aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/llvm12/lib/Transforms/Scalar/MemCpyOptimizer.cpp
blob: a4e695497f3071c47e7b18f9e50e42593214f679 (plain) (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
//===- MemCpyOptimizer.cpp - Optimize use of memcpy and friends -----------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass performs various transformations related to eliminating memcpy
// calls, or transforming sets of stores into memset's.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar/MemCpyOptimizer.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <utility>

using namespace llvm;

#define DEBUG_TYPE "memcpyopt"

static cl::opt<bool>
    EnableMemorySSA("enable-memcpyopt-memoryssa", cl::init(false), cl::Hidden,
                    cl::desc("Use MemorySSA-backed MemCpyOpt."));

STATISTIC(NumMemCpyInstr, "Number of memcpy instructions deleted");
STATISTIC(NumMemSetInfer, "Number of memsets inferred");
STATISTIC(NumMoveToCpy,   "Number of memmoves converted to memcpy");
STATISTIC(NumCpyToSet,    "Number of memcpys converted to memset");
STATISTIC(NumCallSlot,    "Number of call slot optimizations performed");

namespace {

/// Represents a range of memset'd bytes with the ByteVal value.
/// This allows us to analyze stores like:
///   store 0 -> P+1
///   store 0 -> P+0
///   store 0 -> P+3
///   store 0 -> P+2
/// which sometimes happens with stores to arrays of structs etc.  When we see
/// the first store, we make a range [1, 2).  The second store extends the range
/// to [0, 2).  The third makes a new range [2, 3).  The fourth store joins the
/// two ranges into [0, 3) which is memset'able.
struct MemsetRange {
  // Start/End - A semi range that describes the span that this range covers.
  // The range is closed at the start and open at the end: [Start, End).
  int64_t Start, End;

  /// StartPtr - The getelementptr instruction that points to the start of the
  /// range.
  Value *StartPtr;

  /// Alignment - The known alignment of the first store.
  unsigned Alignment;

  /// TheStores - The actual stores that make up this range.
  SmallVector<Instruction*, 16> TheStores;

  bool isProfitableToUseMemset(const DataLayout &DL) const;
};

} // end anonymous namespace

bool MemsetRange::isProfitableToUseMemset(const DataLayout &DL) const {
  // If we found more than 4 stores to merge or 16 bytes, use memset.
  if (TheStores.size() >= 4 || End-Start >= 16) return true;

  // If there is nothing to merge, don't do anything.
  if (TheStores.size() < 2) return false;

  // If any of the stores are a memset, then it is always good to extend the
  // memset.
  for (Instruction *SI : TheStores)
    if (!isa<StoreInst>(SI))
      return true;

  // Assume that the code generator is capable of merging pairs of stores
  // together if it wants to.
  if (TheStores.size() == 2) return false;

  // If we have fewer than 8 stores, it can still be worthwhile to do this.
  // For example, merging 4 i8 stores into an i32 store is useful almost always.
  // However, merging 2 32-bit stores isn't useful on a 32-bit architecture (the
  // memset will be split into 2 32-bit stores anyway) and doing so can
  // pessimize the llvm optimizer.
  //
  // Since we don't have perfect knowledge here, make some assumptions: assume
  // the maximum GPR width is the same size as the largest legal integer
  // size. If so, check to see whether we will end up actually reducing the
  // number of stores used.
  unsigned Bytes = unsigned(End-Start);
  unsigned MaxIntSize = DL.getLargestLegalIntTypeSizeInBits() / 8;
  if (MaxIntSize == 0)
    MaxIntSize = 1;
  unsigned NumPointerStores = Bytes / MaxIntSize;

  // Assume the remaining bytes if any are done a byte at a time.
  unsigned NumByteStores = Bytes % MaxIntSize;

  // If we will reduce the # stores (according to this heuristic), do the
  // transformation.  This encourages merging 4 x i8 -> i32 and 2 x i16 -> i32
  // etc.
  return TheStores.size() > NumPointerStores+NumByteStores;
}

namespace {

class MemsetRanges {
  using range_iterator = SmallVectorImpl<MemsetRange>::iterator;

  /// A sorted list of the memset ranges.
  SmallVector<MemsetRange, 8> Ranges;

  const DataLayout &DL;

public:
  MemsetRanges(const DataLayout &DL) : DL(DL) {}

  using const_iterator = SmallVectorImpl<MemsetRange>::const_iterator;

  const_iterator begin() const { return Ranges.begin(); }
  const_iterator end() const { return Ranges.end(); }
  bool empty() const { return Ranges.empty(); }

  void addInst(int64_t OffsetFromFirst, Instruction *Inst) {
    if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
      addStore(OffsetFromFirst, SI);
    else
      addMemSet(OffsetFromFirst, cast<MemSetInst>(Inst));
  }

  void addStore(int64_t OffsetFromFirst, StoreInst *SI) {
    int64_t StoreSize = DL.getTypeStoreSize(SI->getOperand(0)->getType());

    addRange(OffsetFromFirst, StoreSize, SI->getPointerOperand(),
             SI->getAlign().value(), SI);
  }

  void addMemSet(int64_t OffsetFromFirst, MemSetInst *MSI) {
    int64_t Size = cast<ConstantInt>(MSI->getLength())->getZExtValue();
    addRange(OffsetFromFirst, Size, MSI->getDest(), MSI->getDestAlignment(), MSI);
  }

  void addRange(int64_t Start, int64_t Size, Value *Ptr,
                unsigned Alignment, Instruction *Inst);
};

} // end anonymous namespace

/// Add a new store to the MemsetRanges data structure.  This adds a
/// new range for the specified store at the specified offset, merging into
/// existing ranges as appropriate.
void MemsetRanges::addRange(int64_t Start, int64_t Size, Value *Ptr,
                            unsigned Alignment, Instruction *Inst) {
  int64_t End = Start+Size;

  range_iterator I = partition_point(
      Ranges, [=](const MemsetRange &O) { return O.End < Start; });

  // We now know that I == E, in which case we didn't find anything to merge
  // with, or that Start <= I->End.  If End < I->Start or I == E, then we need
  // to insert a new range.  Handle this now.
  if (I == Ranges.end() || End < I->Start) {
    MemsetRange &R = *Ranges.insert(I, MemsetRange());
    R.Start        = Start;
    R.End          = End;
    R.StartPtr     = Ptr;
    R.Alignment    = Alignment;
    R.TheStores.push_back(Inst);
    return;
  }

  // This store overlaps with I, add it.
  I->TheStores.push_back(Inst);

  // At this point, we may have an interval that completely contains our store.
  // If so, just add it to the interval and return.
  if (I->Start <= Start && I->End >= End)
    return;

  // Now we know that Start <= I->End and End >= I->Start so the range overlaps
  // but is not entirely contained within the range.

  // See if the range extends the start of the range.  In this case, it couldn't
  // possibly cause it to join the prior range, because otherwise we would have
  // stopped on *it*.
  if (Start < I->Start) {
    I->Start = Start;
    I->StartPtr = Ptr;
    I->Alignment = Alignment;
  }

  // Now we know that Start <= I->End and Start >= I->Start (so the startpoint
  // is in or right at the end of I), and that End >= I->Start.  Extend I out to
  // End.
  if (End > I->End) {
    I->End = End;
    range_iterator NextI = I;
    while (++NextI != Ranges.end() && End >= NextI->Start) {
      // Merge the range in.
      I->TheStores.append(NextI->TheStores.begin(), NextI->TheStores.end());
      if (NextI->End > I->End)
        I->End = NextI->End;
      Ranges.erase(NextI);
      NextI = I;
    }
  }
}

