llvm.org GIT mirror llvm / 91abace lib / Transforms / Scalar / ScalarReplAggregates.cpp
91abace

Tree @91abace (Download .tar.gz)

ScalarReplAggregates.cpp @91abaceraw · history · blame

   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
//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation implements the well known scalar replacement of
// aggregates transformation.  This xform breaks up alloca instructions of
// aggregate type (structure or array) into individual alloca instructions for
// each member (if possible).  Then, if possible, it transforms the individual
// alloca instructions into nice clean scalar SSA form.
//
// This combines a simple SRoA algorithm with the Mem2Reg algorithm because
// often interact, especially for C++ programs.  As such, iterating between
// SRoA, then Mem2Reg until we run out of things to promote works well.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "scalarrepl"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;

STATISTIC(NumReplaced,  "Number of allocas broken up");
STATISTIC(NumPromoted,  "Number of allocas promoted");
STATISTIC(NumConverted, "Number of aggregates converted to scalar");
STATISTIC(NumGlobals,   "Number of allocas copied from constant global");

namespace {
  struct SROA : public FunctionPass {
    static char ID; // Pass identification, replacement for typeid
    explicit SROA(signed T = -1) : FunctionPass(ID) {
      if (T == -1)
        SRThreshold = 128;
      else
        SRThreshold = T;
    }

    bool runOnFunction(Function &F);

    bool performScalarRepl(Function &F);
    bool performPromotion(Function &F);

    // getAnalysisUsage - This pass does not require any passes, but we know it
    // will not alter the CFG, so say so.
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<DominatorTree>();
      AU.addRequired<DominanceFrontier>();
      AU.setPreservesCFG();
    }

  private:
    TargetData *TD;
    
    /// DeadInsts - Keep track of instructions we have made dead, so that
    /// we can remove them after we are done working.
    SmallVector<Value*, 32> DeadInsts;

    /// AllocaInfo - When analyzing uses of an alloca instruction, this captures
    /// information about the uses.  All these fields are initialized to false
    /// and set to true when something is learned.
    struct AllocaInfo {
      /// isUnsafe - This is set to true if the alloca cannot be SROA'd.
      bool isUnsafe : 1;
      
      /// isMemCpySrc - This is true if this aggregate is memcpy'd from.
      bool isMemCpySrc : 1;

      /// isMemCpyDst - This is true if this aggregate is memcpy'd into.
      bool isMemCpyDst : 1;

      AllocaInfo()
        : isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false) {}
    };
    
    unsigned SRThreshold;

    void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }

    bool isSafeAllocaToScalarRepl(AllocaInst *AI);

    void isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
                             AllocaInfo &Info);
    void isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t &Offset,
                   AllocaInfo &Info);
    void isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
                         const Type *MemOpType, bool isStore, AllocaInfo &Info);
    bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size);
    uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset,
                                  const Type *&IdxTy);
    
    void DoScalarReplacement(AllocaInst *AI, 
                             std::vector<AllocaInst*> &WorkList);
    void DeleteDeadInstructions();
   
    void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
                              SmallVector<AllocaInst*, 32> &NewElts);
    void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
                        SmallVector<AllocaInst*, 32> &NewElts);
    void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
                    SmallVector<AllocaInst*, 32> &NewElts);
    void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
                                      AllocaInst *AI,
                                      SmallVector<AllocaInst*, 32> &NewElts);
    void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
                                       SmallVector<AllocaInst*, 32> &NewElts);
    void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
                                      SmallVector<AllocaInst*, 32> &NewElts);
    
    static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI);
  };
}

char SROA::ID = 0;
INITIALIZE_PASS(SROA, "scalarrepl",
                "Scalar Replacement of Aggregates", false, false);

// Public interface to the ScalarReplAggregates pass
FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) { 
  return new SROA(Threshold);
}


//===----------------------------------------------------------------------===//
// Convert To Scalar Optimization.
//===----------------------------------------------------------------------===//

namespace {
/// ConvertToScalarInfo - This class implements the "Convert To Scalar"
/// optimization, which scans the uses of an alloca and determines if it can
/// rewrite it in terms of a single new alloca that can be mem2reg'd.
class ConvertToScalarInfo {
  /// AllocaSize - The size of the alloca being considered.
  unsigned AllocaSize;
  const TargetData &TD;
 
  /// IsNotTrivial - This is set to true if there is some access to the object
  /// which means that mem2reg can't promote it.
  bool IsNotTrivial;
  
  /// VectorTy - This tracks the type that we should promote the vector to if
  /// it is possible to turn it into a vector.  This starts out null, and if it
  /// isn't possible to turn into a vector type, it gets set to VoidTy.
  const Type *VectorTy;
  
  /// HadAVector - True if there is at least one vector access to the alloca.
  /// We don't want to turn random arrays into vectors and use vector element
  /// insert/extract, but if there are element accesses to something that is
  /// also declared as a vector, we do want to promote to a vector.
  bool HadAVector;

public:
  explicit ConvertToScalarInfo(unsigned Size, const TargetData &td)
    : AllocaSize(Size), TD(td) {
    IsNotTrivial = false;
    VectorTy = 0;
    HadAVector = false;
  }
  
  AllocaInst *TryConvert(AllocaInst *AI);
  
private:
  bool CanConvertToScalar(Value *V, uint64_t Offset);
  void MergeInType(const Type *In, uint64_t Offset);
  void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset);
  
  Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType,
                                    uint64_t Offset, IRBuilder<> &Builder);
  Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal,
                                   uint64_t Offset, IRBuilder<> &Builder);
};
} // end anonymous namespace.


/// IsVerbotenVectorType - Return true if this is a vector type ScalarRepl isn't
/// allowed to form.  We do this to avoid MMX types, which is a complete hack,
/// but is required until the backend is fixed.
static bool IsVerbotenVectorType(const VectorType *VTy) {
  // Reject all the MMX vector types.
  switch (VTy->getNumElements()) {
  default: return false;
  case 1: return VTy->getElementType()->isIntegerTy(64);
  case 2: return VTy->getElementType()->isIntegerTy(32);
  case 4: return VTy->getElementType()->isIntegerTy(16);
  case 8: return VTy->getElementType()->isIntegerTy(8);
  }
}


/// TryConvert - Analyze the specified alloca, and if it is safe to do so,
/// rewrite it to be a new alloca which is mem2reg'able.  This returns the new
/// alloca if possible or null if not.
AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) {
  // If we can't convert this scalar, or if mem2reg can trivially do it, bail
  // out.
  if (!CanConvertToScalar(AI, 0) || !IsNotTrivial)
    return 0;
  
  // If we were able to find a vector type that can handle this with
  // insert/extract elements, and if there was at least one use that had
  // a vector type, promote this to a vector.  We don't want to promote
  // random stuff that doesn't use vectors (e.g. <9 x double>) because then
  // we just get a lot of insert/extracts.  If at least one vector is
  // involved, then we probably really do have a union of vector/array.
  const Type *NewTy;
  if (VectorTy && VectorTy->isVectorTy() && HadAVector &&
      !IsVerbotenVectorType(cast<VectorType>(VectorTy))) {
    DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n  TYPE = "
          << *VectorTy << '\n');
    NewTy = VectorTy;  // Use the vector type.
  } else {
    DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n");
    // Create and insert the integer alloca.
    NewTy = IntegerType::get(AI->getContext(), AllocaSize*8);
  }
  AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin());
  ConvertUsesToScalar(AI, NewAI, 0);
  return NewAI;
}

/// MergeInType - Add the 'In' type to the accumulated vector type (VectorTy)
/// so far at the offset specified by Offset (which is specified in bytes).
///
/// There are two cases we handle here:
///   1) A union of vector types of the same size and potentially its elements.
///      Here we turn element accesses into insert/extract element operations.
///      This promotes a <4 x float> with a store of float to the third element
///      into a <4 x float> that uses insert element.
///   2) A fully general blob of memory, which we turn into some (potentially
///      large) integer type with extract and insert operations where the loads
///      and stores would mutate the memory.  We mark this by setting VectorTy
///      to VoidTy.
void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) {
  // If we already decided to turn this into a blob of integer memory, there is
  // nothing to be done.
  if (VectorTy && VectorTy->isVoidTy())
    return;
  
  // If this could be contributing to a vector, analyze it.

