llvm.org GIT mirror llvm / d94715e lib / Transforms / Scalar / LoopIdiomRecognize.cpp
d94715e

Tree @d94715e (Download .tar.gz)

LoopIdiomRecognize.cpp @d94715eraw · 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
//===-- LoopIdiomRecognize.cpp - Loop idiom recognition -------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass implements an idiom recognizer that transforms simple loops into a
// non-loop form.  In cases that this kicks in, it can be a significant
// performance win.
//
//===----------------------------------------------------------------------===//
//
// TODO List:
//
// Future loop memory idioms to recognize:
//   memcmp, memmove, strlen, etc.
// Future floating point idioms to recognize in -ffast-math mode:
//   fpowi
// Future integer operation idioms to recognize:
//   ctpop, ctlz, cttz
//
// Beware that isel's default lowering for ctpop is highly inefficient for
// i64 and larger types when i64 is legal and the value has few bits set.  It
// would be good to enhance isel to emit a loop for ctpop in this case.
//
// We should enhance the memset/memcpy recognition to handle multiple stores in
// the loop.  This would handle things like:
//   void foo(_Complex float *P)
//     for (i) { __real__(*P) = 0;  __imag__(*P) = 0; }
//
// We should enhance this to handle negative strides through memory.
// Alternatively (and perhaps better) we could rely on an earlier pass to force
// forward iteration through memory, which is generally better for cache
// behavior.  Negative strides *do* happen for memset/memcpy loops.
//
// This could recognize common matrix multiplies and dot product idioms and
// replace them with calls to BLAS (if linked in??).
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;

#define DEBUG_TYPE "loop-idiom"

STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");

namespace {

  class LoopIdiomRecognize;

  /// This class defines some utility functions for loop idiom recognization.
  class LIRUtil {
  public:
    /// Return true iff the block contains nothing but an uncondition branch
    /// (aka goto instruction).
    static bool isAlmostEmpty(BasicBlock *);

    static BranchInst *getBranch(BasicBlock *BB) {
      return dyn_cast<BranchInst>(BB->getTerminator());
    }

    /// Derive the precondition block (i.e the block that guards the loop
    /// preheader) from the given preheader.
    static BasicBlock *getPrecondBb(BasicBlock *PreHead);
  };

  /// This class is to recoginize idioms of population-count conducted in
  /// a noncountable loop. Currently it only recognizes this pattern:
  /// \code
  ///   while(x) {cnt++; ...; x &= x - 1; ...}
  /// \endcode
  class NclPopcountRecognize {
    LoopIdiomRecognize &LIR;
    Loop *CurLoop;
    BasicBlock *PreCondBB;

    typedef IRBuilder<> IRBuilderTy;

  public:
    explicit NclPopcountRecognize(LoopIdiomRecognize &TheLIR);
    bool recognize();

  private:
    /// Take a glimpse of the loop to see if we need to go ahead recoginizing
    /// the idiom.
    bool preliminaryScreen();

    /// Check if the given conditional branch is based on the comparison
    /// between a variable and zero, and if the variable is non-zero, the
    /// control yields to the loop entry. If the branch matches the behavior,
    /// the variable involved in the comparion is returned. This function will
    /// be called to see if the precondition and postcondition of the loop
    /// are in desirable form.
    Value *matchCondition(BranchInst *Br, BasicBlock *NonZeroTarget) const;

    /// Return true iff the idiom is detected in the loop. and 1) \p CntInst
    /// is set to the instruction counting the population bit. 2) \p CntPhi
    /// is set to the corresponding phi node. 3) \p Var is set to the value
    /// whose population bits are being counted.
    bool detectIdiom
      (Instruction *&CntInst, PHINode *&CntPhi, Value *&Var) const;

    /// Insert ctpop intrinsic function and some obviously dead instructions.
    void transform(Instruction *CntInst, PHINode *CntPhi, Value *Var);

    /// Create llvm.ctpop.* intrinsic function.
    CallInst *createPopcntIntrinsic(IRBuilderTy &IRB, Value *Val, DebugLoc DL);
  };

  class LoopIdiomRecognize : public LoopPass {
    Loop *CurLoop;
    const DataLayout *DL;
    DominatorTree *DT;
    ScalarEvolution *SE;
    TargetLibraryInfo *TLI;
    const TargetTransformInfo *TTI;
  public:
    static char ID;
    explicit LoopIdiomRecognize() : LoopPass(ID) {
      initializeLoopIdiomRecognizePass(*PassRegistry::getPassRegistry());
      DL = nullptr; DT = nullptr; SE = nullptr; TLI = nullptr; TTI = nullptr;
    }

    bool runOnLoop(Loop *L, LPPassManager &LPM) override;
    bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
                        SmallVectorImpl<BasicBlock*> &ExitBlocks);

    bool processLoopStore(StoreInst *SI, const SCEV *BECount);
    bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);

    bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
                                 unsigned StoreAlignment,
                                 Value *SplatValue, Instruction *TheStore,
                                 const SCEVAddRecExpr *Ev,
                                 const SCEV *BECount);
    bool processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
                                    const SCEVAddRecExpr *StoreEv,
                                    const SCEVAddRecExpr *LoadEv,
                                    const SCEV *BECount);

