It is a good idea
//     to to run a DCE pass sometime after running this pass.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sccp"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
#include <map>
using namespace llvm;

STATISTIC(NumInstRemoved, "Number of instructions removed");
STATISTIC(NumDeadBlocks , "Number of basic blocks unreachable");

STATISTIC(IPNumInstRemoved, "Number of instructions removed by IPSCCP");
STATISTIC(IPNumDeadBlocks , "Number of basic blocks unreachable by IPSCCP");
STATISTIC(IPNumArgsElimed ,"Number of arguments constant propagated by IPSCCP");
STATISTIC(IPNumGlobalConst, "Number of globals found to be constant by IPSCCP");

namespace {
/// LatticeVal class - This class represents the different lattice values that
/// an LLVM value may occupy.  It is a simple class with value semantics.
///
class LatticeVal {
  enum {
    /// undefined - This LLVM Value has no known value yet.
    undefined,
    
    /// constant - This LLVM Value has a specific constant value.
    constant,

    /// forcedconstant - This LLVM Value was thought to be undef until
    /// ResolvedUndefsIn.  This is treated just like 'constant', but if merged
    /// with another (different) constant, it goes to overdefined, instead of
    /// asserting.
    forcedconstant,
    
    /// overdefined - This instruction is not known to be constant, and we know
    /// it has a value.
    overdefined
  } LatticeValue;    // The current lattice position
  
  Constant *ConstantVal; // If Constant value, the current value
public:
  inline LatticeVal() : LatticeValue(undefined), ConstantVal(0) {}
  
  // markOverdefined - Return true if this is a new status to be in...
  inline bool markOverdefined() {
    if (LatticeValue != overdefined) {
      LatticeValue = overdefined;
      return true;
    }
    return false;
  }

  // markConstant - Return true if this is a new status for us.
  inline bool markConstant(Constant *V) {
    if (LatticeValue != constant) {
      if (LatticeValue == undefined) {
        LatticeValue = constant;
        assert(V && "Marking constant with NULL");
        ConstantVal = V;
      } else {
        assert(LatticeValue == forcedconstant && 
               "Cannot move from overdefined to constant!");
        // Stay at forcedconstant if the constant is the same.
        if (V == ConstantVal) return false;
        
        // Otherwise, we go to overdefined.  Assumptions made based on the
        // forced value are possibly wrong.  Assuming this is another constant
        // could expose a contradiction.
        LatticeValue = overdefined;
      }
      return true;
    } else {
      assert(ConstantVal == V && "Marking constant with different value");
    }
    return false;
  }

  inline void markForcedConstant(Constant *V) {
    assert(LatticeValue == undefined && "Can't force a defined value!");
    LatticeValue = forcedconstant;
    ConstantVal = V;
  }
  
  inline bool isUndefined() const { return LatticeValue == undefined; }
  inline bool isConstant() const {
    return LatticeValue == constant || LatticeValue == forcedconstant;
  }
  inline bool isOverdefined() const { return LatticeValue == overdefined; }

  inline Constant *getConstant() const {
    assert(isConstant() && "Cannot get the constant of a non-constant!");
    return ConstantVal;
  }
};

//===----------------------------------------------------------------------===//
//
/// SCCPSolver - This class is a general purpose solver for Sparse Conditional
/// Constant Propagation.
///
class SCCPSolver : public InstVisitor<SCCPSolver> {
  LLVMContext *Context;
  DenseSet<BasicBlock*> BBExecutable;// The basic blocks that are executable
  std::map<Value*, LatticeVal> ValueState;  // The state each value is in.

  /// GlobalValue - If we are tracking any values for the contents of a global
  /// variable, we keep a mapping from the constant accessor to the element of
  /// the global, to the currently known value.  If the value becomes
  /// overdefined, it's entry is simply removed from this map.
  DenseMap<GlobalVariable*, LatticeVal> TrackedGlobals;

  /// TrackedRetVals - If we are tracking arguments into and the return
  /// value out of a function, it will have an entry in this map, indicating
  /// what the known return value for the function is.
  DenseMap<Function*, LatticeVal> TrackedRetVals;

  /// TrackedMultipleRetVals - Same as TrackedRetVals, but used for functions
  /// that return multiple values.
  DenseMap<std::pair<Function*, unsigned>, LatticeVal> TrackedMultipleRetVals;

  // The reason for two worklists is that overdefined is the lowest state
  // on the lattice, and moving things to overdefined as fast as possible
  // makes SCCP converge much faster.
  // By having a separate worklist, we accomplish this because everything
  // possibly overdefined will become overdefined at the soonest possible
  // point.
  SmallVector<Value*, 64> OverdefinedInstWorkList;
  SmallVector<Value*, 64> InstWorkList;


  SmallVector<BasicBlock*, 64>  BBWorkList;  // The BasicBlock work list

  /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
  /// overdefined, despite the fact that the PHI node is overdefined.
  std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;

  /// KnownFeasibleEdges - Entries in this set are edges which have already had
  /// PHI nodes retriggered.
  typedef std::pair<BasicBlock*, BasicBlock*> Edge;
  DenseSet<Edge> KnownFeasibleEdges;
public:
  void setContext(LLVMContext *C) { Context = C; }

  /// MarkBlockExecutable - This method can be used by clients to mark all of
  /// the blocks that are known to be intrinsically live in the processed unit.
  void MarkBlockExecutable(BasicBlock *BB) {
    DEBUG(errs() << "Marking Block Executable: " << BB->getName() << "\n");
    BBExecutable.insert(BB);   // Basic block is executable!
    BBWorkList.push_back(BB);  // Add the block to the work list!
  }

  /// TrackValueOfGlobalVariable - Clients can use this method to
  /// inform the SCCPSolver that it should track loads and stores to the
  /// specified global variable if it can.  This is only legal to call if
  /// performing Interprocedural SCCP.
  void TrackValueOfGlobalVariable(GlobalVariable *GV) {
    const Type *ElTy = GV->getType()->getElementType();
    if (ElTy->isFirstClassType()) {
      LatticeVal &IV = TrackedGlobals[GV];
      if (!isa<UndefValue>(GV->getInitializer()))
        IV.markConstant(GV->getInitializer());
    }
  }

  /// AddTrackedFunction - If the SCCP solver is supposed to track calls into
  /// and out of the specified function (which cannot have its address taken),
  /// this method must be called.
  void AddTrackedFunction(Function *F) {
    assert(F->hasLocalLinkage() && "Can only track internal functions!");
    // Add an entry, F -> undef.
    if (const StructType *STy = dyn_cast<StructType>(F->getReturnType())) {
      for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
        TrackedMultipleRetVals.insert(std::make_pair(std::make_pair(F, i),
                                                     LatticeVal()));
    } else
      TrackedRetVals.insert(std::make_pair(F, LatticeVal()));
  }

  /// Solve - Solve for constants and executable blocks.
  ///
  void Solve();

  /// ResolvedUndefsIn - While solving the dataflow for a function, we assume
  /// that branches on undef values cannot reach any of their successors.
  /// However, this is not a safe assumption.  After we solve dataflow, this
  /// method should be use to handle this.  If this returns true, the solver
  /// should be rerun.
  bool ResolvedUndefsIn(Function &F);

  bool isBlockExecutable(BasicBlock *BB) const {
    return BBExecutable.count(BB);
  }

  /// getValueMapping - Once we have solved for constants, return the mapping of
  /// LLVM values to LatticeVals.
  std::map<Value*, LatticeVal> &getValueMapping() {
    return ValueState;
  }

  /// getTrackedRetVals - Get the inferred return value map.
  ///
  const DenseMap<Function*, LatticeVal> &getTrackedRetVals() {
    return TrackedRetVals;
  }

