llvm.org GIT mirror llvm / 906007f lib / Transforms / Scalar / LICM.cpp
906007f

Tree @906007f (Download .tar.gz)

LICM.cpp @906007fraw · 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
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
//===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
//
// 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 loop invariant code motion, attempting to remove as much
// code from the body of a loop as possible.  It does this by either hoisting
// code into the preheader block, or by sinking code to the exit blocks if it is
// safe.  This pass also promotes must-aliased memory locations in the loop to
// live in registers, thus hoisting and sinking "invariant" loads and stores.
//
// This pass uses alias analysis for two purposes:
//
//  1. Moving loop invariant loads and calls out of loops.  If we can determine
//     that a load or call inside of a loop never aliases anything stored to,
//     we can hoist it or sink it like any other instruction.
//  2. Scalar Promotion of Memory - If there is a store instruction inside of
//     the loop, we try to move the store to happen AFTER the loop instead of
//     inside of the loop.  This can only happen if a few conditions are true:
//       A. The pointer stored through is loop invariant
//       B. There are no stores or loads in the loop which _may_ alias the
//          pointer.  There are no calls in the loop which mod/ref the pointer.
//     If these conditions are true, we can promote the loads and stores in the
//     loop of the pointer to use a temporary alloca'd variable.  We then use
//     the SSAUpdater to construct the appropriate SSA form for the value.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar/LICM.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/BasicAliasAnalysis.h"
#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/PredIteratorCache.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/LoopPassManager.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include <algorithm>
#include <utility>
using namespace llvm;

#define DEBUG_TYPE "licm"

STATISTIC(NumCreatedBlocks, "Number of blocks created");
STATISTIC(NumClonedBranches, "Number of branches cloned");
STATISTIC(NumSunk, "Number of instructions sunk out of loop");
STATISTIC(NumHoisted, "Number of instructions hoisted out of loop");
STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk");
STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk");
STATISTIC(NumPromoted, "Number of memory locations promoted to registers");

/// Memory promotion is enabled by default.
static cl::opt<bool>
    DisablePromotion("disable-licm-promotion", cl::Hidden, cl::init(false),
                     cl::desc("Disable memory promotion in LICM pass"));

static cl::opt<bool> ControlFlowHoisting(
    "licm-control-flow-hoisting", cl::Hidden, cl::init(false),
    cl::desc("Enable control flow (and PHI) hoisting in LICM"));

static cl::opt<uint32_t> MaxNumUsesTraversed(
    "licm-max-num-uses-traversed", cl::Hidden, cl::init(8),
    cl::desc("Max num uses visited for identifying load "
             "invariance in loop using invariant start (default = 8)"));

// Default value of zero implies we use the regular alias set tracker mechanism
// instead of the cross product using AA to identify aliasing of the memory
// location we are interested in.
static cl::opt<int>
LICMN2Theshold("licm-n2-threshold", cl::Hidden, cl::init(0),
               cl::desc("How many instruction to cross product using AA"));

// Experimental option to allow imprecision in LICM in pathological cases, in
// exchange for faster compile. This is to be removed if MemorySSA starts to
// address the same issue. This flag applies only when LICM uses MemorySSA
// instead on AliasSetTracker. LICM calls MemorySSAWalker's
// getClobberingMemoryAccess, up to the value of the Cap, getting perfect
// accuracy. Afterwards, LICM will call into MemorySSA's getDefiningAccess,
// which may not be precise, since optimizeUses is capped. The result is
// correct, but we may not get as "far up" as possible to get which access is
// clobbering the one queried.
static cl::opt<int> LicmMssaOptCap(
    "licm-mssa-optimization-cap", cl::init(100), cl::Hidden,
    cl::desc("Enable imprecision in LICM in pathological cases, in exchange "
             "for faster compile. Caps the MemorySSA clobbering calls."));

// Experimentally, memory promotion carries less importance than sinking and
// hoisting. Limit when we do promotion when using MemorySSA, in order to save
// compile time.
static cl::opt<unsigned> AccessCapForMSSAPromotion(
    "max-acc-licm-promotion", cl::init(250), cl::Hidden,
    cl::desc("[LICM & MemorySSA] When MSSA in LICM is disabled, this has no "
             "effect. When MSSA in LICM is enabled, then this is the maximum "
             "number of accesses allowed to be present in a loop in order to "
             "enable memory promotion."));

static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI);
static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
                                  const LoopSafetyInfo *SafetyInfo,
                                  TargetTransformInfo *TTI, bool &FreeInLoop);
static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
                  BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
                  MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE);
static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
                 const Loop *CurLoop, ICFLoopSafetyInfo *SafetyInfo,
                 MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE,
                 bool FreeInLoop);
static bool isSafeToExecuteUnconditionally(Instruction &Inst,
                                           const DominatorTree *DT,
                                           const Loop *CurLoop,
                                           const LoopSafetyInfo *SafetyInfo,
                                           OptimizationRemarkEmitter *ORE,
                                           const Instruction *CtxI = nullptr);
static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
                                     AliasSetTracker *CurAST, Loop *CurLoop,
                                     AliasAnalysis *AA);
static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
                                             Loop *CurLoop,
                                             int &LicmMssaOptCounter);
static Instruction *CloneInstructionInExitBlock(
    Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI,
    const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU);

static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
                             AliasSetTracker *AST, MemorySSAUpdater *MSSAU);

static void moveInstructionBefore(Instruction &I, Instruction &Dest,
                                  ICFLoopSafetyInfo &SafetyInfo,
                                  MemorySSAUpdater *MSSAU);

namespace {
struct LoopInvariantCodeMotion {
  using ASTrackerMapTy = DenseMap<Loop *, std::unique_ptr<AliasSetTracker>>;
  bool runOnLoop(Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT,
                 TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
                 ScalarEvolution *SE, MemorySSA *MSSA,
                 OptimizationRemarkEmitter *ORE, bool DeleteAST);

  ASTrackerMapTy &getLoopToAliasSetMap() { return LoopToAliasSetMap; }

private:
  ASTrackerMapTy LoopToAliasSetMap;

  std::unique_ptr<AliasSetTracker>
  collectAliasInfoForLoop(Loop *L, LoopInfo *LI, AliasAnalysis *AA);
  std::unique_ptr<AliasSetTracker>
  collectAliasInfoForLoopWithMSSA(Loop *L, AliasAnalysis *AA,
                                  MemorySSAUpdater *MSSAU);
};

struct LegacyLICMPass : public LoopPass {
  static char ID; // Pass identification, replacement for typeid
  LegacyLICMPass() : LoopPass(ID) {
    initializeLegacyLICMPassPass(*PassRegistry::getPassRegistry());
  }

  bool runOnLoop(Loop *L, LPPassManager &LPM) override {
    if (skipLoop(L)) {
      // If we have run LICM on a previous loop but now we are skipping
      // (because we've hit the opt-bisect limit), we need to clear the
      // loop alias information.
      LICM.getLoopToAliasSetMap().clear();
      return false;
    }

    auto *SE = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
    MemorySSA *MSSA = EnableMSSALoopDependency
                          ? (&getAnalysis<MemorySSAWrapperPass>().getMSSA())
                          : nullptr;
    // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
    // pass.  Function analyses need to be preserved across loop transformations
    // but ORE cannot be preserved (see comment before the pass definition).
    OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
    return LICM.runOnLoop(L,
                          &getAnalysis<AAResultsWrapperPass>().getAAResults(),
                          &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(),
                          &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
                          &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
                          &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
                              *L->getHeader()->getParent()),
                          SE ? &SE->getSE() : nullptr, MSSA, &ORE, false);
  }

  /// This transformation requires natural loop information & requires that
  /// loop preheaders be inserted into the CFG...
  ///
  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addPreserved<DominatorTreeWrapperPass>();
    AU.addPreserved<LoopInfoWrapperPass>();
    AU.addRequired<TargetLibraryInfoWrapperPass>();
    if (EnableMSSALoopDependency) {
      AU.addRequired<MemorySSAWrapperPass>();
      AU.addPreserved<MemorySSAWrapperPass>();
    }
    AU.addRequired<TargetTransformInfoWrapperPass>();
    getLoopAnalysisUsage(AU);
  }

  using llvm::Pass::doFinalization;

  bool doFinalization() override {
    assert(LICM.getLoopToAliasSetMap().empty() &&
           "Didn't free loop alias sets");
    return false;
  }

private:
  LoopInvariantCodeMotion LICM;

  /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
  void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,
                               Loop *L) override;

  /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
  /// set.
  void deleteAnalysisValue(Value *V, Loop *L) override;

  /// Simple Analysis hook. Delete loop L from alias set map.
  void deleteAnalysisLoop(Loop *L) override;
};
} // namespace

PreservedAnalyses LICMPass::run(Loop &L, LoopAnalysisManager &AM,
                                LoopStandardAnalysisResults &AR, LPMUpdater &) {
  const auto &FAM =
      AM.getResult<FunctionAnalysisManagerLoopProxy>(L, AR).getManager();
  Function *F = L.getHeader()->getParent();

  auto *ORE = FAM.getCachedResult<OptimizationRemarkEmitterAnalysis>(*F);
  // FIXME: This should probably be optional rather than required.
  if (!ORE)
    report_fatal_error("LICM: OptimizationRemarkEmitterAnalysis not "
                       "cached at a higher level");

  LoopInvariantCodeMotion LICM;
  if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, &AR.TLI, &AR.TTI, &AR.SE,
                      AR.MSSA, ORE, true))
    return PreservedAnalyses::all();

  auto PA = getLoopPassPreservedAnalyses();

  PA.preserve<DominatorTreeAnalysis>();
  PA.preserve<LoopAnalysis>();

  return PA;
}

char LegacyLICMPass::ID = 0;
INITIALIZE_PASS_BEGIN(LegacyLICMPass, "licm", "Loop Invariant Code Motion",
                      false, false)
INITIALIZE_PASS_DEPENDENCY(LoopPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
INITIALIZE_PASS_END(LegacyLICMPass, "licm", "Loop Invariant Code Motion", false,
                    false)

Pass *llvm::createLICMPass() { return new LegacyLICMPass(); }

/// Hoist expressions out of the specified loop. Note, alias info for inner
/// loop is not preserved so it is not a good idea to run LICM multiple
/// times on one loop.
/// We should delete AST for inner loops in the new pass manager to avoid
/// memory leak.
///
bool LoopInvariantCodeMotion::runOnLoop(
    Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT,
    TargetLibraryInfo *TLI, TargetTransformInfo *TTI, ScalarEvolution *SE,
    MemorySSA *MSSA, OptimizationRemarkEmitter *ORE, bool DeleteAST) {
  bool Changed = false;

  assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");

  std::unique_ptr<AliasSetTracker> CurAST;
  std::unique_ptr<MemorySSAUpdater> MSSAU;
  bool NoOfMemAccTooLarge = false;
  int LicmMssaOptCounter = 0;

  if (!MSSA) {
    LLVM_DEBUG(dbgs() << "LICM: Using Alias Set Tracker.\n");
    CurAST = collectAliasInfoForLoop(L, LI, AA);
  } else {
    LLVM_DEBUG(dbgs() << "LICM: Using MemorySSA.\n");
    MSSAU = make_unique<MemorySSAUpdater>(MSSA);

    unsigned AccessCapCount = 0;
    for (auto *BB : L->getBlocks()) {
      if (auto *Accesses = MSSA->getBlockAccesses(BB)) {
        for (const auto &MA : *Accesses) {
          (void)MA;
          AccessCapCount++;
          if (AccessCapCount > AccessCapForMSSAPromotion) {
            NoOfMemAccTooLarge = true;
            break;
          }
        }
      }
      if (NoOfMemAccTooLarge)
        break;
    }
  }