    /// This transformation requires natural loop information & requires that
    /// loop preheaders be inserted into the CFG.
    ///
    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.addRequired<LoopInfo>();
      AU.addPreserved<LoopInfo>();
      AU.addRequiredID(LoopSimplifyID);
      AU.addPreservedID(LoopSimplifyID);
      AU.addRequiredID(LCSSAID);
      AU.addPreservedID(LCSSAID);
      AU.addRequired<AliasAnalysis>();
      AU.addPreserved<AliasAnalysis>();
      AU.addRequired<ScalarEvolution>();
      AU.addPreserved<ScalarEvolution>();
      AU.addPreserved<DominatorTreeWrapperPass>();
      AU.addRequired<DominatorTreeWrapperPass>();
      AU.addRequired<TargetLibraryInfo>();
      AU.addRequired<TargetTransformInfo>();
    }

    const DataLayout *getDataLayout() {
      if (DL)
        return DL;
      DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
      DL = DLP ? &DLP->getDataLayout() : nullptr;
      return DL;
    }

    DominatorTree *getDominatorTree() {
      return DT ? DT
                : (DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree());
    }

    ScalarEvolution *getScalarEvolution() {
      return SE ? SE : (SE = &getAnalysis<ScalarEvolution>());
    }

    TargetLibraryInfo *getTargetLibraryInfo() {
      return TLI ? TLI : (TLI = &getAnalysis<TargetLibraryInfo>());
    }

    const TargetTransformInfo *getTargetTransformInfo() {
      return TTI ? TTI : (TTI = &getAnalysis<TargetTransformInfo>());
    }

    Loop *getLoop() const { return CurLoop; }

  private:
    bool runOnNoncountableLoop();
    bool runOnCountableLoop();
  };
}

char LoopIdiomRecognize::ID = 0;
INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
                      false, false)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LCSSA)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
                    false, false)

Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }

/// deleteDeadInstruction - Delete this instruction.  Before we do, go through
/// and zero out all the operands of this instruction.  If any of them become
/// dead, delete them and the computation tree that feeds them.
///
static void deleteDeadInstruction(Instruction *I, ScalarEvolution &SE,
                                  const TargetLibraryInfo *TLI) {
  SmallVector<Instruction*, 32> NowDeadInsts;

  NowDeadInsts.push_back(I);

  // Before we touch this instruction, remove it from SE!
  do {
    Instruction *DeadInst = NowDeadInsts.pop_back_val();

    // This instruction is dead, zap it, in stages.  Start by removing it from
    // SCEV.
    SE.forgetValue(DeadInst);

    for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
      Value *Op = DeadInst->getOperand(op);
      DeadInst->setOperand(op, nullptr);

      // If this operand just became dead, add it to the NowDeadInsts list.
      if (!Op->use_empty()) continue;

      if (Instruction *OpI = dyn_cast<Instruction>(Op))
        if (isInstructionTriviallyDead(OpI, TLI))
          NowDeadInsts.push_back(OpI);
    }

    DeadInst->eraseFromParent();

  } while (!NowDeadInsts.empty());
}

/// deleteIfDeadInstruction - If the specified value is a dead instruction,
/// delete it and any recursively used instructions.
static void deleteIfDeadInstruction(Value *V, ScalarEvolution &SE,
                                    const TargetLibraryInfo *TLI) {
  if (Instruction *I = dyn_cast<Instruction>(V))
    if (isInstructionTriviallyDead(I, TLI))
      deleteDeadInstruction(I, SE, TLI);
}

//===----------------------------------------------------------------------===//
//
//          Implementation of LIRUtil
//
//===----------------------------------------------------------------------===//

// This function will return true iff the given block contains nothing but goto.
// A typical usage of this function is to check if the preheader function is
// "almost" empty such that generated intrinsic functions can be moved across
// the preheader and be placed at the end of the precondition block without
// the concern of breaking data dependence.
bool LIRUtil::isAlmostEmpty(BasicBlock *BB) {
  if (BranchInst *Br = getBranch(BB)) {
    return Br->isUnconditional() && BB->size() == 1;
  }
  return false;
}

BasicBlock *LIRUtil::getPrecondBb(BasicBlock *PreHead) {
  if (BasicBlock *BB = PreHead->getSinglePredecessor()) {
    BranchInst *Br = getBranch(BB);
    return Br && Br->isConditional() ? BB : nullptr;
  }
  return nullptr;
}

//===----------------------------------------------------------------------===//
//
//          Implementation of NclPopcountRecognize
//
//===----------------------------------------------------------------------===//

NclPopcountRecognize::NclPopcountRecognize(LoopIdiomRecognize &TheLIR):
  LIR(TheLIR), CurLoop(TheLIR.getLoop()), PreCondBB(nullptr) {
}

bool NclPopcountRecognize::preliminaryScreen() {
  const TargetTransformInfo *TTI = LIR.getTargetTransformInfo();
  if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
    return false;

  // Counting population are usually conducted by few arithmetic instructions.
  // Such instructions can be easilly "absorbed" by vacant slots in a
  // non-compact loop. Therefore, recognizing popcount idiom only makes sense
  // in a compact loop.