  /// getTrackedGlobals - Get and return the set of inferred initializers for
  /// global variables.
  const DenseMap<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
    return TrackedGlobals;
  }

  inline void markOverdefined(Value *V) {
    markOverdefined(ValueState[V], V);
  }

private:
  // markConstant - Make a value be marked as "constant".  If the value
  // is not already a constant, add it to the instruction work list so that
  // the users of the instruction are updated later.
  //
  inline void markConstant(LatticeVal &IV, Value *V, Constant *C) {
    if (IV.markConstant(C)) {
      DEBUG(errs() << "markConstant: " << *C << ": " << *V << '\n');
      InstWorkList.push_back(V);
    }
  }
  
  inline void markForcedConstant(LatticeVal &IV, Value *V, Constant *C) {
    IV.markForcedConstant(C);
    DEBUG(errs() << "markForcedConstant: " << *C << ": " << *V << '\n');
    InstWorkList.push_back(V);
  }
  
  inline void markConstant(Value *V, Constant *C) {
    markConstant(ValueState[V], V, C);
  }

  // markOverdefined - Make a value be marked as "overdefined". If the
  // value is not already overdefined, add it to the overdefined instruction
  // work list so that the users of the instruction are updated later.
  inline void markOverdefined(LatticeVal &IV, Value *V) {
    if (IV.markOverdefined()) {
      DEBUG(errs() << "markOverdefined: ";
            if (Function *F = dyn_cast<Function>(V))
              errs() << "Function '" << F->getName() << "'\n";
            else
              errs() << *V << '\n');
      // Only instructions go on the work list
      OverdefinedInstWorkList.push_back(V);
    }
  }

  inline void mergeInValue(LatticeVal &IV, Value *V, LatticeVal &MergeWithV) {
    if (IV.isOverdefined() || MergeWithV.isUndefined())
      return;  // Noop.
    if (MergeWithV.isOverdefined())
      markOverdefined(IV, V);
    else if (IV.isUndefined())
      markConstant(IV, V, MergeWithV.getConstant());
    else if (IV.getConstant() != MergeWithV.getConstant())
      markOverdefined(IV, V);
  }
  
  inline void mergeInValue(Value *V, LatticeVal &MergeWithV) {
    return mergeInValue(ValueState[V], V, MergeWithV);
  }


  // getValueState - Return the LatticeVal object that corresponds to the value.
  // This function is necessary because not all values should start out in the
  // underdefined state... Argument's should be overdefined, and
  // constants should be marked as constants.  If a value is not known to be an
  // Instruction object, then use this accessor to get its value from the map.
  //
  inline LatticeVal &getValueState(Value *V) {
    std::map<Value*, LatticeVal>::iterator I = ValueState.find(V);
    if (I != ValueState.end()) return I->second;  // Common case, in the map

    if (Constant *C = dyn_cast<Constant>(V)) {
      if (isa<UndefValue>(V)) {
        // Nothing to do, remain undefined.
      } else {
        LatticeVal &LV = ValueState[C];
        LV.markConstant(C);          // Constants are constant
        return LV;
      }
    }
    // All others are underdefined by default...
    return ValueState[V];
  }

  // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
  // work list if it is not already executable...
  //
  void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
    if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
      return;  // This edge is already known to be executable!

    if (BBExecutable.count(Dest)) {
      DEBUG(errs() << "Marking Edge Executable: " << Source->getName()
            << " -> " << Dest->getName() << "\n");

      // The destination is already executable, but we just made an edge
      // feasible that wasn't before.  Revisit the PHI nodes in the block
      // because they have potentially new operands.
      for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
        visitPHINode(*cast<PHINode>(I));

    } else {
      MarkBlockExecutable(Dest);
    }
  }

  // getFeasibleSuccessors - Return a vector of booleans to indicate which
  // successors are reachable from a given terminator instruction.
  //
  void getFeasibleSuccessors(TerminatorInst &TI, SmallVector<bool, 16> &Succs);

  // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
  // block to the 'To' basic block is currently feasible...
  //
  bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);

  // OperandChangedState - This method is invoked on all of the users of an
  // instruction that was just changed state somehow....  Based on this
  // information, we need to update the specified user of this instruction.
  //
  void OperandChangedState(User *U) {
    // Only instructions use other variable values!
    Instruction &I = cast<Instruction>(*U);
    if (BBExecutable.count(I.getParent()))   // Inst is executable?
      visit(I);
  }

private:
  friend class InstVisitor<SCCPSolver>;

  // visit implementations - Something changed in this instruction... Either an
  // operand made a transition, or the instruction is newly executable.  Change
  // the value type of I to reflect these changes if appropriate.
  //
  void visitPHINode(PHINode &I);

  // Terminators
  void visitReturnInst(ReturnInst &I);
  void visitTerminatorInst(TerminatorInst &TI);

  void visitCastInst(CastInst &I);
  void visitSelectInst(SelectInst &I);
  void visitBinaryOperator(Instruction &I);
  void visitCmpInst(CmpInst &I);
  void visitExtractElementInst(ExtractElementInst &I);
  void visitInsertElementInst(InsertElementInst &I);
  void visitShuffleVectorInst(ShuffleVectorInst &I);
  void visitExtractValueInst(ExtractValueInst &EVI);
  void visitInsertValueInst(InsertValueInst &IVI);

  // Instructions that cannot be folded away...
  void visitStoreInst     (Instruction &I);
  void visitLoadInst      (LoadInst &I);
  void visitGetElementPtrInst(GetElementPtrInst &I);
  void visitCallInst      (CallInst &I) {
    if (isFreeCall(&I))
      return;
    visitCallSite(CallSite::get(&I));
  }
  void visitInvokeInst    (InvokeInst &II) {
    visitCallSite(CallSite::get(&II));
    visitTerminatorInst(II);
  }
  void visitCallSite      (CallSite CS);
  void visitUnwindInst    (TerminatorInst &I) { /*returns void*/ }
  void visitUnreachableInst(TerminatorInst &I) { /*returns void*/ }
  void visitAllocaInst    (Instruction &I) { markOverdefined(&I); }
  void visitVANextInst    (Instruction &I) { markOverdefined(&I); }
  void visitVAArgInst     (Instruction &I) { markOverdefined(&I); }

  void visitInstruction(Instruction &I) {
    // If a new instruction is added to LLVM that we don't handle...
    errs() << "SCCP: Don't know how to handle: " << I;
    markOverdefined(&I);   // Just in case
  }
};

} // end anonymous namespace


// getFeasibleSuccessors - Return a vector of booleans to indicate which
// successors are reachable from a given terminator instruction.
//
void SCCPSolver::getFeasibleSuccessors(TerminatorInst &TI,
                                       SmallVector<bool, 16> &Succs) {
  Succs.resize(TI.getNumSuccessors());
  if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
    if (BI->isUnconditional()) {
      Succs[0] = true;
    } else {
      LatticeVal &BCValue = getValueState(BI->getCondition());
      if (BCValue.isOverdefined() ||
          (BCValue.isConstant() && !isa<ConstantInt>(BCValue.getConstant()))) {
        // Overdefined condition variables, and branches on unfoldable constant
        // conditions, mean the branch could go either way.
        Succs[0] = Succs[1] = true;
      } else if (BCValue.isConstant()) {
        // Constant condition variables mean the branch can only go a single way
        Succs[BCValue.getConstant() == ConstantInt::getFalse(*Context)] = true;
      }
    }
  } else if (isa<InvokeInst>(&TI)) {
    // Invoke instructions successors are always executable.
    Succs[0] = Succs[1] = true;
  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
    LatticeVal &SCValue = getValueState(SI->getCondition());
    if (SCValue.isOverdefined() ||   // Overdefined condition?
        (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
      // All destinations are executable!
      Succs.assign(TI.getNumSuccessors(), true);
    } else if (SCValue.isConstant())
      Succs[SI->findCaseValue(cast<ConstantInt>(SCValue.getConstant()))] = true;
  } else {
    llvm_unreachable("SCCP: Don't know how to handle this terminator!");
  }
}


// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
// block to the 'To' basic block is currently feasible...
//
bool SCCPSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
  assert(BBExecutable.count(To) && "Dest should always be alive!");

  // Make sure the source basic block is executable!!
  if (!BBExecutable.count(From)) return false;

  // Check to make sure this edge itself is actually feasible now...
  TerminatorInst *TI = From->getTerminator();
  if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
    if (BI->isUnconditional())
      return true;
    else {
      LatticeVal &BCValue = getValueState(BI->getCondition());
      if (BCValue.isOverdefined()) {
        // Overdefined condition variables mean the branch could go either way.
        return true;
      } else if (BCValue.isConstant()) {
        // Not branching on an evaluatable constant?
        if (!isa<ConstantInt>(BCValue.getConstant())) return true;

        // Constant condition variables mean the branch can only go a single way
        return BI->getSuccessor(BCValue.getConstant() ==
                                       ConstantInt::getFalse(*Context)) == To;
      }
      return false;
    }
  } else if (isa<InvokeInst>(TI)) {
    // Invoke instructions successors are always executable.
    return true;
  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
    LatticeVal &SCValue = getValueState(SI->getCondition());
    if (SCValue.isOverdefined()) {  // Overdefined condition?
      // All destinations are executable!
      return true;
    } else if (SCValue.isConstant()) {
      Constant *CPV = SCValue.getConstant();
      if (!isa<ConstantInt>(CPV))
        return true;  // not a foldable constant?

