llvm.org GIT mirror llvm / release_80 lib / Analysis / BranchProbabilityInfo.cpp
release_80

Tree @release_80 (Download .tar.gz)

BranchProbabilityInfo.cpp @release_80raw · 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
//===- BranchProbabilityInfo.cpp - Branch Probability Analysis ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Loops should be simplified before this analysis.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <cstdint>
#include <iterator>
#include <utility>

using namespace llvm;

#define DEBUG_TYPE "branch-prob"

static cl::opt<bool> PrintBranchProb(
    "print-bpi", cl::init(false), cl::Hidden,
    cl::desc("Print the branch probability info."));

cl::opt<std::string> PrintBranchProbFuncName(
    "print-bpi-func-name", cl::Hidden,
    cl::desc("The option to specify the name of the function "
             "whose branch probability info is printed."));

INITIALIZE_PASS_BEGIN(BranchProbabilityInfoWrapperPass, "branch-prob",
                      "Branch Probability Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(BranchProbabilityInfoWrapperPass, "branch-prob",
                    "Branch Probability Analysis", false, true)

char BranchProbabilityInfoWrapperPass::ID = 0;

// Weights are for internal use only. They are used by heuristics to help to
// estimate edges' probability. Example:
//
// Using "Loop Branch Heuristics" we predict weights of edges for the
// block BB2.
//         ...
//          |
//          V
//         BB1<-+
//          |   |
//          |   | (Weight = 124)
//          V   |
//         BB2--+
//          |
//          | (Weight = 4)
//          V
//         BB3
//
// Probability of the edge BB2->BB1 = 124 / (124 + 4) = 0.96875
// Probability of the edge BB2->BB3 = 4 / (124 + 4) = 0.03125
static const uint32_t LBH_TAKEN_WEIGHT = 124;
static const uint32_t LBH_NONTAKEN_WEIGHT = 4;
// Unlikely edges within a loop are half as likely as other edges
static const uint32_t LBH_UNLIKELY_WEIGHT = 62;

/// Unreachable-terminating branch taken probability.
///
/// This is the probability for a branch being taken to a block that terminates
/// (eventually) in unreachable. These are predicted as unlikely as possible.
/// All reachable probability will equally share the remaining part.
static const BranchProbability UR_TAKEN_PROB = BranchProbability::getRaw(1);

/// Weight for a branch taken going into a cold block.
///
/// This is the weight for a branch taken toward a block marked
/// cold.  A block is marked cold if it's postdominated by a
/// block containing a call to a cold function.  Cold functions
/// are those marked with attribute 'cold'.
static const uint32_t CC_TAKEN_WEIGHT = 4;

/// Weight for a branch not-taken into a cold block.
///
/// This is the weight for a branch not taken toward a block marked
/// cold.
static const uint32_t CC_NONTAKEN_WEIGHT = 64;

static const uint32_t PH_TAKEN_WEIGHT = 20;
static const uint32_t PH_NONTAKEN_WEIGHT = 12;

static const uint32_t ZH_TAKEN_WEIGHT = 20;
static const uint32_t ZH_NONTAKEN_WEIGHT = 12;

static const uint32_t FPH_TAKEN_WEIGHT = 20;
static const uint32_t FPH_NONTAKEN_WEIGHT = 12;

/// Invoke-terminating normal branch taken weight
///
/// This is the weight for branching to the normal destination of an invoke
/// instruction. We expect this to happen most of the time. Set the weight to an
/// absurdly high value so that nested loops subsume it.
static const uint32_t IH_TAKEN_WEIGHT = 1024 * 1024 - 1;

/// Invoke-terminating normal branch not-taken weight.
///
/// This is the weight for branching to the unwind destination of an invoke
/// instruction. This is essentially never taken.
static const uint32_t IH_NONTAKEN_WEIGHT = 1;

/// Add \p BB to PostDominatedByUnreachable set if applicable.
void
BranchProbabilityInfo::updatePostDominatedByUnreachable(const BasicBlock *BB) {
  const Instruction *TI = BB->getTerminator();
  if (TI->getNumSuccessors() == 0) {
    if (isa<UnreachableInst>(TI) ||
        // If this block is terminated by a call to
        // @llvm.experimental.deoptimize then treat it like an unreachable since
        // the @llvm.experimental.deoptimize call is expected to practically
        // never execute.
        BB->getTerminatingDeoptimizeCall())
      PostDominatedByUnreachable.insert(BB);
    return;
  }

  // If the terminator is an InvokeInst, check only the normal destination block
  // as the unwind edge of InvokeInst is also very unlikely taken.
  if (auto *II = dyn_cast<InvokeInst>(TI)) {
    if (PostDominatedByUnreachable.count(II->getNormalDest()))
      PostDominatedByUnreachable.insert(BB);
    return;
  }

  for (auto *I : successors(BB))
    // If any of successor is not post dominated then BB is also not.
    if (!PostDominatedByUnreachable.count(I))
      return;

