summaryrefslogtreecommitdiffstats
path: root/lib/Transforms/IPO/GlobalOpt.cpp
blob: f5d2baa426a68c649180c7446cd3dc85c53df8b0 (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
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass transforms simple global variables that never have their address
// taken.  If obviously true, it marks read/write globals as constant, deletes
// variables only stored to, etc.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "globalopt"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallingConv.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include <algorithm>
#include <set>
using namespace llvm;

STATISTIC(NumMarked    , "Number of globals marked constant");
STATISTIC(NumSRA       , "Number of aggregate globals broken into scalars");
STATISTIC(NumHeapSRA   , "Number of heap objects SRA'd");
STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
STATISTIC(NumDeleted   , "Number of globals deleted");
STATISTIC(NumFnDeleted , "Number of functions deleted");
STATISTIC(NumGlobUses  , "Number of global uses devirtualized");
STATISTIC(NumLocalized , "Number of globals localized");
STATISTIC(NumShrunkToBool  , "Number of global vars shrunk to booleans");
STATISTIC(NumFastCallFns   , "Number of functions converted to fastcc");
STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");

namespace {
  struct VISIBILITY_HIDDEN GlobalOpt : public ModulePass {
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<TargetData>();
    }
    static char ID; // Pass identification, replacement for typeid
    GlobalOpt() : ModulePass((intptr_t)&ID) {}

    bool runOnModule(Module &M);

  private:
    GlobalVariable *FindGlobalCtors(Module &M);
    bool OptimizeFunctions(Module &M);
    bool OptimizeGlobalVars(Module &M);
    bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
    bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
  };

  char GlobalOpt::ID = 0;
  RegisterPass<GlobalOpt> X("globalopt", "Global Variable Optimizer");
}

ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }

/// GlobalStatus - As we analyze each global, keep track of some information
/// about it.  If we find out that the address of the global is taken, none of
/// this info will be accurate.
struct VISIBILITY_HIDDEN GlobalStatus {
  /// isLoaded - True if the global is ever loaded.  If the global isn't ever
  /// loaded it can be deleted.
  bool isLoaded;

  /// StoredType - Keep track of what stores to the global look like.
  ///
  enum StoredType {
    /// NotStored - There is no store to this global.  It can thus be marked
    /// constant.
    NotStored,

    /// isInitializerStored - This global is stored to, but the only thing
    /// stored is the constant it was initialized with.  This is only tracked
    /// for scalar globals.
    isInitializerStored,

    /// isStoredOnce - This global is stored to, but only its initializer and
    /// one other value is ever stored to it.  If this global isStoredOnce, we
    /// track the value stored to it in StoredOnceValue below.  This is only
    /// tracked for scalar globals.
    isStoredOnce,

    /// isStored - This global is stored to by multiple values or something else
    /// that we cannot track.
    isStored
  } StoredType;

  /// StoredOnceValue - If only one value (besides the initializer constant) is
  /// ever stored to this global, keep track of what value it is.
  Value *StoredOnceValue;

  /// AccessingFunction/HasMultipleAccessingFunctions - These start out
  /// null/false.  When the first accessing function is noticed, it is recorded.
  /// When a second different accessing function is noticed,
  /// HasMultipleAccessingFunctions is set to true.
  Function *AccessingFunction;
  bool HasMultipleAccessingFunctions;

  /// HasNonInstructionUser - Set to true if this global has a user that is not
  /// an instruction (e.g. a constant expr or GV initializer).
  bool HasNonInstructionUser;

  /// HasPHIUser - Set to true if this global has a user that is a PHI node.
  bool HasPHIUser;
  
  /// isNotSuitableForSRA - Keep track of whether any SRA preventing users of
  /// the global exist.  Such users include GEP instruction with variable
  /// indexes, and non-gep/load/store users like constant expr casts.
  bool isNotSuitableForSRA;

  GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0),
                   AccessingFunction(0), HasMultipleAccessingFunctions(false),
                   HasNonInstructionUser(false), HasPHIUser(false),
                   isNotSuitableForSRA(false) {}
};



/// ConstantIsDead - Return true if the specified constant is (transitively)
/// dead.  The constant may be used by other constants (e.g. constant arrays and
/// constant exprs) as long as they are dead, but it cannot be used by anything
/// else.
static bool ConstantIsDead(Constant *C) {
  if (isa<GlobalValue>(C)) return false;

  for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
    if (Constant *CU = dyn_cast<Constant>(*UI)) {
      if (!ConstantIsDead(CU)) return false;
    } else
      return false;
  return true;
}


/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
/// structure.  If the global has its address taken, return true to indicate we
/// can't do anything with it.
///
static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
                          std::set<PHINode*> &PHIUsers) {
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
      GS.HasNonInstructionUser = true;

      if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
      if (CE->getOpcode() != Instruction::GetElementPtr)
        GS.isNotSuitableForSRA = true;
      else if (!GS.isNotSuitableForSRA) {
        // Check to see if this ConstantExpr GEP is SRA'able.  In particular, we
        // don't like < 3 operand CE's, and we don't like non-constant integer
        // indices.
        if (CE->getNumOperands() < 3 || !CE->getOperand(1)->isNullValue())
          GS.isNotSuitableForSRA = true;
        else {
          for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
            if (!isa<ConstantInt>(CE->getOperand(i))) {
              GS.isNotSuitableForSRA = true;
              break;
            }
        }
      }

    } else if (Instruction *I = dyn_cast<Instruction>(*UI)) {
      if (!GS.HasMultipleAccessingFunctions) {
        Function *F = I->getParent()->getParent();
        if (GS.AccessingFunction == 0)
          GS.AccessingFunction = F;
        else if (GS.AccessingFunction != F)
          GS.HasMultipleAccessingFunctions = true;
      }
      if (isa<LoadInst>(I)) {
        GS.isLoaded = true;
      } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
        // Don't allow a store OF the address, only stores TO the address.
        if (SI->getOperand(0) == V) return true;

        // If this is a direct store to the global (i.e., the global is a scalar
        // value, not an aggregate), keep more specific information about
        // stores.
        if (GS.StoredType != GlobalStatus::isStored)
          if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))){
            Value *StoredVal = SI->getOperand(0);
            if (StoredVal == GV->getInitializer()) {
              if (GS.StoredType < GlobalStatus::isInitializerStored)
                GS.StoredType = GlobalStatus::isInitializerStored;
            } else if (isa<LoadInst>(StoredVal) &&
                       cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
              // G = G
              if (GS.StoredType < GlobalStatus::isInitializerStored)
                GS.StoredType = GlobalStatus::isInitializerStored;
            } else if (GS.StoredType < GlobalStatus::isStoredOnce) {
              GS.StoredType = GlobalStatus::isStoredOnce;
              GS.StoredOnceValue = StoredVal;
            } else if (GS.StoredType == GlobalStatus::isStoredOnce &&
                       GS.StoredOnceValue == StoredVal) {
              // noop.
            } else {
              GS.StoredType = GlobalStatus::isStored;
            }
          } else {
            GS.StoredType = GlobalStatus::isStored;
          }
      } else if (isa<GetElementPtrInst>(I)) {
        if (AnalyzeGlobal(I, GS, PHIUsers)) return true;

        // If the first two indices are constants, this can be SRA'd.
        if (isa<GlobalVariable>(I->getOperand(0))) {
          if (I->getNumOperands() < 3 || !isa<Constant>(I->getOperand(1)) ||
              !cast<Constant>(I->getOperand(1))->isNullValue() ||
              !isa<ConstantInt>(I->getOperand(2)))
            GS.isNotSuitableForSRA = true;
        } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(I->getOperand(0))){
          if (CE->getOpcode() != Instruction::GetElementPtr ||
              CE->getNumOperands() < 3 || I->getNumOperands() < 2 ||
              !isa<Constant>(I->getOperand(0)) ||
              !cast<Constant>(I->getOperand(0))->isNullValue())
            GS.isNotSuitableForSRA = true;
        } else {
          GS.isNotSuitableForSRA = true;
        }
      } else if (isa<SelectInst>(I)) {
        if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
        GS.isNotSuitableForSRA = true;
      } else if (PHINode *PN = dyn_cast<PHINode>(I)) {
        // PHI nodes we can check just like select or GEP instructions, but we
        // have to be careful about infinite recursion.
        if (PHIUsers.insert(PN).second)  // Not already visited.
          if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
        GS.isNotSuitableForSRA = true;
        GS.HasPHIUser = true;
      } else if (isa<CmpInst>(I)) {
        GS.isNotSuitableForSRA = true;
      } else if (isa<MemCpyInst>(I) || isa<MemMoveInst>(I)) {
        if (I->getOperand(1) == V)
          GS.StoredType = GlobalStatus::isStored;
        if (I->getOperand(2) == V)
          GS.isLoaded = true;
        GS.isNotSuitableForSRA = true;
      } else if (isa<MemSetInst>(I)) {
        assert(I->getOperand(1) == V && "Memset only takes one pointer!");
        GS.StoredType = GlobalStatus::isStored;
        GS.isNotSuitableForSRA = true;
      } else {
        return true;  // Any other non-load instruction might take address!
      }
    } else if (Constant *C = dyn_cast<Constant>(*UI)) {
      GS.HasNonInstructionUser = true;
      // We might have a dead and dangling constant hanging off of here.
      if (!ConstantIsDead(C))
        return true;
    } else {
      GS.HasNonInstructionUser = true;
      // Otherwise must be some other user.
      return true;
    }