  // Give up if the loop has multiple blocks or multiple backedges.
  if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
    return false;

  BasicBlock *LoopBody = *(CurLoop->block_begin());
  if (LoopBody->size() >= 20) {
    // The loop is too big, bail out.
    return false;
  }

  // It should have a preheader containing nothing but a goto instruction.
  BasicBlock *PreHead = CurLoop->getLoopPreheader();
  if (!PreHead || !LIRUtil::isAlmostEmpty(PreHead))
    return false;

  // It should have a precondition block where the generated popcount instrinsic
  // function will be inserted.
  PreCondBB = LIRUtil::getPrecondBb(PreHead);
  if (!PreCondBB)
    return false;

  return true;
}

Value *NclPopcountRecognize::matchCondition(BranchInst *Br,
                                            BasicBlock *LoopEntry) const {
  if (!Br || !Br->isConditional())
    return nullptr;

  ICmpInst *Cond = dyn_cast<ICmpInst>(Br->getCondition());
  if (!Cond)
    return nullptr;

  ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
  if (!CmpZero || !CmpZero->isZero())
    return nullptr;

  ICmpInst::Predicate Pred = Cond->getPredicate();
  if ((Pred == ICmpInst::ICMP_NE && Br->getSuccessor(0) == LoopEntry) ||
      (Pred == ICmpInst::ICMP_EQ && Br->getSuccessor(1) == LoopEntry))
    return Cond->getOperand(0);

  return nullptr;
}

bool NclPopcountRecognize::detectIdiom(Instruction *&CntInst,
                                       PHINode *&CntPhi,
                                       Value *&Var) const {
  // Following code tries to detect this idiom:
  //
  //    if (x0 != 0)
  //      goto loop-exit // the precondition of the loop
  //    cnt0 = init-val;
  //    do {
  //       x1 = phi (x0, x2);
  //       cnt1 = phi(cnt0, cnt2);
  //
  //       cnt2 = cnt1 + 1;
  //        ...
  //       x2 = x1 & (x1 - 1);
  //        ...
  //    } while(x != 0);
  //
  // loop-exit:
  //

  // step 1: Check to see if the look-back branch match this pattern:
  //    "if (a!=0) goto loop-entry".
  BasicBlock *LoopEntry;
  Instruction *DefX2, *CountInst;
  Value *VarX1, *VarX0;
  PHINode *PhiX, *CountPhi;

  DefX2 = CountInst = nullptr;
  VarX1 = VarX0 = nullptr;
  PhiX = CountPhi = nullptr;
  LoopEntry = *(CurLoop->block_begin());

  // step 1: Check if the loop-back branch is in desirable form.
  {
    if (Value *T = matchCondition (LIRUtil::getBranch(LoopEntry), LoopEntry))
      DefX2 = dyn_cast<Instruction>(T);
    else
      return false;
  }

  // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
  {
    if (!DefX2 || DefX2->getOpcode() != Instruction::And)
      return false;

    BinaryOperator *SubOneOp;

    if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
      VarX1 = DefX2->getOperand(1);
    else {
      VarX1 = DefX2->getOperand(0);
      SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
    }
    if (!SubOneOp)
      return false;

    Instruction *SubInst = cast<Instruction>(SubOneOp);
    ConstantInt *Dec = dyn_cast<ConstantInt>(SubInst->getOperand(1));
    if (!Dec ||
        !((SubInst->getOpcode() == Instruction::Sub && Dec->isOne()) ||
          (SubInst->getOpcode() == Instruction::Add && Dec->isAllOnesValue()))) {
      return false;
    }
  }

  // step 3: Check the recurrence of variable X
  {
    PhiX = dyn_cast<PHINode>(VarX1);
    if (!PhiX ||
        (PhiX->getOperand(0) != DefX2 && PhiX->getOperand(1) != DefX2)) {
      return false;
    }
  }

  // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
  {
    CountInst = nullptr;
    for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI(),
           IterE = LoopEntry->end(); Iter != IterE; Iter++) {
      Instruction *Inst = Iter;
      if (Inst->getOpcode() != Instruction::Add)
        continue;

      ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
      if (!Inc || !Inc->isOne())
        continue;

      PHINode *Phi = dyn_cast<PHINode>(Inst->getOperand(0));
      if (!Phi || Phi->getParent() != LoopEntry)
        continue;