  PostDominatedByUnreachable.insert(BB);
}

/// Add \p BB to PostDominatedByColdCall set if applicable.
void
BranchProbabilityInfo::updatePostDominatedByColdCall(const BasicBlock *BB) {
  assert(!PostDominatedByColdCall.count(BB));
  const Instruction *TI = BB->getTerminator();
  if (TI->getNumSuccessors() == 0)
    return;

  // If all of successor are post dominated then BB is also done.
  if (llvm::all_of(successors(BB), [&](const BasicBlock *SuccBB) {
        return PostDominatedByColdCall.count(SuccBB);
      })) {
    PostDominatedByColdCall.insert(BB);
    return;
  }

  // If the terminator is an InvokeInst, check only the normal destination
  // block as the unwind edge of InvokeInst is also very unlikely taken.
  if (auto *II = dyn_cast<InvokeInst>(TI))
    if (PostDominatedByColdCall.count(II->getNormalDest())) {
      PostDominatedByColdCall.insert(BB);
      return;
    }

  // Otherwise, if the block itself contains a cold function, add it to the
  // set of blocks post-dominated by a cold call.
  for (auto &I : *BB)
    if (const CallInst *CI = dyn_cast<CallInst>(&I))
      if (CI->hasFnAttr(Attribute::Cold)) {
        PostDominatedByColdCall.insert(BB);
        return;
      }
}

/// Calculate edge weights for successors lead to unreachable.
///
/// Predict that a successor which leads necessarily to an
/// unreachable-terminated block as extremely unlikely.
bool BranchProbabilityInfo::calcUnreachableHeuristics(const BasicBlock *BB) {
  const Instruction *TI = BB->getTerminator();
  (void) TI;
  assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
  assert(!isa<InvokeInst>(TI) &&
         "Invokes should have already been handled by calcInvokeHeuristics");

  SmallVector<unsigned, 4> UnreachableEdges;
  SmallVector<unsigned, 4> ReachableEdges;

  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
    if (PostDominatedByUnreachable.count(*I))
      UnreachableEdges.push_back(I.getSuccessorIndex());
    else
      ReachableEdges.push_back(I.getSuccessorIndex());

  // Skip probabilities if all were reachable.
  if (UnreachableEdges.empty())
    return false;

  if (ReachableEdges.empty()) {
    BranchProbability Prob(1, UnreachableEdges.size());
    for (unsigned SuccIdx : UnreachableEdges)
      setEdgeProbability(BB, SuccIdx, Prob);
    return true;
  }

  auto UnreachableProb = UR_TAKEN_PROB;
  auto ReachableProb =
      (BranchProbability::getOne() - UR_TAKEN_PROB * UnreachableEdges.size()) /
      ReachableEdges.size();

  for (unsigned SuccIdx : UnreachableEdges)
    setEdgeProbability(BB, SuccIdx, UnreachableProb);
  for (unsigned SuccIdx : ReachableEdges)
    setEdgeProbability(BB, SuccIdx, ReachableProb);

  return true;
}

// Propagate existing explicit probabilities from either profile data or
// 'expect' intrinsic processing. Examine metadata against unreachable
// heuristic. The probability of the edge coming to unreachable block is
// set to min of metadata and unreachable heuristic.
bool BranchProbabilityInfo::calcMetadataWeights(const BasicBlock *BB) {
  const Instruction *TI = BB->getTerminator();
  assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
  if (!(isa<BranchInst>(TI) || isa<SwitchInst>(TI) || isa<IndirectBrInst>(TI)))
    return false;

  MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
  if (!WeightsNode)
    return false;

  // Check that the number of successors is manageable.
  assert(TI->getNumSuccessors() < UINT32_MAX && "Too many successors");

  // Ensure there are weights for all of the successors. Note that the first
  // operand to the metadata node is a name, not a weight.
  if (WeightsNode->getNumOperands() != TI->getNumSuccessors() + 1)
    return false;

  // Build up the final weights that will be used in a temporary buffer.
  // Compute the sum of all weights to later decide whether they need to
  // be scaled to fit in 32 bits.
  uint64_t WeightSum = 0;
  SmallVector<uint32_t, 2> Weights;
  SmallVector<unsigned, 2> UnreachableIdxs;
  SmallVector<unsigned, 2> ReachableIdxs;
  Weights.reserve(TI->getNumSuccessors());
  for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
    ConstantInt *Weight =
        mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
    if (!Weight)
      return false;
    assert(Weight->getValue().getActiveBits() <= 32 &&
           "Too many bits for uint32_t");
    Weights.push_back(Weight->getZExtValue());
    WeightSum += Weights.back();
    if (PostDominatedByUnreachable.count(TI->getSuccessor(i - 1)))
      UnreachableIdxs.push_back(i - 1);
    else
      ReachableIdxs.push_back(i - 1);
  }
  assert(Weights.size() == TI->getNumSuccessors() && "Checked above");