  return false;
}

static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) {
  ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
  if (!CI) return 0;
  unsigned IdxV = CI->getZExtValue();

  if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) {
    if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV);
  } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) {
    if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV);
  } else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) {
    if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV);
  } else if (isa<ConstantAggregateZero>(Agg)) {
    if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
      if (IdxV < STy->getNumElements())
        return Constant::getNullValue(STy->getElementType(IdxV));
    } else if (const SequentialType *STy =
               dyn_cast<SequentialType>(Agg->getType())) {
      return Constant::getNullValue(STy->getElementType());
    }
  } else if (isa<UndefValue>(Agg)) {
    if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
      if (IdxV < STy->getNumElements())
        return UndefValue::get(STy->getElementType(IdxV));
    } else if (const SequentialType *STy =
               dyn_cast<SequentialType>(Agg->getType())) {
      return UndefValue::get(STy->getElementType());
    }
  }
  return 0;
}


/// CleanupConstantGlobalUsers - We just marked GV constant.  Loop over all
/// users of the global, cleaning up the obvious ones.  This is largely just a
/// quick scan over the use list to clean up the easy and obvious cruft.  This
/// returns true if it made a change.
static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) {
  bool Changed = false;
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
    User *U = *UI++;

    if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
      if (Init) {
        // Replace the load with the initializer.
        LI->replaceAllUsesWith(Init);
        LI->eraseFromParent();
        Changed = true;
      }
    } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
      // Store must be unreachable or storing Init into the global.
      SI->eraseFromParent();
      Changed = true;
    } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
      if (CE->getOpcode() == Instruction::GetElementPtr) {
        Constant *SubInit = 0;
        if (Init)
          SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
        Changed |= CleanupConstantGlobalUsers(CE, SubInit);
      } else if (CE->getOpcode() == Instruction::BitCast && 
                 isa<PointerType>(CE->getType())) {
        // Pointer cast, delete any stores and memsets to the global.
        Changed |= CleanupConstantGlobalUsers(CE, 0);
      }

      if (CE->use_empty()) {
        CE->destroyConstant();
        Changed = true;
      }
    } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
      Constant *SubInit = 0;
      ConstantExpr *CE = 
        dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP));
      if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
        SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
      Changed |= CleanupConstantGlobalUsers(GEP, SubInit);

      if (GEP->use_empty()) {
        GEP->eraseFromParent();
        Changed = true;
      }
    } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
      if (MI->getRawDest() == V) {
        MI->eraseFromParent();
        Changed = true;
      }

    } else if (Constant *C = dyn_cast<Constant>(U)) {
      // If we have a chain of dead constantexprs or other things dangling from
      // us, and if they are all dead, nuke them without remorse.
      if (ConstantIsDead(C)) {
        C->destroyConstant();
        // This could have invalidated UI, start over from scratch.
        CleanupConstantGlobalUsers(V, Init);
        return true;
      }
    }
  }
  return Changed;
}

/// SRAGlobal - Perform scalar replacement of aggregates on the specified global
/// variable.  This opens the door for other optimizations by exposing the
/// behavior of the program in a more fine-grained way.  We have determined that
/// this transformation is safe already.  We return the first global variable we
/// insert so that the caller can reprocess it.
static GlobalVariable *SRAGlobal(GlobalVariable *GV) {
  assert(GV->hasInternalLinkage() && !GV->isConstant());
  Constant *Init = GV->getInitializer();
  const Type *Ty = Init->getType();

  std::vector<GlobalVariable*> NewGlobals;
  Module::GlobalListType &Globals = GV->getParent()->getGlobalList();

  if (const StructType *STy = dyn_cast<StructType>(Ty)) {
    NewGlobals.reserve(STy->getNumElements());
    for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
      Constant *In = getAggregateConstantElement(Init,
                                            ConstantInt::get(Type::Int32Ty, i));
      assert(In && "Couldn't get element of initializer?");
      GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
                                               GlobalVariable::InternalLinkage,
                                               In, GV->getName()+"."+utostr(i),
                                               (Module *)NULL,
                                               GV->isThreadLocal());
      Globals.insert(GV, NGV);
      NewGlobals.push_back(NGV);
    }
  } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
    unsigned NumElements = 0;
    if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
      NumElements = ATy->getNumElements();
    else if (const VectorType *PTy = dyn_cast<VectorType>(STy))
      NumElements = PTy->getNumElements();
    else
      assert(0 && "Unknown aggregate sequential type!");

    if (NumElements > 16 && GV->hasNUsesOrMore(16))
      return 0; // It's not worth it.
    NewGlobals.reserve(NumElements);
    for (unsigned i = 0, e = NumElements; i != e; ++i) {
      Constant *In = getAggregateConstantElement(Init,
                                            ConstantInt::get(Type::Int32Ty, i));
      assert(In && "Couldn't get element of initializer?");

      GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
                                               GlobalVariable::InternalLinkage,
                                               In, GV->getName()+"."+utostr(i),
                                               (Module *)NULL,
                                               GV->isThreadLocal());
      Globals.insert(GV, NGV);
      NewGlobals.push_back(NGV);
    }
  }

  if (NewGlobals.empty())
    return 0;

  DOUT << "PERFORMING GLOBAL SRA ON: " << *GV;

  Constant *NullInt = Constant::getNullValue(Type::Int32Ty);

  // Loop over all of the uses of the global, replacing the constantexpr geps,
  // with smaller constantexpr geps or direct references.
  while (!GV->use_empty()) {
    User *GEP = GV->use_back();
    assert(((isa<ConstantExpr>(GEP) &&
             cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
            isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");

    // Ignore the 1th operand, which has to be zero or else the program is quite
    // broken (undefined).  Get the 2nd operand, which is the structure or array
    // index.
    unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
    if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.

    Value *NewPtr = NewGlobals[Val];

    // Form a shorter GEP if needed.
    if (GEP->getNumOperands() > 3)
      if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
        SmallVector<Constant*, 8> Idxs;
        Idxs.push_back(NullInt);
        for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
          Idxs.push_back(CE->getOperand(i));
        NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr),
                                                &Idxs[0], Idxs.size());
      } else {
        GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
        SmallVector<Value*, 8> Idxs;
        Idxs.push_back(NullInt);
        for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
          Idxs.push_back(GEPI->getOperand(i));
        NewPtr = new GetElementPtrInst(NewPtr, &Idxs[0], Idxs.size(),
                                       GEPI->getName()+"."+utostr(Val), GEPI);
      }
    GEP->replaceAllUsesWith(NewPtr);

    if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
      GEPI->eraseFromParent();
    else
      cast<ConstantExpr>(GEP)->destroyConstant();
  }

  // Delete the old global, now that it is dead.
  Globals.erase(GV);
  ++NumSRA;

  // Loop over the new globals array deleting any globals that are obviously
  // dead.  This can arise due to scalarization of a structure or an array that
  // has elements that are dead.
  unsigned FirstGlobal = 0;
  for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
    if (NewGlobals[i]->use_empty()) {
      Globals.erase(NewGlobals[i]);
      if (FirstGlobal == i) ++FirstGlobal;
    }

  return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
}

/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
/// value will trap if the value is dynamically null.
static bool AllUsesOfValueWillTrapIfNull(Value *V) {
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
    if (isa<LoadInst>(*UI)) {
      // Will trap.
    } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
      if (SI->getOperand(0) == V) {
        //cerr << "NONTRAPPING USE: " << **UI;
        return false;  // Storing the value.
      }
    } else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
      if (CI->getOperand(0) != V) {
        //cerr << "NONTRAPPING USE: " << **UI;
        return false;  // Not calling the ptr
      }
    } else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
      if (II->getOperand(0) != V) {
        //cerr << "NONTRAPPING USE: " << **UI;
        return false;  // Not calling the ptr
      }
    } else if (CastInst *CI = dyn_cast<CastInst>(*UI)) {
      if (!AllUsesOfValueWillTrapIfNull(CI)) return false;
    } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) {
      if (!AllUsesOfValueWillTrapIfNull(GEPI)) return false;
    } else if (isa<ICmpInst>(*UI) &&
               isa<ConstantPointerNull>(UI->getOperand(1))) {
      // Ignore setcc X, null
    } else {
      //cerr << "NONTRAPPING USE: " << **UI;
      return false;
    }
  return true;
}