  // If the In type is a vector that is the same size as the alloca, see if it
  // matches the existing VecTy.
  if (const VectorType *VInTy = dyn_cast<VectorType>(In)) {
    // Remember if we saw a vector type.
    HadAVector = true;
    
    if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) {
      // If we're storing/loading a vector of the right size, allow it as a
      // vector.  If this the first vector we see, remember the type so that
      // we know the element size.  If this is a subsequent access, ignore it
      // even if it is a differing type but the same size.  Worst case we can
      // bitcast the resultant vectors.
      if (VectorTy == 0)
        VectorTy = VInTy;
      return;
    }
  } else if (In->isFloatTy() || In->isDoubleTy() ||
             (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 &&
              isPowerOf2_32(In->getPrimitiveSizeInBits()))) {
    // If we're accessing something that could be an element of a vector, see
    // if the implied vector agrees with what we already have and if Offset is
    // compatible with it.
    unsigned EltSize = In->getPrimitiveSizeInBits()/8;
    if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 &&
        (VectorTy == 0 || 
         cast<VectorType>(VectorTy)->getElementType()
               ->getPrimitiveSizeInBits()/8 == EltSize)) {
      if (VectorTy == 0)
        VectorTy = VectorType::get(In, AllocaSize/EltSize);
      return;
    }
  }
  
  // Otherwise, we have a case that we can't handle with an optimized vector
  // form.  We can still turn this into a large integer.
  VectorTy = Type::getVoidTy(In->getContext());
}

/// CanConvertToScalar - V is a pointer.  If we can convert the pointee and all
/// its accesses to a single vector type, return true and set VecTy to
/// the new type.  If we could convert the alloca into a single promotable
/// integer, return true but set VecTy to VoidTy.  Further, if the use is not a
/// completely trivial use that mem2reg could promote, set IsNotTrivial.  Offset
/// is the current offset from the base of the alloca being analyzed.
///
/// If we see at least one access to the value that is as a vector type, set the
/// SawVec flag.
bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) {
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
    Instruction *User = cast<Instruction>(*UI);
    
    if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
      // Don't break volatile loads.
      if (LI->isVolatile())
        return false;
      MergeInType(LI->getType(), Offset);
      continue;
    }
    
    if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
      // Storing the pointer, not into the value?
      if (SI->getOperand(0) == V || SI->isVolatile()) return false;
      MergeInType(SI->getOperand(0)->getType(), Offset);
      continue;
    }
    
    if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
      IsNotTrivial = true;  // Can't be mem2reg'd.
      if (!CanConvertToScalar(BCI, Offset))
        return false;
      continue;
    }

    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
      // If this is a GEP with a variable indices, we can't handle it.
      if (!GEP->hasAllConstantIndices())
        return false;
      
      // Compute the offset that this GEP adds to the pointer.
      SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
      uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(),
                                               &Indices[0], Indices.size());
      // See if all uses can be converted.
      if (!CanConvertToScalar(GEP, Offset+GEPOffset))
        return false;
      IsNotTrivial = true;  // Can't be mem2reg'd.
      continue;
    }

    // If this is a constant sized memset of a constant value (e.g. 0) we can
    // handle it.
    if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
      // Store of constant value and constant size.
      if (!isa<ConstantInt>(MSI->getValue()) ||
          !isa<ConstantInt>(MSI->getLength()))
        return false;
      IsNotTrivial = true;  // Can't be mem2reg'd.
      continue;
    }

    // If this is a memcpy or memmove into or out of the whole allocation, we
    // can handle it like a load or store of the scalar type.
    if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
      ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength());
      if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0)
        return false;
      
      IsNotTrivial = true;  // Can't be mem2reg'd.
      continue;
    }
    
    // Otherwise, we cannot handle this!
    return false;
  }
  
  return true;
}

/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca
/// directly.  This happens when we are converting an "integer union" to a
/// single integer scalar, or when we are converting a "vector union" to a
/// vector with insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right.  By the end of this, there should be no uses of Ptr.
void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI,
                                              uint64_t Offset) {
  while (!Ptr->use_empty()) {
    Instruction *User = cast<Instruction>(Ptr->use_back());

    if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
      ConvertUsesToScalar(CI, NewAI, Offset);
      CI->eraseFromParent();
      continue;
    }

    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
      // Compute the offset that this GEP adds to the pointer.
      SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
      uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(),
                                               &Indices[0], Indices.size());
      ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8);
      GEP->eraseFromParent();
      continue;
    }
    
    IRBuilder<> Builder(User->getParent(), User);
    
    if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
      // The load is a bit extract from NewAI shifted right by Offset bits.
      Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp");
      Value *NewLoadVal
        = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder);
      LI->replaceAllUsesWith(NewLoadVal);
      LI->eraseFromParent();
      continue;
    }
    
    if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
      assert(SI->getOperand(0) != Ptr && "Consistency error!");
      Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in");
      Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset,
                                             Builder);
      Builder.CreateStore(New, NewAI);
      SI->eraseFromParent();
      
      // If the load we just inserted is now dead, then the inserted store
      // overwrote the entire thing.
      if (Old->use_empty())
        Old->eraseFromParent();
      continue;
    }
    
    // If this is a constant sized memset of a constant value (e.g. 0) we can
    // transform it into a store of the expanded constant value.
    if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
      assert(MSI->getRawDest() == Ptr && "Consistency error!");
      unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
      if (NumBytes != 0) {
        unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue();
        
        // Compute the value replicated the right number of times.
        APInt APVal(NumBytes*8, Val);

        // Splat the value if non-zero.
        if (Val)
          for (unsigned i = 1; i != NumBytes; ++i)
            APVal |= APVal << 8;
        
        Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in");
        Value *New = ConvertScalar_InsertValue(
                                    ConstantInt::get(User->getContext(), APVal),
                                               Old, Offset, Builder);
        Builder.CreateStore(New, NewAI);
        
        // If the load we just inserted is now dead, then the memset overwrote
        // the entire thing.
        if (Old->use_empty())
          Old->eraseFromParent();        
      }
      MSI->eraseFromParent();
      continue;
    }

    // If this is a memcpy or memmove into or out of the whole allocation, we
    // can handle it like a load or store of the scalar type.
    if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
      assert(Offset == 0 && "must be store to start of alloca");
      
      // If the source and destination are both to the same alloca, then this is
      // a noop copy-to-self, just delete it.  Otherwise, emit a load and store
      // as appropriate.
      AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject(0));
      
      if (MTI->getSource()->getUnderlyingObject(0) != OrigAI) {
        // Dest must be OrigAI, change this to be a load from the original
        // pointer (bitcasted), then a store to our new alloca.
        assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?");
        Value *SrcPtr = MTI->getSource();
        SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType());
        
        LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
        SrcVal->setAlignment(MTI->getAlignment());
        Builder.CreateStore(SrcVal, NewAI);
      } else if (MTI->getDest()->getUnderlyingObject(0) != OrigAI) {
        // Src must be OrigAI, change this to be a load from NewAI then a store
        // through the original dest pointer (bitcasted).
        assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?");
        LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval");

        Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType());
        StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr);
        NewStore->setAlignment(MTI->getAlignment());
      } else {
        // Noop transfer. Src == Dst
      }

      MTI->eraseFromParent();
      continue;
    }
    
    llvm_unreachable("Unsupported operation!");
  }
}

/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer
/// or vector value FromVal, extracting the bits from the offset specified by
/// Offset.  This returns the value, which is of type ToType.
///
/// This happens when we are converting an "integer union" to a single
/// integer scalar, or when we are converting a "vector union" to a vector with
/// insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right.
Value *ConvertToScalarInfo::
ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType,
                           uint64_t Offset, IRBuilder<> &Builder) {
  // If the load is of the whole new alloca, no conversion is needed.
  if (FromVal->getType() == ToType && Offset == 0)
    return FromVal;

  // If the result alloca is a vector type, this is either an element
  // access or a bitcast to another vector type of the same size.
  if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) {
    if (ToType->isVectorTy())
      return Builder.CreateBitCast(FromVal, ToType, "tmp");

    // Otherwise it must be an element access.
    unsigned Elt = 0;
    if (Offset) {
      unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType());
      Elt = Offset/EltSize;
      assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
    }
    // Return the element extracted out of it.
    Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get(
                    Type::getInt32Ty(FromVal->getContext()), Elt), "tmp");
    if (V->getType() != ToType)
      V = Builder.CreateBitCast(V, ToType, "tmp");
    return V;
  }
  
  // If ToType is a first class aggregate, extract out each of the pieces and
  // use insertvalue's to form the FCA.
  if (const StructType *ST = dyn_cast<StructType>(ToType)) {
    const StructLayout &Layout = *TD.getStructLayout(ST);
    Value *Res = UndefValue::get(ST);
    for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
      Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i),
                                        Offset+Layout.getElementOffsetInBits(i),
                                              Builder);
      Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
    }
    return Res;
  }
  
  if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) {
    uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType());
    Value *Res = UndefValue::get(AT);
    for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
      Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(),
                                              Offset+i*EltSize, Builder);
      Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
    }
    return Res;
  }

  // Otherwise, this must be a union that was converted to an integer value.
  const IntegerType *NTy = cast<IntegerType>(FromVal->getType());

  // If this is a big-endian system and the load is narrower than the
  // full alloca type, we need to do a shift to get the right bits.
  int ShAmt = 0;
  if (TD.isBigEndian()) {
    // On big-endian machines, the lowest bit is stored at the bit offset
    // from the pointer given by getTypeStoreSizeInBits.  This matters for
    // integers with a bitwidth that is not a multiple of 8.
    ShAmt = TD.getTypeStoreSizeInBits(NTy) -
            TD.getTypeStoreSizeInBits(ToType) - Offset;
  } else {
    ShAmt = Offset;
  }

  // Note: we support negative bitwidths (with shl) which are not defined.
  // We do this to support (f.e.) loads off the end of a structure where
  // only some bits are used.
  if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth())
    FromVal = Builder.CreateLShr(FromVal,
                                 ConstantInt::get(FromVal->getType(),
                                                           ShAmt), "tmp");
  else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
    FromVal = Builder.CreateShl(FromVal, 
                                ConstantInt::get(FromVal->getType(),
                                                          -ShAmt), "tmp");

  // Finally, unconditionally truncate the integer to the right width.
  unsigned LIBitWidth = TD.getTypeSizeInBits(ToType);
  if (LIBitWidth < NTy->getBitWidth())
    FromVal =
      Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(), 
                                                    LIBitWidth), "tmp");
  else if (LIBitWidth > NTy->getBitWidth())
    FromVal =
       Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(), 
                                                    LIBitWidth), "tmp");

  // If the result is an integer, this is a trunc or bitcast.
  if (ToType->isIntegerTy()) {
    // Should be done.
  } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) {
    // Just do a bitcast, we know the sizes match up.
    FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp");
  } else {
    // Otherwise must be a pointer.
    FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp");
  }
  assert(FromVal->getType() == ToType && "Didn't convert right?");
  return FromVal;
}

/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer
/// or vector value "Old" at the offset specified by Offset.
///
/// This happens when we are converting an "integer union" to a
/// single integer scalar, or when we are converting a "vector union" to a
/// vector with insert/extractelement instructions.
///
/// Offset is an offset from the original alloca, in bits that need to be
/// shifted to the right.
Value *ConvertToScalarInfo::
ConvertScalar_InsertValue(Value *SV, Value *Old,
                          uint64_t Offset, IRBuilder<> &Builder) {
  // Convert the stored type to the actual type, shift it left to insert
  // then 'or' into place.
  const Type *AllocaType = Old->getType();
  LLVMContext &Context = Old->getContext();

  if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) {
    uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy);
    uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType());
    
    // Changing the whole vector with memset or with an access of a different
    // vector type?
    if (ValSize == VecSize)
      return Builder.CreateBitCast(SV, AllocaType, "tmp");

    uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType());

    // Must be an element insertion.
    unsigned Elt = Offset/EltSize;
    
    if (SV->getType() != VTy->getElementType())
      SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp");
    
    SV = Builder.CreateInsertElement(Old, SV, 
                     ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt),
                                     "tmp");
    return SV;
  }
  
  // If SV is a first-class aggregate value, insert each value recursively.
  if (const StructType *ST = dyn_cast<StructType>(SV->getType())) {
    const StructLayout &Layout = *TD.getStructLayout(ST);
    for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
      Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
      Old = ConvertScalar_InsertValue(Elt, Old, 
                                      Offset+Layout.getElementOffsetInBits(i),
                                      Builder);
    }
    return Old;
  }
  
  if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) {
    uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType());
    for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
      Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
      Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder);
    }
    return Old;
  }

  // If SV is a float, convert it to the appropriate integer type.
  // If it is a pointer, do the same.
  unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType());
  unsigned DestWidth = TD.getTypeSizeInBits(AllocaType);
  unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType());
  unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType);
  if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy())
    SV = Builder.CreateBitCast(SV,
                            IntegerType::get(SV->getContext(),SrcWidth), "tmp");
  else if (SV->getType()->isPointerTy())
    SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp");

  // Zero extend or truncate the value if needed.
  if (SV->getType() != AllocaType) {
    if (SV->getType()->getPrimitiveSizeInBits() <
             AllocaType->getPrimitiveSizeInBits())
      SV = Builder.CreateZExt(SV, AllocaType, "tmp");
    else {
      // Truncation may be needed if storing more than the alloca can hold
      // (undefined behavior).
      SV = Builder.CreateTrunc(SV, AllocaType, "tmp");
      SrcWidth = DestWidth;
      SrcStoreWidth = DestStoreWidth;
    }
  }

  // If this is a big-endian system and the store is narrower than the
  // full alloca type, we need to do a shift to get the right bits.
  int ShAmt = 0;
  if (TD.isBigEndian()) {
    // On big-endian machines, the lowest bit is stored at the bit offset
    // from the pointer given by getTypeStoreSizeInBits.  This matters for
    // integers with a bitwidth that is not a multiple of 8.
    ShAmt = DestStoreWidth - SrcStoreWidth - Offset;
  } else {
    ShAmt = Offset;
  }