      // Check if the result of the instruction is live of the loop.
      bool LiveOutLoop = false;
      for (User *U : Inst->users()) {
        if ((cast<Instruction>(U))->getParent() != LoopEntry) {
          LiveOutLoop = true; break;
        }
      }

      if (LiveOutLoop) {
        CountInst = Inst;
        CountPhi = Phi;
        break;
      }
    }

    if (!CountInst)
      return false;
  }

  // step 5: check if the precondition is in this form:
  //   "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
  {
    BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
    Value *T = matchCondition (PreCondBr, CurLoop->getLoopPreheader());
    if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
      return false;

    CntInst = CountInst;
    CntPhi = CountPhi;
    Var = T;
  }

  return true;
}

void NclPopcountRecognize::transform(Instruction *CntInst,
                                     PHINode *CntPhi, Value *Var) {

  ScalarEvolution *SE = LIR.getScalarEvolution();
  TargetLibraryInfo *TLI = LIR.getTargetLibraryInfo();
  BasicBlock *PreHead = CurLoop->getLoopPreheader();
  BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
  const DebugLoc DL = CntInst->getDebugLoc();

  // Assuming before transformation, the loop is following:
  //  if (x) // the precondition
  //     do { cnt++; x &= x - 1; } while(x);

  // Step 1: Insert the ctpop instruction at the end of the precondition block
  IRBuilderTy Builder(PreCondBr);
  Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
  {
    PopCnt = createPopcntIntrinsic(Builder, Var, DL);
    NewCount = PopCntZext =
      Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));

    if (NewCount != PopCnt)
      (cast<Instruction>(NewCount))->setDebugLoc(DL);

    // TripCnt is exactly the number of iterations the loop has
    TripCnt = NewCount;

    // If the population counter's initial value is not zero, insert Add Inst.
    Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
    ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
    if (!InitConst || !InitConst->isZero()) {
      NewCount = Builder.CreateAdd(NewCount, CntInitVal);
      (cast<Instruction>(NewCount))->setDebugLoc(DL);
    }
  }

  // Step 2: Replace the precondition from "if(x == 0) goto loop-exit" to
  //   "if(NewCount == 0) loop-exit". Withtout this change, the intrinsic
  //   function would be partial dead code, and downstream passes will drag
  //   it back from the precondition block to the preheader.
  {
    ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());

    Value *Opnd0 = PopCntZext;
    Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
    if (PreCond->getOperand(0) != Var)
      std::swap(Opnd0, Opnd1);

    ICmpInst *NewPreCond =
      cast<ICmpInst>(Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
    PreCond->replaceAllUsesWith(NewPreCond);

    deleteDeadInstruction(PreCond, *SE, TLI);
  }

  // Step 3: Note that the population count is exactly the trip count of the
  // loop in question, which enble us to to convert the loop from noncountable
  // loop into a countable one. The benefit is twofold:
  //
  //  - If the loop only counts population, the entire loop become dead after
  //    the transformation. It is lots easier to prove a countable loop dead
  //    than to prove a noncountable one. (In some C dialects, a infite loop
  //    isn't dead even if it computes nothing useful. In general, DCE needs
  //    to prove a noncountable loop finite before safely delete it.)
  //
  //  - If the loop also performs something else, it remains alive.
  //    Since it is transformed to countable form, it can be aggressively
  //    optimized by some optimizations which are in general not applicable
  //    to a noncountable loop.
  //
  // After this step, this loop (conceptually) would look like following:
  //   newcnt = __builtin_ctpop(x);
  //   t = newcnt;
  //   if (x)
  //     do { cnt++; x &= x-1; t--) } while (t > 0);
  BasicBlock *Body = *(CurLoop->block_begin());
  {
    BranchInst *LbBr = LIRUtil::getBranch(Body);
    ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
    Type *Ty = TripCnt->getType();

    PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", Body->begin());

    Builder.SetInsertPoint(LbCond);
    Value *Opnd1 = cast<Value>(TcPhi);
    Value *Opnd2 = cast<Value>(ConstantInt::get(Ty, 1));
    Instruction *TcDec =
      cast<Instruction>(Builder.CreateSub(Opnd1, Opnd2, "tcdec", false, true));

    TcPhi->addIncoming(TripCnt, PreHead);
    TcPhi->addIncoming(TcDec, Body);

    CmpInst::Predicate Pred = (LbBr->getSuccessor(0) == Body) ?
      CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
    LbCond->setPredicate(Pred);
    LbCond->setOperand(0, TcDec);
    LbCond->setOperand(1, cast<Value>(ConstantInt::get(Ty, 0)));
  }

  // Step 4: All the references to the original population counter outside
  //  the loop are replaced with the NewCount -- the value returned from
  //  __builtin_ctpop().
  {
    SmallVector<Value *, 4> CntUses;
    for (User *U : CntInst->users())
      if (cast<Instruction>(U)->getParent() != Body)
        CntUses.push_back(U);
    for (unsigned Idx = 0; Idx < CntUses.size(); Idx++) {
      (cast<Instruction>(CntUses[Idx]))->replaceUsesOfWith(CntInst, NewCount);
    }
  }