  // If the sum of weights does not fit in 32 bits, scale every weight down
  // accordingly.
  uint64_t ScalingFactor =
      (WeightSum > UINT32_MAX) ? WeightSum / UINT32_MAX + 1 : 1;

  if (ScalingFactor > 1) {
    WeightSum = 0;
    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
      Weights[i] /= ScalingFactor;
      WeightSum += Weights[i];
    }
  }
  assert(WeightSum <= UINT32_MAX &&
         "Expected weights to scale down to 32 bits");

  if (WeightSum == 0 || ReachableIdxs.size() == 0) {
    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
      Weights[i] = 1;
    WeightSum = TI->getNumSuccessors();
  }

  // Set the probability.
  SmallVector<BranchProbability, 2> BP;
  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
    BP.push_back({ Weights[i], static_cast<uint32_t>(WeightSum) });

  // Examine the metadata against unreachable heuristic.
  // If the unreachable heuristic is more strong then we use it for this edge.
  if (UnreachableIdxs.size() > 0 && ReachableIdxs.size() > 0) {
    auto ToDistribute = BranchProbability::getZero();
    auto UnreachableProb = UR_TAKEN_PROB;
    for (auto i : UnreachableIdxs)
      if (UnreachableProb < BP[i]) {
        ToDistribute += BP[i] - UnreachableProb;
        BP[i] = UnreachableProb;
      }

    // If we modified the probability of some edges then we must distribute
    // the difference between reachable blocks.
    if (ToDistribute > BranchProbability::getZero()) {
      BranchProbability PerEdge = ToDistribute / ReachableIdxs.size();
      for (auto i : ReachableIdxs)
        BP[i] += PerEdge;
    }
  }

  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
    setEdgeProbability(BB, i, BP[i]);

  return true;
}

/// Calculate edge weights for edges leading to cold blocks.
///
/// A cold block is one post-dominated by  a block with a call to a
/// cold function.  Those edges are unlikely to be taken, so we give
/// them relatively low weight.
///
/// Return true if we could compute the weights for cold edges.
/// Return false, otherwise.
bool BranchProbabilityInfo::calcColdCallHeuristics(const BasicBlock *BB) {
  const Instruction *TI = BB->getTerminator();
  (void) TI;
  assert(TI->getNumSuccessors() > 1 && "expected more than one successor!");
  assert(!isa<InvokeInst>(TI) &&
         "Invokes should have already been handled by calcInvokeHeuristics");

  // Determine which successors are post-dominated by a cold block.
  SmallVector<unsigned, 4> ColdEdges;
  SmallVector<unsigned, 4> NormalEdges;
  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
    if (PostDominatedByColdCall.count(*I))
      ColdEdges.push_back(I.getSuccessorIndex());
    else
      NormalEdges.push_back(I.getSuccessorIndex());

  // Skip probabilities if no cold edges.
  if (ColdEdges.empty())
    return false;

  if (NormalEdges.empty()) {
    BranchProbability Prob(1, ColdEdges.size());
    for (unsigned SuccIdx : ColdEdges)
      setEdgeProbability(BB, SuccIdx, Prob);
    return true;
  }

  auto ColdProb = BranchProbability::getBranchProbability(
      CC_TAKEN_WEIGHT,
      (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(ColdEdges.size()));
  auto NormalProb = BranchProbability::getBranchProbability(
      CC_NONTAKEN_WEIGHT,
      (CC_TAKEN_WEIGHT + CC_NONTAKEN_WEIGHT) * uint64_t(NormalEdges.size()));

  for (unsigned SuccIdx : ColdEdges)
    setEdgeProbability(BB, SuccIdx, ColdProb);
  for (unsigned SuccIdx : NormalEdges)
    setEdgeProbability(BB, SuccIdx, NormalProb);

  return true;
}

// Calculate Edge Weights using "Pointer Heuristics". Predict a comparison
// between two pointer or pointer and NULL will fail.
bool BranchProbabilityInfo::calcPointerHeuristics(const BasicBlock *BB) {
  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
  if (!BI || !BI->isConditional())
    return false;

  Value *Cond = BI->getCondition();
  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
  if (!CI || !CI->isEquality())
    return false;

  Value *LHS = CI->getOperand(0);

  if (!LHS->getType()->isPointerTy())
    return false;

  assert(CI->getOperand(1)->getType()->isPointerTy());