  // Note: we support negative bitwidths (with shr) which are not defined.
  // We do this to support (f.e.) stores off the end of a structure where
  // only some bits in the structure are set.
  APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth));
  if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) {
    SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(),
                           ShAmt), "tmp");
    Mask <<= ShAmt;
  } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
    SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(),
                            -ShAmt), "tmp");
    Mask = Mask.lshr(-ShAmt);
  }

  // Mask out the bits we are about to insert from the old value, and or
  // in the new bits.
  if (SrcWidth != DestWidth) {
    assert(DestWidth > SrcWidth);
    Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask");
    SV = Builder.CreateOr(Old, SV, "ins");
  }
  return SV;
}


//===----------------------------------------------------------------------===//
// SRoA Driver
//===----------------------------------------------------------------------===//


bool SROA::runOnFunction(Function &F) {
  TD = getAnalysisIfAvailable<TargetData>();

  bool Changed = performPromotion(F);

  // FIXME: ScalarRepl currently depends on TargetData more than it
  // theoretically needs to. It should be refactored in order to support
  // target-independent IR. Until this is done, just skip the actual
  // scalar-replacement portion of this pass.
  if (!TD) return Changed;

  while (1) {
    bool LocalChange = performScalarRepl(F);
    if (!LocalChange) break;   // No need to repromote if no scalarrepl
    Changed = true;
    LocalChange = performPromotion(F);
    if (!LocalChange) break;   // No need to re-scalarrepl if no promotion
  }

  return Changed;
}


bool SROA::performPromotion(Function &F) {
  std::vector<AllocaInst*> Allocas;
  DominatorTree         &DT = getAnalysis<DominatorTree>();
  DominanceFrontier &DF = getAnalysis<DominanceFrontier>();

  BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function

  bool Changed = false;

  while (1) {
    Allocas.clear();

    // Find allocas that are safe to promote, by looking at all instructions in
    // the entry node
    for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
      if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
        if (isAllocaPromotable(AI))
          Allocas.push_back(AI);

    if (Allocas.empty()) break;

    PromoteMemToReg(Allocas, DT, DF);
    NumPromoted += Allocas.size();
    Changed = true;
  }

  return Changed;
}


/// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for
/// SROA.  It must be a struct or array type with a small number of elements.
static bool ShouldAttemptScalarRepl(AllocaInst *AI) {
  const Type *T = AI->getAllocatedType();
  // Do not promote any struct into more than 32 separate vars.
  if (const StructType *ST = dyn_cast<StructType>(T))
    return ST->getNumElements() <= 32;
  // Arrays are much less likely to be safe for SROA; only consider
  // them if they are very small.
  if (const ArrayType *AT = dyn_cast<ArrayType>(T))
    return AT->getNumElements() <= 8;
  return false;
}


// performScalarRepl - This algorithm is a simple worklist driven algorithm,
// which runs on all of the malloc/alloca instructions in the function, removing
// them if they are only used by getelementptr instructions.
//
bool SROA::performScalarRepl(Function &F) {
  std::vector<AllocaInst*> WorkList;

  // Scan the entry basic block, adding allocas to the worklist.
  BasicBlock &BB = F.getEntryBlock();
  for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
    if (AllocaInst *A = dyn_cast<AllocaInst>(I))
      WorkList.push_back(A);

  // Process the worklist
  bool Changed = false;
  while (!WorkList.empty()) {
    AllocaInst *AI = WorkList.back();
    WorkList.pop_back();
    
    // Handle dead allocas trivially.  These can be formed by SROA'ing arrays
    // with unused elements.
    if (AI->use_empty()) {
      AI->eraseFromParent();
      Changed = true;
      continue;
    }

    // If this alloca is impossible for us to promote, reject it early.
    if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized())
      continue;
    
    // Check to see if this allocation is only modified by a memcpy/memmove from
    // a constant global.  If this is the case, we can change all users to use
    // the constant global instead.  This is commonly produced by the CFE by
    // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
    // is only subsequently read.
    if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) {
      DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n');
      DEBUG(dbgs() << "  memcpy = " << *TheCopy << '\n');
      Constant *TheSrc = cast<Constant>(TheCopy->getSource());
      AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType()));
      TheCopy->eraseFromParent();  // Don't mutate the global.
      AI->eraseFromParent();
      ++NumGlobals;
      Changed = true;
      continue;
    }
    
    // Check to see if we can perform the core SROA transformation.  We cannot
    // transform the allocation instruction if it is an array allocation
    // (allocations OF arrays are ok though), and an allocation of a scalar
    // value cannot be decomposed at all.
    uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType());

    // Do not promote [0 x %struct].
    if (AllocaSize == 0) continue;
    
    // Do not promote any struct whose size is too big.
    if (AllocaSize > SRThreshold) continue;
    
    // If the alloca looks like a good candidate for scalar replacement, and if
    // all its users can be transformed, then split up the aggregate into its
    // separate elements.
    if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) {
      DoScalarReplacement(AI, WorkList);
      Changed = true;
      continue;
    }

    // If we can turn this aggregate value (potentially with casts) into a
    // simple scalar value that can be mem2reg'd into a register value.
    // IsNotTrivial tracks whether this is something that mem2reg could have
    // promoted itself.  If so, we don't want to transform it needlessly.  Note
    // that we can't just check based on the type: the alloca may be of an i32
    // but that has pointer arithmetic to set byte 3 of it or something.
    if (AllocaInst *NewAI =
          ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) {
      NewAI->takeName(AI);
      AI->eraseFromParent();
      ++NumConverted;
      Changed = true;
      continue;
    }      
    
    // Otherwise, couldn't process this alloca.
  }

  return Changed;
}

/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl
/// predicate, do SROA now.
void SROA::DoScalarReplacement(AllocaInst *AI, 
                               std::vector<AllocaInst*> &WorkList) {
  DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n');
  SmallVector<AllocaInst*, 32> ElementAllocas;
  if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
    ElementAllocas.reserve(ST->getNumContainedTypes());
    for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
      AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 
                                      AI->getAlignment(),
                                      AI->getName() + "." + Twine(i), AI);
      ElementAllocas.push_back(NA);
      WorkList.push_back(NA);  // Add to worklist for recursive processing
    }
  } else {
    const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
    ElementAllocas.reserve(AT->getNumElements());
    const Type *ElTy = AT->getElementType();
    for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
      AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(),
                                      AI->getName() + "." + Twine(i), AI);
      ElementAllocas.push_back(NA);
      WorkList.push_back(NA);  // Add to worklist for recursive processing
    }
  }

  // Now that we have created the new alloca instructions, rewrite all the
  // uses of the old alloca.
  RewriteForScalarRepl(AI, AI, 0, ElementAllocas);

  // Now erase any instructions that were made dead while rewriting the alloca.
  DeleteDeadInstructions();
  AI->eraseFromParent();

  ++NumReplaced;
}

/// DeleteDeadInstructions - Erase instructions on the DeadInstrs list,
/// recursively including all their operands that become trivially dead.
void SROA::DeleteDeadInstructions() {
  while (!DeadInsts.empty()) {
    Instruction *I = cast<Instruction>(DeadInsts.pop_back_val());

    for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
      if (Instruction *U = dyn_cast<Instruction>(*OI)) {
        // Zero out the operand and see if it becomes trivially dead.
        // (But, don't add allocas to the dead instruction list -- they are
        // already on the worklist and will be deleted separately.)
        *OI = 0;
        if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U))
          DeadInsts.push_back(U);
      }

