llvm.org GIT mirror llvm / release_34 lib / CodeGen / RegisterPressure.cpp
release_34

Tree @release_34 (Download .tar.gz)

RegisterPressure.cpp @release_34raw · 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
//===-- RegisterPressure.cpp - Dynamic Register Pressure ------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the RegisterPressure class which can be used to track
// MachineInstr level register pressure.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/RegisterPressure.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"

using namespace llvm;

/// Increase pressure for each pressure set provided by TargetRegisterInfo.
static void increaseSetPressure(std::vector<unsigned> &CurrSetPressure,
                                PSetIterator PSetI) {
  unsigned Weight = PSetI.getWeight();
  for (; PSetI.isValid(); ++PSetI)
    CurrSetPressure[*PSetI] += Weight;
}

/// Decrease pressure for each pressure set provided by TargetRegisterInfo.
static void decreaseSetPressure(std::vector<unsigned> &CurrSetPressure,
                                PSetIterator PSetI) {
  unsigned Weight = PSetI.getWeight();
  for (; PSetI.isValid(); ++PSetI) {
    assert(CurrSetPressure[*PSetI] >= Weight && "register pressure underflow");
    CurrSetPressure[*PSetI] -= Weight;
  }
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void llvm::dumpRegSetPressure(ArrayRef<unsigned> SetPressure,
                              const TargetRegisterInfo *TRI) {
  bool Empty = true;
  for (unsigned i = 0, e = SetPressure.size(); i < e; ++i) {
    if (SetPressure[i] != 0) {
      dbgs() << TRI->getRegPressureSetName(i) << "=" << SetPressure[i] << '\n';
      Empty = false;
    }
  }
  if (Empty)
    dbgs() << "\n";
}

void RegisterPressure::dump(const TargetRegisterInfo *TRI) const {
  dbgs() << "Max Pressure: ";
  dumpRegSetPressure(MaxSetPressure, TRI);
  dbgs() << "Live In: ";
  for (unsigned i = 0, e = LiveInRegs.size(); i < e; ++i)
    dbgs() << PrintReg(LiveInRegs[i], TRI) << " ";
  dbgs() << '\n';
  dbgs() << "Live Out: ";
  for (unsigned i = 0, e = LiveOutRegs.size(); i < e; ++i)
    dbgs() << PrintReg(LiveOutRegs[i], TRI) << " ";
  dbgs() << '\n';
}

void RegPressureTracker::dump() const {
  if (!isTopClosed() || !isBottomClosed()) {
    dbgs() << "Curr Pressure: ";
    dumpRegSetPressure(CurrSetPressure, TRI);
  }
  P.dump(TRI);
}
#endif

/// Increase the current pressure as impacted by these registers and bump
/// the high water mark if needed.
void RegPressureTracker::increaseRegPressure(ArrayRef<unsigned> RegUnits) {
  for (unsigned i = 0, e = RegUnits.size(); i != e; ++i) {
    PSetIterator PSetI = MRI->getPressureSets(RegUnits[i]);
    unsigned Weight = PSetI.getWeight();
    for (; PSetI.isValid(); ++PSetI) {
      CurrSetPressure[*PSetI] += Weight;
      if (CurrSetPressure[*PSetI] > P.MaxSetPressure[*PSetI]) {
        P.MaxSetPressure[*PSetI] = CurrSetPressure[*PSetI];
      }
    }
  }
}

/// Simply decrease the current pressure as impacted by these registers.
void RegPressureTracker::decreaseRegPressure(ArrayRef<unsigned> RegUnits) {
  for (unsigned I = 0, E = RegUnits.size(); I != E; ++I)
    decreaseSetPressure(CurrSetPressure, MRI->getPressureSets(RegUnits[I]));
}

/// Clear the result so it can be used for another round of pressure tracking.
void IntervalPressure::reset() {
  TopIdx = BottomIdx = SlotIndex();
  MaxSetPressure.clear();
  LiveInRegs.clear();
  LiveOutRegs.clear();
}

/// Clear the result so it can be used for another round of pressure tracking.
void RegionPressure::reset() {
  TopPos = BottomPos = MachineBasicBlock::const_iterator();
  MaxSetPressure.clear();
  LiveInRegs.clear();
  LiveOutRegs.clear();
}