      // Make sure to skip the "default value" which isn't a value
      for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
        if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
          return SI->getSuccessor(i) == To;

      // Constant value not equal to any of the branches... must execute
      // default branch then...
      return SI->getDefaultDest() == To;
    }
    return false;
  } else {
#ifndef NDEBUG
    errs() << "Unknown terminator instruction: " << *TI << '\n';
#endif
    llvm_unreachable(0);
  }
}

// visit Implementations - Something changed in this instruction... Either an
// operand made a transition, or the instruction is newly executable.  Change
// the value type of I to reflect these changes if appropriate.  This method
// makes sure to do the following actions:
//
// 1. If a phi node merges two constants in, and has conflicting value coming
//    from different branches, or if the PHI node merges in an overdefined
//    value, then the PHI node becomes overdefined.
// 2. If a phi node merges only constants in, and they all agree on value, the
//    PHI node becomes a constant value equal to that.
// 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
// 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
// 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
// 6. If a conditional branch has a value that is constant, make the selected
//    destination executable
// 7. If a conditional branch has a value that is overdefined, make all
//    successors executable.
//
void SCCPSolver::visitPHINode(PHINode &PN) {
  LatticeVal &PNIV = getValueState(&PN);
  if (PNIV.isOverdefined()) {
    // There may be instructions using this PHI node that are not overdefined
    // themselves.  If so, make sure that they know that the PHI node operand
    // changed.
    std::multimap<PHINode*, Instruction*>::iterator I, E;
    tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
    if (I != E) {
      SmallVector<Instruction*, 16> Users;
      for (; I != E; ++I) Users.push_back(I->second);
      while (!Users.empty()) {
        visit(Users.back());
        Users.pop_back();
      }
    }
    return;  // Quick exit
  }

  // Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
  // and slow us down a lot.  Just mark them overdefined.
  if (PN.getNumIncomingValues() > 64) {
    markOverdefined(PNIV, &PN);
    return;
  }

  // Look at all of the executable operands of the PHI node.  If any of them
  // are overdefined, the PHI becomes overdefined as well.  If they are all
  // constant, and they agree with each other, the PHI becomes the identical
  // constant.  If they are constant and don't agree, the PHI is overdefined.
  // If there are no executable operands, the PHI remains undefined.
  //
  Constant *OperandVal = 0;
  for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
    LatticeVal &IV = getValueState(PN.getIncomingValue(i));
    if (IV.isUndefined()) continue;  // Doesn't influence PHI node.

    if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
      if (IV.isOverdefined()) {   // PHI node becomes overdefined!
        markOverdefined(&PN);
        return;
      }

      if (OperandVal == 0) {   // Grab the first value...
        OperandVal = IV.getConstant();
      } else {                // Another value is being merged in!
        // There is already a reachable operand.  If we conflict with it,
        // then the PHI node becomes overdefined.  If we agree with it, we
        // can continue on.

        // Check to see if there are two different constants merging...
        if (IV.getConstant() != OperandVal) {
          // Yes there is.  This means the PHI node is not constant.
          // You must be overdefined poor PHI.
          //
          markOverdefined(&PN);    // The PHI node now becomes overdefined
          return;    // I'm done analyzing you
        }
      }
    }
  }

  // If we exited the loop, this means that the PHI node only has constant
  // arguments that agree with each other(and OperandVal is the constant) or
  // OperandVal is null because there are no defined incoming arguments.  If
  // this is the case, the PHI remains undefined.
  //
  if (OperandVal)
    markConstant(&PN, OperandVal);      // Acquire operand value
}

void SCCPSolver::visitReturnInst(ReturnInst &I) {
  if (I.getNumOperands() == 0) return;  // Ret void

  Function *F = I.getParent()->getParent();
  // If we are tracking the return value of this function, merge it in.
  if (!F->hasLocalLinkage())
    return;

  if (!TrackedRetVals.empty() && I.getNumOperands() == 1) {
    DenseMap<Function*, LatticeVal>::iterator TFRVI =
      TrackedRetVals.find(F);
    if (TFRVI != TrackedRetVals.end() &&
        !TFRVI->second.isOverdefined()) {
      LatticeVal &IV = getValueState(I.getOperand(0));
      mergeInValue(TFRVI->second, F, IV);
      return;
    }
  }
  
  // Handle functions that return multiple values.
  if (!TrackedMultipleRetVals.empty() && I.getNumOperands() > 1) {
    for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
      DenseMap<std::pair<Function*, unsigned>, LatticeVal>::iterator
        It = TrackedMultipleRetVals.find(std::make_pair(F, i));
      if (It == TrackedMultipleRetVals.end()) break;
      mergeInValue(It->second, F, getValueState(I.getOperand(i)));
    }
  } else if (!TrackedMultipleRetVals.empty() &&
             I.getNumOperands() == 1 &&
             isa<StructType>(I.getOperand(0)->getType())) {
    for (unsigned i = 0, e = I.getOperand(0)->getType()->getNumContainedTypes();
         i != e; ++i) {
      DenseMap<std::pair<Function*, unsigned>, LatticeVal>::iterator
        It = TrackedMultipleRetVals.find(std::make_pair(F, i));
      if (It == TrackedMultipleRetVals.end()) break;
      if (Value *Val = FindInsertedValue(I.getOperand(0), i, I.getContext()))
        mergeInValue(It->second, F, getValueState(Val));
    }
  }
}

void SCCPSolver::visitTerminatorInst(TerminatorInst &TI) {
  SmallVector<bool, 16> SuccFeasible;
  getFeasibleSuccessors(TI, SuccFeasible);

  BasicBlock *BB = TI.getParent();

  // Mark all feasible successors executable...
  for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
    if (SuccFeasible[i])
      markEdgeExecutable(BB, TI.getSuccessor(i));
}

void SCCPSolver::visitCastInst(CastInst &I) {
  Value *V = I.getOperand(0);
  LatticeVal &VState = getValueState(V);
  if (VState.isOverdefined())          // Inherit overdefinedness of operand
    markOverdefined(&I);
  else if (VState.isConstant())        // Propagate constant value
    markConstant(&I, ConstantExpr::getCast(I.getOpcode(), 
                                           VState.getConstant(), I.getType()));
}

void SCCPSolver::visitExtractValueInst(ExtractValueInst &EVI) {
  Value *Aggr = EVI.getAggregateOperand();

  // If the operand to the extractvalue is an undef, the result is undef.
  if (isa<UndefValue>(Aggr))
    return;

  // Currently only handle single-index extractvalues.
  if (EVI.getNumIndices() != 1) {
    markOverdefined(&EVI);
    return;
  }
  
  Function *F = 0;
  if (CallInst *CI = dyn_cast<CallInst>(Aggr))
    F = CI->getCalledFunction();
  else if (InvokeInst *II = dyn_cast<InvokeInst>(Aggr))
    F = II->getCalledFunction();