    I->eraseFromParent();
  }
}
    
/// isSafeForScalarRepl - Check if instruction I is a safe use with regard to
/// performing scalar replacement of alloca AI.  The results are flagged in
/// the Info parameter.  Offset indicates the position within AI that is
/// referenced by this instruction.
void SROA::isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
                               AllocaInfo &Info) {
  for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
    Instruction *User = cast<Instruction>(*UI);

    if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
      isSafeForScalarRepl(BC, AI, Offset, Info);
    } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
      uint64_t GEPOffset = Offset;
      isSafeGEP(GEPI, AI, GEPOffset, Info);
      if (!Info.isUnsafe)
        isSafeForScalarRepl(GEPI, AI, GEPOffset, Info);
    } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
      ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
      if (Length)
        isSafeMemAccess(AI, Offset, Length->getZExtValue(), 0,
                        UI.getOperandNo() == 0, Info);
      else
        MarkUnsafe(Info);
    } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
      if (!LI->isVolatile()) {
        const Type *LIType = LI->getType();
        isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(LIType),
                        LIType, false, Info);
      } else
        MarkUnsafe(Info);
    } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
      // Store is ok if storing INTO the pointer, not storing the pointer
      if (!SI->isVolatile() && SI->getOperand(0) != I) {
        const Type *SIType = SI->getOperand(0)->getType();
        isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(SIType),
                        SIType, true, Info);
      } else
        MarkUnsafe(Info);
    } else {
      DEBUG(errs() << "  Transformation preventing inst: " << *User << '\n');
      MarkUnsafe(Info);
    }
    if (Info.isUnsafe) return;
  }
}

/// isSafeGEP - Check if a GEP instruction can be handled for scalar
/// replacement.  It is safe when all the indices are constant, in-bounds
/// references, and when the resulting offset corresponds to an element within
/// the alloca type.  The results are flagged in the Info parameter.  Upon
/// return, Offset is adjusted as specified by the GEP indices.
void SROA::isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI,
                     uint64_t &Offset, AllocaInfo &Info) {
  gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI);
  if (GEPIt == E)
    return;

  // Walk through the GEP type indices, checking the types that this indexes
  // into.
  for (; GEPIt != E; ++GEPIt) {
    // Ignore struct elements, no extra checking needed for these.
    if ((*GEPIt)->isStructTy())
      continue;

    ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand());
    if (!IdxVal)
      return MarkUnsafe(Info);
  }

  // Compute the offset due to this GEP and check if the alloca has a
  // component element at that offset.
  SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
  Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
                                 &Indices[0], Indices.size());
  if (!TypeHasComponent(AI->getAllocatedType(), Offset, 0))
    MarkUnsafe(Info);
}

/// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI
/// alloca or has an offset and size that corresponds to a component element
/// within it.  The offset checked here may have been formed from a GEP with a
/// pointer bitcasted to a different type.
void SROA::isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
                           const Type *MemOpType, bool isStore,
                           AllocaInfo &Info) {
  // Check if this is a load/store of the entire alloca.
  if (Offset == 0 && MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) {
    bool UsesAggregateType = (MemOpType == AI->getAllocatedType());
    // This is safe for MemIntrinsics (where MemOpType is 0), integer types
    // (which are essentially the same as the MemIntrinsics, especially with
    // regard to copying padding between elements), or references using the
    // aggregate type of the alloca.
    if (!MemOpType || MemOpType->isIntegerTy() || UsesAggregateType) {
      if (!UsesAggregateType) {
        if (isStore)
          Info.isMemCpyDst = true;
        else
          Info.isMemCpySrc = true;
      }
      return;
    }
  }
  // Check if the offset/size correspond to a component within the alloca type.
  const Type *T = AI->getAllocatedType();
  if (TypeHasComponent(T, Offset, MemSize))
    return;

  return MarkUnsafe(Info);
}

/// TypeHasComponent - Return true if T has a component type with the
/// specified offset and size.  If Size is zero, do not check the size.
bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) {
  const Type *EltTy;
  uint64_t EltSize;
  if (const StructType *ST = dyn_cast<StructType>(T)) {
    const StructLayout *Layout = TD->getStructLayout(ST);
    unsigned EltIdx = Layout->getElementContainingOffset(Offset);
    EltTy = ST->getContainedType(EltIdx);
    EltSize = TD->getTypeAllocSize(EltTy);
    Offset -= Layout->getElementOffset(EltIdx);
  } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) {
    EltTy = AT->getElementType();
    EltSize = TD->getTypeAllocSize(EltTy);
    if (Offset >= AT->getNumElements() * EltSize)
      return false;
    Offset %= EltSize;
  } else {
    return false;
  }
  if (Offset == 0 && (Size == 0 || EltSize == Size))
    return true;
  // Check if the component spans multiple elements.
  if (Offset + Size > EltSize)
    return false;
  return TypeHasComponent(EltTy, Offset, Size);
}

/// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite
/// the instruction I, which references it, to use the separate elements.
/// Offset indicates the position within AI that is referenced by this
/// instruction.
void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
                                SmallVector<AllocaInst*, 32> &NewElts) {
  for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
    Instruction *User = cast<Instruction>(*UI);

    if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
      RewriteBitCast(BC, AI, Offset, NewElts);
    } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
      RewriteGEP(GEPI, AI, Offset, NewElts);
    } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
      ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
      uint64_t MemSize = Length->getZExtValue();
      if (Offset == 0 &&
          MemSize == TD->getTypeAllocSize(AI->getAllocatedType()))
        RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts);
      // Otherwise the intrinsic can only touch a single element and the
      // address operand will be updated, so nothing else needs to be done.
    } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
      const Type *LIType = LI->getType();
      if (LIType == AI->getAllocatedType()) {
        // Replace:
        //   %res = load { i32, i32 }* %alloc
        // with:
        //   %load.0 = load i32* %alloc.0
        //   %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0
        //   %load.1 = load i32* %alloc.1
        //   %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1
        // (Also works for arrays instead of structs)
        Value *Insert = UndefValue::get(LIType);
        for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
          Value *Load = new LoadInst(NewElts[i], "load", LI);
          Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI);
        }
        LI->replaceAllUsesWith(Insert);
        DeadInsts.push_back(LI);
      } else if (LIType->isIntegerTy() &&
                 TD->getTypeAllocSize(LIType) ==
                 TD->getTypeAllocSize(AI->getAllocatedType())) {
        // If this is a load of the entire alloca to an integer, rewrite it.
        RewriteLoadUserOfWholeAlloca(LI, AI, NewElts);
      }
    } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
      Value *Val = SI->getOperand(0);
      const Type *SIType = Val->getType();
      if (SIType == AI->getAllocatedType()) {
        // Replace:
        //   store { i32, i32 } %val, { i32, i32 }* %alloc
        // with:
        //   %val.0 = extractvalue { i32, i32 } %val, 0
        //   store i32 %val.0, i32* %alloc.0
        //   %val.1 = extractvalue { i32, i32 } %val, 1
        //   store i32 %val.1, i32* %alloc.1
        // (Also works for arrays instead of structs)
        for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
          Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI);
          new StoreInst(Extract, NewElts[i], SI);
        }
        DeadInsts.push_back(SI);
      } else if (SIType->isIntegerTy() &&
                 TD->getTypeAllocSize(SIType) ==
                 TD->getTypeAllocSize(AI->getAllocatedType())) {
        // If this is a store of the entire alloca from an integer, rewrite it.
        RewriteStoreUserOfWholeAlloca(SI, AI, NewElts);
      }
    }
  }
}

