llvm.org GIT mirror llvm / 71f7f73 lib / CodeGen / SplitKit.cpp
71f7f73

Tree @71f7f73 (Download .tar.gz)

SplitKit.cpp @71f7f73raw · 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
//===---------- SplitKit.cpp - Toolkit for splitting live ranges ----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the SplitAnalysis class as well as mutator functions for
// live range splitting.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "splitter"
#include "SplitKit.h"
#include "VirtRegMap.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"

using namespace llvm;

static cl::opt<bool>
AllowSplit("spiller-splits-edges",
           cl::desc("Allow critical edge splitting during spilling"));

//===----------------------------------------------------------------------===//
//                                 Split Analysis
//===----------------------------------------------------------------------===//

SplitAnalysis::SplitAnalysis(const MachineFunction &mf,
                             const LiveIntervals &lis,
                             const MachineLoopInfo &mli)
  : mf_(mf),
    lis_(lis),
    loops_(mli),
    tii_(*mf.getTarget().getInstrInfo()),
    curli_(0) {}

void SplitAnalysis::clear() {
  usingInstrs_.clear();
  usingBlocks_.clear();
  usingLoops_.clear();
  curli_ = 0;
}

bool SplitAnalysis::canAnalyzeBranch(const MachineBasicBlock *MBB) {
  MachineBasicBlock *T, *F;
  SmallVector<MachineOperand, 4> Cond;
  return !tii_.AnalyzeBranch(const_cast<MachineBasicBlock&>(*MBB), T, F, Cond);
}

/// analyzeUses - Count instructions, basic blocks, and loops using curli.
void SplitAnalysis::analyzeUses() {
  const MachineRegisterInfo &MRI = mf_.getRegInfo();
  for (MachineRegisterInfo::reg_iterator I = MRI.reg_begin(curli_->reg);
       MachineInstr *MI = I.skipInstruction();) {
    if (MI->isDebugValue() || !usingInstrs_.insert(MI))
      continue;
    MachineBasicBlock *MBB = MI->getParent();
    if (usingBlocks_[MBB]++)
      continue;
    if (MachineLoop *Loop = loops_.getLoopFor(MBB))
      usingLoops_[Loop]++;
  }
  DEBUG(dbgs() << "  counted "
               << usingInstrs_.size() << " instrs, "
               << usingBlocks_.size() << " blocks, "
               << usingLoops_.size()  << " loops.\n");
}

/// removeUse - Update statistics by noting that MI no longer uses curli.
void SplitAnalysis::removeUse(const MachineInstr *MI) {
  if (!usingInstrs_.erase(MI))
    return;

  // Decrement MBB count.
  const MachineBasicBlock *MBB = MI->getParent();
  BlockCountMap::iterator bi = usingBlocks_.find(MBB);
  assert(bi != usingBlocks_.end() && "MBB missing");
  assert(bi->second && "0 count in map");
  if (--bi->second)
    return;
  // No more uses in MBB.
  usingBlocks_.erase(bi);

  // Decrement loop count.
  MachineLoop *Loop = loops_.getLoopFor(MBB);
  if (!Loop)
    return;
  LoopCountMap::iterator li = usingLoops_.find(Loop);
  assert(li != usingLoops_.end() && "Loop missing");
  assert(li->second && "0 count in map");
  if (--li->second)
    return;
  // No more blocks in Loop.
  usingLoops_.erase(li);
}

// Get three sets of basic blocks surrounding a loop: Blocks inside the loop,
// predecessor blocks, and exit blocks.
void SplitAnalysis::getLoopBlocks(const MachineLoop *Loop, LoopBlocks &Blocks) {
  Blocks.clear();

  // Blocks in the loop.
  Blocks.Loop.insert(Loop->block_begin(), Loop->block_end());

  // Predecessor blocks.
  const MachineBasicBlock *Header = Loop->getHeader();
  for (MachineBasicBlock::const_pred_iterator I = Header->pred_begin(),
       E = Header->pred_end(); I != E; ++I)
    if (!Blocks.Loop.count(*I))
      Blocks.Preds.insert(*I);

  // Exit blocks.
  for (MachineLoop::block_iterator I = Loop->block_begin(),
       E = Loop->block_end(); I != E; ++I) {
    const MachineBasicBlock *MBB = *I;
    for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
       SE = MBB->succ_end(); SI != SE; ++SI)
      if (!Blocks.Loop.count(*SI))
        Blocks.Exits.insert(*SI);
  }
}

/// analyzeLoopPeripheralUse - Return an enum describing how curli_ is used in
/// and around the Loop.
SplitAnalysis::LoopPeripheralUse SplitAnalysis::
analyzeLoopPeripheralUse(const SplitAnalysis::LoopBlocks &Blocks) {
  LoopPeripheralUse use = ContainedInLoop;
  for (BlockCountMap::iterator I = usingBlocks_.begin(), E = usingBlocks_.end();
       I != E; ++I) {
    const MachineBasicBlock *MBB = I->first;
    // Is this a peripheral block?
    if (use < MultiPeripheral &&
        (Blocks.Preds.count(MBB) || Blocks.Exits.count(MBB))) {
      if (I->second > 1) use = MultiPeripheral;
      else               use = SinglePeripheral;
      continue;
    }
    // Is it a loop block?
    if (Blocks.Loop.count(MBB))
      continue;
    // It must be an unrelated block.
    return OutsideLoop;
  }
  return use;
}

/// getCriticalExits - It may be necessary to partially break critical edges
/// leaving the loop if an exit block has phi uses of curli. Collect the exit
/// blocks that need special treatment into CriticalExits.
void SplitAnalysis::getCriticalExits(const SplitAnalysis::LoopBlocks &Blocks,
                                     BlockPtrSet &CriticalExits) {
  CriticalExits.clear();