  // Get the preheader block to move instructions into...
  BasicBlock *Preheader = L->getLoopPreheader();

  // Compute loop safety information.
  ICFLoopSafetyInfo SafetyInfo(DT);
  SafetyInfo.computeLoopSafetyInfo(L);

  // We want to visit all of the instructions in this loop... that are not parts
  // of our subloops (they have already had their invariants hoisted out of
  // their loop, into this loop, so there is no need to process the BODIES of
  // the subloops).
  //
  // Traverse the body of the loop in depth first order on the dominator tree so
  // that we are guaranteed to see definitions before we see uses.  This allows
  // us to sink instructions in one pass, without iteration.  After sinking
  // instructions, we perform another pass to hoist them out of the loop.
  //
  if (L->hasDedicatedExits())
    Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, TTI, L,
                          CurAST.get(), MSSAU.get(), &SafetyInfo,
                          NoOfMemAccTooLarge, LicmMssaOptCounter, ORE);
  if (Preheader)
    Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, L,
                           CurAST.get(), MSSAU.get(), &SafetyInfo,
                           NoOfMemAccTooLarge, LicmMssaOptCounter, ORE);

  // Now that all loop invariants have been removed from the loop, promote any
  // memory references to scalars that we can.
  // Don't sink stores from loops without dedicated block exits. Exits
  // containing indirect branches are not transformed by loop simplify,
  // make sure we catch that. An additional load may be generated in the
  // preheader for SSA updater, so also avoid sinking when no preheader
  // is available.
  if (!DisablePromotion && Preheader && L->hasDedicatedExits() &&
      !NoOfMemAccTooLarge) {
    // Figure out the loop exits and their insertion points
    SmallVector<BasicBlock *, 8> ExitBlocks;
    L->getUniqueExitBlocks(ExitBlocks);

    // We can't insert into a catchswitch.
    bool HasCatchSwitch = llvm::any_of(ExitBlocks, [](BasicBlock *Exit) {
      return isa<CatchSwitchInst>(Exit->getTerminator());
    });

    if (!HasCatchSwitch) {
      SmallVector<Instruction *, 8> InsertPts;
      SmallVector<MemoryAccess *, 8> MSSAInsertPts;
      InsertPts.reserve(ExitBlocks.size());
      if (MSSAU)
        MSSAInsertPts.reserve(ExitBlocks.size());
      for (BasicBlock *ExitBlock : ExitBlocks) {
        InsertPts.push_back(&*ExitBlock->getFirstInsertionPt());
        if (MSSAU)
          MSSAInsertPts.push_back(nullptr);
      }

      PredIteratorCache PIC;

      bool Promoted = false;

      // Build an AST using MSSA.
      if (!CurAST.get())
        CurAST = collectAliasInfoForLoopWithMSSA(L, AA, MSSAU.get());

      // Loop over all of the alias sets in the tracker object.
      for (AliasSet &AS : *CurAST) {
        // We can promote this alias set if it has a store, if it is a "Must"
        // alias set, if the pointer is loop invariant, and if we are not
        // eliminating any volatile loads or stores.
        if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
            !L->isLoopInvariant(AS.begin()->getValue()))
          continue;

        assert(
            !AS.empty() &&
            "Must alias set should have at least one pointer element in it!");

        SmallSetVector<Value *, 8> PointerMustAliases;
        for (const auto &ASI : AS)
          PointerMustAliases.insert(ASI.getValue());

        Promoted |= promoteLoopAccessesToScalars(
            PointerMustAliases, ExitBlocks, InsertPts, MSSAInsertPts, PIC, LI,
            DT, TLI, L, CurAST.get(), MSSAU.get(), &SafetyInfo, ORE);
      }

      // Once we have promoted values across the loop body we have to
      // recursively reform LCSSA as any nested loop may now have values defined
      // within the loop used in the outer loop.
      // FIXME: This is really heavy handed. It would be a bit better to use an
      // SSAUpdater strategy during promotion that was LCSSA aware and reformed
      // it as it went.
      if (Promoted)
        formLCSSARecursively(*L, *DT, LI, SE);

      Changed |= Promoted;
    }
  }

  // Check that neither this loop nor its parent have had LCSSA broken. LICM is
  // specifically moving instructions across the loop boundary and so it is
  // especially in need of sanity checking here.
  assert(L->isLCSSAForm(*DT) && "Loop not left in LCSSA form after LICM!");
  assert((!L->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) &&
         "Parent loop not left in LCSSA form after LICM!");

  // If this loop is nested inside of another one, save the alias information
  // for when we process the outer loop.
  if (!MSSAU.get() && CurAST.get() && L->getParentLoop() && !DeleteAST)
    LoopToAliasSetMap[L] = std::move(CurAST);

  if (MSSAU.get() && VerifyMemorySSA)
    MSSAU->getMemorySSA()->verifyMemorySSA();

  if (Changed && SE)
    SE->forgetLoopDispositions(L);
  return Changed;
}

/// Walk the specified region of the CFG (defined by all blocks dominated by
/// the specified block, and that are in the current loop) in reverse depth
/// first order w.r.t the DominatorTree.  This allows us to visit uses before
/// definitions, allowing us to sink a loop body in one pass without iteration.
///
bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
                      DominatorTree *DT, TargetLibraryInfo *TLI,
                      TargetTransformInfo *TTI, Loop *CurLoop,
                      AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
                      ICFLoopSafetyInfo *SafetyInfo, bool NoOfMemAccTooLarge,
                      int &LicmMssaOptCounter, OptimizationRemarkEmitter *ORE) {

  // Verify inputs.
  assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
         CurLoop != nullptr && SafetyInfo != nullptr &&
         "Unexpected input to sinkRegion.");
  assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) &&
         "Either AliasSetTracker or MemorySSA should be initialized.");

  // We want to visit children before parents. We will enque all the parents
  // before their children in the worklist and process the worklist in reverse
  // order.
  SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop);

  bool Changed = false;
  for (DomTreeNode *DTN : reverse(Worklist)) {
    BasicBlock *BB = DTN->getBlock();
    // Only need to process the contents of this block if it is not part of a
    // subloop (which would already have been processed).
    if (inSubLoop(BB, CurLoop, LI))
      continue;

    for (BasicBlock::iterator II = BB->end(); II != BB->begin();) {
      Instruction &I = *--II;

      // If the instruction is dead, we would try to sink it because it isn't
      // used in the loop, instead, just delete it.
      if (isInstructionTriviallyDead(&I, TLI)) {
        LLVM_DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n');
        salvageDebugInfo(I);
        ++II;
        eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);
        Changed = true;
        continue;
      }

      // Check to see if we can sink this instruction to the exit blocks
      // of the loop.  We can do this if the all users of the instruction are
      // outside of the loop.  In this case, it doesn't even matter if the
      // operands of the instruction are loop invariant.
      //
      bool FreeInLoop = false;
      if (isNotUsedOrFreeInLoop(I, CurLoop, SafetyInfo, TTI, FreeInLoop) &&
          canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAU, true,
                             NoOfMemAccTooLarge, &LicmMssaOptCounter, ORE) &&
          !I.mayHaveSideEffects()) {
        if (sink(I, LI, DT, CurLoop, SafetyInfo, MSSAU, ORE, FreeInLoop)) {
          if (!FreeInLoop) {
            ++II;
            eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);
          }
          Changed = true;
        }
      }
    }
  }
  if (MSSAU && VerifyMemorySSA)
    MSSAU->getMemorySSA()->verifyMemorySSA();
  return Changed;
}

namespace {
// This is a helper class for hoistRegion to make it able to hoist control flow
// in order to be able to hoist phis. The way this works is that we initially
// start hoisting to the loop preheader, and when we see a loop invariant branch
// we make note of this. When we then come to hoist an instruction that's
// conditional on such a branch we duplicate the branch and the relevant control
// flow, then hoist the instruction into the block corresponding to its original
// block in the duplicated control flow.
class ControlFlowHoister {
private:
  // Information about the loop we are hoisting from
  LoopInfo *LI;
  DominatorTree *DT;
  Loop *CurLoop;
  MemorySSAUpdater *MSSAU;

  // A map of blocks in the loop to the block their instructions will be hoisted
  // to.
  DenseMap<BasicBlock *, BasicBlock *> HoistDestinationMap;

  // The branches that we can hoist, mapped to the block that marks a
  // convergence point of their control flow.
  DenseMap<BranchInst *, BasicBlock *> HoistableBranches;

public:
  ControlFlowHoister(LoopInfo *LI, DominatorTree *DT, Loop *CurLoop,
                     MemorySSAUpdater *MSSAU)
      : LI(LI), DT(DT), CurLoop(CurLoop), MSSAU(MSSAU) {}

  void registerPossiblyHoistableBranch(BranchInst *BI) {
    // We can only hoist conditional branches with loop invariant operands.
    if (!ControlFlowHoisting || !BI->isConditional() ||
        !CurLoop->hasLoopInvariantOperands(BI))
      return;

    // The branch destinations need to be in the loop, and we don't gain
    // anything by duplicating conditional branches with duplicate successors,
    // as it's essentially the same as an unconditional branch.
    BasicBlock *TrueDest = BI->getSuccessor(0);
    BasicBlock *FalseDest = BI->getSuccessor(1);
    if (!CurLoop->contains(TrueDest) || !CurLoop->contains(FalseDest) ||
        TrueDest == FalseDest)
      return;

    // We can hoist BI if one branch destination is the successor of the other,
    // or both have common successor which we check by seeing if the
    // intersection of their successors is non-empty.
    // TODO: This could be expanded to allowing branches where both ends
    // eventually converge to a single block.
    SmallPtrSet<BasicBlock *, 4> TrueDestSucc, FalseDestSucc;
    TrueDestSucc.insert(succ_begin(TrueDest), succ_end(TrueDest));
    FalseDestSucc.insert(succ_begin(FalseDest), succ_end(FalseDest));
    BasicBlock *CommonSucc = nullptr;
    if (TrueDestSucc.count(FalseDest)) {
      CommonSucc = FalseDest;
    } else if (FalseDestSucc.count(TrueDest)) {
      CommonSucc = TrueDest;
    } else {
      set_intersect(TrueDestSucc, FalseDestSucc);
      // If there's one common successor use that.
      if (TrueDestSucc.size() == 1)
        CommonSucc = *TrueDestSucc.begin();
      // If there's more than one pick whichever appears first in the block list
      // (we can't use the value returned by TrueDestSucc.begin() as it's
      // unpredicatable which element gets returned).
      else if (!TrueDestSucc.empty()) {
        Function *F = TrueDest->getParent();
        auto IsSucc = [&](BasicBlock &BB) { return TrueDestSucc.count(&BB); };
        auto It = std::find_if(F->begin(), F->end(), IsSucc);
        assert(It != F->end() && "Could not find successor in function");
        CommonSucc = &*It;
      }
    }
    // The common successor has to be dominated by the branch, as otherwise
    // there will be some other path to the successor that will not be
    // controlled by this branch so any phi we hoist would be controlled by the
    // wrong condition. This also takes care of avoiding hoisting of loop back
    // edges.
    // TODO: In some cases this could be relaxed if the successor is dominated
    // by another block that's been hoisted and we can guarantee that the
    // control flow has been replicated exactly.
    if (CommonSucc && DT->dominates(BI, CommonSucc))
      HoistableBranches[BI] = CommonSucc;
  }