/// RewriteBitCast - Update a bitcast reference to the alloca being replaced
/// and recursively continue updating all of its uses.
void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
                          SmallVector<AllocaInst*, 32> &NewElts) {
  RewriteForScalarRepl(BC, AI, Offset, NewElts);
  if (BC->getOperand(0) != AI)
    return;

  // The bitcast references the original alloca.  Replace its uses with
  // references to the first new element alloca.
  Instruction *Val = NewElts[0];
  if (Val->getType() != BC->getDestTy()) {
    Val = new BitCastInst(Val, BC->getDestTy(), "", BC);
    Val->takeName(BC);
  }
  BC->replaceAllUsesWith(Val);
  DeadInsts.push_back(BC);
}

/// FindElementAndOffset - Return the index of the element containing Offset
/// within the specified type, which must be either a struct or an array.
/// Sets T to the type of the element and Offset to the offset within that
/// element.  IdxTy is set to the type of the index result to be used in a
/// GEP instruction.
uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset,
                                    const Type *&IdxTy) {
  uint64_t Idx = 0;
  if (const StructType *ST = dyn_cast<StructType>(T)) {
    const StructLayout *Layout = TD->getStructLayout(ST);
    Idx = Layout->getElementContainingOffset(Offset);
    T = ST->getContainedType(Idx);
    Offset -= Layout->getElementOffset(Idx);
    IdxTy = Type::getInt32Ty(T->getContext());
    return Idx;
  }
  const ArrayType *AT = cast<ArrayType>(T);
  T = AT->getElementType();
  uint64_t EltSize = TD->getTypeAllocSize(T);
  Idx = Offset / EltSize;
  Offset -= Idx * EltSize;
  IdxTy = Type::getInt64Ty(T->getContext());
  return Idx;
}

/// RewriteGEP - Check if this GEP instruction moves the pointer across
/// elements of the alloca that are being split apart, and if so, rewrite
/// the GEP to be relative to the new element.
void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
                      SmallVector<AllocaInst*, 32> &NewElts) {
  uint64_t OldOffset = Offset;
  SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
  Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
                                 &Indices[0], Indices.size());

  RewriteForScalarRepl(GEPI, AI, Offset, NewElts);

  const Type *T = AI->getAllocatedType();
  const Type *IdxTy;
  uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy);
  if (GEPI->getOperand(0) == AI)
    OldIdx = ~0ULL; // Force the GEP to be rewritten.

  T = AI->getAllocatedType();
  uint64_t EltOffset = Offset;
  uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy);

  // If this GEP does not move the pointer across elements of the alloca
  // being split, then it does not needs to be rewritten.
  if (Idx == OldIdx)
    return;

  const Type *i32Ty = Type::getInt32Ty(AI->getContext());
  SmallVector<Value*, 8> NewArgs;
  NewArgs.push_back(Constant::getNullValue(i32Ty));
  while (EltOffset != 0) {
    uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy);
    NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx));
  }
  Instruction *Val = NewElts[Idx];
  if (NewArgs.size() > 1) {
    Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(),
                                            NewArgs.end(), "", GEPI);
    Val->takeName(GEPI);
  }
  if (Val->getType() != GEPI->getType())
    Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI);
  GEPI->replaceAllUsesWith(Val);
  DeadInsts.push_back(GEPI);
}

/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI.
/// Rewrite it to copy or set the elements of the scalarized memory.
void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
                                        AllocaInst *AI,
                                        SmallVector<AllocaInst*, 32> &NewElts) {
  // If this is a memcpy/memmove, construct the other pointer as the
  // appropriate type.  The "Other" pointer is the pointer that goes to memory
  // that doesn't have anything to do with the alloca that we are promoting. For
  // memset, this Value* stays null.
  Value *OtherPtr = 0;
  unsigned MemAlignment = MI->getAlignment();
  if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy
    if (Inst == MTI->getRawDest())
      OtherPtr = MTI->getRawSource();
    else {
      assert(Inst == MTI->getRawSource());
      OtherPtr = MTI->getRawDest();
    }
  }

  // If there is an other pointer, we want to convert it to the same pointer
  // type as AI has, so we can GEP through it safely.
  if (OtherPtr) {
    unsigned AddrSpace =
      cast<PointerType>(OtherPtr->getType())->getAddressSpace();

    // Remove bitcasts and all-zero GEPs from OtherPtr.  This is an
    // optimization, but it's also required to detect the corner case where
    // both pointer operands are referencing the same memory, and where
    // OtherPtr may be a bitcast or GEP that currently being rewritten.  (This
    // function is only called for mem intrinsics that access the whole
    // aggregate, so non-zero GEPs are not an issue here.)
    OtherPtr = OtherPtr->stripPointerCasts();
    
    // Copying the alloca to itself is a no-op: just delete it.
    if (OtherPtr == AI || OtherPtr == NewElts[0]) {
      // This code will run twice for a no-op memcpy -- once for each operand.
      // Put only one reference to MI on the DeadInsts list.
      for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(),
             E = DeadInsts.end(); I != E; ++I)
        if (*I == MI) return;
      DeadInsts.push_back(MI);
      return;
    }
    
    // If the pointer is not the right type, insert a bitcast to the right
    // type.
    const Type *NewTy =
      PointerType::get(AI->getType()->getElementType(), AddrSpace);
    
    if (OtherPtr->getType() != NewTy)
      OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI);
  }
  
  // Process each element of the aggregate.
  Value *TheFn = MI->getCalledValue();
  const Type *BytePtrTy = MI->getRawDest()->getType();
  bool SROADest = MI->getRawDest() == Inst;
  
  Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext()));

  for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
    // If this is a memcpy/memmove, emit a GEP of the other element address.
    Value *OtherElt = 0;
    unsigned OtherEltAlign = MemAlignment;
    
    if (OtherPtr) {
      Value *Idx[2] = { Zero,
                      ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) };
      OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2,
                                              OtherPtr->getName()+"."+Twine(i),
                                                   MI);
      uint64_t EltOffset;
      const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType());
      const Type *OtherTy = OtherPtrTy->getElementType();
      if (const StructType *ST = dyn_cast<StructType>(OtherTy)) {
        EltOffset = TD->getStructLayout(ST)->getElementOffset(i);
      } else {
        const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType();
        EltOffset = TD->getTypeAllocSize(EltTy)*i;
      }
      
      // The alignment of the other pointer is the guaranteed alignment of the
      // element, which is affected by both the known alignment of the whole
      // mem intrinsic and the alignment of the element.  If the alignment of
      // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the
      // known alignment is just 4 bytes.
      OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset);
    }
    
    Value *EltPtr = NewElts[i];
    const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType();
    
    // If we got down to a scalar, insert a load or store as appropriate.
    if (EltTy->isSingleValueType()) {
      if (isa<MemTransferInst>(MI)) {
        if (SROADest) {
          // From Other to Alloca.
          Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI);
          new StoreInst(Elt, EltPtr, MI);
        } else {
          // From Alloca to Other.
          Value *Elt = new LoadInst(EltPtr, "tmp", MI);
          new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI);
        }
        continue;
      }
      assert(isa<MemSetInst>(MI));
      