  // p != 0   ->   isProb = true
  // p == 0   ->   isProb = false
  // p != q   ->   isProb = true
  // p == q   ->   isProb = false;
  unsigned TakenIdx = 0, NonTakenIdx = 1;
  bool isProb = CI->getPredicate() == ICmpInst::ICMP_NE;
  if (!isProb)
    std::swap(TakenIdx, NonTakenIdx);

  BranchProbability TakenProb(PH_TAKEN_WEIGHT,
                              PH_TAKEN_WEIGHT + PH_NONTAKEN_WEIGHT);
  setEdgeProbability(BB, TakenIdx, TakenProb);
  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
  return true;
}

static int getSCCNum(const BasicBlock *BB,
                     const BranchProbabilityInfo::SccInfo &SccI) {
  auto SccIt = SccI.SccNums.find(BB);
  if (SccIt == SccI.SccNums.end())
    return -1;
  return SccIt->second;
}

// Consider any block that is an entry point to the SCC as a header.
static bool isSCCHeader(const BasicBlock *BB, int SccNum,
                        BranchProbabilityInfo::SccInfo &SccI) {
  assert(getSCCNum(BB, SccI) == SccNum);

  // Lazily compute the set of headers for a given SCC and cache the results
  // in the SccHeaderMap.
  if (SccI.SccHeaders.size() <= static_cast<unsigned>(SccNum))
    SccI.SccHeaders.resize(SccNum + 1);
  auto &HeaderMap = SccI.SccHeaders[SccNum];
  bool Inserted;
  BranchProbabilityInfo::SccHeaderMap::iterator HeaderMapIt;
  std::tie(HeaderMapIt, Inserted) = HeaderMap.insert(std::make_pair(BB, false));
  if (Inserted) {
    bool IsHeader = llvm::any_of(make_range(pred_begin(BB), pred_end(BB)),
                                 [&](const BasicBlock *Pred) {
                                   return getSCCNum(Pred, SccI) != SccNum;
                                 });
    HeaderMapIt->second = IsHeader;
    return IsHeader;
  } else
    return HeaderMapIt->second;
}

// Compute the unlikely successors to the block BB in the loop L, specifically
// those that are unlikely because this is a loop, and add them to the
// UnlikelyBlocks set.
static void
computeUnlikelySuccessors(const BasicBlock *BB, Loop *L,
                          SmallPtrSetImpl<const BasicBlock*> &UnlikelyBlocks) {
  // Sometimes in a loop we have a branch whose condition is made false by
  // taking it. This is typically something like
  //  int n = 0;
  //  while (...) {
  //    if (++n >= MAX) {
  //      n = 0;
  //    }
  //  }
  // In this sort of situation taking the branch means that at the very least it
  // won't be taken again in the next iteration of the loop, so we should
  // consider it less likely than a typical branch.
  //
  // We detect this by looking back through the graph of PHI nodes that sets the
  // value that the condition depends on, and seeing if we can reach a successor
  // block which can be determined to make the condition false.
  //
  // FIXME: We currently consider unlikely blocks to be half as likely as other
  // blocks, but if we consider the example above the likelyhood is actually
  // 1/MAX. We could therefore be more precise in how unlikely we consider
  // blocks to be, but it would require more careful examination of the form
  // of the comparison expression.
  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
  if (!BI || !BI->isConditional())
    return;

  // Check if the branch is based on an instruction compared with a constant
  CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
  if (!CI || !isa<Instruction>(CI->getOperand(0)) ||
      !isa<Constant>(CI->getOperand(1)))
    return;

  // Either the instruction must be a PHI, or a chain of operations involving
  // constants that ends in a PHI which we can then collapse into a single value
  // if the PHI value is known.
  Instruction *CmpLHS = dyn_cast<Instruction>(CI->getOperand(0));
  PHINode *CmpPHI = dyn_cast<PHINode>(CmpLHS);
  Constant *CmpConst = dyn_cast<Constant>(CI->getOperand(1));
  // Collect the instructions until we hit a PHI
  SmallVector<BinaryOperator *, 1> InstChain;
  while (!CmpPHI && CmpLHS && isa<BinaryOperator>(CmpLHS) &&
         isa<Constant>(CmpLHS->getOperand(1))) {
    // Stop if the chain extends outside of the loop
    if (!L->contains(CmpLHS))
      return;
    InstChain.push_back(cast<BinaryOperator>(CmpLHS));
    CmpLHS = dyn_cast<Instruction>(CmpLHS->getOperand(0));
    if (CmpLHS)
      CmpPHI = dyn_cast<PHINode>(CmpLHS);
  }
  if (!CmpPHI || !L->contains(CmpPHI))
    return;