  // TODO: If IPSCCP resolves the callee of this function, we could propagate a
  // result back!
  if (F == 0 || TrackedMultipleRetVals.empty()) {
    markOverdefined(&EVI);
    return;
  }
  
  // See if we are tracking the result of the callee.  If not tracking this
  // function (for example, it is a declaration) just move to overdefined.
  if (!TrackedMultipleRetVals.count(std::make_pair(F, *EVI.idx_begin()))) {
    markOverdefined(&EVI);
    return;
  }
  
  // Otherwise, the value will be merged in here as a result of CallSite
  // handling.
}

void SCCPSolver::visitInsertValueInst(InsertValueInst &IVI) {
  Value *Aggr = IVI.getAggregateOperand();
  Value *Val = IVI.getInsertedValueOperand();

  // If the operands to the insertvalue are undef, the result is undef.
  if (isa<UndefValue>(Aggr) && isa<UndefValue>(Val))
    return;

  // Currently only handle single-index insertvalues.
  if (IVI.getNumIndices() != 1) {
    markOverdefined(&IVI);
    return;
  }

  // Currently only handle insertvalue instructions that are in a single-use
  // chain that builds up a return value.
  for (const InsertValueInst *TmpIVI = &IVI; ; ) {
    if (!TmpIVI->hasOneUse()) {
      markOverdefined(&IVI);
      return;
    }
    const Value *V = *TmpIVI->use_begin();
    if (isa<ReturnInst>(V))
      break;
    TmpIVI = dyn_cast<InsertValueInst>(V);
    if (!TmpIVI) {
      markOverdefined(&IVI);
      return;
    }
  }
  
  // See if we are tracking the result of the callee.
  Function *F = IVI.getParent()->getParent();
  DenseMap<std::pair<Function*, unsigned>, LatticeVal>::iterator
    It = TrackedMultipleRetVals.find(std::make_pair(F, *IVI.idx_begin()));

  // Merge in the inserted member value.
  if (It != TrackedMultipleRetVals.end())
    mergeInValue(It->second, F, getValueState(Val));

  // Mark the aggregate result of the IVI overdefined; any tracking that we do
  // will be done on the individual member values.
  markOverdefined(&IVI);
}

void SCCPSolver::visitSelectInst(SelectInst &I) {
  LatticeVal &CondValue = getValueState(I.getCondition());
  if (CondValue.isUndefined())
    return;
  if (CondValue.isConstant()) {
    if (ConstantInt *CondCB = dyn_cast<ConstantInt>(CondValue.getConstant())){
      mergeInValue(&I, getValueState(CondCB->getZExtValue() ? I.getTrueValue()
                                                          : I.getFalseValue()));
      return;
    }
  }
  
  // Otherwise, the condition is overdefined or a constant we can't evaluate.
  // See if we can produce something better than overdefined based on the T/F
  // value.
  LatticeVal &TVal = getValueState(I.getTrueValue());
  LatticeVal &FVal = getValueState(I.getFalseValue());
  
  // select ?, C, C -> C.
  if (TVal.isConstant() && FVal.isConstant() && 
      TVal.getConstant() == FVal.getConstant()) {
    markConstant(&I, FVal.getConstant());
    return;
  }

  if (TVal.isUndefined()) {  // select ?, undef, X -> X.
    mergeInValue(&I, FVal);
  } else if (FVal.isUndefined()) {  // select ?, X, undef -> X.
    mergeInValue(&I, TVal);
  } else {
    markOverdefined(&I);
  }
}

// Handle BinaryOperators and Shift Instructions...
void SCCPSolver::visitBinaryOperator(Instruction &I) {
  LatticeVal &IV = ValueState[&I];
  if (IV.isOverdefined()) return;

  LatticeVal &V1State = getValueState(I.getOperand(0));
  LatticeVal &V2State = getValueState(I.getOperand(1));

  if (V1State.isOverdefined() || V2State.isOverdefined()) {
    // If this is an AND or OR with 0 or -1, it doesn't matter that the other
    // operand is overdefined.
    if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
      LatticeVal *NonOverdefVal = 0;
      if (!V1State.isOverdefined()) {
        NonOverdefVal = &V1State;
      } else if (!V2State.isOverdefined()) {
        NonOverdefVal = &V2State;
      }

      if (NonOverdefVal) {
        if (NonOverdefVal->isUndefined()) {
          // Could annihilate value.
          if (I.getOpcode() == Instruction::And)
            markConstant(IV, &I, Constant::getNullValue(I.getType()));
          else if (const VectorType *PT = dyn_cast<VectorType>(I.getType()))
            markConstant(IV, &I, Constant::getAllOnesValue(PT));
          else
            markConstant(IV, &I,
                         Constant::getAllOnesValue(I.getType()));
          return;
        } else {
          if (I.getOpcode() == Instruction::And) {
            if (NonOverdefVal->getConstant()->isNullValue()) {
              markConstant(IV, &I, NonOverdefVal->getConstant());
              return;      // X and 0 = 0
            }
          } else {
            if (ConstantInt *CI =
                     dyn_cast<ConstantInt>(NonOverdefVal->getConstant()))
              if (CI->isAllOnesValue()) {
                markConstant(IV, &I, NonOverdefVal->getConstant());
                return;    // X or -1 = -1
              }
          }
        }
      }
    }


    // If both operands are PHI nodes, it is possible that this instruction has
    // a constant value, despite the fact that the PHI node doesn't.  Check for
    // this condition now.
    if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
      if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
        if (PN1->getParent() == PN2->getParent()) {
          // Since the two PHI nodes are in the same basic block, they must have
          // entries for the same predecessors.  Walk the predecessor list, and
          // if all of the incoming values are constants, and the result of
          // evaluating this expression with all incoming value pairs is the
          // same, then this expression is a constant even though the PHI node
          // is not a constant!
          LatticeVal Result;
          for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
            LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
            BasicBlock *InBlock = PN1->getIncomingBlock(i);
            LatticeVal &In2 =
              getValueState(PN2->getIncomingValueForBlock(InBlock));

            if (In1.isOverdefined() || In2.isOverdefined()) {
              Result.markOverdefined();
              break;  // Cannot fold this operation over the PHI nodes!
            } else if (In1.isConstant() && In2.isConstant()) {
              Constant *V =
                     ConstantExpr::get(I.getOpcode(), In1.getConstant(),
                                              In2.getConstant());
              if (Result.isUndefined())
                Result.markConstant(V);
              else if (Result.isConstant() && Result.getConstant() != V) {
                Result.markOverdefined();
                break;
              }
            }
          }

          // If we found a constant value here, then we know the instruction is
          // constant despite the fact that the PHI nodes are overdefined.
          if (Result.isConstant()) {
            markConstant(IV, &I, Result.getConstant());
            // Remember that this instruction is virtually using the PHI node
            // operands.
            UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
            UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
            return;
          } else if (Result.isUndefined()) {
            return;
          }

          // Okay, this really is overdefined now.  Since we might have
          // speculatively thought that this was not overdefined before, and
          // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
          // make sure to clean out any entries that we put there, for
          // efficiency.
          std::multimap<PHINode*, Instruction*>::iterator It, E;
          tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
          while (It != E) {
            if (It->second == &I) {
              UsersOfOverdefinedPHIs.erase(It++);
            } else
              ++It;
          }
          tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
          while (It != E) {
            if (It->second == &I) {
              UsersOfOverdefinedPHIs.erase(It++);
            } else
              ++It;
          }
        }

    markOverdefined(IV, &I);
  } else if (V1State.isConstant() && V2State.isConstant()) {
    markConstant(IV, &I,
                ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
                                           V2State.getConstant()));
  }
}

// Handle ICmpInst instruction...
void SCCPSolver::visitCmpInst(CmpInst &I) {
  LatticeVal &IV = ValueState[&I];
  if (IV.isOverdefined()) return;