  // A critical exit block contains a phi def of curli, and has a predecessor
  // that is not in the loop nor a loop predecessor.
  // For such an exit block, the edges carrying the new variable must be moved
  // to a new pre-exit block.
  for (BlockPtrSet::iterator I = Blocks.Exits.begin(), E = Blocks.Exits.end();
       I != E; ++I) {
    const MachineBasicBlock *Succ = *I;
    SlotIndex SuccIdx = lis_.getMBBStartIdx(Succ);
    VNInfo *SuccVNI = curli_->getVNInfoAt(SuccIdx);
    // This exit may not have curli live in at all. No need to split.
    if (!SuccVNI)
      continue;
    // If this is not a PHI def, it is either using a value from before the
    // loop, or a value defined inside the loop. Both are safe.
    if (!SuccVNI->isPHIDef() || SuccVNI->def.getBaseIndex() != SuccIdx)
      continue;
    // This exit block does have a PHI. Does it also have a predecessor that is
    // not a loop block or loop predecessor?
    for (MachineBasicBlock::const_pred_iterator PI = Succ->pred_begin(),
         PE = Succ->pred_end(); PI != PE; ++PI) {
      const MachineBasicBlock *Pred = *PI;
      if (Blocks.Loop.count(Pred) || Blocks.Preds.count(Pred))
        continue;
      // This is a critical exit block, and we need to split the exit edge.
      CriticalExits.insert(Succ);
      break;
    }
  }
}

/// canSplitCriticalExits - Return true if it is possible to insert new exit
/// blocks before the blocks in CriticalExits.
bool
SplitAnalysis::canSplitCriticalExits(const SplitAnalysis::LoopBlocks &Blocks,
                                     BlockPtrSet &CriticalExits) {
  // If we don't allow critical edge splitting, require no critical exits.
  if (!AllowSplit)
    return CriticalExits.empty();

  for (BlockPtrSet::iterator I = CriticalExits.begin(), E = CriticalExits.end();
       I != E; ++I) {
    const MachineBasicBlock *Succ = *I;
    // We want to insert a new pre-exit MBB before Succ, and change all the
    // in-loop blocks to branch to the pre-exit instead of Succ.
    // Check that all the in-loop predecessors can be changed.
    for (MachineBasicBlock::const_pred_iterator PI = Succ->pred_begin(),
         PE = Succ->pred_end(); PI != PE; ++PI) {
      const MachineBasicBlock *Pred = *PI;
      // The external predecessors won't be altered.
      if (!Blocks.Loop.count(Pred) && !Blocks.Preds.count(Pred))
        continue;
      if (!canAnalyzeBranch(Pred))
        return false;
    }

    // If Succ's layout predecessor falls through, that too must be analyzable.
    // We need to insert the pre-exit block in the gap.
    MachineFunction::const_iterator MFI = Succ;
    if (MFI == mf_.begin())
      continue;
    if (!canAnalyzeBranch(--MFI))
      return false;
  }
  // No problems found.
  return true;
}

void SplitAnalysis::analyze(const LiveInterval *li) {
  clear();
  curli_ = li;
  analyzeUses();
}

const MachineLoop *SplitAnalysis::getBestSplitLoop() {
  assert(curli_ && "Call analyze() before getBestSplitLoop");
  if (usingLoops_.empty())
    return 0;

  LoopPtrSet Loops, SecondLoops;
  LoopBlocks Blocks;
  BlockPtrSet CriticalExits;

  // Find first-class and second class candidate loops.
  // We prefer to split around loops where curli is used outside the periphery.
  for (LoopCountMap::const_iterator I = usingLoops_.begin(),
       E = usingLoops_.end(); I != E; ++I) {
    const MachineLoop *Loop = I->first;
    getLoopBlocks(Loop, Blocks);

    // FIXME: We need an SSA updater to properly handle multiple exit blocks.
    if (Blocks.Exits.size() > 1) {
      DEBUG(dbgs() << "  multiple exits from " << *Loop);
      continue;
    }

    LoopPtrSet *LPS = 0;
    switch(analyzeLoopPeripheralUse(Blocks)) {
    case OutsideLoop:
      LPS = &Loops;
      break;
    case MultiPeripheral:
      LPS = &SecondLoops;
      break;
    case ContainedInLoop:
      DEBUG(dbgs() << "  contained in " << *Loop);
      continue;
    case SinglePeripheral:
      DEBUG(dbgs() << "  single peripheral use in " << *Loop);
      continue;
    }
    // Will it be possible to split around this loop?
    getCriticalExits(Blocks, CriticalExits);
    DEBUG(dbgs() << "  " << CriticalExits.size() << " critical exits from "
                 << *Loop);
    if (!canSplitCriticalExits(Blocks, CriticalExits))
      continue;
    // This is a possible split.
    assert(LPS);
    LPS->insert(Loop);
  }

  DEBUG(dbgs() << "  getBestSplitLoop found " << Loops.size() << " + "
               << SecondLoops.size() << " candidate loops.\n");

  // If there are no first class loops available, look at second class loops.
  if (Loops.empty())
    Loops = SecondLoops;

  if (Loops.empty())
    return 0;

  // Pick the earliest loop.
  // FIXME: Are there other heuristics to consider?
  const MachineLoop *Best = 0;
  SlotIndex BestIdx;
  for (LoopPtrSet::const_iterator I = Loops.begin(), E = Loops.end(); I != E;
       ++I) {
    SlotIndex Idx = lis_.getMBBStartIdx((*I)->getHeader());
    if (!Best || Idx < BestIdx)
      Best = *I, BestIdx = Idx;
  }
  DEBUG(dbgs() << "  getBestSplitLoop found " << *Best);
  return Best;
}