//===----------------------------------------------------------------------===//
//                         MemCpyOptLegacyPass Pass
//===----------------------------------------------------------------------===//

namespace {

class MemCpyOptLegacyPass : public FunctionPass {
  MemCpyOptPass Impl;

public:
  static char ID; // Pass identification, replacement for typeid

  MemCpyOptLegacyPass() : FunctionPass(ID) {
    initializeMemCpyOptLegacyPassPass(*PassRegistry::getPassRegistry());
  }

  bool runOnFunction(Function &F) override;

private:
  // This transformation requires dominator postdominator info
  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesCFG();
    AU.addRequired<AssumptionCacheTracker>();
    AU.addRequired<DominatorTreeWrapperPass>();
    AU.addPreserved<DominatorTreeWrapperPass>();
    AU.addPreserved<GlobalsAAWrapperPass>();
    AU.addRequired<TargetLibraryInfoWrapperPass>();
    if (!EnableMemorySSA)
      AU.addRequired<MemoryDependenceWrapperPass>();
    AU.addPreserved<MemoryDependenceWrapperPass>();
    AU.addRequired<AAResultsWrapperPass>();
    AU.addPreserved<AAResultsWrapperPass>();
    if (EnableMemorySSA)
      AU.addRequired<MemorySSAWrapperPass>();
    AU.addPreserved<MemorySSAWrapperPass>();
  }
};

} // end anonymous namespace

char MemCpyOptLegacyPass::ID = 0;

/// The public interface to this file...
FunctionPass *llvm::createMemCpyOptPass() { return new MemCpyOptLegacyPass(); }

INITIALIZE_PASS_BEGIN(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
                      false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
INITIALIZE_PASS_END(MemCpyOptLegacyPass, "memcpyopt", "MemCpy Optimization",
                    false, false)

// Check that V is either not accessible by the caller, or unwinding cannot
// occur between Start and End.
static bool mayBeVisibleThroughUnwinding(Value *V, Instruction *Start,
                                         Instruction *End) {
  assert(Start->getParent() == End->getParent() && "Must be in same block");
  if (!Start->getFunction()->doesNotThrow() &&
      !isa<AllocaInst>(getUnderlyingObject(V))) {
    for (const Instruction &I :
         make_range(Start->getIterator(), End->getIterator())) {
      if (I.mayThrow())
        return true;
    }
  }
  return false;
}

void MemCpyOptPass::eraseInstruction(Instruction *I) {
  if (MSSAU)
    MSSAU->removeMemoryAccess(I);
  if (MD)
    MD->removeInstruction(I);
  I->eraseFromParent();
}

// Check for mod or ref of Loc between Start and End, excluding both boundaries.
// Start and End must be in the same block
static bool accessedBetween(AliasAnalysis &AA, MemoryLocation Loc,
                            const MemoryUseOrDef *Start,
                            const MemoryUseOrDef *End) {
  assert(Start->getBlock() == End->getBlock() && "Only local supported");
  for (const MemoryAccess &MA :
       make_range(++Start->getIterator(), End->getIterator())) {
    if (isModOrRefSet(AA.getModRefInfo(cast<MemoryUseOrDef>(MA).getMemoryInst(),
                                       Loc)))
      return true;
  }
  return false;
}

// Check for mod of Loc between Start and End, excluding both boundaries.
// Start and End can be in different blocks.
static bool writtenBetween(MemorySSA *MSSA, MemoryLocation Loc,
                           const MemoryUseOrDef *Start,
                           const MemoryUseOrDef *End) {
  // TODO: Only walk until we hit Start.
  MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
      End->getDefiningAccess(), Loc);
  return !MSSA->dominates(Clobber, Start);
}

/// When scanning forward over instructions, we look for some other patterns to
/// fold away. In particular, this looks for stores to neighboring locations of
/// memory. If it sees enough consecutive ones, it attempts to merge them
/// together into a memcpy/memset.
Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst,
                                                 Value *StartPtr,
                                                 Value *ByteVal) {
  const DataLayout &DL = StartInst->getModule()->getDataLayout();

  // Okay, so we now have a single store that can be splatable.  Scan to find
  // all subsequent stores of the same value to offset from the same pointer.
  // Join these together into ranges, so we can decide whether contiguous blocks
  // are stored.
  MemsetRanges Ranges(DL);

  BasicBlock::iterator BI(StartInst);

  // Keeps track of the last memory use or def before the insertion point for
  // the new memset. The new MemoryDef for the inserted memsets will be inserted
  // after MemInsertPoint. It points to either LastMemDef or to the last user
  // before the insertion point of the memset, if there are any such users.
  MemoryUseOrDef *MemInsertPoint = nullptr;
  // Keeps track of the last MemoryDef between StartInst and the insertion point
  // for the new memset. This will become the defining access of the inserted
  // memsets.
  MemoryDef *LastMemDef = nullptr;
  for (++BI; !BI->isTerminator(); ++BI) {
    if (MSSAU) {
      auto *CurrentAcc = cast_or_null<MemoryUseOrDef>(
          MSSAU->getMemorySSA()->getMemoryAccess(&*BI));
      if (CurrentAcc) {
        MemInsertPoint = CurrentAcc;
        if (auto *CurrentDef = dyn_cast<MemoryDef>(CurrentAcc))
          LastMemDef = CurrentDef;
      }
    }

    if (!isa<StoreInst>(BI) && !isa<MemSetInst>(BI)) {
      // If the instruction is readnone, ignore it, otherwise bail out.  We
      // don't even allow readonly here because we don't want something like:
      // A[1] = 2; strlen(A); A[2] = 2; -> memcpy(A, ...); strlen(A).
      if (BI->mayWriteToMemory() || BI->mayReadFromMemory())
        break;
      continue;
    }

    if (StoreInst *NextStore = dyn_cast<StoreInst>(BI)) {
      // If this is a store, see if we can merge it in.
      if (!NextStore->isSimple()) break;

      Value *StoredVal = NextStore->getValueOperand();

      // Don't convert stores of non-integral pointer types to memsets (which
      // stores integers).
      if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
        break;

      // Check to see if this stored value is of the same byte-splattable value.
      Value *StoredByte = isBytewiseValue(StoredVal, DL);
      if (isa<UndefValue>(ByteVal) && StoredByte)
        ByteVal = StoredByte;
      if (ByteVal != StoredByte)
        break;

      // Check to see if this store is to a constant offset from the start ptr.
      Optional<int64_t> Offset =
          isPointerOffset(StartPtr, NextStore->getPointerOperand(), DL);
      if (!Offset)
        break;

      Ranges.addStore(*Offset, NextStore);
    } else {
      MemSetInst *MSI = cast<MemSetInst>(BI);

      if (MSI->isVolatile() || ByteVal != MSI->getValue() ||
          !isa<ConstantInt>(MSI->getLength()))
        break;

      // Check to see if this store is to a constant offset from the start ptr.
      Optional<int64_t> Offset = isPointerOffset(StartPtr, MSI->getDest(), DL);
      if (!Offset)
        break;

      Ranges.addMemSet(*Offset, MSI);
    }
  }

  // If we have no ranges, then we just had a single store with nothing that
  // could be merged in.  This is a very common case of course.
  if (Ranges.empty())
    return nullptr;

  // If we had at least one store that could be merged in, add the starting
  // store as well.  We try to avoid this unless there is at least something
  // interesting as a small compile-time optimization.
  Ranges.addInst(0, StartInst);

  // If we create any memsets, we put it right before the first instruction that
  // isn't part of the memset block.  This ensure that the memset is dominated
  // by any addressing instruction needed by the start of the block.
  IRBuilder<> Builder(&*BI);

  // Now that we have full information about ranges, loop over the ranges and
  // emit memset's for anything big enough to be worthwhile.
  Instruction *AMemSet = nullptr;
  for (const MemsetRange &Range : Ranges) {
    if (Range.TheStores.size() == 1) continue;

    // If it is profitable to lower this range to memset, do so now.
    if (!Range.isProfitableToUseMemset(DL))
      continue;

    // Otherwise, we do want to transform this!  Create a new memset.
    // Get the starting pointer of the block.
    StartPtr = Range.StartPtr;

    AMemSet = Builder.CreateMemSet(StartPtr, ByteVal, Range.End - Range.Start,
                                   MaybeAlign(Range.Alignment));
    LLVM_DEBUG(dbgs() << "Replace stores:\n"; for (Instruction *SI
                                                   : Range.TheStores) dbgs()
                                              << *SI << '\n';
               dbgs() << "With: " << *AMemSet << '\n');
    if (!Range.TheStores.empty())
      AMemSet->setDebugLoc(Range.TheStores[0]->getDebugLoc());

    if (MSSAU) {
      assert(LastMemDef && MemInsertPoint &&
             "Both LastMemDef and MemInsertPoint need to be set");
      auto *NewDef =
          cast<MemoryDef>(MemInsertPoint->getMemoryInst() == &*BI
                              ? MSSAU->createMemoryAccessBefore(
                                    AMemSet, LastMemDef, MemInsertPoint)
                              : MSSAU->createMemoryAccessAfter(
                                    AMemSet, LastMemDef, MemInsertPoint));
      MSSAU->insertDef(NewDef, /*RenameUses=*/true);
      LastMemDef = NewDef;
      MemInsertPoint = NewDef;
    }