  // Trace the phi node to find all values that come from successors of BB
  SmallPtrSet<PHINode*, 8> VisitedInsts;
  SmallVector<PHINode*, 8> WorkList;
  WorkList.push_back(CmpPHI);
  VisitedInsts.insert(CmpPHI);
  while (!WorkList.empty()) {
    PHINode *P = WorkList.back();
    WorkList.pop_back();
    for (BasicBlock *B : P->blocks()) {
      // Skip blocks that aren't part of the loop
      if (!L->contains(B))
        continue;
      Value *V = P->getIncomingValueForBlock(B);
      // If the source is a PHI add it to the work list if we haven't
      // already visited it.
      if (PHINode *PN = dyn_cast<PHINode>(V)) {
        if (VisitedInsts.insert(PN).second)
          WorkList.push_back(PN);
        continue;
      }
      // If this incoming value is a constant and B is a successor of BB, then
      // we can constant-evaluate the compare to see if it makes the branch be
      // taken or not.
      Constant *CmpLHSConst = dyn_cast<Constant>(V);
      if (!CmpLHSConst ||
          std::find(succ_begin(BB), succ_end(BB), B) == succ_end(BB))
        continue;
      // First collapse InstChain
      for (Instruction *I : llvm::reverse(InstChain)) {
        CmpLHSConst = ConstantExpr::get(I->getOpcode(), CmpLHSConst,
                                        cast<Constant>(I->getOperand(1)), true);
        if (!CmpLHSConst)
          break;
      }
      if (!CmpLHSConst)
        continue;
      // Now constant-evaluate the compare
      Constant *Result = ConstantExpr::getCompare(CI->getPredicate(),
                                                  CmpLHSConst, CmpConst, true);
      // If the result means we don't branch to the block then that block is
      // unlikely.
      if (Result &&
          ((Result->isZeroValue() && B == BI->getSuccessor(0)) ||
           (Result->isOneValue() && B == BI->getSuccessor(1))))
        UnlikelyBlocks.insert(B);
    }
  }
}

// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
// as taken, exiting edges as not-taken.
bool BranchProbabilityInfo::calcLoopBranchHeuristics(const BasicBlock *BB,
                                                     const LoopInfo &LI,
                                                     SccInfo &SccI) {
  int SccNum;
  Loop *L = LI.getLoopFor(BB);
  if (!L) {
    SccNum = getSCCNum(BB, SccI);
    if (SccNum < 0)
      return false;
  }

  SmallPtrSet<const BasicBlock*, 8> UnlikelyBlocks;
  if (L)
    computeUnlikelySuccessors(BB, L, UnlikelyBlocks);

  SmallVector<unsigned, 8> BackEdges;
  SmallVector<unsigned, 8> ExitingEdges;
  SmallVector<unsigned, 8> InEdges; // Edges from header to the loop.
  SmallVector<unsigned, 8> UnlikelyEdges;

  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
    // Use LoopInfo if we have it, otherwise fall-back to SCC info to catch
    // irreducible loops.
    if (L) {
      if (UnlikelyBlocks.count(*I) != 0)
        UnlikelyEdges.push_back(I.getSuccessorIndex());
      else if (!L->contains(*I))
        ExitingEdges.push_back(I.getSuccessorIndex());
      else if (L->getHeader() == *I)
        BackEdges.push_back(I.getSuccessorIndex());
      else
        InEdges.push_back(I.getSuccessorIndex());
    } else {
      if (getSCCNum(*I, SccI) != SccNum)
        ExitingEdges.push_back(I.getSuccessorIndex());
      else if (isSCCHeader(*I, SccNum, SccI))
        BackEdges.push_back(I.getSuccessorIndex());
      else
        InEdges.push_back(I.getSuccessorIndex());
    }
  }

  if (BackEdges.empty() && ExitingEdges.empty() && UnlikelyEdges.empty())
    return false;

  // Collect the sum of probabilities of back-edges/in-edges/exiting-edges, and
  // normalize them so that they sum up to one.
  unsigned Denom = (BackEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
                   (InEdges.empty() ? 0 : LBH_TAKEN_WEIGHT) +
                   (UnlikelyEdges.empty() ? 0 : LBH_UNLIKELY_WEIGHT) +
                   (ExitingEdges.empty() ? 0 : LBH_NONTAKEN_WEIGHT);

  if (uint32_t numBackEdges = BackEdges.size()) {
    BranchProbability TakenProb = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
    auto Prob = TakenProb / numBackEdges;
    for (unsigned SuccIdx : BackEdges)
      setEdgeProbability(BB, SuccIdx, Prob);
  }

  if (uint32_t numInEdges = InEdges.size()) {
    BranchProbability TakenProb = BranchProbability(LBH_TAKEN_WEIGHT, Denom);
    auto Prob = TakenProb / numInEdges;
    for (unsigned SuccIdx : InEdges)
      setEdgeProbability(BB, SuccIdx, Prob);
  }