/// If the current top is not less than or equal to the next index, open it.
/// We happen to need the SlotIndex for the next top for pressure update.
void IntervalPressure::openTop(SlotIndex NextTop) {
  if (TopIdx <= NextTop)
    return;
  TopIdx = SlotIndex();
  LiveInRegs.clear();
}

/// If the current top is the previous instruction (before receding), open it.
void RegionPressure::openTop(MachineBasicBlock::const_iterator PrevTop) {
  if (TopPos != PrevTop)
    return;
  TopPos = MachineBasicBlock::const_iterator();
  LiveInRegs.clear();
}

/// If the current bottom is not greater than the previous index, open it.
void IntervalPressure::openBottom(SlotIndex PrevBottom) {
  if (BottomIdx > PrevBottom)
    return;
  BottomIdx = SlotIndex();
  LiveInRegs.clear();
}

/// If the current bottom is the previous instr (before advancing), open it.
void RegionPressure::openBottom(MachineBasicBlock::const_iterator PrevBottom) {
  if (BottomPos != PrevBottom)
    return;
  BottomPos = MachineBasicBlock::const_iterator();
  LiveInRegs.clear();
}

const LiveRange *RegPressureTracker::getLiveRange(unsigned Reg) const {
  if (TargetRegisterInfo::isVirtualRegister(Reg))
    return &LIS->getInterval(Reg);
  return LIS->getCachedRegUnit(Reg);
}

void RegPressureTracker::reset() {
  MBB = 0;
  LIS = 0;

  CurrSetPressure.clear();
  LiveThruPressure.clear();
  P.MaxSetPressure.clear();

  if (RequireIntervals)
    static_cast<IntervalPressure&>(P).reset();
  else
    static_cast<RegionPressure&>(P).reset();

  LiveRegs.PhysRegs.clear();
  LiveRegs.VirtRegs.clear();
  UntiedDefs.clear();
}

/// Setup the RegPressureTracker.
///
/// TODO: Add support for pressure without LiveIntervals.
void RegPressureTracker::init(const MachineFunction *mf,
                              const RegisterClassInfo *rci,
                              const LiveIntervals *lis,
                              const MachineBasicBlock *mbb,
                              MachineBasicBlock::const_iterator pos,
                              bool ShouldTrackUntiedDefs)
{
  reset();

  MF = mf;
  TRI = MF->getTarget().getRegisterInfo();
  RCI = rci;
  MRI = &MF->getRegInfo();
  MBB = mbb;
  TrackUntiedDefs = ShouldTrackUntiedDefs;

  if (RequireIntervals) {
    assert(lis && "IntervalPressure requires LiveIntervals");
    LIS = lis;
  }

  CurrPos = pos;
  CurrSetPressure.assign(TRI->getNumRegPressureSets(), 0);

  P.MaxSetPressure = CurrSetPressure;

  LiveRegs.PhysRegs.setUniverse(TRI->getNumRegs());
  LiveRegs.VirtRegs.setUniverse(MRI->getNumVirtRegs());
  if (TrackUntiedDefs)
    UntiedDefs.setUniverse(MRI->getNumVirtRegs());
}

/// Does this pressure result have a valid top position and live ins.
bool RegPressureTracker::isTopClosed() const {
  if (RequireIntervals)
    return static_cast<IntervalPressure&>(P).TopIdx.isValid();
  return (static_cast<RegionPressure&>(P).TopPos ==
          MachineBasicBlock::const_iterator());
}

/// Does this pressure result have a valid bottom position and live outs.
bool RegPressureTracker::isBottomClosed() const {
  if (RequireIntervals)
    return static_cast<IntervalPressure&>(P).BottomIdx.isValid();
  return (static_cast<RegionPressure&>(P).BottomPos ==
          MachineBasicBlock::const_iterator());
}


SlotIndex RegPressureTracker::getCurrSlot() const {
  MachineBasicBlock::const_iterator IdxPos = CurrPos;
  while (IdxPos != MBB->end() && IdxPos->isDebugValue())
    ++IdxPos;
  if (IdxPos == MBB->end())
    return LIS->getMBBEndIdx(MBB);
  return LIS->getInstructionIndex(IdxPos).getRegSlot();
}