    // Zap all the stores.
    for (Instruction *SI : Range.TheStores)
      eraseInstruction(SI);

    ++NumMemSetInfer;
  }

  return AMemSet;
}

// This method try to lift a store instruction before position P.
// It will lift the store and its argument + that anything that
// may alias with these.
// The method returns true if it was successful.
bool MemCpyOptPass::moveUp(StoreInst *SI, Instruction *P, const LoadInst *LI) {
  // If the store alias this position, early bail out.
  MemoryLocation StoreLoc = MemoryLocation::get(SI);
  if (isModOrRefSet(AA->getModRefInfo(P, StoreLoc)))
    return false;

  // Keep track of the arguments of all instruction we plan to lift
  // so we can make sure to lift them as well if appropriate.
  DenseSet<Instruction*> Args;
  if (auto *Ptr = dyn_cast<Instruction>(SI->getPointerOperand()))
    if (Ptr->getParent() == SI->getParent())
      Args.insert(Ptr);

  // Instruction to lift before P.
  SmallVector<Instruction *, 8> ToLift{SI};

  // Memory locations of lifted instructions.
  SmallVector<MemoryLocation, 8> MemLocs{StoreLoc};

  // Lifted calls.
  SmallVector<const CallBase *, 8> Calls;

  const MemoryLocation LoadLoc = MemoryLocation::get(LI);

  for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) {
    auto *C = &*I;

    // Make sure hoisting does not perform a store that was not guaranteed to
    // happen.
    if (!isGuaranteedToTransferExecutionToSuccessor(C))
      return false;

    bool MayAlias = isModOrRefSet(AA->getModRefInfo(C, None));

    bool NeedLift = false;
    if (Args.erase(C))
      NeedLift = true;
    else if (MayAlias) {
      NeedLift = llvm::any_of(MemLocs, [C, this](const MemoryLocation &ML) {
        return isModOrRefSet(AA->getModRefInfo(C, ML));
      });

      if (!NeedLift)
        NeedLift = llvm::any_of(Calls, [C, this](const CallBase *Call) {
          return isModOrRefSet(AA->getModRefInfo(C, Call));
        });
    }

    if (!NeedLift)
      continue;

    if (MayAlias) {
      // Since LI is implicitly moved downwards past the lifted instructions,
      // none of them may modify its source.
      if (isModSet(AA->getModRefInfo(C, LoadLoc)))
        return false;
      else if (const auto *Call = dyn_cast<CallBase>(C)) {
        // If we can't lift this before P, it's game over.
        if (isModOrRefSet(AA->getModRefInfo(P, Call)))
          return false;

        Calls.push_back(Call);
      } else if (isa<LoadInst>(C) || isa<StoreInst>(C) || isa<VAArgInst>(C)) {
        // If we can't lift this before P, it's game over.
        auto ML = MemoryLocation::get(C);
        if (isModOrRefSet(AA->getModRefInfo(P, ML)))
          return false;

        MemLocs.push_back(ML);
      } else
        // We don't know how to lift this instruction.
        return false;
    }

    ToLift.push_back(C);
    for (unsigned k = 0, e = C->getNumOperands(); k != e; ++k)
      if (auto *A = dyn_cast<Instruction>(C->getOperand(k))) {
        if (A->getParent() == SI->getParent()) {
          // Cannot hoist user of P above P
          if(A == P) return false;
          Args.insert(A);
        }
      }
  }

  // Find MSSA insertion point. Normally P will always have a corresponding
  // memory access before which we can insert. However, with non-standard AA
  // pipelines, there may be a mismatch between AA and MSSA, in which case we
  // will scan for a memory access before P. In either case, we know for sure
  // that at least the load will have a memory access.
  // TODO: Simplify this once P will be determined by MSSA, in which case the
  // discrepancy can no longer occur.
  MemoryUseOrDef *MemInsertPoint = nullptr;
  if (MSSAU) {
    if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(P)) {
      MemInsertPoint = cast<MemoryUseOrDef>(--MA->getIterator());
    } else {
      const Instruction *ConstP = P;
      for (const Instruction &I : make_range(++ConstP->getReverseIterator(),
                                             ++LI->getReverseIterator())) {
        if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(&I)) {
          MemInsertPoint = MA;
          break;
        }
      }
    }
  }

  // We made it, we need to lift.
  for (auto *I : llvm::reverse(ToLift)) {
    LLVM_DEBUG(dbgs() << "Lifting " << *I << " before " << *P << "\n");
    I->moveBefore(P);
    if (MSSAU) {
      assert(MemInsertPoint && "Must have found insert point");
      if (MemoryUseOrDef *MA = MSSAU->getMemorySSA()->getMemoryAccess(I)) {
        MSSAU->moveAfter(MA, MemInsertPoint);
        MemInsertPoint = MA;
      }
    }
  }

  return true;
}

bool MemCpyOptPass::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
  if (!SI->isSimple()) return false;

  // Avoid merging nontemporal stores since the resulting
  // memcpy/memset would not be able to preserve the nontemporal hint.
  // In theory we could teach how to propagate the !nontemporal metadata to
  // memset calls. However, that change would force the backend to
  // conservatively expand !nontemporal memset calls back to sequences of
  // store instructions (effectively undoing the merging).
  if (SI->getMetadata(LLVMContext::MD_nontemporal))
    return false;

  const DataLayout &DL = SI->getModule()->getDataLayout();

  Value *StoredVal = SI->getValueOperand();

  // Not all the transforms below are correct for non-integral pointers, bail
  // until we've audited the individual pieces.
  if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()))
    return false;

  // Load to store forwarding can be interpreted as memcpy.
  if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
    if (LI->isSimple() && LI->hasOneUse() &&
        LI->getParent() == SI->getParent()) {

      auto *T = LI->getType();
      if (T->isAggregateType()) {
        MemoryLocation LoadLoc = MemoryLocation::get(LI);

        // We use alias analysis to check if an instruction may store to
        // the memory we load from in between the load and the store. If
        // such an instruction is found, we try to promote there instead
        // of at the store position.
        // TODO: Can use MSSA for this.
        Instruction *P = SI;
        for (auto &I : make_range(++LI->getIterator(), SI->getIterator())) {
          if (isModSet(AA->getModRefInfo(&I, LoadLoc))) {
            P = &I;
            break;
          }
        }

        // We found an instruction that may write to the loaded memory.
        // We can try to promote at this position instead of the store
        // position if nothing alias the store memory after this and the store
        // destination is not in the range.
        if (P && P != SI) {
          if (!moveUp(SI, P, LI))
            P = nullptr;
        }

        // If a valid insertion position is found, then we can promote
        // the load/store pair to a memcpy.
        if (P) {
          // If we load from memory that may alias the memory we store to,
          // memmove must be used to preserve semantic. If not, memcpy can
          // be used.
          bool UseMemMove = false;
          if (!AA->isNoAlias(MemoryLocation::get(SI), LoadLoc))
            UseMemMove = true;

          uint64_t Size = DL.getTypeStoreSize(T);

          IRBuilder<> Builder(P);
          Instruction *M;
          if (UseMemMove)
            M = Builder.CreateMemMove(
                SI->getPointerOperand(), SI->getAlign(),
                LI->getPointerOperand(), LI->getAlign(), Size);
          else
            M = Builder.CreateMemCpy(
                SI->getPointerOperand(), SI->getAlign(),
                LI->getPointerOperand(), LI->getAlign(), Size);

          LLVM_DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI << " => "
                            << *M << "\n");

          if (MSSAU) {
            auto *LastDef =
                cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI));
            auto *NewAccess =
                MSSAU->createMemoryAccessAfter(M, LastDef, LastDef);
            MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
          }

          eraseInstruction(SI);
          eraseInstruction(LI);
          ++NumMemCpyInstr;