  if (uint32_t numExitingEdges = ExitingEdges.size()) {
    BranchProbability NotTakenProb = BranchProbability(LBH_NONTAKEN_WEIGHT,
                                                       Denom);
    auto Prob = NotTakenProb / numExitingEdges;
    for (unsigned SuccIdx : ExitingEdges)
      setEdgeProbability(BB, SuccIdx, Prob);
  }

  if (uint32_t numUnlikelyEdges = UnlikelyEdges.size()) {
    BranchProbability UnlikelyProb = BranchProbability(LBH_UNLIKELY_WEIGHT,
                                                       Denom);
    auto Prob = UnlikelyProb / numUnlikelyEdges;
    for (unsigned SuccIdx : UnlikelyEdges)
      setEdgeProbability(BB, SuccIdx, Prob);
  }

  return true;
}

bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB,
                                               const TargetLibraryInfo *TLI) {
  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
  if (!BI || !BI->isConditional())
    return false;

  Value *Cond = BI->getCondition();
  ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
  if (!CI)
    return false;

  Value *RHS = CI->getOperand(1);
  ConstantInt *CV = dyn_cast<ConstantInt>(RHS);
  if (!CV)
    return false;

  // If the LHS is the result of AND'ing a value with a single bit bitmask,
  // we don't have information about probabilities.
  if (Instruction *LHS = dyn_cast<Instruction>(CI->getOperand(0)))
    if (LHS->getOpcode() == Instruction::And)
      if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(LHS->getOperand(1)))
        if (AndRHS->getValue().isPowerOf2())
          return false;

  // Check if the LHS is the return value of a library function
  LibFunc Func = NumLibFuncs;
  if (TLI)
    if (CallInst *Call = dyn_cast<CallInst>(CI->getOperand(0)))
      if (Function *CalledFn = Call->getCalledFunction())
        TLI->getLibFunc(*CalledFn, Func);

  bool isProb;
  if (Func == LibFunc_strcasecmp ||
      Func == LibFunc_strcmp ||
      Func == LibFunc_strncasecmp ||
      Func == LibFunc_strncmp ||
      Func == LibFunc_memcmp) {
    // strcmp and similar functions return zero, negative, or positive, if the
    // first string is equal, less, or greater than the second. We consider it
    // likely that the strings are not equal, so a comparison with zero is
    // probably false, but also a comparison with any other number is also
    // probably false given that what exactly is returned for nonzero values is
    // not specified. Any kind of comparison other than equality we know
    // nothing about.
    switch (CI->getPredicate()) {
    case CmpInst::ICMP_EQ:
      isProb = false;
      break;
    case CmpInst::ICMP_NE:
      isProb = true;
      break;
    default:
      return false;
    }
  } else if (CV->isZero()) {
    switch (CI->getPredicate()) {
    case CmpInst::ICMP_EQ:
      // X == 0   ->  Unlikely
      isProb = false;
      break;
    case CmpInst::ICMP_NE:
      // X != 0   ->  Likely
      isProb = true;
      break;
    case CmpInst::ICMP_SLT:
      // X < 0   ->  Unlikely
      isProb = false;
      break;
    case CmpInst::ICMP_SGT:
      // X > 0   ->  Likely
      isProb = true;
      break;
    default:
      return false;
    }
  } else if (CV->isOne() && CI->getPredicate() == CmpInst::ICMP_SLT) {
    // InstCombine canonicalizes X <= 0 into X < 1.
    // X <= 0   ->  Unlikely
    isProb = false;
  } else if (CV->isMinusOne()) {
    switch (CI->getPredicate()) {
    case CmpInst::ICMP_EQ:
      // X == -1  ->  Unlikely
      isProb = false;
      break;
    case CmpInst::ICMP_NE:
      // X != -1  ->  Likely
      isProb = true;
      break;
    case CmpInst::ICMP_SGT:
      // InstCombine canonicalizes X >= 0 into X > -1.
      // X >= 0   ->  Likely
      isProb = true;
      break;
    default:
      return false;
    }
  } else {
    return false;
  }

  unsigned TakenIdx = 0, NonTakenIdx = 1;

  if (!isProb)
    std::swap(TakenIdx, NonTakenIdx);

  BranchProbability TakenProb(ZH_TAKEN_WEIGHT,
                              ZH_TAKEN_WEIGHT + ZH_NONTAKEN_WEIGHT);
  setEdgeProbability(BB, TakenIdx, TakenProb);
  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
  return true;
}

bool BranchProbabilityInfo::calcFloatingPointHeuristics(const BasicBlock *BB) {
  const BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
  if (!BI || !BI->isConditional())
    return false;