/// getMultiUseBlocks - if curli has more than one use in a basic block, it
/// may be an advantage to split curli for the duration of the block.
bool SplitAnalysis::getMultiUseBlocks(BlockPtrSet &Blocks) {
  // If curli is local to one block, there is no point to splitting it.
  if (usingBlocks_.size() <= 1)
    return false;
  // Add blocks with multiple uses.
  for (BlockCountMap::iterator I = usingBlocks_.begin(), E = usingBlocks_.end();
       I != E; ++I)
    switch (I->second) {
    case 0:
    case 1:
      continue;
    case 2: {
      // It doesn't pay to split a 2-instr block if it redefines curli.
      VNInfo *VN1 = curli_->getVNInfoAt(lis_.getMBBStartIdx(I->first));
      VNInfo *VN2 =
        curli_->getVNInfoAt(lis_.getMBBEndIdx(I->first).getPrevIndex());
      // live-in and live-out with a different value.
      if (VN1 && VN2 && VN1 != VN2)
        continue;
    } // Fall through.
    default:
      Blocks.insert(I->first);
    }
  return !Blocks.empty();
}

//===----------------------------------------------------------------------===//
//                               LiveIntervalMap
//===----------------------------------------------------------------------===//

// defValue - Introduce a li_ def for ParentVNI that could be later than
// ParentVNI->def.
VNInfo *LiveIntervalMap::defValue(const VNInfo *ParentVNI, SlotIndex Idx) {
  assert(ParentVNI && "Mapping  NULL value");
  assert(Idx.isValid() && "Invalid SlotIndex");
  assert(parentli_.getVNInfoAt(Idx) == ParentVNI && "Bad ParentVNI");

  // Is this a simple 1-1 mapping? Not likely.
  if (Idx == ParentVNI->def)
    return mapValue(ParentVNI, Idx);

  // This is a complex def. Mark with a NULL in valueMap.
  VNInfo *OldVNI =
    valueMap_.insert(
      ValueMap::value_type(ParentVNI, static_cast<VNInfo *>(0))).first->second;
      // The static_cast<VNInfo *> is only needed to work around a bug in an
      // old version of the C++0x standard which the following compilers
      // implemented and have yet to fix:
      //
      // Microsoft Visual Studio 2010 Version 10.0.30319.1 RTMRel
      // Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.30319.01
      //
      // If/When we move to C++0x, this can be replaced by nullptr.
  (void)OldVNI;
  assert(OldVNI == 0 && "Simple/Complex values mixed");

  // Should we insert a minimal snippet of VNI LiveRange, or can we count on
  // callers to do that? We need it for lookups of complex values.
  VNInfo *VNI = li_.getNextValue(Idx, 0, true, lis_.getVNInfoAllocator());
  return VNI;
}

// mapValue - Find the mapped value for ParentVNI at Idx.
// Potentially create phi-def values.
VNInfo *LiveIntervalMap::mapValue(const VNInfo *ParentVNI, SlotIndex Idx) {
  assert(ParentVNI && "Mapping  NULL value");
  assert(Idx.isValid() && "Invalid SlotIndex");
  assert(parentli_.getVNInfoAt(Idx) == ParentVNI && "Bad ParentVNI");

  // Use insert for lookup, so we can add missing values with a second lookup.
  std::pair<ValueMap::iterator,bool> InsP =
    valueMap_.insert(ValueMap::value_type(ParentVNI, static_cast<VNInfo *>(0)));
    // The static_cast<VNInfo *> is only needed to work around a bug in an
    // old version of the C++0x standard which the following compilers
    // implemented and have yet to fix:
    //
    // Microsoft Visual Studio 2010 Version 10.0.30319.1 RTMRel
    // Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.30319.01
    //
    // If/When we move to C++0x, this can be replaced by nullptr.

  // This was an unknown value. Create a simple mapping.
  if (InsP.second)
    return InsP.first->second = li_.createValueCopy(ParentVNI,
                                                    lis_.getVNInfoAllocator());
  // This was a simple mapped value.
  if (InsP.first->second)
    return InsP.first->second;

  // This is a complex mapped value. There may be multiple defs, and we may need
  // to create phi-defs.
  MachineBasicBlock *IdxMBB = lis_.getMBBFromIndex(Idx);
  assert(IdxMBB && "No MBB at Idx");

  // Is there a def in the same MBB we can extend?
  if (VNInfo *VNI = extendTo(IdxMBB, Idx))
    return VNI;

  // Now for the fun part. We know that ParentVNI potentially has multiple defs,
  // and we may need to create even more phi-defs to preserve VNInfo SSA form.
  // Perform a depth-first search for predecessor blocks where we know the
  // dominating VNInfo. Insert phi-def VNInfos along the path back to IdxMBB.