          // Make sure we do not invalidate the iterator.
          BBI = M->getIterator();
          return true;
        }
      }

      // Detect cases where we're performing call slot forwarding, but
      // happen to be using a load-store pair to implement it, rather than
      // a memcpy.
      CallInst *C = nullptr;
      if (EnableMemorySSA) {
        if (auto *LoadClobber = dyn_cast<MemoryUseOrDef>(
                MSSA->getWalker()->getClobberingMemoryAccess(LI))) {
          // The load most post-dom the call. Limit to the same block for now.
          // TODO: Support non-local call-slot optimization?
          if (LoadClobber->getBlock() == SI->getParent())
            C = dyn_cast_or_null<CallInst>(LoadClobber->getMemoryInst());
        }
      } else {
        MemDepResult ldep = MD->getDependency(LI);
        if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst()))
          C = dyn_cast<CallInst>(ldep.getInst());
      }

      if (C) {
        // Check that nothing touches the dest of the "copy" between
        // the call and the store.
        MemoryLocation StoreLoc = MemoryLocation::get(SI);
        if (EnableMemorySSA) {
          if (accessedBetween(*AA, StoreLoc, MSSA->getMemoryAccess(C),
                              MSSA->getMemoryAccess(SI)))
            C = nullptr;
        } else {
          for (BasicBlock::iterator I = --SI->getIterator(),
                                    E = C->getIterator();
               I != E; --I) {
            if (isModOrRefSet(AA->getModRefInfo(&*I, StoreLoc))) {
              C = nullptr;
              break;
            }
          }
        }
      }

      if (C) {
        bool changed = performCallSlotOptzn(
            LI, SI, SI->getPointerOperand()->stripPointerCasts(),
            LI->getPointerOperand()->stripPointerCasts(),
            DL.getTypeStoreSize(SI->getOperand(0)->getType()),
            commonAlignment(SI->getAlign(), LI->getAlign()), C);
        if (changed) {
          eraseInstruction(SI);
          eraseInstruction(LI);
          ++NumMemCpyInstr;
          return true;
        }
      }
    }
  }

  // There are two cases that are interesting for this code to handle: memcpy
  // and memset.  Right now we only handle memset.

  // Ensure that the value being stored is something that can be memset'able a
  // byte at a time like "0" or "-1" or any width, as well as things like
  // 0xA0A0A0A0 and 0.0.
  auto *V = SI->getOperand(0);
  if (Value *ByteVal = isBytewiseValue(V, DL)) {
    if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
                                              ByteVal)) {
      BBI = I->getIterator(); // Don't invalidate iterator.
      return true;
    }

    // If we have an aggregate, we try to promote it to memset regardless
    // of opportunity for merging as it can expose optimization opportunities
    // in subsequent passes.
    auto *T = V->getType();
    if (T->isAggregateType()) {
      uint64_t Size = DL.getTypeStoreSize(T);
      IRBuilder<> Builder(SI);
      auto *M = Builder.CreateMemSet(SI->getPointerOperand(), ByteVal, Size,
                                     SI->getAlign());

      LLVM_DEBUG(dbgs() << "Promoting " << *SI << " to " << *M << "\n");

      if (MSSAU) {
        assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI)));
        auto *LastDef =
            cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(SI));
        auto *NewAccess = MSSAU->createMemoryAccessAfter(M, LastDef, LastDef);
        MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
      }

      eraseInstruction(SI);
      NumMemSetInfer++;

      // Make sure we do not invalidate the iterator.
      BBI = M->getIterator();
      return true;
    }
  }

  return false;
}

bool MemCpyOptPass::processMemSet(MemSetInst *MSI, BasicBlock::iterator &BBI) {
  // See if there is another memset or store neighboring this memset which
  // allows us to widen out the memset to do a single larger store.
  if (isa<ConstantInt>(MSI->getLength()) && !MSI->isVolatile())
    if (Instruction *I = tryMergingIntoMemset(MSI, MSI->getDest(),
                                              MSI->getValue())) {
      BBI = I->getIterator(); // Don't invalidate iterator.
      return true;
    }
  return false;
}

/// Takes a memcpy and a call that it depends on,
/// and checks for the possibility of a call slot optimization by having
/// the call write its result directly into the destination of the memcpy.
bool MemCpyOptPass::performCallSlotOptzn(Instruction *cpyLoad,
                                         Instruction *cpyStore, Value *cpyDest,
                                         Value *cpySrc, uint64_t cpyLen,
                                         Align cpyAlign, CallInst *C) {
  // The general transformation to keep in mind is
  //
  //   call @func(..., src, ...)
  //   memcpy(dest, src, ...)
  //
  // ->
  //
  //   memcpy(dest, src, ...)
  //   call @func(..., dest, ...)
  //
  // Since moving the memcpy is technically awkward, we additionally check that
  // src only holds uninitialized values at the moment of the call, meaning that
  // the memcpy can be discarded rather than moved.

  // Lifetime marks shouldn't be operated on.
  if (Function *F = C->getCalledFunction())
    if (F->isIntrinsic() && F->getIntrinsicID() == Intrinsic::lifetime_start)
      return false;

  // Require that src be an alloca.  This simplifies the reasoning considerably.
  AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
  if (!srcAlloca)
    return false;

  ConstantInt *srcArraySize = dyn_cast<ConstantInt>(srcAlloca->getArraySize());
  if (!srcArraySize)
    return false;

  const DataLayout &DL = cpyLoad->getModule()->getDataLayout();
  uint64_t srcSize = DL.getTypeAllocSize(srcAlloca->getAllocatedType()) *
                     srcArraySize->getZExtValue();

  if (cpyLen < srcSize)
    return false;

  // Check that accessing the first srcSize bytes of dest will not cause a
  // trap.  Otherwise the transform is invalid since it might cause a trap
  // to occur earlier than it otherwise would.
  if (!isDereferenceableAndAlignedPointer(cpyDest, Align(1), APInt(64, cpyLen),
                                          DL, C, DT))
    return false;

  // Make sure that nothing can observe cpyDest being written early. There are
  // a number of cases to consider:
  //  1. cpyDest cannot be accessed between C and cpyStore as a precondition of
  //     the transform.
  //  2. C itself may not access cpyDest (prior to the transform). This is
  //     checked further below.
  //  3. If cpyDest is accessible to the caller of this function (potentially
  //     captured and not based on an alloca), we need to ensure that we cannot
  //     unwind between C and cpyStore. This is checked here.
  //  4. If cpyDest is potentially captured, there may be accesses to it from
  //     another thread. In this case, we need to check that cpyStore is
  //     guaranteed to be executed if C is. As it is a non-atomic access, it
  //     renders accesses from other threads undefined.
  //     TODO: This is currently not checked.
  if (mayBeVisibleThroughUnwinding(cpyDest, C, cpyStore))
    return false;

  // Check that dest points to memory that is at least as aligned as src.
  Align srcAlign = srcAlloca->getAlign();
  bool isDestSufficientlyAligned = srcAlign <= cpyAlign;
  // If dest is not aligned enough and we can't increase its alignment then
  // bail out.
  if (!isDestSufficientlyAligned && !isa<AllocaInst>(cpyDest))
    return false;

  // Check that src is not accessed except via the call and the memcpy.  This
  // guarantees that it holds only undefined values when passed in (so the final
  // memcpy can be dropped), that it is not read or written between the call and
  // the memcpy, and that writing beyond the end of it is undefined.
  SmallVector<User *, 8> srcUseList(srcAlloca->users());
  while (!srcUseList.empty()) {
    User *U = srcUseList.pop_back_val();

    if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) {
      append_range(srcUseList, U->users());
      continue;
    }
    if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
      if (!G->hasAllZeroIndices())
        return false;

      append_range(srcUseList, U->users());
      continue;
    }
    if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U))
      if (IT->isLifetimeStartOrEnd())
        continue;

    if (U != C && U != cpyLoad)
      return false;
  }

  // Check that src isn't captured by the called function since the
  // transformation can cause aliasing issues in that case.
  for (unsigned ArgI = 0, E = C->arg_size(); ArgI != E; ++ArgI)
    if (C->getArgOperand(ArgI) == cpySrc && !C->doesNotCapture(ArgI))
      return false;