  LatticeVal &V1State = getValueState(I.getOperand(0));
  LatticeVal &V2State = getValueState(I.getOperand(1));

  if (V1State.isOverdefined() || V2State.isOverdefined()) {
    // If both operands are PHI nodes, it is possible that this instruction has
    // a constant value, despite the fact that the PHI node doesn't.  Check for
    // this condition now.
    if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
      if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
        if (PN1->getParent() == PN2->getParent()) {
          // Since the two PHI nodes are in the same basic block, they must have
          // entries for the same predecessors.  Walk the predecessor list, and
          // if all of the incoming values are constants, and the result of
          // evaluating this expression with all incoming value pairs is the
          // same, then this expression is a constant even though the PHI node
          // is not a constant!
          LatticeVal Result;
          for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
            LatticeVal &In1 = getValueState(PN1->getIncomingValue(i));
            BasicBlock *InBlock = PN1->getIncomingBlock(i);
            LatticeVal &In2 =
              getValueState(PN2->getIncomingValueForBlock(InBlock));

            if (In1.isOverdefined() || In2.isOverdefined()) {
              Result.markOverdefined();
              break;  // Cannot fold this operation over the PHI nodes!
            } else if (In1.isConstant() && In2.isConstant()) {
              Constant *V = ConstantExpr::getCompare(I.getPredicate(), 
                                                     In1.getConstant(), 
                                                     In2.getConstant());
              if (Result.isUndefined())
                Result.markConstant(V);
              else if (Result.isConstant() && Result.getConstant() != V) {
                Result.markOverdefined();
                break;
              }
            }
          }

          // If we found a constant value here, then we know the instruction is
          // constant despite the fact that the PHI nodes are overdefined.
          if (Result.isConstant()) {
            markConstant(IV, &I, Result.getConstant());
            // Remember that this instruction is virtually using the PHI node
            // operands.
            UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
            UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
            return;
          } else if (Result.isUndefined()) {
            return;
          }

          // Okay, this really is overdefined now.  Since we might have
          // speculatively thought that this was not overdefined before, and
          // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
          // make sure to clean out any entries that we put there, for
          // efficiency.
          std::multimap<PHINode*, Instruction*>::iterator It, E;
          tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
          while (It != E) {
            if (It->second == &I) {
              UsersOfOverdefinedPHIs.erase(It++);
            } else
              ++It;
          }
          tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
          while (It != E) {
            if (It->second == &I) {
              UsersOfOverdefinedPHIs.erase(It++);
            } else
              ++It;
          }
        }

    markOverdefined(IV, &I);
  } else if (V1State.isConstant() && V2State.isConstant()) {
    markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(), 
                                                  V1State.getConstant(), 
                                                  V2State.getConstant()));
  }
}

void SCCPSolver::visitExtractElementInst(ExtractElementInst &I) {
  // FIXME : SCCP does not handle vectors properly.
  markOverdefined(&I);
  return;

#if 0
  LatticeVal &ValState = getValueState(I.getOperand(0));
  LatticeVal &IdxState = getValueState(I.getOperand(1));

  if (ValState.isOverdefined() || IdxState.isOverdefined())
    markOverdefined(&I);
  else if(ValState.isConstant() && IdxState.isConstant())
    markConstant(&I, ConstantExpr::getExtractElement(ValState.getConstant(),
                                                     IdxState.getConstant()));
#endif
}

void SCCPSolver::visitInsertElementInst(InsertElementInst &I) {
  // FIXME : SCCP does not handle vectors properly.
  markOverdefined(&I);
  return;
#if 0
  LatticeVal &ValState = getValueState(I.getOperand(0));
  LatticeVal &EltState = getValueState(I.getOperand(1));
  LatticeVal &IdxState = getValueState(I.getOperand(2));

  if (ValState.isOverdefined() || EltState.isOverdefined() ||
      IdxState.isOverdefined())
    markOverdefined(&I);
  else if(ValState.isConstant() && EltState.isConstant() &&
          IdxState.isConstant())
    markConstant(&I, ConstantExpr::getInsertElement(ValState.getConstant(),
                                                    EltState.getConstant(),
                                                    IdxState.getConstant()));
  else if (ValState.isUndefined() && EltState.isConstant() &&
           IdxState.isConstant()) 
    markConstant(&I,ConstantExpr::getInsertElement(UndefValue::get(I.getType()),
                                                   EltState.getConstant(),
                                                   IdxState.getConstant()));
#endif
}

void SCCPSolver::visitShuffleVectorInst(ShuffleVectorInst &I) {
  // FIXME : SCCP does not handle vectors properly.
  markOverdefined(&I);
  return;
#if 0
  LatticeVal &V1State   = getValueState(I.getOperand(0));
  LatticeVal &V2State   = getValueState(I.getOperand(1));
  LatticeVal &MaskState = getValueState(I.getOperand(2));

  if (MaskState.isUndefined() ||
      (V1State.isUndefined() && V2State.isUndefined()))
    return;  // Undefined output if mask or both inputs undefined.
  
  if (V1State.isOverdefined() || V2State.isOverdefined() ||
      MaskState.isOverdefined()) {
    markOverdefined(&I);
  } else {
    // A mix of constant/undef inputs.
    Constant *V1 = V1State.isConstant() ? 
        V1State.getConstant() : UndefValue::get(I.getType());
    Constant *V2 = V2State.isConstant() ? 
        V2State.getConstant() : UndefValue::get(I.getType());
    Constant *Mask = MaskState.isConstant() ? 
      MaskState.getConstant() : UndefValue::get(I.getOperand(2)->getType());
    markConstant(&I, ConstantExpr::getShuffleVector(V1, V2, Mask));
  }
#endif
}

// Handle getelementptr instructions... if all operands are constants then we
// can turn this into a getelementptr ConstantExpr.
//
void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
  LatticeVal &IV = ValueState[&I];
  if (IV.isOverdefined()) return;

  SmallVector<Constant*, 8> Operands;
  Operands.reserve(I.getNumOperands());

  for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
    LatticeVal &State = getValueState(I.getOperand(i));
    if (State.isUndefined())
      return;  // Operands are not resolved yet...
    else if (State.isOverdefined()) {
      markOverdefined(IV, &I);
      return;
    }
    assert(State.isConstant() && "Unknown state!");
    Operands.push_back(State.getConstant());
  }

  Constant *Ptr = Operands[0];
  Operands.erase(Operands.begin());  // Erase the pointer from idx list...

  markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, &Operands[0],
                                                      Operands.size()));
}

void SCCPSolver::visitStoreInst(Instruction &SI) {
  if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
    return;
  GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
  DenseMap<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
  if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;

  // Get the value we are storing into the global.
  LatticeVal &PtrVal = getValueState(SI.getOperand(0));

  mergeInValue(I->second, GV, PtrVal);
  if (I->second.isOverdefined())
    TrackedGlobals.erase(I);      // No need to keep tracking this!
}


// Handle load instructions.  If the operand is a constant pointer to a constant
// global, we can replace the load with the loaded constant value!
void SCCPSolver::visitLoadInst(LoadInst &I) {
  LatticeVal &IV = ValueState[&I];
  if (IV.isOverdefined()) return;

  LatticeVal &PtrVal = getValueState(I.getOperand(0));
  if (PtrVal.isUndefined()) return;   // The pointer is not resolved yet!
  if (PtrVal.isConstant() && !I.isVolatile()) {
    Value *Ptr = PtrVal.getConstant();
    // TODO: Consider a target hook for valid address spaces for this xform.
    if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0) {
      // load null -> null
      markConstant(IV, &I, Constant::getNullValue(I.getType()));
      return;
    }

    // Transform load (constant global) into the value loaded.
    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
      if (GV->isConstant()) {
        if (GV->hasDefinitiveInitializer()) {
          markConstant(IV, &I, GV->getInitializer());
          return;
        }
      } else if (!TrackedGlobals.empty()) {
        // If we are tracking this global, merge in the known value for it.
        DenseMap<GlobalVariable*, LatticeVal>::iterator It =
          TrackedGlobals.find(GV);
        if (It != TrackedGlobals.end()) {
          mergeInValue(IV, &I, It->second);
          return;
        }
      }
    }

    // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
      if (CE->getOpcode() == Instruction::GetElementPtr)
    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
      if (GV->isConstant() && GV->hasDefinitiveInitializer())
        if (Constant *V =
             ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) {
          markConstant(IV, &I, V);
          return;
        }
  }

  // Otherwise we cannot say for certain what value this load will produce.
  // Bail out.
  markOverdefined(IV, &I);
}

void SCCPSolver::visitCallSite(CallSite CS) {
  Function *F = CS.getCalledFunction();
  Instruction *I = CS.getInstruction();
  
  // The common case is that we aren't tracking the callee, either because we
  // are not doing interprocedural analysis or the callee is indirect, or is
  // external.  Handle these cases first.
  if (F == 0 || !F->hasLocalLinkage()) {
CallOverdefined:
    // Void return and not tracking callee, just bail.
    if (I->getType()->isVoidTy()) return;
    
    // Otherwise, if we have a single return value case, and if the function is
    // a declaration, maybe we can constant fold it.
    if (!isa<StructType>(I->getType()) && F && F->isDeclaration() && 
        canConstantFoldCallTo(F)) {
      
      SmallVector<Constant*, 8> Operands;
      for (CallSite::arg_iterator AI = CS.arg_begin(), E = CS.arg_end();
           AI != E; ++AI) {
        LatticeVal &State = getValueState(*AI);
        if (State.isUndefined())
          return;  // Operands are not resolved yet.
        else if (State.isOverdefined()) {
          markOverdefined(I);
          return;
        }
        assert(State.isConstant() && "Unknown state!");
        Operands.push_back(State.getConstant());
      }
     
      // If we can constant fold this, mark the result of the call as a
      // constant.
      if (Constant *C = ConstantFoldCall(F, Operands.data(), Operands.size())) {
        markConstant(I, C);
        return;
      }
    }

    // Otherwise, we don't know anything about this call, mark it overdefined.
    markOverdefined(I);
    return;
  }

  // If this is a single/zero retval case, see if we're tracking the function.
  DenseMap<Function*, LatticeVal>::iterator TFRVI = TrackedRetVals.find(F);
  if (TFRVI != TrackedRetVals.end()) {
    // If so, propagate the return value of the callee into this call result.
    mergeInValue(I, TFRVI->second);
  } else if (isa<StructType>(I->getType())) {
    // Check to see if we're tracking this callee, if not, handle it in the
    // common path above.
    DenseMap<std::pair<Function*, unsigned>, LatticeVal>::iterator
    TMRVI = TrackedMultipleRetVals.find(std::make_pair(F, 0));
    if (TMRVI == TrackedMultipleRetVals.end())
      goto CallOverdefined;

    // Need to mark as overdefined, otherwise it stays undefined which
    // creates extractvalue undef, <idx>
    markOverdefined(I);
    // If we are tracking this callee, propagate the return values of the call
    // into this call site.  We do this by walking all the uses. Single-index
    // ExtractValueInst uses can be tracked; anything more complicated is
    // currently handled conservatively.
    for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
         UI != E; ++UI) {
      if (ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(*UI)) {
        if (EVI->getNumIndices() == 1) {
          mergeInValue(EVI, 
                  TrackedMultipleRetVals[std::make_pair(F, *EVI->idx_begin())]);
          continue;
        }
      }
      // The aggregate value is used in a way not handled here. Assume nothing.
      markOverdefined(*UI);
    }
  } else {
    // Otherwise we're not tracking this callee, so handle it in the
    // common path above.
    goto CallOverdefined;
  }
   
  // Finally, if this is the first call to the function hit, mark its entry
  // block executable.
  if (!BBExecutable.count(F->begin()))
    MarkBlockExecutable(F->begin());
  
  // Propagate information from this call site into the callee.
  CallSite::arg_iterator CAI = CS.arg_begin();
  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
       AI != E; ++AI, ++CAI) {
    LatticeVal &IV = ValueState[AI];
    if (AI->hasByValAttr() && !F->onlyReadsMemory()) {
      IV.markOverdefined();
      continue;
    }
    if (!IV.isOverdefined())
      mergeInValue(IV, AI, getValueState(*CAI));
  }
}

void SCCPSolver::Solve() {
  // Process the work lists until they are empty!
  while (!BBWorkList.empty() || !InstWorkList.empty() ||
         !OverdefinedInstWorkList.empty()) {
    // Process the instruction work list...
    while (!OverdefinedInstWorkList.empty()) {
      Value *I = OverdefinedInstWorkList.back();
      OverdefinedInstWorkList.pop_back();

      DEBUG(errs() << "\nPopped off OI-WL: " << *I << '\n');

      // "I" got into the work list because it either made the transition from
      // bottom to constant
      //
      // Anything on this worklist that is overdefined need not be visited
      // since all of its users will have already been marked as overdefined
      // Update all of the users of this instruction's value...
      //
      for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
           UI != E; ++UI)
        OperandChangedState(*UI);
    }
    // Process the instruction work list...
    while (!InstWorkList.empty()) {
      Value *I = InstWorkList.back();
      InstWorkList.pop_back();

      DEBUG(errs() << "\nPopped off I-WL: " << *I << '\n');

      // "I" got into the work list because it either made the transition from
      // bottom to constant
      //
      // Anything on this worklist that is overdefined need not be visited
      // since all of its users will have already been marked as overdefined.
      // Update all of the users of this instruction's value...
      //
      if (!getValueState(I).isOverdefined())
        for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
             UI != E; ++UI)
          OperandChangedState(*UI);
    }

    // Process the basic block work list...
    while (!BBWorkList.empty()) {
      BasicBlock *BB = BBWorkList.back();
      BBWorkList.pop_back();

      DEBUG(errs() << "\nPopped off BBWL: " << *BB << '\n');

      // Notify all instructions in this basic block that they are newly
      // executable.
      visit(BB);
    }
  }
}

/// ResolvedUndefsIn - While solving the dataflow for a function, we assume
/// that branches on undef values cannot reach any of their successors.
/// However, this is not a safe assumption.  After we solve dataflow, this
/// method should be use to handle this.  If this returns true, the solver
/// should be rerun.
///
/// This method handles this by finding an unresolved branch and marking it one
/// of the edges from the block as being feasible, even though the condition
/// doesn't say it would otherwise be.  This allows SCCP to find the rest of the
/// CFG and only slightly pessimizes the analysis results (by marking one,
/// potentially infeasible, edge feasible).  This cannot usefully modify the
/// constraints on the condition of the branch, as that would impact other users
/// of the value.
///
/// This scan also checks for values that use undefs, whose results are actually
/// defined.  For example, 'zext i8 undef to i32' should produce all zeros
/// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
/// even if X isn't defined.
bool SCCPSolver::ResolvedUndefsIn(Function &F) {
  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    if (!BBExecutable.count(BB))
      continue;
    
    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
      // Look for instructions which produce undef values.
      if (I->getType()->isVoidTy()) continue;
      
      LatticeVal &LV = getValueState(I);
      if (!LV.isUndefined()) continue;

      // Get the lattice values of the first two operands for use below.
      LatticeVal &Op0LV = getValueState(I->getOperand(0));
      LatticeVal Op1LV;
      if (I->getNumOperands() == 2) {
        // If this is a two-operand instruction, and if both operands are
        // undefs, the result stays undef.
        Op1LV = getValueState(I->getOperand(1));
        if (Op0LV.isUndefined() && Op1LV.isUndefined())
          continue;
      }
      