  // step 5: Forget the "non-computable" trip-count SCEV associated with the
  //   loop. The loop would otherwise not be deleted even if it becomes empty.
  SE->forgetLoop(CurLoop);
}

CallInst *NclPopcountRecognize::createPopcntIntrinsic(IRBuilderTy &IRBuilder,
                                                      Value *Val, DebugLoc DL) {
  Value *Ops[] = { Val };
  Type *Tys[] = { Val->getType() };

  Module *M = (*(CurLoop->block_begin()))->getParent()->getParent();
  Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
  CallInst *CI = IRBuilder.CreateCall(Func, Ops);
  CI->setDebugLoc(DL);

  return CI;
}

/// recognize - detect population count idiom in a non-countable loop. If
///   detected, transform the relevant code to popcount intrinsic function
///   call, and return true; otherwise, return false.
bool NclPopcountRecognize::recognize() {

  if (!LIR.getTargetTransformInfo())
    return false;

  LIR.getScalarEvolution();

  if (!preliminaryScreen())
    return false;

  Instruction *CntInst;
  PHINode *CntPhi;
  Value *Val;
  if (!detectIdiom(CntInst, CntPhi, Val))
    return false;

  transform(CntInst, CntPhi, Val);
  return true;
}

//===----------------------------------------------------------------------===//
//
//          Implementation of LoopIdiomRecognize
//
//===----------------------------------------------------------------------===//

bool LoopIdiomRecognize::runOnCountableLoop() {
  const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
  if (isa<SCEVCouldNotCompute>(BECount)) return false;

  // If this loop executes exactly one time, then it should be peeled, not
  // optimized by this pass.
  if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
    if (BECst->getValue()->getValue() == 0)
      return false;

  // We require target data for now.
  if (!getDataLayout())
    return false;

  // set DT
  (void)getDominatorTree();

  LoopInfo &LI = getAnalysis<LoopInfo>();
  TLI = &getAnalysis<TargetLibraryInfo>();

  // set TLI
  (void)getTargetLibraryInfo();

  SmallVector<BasicBlock*, 8> ExitBlocks;
  CurLoop->getUniqueExitBlocks(ExitBlocks);

  DEBUG(dbgs() << "loop-idiom Scanning: F["
               << CurLoop->getHeader()->getParent()->getName()
               << "] Loop %" << CurLoop->getHeader()->getName() << "\n");

  bool MadeChange = false;
  // Scan all the blocks in the loop that are not in subloops.
  for (Loop::block_iterator BI = CurLoop->block_begin(),
         E = CurLoop->block_end(); BI != E; ++BI) {
    // Ignore blocks in subloops.
    if (LI.getLoopFor(*BI) != CurLoop)
      continue;

    MadeChange |= runOnLoopBlock(*BI, BECount, ExitBlocks);
  }
  return MadeChange;
}

bool LoopIdiomRecognize::runOnNoncountableLoop() {
  NclPopcountRecognize Popcount(*this);
  if (Popcount.recognize())
    return true;

  return false;
}

bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
  if (skipOptnoneFunction(L))
    return false;

  CurLoop = L;

  // If the loop could not be converted to canonical form, it must have an
  // indirectbr in it, just give up.
  if (!L->getLoopPreheader())
    return false;

  // Disable loop idiom recognition if the function's name is a common idiom.
  StringRef Name = L->getHeader()->getParent()->getName();
  if (Name == "memset" || Name == "memcpy")
    return false;

  SE = &getAnalysis<ScalarEvolution>();
  if (SE->hasLoopInvariantBackedgeTakenCount(L))
    return runOnCountableLoop();
  return runOnNoncountableLoop();
}

/// runOnLoopBlock - Process the specified block, which lives in a counted loop
/// with the specified backedge count.  This block is known to be in the current
/// loop and not in any subloops.
bool LoopIdiomRecognize::runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
                                     SmallVectorImpl<BasicBlock*> &ExitBlocks) {
  // We can only promote stores in this block if they are unconditionally
  // executed in the loop.  For a block to be unconditionally executed, it has
  // to dominate all the exit blocks of the loop.  Verify this now.
  for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
    if (!DT->dominates(BB, ExitBlocks[i]))
      return false;

  bool MadeChange = false;
  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
    Instruction *Inst = I++;
    // Look for store instructions, which may be optimized to memset/memcpy.
    if (StoreInst *SI = dyn_cast<StoreInst>(Inst))  {
      WeakVH InstPtr(I);
      if (!processLoopStore(SI, BECount)) continue;
      MadeChange = true;

      // If processing the store invalidated our iterator, start over from the
      // top of the block.
      if (!InstPtr)
        I = BB->begin();
      continue;
    }