  // Since we're changing the parameter to the callsite, we need to make sure
  // that what would be the new parameter dominates the callsite.
  if (!DT->dominates(cpyDest, C)) {
    // Support moving a constant index GEP before the call.
    auto *GEP = dyn_cast<GetElementPtrInst>(cpyDest);
    if (GEP && GEP->hasAllConstantIndices() &&
        DT->dominates(GEP->getPointerOperand(), C))
      GEP->moveBefore(C);
    else
      return false;
  }

  // In addition to knowing that the call does not access src in some
  // unexpected manner, for example via a global, which we deduce from
  // the use analysis, we also need to know that it does not sneakily
  // access dest.  We rely on AA to figure this out for us.
  ModRefInfo MR = AA->getModRefInfo(C, cpyDest, LocationSize::precise(srcSize));
  // If necessary, perform additional analysis.
  if (isModOrRefSet(MR))
    MR = AA->callCapturesBefore(C, cpyDest, LocationSize::precise(srcSize), DT);
  if (isModOrRefSet(MR))
    return false;

  // We can't create address space casts here because we don't know if they're
  // safe for the target.
  if (cpySrc->getType()->getPointerAddressSpace() !=
      cpyDest->getType()->getPointerAddressSpace())
    return false;
  for (unsigned ArgI = 0; ArgI < C->arg_size(); ++ArgI)
    if (C->getArgOperand(ArgI)->stripPointerCasts() == cpySrc &&
        cpySrc->getType()->getPointerAddressSpace() !=
            C->getArgOperand(ArgI)->getType()->getPointerAddressSpace())
      return false;

  // All the checks have passed, so do the transformation.
  bool changedArgument = false;
  for (unsigned ArgI = 0; ArgI < C->arg_size(); ++ArgI)
    if (C->getArgOperand(ArgI)->stripPointerCasts() == cpySrc) {
      Value *Dest = cpySrc->getType() == cpyDest->getType() ?  cpyDest
        : CastInst::CreatePointerCast(cpyDest, cpySrc->getType(),
                                      cpyDest->getName(), C);
      changedArgument = true;
      if (C->getArgOperand(ArgI)->getType() == Dest->getType())
        C->setArgOperand(ArgI, Dest);
      else
        C->setArgOperand(ArgI, CastInst::CreatePointerCast(
                                   Dest, C->getArgOperand(ArgI)->getType(),
                                   Dest->getName(), C));
    }

  if (!changedArgument)
    return false;

  // If the destination wasn't sufficiently aligned then increase its alignment.
  if (!isDestSufficientlyAligned) {
    assert(isa<AllocaInst>(cpyDest) && "Can only increase alloca alignment!");
    cast<AllocaInst>(cpyDest)->setAlignment(srcAlign);
  }

  // Drop any cached information about the call, because we may have changed
  // its dependence information by changing its parameter.
  if (MD)
    MD->removeInstruction(C);

  // Update AA metadata
  // FIXME: MD_tbaa_struct and MD_mem_parallel_loop_access should also be
  // handled here, but combineMetadata doesn't support them yet
  unsigned KnownIDs[] = {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
                         LLVMContext::MD_noalias,
                         LLVMContext::MD_invariant_group,
                         LLVMContext::MD_access_group};
  combineMetadata(C, cpyLoad, KnownIDs, true);

  ++NumCallSlot;
  return true;
}

/// We've found that the (upward scanning) memory dependence of memcpy 'M' is
/// the memcpy 'MDep'. Try to simplify M to copy from MDep's input if we can.
bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
                                                  MemCpyInst *MDep) {
  // We can only transforms memcpy's where the dest of one is the source of the
  // other.
  if (M->getSource() != MDep->getDest() || MDep->isVolatile())
    return false;

  // If dep instruction is reading from our current input, then it is a noop
  // transfer and substituting the input won't change this instruction.  Just
  // ignore the input and let someone else zap MDep.  This handles cases like:
  //    memcpy(a <- a)
  //    memcpy(b <- a)
  if (M->getSource() == MDep->getSource())
    return false;

  // Second, the length of the memcpy's must be the same, or the preceding one
  // must be larger than the following one.
  ConstantInt *MDepLen = dyn_cast<ConstantInt>(MDep->getLength());
  ConstantInt *MLen = dyn_cast<ConstantInt>(M->getLength());
  if (!MDepLen || !MLen || MDepLen->getZExtValue() < MLen->getZExtValue())
    return false;

  // Verify that the copied-from memory doesn't change in between the two
  // transfers.  For example, in:
  //    memcpy(a <- b)
  //    *b = 42;
  //    memcpy(c <- a)
  // It would be invalid to transform the second memcpy into memcpy(c <- b).
  //
  // TODO: If the code between M and MDep is transparent to the destination "c",
  // then we could still perform the xform by moving M up to the first memcpy.
  if (EnableMemorySSA) {
    // TODO: It would be sufficient to check the MDep source up to the memcpy
    // size of M, rather than MDep.
    if (writtenBetween(MSSA, MemoryLocation::getForSource(MDep),
                       MSSA->getMemoryAccess(MDep), MSSA->getMemoryAccess(M)))
      return false;
  } else {
    // NOTE: This is conservative, it will stop on any read from the source loc,
    // not just the defining memcpy.
    MemDepResult SourceDep =
        MD->getPointerDependencyFrom(MemoryLocation::getForSource(MDep), false,
                                     M->getIterator(), M->getParent());
    if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
      return false;
  }

  // If the dest of the second might alias the source of the first, then the
  // source and dest might overlap.  We still want to eliminate the intermediate
  // value, but we have to generate a memmove instead of memcpy.
  bool UseMemMove = false;
  if (!AA->isNoAlias(MemoryLocation::getForDest(M),
                     MemoryLocation::getForSource(MDep)))
    UseMemMove = true;

  // If all checks passed, then we can transform M.
  LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy->memcpy src:\n"
                    << *MDep << '\n' << *M << '\n');

  // TODO: Is this worth it if we're creating a less aligned memcpy? For
  // example we could be moving from movaps -> movq on x86.
  IRBuilder<> Builder(M);
  Instruction *NewM;
  if (UseMemMove)
    NewM = Builder.CreateMemMove(M->getRawDest(), M->getDestAlign(),
                                 MDep->getRawSource(), MDep->getSourceAlign(),
                                 M->getLength(), M->isVolatile());
  else
    NewM = Builder.CreateMemCpy(M->getRawDest(), M->getDestAlign(),
                                MDep->getRawSource(), MDep->getSourceAlign(),
                                M->getLength(), M->isVolatile());

  if (MSSAU) {
    assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M)));
    auto *LastDef = cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M));
    auto *NewAccess = MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
    MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
  }

  // Remove the instruction we're replacing.
  eraseInstruction(M);
  ++NumMemCpyInstr;
  return true;
}

/// We've found that the (upward scanning) memory dependence of \p MemCpy is
/// \p MemSet.  Try to simplify \p MemSet to only set the trailing bytes that
/// weren't copied over by \p MemCpy.
///
/// In other words, transform:
/// \code
///   memset(dst, c, dst_size);
///   memcpy(dst, src, src_size);
/// \endcode
/// into:
/// \code
///   memcpy(dst, src, src_size);
///   memset(dst + src_size, c, dst_size <= src_size ? 0 : dst_size - src_size);
/// \endcode
bool MemCpyOptPass::processMemSetMemCpyDependence(MemCpyInst *MemCpy,
                                                  MemSetInst *MemSet) {
  // We can only transform memset/memcpy with the same destination.
  if (MemSet->getDest() != MemCpy->getDest())
    return false;

  // Check that src and dst of the memcpy aren't the same. While memcpy
  // operands cannot partially overlap, exact equality is allowed.
  if (!AA->isNoAlias(MemoryLocation(MemCpy->getSource(),
                                    LocationSize::precise(1)),
                     MemoryLocation(MemCpy->getDest(),
                                    LocationSize::precise(1))))
    return false;

  if (EnableMemorySSA) {
    // We know that dst up to src_size is not written. We now need to make sure
    // that dst up to dst_size is not accessed. (If we did not move the memset,
    // checking for reads would be sufficient.)
    if (accessedBetween(*AA, MemoryLocation::getForDest(MemSet),
                        MSSA->getMemoryAccess(MemSet),
                        MSSA->getMemoryAccess(MemCpy))) {
      return false;
    }
  } else {
    // We have already checked that dst up to src_size is not accessed. We
    // need to make sure that there are no accesses up to dst_size either.
    MemDepResult DstDepInfo = MD->getPointerDependencyFrom(
        MemoryLocation::getForDest(MemSet), false, MemCpy->getIterator(),
        MemCpy->getParent());
    if (DstDepInfo.getInst() != MemSet)
      return false;
  }