  // Track MBBs where we have created or learned the dominating value.
  // This may change during the DFS as we create new phi-defs.
  typedef DenseMap<MachineBasicBlock*, VNInfo*> MBBValueMap;
  MBBValueMap DomValue;

  for (idf_iterator<MachineBasicBlock*>
         IDFI = idf_begin(IdxMBB),
         IDFE = idf_end(IdxMBB); IDFI != IDFE;) {
    MachineBasicBlock *MBB = *IDFI;
    SlotIndex End = lis_.getMBBEndIdx(MBB);

    // We are operating on the restricted CFG where ParentVNI is live.
    if (parentli_.getVNInfoAt(End.getPrevSlot()) != ParentVNI) {
      IDFI.skipChildren();
      continue;
    }

    // Do we have a dominating value in this block?
    VNInfo *VNI = extendTo(MBB, End);
    if (!VNI) {
      ++IDFI;
      continue;
    }

    // Yes, VNI dominates MBB. Track the path back to IdxMBB, creating phi-defs
    // as needed along the way.
    for (unsigned PI = IDFI.getPathLength()-1; PI != 0; --PI) {
      // Start from MBB's immediate successor. End at IdxMBB.
      MachineBasicBlock *Succ = IDFI.getPath(PI-1);
      std::pair<MBBValueMap::iterator, bool> InsP =
        DomValue.insert(MBBValueMap::value_type(Succ, VNI));

      // This is the first time we backtrack to Succ.
      if (InsP.second)
        continue;

      // We reached Succ again with the same VNI. Nothing is going to change.
      VNInfo *OVNI = InsP.first->second;
      if (OVNI == VNI)
        break;

      // Succ already has a phi-def. No need to continue.
      SlotIndex Start = lis_.getMBBStartIdx(Succ);
      if (OVNI->def == Start)
        break;

      // We have a collision between the old and new VNI at Succ. That means
      // neither dominates and we need a new phi-def.
      VNI = li_.getNextValue(Start, 0, true, lis_.getVNInfoAllocator());
      VNI->setIsPHIDef(true);
      InsP.first->second = VNI;

      // Replace OVNI with VNI in the remaining path.
      for (; PI > 1 ; --PI) {
        MBBValueMap::iterator I = DomValue.find(IDFI.getPath(PI-2));
        if (I == DomValue.end() || I->second != OVNI)
          break;
        I->second = VNI;
      }
    }

    // No need to search the children, we found a dominating value.
    IDFI.skipChildren();
  }

  // The search should at least find a dominating value for IdxMBB.
  assert(!DomValue.empty() && "Couldn't find a reaching definition");

  // Since we went through the trouble of a full DFS visiting all reaching defs,
  // the values in DomValue are now accurate. No more phi-defs are needed for
  // these blocks, so we can color the live ranges.
  // This makes the next mapValue call much faster.
  VNInfo *IdxVNI = 0;
  for (MBBValueMap::iterator I = DomValue.begin(), E = DomValue.end(); I != E;
       ++I) {
     MachineBasicBlock *MBB = I->first;
     VNInfo *VNI = I->second;
     SlotIndex Start = lis_.getMBBStartIdx(MBB);
     if (MBB == IdxMBB) {
       // Don't add full liveness to IdxMBB, stop at Idx.
       if (Start != Idx)
         li_.addRange(LiveRange(Start, Idx, VNI));
       // The caller had better add some liveness to IdxVNI, or it leaks.
       IdxVNI = VNI;
     } else
      li_.addRange(LiveRange(Start, lis_.getMBBEndIdx(MBB), VNI));
  }

  assert(IdxVNI && "Didn't find value for Idx");
  return IdxVNI;
}

// extendTo - Find the last li_ value defined in MBB at or before Idx. The
// parentli_ is assumed to be live at Idx. Extend the live range to Idx.
// Return the found VNInfo, or NULL.
VNInfo *LiveIntervalMap::extendTo(MachineBasicBlock *MBB, SlotIndex Idx) {
  LiveInterval::iterator I = std::upper_bound(li_.begin(), li_.end(), Idx);
  if (I == li_.begin())
    return 0;
  --I;
  if (I->start < lis_.getMBBStartIdx(MBB))
    return 0;
  if (I->end < Idx)
    I->end = Idx;
  return I->valno;
}

// addSimpleRange - Add a simple range from parentli_ to li_.
// ParentVNI must be live in the [Start;End) interval.
void LiveIntervalMap::addSimpleRange(SlotIndex Start, SlotIndex End,
                                     const VNInfo *ParentVNI) {
  VNInfo *VNI = mapValue(ParentVNI, Start);
  // A simple mappoing is easy.
  if (VNI->def == ParentVNI->def) {
    li_.addRange(LiveRange(Start, End, VNI));
    return;
  }

  // ParentVNI is a complex value. We must map per MBB.
  MachineFunction::iterator MBB = lis_.getMBBFromIndex(Start);
  MachineFunction::iterator MBBE = lis_.getMBBFromIndex(End);

  if (MBB == MBBE) {
    li_.addRange(LiveRange(Start, End, VNI));
    return;
  }

  // First block.
  li_.addRange(LiveRange(Start, lis_.getMBBEndIdx(MBB), VNI));

  // Run sequence of full blocks.
  for (++MBB; MBB != MBBE; ++MBB) {
    Start = lis_.getMBBStartIdx(MBB);
    li_.addRange(LiveRange(Start, lis_.getMBBEndIdx(MBB),
                           mapValue(ParentVNI, Start)));
  }

  // Final block.
  Start = lis_.getMBBStartIdx(MBB);
  if (Start != End)
    li_.addRange(LiveRange(Start, End, mapValue(ParentVNI, Start)));
}

/// addRange - Add live ranges to li_ where [Start;End) intersects parentli_.
/// All needed values whose def is not inside [Start;End) must be defined
/// beforehand so mapValue will work.
void LiveIntervalMap::addRange(SlotIndex Start, SlotIndex End) {
  LiveInterval::const_iterator B = parentli_.begin(), E = parentli_.end();
  LiveInterval::const_iterator I = std::lower_bound(B, E, Start);

  // Check if --I begins before Start and overlaps.
  if (I != B) {
    --I;
    if (I->end > Start)
      addSimpleRange(Start, std::min(End, I->end), I->valno);
    ++I;
  }