    // Look for memset instructions, which may be optimized to a larger memset.
    if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst))  {
      WeakVH InstPtr(I);
      if (!processLoopMemSet(MSI, BECount)) continue;
      MadeChange = true;

      // If processing the memset invalidated our iterator, start over from the
      // top of the block.
      if (!InstPtr)
        I = BB->begin();
      continue;
    }
  }

  return MadeChange;
}


/// processLoopStore - See if this store can be promoted to a memset or memcpy.
bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
  if (!SI->isSimple()) return false;

  Value *StoredVal = SI->getValueOperand();
  Value *StorePtr = SI->getPointerOperand();

  // Reject stores that are so large that they overflow an unsigned.
  uint64_t SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
  if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
    return false;

  // See if the pointer expression is an AddRec like {base,+,1} on the current
  // loop, which indicates a strided store.  If we have something else, it's a
  // random store we can't handle.
  const SCEVAddRecExpr *StoreEv =
    dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
  if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
    return false;

  // Check to see if the stride matches the size of the store.  If so, then we
  // know that every byte is touched in the loop.
  unsigned StoreSize = (unsigned)SizeInBits >> 3;
  const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));

  if (!Stride || StoreSize != Stride->getValue()->getValue()) {
    // TODO: Could also handle negative stride here someday, that will require
    // the validity check in mayLoopAccessLocation to be updated though.
    // Enable this to print exact negative strides.
    if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
      dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
      dbgs() << "BB: " << *SI->getParent();
    }

    return false;
  }

  // See if we can optimize just this store in isolation.
  if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
                              StoredVal, SI, StoreEv, BECount))
    return true;

  // If the stored value is a strided load in the same loop with the same stride
  // this this may be transformable into a memcpy.  This kicks in for stuff like
  //   for (i) A[i] = B[i];
  if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
    const SCEVAddRecExpr *LoadEv =
      dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getOperand(0)));
    if (LoadEv && LoadEv->getLoop() == CurLoop && LoadEv->isAffine() &&
        StoreEv->getOperand(1) == LoadEv->getOperand(1) && LI->isSimple())
      if (processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, LoadEv, BECount))
        return true;
  }
  //errs() << "UNHANDLED strided store: " << *StoreEv << " - " << *SI << "\n";

  return false;
}

/// processLoopMemSet - See if this memset can be promoted to a large memset.
bool LoopIdiomRecognize::
processLoopMemSet(MemSetInst *MSI, const SCEV *BECount) {
  // We can only handle non-volatile memsets with a constant size.
  if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength())) return false;

  // If we're not allowed to hack on memset, we fail.
  if (!TLI->has(LibFunc::memset))
    return false;

  Value *Pointer = MSI->getDest();

  // See if the pointer expression is an AddRec like {base,+,1} on the current
  // loop, which indicates a strided store.  If we have something else, it's a
  // random store we can't handle.
  const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
  if (!Ev || Ev->getLoop() != CurLoop || !Ev->isAffine())
    return false;

  // Reject memsets that are so large that they overflow an unsigned.
  uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
  if ((SizeInBytes >> 32) != 0)
    return false;

  // Check to see if the stride matches the size of the memset.  If so, then we
  // know that every byte is touched in the loop.
  const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));

  // TODO: Could also handle negative stride here someday, that will require the
  // validity check in mayLoopAccessLocation to be updated though.
  if (!Stride || MSI->getLength() != Stride->getValue())
    return false;

  return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
                                 MSI->getAlignment(), MSI->getValue(),
                                 MSI, Ev, BECount);
}


/// mayLoopAccessLocation - Return true if the specified loop might access the
/// specified pointer location, which is a loop-strided access.  The 'Access'
/// argument specifies what the verboten forms of access are (read or write).
static bool mayLoopAccessLocation(Value *Ptr,AliasAnalysis::ModRefResult Access,
                                  Loop *L, const SCEV *BECount,
                                  unsigned StoreSize, AliasAnalysis &AA,
                                  Instruction *IgnoredStore) {
  // Get the location that may be stored across the loop.  Since the access is
  // strided positively through memory, we say that the modified location starts
  // at the pointer and has infinite size.
  uint64_t AccessSize = AliasAnalysis::UnknownSize;

  // If the loop iterates a fixed number of times, we can refine the access size
  // to be exactly the size of the memset, which is (BECount+1)*StoreSize
  if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
    AccessSize = (BECst->getValue()->getZExtValue()+1)*StoreSize;