  // Use the same i8* dest as the memcpy, killing the memset dest if different.
  Value *Dest = MemCpy->getRawDest();
  Value *DestSize = MemSet->getLength();
  Value *SrcSize = MemCpy->getLength();

  if (mayBeVisibleThroughUnwinding(Dest, MemSet, MemCpy))
    return false;

  // By default, create an unaligned memset.
  unsigned Align = 1;
  // If Dest is aligned, and SrcSize is constant, use the minimum alignment
  // of the sum.
  const unsigned DestAlign =
      std::max(MemSet->getDestAlignment(), MemCpy->getDestAlignment());
  if (DestAlign > 1)
    if (ConstantInt *SrcSizeC = dyn_cast<ConstantInt>(SrcSize))
      Align = MinAlign(SrcSizeC->getZExtValue(), DestAlign);

  IRBuilder<> Builder(MemCpy);

  // If the sizes have different types, zext the smaller one.
  if (DestSize->getType() != SrcSize->getType()) {
    if (DestSize->getType()->getIntegerBitWidth() >
        SrcSize->getType()->getIntegerBitWidth())
      SrcSize = Builder.CreateZExt(SrcSize, DestSize->getType());
    else
      DestSize = Builder.CreateZExt(DestSize, SrcSize->getType());
  }

  Value *Ule = Builder.CreateICmpULE(DestSize, SrcSize);
  Value *SizeDiff = Builder.CreateSub(DestSize, SrcSize);
  Value *MemsetLen = Builder.CreateSelect(
      Ule, ConstantInt::getNullValue(DestSize->getType()), SizeDiff);
  Instruction *NewMemSet = Builder.CreateMemSet(
      Builder.CreateGEP(Dest->getType()->getPointerElementType(), Dest,
                        SrcSize),
      MemSet->getOperand(1), MemsetLen, MaybeAlign(Align));

  if (MSSAU) {
    assert(isa<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy)) &&
           "MemCpy must be a MemoryDef");
    // The new memset is inserted after the memcpy, but it is known that its
    // defining access is the memset about to be removed which immediately
    // precedes the memcpy.
    auto *LastDef =
        cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy));
    auto *NewAccess = MSSAU->createMemoryAccessBefore(
        NewMemSet, LastDef->getDefiningAccess(), LastDef);
    MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
  }

  eraseInstruction(MemSet);
  return true;
}

/// Determine whether the instruction has undefined content for the given Size,
/// either because it was freshly alloca'd or started its lifetime.
static bool hasUndefContents(Instruction *I, ConstantInt *Size) {
  if (isa<AllocaInst>(I))
    return true;

  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
    if (II->getIntrinsicID() == Intrinsic::lifetime_start)
      if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0)))
        if (LTSize->getZExtValue() >= Size->getZExtValue())
          return true;

  return false;
}

static bool hasUndefContentsMSSA(MemorySSA *MSSA, AliasAnalysis *AA, Value *V,
                                 MemoryDef *Def, ConstantInt *Size) {
  if (MSSA->isLiveOnEntryDef(Def))
    return isa<AllocaInst>(getUnderlyingObject(V));

  if (IntrinsicInst *II =
          dyn_cast_or_null<IntrinsicInst>(Def->getMemoryInst())) {
    if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
      ConstantInt *LTSize = cast<ConstantInt>(II->getArgOperand(0));
      if (AA->isMustAlias(V, II->getArgOperand(1)) &&
          LTSize->getZExtValue() >= Size->getZExtValue())
        return true;
    }
  }

  return false;
}

/// Transform memcpy to memset when its source was just memset.
/// In other words, turn:
/// \code
///   memset(dst1, c, dst1_size);
///   memcpy(dst2, dst1, dst2_size);
/// \endcode
/// into:
/// \code
///   memset(dst1, c, dst1_size);
///   memset(dst2, c, dst2_size);
/// \endcode
/// When dst2_size <= dst1_size.
///
/// The \p MemCpy must have a Constant length.
bool MemCpyOptPass::performMemCpyToMemSetOptzn(MemCpyInst *MemCpy,
                                               MemSetInst *MemSet) {
  // Make sure that memcpy(..., memset(...), ...), that is we are memsetting and
  // memcpying from the same address. Otherwise it is hard to reason about.
  if (!AA->isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource()))
    return false;

  // A known memset size is required.
  ConstantInt *MemSetSize = dyn_cast<ConstantInt>(MemSet->getLength());
  if (!MemSetSize)
    return false;

  // Make sure the memcpy doesn't read any more than what the memset wrote.
  // Don't worry about sizes larger than i64.
  ConstantInt *CopySize = cast<ConstantInt>(MemCpy->getLength());
  if (CopySize->getZExtValue() > MemSetSize->getZExtValue()) {
    // If the memcpy is larger than the memset, but the memory was undef prior
    // to the memset, we can just ignore the tail. Technically we're only
    // interested in the bytes from MemSetSize..CopySize here, but as we can't
    // easily represent this location, we use the full 0..CopySize range.
    MemoryLocation MemCpyLoc = MemoryLocation::getForSource(MemCpy);
    bool CanReduceSize = false;
    if (EnableMemorySSA) {
      MemoryUseOrDef *MemSetAccess = MSSA->getMemoryAccess(MemSet);
      MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
          MemSetAccess->getDefiningAccess(), MemCpyLoc);
      if (auto *MD = dyn_cast<MemoryDef>(Clobber))
        if (hasUndefContentsMSSA(MSSA, AA, MemCpy->getSource(), MD, CopySize))
          CanReduceSize = true;
    } else {
      MemDepResult DepInfo = MD->getPointerDependencyFrom(
          MemCpyLoc, true, MemSet->getIterator(), MemSet->getParent());
      if (DepInfo.isDef() && hasUndefContents(DepInfo.getInst(), CopySize))
        CanReduceSize = true;
    }

    if (!CanReduceSize)
      return false;
    CopySize = MemSetSize;
  }

  IRBuilder<> Builder(MemCpy);
  Instruction *NewM =
      Builder.CreateMemSet(MemCpy->getRawDest(), MemSet->getOperand(1),
                           CopySize, MaybeAlign(MemCpy->getDestAlignment()));
  if (MSSAU) {
    auto *LastDef =
        cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(MemCpy));
    auto *NewAccess = MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
    MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
  }

  return true;
}

/// Perform simplification of memcpy's.  If we have memcpy A
/// which copies X to Y, and memcpy B which copies Y to Z, then we can rewrite
/// B to be a memcpy from X to Z (or potentially a memmove, depending on
/// circumstances). This allows later passes to remove the first memcpy
/// altogether.
bool MemCpyOptPass::processMemCpy(MemCpyInst *M, BasicBlock::iterator &BBI) {
  // We can only optimize non-volatile memcpy's.
  if (M->isVolatile()) return false;

  // If the source and destination of the memcpy are the same, then zap it.
  if (M->getSource() == M->getDest()) {
    ++BBI;
    eraseInstruction(M);
    return true;
  }