/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
/// from GV will trap if the loaded value is null.  Note that this also permits
/// comparisons of the loaded value against null, as a special case.
static bool AllUsesOfLoadedValueWillTrapIfNull(GlobalVariable *GV) {
  for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI)
    if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
      if (!AllUsesOfValueWillTrapIfNull(LI))
        return false;
    } else if (isa<StoreInst>(*UI)) {
      // Ignore stores to the global.
    } else {
      // We don't know or understand this user, bail out.
      //cerr << "UNKNOWN USER OF GLOBAL!: " << **UI;
      return false;
    }

  return true;
}

static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
  bool Changed = false;
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
    Instruction *I = cast<Instruction>(*UI++);
    if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
      LI->setOperand(0, NewV);
      Changed = true;
    } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
      if (SI->getOperand(1) == V) {
        SI->setOperand(1, NewV);
        Changed = true;
      }
    } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
      if (I->getOperand(0) == V) {
        // Calling through the pointer!  Turn into a direct call, but be careful
        // that the pointer is not also being passed as an argument.
        I->setOperand(0, NewV);
        Changed = true;
        bool PassedAsArg = false;
        for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i)
          if (I->getOperand(i) == V) {
            PassedAsArg = true;
            I->setOperand(i, NewV);
          }

        if (PassedAsArg) {
          // Being passed as an argument also.  Be careful to not invalidate UI!
          UI = V->use_begin();
        }
      }
    } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
      Changed |= OptimizeAwayTrappingUsesOfValue(CI,
                                ConstantExpr::getCast(CI->getOpcode(),
                                                      NewV, CI->getType()));
      if (CI->use_empty()) {
        Changed = true;
        CI->eraseFromParent();
      }
    } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
      // Should handle GEP here.
      SmallVector<Constant*, 8> Idxs;
      Idxs.reserve(GEPI->getNumOperands()-1);
      for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
        if (Constant *C = dyn_cast<Constant>(GEPI->getOperand(i)))
          Idxs.push_back(C);
        else
          break;
      if (Idxs.size() == GEPI->getNumOperands()-1)
        Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
                                ConstantExpr::getGetElementPtr(NewV, &Idxs[0],
                                                               Idxs.size()));
      if (GEPI->use_empty()) {
        Changed = true;
        GEPI->eraseFromParent();
      }
    }
  }

  return Changed;
}


/// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
/// value stored into it.  If there are uses of the loaded value that would trap
/// if the loaded value is dynamically null, then we know that they cannot be
/// reachable with a null optimize away the load.
static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) {
  std::vector<LoadInst*> Loads;
  bool Changed = false;

  // Replace all uses of loads with uses of uses of the stored value.
  for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end();
       GUI != E; ++GUI)
    if (LoadInst *LI = dyn_cast<LoadInst>(*GUI)) {
      Loads.push_back(LI);
      Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
    } else {
      assert(isa<StoreInst>(*GUI) && "Only expect load and stores!");
    }

  if (Changed) {
    DOUT << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV;
    ++NumGlobUses;
  }

  // Delete all of the loads we can, keeping track of whether we nuked them all!
  bool AllLoadsGone = true;
  while (!Loads.empty()) {
    LoadInst *L = Loads.back();
    if (L->use_empty()) {
      L->eraseFromParent();
      Changed = true;
    } else {
      AllLoadsGone = false;
    }
    Loads.pop_back();
  }

  // If we nuked all of the loads, then none of the stores are needed either,
  // nor is the global.
  if (AllLoadsGone) {
    DOUT << "  *** GLOBAL NOW DEAD!\n";
    CleanupConstantGlobalUsers(GV, 0);
    if (GV->use_empty()) {
      GV->eraseFromParent();
      ++NumDeleted;
    }
    Changed = true;
  }
  return Changed;
}

/// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
/// instructions that are foldable.
static void ConstantPropUsersOf(Value *V) {
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
    if (Instruction *I = dyn_cast<Instruction>(*UI++))
      if (Constant *NewC = ConstantFoldInstruction(I)) {
        I->replaceAllUsesWith(NewC);

        // Advance UI to the next non-I use to avoid invalidating it!
        // Instructions could multiply use V.
        while (UI != E && *UI == I)
          ++UI;
        I->eraseFromParent();
      }
}

/// OptimizeGlobalAddressOfMalloc - This function takes the specified global
/// variable, and transforms the program as if it always contained the result of
/// the specified malloc.  Because it is always the result of the specified
/// malloc, there is no reason to actually DO the malloc.  Instead, turn the
/// malloc into a global, and any loads of GV as uses of the new global.
static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
                                                     MallocInst *MI) {
  DOUT << "PROMOTING MALLOC GLOBAL: " << *GV << "  MALLOC = " << *MI;
  ConstantInt *NElements = cast<ConstantInt>(MI->getArraySize());

  if (NElements->getZExtValue() != 1) {
    // If we have an array allocation, transform it to a single element
    // allocation to make the code below simpler.
    Type *NewTy = ArrayType::get(MI->getAllocatedType(),
                                 NElements->getZExtValue());
    MallocInst *NewMI =
      new MallocInst(NewTy, Constant::getNullValue(Type::Int32Ty),
                     MI->getAlignment(), MI->getName(), MI);
    Value* Indices[2];
    Indices[0] = Indices[1] = Constant::getNullValue(Type::Int32Ty);
    Value *NewGEP = new GetElementPtrInst(NewMI, Indices, 2,
                                          NewMI->getName()+".el0", MI);
    MI->replaceAllUsesWith(NewGEP);
    MI->eraseFromParent();
    MI = NewMI;
  }

  // Create the new global variable.  The contents of the malloc'd memory is
  // undefined, so initialize with an undef value.
  Constant *Init = UndefValue::get(MI->getAllocatedType());
  GlobalVariable *NewGV = new GlobalVariable(MI->getAllocatedType(), false,
                                             GlobalValue::InternalLinkage, Init,
                                             GV->getName()+".body",
                                             (Module *)NULL,
                                             GV->isThreadLocal());
  GV->getParent()->getGlobalList().insert(GV, NewGV);

  // Anything that used the malloc now uses the global directly.
  MI->replaceAllUsesWith(NewGV);

  Constant *RepValue = NewGV;
  if (NewGV->getType() != GV->getType()->getElementType())
    RepValue = ConstantExpr::getBitCast(RepValue, 
                                        GV->getType()->getElementType());

  // If there is a comparison against null, we will insert a global bool to
  // keep track of whether the global was initialized yet or not.
  GlobalVariable *InitBool =
    new GlobalVariable(Type::Int1Ty, false, GlobalValue::InternalLinkage,
                       ConstantInt::getFalse(), GV->getName()+".init",
                       (Module *)NULL, GV->isThreadLocal());
  bool InitBoolUsed = false;

  // Loop over all uses of GV, processing them in turn.
  std::vector<StoreInst*> Stores;
  while (!GV->use_empty())
    if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) {
      while (!LI->use_empty()) {
        Use &LoadUse = LI->use_begin().getUse();
        if (!isa<ICmpInst>(LoadUse.getUser()))
          LoadUse = RepValue;
        else {
          ICmpInst *CI = cast<ICmpInst>(LoadUse.getUser());
          // Replace the cmp X, 0 with a use of the bool value.
          Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", CI);
          InitBoolUsed = true;
          switch (CI->getPredicate()) {
          default: assert(0 && "Unknown ICmp Predicate!");
          case ICmpInst::ICMP_ULT:
          case ICmpInst::ICMP_SLT:
            LV = ConstantInt::getFalse();   // X < null -> always false
            break;
          case ICmpInst::ICMP_ULE:
          case ICmpInst::ICMP_SLE:
          case ICmpInst::ICMP_EQ:
            LV = BinaryOperator::createNot(LV, "notinit", CI);
            break;
          case ICmpInst::ICMP_NE:
          case ICmpInst::ICMP_UGE:
          case ICmpInst::ICMP_SGE:
          case ICmpInst::ICMP_UGT:
          case ICmpInst::ICMP_SGT:
            break;  // no change.
          }
          CI->replaceAllUsesWith(LV);
          CI->eraseFromParent();
        }
      }
      LI->eraseFromParent();
    } else {
      StoreInst *SI = cast<StoreInst>(GV->use_back());
      // The global is initialized when the store to it occurs.
      new StoreInst(ConstantInt::getTrue(), InitBool, SI);
      SI->eraseFromParent();
    }