/// Set the boundary for the top of the region and summarize live ins.
void RegPressureTracker::closeTop() {
  if (RequireIntervals)
    static_cast<IntervalPressure&>(P).TopIdx = getCurrSlot();
  else
    static_cast<RegionPressure&>(P).TopPos = CurrPos;

  assert(P.LiveInRegs.empty() && "inconsistent max pressure result");
  P.LiveInRegs.reserve(LiveRegs.PhysRegs.size() + LiveRegs.VirtRegs.size());
  P.LiveInRegs.append(LiveRegs.PhysRegs.begin(), LiveRegs.PhysRegs.end());
  for (SparseSet<unsigned>::const_iterator I =
         LiveRegs.VirtRegs.begin(), E = LiveRegs.VirtRegs.end(); I != E; ++I)
    P.LiveInRegs.push_back(*I);
  std::sort(P.LiveInRegs.begin(), P.LiveInRegs.end());
  P.LiveInRegs.erase(std::unique(P.LiveInRegs.begin(), P.LiveInRegs.end()),
                     P.LiveInRegs.end());
}

/// Set the boundary for the bottom of the region and summarize live outs.
void RegPressureTracker::closeBottom() {
  if (RequireIntervals)
    static_cast<IntervalPressure&>(P).BottomIdx = getCurrSlot();
  else
    static_cast<RegionPressure&>(P).BottomPos = CurrPos;

  assert(P.LiveOutRegs.empty() && "inconsistent max pressure result");
  P.LiveOutRegs.reserve(LiveRegs.PhysRegs.size() + LiveRegs.VirtRegs.size());
  P.LiveOutRegs.append(LiveRegs.PhysRegs.begin(), LiveRegs.PhysRegs.end());
  for (SparseSet<unsigned>::const_iterator I =
         LiveRegs.VirtRegs.begin(), E = LiveRegs.VirtRegs.end(); I != E; ++I)
    P.LiveOutRegs.push_back(*I);
  std::sort(P.LiveOutRegs.begin(), P.LiveOutRegs.end());
  P.LiveOutRegs.erase(std::unique(P.LiveOutRegs.begin(), P.LiveOutRegs.end()),
                      P.LiveOutRegs.end());
}

/// Finalize the region boundaries and record live ins and live outs.
void RegPressureTracker::closeRegion() {
  if (!isTopClosed() && !isBottomClosed()) {
    assert(LiveRegs.PhysRegs.empty() && LiveRegs.VirtRegs.empty() &&
           "no region boundary");
    return;
  }
  if (!isBottomClosed())
    closeBottom();
  else if (!isTopClosed())
    closeTop();
  // If both top and bottom are closed, do nothing.
}

/// The register tracker is unaware of global liveness so ignores normal
/// live-thru ranges. However, two-address or coalesced chains can also lead
/// to live ranges with no holes. Count these to inform heuristics that we
/// can never drop below this pressure.
void RegPressureTracker::initLiveThru(const RegPressureTracker &RPTracker) {
  LiveThruPressure.assign(TRI->getNumRegPressureSets(), 0);
  assert(isBottomClosed() && "need bottom-up tracking to intialize.");
  for (unsigned i = 0, e = P.LiveOutRegs.size(); i < e; ++i) {
    unsigned Reg = P.LiveOutRegs[i];
    if (TargetRegisterInfo::isVirtualRegister(Reg)
        && !RPTracker.hasUntiedDef(Reg)) {
      increaseSetPressure(LiveThruPressure, MRI->getPressureSets(Reg));
    }
  }
}

/// \brief Convenient wrapper for checking membership in RegisterOperands.
/// (std::count() doesn't have an early exit).
static bool containsReg(ArrayRef<unsigned> RegUnits, unsigned RegUnit) {
  return std::find(RegUnits.begin(), RegUnits.end(), RegUnit) != RegUnits.end();
}

/// Collect this instruction's unique uses and defs into SmallVectors for
/// processing defs and uses in order.
///
/// FIXME: always ignore tied opers
class RegisterOperands {
  const TargetRegisterInfo *TRI;
  const MachineRegisterInfo *MRI;
  bool IgnoreDead;

public:
  SmallVector<unsigned, 8> Uses;
  SmallVector<unsigned, 8> Defs;
  SmallVector<unsigned, 8> DeadDefs;