  // The remaining ranges begin after Start.
  for (;I != E && I->start < End; ++I)
    addSimpleRange(I->start, std::min(End, I->end), I->valno);
}

//===----------------------------------------------------------------------===//
//                               Split Editor
//===----------------------------------------------------------------------===//

/// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
SplitEditor::SplitEditor(SplitAnalysis &sa, LiveIntervals &lis, VirtRegMap &vrm,
                         SmallVectorImpl<LiveInterval*> &intervals)
  : sa_(sa), lis_(lis), vrm_(vrm),
    mri_(vrm.getMachineFunction().getRegInfo()),
    tii_(*vrm.getMachineFunction().getTarget().getInstrInfo()),
    curli_(sa_.getCurLI()),
    dupli_(0), openli_(0),
    intervals_(intervals),
    firstInterval(intervals_.size())
{
  assert(curli_ && "SplitEditor created from empty SplitAnalysis");

  // Make sure curli_ is assigned a stack slot, so all our intervals get the
  // same slot as curli_.
  if (vrm_.getStackSlot(curli_->reg) == VirtRegMap::NO_STACK_SLOT)
    vrm_.assignVirt2StackSlot(curli_->reg);

}

LiveInterval *SplitEditor::createInterval() {
  unsigned curli = sa_.getCurLI()->reg;
  unsigned Reg = mri_.createVirtualRegister(mri_.getRegClass(curli));
  LiveInterval &Intv = lis_.getOrCreateInterval(Reg);
  vrm_.grow();
  vrm_.assignVirt2StackSlot(Reg, vrm_.getStackSlot(curli));
  return &Intv;
}

LiveInterval *SplitEditor::getDupLI() {
  if (!dupli_) {
    // Create an interval for dupli that is a copy of curli.
    dupli_ = createInterval();
    dupli_->Copy(*curli_, &mri_, lis_.getVNInfoAllocator());
  }
  return dupli_;
}

VNInfo *SplitEditor::mapValue(const VNInfo *curliVNI) {
  VNInfo *&VNI = valueMap_[curliVNI];
  if (!VNI)
    VNI = openli_->createValueCopy(curliVNI, lis_.getVNInfoAllocator());
  return VNI;
}

/// Insert a COPY instruction curli -> li. Allocate a new value from li
/// defined by the COPY. Note that rewrite() will deal with the curli
/// register, so this function can be used to copy from any interval - openli,
/// curli, or dupli.
VNInfo *SplitEditor::insertCopy(LiveInterval &LI,
                                MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator I) {
  MachineInstr *MI = BuildMI(MBB, I, DebugLoc(), tii_.get(TargetOpcode::COPY),
                             LI.reg).addReg(curli_->reg);
  SlotIndex DefIdx = lis_.InsertMachineInstrInMaps(MI).getDefIndex();
  return LI.getNextValue(DefIdx, MI, true, lis_.getVNInfoAllocator());
}

/// Create a new virtual register and live interval.
void SplitEditor::openIntv() {
  assert(!openli_ && "Previous LI not closed before openIntv");
  openli_ = createInterval();
  intervals_.push_back(openli_);
  liveThrough_ = false;
}

/// enterIntvBefore - Enter openli before the instruction at Idx. If curli is
/// not live before Idx, a COPY is not inserted.
void SplitEditor::enterIntvBefore(SlotIndex Idx) {
  assert(openli_ && "openIntv not called before enterIntvBefore");

  // Copy from curli_ if it is live.
  if (VNInfo *CurVNI = curli_->getVNInfoAt(Idx.getUseIndex())) {
    MachineInstr *MI = lis_.getInstructionFromIndex(Idx);
    assert(MI && "enterIntvBefore called with invalid index");
    VNInfo *VNI = insertCopy(*openli_, *MI->getParent(), MI);
    openli_->addRange(LiveRange(VNI->def, Idx.getDefIndex(), VNI));

    // Make sure CurVNI is properly mapped.
    VNInfo *&mapVNI = valueMap_[CurVNI];
    // We dont have SSA update yet, so only one entry per value is allowed.
    assert(!mapVNI && "enterIntvBefore called more than once for the same value");
    mapVNI = VNI;
  }
  DEBUG(dbgs() << "    enterIntvBefore " << Idx << ": " << *openli_ << '\n');
}

/// enterIntvAtEnd - Enter openli at the end of MBB.
/// PhiMBB is a successor inside openli where a PHI value is created.
/// Currently, all entries must share the same PhiMBB.
void SplitEditor::enterIntvAtEnd(MachineBasicBlock &A, MachineBasicBlock &B) {
  assert(openli_ && "openIntv not called before enterIntvAtEnd");

  SlotIndex EndA = lis_.getMBBEndIdx(&A);
  VNInfo *CurVNIA = curli_->getVNInfoAt(EndA.getPrevIndex());
  if (!CurVNIA) {
    DEBUG(dbgs() << "    enterIntvAtEnd, curli not live out of BB#"
                 << A.getNumber() << ".\n");
    return;
  }

  // Add a phi kill value and live range out of A.
  VNInfo *VNIA = insertCopy(*openli_, A, A.getFirstTerminator());
  openli_->addRange(LiveRange(VNIA->def, EndA, VNIA));

  // FIXME: If this is the only entry edge, we don't need the extra PHI value.
  // FIXME: If there are multiple entry blocks (so not a loop), we need proper
  // SSA update.