  bool canHoistPHI(PHINode *PN) {
    // The phi must have loop invariant operands.
    if (!ControlFlowHoisting || !CurLoop->hasLoopInvariantOperands(PN))
      return false;
    // We can hoist phis if the block they are in is the target of hoistable
    // branches which cover all of the predecessors of the block.
    SmallPtrSet<BasicBlock *, 8> PredecessorBlocks;
    BasicBlock *BB = PN->getParent();
    for (BasicBlock *PredBB : predecessors(BB))
      PredecessorBlocks.insert(PredBB);
    // If we have less predecessor blocks than predecessors then the phi will
    // have more than one incoming value for the same block which we can't
    // handle.
    // TODO: This could be handled be erasing some of the duplicate incoming
    // values.
    if (PredecessorBlocks.size() != pred_size(BB))
      return false;
    for (auto &Pair : HoistableBranches) {
      if (Pair.second == BB) {
        // Which blocks are predecessors via this branch depends on if the
        // branch is triangle-like or diamond-like.
        if (Pair.first->getSuccessor(0) == BB) {
          PredecessorBlocks.erase(Pair.first->getParent());
          PredecessorBlocks.erase(Pair.first->getSuccessor(1));
        } else if (Pair.first->getSuccessor(1) == BB) {
          PredecessorBlocks.erase(Pair.first->getParent());
          PredecessorBlocks.erase(Pair.first->getSuccessor(0));
        } else {
          PredecessorBlocks.erase(Pair.first->getSuccessor(0));
          PredecessorBlocks.erase(Pair.first->getSuccessor(1));
        }
      }
    }
    // PredecessorBlocks will now be empty if for every predecessor of BB we
    // found a hoistable branch source.
    return PredecessorBlocks.empty();
  }

  BasicBlock *getOrCreateHoistedBlock(BasicBlock *BB) {
    if (!ControlFlowHoisting)
      return CurLoop->getLoopPreheader();
    // If BB has already been hoisted, return that
    if (HoistDestinationMap.count(BB))
      return HoistDestinationMap[BB];

    // Check if this block is conditional based on a pending branch
    auto HasBBAsSuccessor =
        [&](DenseMap<BranchInst *, BasicBlock *>::value_type &Pair) {
          return BB != Pair.second && (Pair.first->getSuccessor(0) == BB ||
                                       Pair.first->getSuccessor(1) == BB);
        };
    auto It = std::find_if(HoistableBranches.begin(), HoistableBranches.end(),
                           HasBBAsSuccessor);

    // If not involved in a pending branch, hoist to preheader
    BasicBlock *InitialPreheader = CurLoop->getLoopPreheader();
    if (It == HoistableBranches.end()) {
      LLVM_DEBUG(dbgs() << "LICM using " << InitialPreheader->getName()
                        << " as hoist destination for " << BB->getName()
                        << "\n");
      HoistDestinationMap[BB] = InitialPreheader;
      return InitialPreheader;
    }
    BranchInst *BI = It->first;
    assert(std::find_if(++It, HoistableBranches.end(), HasBBAsSuccessor) ==
               HoistableBranches.end() &&
           "BB is expected to be the target of at most one branch");

    LLVMContext &C = BB->getContext();
    BasicBlock *TrueDest = BI->getSuccessor(0);
    BasicBlock *FalseDest = BI->getSuccessor(1);
    BasicBlock *CommonSucc = HoistableBranches[BI];
    BasicBlock *HoistTarget = getOrCreateHoistedBlock(BI->getParent());

    // Create hoisted versions of blocks that currently don't have them
    auto CreateHoistedBlock = [&](BasicBlock *Orig) {
      if (HoistDestinationMap.count(Orig))
        return HoistDestinationMap[Orig];
      BasicBlock *New =
          BasicBlock::Create(C, Orig->getName() + ".licm", Orig->getParent());
      HoistDestinationMap[Orig] = New;
      DT->addNewBlock(New, HoistTarget);
      if (CurLoop->getParentLoop())
        CurLoop->getParentLoop()->addBasicBlockToLoop(New, *LI);
      ++NumCreatedBlocks;
      LLVM_DEBUG(dbgs() << "LICM created " << New->getName()
                        << " as hoist destination for " << Orig->getName()
                        << "\n");
      return New;
    };
    BasicBlock *HoistTrueDest = CreateHoistedBlock(TrueDest);
    BasicBlock *HoistFalseDest = CreateHoistedBlock(FalseDest);
    BasicBlock *HoistCommonSucc = CreateHoistedBlock(CommonSucc);

    // Link up these blocks with branches.
    if (!HoistCommonSucc->getTerminator()) {
      // The new common successor we've generated will branch to whatever that
      // hoist target branched to.
      BasicBlock *TargetSucc = HoistTarget->getSingleSuccessor();
      assert(TargetSucc && "Expected hoist target to have a single successor");
      HoistCommonSucc->moveBefore(TargetSucc);
      BranchInst::Create(TargetSucc, HoistCommonSucc);
    }
    if (!HoistTrueDest->getTerminator()) {
      HoistTrueDest->moveBefore(HoistCommonSucc);
      BranchInst::Create(HoistCommonSucc, HoistTrueDest);
    }
    if (!HoistFalseDest->getTerminator()) {
      HoistFalseDest->moveBefore(HoistCommonSucc);
      BranchInst::Create(HoistCommonSucc, HoistFalseDest);
    }

    // If BI is being cloned to what was originally the preheader then
    // HoistCommonSucc will now be the new preheader.
    if (HoistTarget == InitialPreheader) {
      // Phis in the loop header now need to use the new preheader.
      InitialPreheader->replaceSuccessorsPhiUsesWith(HoistCommonSucc);
      if (MSSAU)
        MSSAU->wireOldPredecessorsToNewImmediatePredecessor(
            HoistTarget->getSingleSuccessor(), HoistCommonSucc, {HoistTarget});
      // The new preheader dominates the loop header.
      DomTreeNode *PreheaderNode = DT->getNode(HoistCommonSucc);
      DomTreeNode *HeaderNode = DT->getNode(CurLoop->getHeader());
      DT->changeImmediateDominator(HeaderNode, PreheaderNode);
      // The preheader hoist destination is now the new preheader, with the
      // exception of the hoist destination of this branch.
      for (auto &Pair : HoistDestinationMap)
        if (Pair.second == InitialPreheader && Pair.first != BI->getParent())
          Pair.second = HoistCommonSucc;
    }

    // Now finally clone BI.
    ReplaceInstWithInst(
        HoistTarget->getTerminator(),
        BranchInst::Create(HoistTrueDest, HoistFalseDest, BI->getCondition()));
    ++NumClonedBranches;

    assert(CurLoop->getLoopPreheader() &&
           "Hoisting blocks should not have destroyed preheader");
    return HoistDestinationMap[BB];
  }
};
} // namespace

/// Walk the specified region of the CFG (defined by all blocks dominated by
/// the specified block, and that are in the current loop) in depth first
/// order w.r.t the DominatorTree.  This allows us to visit definitions before
/// uses, allowing us to hoist a loop body in one pass without iteration.
///
bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
                       DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
                       AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
                       ICFLoopSafetyInfo *SafetyInfo, bool NoOfMemAccTooLarge,
                       int &LicmMssaOptCounter,
                       OptimizationRemarkEmitter *ORE) {
  // Verify inputs.
  assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&
         CurLoop != nullptr && SafetyInfo != nullptr &&
         "Unexpected input to hoistRegion.");
  assert(((CurAST != nullptr) ^ (MSSAU != nullptr)) &&
         "Either AliasSetTracker or MemorySSA should be initialized.");

  ControlFlowHoister CFH(LI, DT, CurLoop, MSSAU);

  // Keep track of instructions that have been hoisted, as they may need to be
  // re-hoisted if they end up not dominating all of their uses.
  SmallVector<Instruction *, 16> HoistedInstructions;

  // For PHI hoisting to work we need to hoist blocks before their successors.
  // We can do this by iterating through the blocks in the loop in reverse
  // post-order.
  LoopBlocksRPO Worklist(CurLoop);
  Worklist.perform(LI);
  bool Changed = false;
  for (BasicBlock *BB : Worklist) {
    // Only need to process the contents of this block if it is not part of a
    // subloop (which would already have been processed).
    if (inSubLoop(BB, CurLoop, LI))
      continue;

    for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
      Instruction &I = *II++;
      // Try constant folding this instruction.  If all the operands are
      // constants, it is technically hoistable, but it would be better to
      // just fold it.
      if (Constant *C = ConstantFoldInstruction(
              &I, I.getModule()->getDataLayout(), TLI)) {
        LLVM_DEBUG(dbgs() << "LICM folding inst: " << I << "  --> " << *C
                          << '\n');
        if (CurAST)
          CurAST->copyValue(&I, C);
        // FIXME MSSA: Such replacements may make accesses unoptimized (D51960).
        I.replaceAllUsesWith(C);
        if (isInstructionTriviallyDead(&I, TLI))
          eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);
        Changed = true;
        continue;
      }

      // Try hoisting the instruction out to the preheader.  We can only do
      // this if all of the operands of the instruction are loop invariant and
      // if it is safe to hoist the instruction.
      // TODO: It may be safe to hoist if we are hoisting to a conditional block
      // and we have accurately duplicated the control flow from the loop header
      // to that block.
      if (CurLoop->hasLoopInvariantOperands(&I) &&
          canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, MSSAU, true,
                             NoOfMemAccTooLarge, &LicmMssaOptCounter, ORE) &&
          isSafeToExecuteUnconditionally(
              I, DT, CurLoop, SafetyInfo, ORE,
              CurLoop->getLoopPreheader()->getTerminator())) {
        hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
              MSSAU, ORE);
        HoistedInstructions.push_back(&I);
        Changed = true;
        continue;
      }

      // Attempt to remove floating point division out of the loop by
      // converting it to a reciprocal multiplication.
      if (I.getOpcode() == Instruction::FDiv &&
          CurLoop->isLoopInvariant(I.getOperand(1)) &&
          I.hasAllowReciprocal()) {
        auto Divisor = I.getOperand(1);
        auto One = llvm::ConstantFP::get(Divisor->getType(), 1.0);
        auto ReciprocalDivisor = BinaryOperator::CreateFDiv(One, Divisor);
        ReciprocalDivisor->setFastMathFlags(I.getFastMathFlags());
        SafetyInfo->insertInstructionTo(ReciprocalDivisor, I.getParent());
        ReciprocalDivisor->insertBefore(&I);

        auto Product =
            BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor);
        Product->setFastMathFlags(I.getFastMathFlags());
        SafetyInfo->insertInstructionTo(Product, I.getParent());
        Product->insertAfter(&I);
        I.replaceAllUsesWith(Product);
        eraseInstruction(I, *SafetyInfo, CurAST, MSSAU);

        hoist(*ReciprocalDivisor, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB),
              SafetyInfo, MSSAU, ORE);
        HoistedInstructions.push_back(ReciprocalDivisor);
        Changed = true;
        continue;
      }

      auto IsInvariantStart = [&](Instruction &I) {
        using namespace PatternMatch;
        return I.use_empty() &&
               match(&I, m_Intrinsic<Intrinsic::invariant_start>());
      };
      auto MustExecuteWithoutWritesBefore = [&](Instruction &I) {
        return SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop) &&
               SafetyInfo->doesNotWriteMemoryBefore(I, CurLoop);
      };
      if ((IsInvariantStart(I) || isGuard(&I)) &&
          CurLoop->hasLoopInvariantOperands(&I) &&
          MustExecuteWithoutWritesBefore(I)) {
        hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
              MSSAU, ORE);
        HoistedInstructions.push_back(&I);
        Changed = true;
        continue;
      }

      if (PHINode *PN = dyn_cast<PHINode>(&I)) {
        if (CFH.canHoistPHI(PN)) {
          // Redirect incoming blocks first to ensure that we create hoisted
          // versions of those blocks before we hoist the phi.
          for (unsigned int i = 0; i < PN->getNumIncomingValues(); ++i)
            PN->setIncomingBlock(
                i, CFH.getOrCreateHoistedBlock(PN->getIncomingBlock(i)));
          hoist(*PN, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
                MSSAU, ORE);
          assert(DT->dominates(PN, BB) && "Conditional PHIs not expected");
          Changed = true;
          continue;
        }
      }