  // If the initialization boolean was used, insert it, otherwise delete it.
  if (!InitBoolUsed) {
    while (!InitBool->use_empty())  // Delete initializations
      cast<Instruction>(InitBool->use_back())->eraseFromParent();
    delete InitBool;
  } else
    GV->getParent()->getGlobalList().insert(GV, InitBool);


  // Now the GV is dead, nuke it and the malloc.
  GV->eraseFromParent();
  MI->eraseFromParent();

  // To further other optimizations, loop over all users of NewGV and try to
  // constant prop them.  This will promote GEP instructions with constant
  // indices into GEP constant-exprs, which will allow global-opt to hack on it.
  ConstantPropUsersOf(NewGV);
  if (RepValue != NewGV)
    ConstantPropUsersOf(RepValue);

  return NewGV;
}

/// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
/// to make sure that there are no complex uses of V.  We permit simple things
/// like dereferencing the pointer, but not storing through the address, unless
/// it is to the specified global.
static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Instruction *V,
                                                      GlobalVariable *GV) {
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI)
    if (isa<LoadInst>(*UI) || isa<CmpInst>(*UI)) {
      // Fine, ignore.
    } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
      if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
        return false;  // Storing the pointer itself... bad.
      // Otherwise, storing through it, or storing into GV... fine.
    } else if (isa<GetElementPtrInst>(*UI) || isa<SelectInst>(*UI)) {
      if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(cast<Instruction>(*UI),GV))
        return false;
    } else {
      return false;
    }
  return true;
}

/// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV
/// somewhere.  Transform all uses of the allocation into loads from the
/// global and uses of the resultant pointer.  Further, delete the store into
/// GV.  This assumes that these value pass the 
/// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc, 
                                          GlobalVariable *GV) {
  while (!Alloc->use_empty()) {
    Instruction *U = Alloc->use_back();
    if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
      // If this is the store of the allocation into the global, remove it.
      if (SI->getOperand(1) == GV) {
        SI->eraseFromParent();
        continue;
      }
    }
    
    // Insert a load from the global, and use it instead of the malloc.
    Value *NL = new LoadInst(GV, GV->getName()+".val", U);
    U->replaceUsesOfWith(Alloc, NL);
  }
}

/// GlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
/// GV are simple enough to perform HeapSRA, return true.
static bool GlobalLoadUsesSimpleEnoughForHeapSRA(GlobalVariable *GV) {
  for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E; 
       ++UI)
    if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
      // We permit two users of the load: setcc comparing against the null
      // pointer, and a getelementptr of a specific form.
      for (Value::use_iterator UI = LI->use_begin(), E = LI->use_end(); UI != E; 
           ++UI) {
        // Comparison against null is ok.
        if (ICmpInst *ICI = dyn_cast<ICmpInst>(*UI)) {
          if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
            return false;
          continue;
        }
        
        // getelementptr is also ok, but only a simple form.
        GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI);
        if (!GEPI) return false;
        
        // Must index into the array and into the struct.
        if (GEPI->getNumOperands() < 3)
          return false;
        
        // Otherwise the GEP is ok.
        continue;
      }
    }
  return true;
}

/// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global.  Ptr
/// is a value loaded from the global.  Eliminate all uses of Ptr, making them
/// use FieldGlobals instead.  All uses of loaded values satisfy
/// GlobalLoadUsesSimpleEnoughForHeapSRA.
static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Ptr, 
                             const std::vector<GlobalVariable*> &FieldGlobals) {
  std::vector<Value *> InsertedLoadsForPtr;
  //InsertedLoadsForPtr.resize(FieldGlobals.size());
  while (!Ptr->use_empty()) {
    Instruction *User = Ptr->use_back();
    
    // If this is a comparison against null, handle it.
    if (ICmpInst *SCI = dyn_cast<ICmpInst>(User)) {
      assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
      // If we have a setcc of the loaded pointer, we can use a setcc of any
      // field.
      Value *NPtr;
      if (InsertedLoadsForPtr.empty()) {
        NPtr = new LoadInst(FieldGlobals[0], Ptr->getName()+".f0", Ptr);
        InsertedLoadsForPtr.push_back(Ptr);
      } else {
        NPtr = InsertedLoadsForPtr.back();
      }
      
      Value *New = new ICmpInst(SCI->getPredicate(), NPtr,
                                Constant::getNullValue(NPtr->getType()),
                                SCI->getName(), SCI);
      SCI->replaceAllUsesWith(New);
      SCI->eraseFromParent();
      continue;
    }
    
    // Otherwise, this should be: 'getelementptr Ptr, Idx, uint FieldNo ...'
    GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User);
    assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
           && "Unexpected GEPI!");
    
    // Load the pointer for this field.
    unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
    if (InsertedLoadsForPtr.size() <= FieldNo)
      InsertedLoadsForPtr.resize(FieldNo+1);
    if (InsertedLoadsForPtr[FieldNo] == 0)
      InsertedLoadsForPtr[FieldNo] = new LoadInst(FieldGlobals[FieldNo],
                                                  Ptr->getName()+".f" + 
                                                  utostr(FieldNo), Ptr);
    Value *NewPtr = InsertedLoadsForPtr[FieldNo];

    // Create the new GEP idx vector.
    SmallVector<Value*, 8> GEPIdx;
    GEPIdx.push_back(GEPI->getOperand(1));
    GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());

    Value *NGEPI = new GetElementPtrInst(NewPtr, &GEPIdx[0], GEPIdx.size(),
                                         GEPI->getName(), GEPI);
    GEPI->replaceAllUsesWith(NGEPI);
    GEPI->eraseFromParent();
  }
}

/// PerformHeapAllocSRoA - MI is an allocation of an array of structures.  Break
/// it up into multiple allocations of arrays of the fields.
static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, MallocInst *MI){
  DOUT << "SROA HEAP ALLOC: " << *GV << "  MALLOC = " << *MI;
  const StructType *STy = cast<StructType>(MI->getAllocatedType());

  // There is guaranteed to be at least one use of the malloc (storing
  // it into GV).  If there are other uses, change them to be uses of
  // the global to simplify later code.  This also deletes the store
  // into GV.
  ReplaceUsesOfMallocWithGlobal(MI, GV);
  
  // Okay, at this point, there are no users of the malloc.  Insert N
  // new mallocs at the same place as MI, and N globals.
  std::vector<GlobalVariable*> FieldGlobals;
  std::vector<MallocInst*> FieldMallocs;
  
  for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
    const Type *FieldTy = STy->getElementType(FieldNo);
    const Type *PFieldTy = PointerType::get(FieldTy);
    
    GlobalVariable *NGV =
      new GlobalVariable(PFieldTy, false, GlobalValue::InternalLinkage,
                         Constant::getNullValue(PFieldTy),
                         GV->getName() + ".f" + utostr(FieldNo), GV,
                         GV->isThreadLocal());
    FieldGlobals.push_back(NGV);
    
    MallocInst *NMI = new MallocInst(FieldTy, MI->getArraySize(),
                                     MI->getName() + ".f" + utostr(FieldNo),MI);
    FieldMallocs.push_back(NMI);
    new StoreInst(NMI, NGV, MI);
  }
  
  // The tricky aspect of this transformation is handling the case when malloc
  // fails.  In the original code, malloc failing would set the result pointer
  // of malloc to null.  In this case, some mallocs could succeed and others
  // could fail.  As such, we emit code that looks like this:
  //    F0 = malloc(field0)
  //    F1 = malloc(field1)
  //    F2 = malloc(field2)
  //    if (F0 == 0 || F1 == 0 || F2 == 0) {
  //      if (F0) { free(F0); F0 = 0; }
  //      if (F1) { free(F1); F1 = 0; }
  //      if (F2) { free(F2); F2 = 0; }
  //    }
  Value *RunningOr = 0;
  for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
    Value *Cond = new ICmpInst(ICmpInst::ICMP_EQ, FieldMallocs[i],
                             Constant::getNullValue(FieldMallocs[i]->getType()),
                                  "isnull", MI);
    if (!RunningOr)
      RunningOr = Cond;   // First seteq
    else
      RunningOr = BinaryOperator::createOr(RunningOr, Cond, "tmp", MI);
  }

  // Split the basic block at the old malloc.
  BasicBlock *OrigBB = MI->getParent();
  BasicBlock *ContBB = OrigBB->splitBasicBlock(MI, "malloc_cont");
  
  // Create the block to check the first condition.  Put all these blocks at the
  // end of the function as they are unlikely to be executed.
  BasicBlock *NullPtrBlock = new BasicBlock("malloc_ret_null",
                                            OrigBB->getParent());
  
  // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
  // branch on RunningOr.
  OrigBB->getTerminator()->eraseFromParent();
  new BranchInst(NullPtrBlock, ContBB, RunningOr, OrigBB);
  
  // Within the NullPtrBlock, we need to emit a comparison and branch for each
  // pointer, because some may be null while others are not.
  for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
    Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
    Value *Cmp = new ICmpInst(ICmpInst::ICMP_NE, GVVal, 
                              Constant::getNullValue(GVVal->getType()),
                              "tmp", NullPtrBlock);
    BasicBlock *FreeBlock = new BasicBlock("free_it", OrigBB->getParent());
    BasicBlock *NextBlock = new BasicBlock("next", OrigBB->getParent());
    new BranchInst(FreeBlock, NextBlock, Cmp, NullPtrBlock);

    // Fill in FreeBlock.
    new FreeInst(GVVal, FreeBlock);
    new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
                  FreeBlock);
    new BranchInst(NextBlock, FreeBlock);
    
    NullPtrBlock = NextBlock;
  }
  
  new BranchInst(ContBB, NullPtrBlock);
  
  
  // MI is no longer needed, remove it.
  MI->eraseFromParent();

  
  // Okay, the malloc site is completely handled.  All of the uses of GV are now
  // loads, and all uses of those loads are simple.  Rewrite them to use loads
  // of the per-field globals instead.
  while (!GV->use_empty()) {
    if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) {
      RewriteUsesOfLoadForHeapSRoA(LI, FieldGlobals);
      LI->eraseFromParent();
    } else {
      // Must be a store of null.
      StoreInst *SI = cast<StoreInst>(GV->use_back());
      assert(isa<Constant>(SI->getOperand(0)) &&
             cast<Constant>(SI->getOperand(0))->isNullValue() &&
             "Unexpected heap-sra user!");
      
      // Insert a store of null into each global.
      for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
        Constant *Null = 
          Constant::getNullValue(FieldGlobals[i]->getType()->getElementType());
        new StoreInst(Null, FieldGlobals[i], SI);
      }
      // Erase the original store.
      SI->eraseFromParent();
    }
  }

  // The old global is now dead, remove it.
  GV->eraseFromParent();

  ++NumHeapSRA;
  return FieldGlobals[0];
}


// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
// that only one value (besides its initializer) is ever stored to the global.
static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
                                     Module::global_iterator &GVI,
                                     TargetData &TD) {
  if (CastInst *CI = dyn_cast<CastInst>(StoredOnceVal))
    StoredOnceVal = CI->getOperand(0);
  else if (GetElementPtrInst *GEPI =dyn_cast<GetElementPtrInst>(StoredOnceVal)){
    // "getelementptr Ptr, 0, 0, 0" is really just a cast.
    bool IsJustACast = true;
    for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
      if (!isa<Constant>(GEPI->getOperand(i)) ||
          !cast<Constant>(GEPI->getOperand(i))->isNullValue()) {
        IsJustACast = false;
        break;
      }
    if (IsJustACast)
      StoredOnceVal = GEPI->getOperand(0);
  }

  // If we are dealing with a pointer global that is initialized to null and
  // only has one (non-null) value stored into it, then we can optimize any
  // users of the loaded value (often calls and loads) that would trap if the
  // value was null.
  if (isa<PointerType>(GV->getInitializer()->getType()) &&
      GV->getInitializer()->isNullValue()) {
    if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
      if (GV->getInitializer()->getType() != SOVC->getType())
        SOVC = ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());

      // Optimize away any trapping uses of the loaded value.
      if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC))
        return true;
    } else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) {
      // If this is a malloc of an abstract type, don't touch it.
      if (!MI->getAllocatedType()->isSized())
        return false;
      
      // We can't optimize this global unless all uses of it are *known* to be
      // of the malloc value, not of the null initializer value (consider a use
      // that compares the global's value against zero to see if the malloc has
      // been reached).  To do this, we check to see if all uses of the global
      // would trap if the global were null: this proves that they must all
      // happen after the malloc.
      if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
        return false;

      // We can't optimize this if the malloc itself is used in a complex way,
      // for example, being stored into multiple globals.  This allows the
      // malloc to be stored into the specified global, loaded setcc'd, and
      // GEP'd.  These are all things we could transform to using the global
      // for.
      if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV))
        return false;

      
      // If we have a global that is only initialized with a fixed size malloc,
      // transform the program to use global memory instead of malloc'd memory.
      // This eliminates dynamic allocation, avoids an indirection accessing the
      // data, and exposes the resultant global to further GlobalOpt.
      if (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize())) {
        // Restrict this transformation to only working on small allocations
        // (2048 bytes currently), as we don't want to introduce a 16M global or
        // something.
        if (NElements->getZExtValue()*
                     TD.getTypeSize(MI->getAllocatedType()) < 2048) {
          GVI = OptimizeGlobalAddressOfMalloc(GV, MI);
          return true;
        }
      }

      // If the allocation is an array of structures, consider transforming this
      // into multiple malloc'd arrays, one for each field.  This is basically
      // SRoA for malloc'd memory.
      if (const StructType *AllocTy = 
                  dyn_cast<StructType>(MI->getAllocatedType())) {
        // This the structure has an unreasonable number of fields, leave it
        // alone.
        if (AllocTy->getNumElements() <= 16 && AllocTy->getNumElements() > 0 &&
            GlobalLoadUsesSimpleEnoughForHeapSRA(GV)) {
          GVI = PerformHeapAllocSRoA(GV, MI);
          return true;
        }
      }
    }
  }

  return false;
}

/// ShrinkGlobalToBoolean - At this point, we have learned that the only two
/// values ever stored into GV are its initializer and OtherVal.
static void ShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
  // Create the new global, initializing it to false.
  GlobalVariable *NewGV = new GlobalVariable(Type::Int1Ty, false,
         GlobalValue::InternalLinkage, ConstantInt::getFalse(),
                                             GV->getName()+".b",
                                             (Module *)NULL,
                                             GV->isThreadLocal());
  GV->getParent()->getGlobalList().insert(GV, NewGV);

  Constant *InitVal = GV->getInitializer();
  assert(InitVal->getType() != Type::Int1Ty && "No reason to shrink to bool!");

  // If initialized to zero and storing one into the global, we can use a cast
  // instead of a select to synthesize the desired value.
  bool IsOneZero = false;
  if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
    IsOneZero = InitVal->isNullValue() && CI->isOne();

  while (!GV->use_empty()) {
    Instruction *UI = cast<Instruction>(GV->use_back());
    if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
      // Change the store into a boolean store.
      bool StoringOther = SI->getOperand(0) == OtherVal;
      // Only do this if we weren't storing a loaded value.
      Value *StoreVal;
      if (StoringOther || SI->getOperand(0) == InitVal)
        StoreVal = ConstantInt::get(Type::Int1Ty, StoringOther);
      else {
        // Otherwise, we are storing a previously loaded copy.  To do this,
        // change the copy from copying the original value to just copying the
        // bool.
        Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));

        // If we're already replaced the input, StoredVal will be a cast or
        // select instruction.  If not, it will be a load of the original
        // global.
        if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
          assert(LI->getOperand(0) == GV && "Not a copy!");
          // Insert a new load, to preserve the saved value.
          StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI);
        } else {
          assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
                 "This is not a form that we understand!");
          StoreVal = StoredVal->getOperand(0);
          assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
        }
      }
      new StoreInst(StoreVal, NewGV, SI);
    } else if (!UI->use_empty()) {
      // Change the load into a load of bool then a select.
      LoadInst *LI = cast<LoadInst>(UI);
      LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI);
      Value *NSI;
      if (IsOneZero)
        NSI = new ZExtInst(NLI, LI->getType(), "", LI);
      else
        NSI = new SelectInst(NLI, OtherVal, InitVal, "", LI);
      NSI->takeName(LI);
      LI->replaceAllUsesWith(NSI);
    }
    UI->eraseFromParent();
  }