  // If copying from a constant, try to turn the memcpy into a memset.
  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(M->getSource()))
    if (GV->isConstant() && GV->hasDefinitiveInitializer())
      if (Value *ByteVal = isBytewiseValue(GV->getInitializer(),
                                           M->getModule()->getDataLayout())) {
        IRBuilder<> Builder(M);
        Instruction *NewM =
            Builder.CreateMemSet(M->getRawDest(), ByteVal, M->getLength(),
                                 MaybeAlign(M->getDestAlignment()), false);
        if (MSSAU) {
          auto *LastDef =
              cast<MemoryDef>(MSSAU->getMemorySSA()->getMemoryAccess(M));
          auto *NewAccess =
              MSSAU->createMemoryAccessAfter(NewM, LastDef, LastDef);
          MSSAU->insertDef(cast<MemoryDef>(NewAccess), /*RenameUses=*/true);
        }

        eraseInstruction(M);
        ++NumCpyToSet;
        return true;
      }

  if (EnableMemorySSA) {
    MemoryUseOrDef *MA = MSSA->getMemoryAccess(M);
    MemoryAccess *AnyClobber = MSSA->getWalker()->getClobberingMemoryAccess(MA);
    MemoryLocation DestLoc = MemoryLocation::getForDest(M);
    const MemoryAccess *DestClobber =
        MSSA->getWalker()->getClobberingMemoryAccess(AnyClobber, DestLoc);

    // Try to turn a partially redundant memset + memcpy into
    // memcpy + smaller memset.  We don't need the memcpy size for this.
    // The memcpy most post-dom the memset, so limit this to the same basic
    // block. A non-local generalization is likely not worthwhile.
    if (auto *MD = dyn_cast<MemoryDef>(DestClobber))
      if (auto *MDep = dyn_cast_or_null<MemSetInst>(MD->getMemoryInst()))
        if (DestClobber->getBlock() == M->getParent())
          if (processMemSetMemCpyDependence(M, MDep))
            return true;

    // The optimizations after this point require the memcpy size.
    ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
    if (!CopySize) return false;

    MemoryAccess *SrcClobber = MSSA->getWalker()->getClobberingMemoryAccess(
        AnyClobber, MemoryLocation::getForSource(M));

    // There are four possible optimizations we can do for memcpy:
    //   a) memcpy-memcpy xform which exposes redundance for DSE.
    //   b) call-memcpy xform for return slot optimization.
    //   c) memcpy from freshly alloca'd space or space that has just started
    //      its lifetime copies undefined data, and we can therefore eliminate
    //      the memcpy in favor of the data that was already at the destination.
    //   d) memcpy from a just-memset'd source can be turned into memset.
    if (auto *MD = dyn_cast<MemoryDef>(SrcClobber)) {
      if (Instruction *MI = MD->getMemoryInst()) {
        if (auto *C = dyn_cast<CallInst>(MI)) {
          // The memcpy must post-dom the call. Limit to the same block for now.
          // Additionally, we need to ensure that there are no accesses to dest
          // between the call and the memcpy. Accesses to src will be checked
          // by performCallSlotOptzn().
          // TODO: Support non-local call-slot optimization?
          if (C->getParent() == M->getParent() &&
              !accessedBetween(*AA, DestLoc, MD, MA)) {
            // FIXME: Can we pass in either of dest/src alignment here instead
            // of conservatively taking the minimum?
            Align Alignment = std::min(M->getDestAlign().valueOrOne(),
                                       M->getSourceAlign().valueOrOne());
            if (performCallSlotOptzn(M, M, M->getDest(), M->getSource(),
                                     CopySize->getZExtValue(), Alignment, C)) {
              LLVM_DEBUG(dbgs() << "Performed call slot optimization:\n"
                                << "    call: " << *C << "\n"
                                << "    memcpy: " << *M << "\n");
              eraseInstruction(M);
              ++NumMemCpyInstr;
              return true;
            }
          }
        }
        if (auto *MDep = dyn_cast<MemCpyInst>(MI))
          return processMemCpyMemCpyDependence(M, MDep);
        if (auto *MDep = dyn_cast<MemSetInst>(MI)) {
          if (performMemCpyToMemSetOptzn(M, MDep)) {
            LLVM_DEBUG(dbgs() << "Converted memcpy to memset\n");
            eraseInstruction(M);
            ++NumCpyToSet;
            return true;
          }
        }
      }

      if (hasUndefContentsMSSA(MSSA, AA, M->getSource(), MD, CopySize)) {
        LLVM_DEBUG(dbgs() << "Removed memcpy from undef\n");
        eraseInstruction(M);
        ++NumMemCpyInstr;
        return true;
      }
    }
  } else {
    MemDepResult DepInfo = MD->getDependency(M);

    // Try to turn a partially redundant memset + memcpy into
    // memcpy + smaller memset.  We don't need the memcpy size for this.
    if (DepInfo.isClobber())
      if (MemSetInst *MDep = dyn_cast<MemSetInst>(DepInfo.getInst()))
        if (processMemSetMemCpyDependence(M, MDep))
          return true;

    // The optimizations after this point require the memcpy size.
    ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength());
    if (!CopySize) return false;

    // There are four possible optimizations we can do for memcpy:
    //   a) memcpy-memcpy xform which exposes redundance for DSE.
    //   b) call-memcpy xform for return slot optimization.
    //   c) memcpy from freshly alloca'd space or space that has just started
    //      its lifetime copies undefined data, and we can therefore eliminate
    //      the memcpy in favor of the data that was already at the destination.
    //   d) memcpy from a just-memset'd source can be turned into memset.
    if (DepInfo.isClobber()) {
      if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
        // FIXME: Can we pass in either of dest/src alignment here instead
        // of conservatively taking the minimum?
        Align Alignment = std::min(M->getDestAlign().valueOrOne(),
                                   M->getSourceAlign().valueOrOne());
        if (performCallSlotOptzn(M, M, M->getDest(), M->getSource(),
                                 CopySize->getZExtValue(), Alignment, C)) {
          eraseInstruction(M);
          ++NumMemCpyInstr;
          return true;
        }
      }
    }

    MemoryLocation SrcLoc = MemoryLocation::getForSource(M);
    MemDepResult SrcDepInfo = MD->getPointerDependencyFrom(
        SrcLoc, true, M->getIterator(), M->getParent());

    if (SrcDepInfo.isClobber()) {
      if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
        return processMemCpyMemCpyDependence(M, MDep);
    } else if (SrcDepInfo.isDef()) {
      if (hasUndefContents(SrcDepInfo.getInst(), CopySize)) {
        eraseInstruction(M);
        ++NumMemCpyInstr;
        return true;
      }
    }

    if (SrcDepInfo.isClobber())
      if (MemSetInst *MDep = dyn_cast<MemSetInst>(SrcDepInfo.getInst()))
        if (performMemCpyToMemSetOptzn(M, MDep)) {
          eraseInstruction(M);
          ++NumCpyToSet;
          return true;
        }
  }

  return false;
}

/// Transforms memmove calls to memcpy calls when the src/dst are guaranteed
/// not to alias.
bool MemCpyOptPass::processMemMove(MemMoveInst *M) {
  if (!TLI->has(LibFunc_memmove))
    return false;

  // See if the pointers alias.
  if (!AA->isNoAlias(MemoryLocation::getForDest(M),
                     MemoryLocation::getForSource(M)))
    return false;

  LLVM_DEBUG(dbgs() << "MemCpyOptPass: Optimizing memmove -> memcpy: " << *M
                    << "\n");

  // If not, then we know we can transform this.
  Type *ArgTys[3] = { M->getRawDest()->getType(),
                      M->getRawSource()->getType(),
                      M->getLength()->getType() };
  M->setCalledFunction(Intrinsic::getDeclaration(M->getModule(),
                                                 Intrinsic::memcpy, ArgTys));

  // For MemorySSA nothing really changes (except that memcpy may imply stricter
  // aliasing guarantees).