  RegisterOperands(const TargetRegisterInfo *tri,
                   const MachineRegisterInfo *mri, bool ID = false):
    TRI(tri), MRI(mri), IgnoreDead(ID) {}

  /// Push this operand's register onto the correct vector.
  void collect(const MachineOperand &MO) {
    if (!MO.isReg() || !MO.getReg())
      return;
    if (MO.readsReg())
      pushRegUnits(MO.getReg(), Uses);
    if (MO.isDef()) {
      if (MO.isDead()) {
        if (!IgnoreDead)
          pushRegUnits(MO.getReg(), DeadDefs);
      }
      else
        pushRegUnits(MO.getReg(), Defs);
    }
  }

protected:
  void pushRegUnits(unsigned Reg, SmallVectorImpl<unsigned> &RegUnits) {
    if (TargetRegisterInfo::isVirtualRegister(Reg)) {
      if (containsReg(RegUnits, Reg))
        return;
      RegUnits.push_back(Reg);
    }
    else if (MRI->isAllocatable(Reg)) {
      for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units) {
        if (containsReg(RegUnits, *Units))
          continue;
        RegUnits.push_back(*Units);
      }
    }
  }
};

/// Collect physical and virtual register operands.
static void collectOperands(const MachineInstr *MI,
                            RegisterOperands &RegOpers) {
  for (ConstMIBundleOperands OperI(MI); OperI.isValid(); ++OperI)
    RegOpers.collect(*OperI);

  // Remove redundant physreg dead defs.
  SmallVectorImpl<unsigned>::iterator I =
    std::remove_if(RegOpers.DeadDefs.begin(), RegOpers.DeadDefs.end(),
                   std::bind1st(std::ptr_fun(containsReg), RegOpers.Defs));
  RegOpers.DeadDefs.erase(I, RegOpers.DeadDefs.end());
}

/// Initialize an array of N PressureDiffs.
void PressureDiffs::init(unsigned N) {
  Size = N;
  if (N <= Max) {
    memset(PDiffArray, 0, N * sizeof(PressureDiff));
    return;
  }
  Max = Size;
  free(PDiffArray);
  PDiffArray = reinterpret_cast<PressureDiff*>(calloc(N, sizeof(PressureDiff)));
}

/// Add a change in pressure to the pressure diff of a given instruction.
void PressureDiff::addPressureChange(unsigned RegUnit, bool IsDec,
                                     const MachineRegisterInfo *MRI) {
  PSetIterator PSetI = MRI->getPressureSets(RegUnit);
  int Weight = IsDec ? -PSetI.getWeight() : PSetI.getWeight();
  for (; PSetI.isValid(); ++PSetI) {
    // Find an existing entry in the pressure diff for this PSet.
    PressureDiff::iterator I = begin(), E = end();
    for (; I != E && I->isValid(); ++I) {
      if (I->getPSet() >= *PSetI)
        break;
    }
    // If all pressure sets are more constrained, skip the remaining PSets.
    if (I == E)
      break;
    // Insert this PressureChange.
    if (!I->isValid() || I->getPSet() != *PSetI) {
      PressureChange PTmp = PressureChange(*PSetI);
      for (PressureDiff::iterator J = I; J != E && PTmp.isValid(); ++J)
        std::swap(*J,PTmp);
    }
    // Update the units for this pressure set.
    I->setUnitInc(I->getUnitInc() + Weight);
  }
}

/// Record the pressure difference induced by the given operand list.
static void collectPDiff(PressureDiff &PDiff, RegisterOperands &RegOpers,
                         const MachineRegisterInfo *MRI) {
  assert(!PDiff.begin()->isValid() && "stale PDiff");

  for (unsigned i = 0, e = RegOpers.Defs.size(); i != e; ++i)
    PDiff.addPressureChange(RegOpers.Defs[i], true, MRI);

  for (unsigned i = 0, e = RegOpers.Uses.size(); i != e; ++i)
    PDiff.addPressureChange(RegOpers.Uses[i], false, MRI);
}

/// Force liveness of registers.
void RegPressureTracker::addLiveRegs(ArrayRef<unsigned> Regs) {
  for (unsigned i = 0, e = Regs.size(); i != e; ++i) {
    if (LiveRegs.insert(Regs[i]))
      increaseRegPressure(Regs[i]);
  }
}