  GV->eraseFromParent();
}


/// ProcessInternalGlobal - Analyze the specified global variable and optimize
/// it if possible.  If we make a change, return true.
bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
                                      Module::global_iterator &GVI) {
  std::set<PHINode*> PHIUsers;
  GlobalStatus GS;
  GV->removeDeadConstantUsers();

  if (GV->use_empty()) {
    DOUT << "GLOBAL DEAD: " << *GV;
    GV->eraseFromParent();
    ++NumDeleted;
    return true;
  }

  if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
#if 0
    cerr << "Global: " << *GV;
    cerr << "  isLoaded = " << GS.isLoaded << "\n";
    cerr << "  StoredType = ";
    switch (GS.StoredType) {
    case GlobalStatus::NotStored: cerr << "NEVER STORED\n"; break;
    case GlobalStatus::isInitializerStored: cerr << "INIT STORED\n"; break;
    case GlobalStatus::isStoredOnce: cerr << "STORED ONCE\n"; break;
    case GlobalStatus::isStored: cerr << "stored\n"; break;
    }
    if (GS.StoredType == GlobalStatus::isStoredOnce && GS.StoredOnceValue)
      cerr << "  StoredOnceValue = " << *GS.StoredOnceValue << "\n";
    if (GS.AccessingFunction && !GS.HasMultipleAccessingFunctions)
      cerr << "  AccessingFunction = " << GS.AccessingFunction->getName()
                << "\n";
    cerr << "  HasMultipleAccessingFunctions =  "
              << GS.HasMultipleAccessingFunctions << "\n";
    cerr << "  HasNonInstructionUser = " << GS.HasNonInstructionUser<<"\n";
    cerr << "  isNotSuitableForSRA = " << GS.isNotSuitableForSRA << "\n";
    cerr << "\n";
#endif
    
    // If this is a first class global and has only one accessing function
    // and this function is main (which we know is not recursive we can make
    // this global a local variable) we replace the global with a local alloca
    // in this function.
    //
    // NOTE: It doesn't make sense to promote non first class types since we
    // are just replacing static memory to stack memory.
    if (!GS.HasMultipleAccessingFunctions &&
        GS.AccessingFunction && !GS.HasNonInstructionUser &&
        GV->getType()->getElementType()->isFirstClassType() &&
        GS.AccessingFunction->getName() == "main" &&
        GS.AccessingFunction->hasExternalLinkage()) {
      DOUT << "LOCALIZING GLOBAL: " << *GV;
      Instruction* FirstI = GS.AccessingFunction->getEntryBlock().begin();
      const Type* ElemTy = GV->getType()->getElementType();
      // FIXME: Pass Global's alignment when globals have alignment
      AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), FirstI);
      if (!isa<UndefValue>(GV->getInitializer()))
        new StoreInst(GV->getInitializer(), Alloca, FirstI);

      GV->replaceAllUsesWith(Alloca);
      GV->eraseFromParent();
      ++NumLocalized;
      return true;
    }
    
    // If the global is never loaded (but may be stored to), it is dead.
    // Delete it now.
    if (!GS.isLoaded) {
      DOUT << "GLOBAL NEVER LOADED: " << *GV;

      // Delete any stores we can find to the global.  We may not be able to
      // make it completely dead though.
      bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer());

      // If the global is dead now, delete it.
      if (GV->use_empty()) {
        GV->eraseFromParent();
        ++NumDeleted;
        Changed = true;
      }
      return Changed;

    } else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
      DOUT << "MARKING CONSTANT: " << *GV;
      GV->setConstant(true);

      // Clean up any obviously simplifiable users now.
      CleanupConstantGlobalUsers(GV, GV->getInitializer());

      // If the global is dead now, just nuke it.
      if (GV->use_empty()) {
        DOUT << "   *** Marking constant allowed us to simplify "
             << "all users and delete global!\n";
        GV->eraseFromParent();
        ++NumDeleted;
      }

      ++NumMarked;
      return true;
    } else if (!GS.isNotSuitableForSRA &&
               !GV->getInitializer()->getType()->isFirstClassType()) {
      if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) {
        GVI = FirstNewGV;  // Don't skip the newly produced globals!
        return true;
      }
    } else if (GS.StoredType == GlobalStatus::isStoredOnce) {
      // If the initial value for the global was an undef value, and if only
      // one other value was stored into it, we can just change the
      // initializer to be an undef value, then delete all stores to the
      // global.  This allows us to mark it constant.
      if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
        if (isa<UndefValue>(GV->getInitializer())) {
          // Change the initial value here.
          GV->setInitializer(SOVConstant);

          // Clean up any obviously simplifiable users now.
          CleanupConstantGlobalUsers(GV, GV->getInitializer());

          if (GV->use_empty()) {
            DOUT << "   *** Substituting initializer allowed us to "
                 << "simplify all users and delete global!\n";
            GV->eraseFromParent();
            ++NumDeleted;
          } else {
            GVI = GV;
          }
          ++NumSubstitute;
          return true;
        }

      // Try to optimize globals based on the knowledge that only one value
      // (besides its initializer) is ever stored to the global.
      if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI,
                                   getAnalysis<TargetData>()))
        return true;

      // Otherwise, if the global was not a boolean, we can shrink it to be a
      // boolean.
      if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
        if (GV->getType()->getElementType() != Type::Int1Ty &&
            !GV->getType()->getElementType()->isFloatingPoint() &&
            !isa<VectorType>(GV->getType()->getElementType()) &&
            !GS.HasPHIUser && !GS.isNotSuitableForSRA) {
          DOUT << "   *** SHRINKING TO BOOL: " << *GV;
          ShrinkGlobalToBoolean(GV, SOVConstant);
          ++NumShrunkToBool;
          return true;
        }
    }
  }
  return false;
}

/// OnlyCalledDirectly - Return true if the specified function is only called
/// directly.  In other words, its address is never taken.
static bool OnlyCalledDirectly(Function *F) {
  for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
    Instruction *User = dyn_cast<Instruction>(*UI);
    if (!User) return false;
    if (!isa<CallInst>(User) && !isa<InvokeInst>(User)) return false;

    // See if the function address is passed as an argument.
    for (unsigned i = 1, e = User->getNumOperands(); i != e; ++i)
      if (User->getOperand(i) == F) return false;
  }
  return true;
}

/// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
/// function, changing them to FastCC.
static void ChangeCalleesToFastCall(Function *F) {
  for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
    Instruction *User = cast<Instruction>(*UI);
    if (CallInst *CI = dyn_cast<CallInst>(User))
      CI->setCallingConv(CallingConv::Fast);
    else
      cast<InvokeInst>(User)->setCallingConv(CallingConv::Fast);
  }
}

bool GlobalOpt::OptimizeFunctions(Module &M) {
  bool Changed = false;
  // Optimize functions.
  for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
    Function *F = FI++;
    F->removeDeadConstantUsers();
    if (F->use_empty() && (F->hasInternalLinkage() ||
                           F->hasLinkOnceLinkage())) {
      M.getFunctionList().erase(F);
      Changed = true;
      ++NumFnDeleted;
    } else if (F->hasInternalLinkage() &&
               F->getCallingConv() == CallingConv::C &&  !F->isVarArg() &&
               OnlyCalledDirectly(F)) {
      // If this function has C calling conventions, is not a varargs
      // function, and is only called directly, promote it to use the Fast
      // calling convention.
      F->setCallingConv(CallingConv::Fast);
      ChangeCalleesToFastCall(F);
      ++NumFastCallFns;
      Changed = true;
    }
  }
  return Changed;
}

bool GlobalOpt::OptimizeGlobalVars(Module &M) {
  bool Changed = false;
  for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
       GVI != E; ) {
    GlobalVariable *GV = GVI++;
    if (!GV->isConstant() && GV->hasInternalLinkage() &&
        GV->hasInitializer())
      Changed |= ProcessInternalGlobal(GV, GVI);
  }
  return Changed;
}

/// FindGlobalCtors - Find the llvm.globalctors list, verifying that all
/// initializers have an init priority of 65535.
GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
  for (Module::global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I)
    if (I->getName() == "llvm.global_ctors") {
      // Found it, verify it's an array of { int, void()* }.
      const ArrayType *ATy =dyn_cast<ArrayType>(I->getType()->getElementType());
      if (!ATy) return 0;
      const StructType *STy = dyn_cast<StructType>(ATy->getElementType());
      if (!STy || STy->getNumElements() != 2 ||
          STy->getElementType(0) != Type::Int32Ty) return 0;
      const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1));
      if (!PFTy) return 0;
      const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType());
      if (!FTy || FTy->getReturnType() != Type::VoidTy || FTy->isVarArg() ||
          FTy->getNumParams() != 0)
        return 0;
      
      // Verify that the initializer is simple enough for us to handle.
      if (!I->hasInitializer()) return 0;
      ConstantArray *CA = dyn_cast<ConstantArray>(I->getInitializer());
      if (!CA) return 0;
      for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i)
        if (ConstantStruct *CS = dyn_cast<ConstantStruct>(CA->getOperand(i))) {
          if (isa<ConstantPointerNull>(CS->getOperand(1)))
            continue;

          // Must have a function or null ptr.
          if (!isa<Function>(CS->getOperand(1)))
            return 0;
          