  // Now look at the start of B.
  SlotIndex StartB = lis_.getMBBStartIdx(&B);
  SlotIndex EndB = lis_.getMBBEndIdx(&B);
  const LiveRange *CurB = curli_->getLiveRangeContaining(StartB);
  if (!CurB) {
    DEBUG(dbgs() << "    enterIntvAtEnd: curli not live in to BB#"
                 << B.getNumber() << ".\n");
    return;
  }

  VNInfo *VNIB = openli_->getVNInfoAt(StartB);
  if (!VNIB) {
    // Create a phi value.
    VNIB = openli_->getNextValue(SlotIndex(StartB, true), 0, false,
                                 lis_.getVNInfoAllocator());
    VNIB->setIsPHIDef(true);
    VNInfo *&mapVNI = valueMap_[CurB->valno];
    if (mapVNI) {
      // Multiple copies - must create PHI value.
      abort();
    } else {
      // This is the first copy of dupLR. Mark the mapping.
      mapVNI = VNIB;
    }

  }

  DEBUG(dbgs() << "    enterIntvAtEnd: " << *openli_ << '\n');
}

/// useIntv - indicate that all instructions in MBB should use openli.
void SplitEditor::useIntv(const MachineBasicBlock &MBB) {
  useIntv(lis_.getMBBStartIdx(&MBB), lis_.getMBBEndIdx(&MBB));
}

void SplitEditor::useIntv(SlotIndex Start, SlotIndex End) {
  assert(openli_ && "openIntv not called before useIntv");

  // Map the curli values from the interval into openli_
  LiveInterval::const_iterator B = curli_->begin(), E = curli_->end();
  LiveInterval::const_iterator I = std::lower_bound(B, E, Start);

  if (I != B) {
    --I;
    // I begins before Start, but overlaps.
    if (I->end > Start)
      openli_->addRange(LiveRange(Start, std::min(End, I->end),
                        mapValue(I->valno)));
    ++I;
  }

  // The remaining ranges begin after Start.
  for (;I != E && I->start < End; ++I)
    openli_->addRange(LiveRange(I->start, std::min(End, I->end),
                                mapValue(I->valno)));
  DEBUG(dbgs() << "    use [" << Start << ';' << End << "): " << *openli_
               << '\n');
}

/// leaveIntvAfter - Leave openli after the instruction at Idx.
void SplitEditor::leaveIntvAfter(SlotIndex Idx) {
  assert(openli_ && "openIntv not called before leaveIntvAfter");

  const LiveRange *CurLR = curli_->getLiveRangeContaining(Idx.getDefIndex());
  if (!CurLR || CurLR->end <= Idx.getBoundaryIndex()) {
    DEBUG(dbgs() << "    leaveIntvAfter " << Idx << ": not live\n");
    return;
  }

  // Was this value of curli live through openli?
  if (!openli_->liveAt(CurLR->valno->def)) {
    DEBUG(dbgs() << "    leaveIntvAfter " << Idx << ": using external value\n");
    liveThrough_ = true;
    return;
  }

  // We are going to insert a back copy, so we must have a dupli_.
  LiveRange *DupLR = getDupLI()->getLiveRangeContaining(Idx.getDefIndex());
  assert(DupLR && "dupli not live into black, but curli is?");

  // Insert the COPY instruction.
  MachineBasicBlock::iterator I = lis_.getInstructionFromIndex(Idx);
  MachineInstr *MI = BuildMI(*I->getParent(), llvm::next(I), I->getDebugLoc(),
                             tii_.get(TargetOpcode::COPY), dupli_->reg)
                       .addReg(openli_->reg);
  SlotIndex CopyIdx = lis_.InsertMachineInstrInMaps(MI).getDefIndex();
  openli_->addRange(LiveRange(Idx.getDefIndex(), CopyIdx,
                    mapValue(CurLR->valno)));
  DupLR->valno->def = CopyIdx;
  DEBUG(dbgs() << "    leaveIntvAfter " << Idx << ": " << *openli_ << '\n');
}

/// leaveIntvAtTop - Leave the interval at the top of MBB.
/// Currently, only one value can leave the interval.
void SplitEditor::leaveIntvAtTop(MachineBasicBlock &MBB) {
  assert(openli_ && "openIntv not called before leaveIntvAtTop");

  SlotIndex Start = lis_.getMBBStartIdx(&MBB);
  const LiveRange *CurLR = curli_->getLiveRangeContaining(Start);

  // Is curli even live-in to MBB?
  if (!CurLR) {
    DEBUG(dbgs() << "    leaveIntvAtTop at " << Start << ": not live\n");
    return;
  }

  // Is curli defined by PHI at the beginning of MBB?
  bool isPHIDef = CurLR->valno->isPHIDef() &&
                  CurLR->valno->def.getBaseIndex() == Start;

  // If MBB is using a value of curli that was defined outside the openli range,
  // we don't want to copy it back here.
  if (!isPHIDef && !openli_->liveAt(CurLR->valno->def)) {
    DEBUG(dbgs() << "    leaveIntvAtTop at " << Start
                 << ": using external value\n");
    liveThrough_ = true;
    return;
  }

  // We are going to insert a back copy, so we must have a dupli_.
  LiveRange *DupLR = getDupLI()->getLiveRangeContaining(Start);
  assert(DupLR && "dupli not live into black, but curli is?");

  // Insert the COPY instruction.
  MachineInstr *MI = BuildMI(MBB, MBB.begin(), DebugLoc(),
                             tii_.get(TargetOpcode::COPY), dupli_->reg)
                       .addReg(openli_->reg);
  SlotIndex Idx = lis_.InsertMachineInstrInMaps(MI).getDefIndex();