      // If this is an instructions whose result is defined even if the input is
      // not fully defined, propagate the information.
      const Type *ITy = I->getType();
      switch (I->getOpcode()) {
      default: break;          // Leave the instruction as an undef.
      case Instruction::ZExt:
        // After a zero extend, we know the top part is zero.  SExt doesn't have
        // to be handled here, because we don't know whether the top part is 1's
        // or 0's.
        assert(Op0LV.isUndefined());
        markForcedConstant(LV, I, Constant::getNullValue(ITy));
        return true;
      case Instruction::Mul:
      case Instruction::And:
        // undef * X -> 0.   X could be zero.
        // undef & X -> 0.   X could be zero.
        markForcedConstant(LV, I, Constant::getNullValue(ITy));
        return true;

      case Instruction::Or:
        // undef | X -> -1.   X could be -1.
        if (const VectorType *PTy = dyn_cast<VectorType>(ITy))
          markForcedConstant(LV, I,
                             Constant::getAllOnesValue(PTy));
        else          
          markForcedConstant(LV, I, Constant::getAllOnesValue(ITy));
        return true;

      case Instruction::SDiv:
      case Instruction::UDiv:
      case Instruction::SRem:
      case Instruction::URem:
        // X / undef -> undef.  No change.
        // X % undef -> undef.  No change.
        if (Op1LV.isUndefined()) break;
        
        // undef / X -> 0.   X could be maxint.
        // undef % X -> 0.   X could be 1.
        markForcedConstant(LV, I, Constant::getNullValue(ITy));
        return true;
        
      case Instruction::AShr:
        // undef >>s X -> undef.  No change.
        if (Op0LV.isUndefined()) break;
        
        // X >>s undef -> X.  X could be 0, X could have the high-bit known set.
        if (Op0LV.isConstant())
          markForcedConstant(LV, I, Op0LV.getConstant());
        else
          markOverdefined(LV, I);
        return true;
      case Instruction::LShr:
      case Instruction::Shl:
        // undef >> X -> undef.  No change.
        // undef << X -> undef.  No change.
        if (Op0LV.isUndefined()) break;
        
        // X >> undef -> 0.  X could be 0.
        // X << undef -> 0.  X could be 0.
        markForcedConstant(LV, I, Constant::getNullValue(ITy));
        return true;
      case Instruction::Select:
        // undef ? X : Y  -> X or Y.  There could be commonality between X/Y.
        if (Op0LV.isUndefined()) {
          if (!Op1LV.isConstant())  // Pick the constant one if there is any.
            Op1LV = getValueState(I->getOperand(2));
        } else if (Op1LV.isUndefined()) {
          // c ? undef : undef -> undef.  No change.
          Op1LV = getValueState(I->getOperand(2));
          if (Op1LV.isUndefined())
            break;
          // Otherwise, c ? undef : x -> x.
        } else {
          // Leave Op1LV as Operand(1)'s LatticeValue.
        }
        
        if (Op1LV.isConstant())
          markForcedConstant(LV, I, Op1LV.getConstant());
        else
          markOverdefined(LV, I);
        return true;
      case Instruction::Call:
        // If a call has an undef result, it is because it is constant foldable
        // but one of the inputs was undef.  Just force the result to
        // overdefined.
        markOverdefined(LV, I);
        return true;
      }
    }
  
    TerminatorInst *TI = BB->getTerminator();
    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
      if (!BI->isConditional()) continue;
      if (!getValueState(BI->getCondition()).isUndefined())
        continue;
    } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
      if (SI->getNumSuccessors()<2)   // no cases
        continue;
      if (!getValueState(SI->getCondition()).isUndefined())
        continue;
    } else {
      continue;
    }
    
    // If the edge to the second successor isn't thought to be feasible yet,
    // mark it so now.  We pick the second one so that this goes to some
    // enumerated value in a switch instead of going to the default destination.
    if (KnownFeasibleEdges.count(Edge(BB, TI->getSuccessor(1))))
      continue;
    
    // Otherwise, it isn't already thought to be feasible.  Mark it as such now
    // and return.  This will make other blocks reachable, which will allow new
    // values to be discovered and existing ones to be moved in the lattice.
    markEdgeExecutable(BB, TI->getSuccessor(1));
    
    // This must be a conditional branch of switch on undef.  At this point,
    // force the old terminator to branch to the first successor.  This is
    // required because we are now influencing the dataflow of the function with
    // the assumption that this edge is taken.  If we leave the branch condition
    // as undef, then further analysis could think the undef went another way
    // leading to an inconsistent set of conclusions.
    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
      BI->setCondition(ConstantInt::getFalse(*Context));
    } else {
      SwitchInst *SI = cast<SwitchInst>(TI);
      SI->setCondition(SI->getCaseValue(1));
    }
    
    return true;
  }

  return false;
}


namespace {
  //===--------------------------------------------------------------------===//
  //
  /// SCCP Class - This class uses the SCCPSolver to implement a per-function
  /// Sparse Conditional Constant Propagator.
  ///
  struct SCCP : public FunctionPass {
    static char ID; // Pass identification, replacement for typeid
    SCCP() : FunctionPass(&ID) {}

    // runOnFunction - Run the Sparse Conditional Constant Propagation
    // algorithm, and return true if the function was modified.
    //
    bool runOnFunction(Function &F);

    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.setPreservesCFG();
    }
  };
} // end anonymous namespace

char SCCP::ID = 0;
static RegisterPass<SCCP>
X("sccp", "Sparse Conditional Constant Propagation");

// createSCCPPass - This is the public interface to this file...
FunctionPass *llvm::createSCCPPass() {
  return new SCCP();
}


// runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
// and return true if the function was modified.
//
bool SCCP::runOnFunction(Function &F) {
  DEBUG(errs() << "SCCP on function '" << F.getName() << "'\n");
  SCCPSolver Solver;
  Solver.setContext(&F.getContext());

  // Mark the first block of the function as being executable.
  Solver.MarkBlockExecutable(F.begin());

  // Mark all arguments to the function as being overdefined.
  for (Function::arg_iterator AI = F.arg_begin(), E = F.arg_end(); AI != E;++AI)
    Solver.markOverdefined(AI);

  // Solve for constants.
  bool ResolvedUndefs = true;
  while (ResolvedUndefs) {
    Solver.Solve();
    DEBUG(errs() << "RESOLVING UNDEFs\n");
    ResolvedUndefs = Solver.ResolvedUndefsIn(F);
  }

  bool MadeChanges = false;

  // If we decided that there are basic blocks that are dead in this function,
  // delete their contents now.  Note that we cannot actually delete the blocks,
  // as we cannot modify the CFG of the function.
  //
  SmallVector<Instruction*, 512> Insts;
  std::map<Value*, LatticeVal> &Values = Solver.getValueMapping();

  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
    if (!Solver.isBlockExecutable(BB)) {
      DEBUG(errs() << "  BasicBlock Dead:" << *BB);
      ++NumDeadBlocks;

      // Delete the instructions backwards, as it has a reduced likelihood of
      // having to update as many def-use and use-def chains.
      for (BasicBlock::iterator I = BB->begin(), E = BB->getTerminator();
           I != E; ++I)
        Insts.push_back(I);
      while (!Insts.empty()) {
        Instruction *I = Insts.back();
        Insts.pop_back();
        if (!I->use_empty())
          I->replaceAllUsesWith(UndefValue::get(I->getType()));
        BB->getInstList().erase(I);
        MadeChanges = true;
        ++NumInstRemoved;
      }
    } else {
      // Iterate over all of the instructions in a function, replacing them with
      // constants if we have found them to be of constant values.
      //
      for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
        Instruction *Inst = BI++;
        if (Inst->getType()->isVoidTy() || isa<TerminatorInst>(Inst))
          continue;
        
        LatticeVal &IV = Values[Inst];
        if (!IV.isConstant() && !IV.isUndefined())
          continue;
        
        Constant *Const = IV.isConstant()
          ? IV.getConstant() : UndefValue::get(Inst->getType());
        DEBUG(errs() << "  Constant: " << *Const << " = " << *Inst);

        // Replaces all of the uses of a variable with uses of the constant.
        Inst->replaceAllUsesWith(Const);
        
        // Delete the instruction.
        Inst->eraseFromParent();
        
        // Hey, we just changed something!
        MadeChanges = true;
        ++NumInstRemoved;
      }
    }

  return MadeChanges;
}

namespace {
  //===--------------------------------------------------------------------===//
  //
  /// IPSCCP Class - This class implements interprocedural Sparse Conditional
  /// Constant Propagation.
  ///
  struct IPSCCP : public ModulePass {
    static char ID;
    IPSCCP() : ModulePass(&ID) {}
    bool runOnModule(Module &M);
  };
} // end anonymous namespace

char IPSCCP::ID = 0;
static RegisterPass<IPSCCP>
Y("ipsccp", "Interprocedural Sparse Conditional Constant Propagation");