      // Remember possibly hoistable branches so we can actually hoist them
      // later if needed.
      if (BranchInst *BI = dyn_cast<BranchInst>(&I))
        CFH.registerPossiblyHoistableBranch(BI);
    }
  }

  // If we hoisted instructions to a conditional block they may not dominate
  // their uses that weren't hoisted (such as phis where some operands are not
  // loop invariant). If so make them unconditional by moving them to their
  // immediate dominator. We iterate through the instructions in reverse order
  // which ensures that when we rehoist an instruction we rehoist its operands,
  // and also keep track of where in the block we are rehoisting to to make sure
  // that we rehoist instructions before the instructions that use them.
  Instruction *HoistPoint = nullptr;
  if (ControlFlowHoisting) {
    for (Instruction *I : reverse(HoistedInstructions)) {
      if (!llvm::all_of(I->uses(),
                        [&](Use &U) { return DT->dominates(I, U); })) {
        BasicBlock *Dominator =
            DT->getNode(I->getParent())->getIDom()->getBlock();
        if (!HoistPoint || !DT->dominates(HoistPoint->getParent(), Dominator)) {
          if (HoistPoint)
            assert(DT->dominates(Dominator, HoistPoint->getParent()) &&
                   "New hoist point expected to dominate old hoist point");
          HoistPoint = Dominator->getTerminator();
        }
        LLVM_DEBUG(dbgs() << "LICM rehoisting to "
                          << HoistPoint->getParent()->getName()
                          << ": " << *I << "\n");
        moveInstructionBefore(*I, *HoistPoint, *SafetyInfo, MSSAU);
        HoistPoint = I;
        Changed = true;
      }
    }
  }
  if (MSSAU && VerifyMemorySSA)
    MSSAU->getMemorySSA()->verifyMemorySSA();

    // Now that we've finished hoisting make sure that LI and DT are still
    // valid.
#ifndef NDEBUG
  if (Changed) {
    assert(DT->verify(DominatorTree::VerificationLevel::Fast) &&
           "Dominator tree verification failed");
    LI->verify(*DT);
  }
#endif

  return Changed;
}

// Return true if LI is invariant within scope of the loop. LI is invariant if
// CurLoop is dominated by an invariant.start representing the same memory
// location and size as the memory location LI loads from, and also the
// invariant.start has no uses.
static bool isLoadInvariantInLoop(LoadInst *LI, DominatorTree *DT,
                                  Loop *CurLoop) {
  Value *Addr = LI->getOperand(0);
  const DataLayout &DL = LI->getModule()->getDataLayout();
  const uint32_t LocSizeInBits = DL.getTypeSizeInBits(
      cast<PointerType>(Addr->getType())->getElementType());

  // if the type is i8 addrspace(x)*, we know this is the type of
  // llvm.invariant.start operand
  auto *PtrInt8Ty = PointerType::get(Type::getInt8Ty(LI->getContext()),
                                     LI->getPointerAddressSpace());
  unsigned BitcastsVisited = 0;
  // Look through bitcasts until we reach the i8* type (this is invariant.start
  // operand type).
  while (Addr->getType() != PtrInt8Ty) {
    auto *BC = dyn_cast<BitCastInst>(Addr);
    // Avoid traversing high number of bitcast uses.
    if (++BitcastsVisited > MaxNumUsesTraversed || !BC)
      return false;
    Addr = BC->getOperand(0);
  }

  unsigned UsesVisited = 0;
  // Traverse all uses of the load operand value, to see if invariant.start is
  // one of the uses, and whether it dominates the load instruction.
  for (auto *U : Addr->users()) {
    // Avoid traversing for Load operand with high number of users.
    if (++UsesVisited > MaxNumUsesTraversed)
      return false;
    IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
    // If there are escaping uses of invariant.start instruction, the load maybe
    // non-invariant.
    if (!II || II->getIntrinsicID() != Intrinsic::invariant_start ||
        !II->use_empty())
      continue;
    unsigned InvariantSizeInBits =
        cast<ConstantInt>(II->getArgOperand(0))->getSExtValue() * 8;
    // Confirm the invariant.start location size contains the load operand size
    // in bits. Also, the invariant.start should dominate the load, and we
    // should not hoist the load out of a loop that contains this dominating
    // invariant.start.
    if (LocSizeInBits <= InvariantSizeInBits &&
        DT->properlyDominates(II->getParent(), CurLoop->getHeader()))
      return true;
  }

  return false;
}

namespace {
/// Return true if-and-only-if we know how to (mechanically) both hoist and
/// sink a given instruction out of a loop.  Does not address legality
/// concerns such as aliasing or speculation safety.  
bool isHoistableAndSinkableInst(Instruction &I) {
  // Only these instructions are hoistable/sinkable.
  return (isa<LoadInst>(I) || isa<StoreInst>(I) ||
          isa<CallInst>(I) || isa<FenceInst>(I) || 
          isa<BinaryOperator>(I) || isa<CastInst>(I) ||
          isa<SelectInst>(I) || isa<GetElementPtrInst>(I) ||
          isa<CmpInst>(I) || isa<InsertElementInst>(I) ||
          isa<ExtractElementInst>(I) || isa<ShuffleVectorInst>(I) ||
          isa<ExtractValueInst>(I) || isa<InsertValueInst>(I));
}
/// Return true if all of the alias sets within this AST are known not to
/// contain a Mod, or if MSSA knows thare are no MemoryDefs in the loop.
bool isReadOnly(AliasSetTracker *CurAST, const MemorySSAUpdater *MSSAU,
                const Loop *L) {
  if (CurAST) {
    for (AliasSet &AS : *CurAST) {
      if (!AS.isForwardingAliasSet() && AS.isMod()) {
        return false;
      }
    }
    return true;
  } else { /*MSSAU*/
    for (auto *BB : L->getBlocks())
      if (MSSAU->getMemorySSA()->getBlockDefs(BB))
        return false;
    return true;
  }
}

/// Return true if I is the only Instruction with a MemoryAccess in L.
bool isOnlyMemoryAccess(const Instruction *I, const Loop *L,
                        const MemorySSAUpdater *MSSAU) {
  for (auto *BB : L->getBlocks())
    if (auto *Accs = MSSAU->getMemorySSA()->getBlockAccesses(BB)) {
      int NotAPhi = 0;
      for (const auto &Acc : *Accs) {
        if (isa<MemoryPhi>(&Acc))
          continue;
        const auto *MUD = cast<MemoryUseOrDef>(&Acc);
        if (MUD->getMemoryInst() != I || NotAPhi++ == 1)
          return false;
      }
    }
  return true;
}
}

bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
                              Loop *CurLoop, AliasSetTracker *CurAST,
                              MemorySSAUpdater *MSSAU,
                              bool TargetExecutesOncePerLoop,
                              bool NoOfMemAccTooLarge, int *LicmMssaOptCounter,
                              OptimizationRemarkEmitter *ORE) {
  // If we don't understand the instruction, bail early.
  if (!isHoistableAndSinkableInst(I))
    return false;

  MemorySSA *MSSA = MSSAU ? MSSAU->getMemorySSA() : nullptr;
  if (MSSA)
    assert(LicmMssaOptCounter != nullptr && "Counter cannot be null.");

  // Loads have extra constraints we have to verify before we can hoist them.
  if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
    if (!LI->isUnordered())
      return false; // Don't sink/hoist volatile or ordered atomic loads!

    // Loads from constant memory are always safe to move, even if they end up
    // in the same alias set as something that ends up being modified.
    if (AA->pointsToConstantMemory(LI->getOperand(0)))
      return true;
    if (LI->getMetadata(LLVMContext::MD_invariant_load))
      return true;

    if (LI->isAtomic() && !TargetExecutesOncePerLoop)
      return false; // Don't risk duplicating unordered loads

    // This checks for an invariant.start dominating the load.
    if (isLoadInvariantInLoop(LI, DT, CurLoop))
      return true;

    bool Invalidated;
    if (CurAST)
      Invalidated = pointerInvalidatedByLoop(MemoryLocation::get(LI), CurAST,
                                             CurLoop, AA);
    else
      Invalidated = pointerInvalidatedByLoopWithMSSA(
          MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(LI)), CurLoop,
          *LicmMssaOptCounter);
    // Check loop-invariant address because this may also be a sinkable load
    // whose address is not necessarily loop-invariant.
    if (ORE && Invalidated && CurLoop->isLoopInvariant(LI->getPointerOperand()))
      ORE->emit([&]() {
        return OptimizationRemarkMissed(
                   DEBUG_TYPE, "LoadWithLoopInvariantAddressInvalidated", LI)
               << "failed to move load with loop-invariant address "
                  "because the loop may invalidate its value";
      });

    return !Invalidated;
  } else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
    // Don't sink or hoist dbg info; it's legal, but not useful.
    if (isa<DbgInfoIntrinsic>(I))
      return false;

    // Don't sink calls which can throw.
    if (CI->mayThrow())
      return false;

    using namespace PatternMatch;
    if (match(CI, m_Intrinsic<Intrinsic::assume>()))
      // Assumes don't actually alias anything or throw
      return true;

    // Handle simple cases by querying alias analysis.
    FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI);
    if (Behavior == FMRB_DoesNotAccessMemory)
      return true;
    if (AliasAnalysis::onlyReadsMemory(Behavior)) {
      // A readonly argmemonly function only reads from memory pointed to by
      // it's arguments with arbitrary offsets.  If we can prove there are no
      // writes to this memory in the loop, we can hoist or sink.
      if (AliasAnalysis::onlyAccessesArgPointees(Behavior)) {
        // TODO: expand to writeable arguments
        for (Value *Op : CI->arg_operands())
          if (Op->getType()->isPointerTy()) {
            bool Invalidated;
            if (CurAST)
              Invalidated = pointerInvalidatedByLoop(
                  MemoryLocation(Op, LocationSize::unknown(), AAMDNodes()),
                  CurAST, CurLoop, AA);
            else
              Invalidated = pointerInvalidatedByLoopWithMSSA(
                  MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(CI)), CurLoop,
                  *LicmMssaOptCounter);
            if (Invalidated)
              return false;
          }
        return true;
      }

      // If this call only reads from memory and there are no writes to memory
      // in the loop, we can hoist or sink the call as appropriate.
      if (isReadOnly(CurAST, MSSAU, CurLoop))
        return true;
    }

    // FIXME: This should use mod/ref information to see if we can hoist or
    // sink the call.

    return false;
  } else if (auto *FI = dyn_cast<FenceInst>(&I)) {
    // Fences alias (most) everything to provide ordering.  For the moment,
    // just give up if there are any other memory operations in the loop.
    if (CurAST) {
      auto Begin = CurAST->begin();
      assert(Begin != CurAST->end() && "must contain FI");
      if (std::next(Begin) != CurAST->end())
        // constant memory for instance, TODO: handle better
        return false;
      auto *UniqueI = Begin->getUniqueInstruction();
      if (!UniqueI)
        // other memory op, give up
        return false;
      (void)FI; // suppress unused variable warning
      assert(UniqueI == FI && "AS must contain FI");
      return true;
    } else // MSSAU
      return isOnlyMemoryAccess(FI, CurLoop, MSSAU);
  } else if (auto *SI = dyn_cast<StoreInst>(&I)) {
    if (!SI->isUnordered())
      return false; // Don't sink/hoist volatile or ordered atomic store!