/// Add Reg to the live in set and increase max pressure.
void RegPressureTracker::discoverLiveIn(unsigned Reg) {
  assert(!LiveRegs.contains(Reg) && "avoid bumping max pressure twice");
  if (containsReg(P.LiveInRegs, Reg))
    return;

  // At live in discovery, unconditionally increase the high water mark.
  P.LiveInRegs.push_back(Reg);
  increaseSetPressure(P.MaxSetPressure, MRI->getPressureSets(Reg));
}

/// Add Reg to the live out set and increase max pressure.
void RegPressureTracker::discoverLiveOut(unsigned Reg) {
  assert(!LiveRegs.contains(Reg) && "avoid bumping max pressure twice");
  if (containsReg(P.LiveOutRegs, Reg))
    return;

  // At live out discovery, unconditionally increase the high water mark.
  P.LiveOutRegs.push_back(Reg);
  increaseSetPressure(P.MaxSetPressure, MRI->getPressureSets(Reg));
}

/// Recede across the previous instruction. If LiveUses is provided, record any
/// RegUnits that are made live by the current instruction's uses. This includes
/// registers that are both defined and used by the instruction.  If a pressure
/// difference pointer is provided record the changes is pressure caused by this
/// instruction independent of liveness.
bool RegPressureTracker::recede(SmallVectorImpl<unsigned> *LiveUses,
                                PressureDiff *PDiff) {
  // Check for the top of the analyzable region.
  if (CurrPos == MBB->begin()) {
    closeRegion();
    return false;
  }
  if (!isBottomClosed())
    closeBottom();

  // Open the top of the region using block iterators.
  if (!RequireIntervals && isTopClosed())
    static_cast<RegionPressure&>(P).openTop(CurrPos);

  // Find the previous instruction.
  do
    --CurrPos;
  while (CurrPos != MBB->begin() && CurrPos->isDebugValue());

  if (CurrPos->isDebugValue()) {
    closeRegion();
    return false;
  }
  SlotIndex SlotIdx;
  if (RequireIntervals)
    SlotIdx = LIS->getInstructionIndex(CurrPos).getRegSlot();

  // Open the top of the region using slot indexes.
  if (RequireIntervals && isTopClosed())
    static_cast<IntervalPressure&>(P).openTop(SlotIdx);

  RegisterOperands RegOpers(TRI, MRI);
  collectOperands(CurrPos, RegOpers);

  if (PDiff)
    collectPDiff(*PDiff, RegOpers, MRI);

  // Boost pressure for all dead defs together.
  increaseRegPressure(RegOpers.DeadDefs);
  decreaseRegPressure(RegOpers.DeadDefs);

  // Kill liveness at live defs.
  // TODO: consider earlyclobbers?
  for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
    unsigned Reg = RegOpers.Defs[i];
    bool DeadDef = false;
    if (RequireIntervals) {
      const LiveRange *LR = getLiveRange(Reg);
      if (LR) {
        LiveQueryResult LRQ = LR->Query(SlotIdx);
        DeadDef = LRQ.isDeadDef();
      }
    }
    if (!DeadDef) {
      if (LiveRegs.erase(Reg))
        decreaseRegPressure(Reg);
      else
        discoverLiveOut(Reg);
    }
  }

  // Generate liveness for uses.
  for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
    unsigned Reg = RegOpers.Uses[i];
    if (!LiveRegs.contains(Reg)) {
      // Adjust liveouts if LiveIntervals are available.
      if (RequireIntervals) {
        const LiveRange *LR = getLiveRange(Reg);
        if (LR) {
          LiveQueryResult LRQ = LR->Query(SlotIdx);
          if (!LRQ.isKill() && !LRQ.valueDefined())
            discoverLiveOut(Reg);
        }
      }
      increaseRegPressure(Reg);
      LiveRegs.insert(Reg);
      if (LiveUses && !containsReg(*LiveUses, Reg))
        LiveUses->push_back(Reg);
    }
  }
  if (TrackUntiedDefs) {
    for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
      unsigned Reg = RegOpers.Defs[i];
      if (TargetRegisterInfo::isVirtualRegister(Reg) && !LiveRegs.contains(Reg))
        UntiedDefs.insert(Reg);
    }
  }
  return true;
}

/// Advance across the current instruction.
bool RegPressureTracker::advance() {
  assert(!TrackUntiedDefs && "unsupported mode");