          // Init priority must be standard.
          ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0));
          if (!CI || CI->getZExtValue() != 65535)
            return 0;
        } else {
          return 0;
        }
      
      return I;
    }
  return 0;
}

/// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
/// return a list of the functions and null terminator as a vector.
static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
  ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
  std::vector<Function*> Result;
  Result.reserve(CA->getNumOperands());
  for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i) {
    ConstantStruct *CS = cast<ConstantStruct>(CA->getOperand(i));
    Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
  }
  return Result;
}

/// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
/// specified array, returning the new global to use.
static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL, 
                                          const std::vector<Function*> &Ctors) {
  // If we made a change, reassemble the initializer list.
  std::vector<Constant*> CSVals;
  CSVals.push_back(ConstantInt::get(Type::Int32Ty, 65535));
  CSVals.push_back(0);
  
  // Create the new init list.
  std::vector<Constant*> CAList;
  for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
    if (Ctors[i]) {
      CSVals[1] = Ctors[i];
    } else {
      const Type *FTy = FunctionType::get(Type::VoidTy,
                                          std::vector<const Type*>(), false);
      const PointerType *PFTy = PointerType::get(FTy);
      CSVals[1] = Constant::getNullValue(PFTy);
      CSVals[0] = ConstantInt::get(Type::Int32Ty, 2147483647);
    }
    CAList.push_back(ConstantStruct::get(CSVals));
  }
  
  // Create the array initializer.
  const Type *StructTy =
    cast<ArrayType>(GCL->getType()->getElementType())->getElementType();
  Constant *CA = ConstantArray::get(ArrayType::get(StructTy, CAList.size()),
                                    CAList);
  
  // If we didn't change the number of elements, don't create a new GV.
  if (CA->getType() == GCL->getInitializer()->getType()) {
    GCL->setInitializer(CA);
    return GCL;
  }
  
  // Create the new global and insert it next to the existing list.
  GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(),
                                           GCL->getLinkage(), CA, "",
                                           (Module *)NULL,
                                           GCL->isThreadLocal());
  GCL->getParent()->getGlobalList().insert(GCL, NGV);
  NGV->takeName(GCL);
  
  // Nuke the old list, replacing any uses with the new one.
  if (!GCL->use_empty()) {
    Constant *V = NGV;
    if (V->getType() != GCL->getType())
      V = ConstantExpr::getBitCast(V, GCL->getType());
    GCL->replaceAllUsesWith(V);
  }
  GCL->eraseFromParent();
  
  if (Ctors.size())
    return NGV;
  else
    return 0;
}


static Constant *getVal(std::map<Value*, Constant*> &ComputedValues,
                        Value *V) {
  if (Constant *CV = dyn_cast<Constant>(V)) return CV;
  Constant *R = ComputedValues[V];
  assert(R && "Reference to an uncomputed value!");
  return R;
}

/// isSimpleEnoughPointerToCommit - Return true if this constant is simple
/// enough for us to understand.  In particular, if it is a cast of something,
/// we punt.  We basically just support direct accesses to globals and GEP's of
/// globals.  This should be kept up to date with CommitValueTo.
static bool isSimpleEnoughPointerToCommit(Constant *C) {
  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
    if (!GV->hasExternalLinkage() && !GV->hasInternalLinkage())
      return false;  // do not allow weak/linkonce/dllimport/dllexport linkage.
    return !GV->isDeclaration();  // reject external globals.
  }
  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
    // Handle a constantexpr gep.
    if (CE->getOpcode() == Instruction::GetElementPtr &&
        isa<GlobalVariable>(CE->getOperand(0))) {
      GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
      if (!GV->hasExternalLinkage() && !GV->hasInternalLinkage())
        return false;  // do not allow weak/linkonce/dllimport/dllexport linkage.
      return GV->hasInitializer() &&
             ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
    }
  return false;
}

/// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global
/// initializer.  This returns 'Init' modified to reflect 'Val' stored into it.
/// At this point, the GEP operands of Addr [0, OpNo) have been stepped into.
static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
                                   ConstantExpr *Addr, unsigned OpNo) {
  // Base case of the recursion.
  if (OpNo == Addr->getNumOperands()) {
    assert(Val->getType() == Init->getType() && "Type mismatch!");
    return Val;
  }
  
  if (const StructType *STy = dyn_cast<StructType>(Init->getType())) {
    std::vector<Constant*> Elts;

    // Break up the constant into its elements.
    if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) {
      for (unsigned i = 0, e = CS->getNumOperands(); i != e; ++i)
        Elts.push_back(CS->getOperand(i));
    } else if (isa<ConstantAggregateZero>(Init)) {
      for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
        Elts.push_back(Constant::getNullValue(STy->getElementType(i)));
    } else if (isa<UndefValue>(Init)) {
      for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
        Elts.push_back(UndefValue::get(STy->getElementType(i)));
    } else {
      assert(0 && "This code is out of sync with "
             " ConstantFoldLoadThroughGEPConstantExpr");
    }
    
    // Replace the element that we are supposed to.
    ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
    unsigned Idx = CU->getZExtValue();
    assert(Idx < STy->getNumElements() && "Struct index out of range!");
    Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
    
    // Return the modified struct.
    return ConstantStruct::get(Elts);
  } else {
    ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
    const ArrayType *ATy = cast<ArrayType>(Init->getType());

    // Break up the array into elements.
    std::vector<Constant*> Elts;
    if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) {
      for (unsigned i = 0, e = CA->getNumOperands(); i != e; ++i)
        Elts.push_back(CA->getOperand(i));
    } else if (isa<ConstantAggregateZero>(Init)) {
      Constant *Elt = Constant::getNullValue(ATy->getElementType());
      Elts.assign(ATy->getNumElements(), Elt);
    } else if (isa<UndefValue>(Init)) {
      Constant *Elt = UndefValue::get(ATy->getElementType());
      Elts.assign(ATy->getNumElements(), Elt);
    } else {
      assert(0 && "This code is out of sync with "
             " ConstantFoldLoadThroughGEPConstantExpr");
    }
    
    assert(CI->getZExtValue() < ATy->getNumElements());
    Elts[CI->getZExtValue()] =
      EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
    return ConstantArray::get(ATy, Elts);
  }    
}

/// CommitValueTo - We have decided that Addr (which satisfies the predicate
/// isSimpleEnoughPointerToCommit) should get Val as its value.  Make it happen.
static void CommitValueTo(Constant *Val, Constant *Addr) {
  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
    assert(GV->hasInitializer());
    GV->setInitializer(Val);
    return;
  }
  
  ConstantExpr *CE = cast<ConstantExpr>(Addr);
  GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
  
  Constant *Init = GV->getInitializer();
  Init = EvaluateStoreInto(Init, Val, CE, 2);
  GV->setInitializer(Init);
}

/// ComputeLoadResult - Return the value that would be computed by a load from
/// P after the stores reflected by 'memory' have been performed.  If we can't
/// decide, return null.
static Constant *ComputeLoadResult(Constant *P,
                                const std::map<Constant*, Constant*> &Memory) {
  // If this memory location has been recently stored, use the stored value: it
  // is the most up-to-date.
  std::map<Constant*, Constant*>::const_iterator I = Memory.find(P);
  if (I != Memory.end()) return I->second;
 
  // Access it.
  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
    if (GV->hasInitializer())
      return GV->getInitializer();
    return 0;
  }
  
  // Handle a constantexpr getelementptr.
  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
    if (CE->getOpcode() == Instruction::GetElementPtr &&
        isa<GlobalVariable>(CE->getOperand(0))) {
      GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
      if (GV->hasInitializer())
        return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
    }

  return 0;  // don't know how to evaluate.
}

/// EvaluateFunction - Evaluate a call to function F, returning true if
/// successful, false if we can't evaluate it.  ActualArgs contains the formal
/// arguments for the function.
static bool EvaluateFunction(Function *F, Constant *&RetVal,
                             const std::vector<Constant*> &ActualArgs,
                             std::vector<Function*> &CallStack,
                             std::map<Constant*, Constant*> &MutatedMemory,
                             std::vector<GlobalVariable*> &AllocaTmps) {
  // Check to see if this function is already executing (recursion).  If so,
  // bail out.  TODO: we might want to accept limited recursion.
  if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
    return false;
  
  CallStack.push_back(F);
  
  /// Values - As we compute SSA register values, we store their contents here.
  std::map<Value*, Constant*> Values;
  
  // Initialize arguments to the incoming values specified.
  unsigned ArgNo = 0;
  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
       ++AI, ++ArgNo)
    Values[AI] = ActualArgs[ArgNo];

  /// ExecutedBlocks - We only handle non-looping, non-recursive code.  As such,
  /// we can only evaluate any one basic block at most once.  This set keeps
  /// track of what we have executed so we can detect recursive cases etc.
  std::set<BasicBlock*> ExecutedBlocks;
  