    // We can only hoist a store that we can prove writes a value which is not
    // read or overwritten within the loop.  For those cases, we fallback to
    // load store promotion instead.  TODO: We can extend this to cases where
    // there is exactly one write to the location and that write dominates an
    // arbitrary number of reads in the loop.
    if (CurAST) {
      auto &AS = CurAST->getAliasSetFor(MemoryLocation::get(SI));

      if (AS.isRef() || !AS.isMustAlias())
        // Quick exit test, handled by the full path below as well.
        return false;
      auto *UniqueI = AS.getUniqueInstruction();
      if (!UniqueI)
        // other memory op, give up
        return false;
      assert(UniqueI == SI && "AS must contain SI");
      return true;
    } else { // MSSAU
      if (isOnlyMemoryAccess(SI, CurLoop, MSSAU))
        return true;
      // If there are more accesses than the Promotion cap, give up, we're not
      // walking a list that long.
      if (NoOfMemAccTooLarge)
        return false;
      // Check store only if there's still "quota" to check clobber.
      if (*LicmMssaOptCounter >= LicmMssaOptCap)
        return false;
      // If there are interfering Uses (i.e. their defining access is in the
      // loop), or ordered loads (stored as Defs!), don't move this store.
      // Could do better here, but this is conservatively correct.
      // TODO: Cache set of Uses on the first walk in runOnLoop, update when
      // moving accesses. Can also extend to dominating uses.
      for (auto *BB : CurLoop->getBlocks())
        if (auto *Accesses = MSSA->getBlockAccesses(BB)) {
          for (const auto &MA : *Accesses)
            if (const auto *MU = dyn_cast<MemoryUse>(&MA)) {
              auto *MD = MU->getDefiningAccess();
              if (!MSSA->isLiveOnEntryDef(MD) &&
                  CurLoop->contains(MD->getBlock()))
                return false;
            } else if (const auto *MD = dyn_cast<MemoryDef>(&MA))
              if (auto *LI = dyn_cast<LoadInst>(MD->getMemoryInst())) {
                assert(!LI->isUnordered() && "Expected unordered load");
                return false;
              }
        }

        auto *Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(SI);
        (*LicmMssaOptCounter)++;
        // If there are no clobbering Defs in the loop, store is safe to hoist.
        return MSSA->isLiveOnEntryDef(Source) ||
               !CurLoop->contains(Source->getBlock());
    }
  }

  assert(!I.mayReadOrWriteMemory() && "unhandled aliasing");

  // We've established mechanical ability and aliasing, it's up to the caller
  // to check fault safety
  return true;
}

/// Returns true if a PHINode is a trivially replaceable with an
/// Instruction.
/// This is true when all incoming values are that instruction.
/// This pattern occurs most often with LCSSA PHI nodes.
///
static bool isTriviallyReplaceablePHI(const PHINode &PN, const Instruction &I) {
  for (const Value *IncValue : PN.incoming_values())
    if (IncValue != &I)
      return false;

  return true;
}

/// Return true if the instruction is free in the loop.
static bool isFreeInLoop(const Instruction &I, const Loop *CurLoop,
                         const TargetTransformInfo *TTI) {

  if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(&I)) {
    if (TTI->getUserCost(GEP) != TargetTransformInfo::TCC_Free)
      return false;
    // For a GEP, we cannot simply use getUserCost because currently it
    // optimistically assume that a GEP will fold into addressing mode
    // regardless of its users.
    const BasicBlock *BB = GEP->getParent();
    for (const User *U : GEP->users()) {
      const Instruction *UI = cast<Instruction>(U);
      if (CurLoop->contains(UI) &&
          (BB != UI->getParent() ||
           (!isa<StoreInst>(UI) && !isa<LoadInst>(UI))))
        return false;
    }
    return true;
  } else
    return TTI->getUserCost(&I) == TargetTransformInfo::TCC_Free;
}

/// Return true if the only users of this instruction are outside of
/// the loop. If this is true, we can sink the instruction to the exit
/// blocks of the loop.
///
/// We also return true if the instruction could be folded away in lowering.
/// (e.g.,  a GEP can be folded into a load as an addressing mode in the loop).
static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
                                  const LoopSafetyInfo *SafetyInfo,
                                  TargetTransformInfo *TTI, bool &FreeInLoop) {
  const auto &BlockColors = SafetyInfo->getBlockColors();
  bool IsFree = isFreeInLoop(I, CurLoop, TTI);
  for (const User *U : I.users()) {
    const Instruction *UI = cast<Instruction>(U);
    if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
      const BasicBlock *BB = PN->getParent();
      // We cannot sink uses in catchswitches.
      if (isa<CatchSwitchInst>(BB->getTerminator()))
        return false;

      // We need to sink a callsite to a unique funclet.  Avoid sinking if the
      // phi use is too muddled.
      if (isa<CallInst>(I))
        if (!BlockColors.empty() &&
            BlockColors.find(const_cast<BasicBlock *>(BB))->second.size() != 1)
          return false;
    }

    if (CurLoop->contains(UI)) {
      if (IsFree) {
        FreeInLoop = true;
        continue;
      }
      return false;
    }
  }
  return true;
}

static Instruction *CloneInstructionInExitBlock(
    Instruction &I, BasicBlock &ExitBlock, PHINode &PN, const LoopInfo *LI,
    const LoopSafetyInfo *SafetyInfo, MemorySSAUpdater *MSSAU) {
  Instruction *New;
  if (auto *CI = dyn_cast<CallInst>(&I)) {
    const auto &BlockColors = SafetyInfo->getBlockColors();

    // Sinking call-sites need to be handled differently from other
    // instructions.  The cloned call-site needs a funclet bundle operand
    // appropriate for it's location in the CFG.
    SmallVector<OperandBundleDef, 1> OpBundles;
    for (unsigned BundleIdx = 0, BundleEnd = CI->getNumOperandBundles();
         BundleIdx != BundleEnd; ++BundleIdx) {
      OperandBundleUse Bundle = CI->getOperandBundleAt(BundleIdx);
      if (Bundle.getTagID() == LLVMContext::OB_funclet)
        continue;

      OpBundles.emplace_back(Bundle);
    }

    if (!BlockColors.empty()) {
      const ColorVector &CV = BlockColors.find(&ExitBlock)->second;
      assert(CV.size() == 1 && "non-unique color for exit block!");
      BasicBlock *BBColor = CV.front();
      Instruction *EHPad = BBColor->getFirstNonPHI();
      if (EHPad->isEHPad())
        OpBundles.emplace_back("funclet", EHPad);
    }

    New = CallInst::Create(CI, OpBundles);
  } else {
    New = I.clone();
  }

  ExitBlock.getInstList().insert(ExitBlock.getFirstInsertionPt(), New);
  if (!I.getName().empty())
    New->setName(I.getName() + ".le");

  MemoryAccess *OldMemAcc;
  if (MSSAU && (OldMemAcc = MSSAU->getMemorySSA()->getMemoryAccess(&I))) {
    // Create a new MemoryAccess and let MemorySSA set its defining access.
    MemoryAccess *NewMemAcc = MSSAU->createMemoryAccessInBB(
        New, nullptr, New->getParent(), MemorySSA::Beginning);
    if (NewMemAcc) {
      if (auto *MemDef = dyn_cast<MemoryDef>(NewMemAcc))
        MSSAU->insertDef(MemDef, /*RenameUses=*/true);
      else {
        auto *MemUse = cast<MemoryUse>(NewMemAcc);
        MSSAU->insertUse(MemUse);
      }
    }
  }

  // Build LCSSA PHI nodes for any in-loop operands. Note that this is
  // particularly cheap because we can rip off the PHI node that we're
  // replacing for the number and blocks of the predecessors.
  // OPT: If this shows up in a profile, we can instead finish sinking all
  // invariant instructions, and then walk their operands to re-establish
  // LCSSA. That will eliminate creating PHI nodes just to nuke them when
  // sinking bottom-up.
  for (User::op_iterator OI = New->op_begin(), OE = New->op_end(); OI != OE;
       ++OI)
    if (Instruction *OInst = dyn_cast<Instruction>(*OI))
      if (Loop *OLoop = LI->getLoopFor(OInst->getParent()))
        if (!OLoop->contains(&PN)) {
          PHINode *OpPN =
              PHINode::Create(OInst->getType(), PN.getNumIncomingValues(),
                              OInst->getName() + ".lcssa", &ExitBlock.front());
          for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
            OpPN->addIncoming(OInst, PN.getIncomingBlock(i));
          *OI = OpPN;
        }
  return New;
}

static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
                             AliasSetTracker *AST, MemorySSAUpdater *MSSAU) {
  if (AST)
    AST->deleteValue(&I);
  if (MSSAU)
    MSSAU->removeMemoryAccess(&I);
  SafetyInfo.removeInstruction(&I);
  I.eraseFromParent();
}

static void moveInstructionBefore(Instruction &I, Instruction &Dest,
                                  ICFLoopSafetyInfo &SafetyInfo,
                                  MemorySSAUpdater *MSSAU) {
  SafetyInfo.removeInstruction(&I);
  SafetyInfo.insertInstructionTo(&I, Dest.getParent());
  I.moveBefore(&Dest);
  if (MSSAU)
    if (MemoryUseOrDef *OldMemAcc = cast_or_null<MemoryUseOrDef>(
            MSSAU->getMemorySSA()->getMemoryAccess(&I)))
      MSSAU->moveToPlace(OldMemAcc, Dest.getParent(), MemorySSA::End);
}

static Instruction *sinkThroughTriviallyReplaceablePHI(
    PHINode *TPN, Instruction *I, LoopInfo *LI,
    SmallDenseMap<BasicBlock *, Instruction *, 32> &SunkCopies,
    const LoopSafetyInfo *SafetyInfo, const Loop *CurLoop,
    MemorySSAUpdater *MSSAU) {
  assert(isTriviallyReplaceablePHI(*TPN, *I) &&
         "Expect only trivially replaceable PHI");
  BasicBlock *ExitBlock = TPN->getParent();
  Instruction *New;
  auto It = SunkCopies.find(ExitBlock);
  if (It != SunkCopies.end())
    New = It->second;
  else
    New = SunkCopies[ExitBlock] = CloneInstructionInExitBlock(
        *I, *ExitBlock, *TPN, LI, SafetyInfo, MSSAU);
  return New;
}

static bool canSplitPredecessors(PHINode *PN, LoopSafetyInfo *SafetyInfo) {
  BasicBlock *BB = PN->getParent();
  if (!BB->canSplitPredecessors())
    return false;
  // It's not impossible to split EHPad blocks, but if BlockColors already exist
  // it require updating BlockColors for all offspring blocks accordingly. By
  // skipping such corner case, we can make updating BlockColors after splitting
  // predecessor fairly simple.
  if (!SafetyInfo->getBlockColors().empty() && BB->getFirstNonPHI()->isEHPad())
    return false;
  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
    BasicBlock *BBPred = *PI;
    if (isa<IndirectBrInst>(BBPred->getTerminator()))
      return false;
  }
  return true;
}

static void splitPredecessorsOfLoopExit(PHINode *PN, DominatorTree *DT,
                                        LoopInfo *LI, const Loop *CurLoop,
                                        LoopSafetyInfo *SafetyInfo,
                                        MemorySSAUpdater *MSSAU) {
#ifndef NDEBUG
  SmallVector<BasicBlock *, 32> ExitBlocks;
  CurLoop->getUniqueExitBlocks(ExitBlocks);
  SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
                                             ExitBlocks.end());
#endif
  BasicBlock *ExitBB = PN->getParent();
  assert(ExitBlockSet.count(ExitBB) && "Expect the PHI is in an exit block.");