  Value *Cond = BI->getCondition();
  FCmpInst *FCmp = dyn_cast<FCmpInst>(Cond);
  if (!FCmp)
    return false;

  bool isProb;
  if (FCmp->isEquality()) {
    // f1 == f2 -> Unlikely
    // f1 != f2 -> Likely
    isProb = !FCmp->isTrueWhenEqual();
  } else if (FCmp->getPredicate() == FCmpInst::FCMP_ORD) {
    // !isnan -> Likely
    isProb = true;
  } else if (FCmp->getPredicate() == FCmpInst::FCMP_UNO) {
    // isnan -> Unlikely
    isProb = false;
  } else {
    return false;
  }

  unsigned TakenIdx = 0, NonTakenIdx = 1;

  if (!isProb)
    std::swap(TakenIdx, NonTakenIdx);

  BranchProbability TakenProb(FPH_TAKEN_WEIGHT,
                              FPH_TAKEN_WEIGHT + FPH_NONTAKEN_WEIGHT);
  setEdgeProbability(BB, TakenIdx, TakenProb);
  setEdgeProbability(BB, NonTakenIdx, TakenProb.getCompl());
  return true;
}

bool BranchProbabilityInfo::calcInvokeHeuristics(const BasicBlock *BB) {
  const InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator());
  if (!II)
    return false;

  BranchProbability TakenProb(IH_TAKEN_WEIGHT,
                              IH_TAKEN_WEIGHT + IH_NONTAKEN_WEIGHT);
  setEdgeProbability(BB, 0 /*Index for Normal*/, TakenProb);
  setEdgeProbability(BB, 1 /*Index for Unwind*/, TakenProb.getCompl());
  return true;
}

void BranchProbabilityInfo::releaseMemory() {
  Probs.clear();
}

void BranchProbabilityInfo::print(raw_ostream &OS) const {
  OS << "---- Branch Probabilities ----\n";
  // We print the probabilities from the last function the analysis ran over,
  // or the function it is currently running over.
  assert(LastF && "Cannot print prior to running over a function");
  for (const auto &BI : *LastF) {
    for (succ_const_iterator SI = succ_begin(&BI), SE = succ_end(&BI); SI != SE;
         ++SI) {
      printEdgeProbability(OS << "  ", &BI, *SI);
    }
  }
}

bool BranchProbabilityInfo::
isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const {
  // Hot probability is at least 4/5 = 80%
  // FIXME: Compare against a static "hot" BranchProbability.
  return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
}

const BasicBlock *
BranchProbabilityInfo::getHotSucc(const BasicBlock *BB) const {
  auto MaxProb = BranchProbability::getZero();
  const BasicBlock *MaxSucc = nullptr;

  for (succ_const_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
    const BasicBlock *Succ = *I;
    auto Prob = getEdgeProbability(BB, Succ);
    if (Prob > MaxProb) {
      MaxProb = Prob;
      MaxSucc = Succ;
    }
  }

  // Hot probability is at least 4/5 = 80%
  if (MaxProb > BranchProbability(4, 5))
    return MaxSucc;

  return nullptr;
}

/// Get the raw edge probability for the edge. If can't find it, return a
/// default probability 1/N where N is the number of successors. Here an edge is
/// specified using PredBlock and an
/// index to the successors.
BranchProbability
BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
                                          unsigned IndexInSuccessors) const {
  auto I = Probs.find(std::make_pair(Src, IndexInSuccessors));

  if (I != Probs.end())
    return I->second;

  return {1, static_cast<uint32_t>(succ_size(Src))};
}

BranchProbability
BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
                                          succ_const_iterator Dst) const {
  return getEdgeProbability(Src, Dst.getSuccessorIndex());
}

/// Get the raw edge probability calculated for the block pair. This returns the
/// sum of all raw edge probabilities from Src to Dst.
BranchProbability
BranchProbabilityInfo::getEdgeProbability(const BasicBlock *Src,
                                          const BasicBlock *Dst) const {
  auto Prob = BranchProbability::getZero();
  bool FoundProb = false;
  for (succ_const_iterator I = succ_begin(Src), E = succ_end(Src); I != E; ++I)
    if (*I == Dst) {
      auto MapI = Probs.find(std::make_pair(Src, I.getSuccessorIndex()));
      if (MapI != Probs.end()) {
        FoundProb = true;
        Prob += MapI->second;
      }
    }
  uint32_t succ_num = std::distance(succ_begin(Src), succ_end(Src));
  return FoundProb ? Prob : BranchProbability(1, succ_num);
}