  // TODO: For this to be really effective, we have to dive into the pointer
  // operand in the store.  Store to &A[i] of 100 will always return may alias
  // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
  // which will then no-alias a store to &A[100].
  AliasAnalysis::Location StoreLoc(Ptr, AccessSize);

  for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
       ++BI)
    for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
      if (&*I != IgnoredStore &&
          (AA.getModRefInfo(I, StoreLoc) & Access))
        return true;

  return false;
}

/// getMemSetPatternValue - If a strided store of the specified value is safe to
/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
/// be passed in.  Otherwise, return null.
///
/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
/// just replicate their input array and then pass on to memset_pattern16.
static Constant *getMemSetPatternValue(Value *V, const DataLayout &DL) {
  // If the value isn't a constant, we can't promote it to being in a constant
  // array.  We could theoretically do a store to an alloca or something, but
  // that doesn't seem worthwhile.
  Constant *C = dyn_cast<Constant>(V);
  if (!C) return nullptr;

  // Only handle simple values that are a power of two bytes in size.
  uint64_t Size = DL.getTypeSizeInBits(V->getType());
  if (Size == 0 || (Size & 7) || (Size & (Size-1)))
    return nullptr;

  // Don't care enough about darwin/ppc to implement this.
  if (DL.isBigEndian())
    return nullptr;

  // Convert to size in bytes.
  Size /= 8;

  // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
  // if the top and bottom are the same (e.g. for vectors and large integers).
  if (Size > 16) return nullptr;

  // If the constant is exactly 16 bytes, just use it.
  if (Size == 16) return C;

  // Otherwise, we'll use an array of the constants.
  unsigned ArraySize = 16/Size;
  ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
  return ConstantArray::get(AT, std::vector<Constant*>(ArraySize, C));
}


/// processLoopStridedStore - We see a strided store of some value.  If we can
/// transform this into a memset or memset_pattern in the loop preheader, do so.
bool LoopIdiomRecognize::
processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
                        unsigned StoreAlignment, Value *StoredVal,
                        Instruction *TheStore, const SCEVAddRecExpr *Ev,
                        const SCEV *BECount) {

  // If the stored value is a byte-wise value (like i32 -1), then it may be
  // turned into a memset of i8 -1, assuming that all the consecutive bytes
  // are stored.  A store of i32 0x01020304 can never be turned into a memset,
  // but it can be turned into memset_pattern if the target supports it.
  Value *SplatValue = isBytewiseValue(StoredVal);
  Constant *PatternValue = nullptr;

  unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();

  // If we're allowed to form a memset, and the stored value would be acceptable
  // for memset, use it.
  if (SplatValue && TLI->has(LibFunc::memset) &&
      // Verify that the stored value is loop invariant.  If not, we can't
      // promote the memset.
      CurLoop->isLoopInvariant(SplatValue)) {
    // Keep and use SplatValue.
    PatternValue = nullptr;
  } else if (DestAS == 0 &&
             TLI->has(LibFunc::memset_pattern16) &&
             (PatternValue = getMemSetPatternValue(StoredVal, *DL))) {
    // Don't create memset_pattern16s with address spaces.
    // It looks like we can use PatternValue!
    SplatValue = nullptr;
  } else {
    // Otherwise, this isn't an idiom we can transform.  For example, we can't
    // do anything with a 3-byte store.
    return false;
  }

  // The trip count of the loop and the base pointer of the addrec SCEV is
  // guaranteed to be loop invariant, which means that it should dominate the
  // header.  This allows us to insert code for it in the preheader.
  BasicBlock *Preheader = CurLoop->getLoopPreheader();
  IRBuilder<> Builder(Preheader->getTerminator());
  SCEVExpander Expander(*SE, "loop-idiom");

  Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);

  // Okay, we have a strided store "p[i]" of a splattable value.  We can turn
  // this into a memset in the loop preheader now if we want.  However, this
  // would be unsafe to do if there is anything else in the loop that may read
  // or write to the aliased location.  Check for any overlap by generating the
  // base pointer and checking the region.
  Value *BasePtr =
    Expander.expandCodeFor(Ev->getStart(), DestInt8PtrTy,
                           Preheader->getTerminator());

  if (mayLoopAccessLocation(BasePtr, AliasAnalysis::ModRef,
                            CurLoop, BECount,
                            StoreSize, getAnalysis<AliasAnalysis>(), TheStore)) {
    Expander.clear();
    // If we generated new code for the base pointer, clean up.
    deleteIfDeadInstruction(BasePtr, *SE, TLI);
    return false;
  }

  // Okay, everything looks good, insert the memset.