// createIPSCCPPass - This is the public interface to this file...
ModulePass *llvm::createIPSCCPPass() {
  return new IPSCCP();
}


static bool AddressIsTaken(GlobalValue *GV) {
  // Delete any dead constantexpr klingons.
  GV->removeDeadConstantUsers();

  for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
       UI != E; ++UI)
    if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
      if (SI->getOperand(0) == GV || SI->isVolatile())
        return true;  // Storing addr of GV.
    } else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
      // Make sure we are calling the function, not passing the address.
      CallSite CS = CallSite::get(cast<Instruction>(*UI));
      if (CS.hasArgument(GV))
        return true;
    } else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
      if (LI->isVolatile())
        return true;
    } else {
      return true;
    }
  return false;
}

bool IPSCCP::runOnModule(Module &M) {
  LLVMContext *Context = &M.getContext();
  
  SCCPSolver Solver;
  Solver.setContext(Context);

  // Loop over all functions, marking arguments to those with their addresses
  // taken or that are external as overdefined.
  //
  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
    if (!F->hasLocalLinkage() || AddressIsTaken(F)) {
      if (!F->isDeclaration())
        Solver.MarkBlockExecutable(F->begin());
      for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
           AI != E; ++AI)
        Solver.markOverdefined(AI);
    } else {
      Solver.AddTrackedFunction(F);
    }

  // Loop over global variables.  We inform the solver about any internal global
  // variables that do not have their 'addresses taken'.  If they don't have
  // their addresses taken, we can propagate constants through them.
  for (Module::global_iterator G = M.global_begin(), E = M.global_end();
       G != E; ++G)
    if (!G->isConstant() && G->hasLocalLinkage() && !AddressIsTaken(G))
      Solver.TrackValueOfGlobalVariable(G);

  // Solve for constants.
  bool ResolvedUndefs = true;
  while (ResolvedUndefs) {
    Solver.Solve();

    DEBUG(errs() << "RESOLVING UNDEFS\n");
    ResolvedUndefs = false;
    for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
      ResolvedUndefs |= Solver.ResolvedUndefsIn(*F);
  }

  bool MadeChanges = false;

  // Iterate over all of the instructions in the module, replacing them with
  // constants if we have found them to be of constant values.
  //
  SmallVector<Instruction*, 512> Insts;
  SmallVector<BasicBlock*, 512> BlocksToErase;
  std::map<Value*, LatticeVal> &Values = Solver.getValueMapping();

  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
    for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
         AI != E; ++AI)
      if (!AI->use_empty()) {
        LatticeVal &IV = Values[AI];
        if (IV.isConstant() || IV.isUndefined()) {
          Constant *CST = IV.isConstant() ?
            IV.getConstant() : UndefValue::get(AI->getType());
          DEBUG(errs() << "***  Arg " << *AI << " = " << *CST <<"\n");

          // Replaces all of the uses of a variable with uses of the
          // constant.
          AI->replaceAllUsesWith(CST);
          ++IPNumArgsElimed;
        }
      }

    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
      if (!Solver.isBlockExecutable(BB)) {
        DEBUG(errs() << "  BasicBlock Dead:" << *BB);
        ++IPNumDeadBlocks;

        // Delete the instructions backwards, as it has a reduced likelihood of
        // having to update as many def-use and use-def chains.
        TerminatorInst *TI = BB->getTerminator();
        for (BasicBlock::iterator I = BB->begin(), E = TI; I != E; ++I)
          Insts.push_back(I);

        while (!Insts.empty()) {
          Instruction *I = Insts.back();
          Insts.pop_back();
          if (!I->use_empty())
            I->replaceAllUsesWith(UndefValue::get(I->getType()));
          BB->getInstList().erase(I);
          MadeChanges = true;
          ++IPNumInstRemoved;
        }

        for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
          BasicBlock *Succ = TI->getSuccessor(i);
          if (!Succ->empty() && isa<PHINode>(Succ->begin()))
            TI->getSuccessor(i)->removePredecessor(BB);
        }
        if (!TI->use_empty())
          TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
        BB->getInstList().erase(TI);

        if (&*BB != &F->front())
          BlocksToErase.push_back(BB);
        else
          new UnreachableInst(M.getContext(), BB);

      } else {
        for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
          Instruction *Inst = BI++;
          if (Inst->getType()->isVoidTy())
            continue;
          
          LatticeVal &IV = Values[Inst];
          if (!IV.isConstant() && !IV.isUndefined())
            continue;
          
          Constant *Const = IV.isConstant()
            ? IV.getConstant() : UndefValue::get(Inst->getType());
          DEBUG(errs() << "  Constant: " << *Const << " = " << *Inst);

          // Replaces all of the uses of a variable with uses of the
          // constant.
          Inst->replaceAllUsesWith(Const);
          
          // Delete the instruction.
          if (!isa<CallInst>(Inst) && !isa<TerminatorInst>(Inst))
            Inst->eraseFromParent();

          // Hey, we just changed something!
          MadeChanges = true;
          ++IPNumInstRemoved;
        }
      }

    // Now that all instructions in the function are constant folded, erase dead
    // blocks, because we can now use ConstantFoldTerminator to get rid of
    // in-edges.
    for (unsigned i = 0, e = BlocksToErase.size(); i != e; ++i) {
      // If there are any PHI nodes in this successor, drop entries for BB now.
      BasicBlock *DeadBB = BlocksToErase[i];
      while (!DeadBB->use_empty()) {
        Instruction *I = cast<Instruction>(DeadBB->use_back());
        bool Folded = ConstantFoldTerminator(I->getParent());
        if (!Folded) {
          // The constant folder may not have been able to fold the terminator
          // if this is a branch or switch on undef.  Fold it manually as a
          // branch to the first successor.
#ifndef NDEBUG
          if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
            assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
                   "Branch should be foldable!");
          } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
            assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
          } else {
            llvm_unreachable("Didn't fold away reference to block!");
          }
#endif
          
          // Make this an uncond branch to the first successor.
          TerminatorInst *TI = I->getParent()->getTerminator();
          BranchInst::Create(TI->getSuccessor(0), TI);
          
          // Remove entries in successor phi nodes to remove edges.
          for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
            TI->getSuccessor(i)->removePredecessor(TI->getParent());
          
          // Remove the old terminator.
          TI->eraseFromParent();
        }
      }

      // Finally, delete the basic block.
      F->getBasicBlockList().erase(DeadBB);
    }
    BlocksToErase.clear();
  }

  // If we inferred constant or undef return values for a function, we replaced
  // all call uses with the inferred value.  This means we don't need to bother
  // actually returning anything from the function.  Replace all return
  // instructions with return undef.
  // TODO: Process multiple value ret instructions also.
  const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
  for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
         E = RV.end(); I != E; ++I)
    if (!I->second.isOverdefined() &&
        !I->first->getReturnType()->isVoidTy()) {
      Function *F = I->first;
      for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
        if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
          if (!isa<UndefValue>(RI->getOperand(0)))
            RI->setOperand(0, UndefValue::get(F->getReturnType()));
    }

  // If we infered constant or undef values for globals variables, we can delete
  // the global and any stores that remain to it.
  const DenseMap<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
  for (DenseMap<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
         E = TG.end(); I != E; ++I) {
    GlobalVariable *GV = I->first;
    assert(!I->second.isOverdefined() &&
           "Overdefined values should have been taken out of the map!");
    DEBUG(errs() << "Found that GV '" << GV->getName() << "' is constant!\n");
    while (!GV->use_empty()) {
      StoreInst *SI = cast<StoreInst>(GV->use_back());
      SI->eraseFromParent();
    }
    M.getGlobalList().erase(GV);
    ++IPNumGlobalConst;
  }

  return MadeChanges;
}