  // Adjust dupli and openli values.
  if (isPHIDef) {
    // dupli was already a PHI on entry to MBB. Simply insert an openli PHI,
    // and shift the dupli def down to the COPY.
    VNInfo *VNI = openli_->getNextValue(SlotIndex(Start, true), 0, false,
                                        lis_.getVNInfoAllocator());
    VNI->setIsPHIDef(true);
    openli_->addRange(LiveRange(VNI->def, Idx, VNI));

    dupli_->removeRange(Start, Idx);
    DupLR->valno->def = Idx;
    DupLR->valno->setIsPHIDef(false);
  } else {
    // The dupli value was defined somewhere inside the openli range.
    DEBUG(dbgs() << "    leaveIntvAtTop source value defined at "
                 << DupLR->valno->def << "\n");
    // FIXME: We may not need a PHI here if all predecessors have the same
    // value.
    VNInfo *VNI = openli_->getNextValue(SlotIndex(Start, true), 0, false,
                                        lis_.getVNInfoAllocator());
    VNI->setIsPHIDef(true);
    openli_->addRange(LiveRange(VNI->def, Idx, VNI));

    // FIXME: What if DupLR->valno is used by multiple exits? SSA Update.

    // closeIntv is going to remove the superfluous live ranges.
    DupLR->valno->def = Idx;
    DupLR->valno->setIsPHIDef(false);
  }

  DEBUG(dbgs() << "    leaveIntvAtTop at " << Idx << ": " << *openli_ << '\n');
}

/// closeIntv - Indicate that we are done editing the currently open
/// LiveInterval, and ranges can be trimmed.
void SplitEditor::closeIntv() {
  assert(openli_ && "openIntv not called before closeIntv");

  DEBUG(dbgs() << "    closeIntv cleaning up\n");
  DEBUG(dbgs() << "    open " << *openli_ << '\n');

  if (liveThrough_) {
    DEBUG(dbgs() << "    value live through region, leaving dupli as is.\n");
  } else {
    // live out with copies inserted, or killed by region. Either way we need to
    // remove the overlapping region from dupli.
    getDupLI();
    for (LiveInterval::iterator I = openli_->begin(), E = openli_->end();
         I != E; ++I) {
      dupli_->removeRange(I->start, I->end);
    }
    // FIXME: A block branching to the entry block may also branch elsewhere
    // curli is live. We need both openli and curli to be live in that case.
    DEBUG(dbgs() << "    dup2 " << *dupli_ << '\n');
  }
  openli_ = 0;
  valueMap_.clear();
}

/// rewrite - after all the new live ranges have been created, rewrite
/// instructions using curli to use the new intervals.
void SplitEditor::rewrite() {
  assert(!openli_ && "Previous LI not closed before rewrite");
  const LiveInterval *curli = sa_.getCurLI();
  for (MachineRegisterInfo::reg_iterator RI = mri_.reg_begin(curli->reg),
       RE = mri_.reg_end(); RI != RE;) {
    MachineOperand &MO = RI.getOperand();
    MachineInstr *MI = MO.getParent();
    ++RI;
    if (MI->isDebugValue()) {
      DEBUG(dbgs() << "Zapping " << *MI);
      // FIXME: We can do much better with debug values.
      MO.setReg(0);
      continue;
    }
    SlotIndex Idx = lis_.getInstructionIndex(MI);
    Idx = MO.isUse() ? Idx.getUseIndex() : Idx.getDefIndex();
    LiveInterval *LI = dupli_;
    for (unsigned i = firstInterval, e = intervals_.size(); i != e; ++i) {
      LiveInterval *testli = intervals_[i];
      if (testli->liveAt(Idx)) {
        LI = testli;
        break;
      }
    }
    if (LI) {
      MO.setReg(LI->reg);
      sa_.removeUse(MI);
      DEBUG(dbgs() << "  rewrite " << Idx << '\t' << *MI);
    }
  }

  // dupli_ goes in last, after rewriting.
  if (dupli_) {
    if (dupli_->empty()) {
      DEBUG(dbgs() << "  dupli became empty?\n");
      lis_.removeInterval(dupli_->reg);
      dupli_ = 0;
    } else {
      dupli_->RenumberValues(lis_);
      intervals_.push_back(dupli_);
    }
  }

  // Calculate spill weight and allocation hints for new intervals.
  VirtRegAuxInfo vrai(vrm_.getMachineFunction(), lis_, sa_.loops_);
  for (unsigned i = firstInterval, e = intervals_.size(); i != e; ++i) {
    LiveInterval &li = *intervals_[i];
    vrai.CalculateRegClass(li.reg);
    vrai.CalculateWeightAndHint(li);
    DEBUG(dbgs() << "  new interval " << mri_.getRegClass(li.reg)->getName()
                 << ":" << li << '\n');
  }
}


//===----------------------------------------------------------------------===//
//                               Loop Splitting
//===----------------------------------------------------------------------===//

bool SplitEditor::splitAroundLoop(const MachineLoop *Loop) {
  SplitAnalysis::LoopBlocks Blocks;
  sa_.getLoopBlocks(Loop, Blocks);

  // Break critical edges as needed.
  SplitAnalysis::BlockPtrSet CriticalExits;
  sa_.getCriticalExits(Blocks, CriticalExits);
  assert(CriticalExits.empty() && "Cannot break critical exits yet");

  // Create new live interval for the loop.
  openIntv();

  // Insert copies in the predecessors.
  for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Preds.begin(),
       E = Blocks.Preds.end(); I != E; ++I) {
    MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);
    enterIntvAtEnd(MBB, *Loop->getHeader());
  }

  // Switch all loop blocks.
  for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Loop.begin(),
       E = Blocks.Loop.end(); I != E; ++I)
     useIntv(**I);

  // Insert back copies in the exit blocks.
  for (SplitAnalysis::BlockPtrSet::iterator I = Blocks.Exits.begin(),
       E = Blocks.Exits.end(); I != E; ++I) {
    MachineBasicBlock &MBB = const_cast<MachineBasicBlock&>(**I);
    leaveIntvAtTop(MBB);
  }