  // Split predecessors of the loop exit to make instructions in the loop are
  // exposed to exit blocks through trivially replaceable PHIs while keeping the
  // loop in the canonical form where each predecessor of each exit block should
  // be contained within the loop. For example, this will convert the loop below
  // from
  //
  // LB1:
  //   %v1 =
  //   br %LE, %LB2
  // LB2:
  //   %v2 =
  //   br %LE, %LB1
  // LE:
  //   %p = phi [%v1, %LB1], [%v2, %LB2] <-- non-trivially replaceable
  //
  // to
  //
  // LB1:
  //   %v1 =
  //   br %LE.split, %LB2
  // LB2:
  //   %v2 =
  //   br %LE.split2, %LB1
  // LE.split:
  //   %p1 = phi [%v1, %LB1]  <-- trivially replaceable
  //   br %LE
  // LE.split2:
  //   %p2 = phi [%v2, %LB2]  <-- trivially replaceable
  //   br %LE
  // LE:
  //   %p = phi [%p1, %LE.split], [%p2, %LE.split2]
  //
  const auto &BlockColors = SafetyInfo->getBlockColors();
  SmallSetVector<BasicBlock *, 8> PredBBs(pred_begin(ExitBB), pred_end(ExitBB));
  while (!PredBBs.empty()) {
    BasicBlock *PredBB = *PredBBs.begin();
    assert(CurLoop->contains(PredBB) &&
           "Expect all predecessors are in the loop");
    if (PN->getBasicBlockIndex(PredBB) >= 0) {
      BasicBlock *NewPred = SplitBlockPredecessors(
          ExitBB, PredBB, ".split.loop.exit", DT, LI, MSSAU, true);
      // Since we do not allow splitting EH-block with BlockColors in
      // canSplitPredecessors(), we can simply assign predecessor's color to
      // the new block.
      if (!BlockColors.empty())
        // Grab a reference to the ColorVector to be inserted before getting the
        // reference to the vector we are copying because inserting the new
        // element in BlockColors might cause the map to be reallocated.
        SafetyInfo->copyColors(NewPred, PredBB);
    }
    PredBBs.remove(PredBB);
  }
}

/// When an instruction is found to only be used outside of the loop, this
/// function moves it to the exit blocks and patches up SSA form as needed.
/// This method is guaranteed to remove the original instruction from its
/// position, and may either delete it or move it to outside of the loop.
///
static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
                 const Loop *CurLoop, ICFLoopSafetyInfo *SafetyInfo,
                 MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE,
                 bool FreeInLoop) {
  LLVM_DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
  ORE->emit([&]() {
    return OptimizationRemark(DEBUG_TYPE, "InstSunk", &I)
           << "sinking " << ore::NV("Inst", &I);
  });
  bool Changed = false;
  if (isa<LoadInst>(I))
    ++NumMovedLoads;
  else if (isa<CallInst>(I))
    ++NumMovedCalls;
  ++NumSunk;

  // Iterate over users to be ready for actual sinking. Replace users via
  // unrechable blocks with undef and make all user PHIs trivially replcable.
  SmallPtrSet<Instruction *, 8> VisitedUsers;
  for (Value::user_iterator UI = I.user_begin(), UE = I.user_end(); UI != UE;) {
    auto *User = cast<Instruction>(*UI);
    Use &U = UI.getUse();
    ++UI;

    if (VisitedUsers.count(User) || CurLoop->contains(User))
      continue;

    if (!DT->isReachableFromEntry(User->getParent())) {
      U = UndefValue::get(I.getType());
      Changed = true;
      continue;
    }

    // The user must be a PHI node.
    PHINode *PN = cast<PHINode>(User);

    // Surprisingly, instructions can be used outside of loops without any
    // exits.  This can only happen in PHI nodes if the incoming block is
    // unreachable.
    BasicBlock *BB = PN->getIncomingBlock(U);
    if (!DT->isReachableFromEntry(BB)) {
      U = UndefValue::get(I.getType());
      Changed = true;
      continue;
    }

    VisitedUsers.insert(PN);
    if (isTriviallyReplaceablePHI(*PN, I))
      continue;

    if (!canSplitPredecessors(PN, SafetyInfo))
      return Changed;

    // Split predecessors of the PHI so that we can make users trivially
    // replaceable.
    splitPredecessorsOfLoopExit(PN, DT, LI, CurLoop, SafetyInfo, MSSAU);

    // Should rebuild the iterators, as they may be invalidated by
    // splitPredecessorsOfLoopExit().
    UI = I.user_begin();
    UE = I.user_end();
  }

  if (VisitedUsers.empty())
    return Changed;

#ifndef NDEBUG
  SmallVector<BasicBlock *, 32> ExitBlocks;
  CurLoop->getUniqueExitBlocks(ExitBlocks);
  SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
                                             ExitBlocks.end());
#endif

  // Clones of this instruction. Don't create more than one per exit block!
  SmallDenseMap<BasicBlock *, Instruction *, 32> SunkCopies;

  // If this instruction is only used outside of the loop, then all users are
  // PHI nodes in exit blocks due to LCSSA form. Just RAUW them with clones of
  // the instruction.
  SmallSetVector<User*, 8> Users(I.user_begin(), I.user_end());
  for (auto *UI : Users) {
    auto *User = cast<Instruction>(UI);

    if (CurLoop->contains(User))
      continue;

    PHINode *PN = cast<PHINode>(User);
    assert(ExitBlockSet.count(PN->getParent()) &&
           "The LCSSA PHI is not in an exit block!");
    // The PHI must be trivially replaceable.
    Instruction *New = sinkThroughTriviallyReplaceablePHI(
        PN, &I, LI, SunkCopies, SafetyInfo, CurLoop, MSSAU);
    PN->replaceAllUsesWith(New);
    eraseInstruction(*PN, *SafetyInfo, nullptr, nullptr);
    Changed = true;
  }
  return Changed;
}

/// When an instruction is found to only use loop invariant operands that
/// is safe to hoist, this instruction is called to do the dirty work.
///
static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
                  BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
                  MemorySSAUpdater *MSSAU, OptimizationRemarkEmitter *ORE) {
  LLVM_DEBUG(dbgs() << "LICM hoisting to " << Dest->getName() << ": " << I
                    << "\n");
  ORE->emit([&]() {
    return OptimizationRemark(DEBUG_TYPE, "Hoisted", &I) << "hoisting "
                                                         << ore::NV("Inst", &I);
  });

  // Metadata can be dependent on conditions we are hoisting above.
  // Conservatively strip all metadata on the instruction unless we were
  // guaranteed to execute I if we entered the loop, in which case the metadata
  // is valid in the loop preheader.
  if (I.hasMetadataOtherThanDebugLoc() &&
      // The check on hasMetadataOtherThanDebugLoc is to prevent us from burning
      // time in isGuaranteedToExecute if we don't actually have anything to
      // drop.  It is a compile time optimization, not required for correctness.
      !SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop))
    I.dropUnknownNonDebugMetadata();

  if (isa<PHINode>(I))
    // Move the new node to the end of the phi list in the destination block.
    moveInstructionBefore(I, *Dest->getFirstNonPHI(), *SafetyInfo, MSSAU);
  else
    // Move the new node to the destination block, before its terminator.
    moveInstructionBefore(I, *Dest->getTerminator(), *SafetyInfo, MSSAU);

  // Do not retain debug locations when we are moving instructions to different
  // basic blocks, because we want to avoid jumpy line tables. Calls, however,
  // need to retain their debug locs because they may be inlined.
  // FIXME: How do we retain source locations without causing poor debugging
  // behavior?
  if (!isa<CallInst>(I))
    I.setDebugLoc(DebugLoc());

  if (isa<LoadInst>(I))
    ++NumMovedLoads;
  else if (isa<CallInst>(I))
    ++NumMovedCalls;
  ++NumHoisted;
}

/// Only sink or hoist an instruction if it is not a trapping instruction,
/// or if the instruction is known not to trap when moved to the preheader.
/// or if it is a trapping instruction and is guaranteed to execute.
static bool isSafeToExecuteUnconditionally(Instruction &Inst,
                                           const DominatorTree *DT,
                                           const Loop *CurLoop,
                                           const LoopSafetyInfo *SafetyInfo,
                                           OptimizationRemarkEmitter *ORE,
                                           const Instruction *CtxI) {
  if (isSafeToSpeculativelyExecute(&Inst, CtxI, DT))
    return true;

  bool GuaranteedToExecute =
      SafetyInfo->isGuaranteedToExecute(Inst, DT, CurLoop);

  if (!GuaranteedToExecute) {
    auto *LI = dyn_cast<LoadInst>(&Inst);
    if (LI && CurLoop->isLoopInvariant(LI->getPointerOperand()))
      ORE->emit([&]() {
        return OptimizationRemarkMissed(
                   DEBUG_TYPE, "LoadWithLoopInvariantAddressCondExecuted", LI)
               << "failed to hoist load with loop-invariant address "
                  "because load is conditionally executed";
      });
  }

  return GuaranteedToExecute;
}

namespace {
class LoopPromoter : public LoadAndStorePromoter {
  Value *SomePtr; // Designated pointer to store to.
  const SmallSetVector<Value *, 8> &PointerMustAliases;
  SmallVectorImpl<BasicBlock *> &LoopExitBlocks;
  SmallVectorImpl<Instruction *> &LoopInsertPts;
  SmallVectorImpl<MemoryAccess *> &MSSAInsertPts;
  PredIteratorCache &PredCache;
  AliasSetTracker &AST;
  MemorySSAUpdater *MSSAU;
  LoopInfo &LI;
  DebugLoc DL;
  int Alignment;
  bool UnorderedAtomic;
  AAMDNodes AATags;
  ICFLoopSafetyInfo &SafetyInfo;