      // If the stored element is zero (common case), just store a null
      // constant.
      Constant *StoreVal;
      if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) {
        if (CI->isZero()) {
          StoreVal = Constant::getNullValue(EltTy);  // 0.0, null, 0, <0,0>
        } else {
          // If EltTy is a vector type, get the element type.
          const Type *ValTy = EltTy->getScalarType();

          // Construct an integer with the right value.
          unsigned EltSize = TD->getTypeSizeInBits(ValTy);
          APInt OneVal(EltSize, CI->getZExtValue());
          APInt TotalVal(OneVal);
          // Set each byte.
          for (unsigned i = 0; 8*i < EltSize; ++i) {
            TotalVal = TotalVal.shl(8);
            TotalVal |= OneVal;
          }
          
          // Convert the integer value to the appropriate type.
          StoreVal = ConstantInt::get(CI->getContext(), TotalVal);
          if (ValTy->isPointerTy())
            StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy);
          else if (ValTy->isFloatingPointTy())
            StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy);
          assert(StoreVal->getType() == ValTy && "Type mismatch!");
          
          // If the requested value was a vector constant, create it.
          if (EltTy != ValTy) {
            unsigned NumElts = cast<VectorType>(ValTy)->getNumElements();
            SmallVector<Constant*, 16> Elts(NumElts, StoreVal);
            StoreVal = ConstantVector::get(&Elts[0], NumElts);
          }
        }
        new StoreInst(StoreVal, EltPtr, MI);
        continue;
      }
      // Otherwise, if we're storing a byte variable, use a memset call for
      // this element.
    }
    
    // Cast the element pointer to BytePtrTy.
    if (EltPtr->getType() != BytePtrTy)
      EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getName(), MI);
    
    // Cast the other pointer (if we have one) to BytePtrTy. 
    if (OtherElt && OtherElt->getType() != BytePtrTy) {
      // Preserve address space of OtherElt
      const PointerType* OtherPTy = cast<PointerType>(OtherElt->getType());
      const PointerType* PTy = cast<PointerType>(BytePtrTy);
      if (OtherPTy->getElementType() != PTy->getElementType()) {
        Type *NewOtherPTy = PointerType::get(PTy->getElementType(),
                                             OtherPTy->getAddressSpace());
        OtherElt = new BitCastInst(OtherElt, NewOtherPTy,
                                   OtherElt->getNameStr(), MI);
      }
    }
    
    unsigned EltSize = TD->getTypeAllocSize(EltTy);
    
    // Finally, insert the meminst for this element.
    if (isa<MemTransferInst>(MI)) {
      Value *Ops[] = {
        SROADest ? EltPtr : OtherElt,  // Dest ptr
        SROADest ? OtherElt : EltPtr,  // Src ptr
        ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size
        // Align
        ConstantInt::get(Type::getInt32Ty(MI->getContext()), OtherEltAlign),
        MI->getVolatileCst()
      };
      // In case we fold the address space overloaded memcpy of A to B
      // with memcpy of B to C, change the function to be a memcpy of A to C.
      const Type *Tys[] = { Ops[0]->getType(), Ops[1]->getType(),
                            Ops[2]->getType() };
      Module *M = MI->getParent()->getParent()->getParent();
      TheFn = Intrinsic::getDeclaration(M, MI->getIntrinsicID(), Tys, 3);
      CallInst::Create(TheFn, Ops, Ops + 5, "", MI);
    } else {
      assert(isa<MemSetInst>(MI));
      Value *Ops[] = {
        EltPtr, MI->getArgOperand(1),  // Dest, Value,
        ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size
        Zero,  // Align
        ConstantInt::get(Type::getInt1Ty(MI->getContext()), 0) // isVolatile
      };
      const Type *Tys[] = { Ops[0]->getType(), Ops[2]->getType() };
      Module *M = MI->getParent()->getParent()->getParent();
      TheFn = Intrinsic::getDeclaration(M, Intrinsic::memset, Tys, 2);
      CallInst::Create(TheFn, Ops, Ops + 5, "", MI);
    }
  }
  DeadInsts.push_back(MI);
}

/// RewriteStoreUserOfWholeAlloca - We found a store of an integer that
/// overwrites the entire allocation.  Extract out the pieces of the stored
/// integer and store them individually.
void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
                                         SmallVector<AllocaInst*, 32> &NewElts){
  // Extract each element out of the integer according to its structure offset
  // and store the element value to the individual alloca.
  Value *SrcVal = SI->getOperand(0);
  const Type *AllocaEltTy = AI->getAllocatedType();
  uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
  
  // Handle tail padding by extending the operand
  if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits)
    SrcVal = new ZExtInst(SrcVal,
                          IntegerType::get(SI->getContext(), AllocaSizeBits), 
                          "", SI);

  DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI
               << '\n');

  // There are two forms here: AI could be an array or struct.  Both cases
  // have different ways to compute the element offset.
  if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
    const StructLayout *Layout = TD->getStructLayout(EltSTy);
    
    for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
      // Get the number of bits to shift SrcVal to get the value.
      const Type *FieldTy = EltSTy->getElementType(i);
      uint64_t Shift = Layout->getElementOffsetInBits(i);
      
      if (TD->isBigEndian())
        Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy);
      
      Value *EltVal = SrcVal;
      if (Shift) {
        Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
        EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
                                            "sroa.store.elt", SI);
      }
      
      // Truncate down to an integer of the right size.
      uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
      
      // Ignore zero sized fields like {}, they obviously contain no data.
      if (FieldSizeBits == 0) continue;
      
      if (FieldSizeBits != AllocaSizeBits)
        EltVal = new TruncInst(EltVal,
                             IntegerType::get(SI->getContext(), FieldSizeBits),
                              "", SI);
      Value *DestField = NewElts[i];
      if (EltVal->getType() == FieldTy) {
        // Storing to an integer field of this size, just do it.
      } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) {
        // Bitcast to the right element type (for fp/vector values).
        EltVal = new BitCastInst(EltVal, FieldTy, "", SI);
      } else {
        // Otherwise, bitcast the dest pointer (for aggregates).
        DestField = new BitCastInst(DestField,
                              PointerType::getUnqual(EltVal->getType()),
                                    "", SI);
      }
      new StoreInst(EltVal, DestField, SI);
    }
    
  } else {
    const ArrayType *ATy = cast<ArrayType>(AllocaEltTy);
    const Type *ArrayEltTy = ATy->getElementType();
    uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
    uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy);

    uint64_t Shift;
    
    if (TD->isBigEndian())
      Shift = AllocaSizeBits-ElementOffset;
    else 
      Shift = 0;
    
    for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
      // Ignore zero sized fields like {}, they obviously contain no data.
      if (ElementSizeBits == 0) continue;
      
      Value *EltVal = SrcVal;
      if (Shift) {
        Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
        EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
                                            "sroa.store.elt", SI);
      }
      
      // Truncate down to an integer of the right size.
      if (ElementSizeBits != AllocaSizeBits)
        EltVal = new TruncInst(EltVal, 
                               IntegerType::get(SI->getContext(), 
                                                ElementSizeBits),"",SI);
      Value *DestField = NewElts[i];
      if (EltVal->getType() == ArrayEltTy) {
        // Storing to an integer field of this size, just do it.
      } else if (ArrayEltTy->isFloatingPointTy() ||
                 ArrayEltTy->isVectorTy()) {
        // Bitcast to the right element type (for fp/vector values).
        EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI);
      } else {
        // Otherwise, bitcast the dest pointer (for aggregates).
        DestField = new BitCastInst(DestField,
                              PointerType::getUnqual(EltVal->getType()),
                                    "", SI);
      }
      new StoreInst(EltVal, DestField, SI);
      
      if (TD->isBigEndian())
        Shift -= ElementOffset;
      else 
        Shift += ElementOffset;
    }
  }
  