  // Done.
  closeIntv();
  rewrite();
  return dupli_;
}


//===----------------------------------------------------------------------===//
//                            Single Block Splitting
//===----------------------------------------------------------------------===//

/// splitSingleBlocks - Split curli into a separate live interval inside each
/// basic block in Blocks. Return true if curli has been completely replaced,
/// false if curli is still intact, and needs to be spilled or split further.
bool SplitEditor::splitSingleBlocks(const SplitAnalysis::BlockPtrSet &Blocks) {
  DEBUG(dbgs() << "  splitSingleBlocks for " << Blocks.size() << " blocks.\n");
  // Determine the first and last instruction using curli in each block.
  typedef std::pair<SlotIndex,SlotIndex> IndexPair;
  typedef DenseMap<const MachineBasicBlock*,IndexPair> IndexPairMap;
  IndexPairMap MBBRange;
  for (SplitAnalysis::InstrPtrSet::const_iterator I = sa_.usingInstrs_.begin(),
       E = sa_.usingInstrs_.end(); I != E; ++I) {
    const MachineBasicBlock *MBB = (*I)->getParent();
    if (!Blocks.count(MBB))
      continue;
    SlotIndex Idx = lis_.getInstructionIndex(*I);
    DEBUG(dbgs() << "  BB#" << MBB->getNumber() << '\t' << Idx << '\t' << **I);
    IndexPair &IP = MBBRange[MBB];
    if (!IP.first.isValid() || Idx < IP.first)
      IP.first = Idx;
    if (!IP.second.isValid() || Idx > IP.second)
      IP.second = Idx;
  }

  // Create a new interval for each block.
  for (SplitAnalysis::BlockPtrSet::const_iterator I = Blocks.begin(),
       E = Blocks.end(); I != E; ++I) {
    IndexPair &IP = MBBRange[*I];
    DEBUG(dbgs() << "  splitting for BB#" << (*I)->getNumber() << ": ["
                 << IP.first << ';' << IP.second << ")\n");
    assert(IP.first.isValid() && IP.second.isValid());

    openIntv();
    enterIntvBefore(IP.first);
    useIntv(IP.first.getBaseIndex(), IP.second.getBoundaryIndex());
    leaveIntvAfter(IP.second);
    closeIntv();
  }
  rewrite();
  return dupli_;
}


//===----------------------------------------------------------------------===//
//                            Sub Block Splitting
//===----------------------------------------------------------------------===//

/// getBlockForInsideSplit - If curli is contained inside a single basic block,
/// and it wou pay to subdivide the interval inside that block, return it.
/// Otherwise return NULL. The returned block can be passed to
/// SplitEditor::splitInsideBlock.
const MachineBasicBlock *SplitAnalysis::getBlockForInsideSplit() {
  // The interval must be exclusive to one block.
  if (usingBlocks_.size() != 1)
    return 0;
  // Don't to this for less than 4 instructions. We want to be sure that
  // splitting actually reduces the instruction count per interval.
  if (usingInstrs_.size() < 4)
    return 0;
  return usingBlocks_.begin()->first;
}

/// splitInsideBlock - Split curli into multiple intervals inside MBB. Return
/// true if curli has been completely replaced, false if curli is still
/// intact, and needs to be spilled or split further.
bool SplitEditor::splitInsideBlock(const MachineBasicBlock *MBB) {
  SmallVector<SlotIndex, 32> Uses;
  Uses.reserve(sa_.usingInstrs_.size());
  for (SplitAnalysis::InstrPtrSet::const_iterator I = sa_.usingInstrs_.begin(),
       E = sa_.usingInstrs_.end(); I != E; ++I)
    if ((*I)->getParent() == MBB)
      Uses.push_back(lis_.getInstructionIndex(*I));
  DEBUG(dbgs() << "  splitInsideBlock BB#" << MBB->getNumber() << " for "
               << Uses.size() << " instructions.\n");
  assert(Uses.size() >= 3 && "Need at least 3 instructions");
  array_pod_sort(Uses.begin(), Uses.end());

  // Simple algorithm: Find the largest gap between uses as determined by slot
  // indices. Create new intervals for instructions before the gap and after the
  // gap.
  unsigned bestPos = 0;
  int bestGap = 0;
  DEBUG(dbgs() << "    dist (" << Uses[0]);
  for (unsigned i = 1, e = Uses.size(); i != e; ++i) {
    int g = Uses[i-1].distance(Uses[i]);
    DEBUG(dbgs() << ") -" << g << "- (" << Uses[i]);
    if (g > bestGap)
      bestPos = i, bestGap = g;
  }
  DEBUG(dbgs() << "), best: -" << bestGap << "-\n");

  // bestPos points to the first use after the best gap.
  assert(bestPos > 0 && "Invalid gap");

  // FIXME: Don't create intervals for low densities.

  // First interval before the gap. Don't create single-instr intervals.
  if (bestPos > 1) {
    openIntv();
    enterIntvBefore(Uses.front());
    useIntv(Uses.front().getBaseIndex(), Uses[bestPos-1].getBoundaryIndex());
    leaveIntvAfter(Uses[bestPos-1]);
    closeIntv();
  }

  // Second interval after the gap.
  if (bestPos < Uses.size()-1) {
    openIntv();
    enterIntvBefore(Uses[bestPos]);
    useIntv(Uses[bestPos].getBaseIndex(), Uses.back().getBoundaryIndex());
    leaveIntvAfter(Uses.back());
    closeIntv();
  }

  rewrite();
  return dupli_;
}