/// Set the edge probability for a given edge specified by PredBlock and an
/// index to the successors.
void BranchProbabilityInfo::setEdgeProbability(const BasicBlock *Src,
                                               unsigned IndexInSuccessors,
                                               BranchProbability Prob) {
  Probs[std::make_pair(Src, IndexInSuccessors)] = Prob;
  Handles.insert(BasicBlockCallbackVH(Src, this));
  LLVM_DEBUG(dbgs() << "set edge " << Src->getName() << " -> "
                    << IndexInSuccessors << " successor probability to " << Prob
                    << "\n");
}

raw_ostream &
BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS,
                                            const BasicBlock *Src,
                                            const BasicBlock *Dst) const {
  const BranchProbability Prob = getEdgeProbability(Src, Dst);
  OS << "edge " << Src->getName() << " -> " << Dst->getName()
     << " probability is " << Prob
     << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");

  return OS;
}

void BranchProbabilityInfo::eraseBlock(const BasicBlock *BB) {
  for (auto I = Probs.begin(), E = Probs.end(); I != E; ++I) {
    auto Key = I->first;
    if (Key.first == BB)
      Probs.erase(Key);
  }
}

void BranchProbabilityInfo::calculate(const Function &F, const LoopInfo &LI,
                                      const TargetLibraryInfo *TLI) {
  LLVM_DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
                    << " ----\n\n");
  LastF = &F; // Store the last function we ran on for printing.
  assert(PostDominatedByUnreachable.empty());
  assert(PostDominatedByColdCall.empty());

  // Record SCC numbers of blocks in the CFG to identify irreducible loops.
  // FIXME: We could only calculate this if the CFG is known to be irreducible
  // (perhaps cache this info in LoopInfo if we can easily calculate it there?).
  int SccNum = 0;
  SccInfo SccI;
  for (scc_iterator<const Function *> It = scc_begin(&F); !It.isAtEnd();
       ++It, ++SccNum) {
    // Ignore single-block SCCs since they either aren't loops or LoopInfo will
    // catch them.
    const std::vector<const BasicBlock *> &Scc = *It;
    if (Scc.size() == 1)
      continue;

    LLVM_DEBUG(dbgs() << "BPI: SCC " << SccNum << ":");
    for (auto *BB : Scc) {
      LLVM_DEBUG(dbgs() << " " << BB->getName());
      SccI.SccNums[BB] = SccNum;
    }
    LLVM_DEBUG(dbgs() << "\n");
  }

  // Walk the basic blocks in post-order so that we can build up state about
  // the successors of a block iteratively.
  for (auto BB : post_order(&F.getEntryBlock())) {
    LLVM_DEBUG(dbgs() << "Computing probabilities for " << BB->getName()
                      << "\n");
    updatePostDominatedByUnreachable(BB);
    updatePostDominatedByColdCall(BB);
    // If there is no at least two successors, no sense to set probability.
    if (BB->getTerminator()->getNumSuccessors() < 2)
      continue;
    if (calcMetadataWeights(BB))
      continue;
    if (calcInvokeHeuristics(BB))
      continue;
    if (calcUnreachableHeuristics(BB))
      continue;
    if (calcColdCallHeuristics(BB))
      continue;
    if (calcLoopBranchHeuristics(BB, LI, SccI))
      continue;
    if (calcPointerHeuristics(BB))
      continue;
    if (calcZeroHeuristics(BB, TLI))
      continue;
    if (calcFloatingPointHeuristics(BB))
      continue;
  }

  PostDominatedByUnreachable.clear();
  PostDominatedByColdCall.clear();

  if (PrintBranchProb &&
      (PrintBranchProbFuncName.empty() ||
       F.getName().equals(PrintBranchProbFuncName))) {
    print(dbgs());
  }
}

void BranchProbabilityInfoWrapperPass::getAnalysisUsage(
    AnalysisUsage &AU) const {
  // We require DT so it's available when LI is available. The LI updating code
  // asserts that DT is also present so if we don't make sure that we have DT
  // here, that assert will trigger.
  AU.addRequired<DominatorTreeWrapperPass>();
  AU.addRequired<LoopInfoWrapperPass>();
  AU.addRequired<TargetLibraryInfoWrapperPass>();
  AU.setPreservesAll();
}

bool BranchProbabilityInfoWrapperPass::runOnFunction(Function &F) {
  const LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
  const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
  BPI.calculate(F, LI, &TLI);
  return false;
}

void BranchProbabilityInfoWrapperPass::releaseMemory() { BPI.releaseMemory(); }

void BranchProbabilityInfoWrapperPass::print(raw_ostream &OS,
                                             const Module *) const {
  BPI.print(OS);
}

AnalysisKey BranchProbabilityAnalysis::Key;
BranchProbabilityInfo
BranchProbabilityAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
  BranchProbabilityInfo BPI;
  BPI.calculate(F, AM.getResult<LoopAnalysis>(F), &AM.getResult<TargetLibraryAnalysis>(F));
  return BPI;
}

PreservedAnalyses
BranchProbabilityPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
  OS << "Printing analysis results of BPI for function "
     << "'" << F.getName() << "':"
     << "\n";
  AM.getResult<BranchProbabilityAnalysis>(F).print(OS);
  return PreservedAnalyses::all();
}