  Value *maybeInsertLCSSAPHI(Value *V, BasicBlock *BB) const {
    if (Instruction *I = dyn_cast<Instruction>(V))
      if (Loop *L = LI.getLoopFor(I->getParent()))
        if (!L->contains(BB)) {
          // We need to create an LCSSA PHI node for the incoming value and
          // store that.
          PHINode *PN = PHINode::Create(I->getType(), PredCache.size(BB),
                                        I->getName() + ".lcssa", &BB->front());
          for (BasicBlock *Pred : PredCache.get(BB))
            PN->addIncoming(I, Pred);
          return PN;
        }
    return V;
  }

public:
  LoopPromoter(Value *SP, ArrayRef<const Instruction *> Insts, SSAUpdater &S,
               const SmallSetVector<Value *, 8> &PMA,
               SmallVectorImpl<BasicBlock *> &LEB,
               SmallVectorImpl<Instruction *> &LIP,
               SmallVectorImpl<MemoryAccess *> &MSSAIP, PredIteratorCache &PIC,
               AliasSetTracker &ast, MemorySSAUpdater *MSSAU, LoopInfo &li,
               DebugLoc dl, int alignment, bool UnorderedAtomic,
               const AAMDNodes &AATags, ICFLoopSafetyInfo &SafetyInfo)
      : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
        LoopExitBlocks(LEB), LoopInsertPts(LIP), MSSAInsertPts(MSSAIP),
        PredCache(PIC), AST(ast), MSSAU(MSSAU), LI(li), DL(std::move(dl)),
        Alignment(alignment), UnorderedAtomic(UnorderedAtomic), AATags(AATags),
        SafetyInfo(SafetyInfo) {}

  bool isInstInList(Instruction *I,
                    const SmallVectorImpl<Instruction *> &) const override {
    Value *Ptr;
    if (LoadInst *LI = dyn_cast<LoadInst>(I))
      Ptr = LI->getOperand(0);
    else
      Ptr = cast<StoreInst>(I)->getPointerOperand();
    return PointerMustAliases.count(Ptr);
  }

  void doExtraRewritesBeforeFinalDeletion() override {
    // Insert stores after in the loop exit blocks.  Each exit block gets a
    // store of the live-out values that feed them.  Since we've already told
    // the SSA updater about the defs in the loop and the preheader
    // definition, it is all set and we can start using it.
    for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) {
      BasicBlock *ExitBlock = LoopExitBlocks[i];
      Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
      LiveInValue = maybeInsertLCSSAPHI(LiveInValue, ExitBlock);
      Value *Ptr = maybeInsertLCSSAPHI(SomePtr, ExitBlock);
      Instruction *InsertPos = LoopInsertPts[i];
      StoreInst *NewSI = new StoreInst(LiveInValue, Ptr, InsertPos);
      if (UnorderedAtomic)
        NewSI->setOrdering(AtomicOrdering::Unordered);
      NewSI->setAlignment(Alignment);
      NewSI->setDebugLoc(DL);
      if (AATags)
        NewSI->setAAMetadata(AATags);

      if (MSSAU) {
        MemoryAccess *MSSAInsertPoint = MSSAInsertPts[i];
        MemoryAccess *NewMemAcc;
        if (!MSSAInsertPoint) {
          NewMemAcc = MSSAU->createMemoryAccessInBB(
              NewSI, nullptr, NewSI->getParent(), MemorySSA::Beginning);
        } else {
          NewMemAcc =
              MSSAU->createMemoryAccessAfter(NewSI, nullptr, MSSAInsertPoint);
        }
        MSSAInsertPts[i] = NewMemAcc;
        MSSAU->insertDef(cast<MemoryDef>(NewMemAcc), true);
        // FIXME: true for safety, false may still be correct.
      }
    }
  }

  void replaceLoadWithValue(LoadInst *LI, Value *V) const override {
    // Update alias analysis.
    AST.copyValue(LI, V);
  }
  void instructionDeleted(Instruction *I) const override {
    SafetyInfo.removeInstruction(I);
    AST.deleteValue(I);
    if (MSSAU)
      MSSAU->removeMemoryAccess(I);
  }
};


/// Return true iff we can prove that a caller of this function can not inspect
/// the contents of the provided object in a well defined program.
bool isKnownNonEscaping(Value *Object, const TargetLibraryInfo *TLI) {
  if (isa<AllocaInst>(Object))
    // Since the alloca goes out of scope, we know the caller can't retain a
    // reference to it and be well defined.  Thus, we don't need to check for
    // capture.
    return true;

  // For all other objects we need to know that the caller can't possibly
  // have gotten a reference to the object.  There are two components of
  // that:
  //   1) Object can't be escaped by this function.  This is what
  //      PointerMayBeCaptured checks.
  //   2) Object can't have been captured at definition site.  For this, we
  //      need to know the return value is noalias.  At the moment, we use a
  //      weaker condition and handle only AllocLikeFunctions (which are
  //      known to be noalias).  TODO
  return isAllocLikeFn(Object, TLI) &&
    !PointerMayBeCaptured(Object, true, true);
}

} // namespace

/// Try to promote memory values to scalars by sinking stores out of the
/// loop and moving loads to before the loop.  We do this by looping over
/// the stores in the loop, looking for stores to Must pointers which are
/// loop invariant.
///
bool llvm::promoteLoopAccessesToScalars(
    const SmallSetVector<Value *, 8> &PointerMustAliases,
    SmallVectorImpl<BasicBlock *> &ExitBlocks,
    SmallVectorImpl<Instruction *> &InsertPts,
    SmallVectorImpl<MemoryAccess *> &MSSAInsertPts, PredIteratorCache &PIC,
    LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
    Loop *CurLoop, AliasSetTracker *CurAST, MemorySSAUpdater *MSSAU,
    ICFLoopSafetyInfo *SafetyInfo, OptimizationRemarkEmitter *ORE) {
  // Verify inputs.
  assert(LI != nullptr && DT != nullptr && CurLoop != nullptr &&
         CurAST != nullptr && SafetyInfo != nullptr &&
         "Unexpected Input to promoteLoopAccessesToScalars");

  Value *SomePtr = *PointerMustAliases.begin();
  BasicBlock *Preheader = CurLoop->getLoopPreheader();

  // It is not safe to promote a load/store from the loop if the load/store is
  // conditional.  For example, turning:
  //
  //    for () { if (c) *P += 1; }
  //
  // into:
  //
  //    tmp = *P;  for () { if (c) tmp +=1; } *P = tmp;
  //
  // is not safe, because *P may only be valid to access if 'c' is true.
  //
  // The safety property divides into two parts:
  // p1) The memory may not be dereferenceable on entry to the loop.  In this
  //    case, we can't insert the required load in the preheader.
  // p2) The memory model does not allow us to insert a store along any dynamic
  //    path which did not originally have one.
  //
  // If at least one store is guaranteed to execute, both properties are
  // satisfied, and promotion is legal.
  //
  // This, however, is not a necessary condition. Even if no store/load is
  // guaranteed to execute, we can still establish these properties.
  // We can establish (p1) by proving that hoisting the load into the preheader
  // is safe (i.e. proving dereferenceability on all paths through the loop). We
  // can use any access within the alias set to prove dereferenceability,
  // since they're all must alias.
  //
  // There are two ways establish (p2):
  // a) Prove the location is thread-local. In this case the memory model
  // requirement does not apply, and stores are safe to insert.
  // b) Prove a store dominates every exit block. In this case, if an exit
  // blocks is reached, the original dynamic path would have taken us through
  // the store, so inserting a store into the exit block is safe. Note that this
  // is different from the store being guaranteed to execute. For instance,
  // if an exception is thrown on the first iteration of the loop, the original
  // store is never executed, but the exit blocks are not executed either.

  bool DereferenceableInPH = false;
  bool SafeToInsertStore = false;

  SmallVector<Instruction *, 64> LoopUses;

  // We start with an alignment of one and try to find instructions that allow
  // us to prove better alignment.
  unsigned Alignment = 1;
  // Keep track of which types of access we see
  bool SawUnorderedAtomic = false;
  bool SawNotAtomic = false;
  AAMDNodes AATags;

  const DataLayout &MDL = Preheader->getModule()->getDataLayout();

  bool IsKnownThreadLocalObject = false;
  if (SafetyInfo->anyBlockMayThrow()) {
    // If a loop can throw, we have to insert a store along each unwind edge.
    // That said, we can't actually make the unwind edge explicit. Therefore,
    // we have to prove that the store is dead along the unwind edge.  We do
    // this by proving that the caller can't have a reference to the object
    // after return and thus can't possibly load from the object.
    Value *Object = GetUnderlyingObject(SomePtr, MDL);
    if (!isKnownNonEscaping(Object, TLI))
      return false;
    // Subtlety: Alloca's aren't visible to callers, but *are* potentially
    // visible to other threads if captured and used during their lifetimes.
    IsKnownThreadLocalObject = !isa<AllocaInst>(Object);
  }

  // Check that all of the pointers in the alias set have the same type.  We
  // cannot (yet) promote a memory location that is loaded and stored in
  // different sizes.  While we are at it, collect alignment and AA info.
  for (Value *ASIV : PointerMustAliases) {
    // Check that all of the pointers in the alias set have the same type.  We
    // cannot (yet) promote a memory location that is loaded and stored in
    // different sizes.
    if (SomePtr->getType() != ASIV->getType())
      return false;

    for (User *U : ASIV->users()) {
      // Ignore instructions that are outside the loop.
      Instruction *UI = dyn_cast<Instruction>(U);
      if (!UI || !CurLoop->contains(UI))
        continue;

      // If there is an non-load/store instruction in the loop, we can't promote
      // it.
      if (LoadInst *Load = dyn_cast<LoadInst>(UI)) {
        if (!Load->isUnordered())
          return false;

        SawUnorderedAtomic |= Load->isAtomic();
        SawNotAtomic |= !Load->isAtomic();

        unsigned InstAlignment = Load->getAlignment();
        if (!InstAlignment)
          InstAlignment =
              MDL.getABITypeAlignment(Load->getType());

        // Note that proving a load safe to speculate requires proving
        // sufficient alignment at the target location.  Proving it guaranteed
        // to execute does as well.  Thus we can increase our guaranteed
        // alignment as well. 
        if (!DereferenceableInPH || (InstAlignment > Alignment))
          if (isSafeToExecuteUnconditionally(*Load, DT, CurLoop, SafetyInfo,
                                             ORE, Preheader->getTerminator())) {
            DereferenceableInPH = true;
            Alignment = std::max(Alignment, InstAlignment);
          }
      } else if (const StoreInst *Store = dyn_cast<StoreInst>(UI)) {
        // Stores *of* the pointer are not interesting, only stores *to* the
        // pointer.
        if (UI->getOperand(1) != ASIV)
          continue;
        if (!Store->isUnordered())
          return false;

        SawUnorderedAtomic |= Store->isAtomic();
        SawNotAtomic |= !Store->isAtomic();

        // If the store is guaranteed to execute, both properties are satisfied.
        // We may want to check if a store is guaranteed to execute even if we
        // already know that promotion is safe, since it may have higher
        // alignment than any other guaranteed stores, in which case we can
        // raise the alignment on the promoted store.
        unsigned InstAlignment = Store->getAlignment();
        if (!InstAlignment)
          InstAlignment =
              MDL.getABITypeAlignment(Store->getValueOperand()->getType());

        if (!DereferenceableInPH || !SafeToInsertStore ||
            (InstAlignment > Alignment)) {
          if (SafetyInfo->isGuaranteedToExecute(*UI, DT, CurLoop)) {
            DereferenceableInPH = true;
            SafeToInsertStore = true;
            Alignment = std::max(Alignment, InstAlignment);
          }
        }

        // If a store dominates all exit blocks, it is safe to sink.
        // As explained above, if an exit block was executed, a dominating
        // store must have been executed at least once, so we are not
        // introducing stores on paths that did not have them.
        // Note that this only looks at explicit exit blocks. If we ever
        // start sinking stores into unwind edges (see above), this will break.
        if (!SafeToInsertStore)
          SafeToInsertStore = llvm::all_of(ExitBlocks, [&](BasicBlock *Exit) {
            return DT->dominates(Store->getParent(), Exit);
          });

        // If the store is not guaranteed to execute, we may still get
        // deref info through it.
        if (!DereferenceableInPH) {
          DereferenceableInPH = isDereferenceableAndAlignedPointer(
              Store->getPointerOperand(), Store->getAlignment(), MDL,
              Preheader->getTerminator(), DT);
        }
      } else
        return false; // Not a load or store.