  // CurInst - The current instruction we're evaluating.
  BasicBlock::iterator CurInst = F->begin()->begin();
  
  // This is the main evaluation loop.
  while (1) {
    Constant *InstResult = 0;
    
    if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
      if (SI->isVolatile()) return false;  // no volatile accesses.
      Constant *Ptr = getVal(Values, SI->getOperand(1));
      if (!isSimpleEnoughPointerToCommit(Ptr))
        // If this is too complex for us to commit, reject it.
        return false;
      Constant *Val = getVal(Values, SI->getOperand(0));
      MutatedMemory[Ptr] = Val;
    } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
      InstResult = ConstantExpr::get(BO->getOpcode(),
                                     getVal(Values, BO->getOperand(0)),
                                     getVal(Values, BO->getOperand(1)));
    } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
      InstResult = ConstantExpr::getCompare(CI->getPredicate(),
                                            getVal(Values, CI->getOperand(0)),
                                            getVal(Values, CI->getOperand(1)));
    } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
      InstResult = ConstantExpr::getCast(CI->getOpcode(),
                                         getVal(Values, CI->getOperand(0)),
                                         CI->getType());
    } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
      InstResult = ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)),
                                           getVal(Values, SI->getOperand(1)),
                                           getVal(Values, SI->getOperand(2)));
    } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
      Constant *P = getVal(Values, GEP->getOperand(0));
      SmallVector<Constant*, 8> GEPOps;
      for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
        GEPOps.push_back(getVal(Values, GEP->getOperand(i)));
      InstResult = ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size());
    } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
      if (LI->isVolatile()) return false;  // no volatile accesses.
      InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)),
                                     MutatedMemory);
      if (InstResult == 0) return false; // Could not evaluate load.
    } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
      if (AI->isArrayAllocation()) return false;  // Cannot handle array allocs.
      const Type *Ty = AI->getType()->getElementType();
      AllocaTmps.push_back(new GlobalVariable(Ty, false,
                                              GlobalValue::InternalLinkage,
                                              UndefValue::get(Ty),
                                              AI->getName()));
      InstResult = AllocaTmps.back();     
    } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) {
      // Cannot handle inline asm.
      if (isa<InlineAsm>(CI->getOperand(0))) return false;

      // Resolve function pointers.
      Function *Callee = dyn_cast<Function>(getVal(Values, CI->getOperand(0)));
      if (!Callee) return false;  // Cannot resolve.

      std::vector<Constant*> Formals;
      for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
        Formals.push_back(getVal(Values, CI->getOperand(i)));
      
      if (Callee->isDeclaration()) {
        // If this is a function we can constant fold, do it.
        if (Constant *C = ConstantFoldCall(Callee, &Formals[0],
                                           Formals.size())) {
          InstResult = C;
        } else {
          return false;
        }
      } else {
        if (Callee->getFunctionType()->isVarArg())
          return false;
        
        Constant *RetVal;
        
        // Execute the call, if successful, use the return value.
        if (!EvaluateFunction(Callee, RetVal, Formals, CallStack,
                              MutatedMemory, AllocaTmps))
          return false;
        InstResult = RetVal;
      }
    } else if (isa<TerminatorInst>(CurInst)) {
      BasicBlock *NewBB = 0;
      if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
        if (BI->isUnconditional()) {
          NewBB = BI->getSuccessor(0);
        } else {
          ConstantInt *Cond =
            dyn_cast<ConstantInt>(getVal(Values, BI->getCondition()));
          if (!Cond) return false;  // Cannot determine.

          NewBB = BI->getSuccessor(!Cond->getZExtValue());          
        }
      } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
        ConstantInt *Val =
          dyn_cast<ConstantInt>(getVal(Values, SI->getCondition()));
        if (!Val) return false;  // Cannot determine.
        NewBB = SI->getSuccessor(SI->findCaseValue(Val));
      } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) {
        if (RI->getNumOperands())
          RetVal = getVal(Values, RI->getOperand(0));
        
        CallStack.pop_back();  // return from fn.
        return true;  // We succeeded at evaluating this ctor!
      } else {
        // invoke, unwind, unreachable.
        return false;  // Cannot handle this terminator.
      }
      
      // Okay, we succeeded in evaluating this control flow.  See if we have
      // executed the new block before.  If so, we have a looping function,
      // which we cannot evaluate in reasonable time.
      if (!ExecutedBlocks.insert(NewBB).second)
        return false;  // looped!
      
      // Okay, we have never been in this block before.  Check to see if there
      // are any PHI nodes.  If so, evaluate them with information about where
      // we came from.
      BasicBlock *OldBB = CurInst->getParent();
      CurInst = NewBB->begin();
      PHINode *PN;
      for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
        Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB));

      // Do NOT increment CurInst.  We know that the terminator had no value.
      continue;
    } else {
      // Did not know how to evaluate this!
      return false;
    }
    
    if (!CurInst->use_empty())
      Values[CurInst] = InstResult;
    
    // Advance program counter.
    ++CurInst;
  }
}

/// EvaluateStaticConstructor - Evaluate static constructors in the function, if
/// we can.  Return true if we can, false otherwise.
static bool EvaluateStaticConstructor(Function *F) {
  /// MutatedMemory - For each store we execute, we update this map.  Loads
  /// check this to get the most up-to-date value.  If evaluation is successful,
  /// this state is committed to the process.
  std::map<Constant*, Constant*> MutatedMemory;

  /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
  /// to represent its body.  This vector is needed so we can delete the
  /// temporary globals when we are done.
  std::vector<GlobalVariable*> AllocaTmps;
  
  /// CallStack - This is used to detect recursion.  In pathological situations
  /// we could hit exponential behavior, but at least there is nothing
  /// unbounded.
  std::vector<Function*> CallStack;

  // Call the function.
  Constant *RetValDummy;
  bool EvalSuccess = EvaluateFunction(F, RetValDummy, std::vector<Constant*>(),
                                       CallStack, MutatedMemory, AllocaTmps);
  if (EvalSuccess) {
    // We succeeded at evaluation: commit the result.
    DOUT << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
         << F->getName() << "' to " << MutatedMemory.size()
         << " stores.\n";
    for (std::map<Constant*, Constant*>::iterator I = MutatedMemory.begin(),
         E = MutatedMemory.end(); I != E; ++I)
      CommitValueTo(I->second, I->first);
  }
  
  // At this point, we are done interpreting.  If we created any 'alloca'
  // temporaries, release them now.
  while (!AllocaTmps.empty()) {
    GlobalVariable *Tmp = AllocaTmps.back();
    AllocaTmps.pop_back();
    
    // If there are still users of the alloca, the program is doing something
    // silly, e.g. storing the address of the alloca somewhere and using it
    // later.  Since this is undefined, we'll just make it be null.
    if (!Tmp->use_empty())
      Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
    delete Tmp;
  }
  
  return EvalSuccess;
}



/// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
/// Return true if anything changed.
bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
  std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
  bool MadeChange = false;
  if (Ctors.empty()) return false;
  
  // Loop over global ctors, optimizing them when we can.
  for (unsigned i = 0; i != Ctors.size(); ++i) {
    Function *F = Ctors[i];
    // Found a null terminator in the middle of the list, prune off the rest of
    // the list.
    if (F == 0) {
      if (i != Ctors.size()-1) {
        Ctors.resize(i+1);
        MadeChange = true;
      }
      break;
    }
    
    // We cannot simplify external ctor functions.
    if (F->empty()) continue;
    
    // If we can evaluate the ctor at compile time, do.
    if (EvaluateStaticConstructor(F)) {
      Ctors.erase(Ctors.begin()+i);
      MadeChange = true;
      --i;
      ++NumCtorsEvaluated;
      continue;
    }
  }
  
  if (!MadeChange) return false;
  
  GCL = InstallGlobalCtors(GCL, Ctors);
  return true;
}


bool GlobalOpt::runOnModule(Module &M) {
  bool Changed = false;
  
  // Try to find the llvm.globalctors list.
  GlobalVariable *GlobalCtors = FindGlobalCtors(M);

  bool LocalChange = true;
  while (LocalChange) {
    LocalChange = false;
    
    // Delete functions that are trivially dead, ccc -> fastcc
    LocalChange |= OptimizeFunctions(M);
    
    // Optimize global_ctors list.
    if (GlobalCtors)
      LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
    
    // Optimize non-address-taken globals.
    LocalChange |= OptimizeGlobalVars(M);
    Changed |= LocalChange;
  }
  
  // TODO: Move all global ctors functions to the end of the module for code
  // layout.
  
  return Changed;
}