  // The # stored bytes is (BECount+1)*Size.  Expand the trip count out to
  // pointer size if it isn't already.
  Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
  BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);

  const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1),
                                         SCEV::FlagNUW);
  if (StoreSize != 1) {
    NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
                               SCEV::FlagNUW);
  }

  Value *NumBytes =
    Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());

  CallInst *NewCall;
  if (SplatValue) {
    NewCall = Builder.CreateMemSet(BasePtr,
                                   SplatValue,
                                   NumBytes,
                                   StoreAlignment);
  } else {
    // Everything is emitted in default address space
    Type *Int8PtrTy = DestInt8PtrTy;

    Module *M = TheStore->getParent()->getParent()->getParent();
    Value *MSP = M->getOrInsertFunction("memset_pattern16",
                                        Builder.getVoidTy(),
                                        Int8PtrTy,
                                        Int8PtrTy,
                                        IntPtr,
                                        (void*)nullptr);

    // Otherwise we should form a memset_pattern16.  PatternValue is known to be
    // an constant array of 16-bytes.  Plop the value into a mergable global.
    GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
                                            GlobalValue::InternalLinkage,
                                            PatternValue, ".memset_pattern");
    GV->setUnnamedAddr(true); // Ok to merge these.
    GV->setAlignment(16);
    Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
    NewCall = Builder.CreateCall3(MSP, BasePtr, PatternPtr, NumBytes);
  }

  DEBUG(dbgs() << "  Formed memset: " << *NewCall << "\n"
               << "    from store to: " << *Ev << " at: " << *TheStore << "\n");
  NewCall->setDebugLoc(TheStore->getDebugLoc());

  // Okay, the memset has been formed.  Zap the original store and anything that
  // feeds into it.
  deleteDeadInstruction(TheStore, *SE, TLI);
  ++NumMemSet;
  return true;
}

/// processLoopStoreOfLoopLoad - We see a strided store whose value is a
/// same-strided load.
bool LoopIdiomRecognize::
processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
                           const SCEVAddRecExpr *StoreEv,
                           const SCEVAddRecExpr *LoadEv,
                           const SCEV *BECount) {
  // If we're not allowed to form memcpy, we fail.
  if (!TLI->has(LibFunc::memcpy))
    return false;

  LoadInst *LI = cast<LoadInst>(SI->getValueOperand());

  // The trip count of the loop and the base pointer of the addrec SCEV is
  // guaranteed to be loop invariant, which means that it should dominate the
  // header.  This allows us to insert code for it in the preheader.
  BasicBlock *Preheader = CurLoop->getLoopPreheader();
  IRBuilder<> Builder(Preheader->getTerminator());
  SCEVExpander Expander(*SE, "loop-idiom");

  // Okay, we have a strided store "p[i]" of a loaded value.  We can turn
  // this into a memcpy in the loop preheader now if we want.  However, this
  // would be unsafe to do if there is anything else in the loop that may read
  // or write the memory region we're storing to.  This includes the load that
  // feeds the stores.  Check for an alias by generating the base address and
  // checking everything.
  Value *StoreBasePtr =
    Expander.expandCodeFor(StoreEv->getStart(),
                           Builder.getInt8PtrTy(SI->getPointerAddressSpace()),
                           Preheader->getTerminator());

  if (mayLoopAccessLocation(StoreBasePtr, AliasAnalysis::ModRef,
                            CurLoop, BECount, StoreSize,
                            getAnalysis<AliasAnalysis>(), SI)) {
    Expander.clear();
    // If we generated new code for the base pointer, clean up.
    deleteIfDeadInstruction(StoreBasePtr, *SE, TLI);
    return false;
  }

  // For a memcpy, we have to make sure that the input array is not being
  // mutated by the loop.
  Value *LoadBasePtr =
    Expander.expandCodeFor(LoadEv->getStart(),
                           Builder.getInt8PtrTy(LI->getPointerAddressSpace()),
                           Preheader->getTerminator());

  if (mayLoopAccessLocation(LoadBasePtr, AliasAnalysis::Mod, CurLoop, BECount,
                            StoreSize, getAnalysis<AliasAnalysis>(), SI)) {
    Expander.clear();
    // If we generated new code for the base pointer, clean up.
    deleteIfDeadInstruction(LoadBasePtr, *SE, TLI);
    deleteIfDeadInstruction(StoreBasePtr, *SE, TLI);
    return false;
  }

  // Okay, everything is safe, we can transform this!


  // The # stored bytes is (BECount+1)*Size.  Expand the trip count out to
  // pointer size if it isn't already.
  Type *IntPtrTy = Builder.getIntPtrTy(DL, SI->getPointerAddressSpace());
  BECount = SE->getTruncateOrZeroExtend(BECount, IntPtrTy);

  const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtrTy, 1),
                                         SCEV::FlagNUW);
  if (StoreSize != 1)
    NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtrTy, StoreSize),
                               SCEV::FlagNUW);

  Value *NumBytes =
    Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());

  CallInst *NewCall =
    Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
                         std::min(SI->getAlignment(), LI->getAlignment()));
  NewCall->setDebugLoc(SI->getDebugLoc());

  DEBUG(dbgs() << "  Formed memcpy: " << *NewCall << "\n"
               << "    from load ptr=" << *LoadEv << " at: " << *LI << "\n"
               << "    from store ptr=" << *StoreEv << " at: " << *SI << "\n");


  // Okay, the memset has been formed.  Zap the original store and anything that
  // feeds into it.
  deleteDeadInstruction(SI, *SE, TLI);
  ++NumMemCpy;
  return true;
}