      // Merge the AA tags.
      if (LoopUses.empty()) {
        // On the first load/store, just take its AA tags.
        UI->getAAMetadata(AATags);
      } else if (AATags) {
        UI->getAAMetadata(AATags, /* Merge = */ true);
      }

      LoopUses.push_back(UI);
    }
  }

  // If we found both an unordered atomic instruction and a non-atomic memory
  // access, bail.  We can't blindly promote non-atomic to atomic since we
  // might not be able to lower the result.  We can't downgrade since that
  // would violate memory model.  Also, align 0 is an error for atomics.
  if (SawUnorderedAtomic && SawNotAtomic)
    return false;

  // If we're inserting an atomic load in the preheader, we must be able to
  // lower it.  We're only guaranteed to be able to lower naturally aligned
  // atomics.
  auto *SomePtrElemType = SomePtr->getType()->getPointerElementType();
  if (SawUnorderedAtomic &&
      Alignment < MDL.getTypeStoreSize(SomePtrElemType))
    return false;

  // If we couldn't prove we can hoist the load, bail.
  if (!DereferenceableInPH)
    return false;

  // We know we can hoist the load, but don't have a guaranteed store.
  // Check whether the location is thread-local. If it is, then we can insert
  // stores along paths which originally didn't have them without violating the
  // memory model.
  if (!SafeToInsertStore) {
    if (IsKnownThreadLocalObject)
      SafeToInsertStore = true;
    else {
      Value *Object = GetUnderlyingObject(SomePtr, MDL);
      SafeToInsertStore =
          (isAllocLikeFn(Object, TLI) || isa<AllocaInst>(Object)) &&
          !PointerMayBeCaptured(Object, true, true);
    }
  }

  // If we've still failed to prove we can sink the store, give up.
  if (!SafeToInsertStore)
    return false;

  // Otherwise, this is safe to promote, lets do it!
  LLVM_DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " << *SomePtr
                    << '\n');
  ORE->emit([&]() {
    return OptimizationRemark(DEBUG_TYPE, "PromoteLoopAccessesToScalar",
                              LoopUses[0])
           << "Moving accesses to memory location out of the loop";
  });
  ++NumPromoted;

  // Grab a debug location for the inserted loads/stores; given that the
  // inserted loads/stores have little relation to the original loads/stores,
  // this code just arbitrarily picks a location from one, since any debug
  // location is better than none.
  DebugLoc DL = LoopUses[0]->getDebugLoc();

  // We use the SSAUpdater interface to insert phi nodes as required.
  SmallVector<PHINode *, 16> NewPHIs;
  SSAUpdater SSA(&NewPHIs);
  LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
                        InsertPts, MSSAInsertPts, PIC, *CurAST, MSSAU, *LI, DL,
                        Alignment, SawUnorderedAtomic, AATags, *SafetyInfo);

  // Set up the preheader to have a definition of the value.  It is the live-out
  // value from the preheader that uses in the loop will use.
  LoadInst *PreheaderLoad = new LoadInst(
      SomePtr->getType()->getPointerElementType(), SomePtr,
      SomePtr->getName() + ".promoted", Preheader->getTerminator());
  if (SawUnorderedAtomic)
    PreheaderLoad->setOrdering(AtomicOrdering::Unordered);
  PreheaderLoad->setAlignment(Alignment);
  PreheaderLoad->setDebugLoc(DL);
  if (AATags)
    PreheaderLoad->setAAMetadata(AATags);
  SSA.AddAvailableValue(Preheader, PreheaderLoad);

  MemoryAccess *PreheaderLoadMemoryAccess;
  if (MSSAU) {
    PreheaderLoadMemoryAccess = MSSAU->createMemoryAccessInBB(
        PreheaderLoad, nullptr, PreheaderLoad->getParent(), MemorySSA::End);
    MemoryUse *NewMemUse = cast<MemoryUse>(PreheaderLoadMemoryAccess);
    MSSAU->insertUse(NewMemUse);
  }

  // Rewrite all the loads in the loop and remember all the definitions from
  // stores in the loop.
  Promoter.run(LoopUses);

  if (MSSAU && VerifyMemorySSA)
    MSSAU->getMemorySSA()->verifyMemorySSA();
  // If the SSAUpdater didn't use the load in the preheader, just zap it now.
  if (PreheaderLoad->use_empty())
    eraseInstruction(*PreheaderLoad, *SafetyInfo, CurAST, MSSAU);

  return true;
}

/// Returns an owning pointer to an alias set which incorporates aliasing info
/// from L and all subloops of L.
/// FIXME: In new pass manager, there is no helper function to handle loop
/// analysis such as cloneBasicBlockAnalysis, so the AST needs to be recomputed
/// from scratch for every loop. Hook up with the helper functions when
/// available in the new pass manager to avoid redundant computation.
std::unique_ptr<AliasSetTracker>
LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
                                                 AliasAnalysis *AA) {
  std::unique_ptr<AliasSetTracker> CurAST;
  SmallVector<Loop *, 4> RecomputeLoops;
  for (Loop *InnerL : L->getSubLoops()) {
    auto MapI = LoopToAliasSetMap.find(InnerL);
    // If the AST for this inner loop is missing it may have been merged into
    // some other loop's AST and then that loop unrolled, and so we need to
    // recompute it.
    if (MapI == LoopToAliasSetMap.end()) {
      RecomputeLoops.push_back(InnerL);
      continue;
    }
    std::unique_ptr<AliasSetTracker> InnerAST = std::move(MapI->second);

    if (CurAST) {
      // What if InnerLoop was modified by other passes ?
      // Once we've incorporated the inner loop's AST into ours, we don't need
      // the subloop's anymore.
      CurAST->add(*InnerAST);
    } else {
      CurAST = std::move(InnerAST);
    }
    LoopToAliasSetMap.erase(MapI);
  }
  if (!CurAST)
    CurAST = make_unique<AliasSetTracker>(*AA);

  // Add everything from the sub loops that are no longer directly available.
  for (Loop *InnerL : RecomputeLoops)
    for (BasicBlock *BB : InnerL->blocks())
      CurAST->add(*BB);

  // And merge in this loop (without anything from inner loops).
  for (BasicBlock *BB : L->blocks())
    if (LI->getLoopFor(BB) == L)
      CurAST->add(*BB);

  return CurAST;
}

std::unique_ptr<AliasSetTracker>
LoopInvariantCodeMotion::collectAliasInfoForLoopWithMSSA(
    Loop *L, AliasAnalysis *AA, MemorySSAUpdater *MSSAU) {
  auto *MSSA = MSSAU->getMemorySSA();
  auto CurAST = make_unique<AliasSetTracker>(*AA, MSSA, L);
  CurAST->addAllInstructionsInLoopUsingMSSA();
  return CurAST;
}

/// Simple analysis hook. Clone alias set info.
///
void LegacyLICMPass::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,
                                             Loop *L) {
  auto ASTIt = LICM.getLoopToAliasSetMap().find(L);
  if (ASTIt == LICM.getLoopToAliasSetMap().end())
    return;

  ASTIt->second->copyValue(From, To);
}

/// Simple Analysis hook. Delete value V from alias set
///
void LegacyLICMPass::deleteAnalysisValue(Value *V, Loop *L) {
  auto ASTIt = LICM.getLoopToAliasSetMap().find(L);
  if (ASTIt == LICM.getLoopToAliasSetMap().end())
    return;

  ASTIt->second->deleteValue(V);
}

/// Simple Analysis hook. Delete value L from alias set map.
///
void LegacyLICMPass::deleteAnalysisLoop(Loop *L) {
  if (!LICM.getLoopToAliasSetMap().count(L))
    return;

  LICM.getLoopToAliasSetMap().erase(L);
}

static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
                                     AliasSetTracker *CurAST, Loop *CurLoop,
                                     AliasAnalysis *AA) {
  // First check to see if any of the basic blocks in CurLoop invalidate *V.
  bool isInvalidatedAccordingToAST = CurAST->getAliasSetFor(MemLoc).isMod();

  if (!isInvalidatedAccordingToAST || !LICMN2Theshold)
    return isInvalidatedAccordingToAST;

  // Check with a diagnostic analysis if we can refine the information above.
  // This is to identify the limitations of using the AST.
  // The alias set mechanism used by LICM has a major weakness in that it
  // combines all things which may alias into a single set *before* asking
  // modref questions. As a result, a single readonly call within a loop will
  // collapse all loads and stores into a single alias set and report
  // invalidation if the loop contains any store. For example, readonly calls
  // with deopt states have this form and create a general alias set with all
  // loads and stores.  In order to get any LICM in loops containing possible
  // deopt states we need a more precise invalidation of checking the mod ref
  // info of each instruction within the loop and LI. This has a complexity of
  // O(N^2), so currently, it is used only as a diagnostic tool since the
  // default value of LICMN2Threshold is zero.

  // Don't look at nested loops.
  if (CurLoop->begin() != CurLoop->end())
    return true;

  int N = 0;
  for (BasicBlock *BB : CurLoop->getBlocks())
    for (Instruction &I : *BB) {
      if (N >= LICMN2Theshold) {
        LLVM_DEBUG(dbgs() << "Alasing N2 threshold exhausted for "
                          << *(MemLoc.Ptr) << "\n");
        return true;
      }
      N++;
      auto Res = AA->getModRefInfo(&I, MemLoc);
      if (isModSet(Res)) {
        LLVM_DEBUG(dbgs() << "Aliasing failed on " << I << " for "
                          << *(MemLoc.Ptr) << "\n");
        return true;
      }
    }
  LLVM_DEBUG(dbgs() << "Aliasing okay for " << *(MemLoc.Ptr) << "\n");
  return false;
}

static bool pointerInvalidatedByLoopWithMSSA(MemorySSA *MSSA, MemoryUse *MU,
                                             Loop *CurLoop,
                                             int &LicmMssaOptCounter) {
  MemoryAccess *Source;
  // See declaration of LicmMssaOptCap for usage details.
  if (LicmMssaOptCounter >= LicmMssaOptCap)
    Source = MU->getDefiningAccess();
  else {
    Source = MSSA->getSkipSelfWalker()->getClobberingMemoryAccess(MU);
    LicmMssaOptCounter++;
  }
  return !MSSA->isLiveOnEntryDef(Source) &&
         CurLoop->contains(Source->getBlock());
}

/// Little predicate that returns true if the specified basic block is in
/// a subloop of the current one, not the current one itself.
///
static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI) {
  assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
  return LI->getLoopFor(BB) != CurLoop;
}