  // MemDep may have over conservative information about this instruction, just
  // conservatively flush it from the cache.
  if (MD)
    MD->removeInstruction(M);

  ++NumMoveToCpy;
  return true;
}

/// This is called on every byval argument in call sites.
bool MemCpyOptPass::processByValArgument(CallBase &CB, unsigned ArgNo) {
  const DataLayout &DL = CB.getCaller()->getParent()->getDataLayout();
  // Find out what feeds this byval argument.
  Value *ByValArg = CB.getArgOperand(ArgNo);
  Type *ByValTy = cast<PointerType>(ByValArg->getType())->getElementType();
  uint64_t ByValSize = DL.getTypeAllocSize(ByValTy);
  MemoryLocation Loc(ByValArg, LocationSize::precise(ByValSize));
  MemCpyInst *MDep = nullptr;
  if (EnableMemorySSA) {
    MemoryUseOrDef *CallAccess = MSSA->getMemoryAccess(&CB);
    MemoryAccess *Clobber = MSSA->getWalker()->getClobberingMemoryAccess(
        CallAccess->getDefiningAccess(), Loc);
    if (auto *MD = dyn_cast<MemoryDef>(Clobber))
      MDep = dyn_cast_or_null<MemCpyInst>(MD->getMemoryInst());
  } else {
    MemDepResult DepInfo = MD->getPointerDependencyFrom(
        Loc, true, CB.getIterator(), CB.getParent());
    if (!DepInfo.isClobber())
      return false;
    MDep = dyn_cast<MemCpyInst>(DepInfo.getInst());
  }

  // If the byval argument isn't fed by a memcpy, ignore it.  If it is fed by
  // a memcpy, see if we can byval from the source of the memcpy instead of the
  // result.
  if (!MDep || MDep->isVolatile() ||
      ByValArg->stripPointerCasts() != MDep->getDest())
    return false;

  // The length of the memcpy must be larger or equal to the size of the byval.
  ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());
  if (!C1 || C1->getValue().getZExtValue() < ByValSize)
    return false;

  // Get the alignment of the byval.  If the call doesn't specify the alignment,
  // then it is some target specific value that we can't know.
  MaybeAlign ByValAlign = CB.getParamAlign(ArgNo);
  if (!ByValAlign) return false;

  // If it is greater than the memcpy, then we check to see if we can force the
  // source of the memcpy to the alignment we need.  If we fail, we bail out.
  MaybeAlign MemDepAlign = MDep->getSourceAlign();
  if ((!MemDepAlign || *MemDepAlign < *ByValAlign) &&
      getOrEnforceKnownAlignment(MDep->getSource(), ByValAlign, DL, &CB, AC,
                                 DT) < *ByValAlign)
    return false;

  // The address space of the memcpy source must match the byval argument
  if (MDep->getSource()->getType()->getPointerAddressSpace() !=
      ByValArg->getType()->getPointerAddressSpace())
    return false;

  // Verify that the copied-from memory doesn't change in between the memcpy and
  // the byval call.
  //    memcpy(a <- b)
  //    *b = 42;
  //    foo(*a)
  // It would be invalid to transform the second memcpy into foo(*b).
  if (EnableMemorySSA) {
    if (writtenBetween(MSSA, MemoryLocation::getForSource(MDep),
                       MSSA->getMemoryAccess(MDep), MSSA->getMemoryAccess(&CB)))
      return false;
  } else {
    // NOTE: This is conservative, it will stop on any read from the source loc,
    // not just the defining memcpy.
    MemDepResult SourceDep = MD->getPointerDependencyFrom(
        MemoryLocation::getForSource(MDep), false,
        CB.getIterator(), MDep->getParent());
    if (!SourceDep.isClobber() || SourceDep.getInst() != MDep)
      return false;
  }

  Value *TmpCast = MDep->getSource();
  if (MDep->getSource()->getType() != ByValArg->getType()) {
    BitCastInst *TmpBitCast = new BitCastInst(MDep->getSource(), ByValArg->getType(),
                                              "tmpcast", &CB);
    // Set the tmpcast's DebugLoc to MDep's
    TmpBitCast->setDebugLoc(MDep->getDebugLoc());
    TmpCast = TmpBitCast;
  }

  LLVM_DEBUG(dbgs() << "MemCpyOptPass: Forwarding memcpy to byval:\n"
                    << "  " << *MDep << "\n"
                    << "  " << CB << "\n");

  // Otherwise we're good!  Update the byval argument.
  CB.setArgOperand(ArgNo, TmpCast);
  ++NumMemCpyInstr;
  return true;
}

/// Executes one iteration of MemCpyOptPass.
bool MemCpyOptPass::iterateOnFunction(Function &F) {
  bool MadeChange = false;

  // Walk all instruction in the function.
  for (BasicBlock &BB : F) {
    // Skip unreachable blocks. For example processStore assumes that an
    // instruction in a BB can't be dominated by a later instruction in the
    // same BB (which is a scenario that can happen for an unreachable BB that
    // has itself as a predecessor).
    if (!DT->isReachableFromEntry(&BB))
      continue;

    for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) {
        // Avoid invalidating the iterator.
      Instruction *I = &*BI++;

      bool RepeatInstruction = false;

      if (StoreInst *SI = dyn_cast<StoreInst>(I))
        MadeChange |= processStore(SI, BI);
      else if (MemSetInst *M = dyn_cast<MemSetInst>(I))
        RepeatInstruction = processMemSet(M, BI);
      else if (MemCpyInst *M = dyn_cast<MemCpyInst>(I))
        RepeatInstruction = processMemCpy(M, BI);
      else if (MemMoveInst *M = dyn_cast<MemMoveInst>(I))
        RepeatInstruction = processMemMove(M);
      else if (auto *CB = dyn_cast<CallBase>(I)) {
        for (unsigned i = 0, e = CB->arg_size(); i != e; ++i)
          if (CB->isByValArgument(i))
            MadeChange |= processByValArgument(*CB, i);
      }

      // Reprocess the instruction if desired.
      if (RepeatInstruction) {
        if (BI != BB.begin())
          --BI;
        MadeChange = true;
      }
    }
  }

  return MadeChange;
}

PreservedAnalyses MemCpyOptPass::run(Function &F, FunctionAnalysisManager &AM) {
  auto *MD = !EnableMemorySSA ? &AM.getResult<MemoryDependenceAnalysis>(F)
                              : AM.getCachedResult<MemoryDependenceAnalysis>(F);
  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
  auto *AA = &AM.getResult<AAManager>(F);
  auto *AC = &AM.getResult<AssumptionAnalysis>(F);
  auto *DT = &AM.getResult<DominatorTreeAnalysis>(F);
  auto *MSSA = EnableMemorySSA ? &AM.getResult<MemorySSAAnalysis>(F)
                               : AM.getCachedResult<MemorySSAAnalysis>(F);

  bool MadeChange =
      runImpl(F, MD, &TLI, AA, AC, DT, MSSA ? &MSSA->getMSSA() : nullptr);
  if (!MadeChange)
    return PreservedAnalyses::all();

  PreservedAnalyses PA;
  PA.preserveSet<CFGAnalyses>();
  PA.preserve<GlobalsAA>();
  if (MD)
    PA.preserve<MemoryDependenceAnalysis>();
  if (MSSA)
    PA.preserve<MemorySSAAnalysis>();
  return PA;
}

bool MemCpyOptPass::runImpl(Function &F, MemoryDependenceResults *MD_,
                            TargetLibraryInfo *TLI_, AliasAnalysis *AA_,
                            AssumptionCache *AC_, DominatorTree *DT_,
                            MemorySSA *MSSA_) {
  bool MadeChange = false;
  MD = MD_;
  TLI = TLI_;
  AA = AA_;
  AC = AC_;
  DT = DT_;
  MSSA = MSSA_;
  MemorySSAUpdater MSSAU_(MSSA_);
  MSSAU = MSSA_ ? &MSSAU_ : nullptr;
  // If we don't have at least memset and memcpy, there is little point of doing
  // anything here.  These are required by a freestanding implementation, so if
  // even they are disabled, there is no point in trying hard.
  if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy))
    return false;

  while (true) {
    if (!iterateOnFunction(F))
      break;
    MadeChange = true;
  }

  if (MSSA_ && VerifyMemorySSA)
    MSSA_->verifyMemorySSA();

  MD = nullptr;
  return MadeChange;
}

/// This is the main transformation entry point for a function.
bool MemCpyOptLegacyPass::runOnFunction(Function &F) {
  if (skipFunction(F))
    return false;

  auto *MDWP = !EnableMemorySSA
      ? &getAnalysis<MemoryDependenceWrapperPass>()
      : getAnalysisIfAvailable<MemoryDependenceWrapperPass>();
  auto *TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
  auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
  auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
  auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  auto *MSSAWP = EnableMemorySSA
      ? &getAnalysis<MemorySSAWrapperPass>()
      : getAnalysisIfAvailable<MemorySSAWrapperPass>();

  return Impl.runImpl(F, MDWP ? & MDWP->getMemDep() : nullptr, TLI, AA, AC, DT,
                      MSSAWP ? &MSSAWP->getMSSA() : nullptr);
}