  DeadInsts.push_back(SI);
}

/// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to
/// an integer.  Load the individual pieces to form the aggregate value.
void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
                                        SmallVector<AllocaInst*, 32> &NewElts) {
  // Extract each element out of the NewElts according to its structure offset
  // and form the result value.
  const Type *AllocaEltTy = AI->getAllocatedType();
  uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
  
  DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI
               << '\n');
  
  // There are two forms here: AI could be an array or struct.  Both cases
  // have different ways to compute the element offset.
  const StructLayout *Layout = 0;
  uint64_t ArrayEltBitOffset = 0;
  if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
    Layout = TD->getStructLayout(EltSTy);
  } else {
    const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType();
    ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
  }    
  
  Value *ResultVal = 
    Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits));
  
  for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
    // Load the value from the alloca.  If the NewElt is an aggregate, cast
    // the pointer to an integer of the same size before doing the load.
    Value *SrcField = NewElts[i];
    const Type *FieldTy =
      cast<PointerType>(SrcField->getType())->getElementType();
    uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
    
    // Ignore zero sized fields like {}, they obviously contain no data.
    if (FieldSizeBits == 0) continue;
    
    const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(), 
                                                     FieldSizeBits);
    if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() &&
        !FieldTy->isVectorTy())
      SrcField = new BitCastInst(SrcField,
                                 PointerType::getUnqual(FieldIntTy),
                                 "", LI);
    SrcField = new LoadInst(SrcField, "sroa.load.elt", LI);

    // If SrcField is a fp or vector of the right size but that isn't an
    // integer type, bitcast to an integer so we can shift it.
    if (SrcField->getType() != FieldIntTy)
      SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI);

    // Zero extend the field to be the same size as the final alloca so that
    // we can shift and insert it.
    if (SrcField->getType() != ResultVal->getType())
      SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI);
    
    // Determine the number of bits to shift SrcField.
    uint64_t Shift;
    if (Layout) // Struct case.
      Shift = Layout->getElementOffsetInBits(i);
    else  // Array case.
      Shift = i*ArrayEltBitOffset;
    
    if (TD->isBigEndian())
      Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth();
    
    if (Shift) {
      Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift);
      SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI);
    }

    // Don't create an 'or x, 0' on the first iteration.
    if (!isa<Constant>(ResultVal) ||
        !cast<Constant>(ResultVal)->isNullValue())
      ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
    else
      ResultVal = SrcField;
  }

  // Handle tail padding by truncating the result
  if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits)
    ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI);

  LI->replaceAllUsesWith(ResultVal);
  DeadInsts.push_back(LI);
}

/// HasPadding - Return true if the specified type has any structure or
/// alignment padding, false otherwise.
static bool HasPadding(const Type *Ty, const TargetData &TD) {
  if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty))
    return HasPadding(ATy->getElementType(), TD);
  
  if (const VectorType *VTy = dyn_cast<VectorType>(Ty))
    return HasPadding(VTy->getElementType(), TD);
  
  if (const StructType *STy = dyn_cast<StructType>(Ty)) {
    const StructLayout *SL = TD.getStructLayout(STy);
    unsigned PrevFieldBitOffset = 0;
    for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
      unsigned FieldBitOffset = SL->getElementOffsetInBits(i);

      // Padding in sub-elements?
      if (HasPadding(STy->getElementType(i), TD))
        return true;

      // Check to see if there is any padding between this element and the
      // previous one.
      if (i) {
        unsigned PrevFieldEnd =
        PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1));
        if (PrevFieldEnd < FieldBitOffset)
          return true;
      }

      PrevFieldBitOffset = FieldBitOffset;
    }

    //  Check for tail padding.
    if (unsigned EltCount = STy->getNumElements()) {
      unsigned PrevFieldEnd = PrevFieldBitOffset +
                   TD.getTypeSizeInBits(STy->getElementType(EltCount-1));
      if (PrevFieldEnd < SL->getSizeInBits())
        return true;
    }
  }
  
  return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty);
}

/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
/// an aggregate can be broken down into elements.  Return 0 if not, 3 if safe,
/// or 1 if safe after canonicalization has been performed.
bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) {
  // Loop over the use list of the alloca.  We can only transform it if all of
  // the users are safe to transform.
  AllocaInfo Info;
  
  isSafeForScalarRepl(AI, AI, 0, Info);
  if (Info.isUnsafe) {
    DEBUG(dbgs() << "Cannot transform: " << *AI << '\n');
    return false;
  }
  
  // Okay, we know all the users are promotable.  If the aggregate is a memcpy
  // source and destination, we have to be careful.  In particular, the memcpy
  // could be moving around elements that live in structure padding of the LLVM
  // types, but may actually be used.  In these cases, we refuse to promote the
  // struct.
  if (Info.isMemCpySrc && Info.isMemCpyDst &&
      HasPadding(AI->getAllocatedType(), *TD))
    return false;

  return true;
}



/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to
/// some part of a constant global variable.  This intentionally only accepts
/// constant expressions because we don't can't rewrite arbitrary instructions.
static bool PointsToConstantGlobal(Value *V) {
  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
    return GV->isConstant();
  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
    if (CE->getOpcode() == Instruction::BitCast || 
        CE->getOpcode() == Instruction::GetElementPtr)
      return PointsToConstantGlobal(CE->getOperand(0));
  return false;
}

/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
/// pointer to an alloca.  Ignore any reads of the pointer, return false if we
/// see any stores or other unknown uses.  If we see pointer arithmetic, keep
/// track of whether it moves the pointer (with isOffset) but otherwise traverse
/// the uses.  If we see a memcpy/memmove that targets an unoffseted pointer to
/// the alloca, and if the source pointer is a pointer to a constant  global, we
/// can optimize this.
static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
                                           bool isOffset) {
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
    User *U = cast<Instruction>(*UI);

    if (LoadInst *LI = dyn_cast<LoadInst>(U))
      // Ignore non-volatile loads, they are always ok.
      if (!LI->isVolatile())
        continue;
    
    if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
      // If uses of the bitcast are ok, we are ok.
      if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset))
        return false;
      continue;
    }
    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
      // If the GEP has all zero indices, it doesn't offset the pointer.  If it
      // doesn't, it does.
      if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy,
                                         isOffset || !GEP->hasAllZeroIndices()))
        return false;
      continue;
    }
    
    // If this is isn't our memcpy/memmove, reject it as something we can't
    // handle.
    MemTransferInst *MI = dyn_cast<MemTransferInst>(U);
    if (MI == 0)
      return false;

    // If we already have seen a copy, reject the second one.
    if (TheCopy) return false;
    
    // If the pointer has been offset from the start of the alloca, we can't
    // safely handle this.
    if (isOffset) return false;

    // If the memintrinsic isn't using the alloca as the dest, reject it.
    if (UI.getOperandNo() != 0) return false;
    
    // If the source of the memcpy/move is not a constant global, reject it.
    if (!PointsToConstantGlobal(MI->getSource()))
      return false;
    
    // Otherwise, the transform is safe.  Remember the copy instruction.
    TheCopy = MI;
  }
  return true;
}

/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
/// modified by a copy from a constant global.  If we can prove this, we can
/// replace any uses of the alloca with uses of the global directly.
MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) {
  MemTransferInst *TheCopy = 0;
  if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false))
    return TheCopy;
  return 0;
}