  // Check for the bottom of the analyzable region.
  if (CurrPos == MBB->end()) {
    closeRegion();
    return false;
  }
  if (!isTopClosed())
    closeTop();

  SlotIndex SlotIdx;
  if (RequireIntervals)
    SlotIdx = getCurrSlot();

  // Open the bottom of the region using slot indexes.
  if (isBottomClosed()) {
    if (RequireIntervals)
      static_cast<IntervalPressure&>(P).openBottom(SlotIdx);
    else
      static_cast<RegionPressure&>(P).openBottom(CurrPos);
  }

  RegisterOperands RegOpers(TRI, MRI);
  collectOperands(CurrPos, RegOpers);

  for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
    unsigned Reg = RegOpers.Uses[i];
    // Discover live-ins.
    bool isLive = LiveRegs.contains(Reg);
    if (!isLive)
      discoverLiveIn(Reg);
    // Kill liveness at last uses.
    bool lastUse = false;
    if (RequireIntervals) {
      const LiveRange *LR = getLiveRange(Reg);
      lastUse = LR && LR->Query(SlotIdx).isKill();
    }
    else {
      // Allocatable physregs are always single-use before register rewriting.
      lastUse = !TargetRegisterInfo::isVirtualRegister(Reg);
    }
    if (lastUse && isLive) {
      LiveRegs.erase(Reg);
      decreaseRegPressure(Reg);
    }
    else if (!lastUse && !isLive)
      increaseRegPressure(Reg);
  }

  // Generate liveness for defs.
  for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
    unsigned Reg = RegOpers.Defs[i];
    if (LiveRegs.insert(Reg))
      increaseRegPressure(Reg);
  }

  // Boost pressure for all dead defs together.
  increaseRegPressure(RegOpers.DeadDefs);
  decreaseRegPressure(RegOpers.DeadDefs);

  // Find the next instruction.
  do
    ++CurrPos;
  while (CurrPos != MBB->end() && CurrPos->isDebugValue());
  return true;
}

/// Find the max change in excess pressure across all sets.
static void computeExcessPressureDelta(ArrayRef<unsigned> OldPressureVec,
                                       ArrayRef<unsigned> NewPressureVec,
                                       RegPressureDelta &Delta,
                                       const RegisterClassInfo *RCI,
                                       ArrayRef<unsigned> LiveThruPressureVec) {
  Delta.Excess = PressureChange();
  for (unsigned i = 0, e = OldPressureVec.size(); i < e; ++i) {
    unsigned POld = OldPressureVec[i];
    unsigned PNew = NewPressureVec[i];
    int PDiff = (int)PNew - (int)POld;
    if (!PDiff) // No change in this set in the common case.
      continue;
    // Only consider change beyond the limit.
    unsigned Limit = RCI->getRegPressureSetLimit(i);
    if (!LiveThruPressureVec.empty())
      Limit += LiveThruPressureVec[i];

    if (Limit > POld) {
      if (Limit > PNew)
        PDiff = 0;            // Under the limit
      else
        PDiff = PNew - Limit; // Just exceeded limit.
    }
    else if (Limit > PNew)
      PDiff = Limit - POld;   // Just obeyed limit.

    if (PDiff) {
      Delta.Excess = PressureChange(i);
      Delta.Excess.setUnitInc(PDiff);
      break;
    }
  }
}

/// Find the max change in max pressure that either surpasses a critical PSet
/// limit or exceeds the current MaxPressureLimit.
///
/// FIXME: comparing each element of the old and new MaxPressure vectors here is
/// silly. It's done now to demonstrate the concept but will go away with a
/// RegPressureTracker API change to work with pressure differences.
static void computeMaxPressureDelta(ArrayRef<unsigned> OldMaxPressureVec,
                                    ArrayRef<unsigned> NewMaxPressureVec,
                                    ArrayRef<PressureChange> CriticalPSets,
                                    ArrayRef<unsigned> MaxPressureLimit,
                                    RegPressureDelta &Delta) {
  Delta.CriticalMax = PressureChange();
  Delta.CurrentMax = PressureChange();

  unsigned CritIdx = 0, CritEnd = CriticalPSets.size();
  for (unsigned i = 0, e = OldMaxPressureVec.size(); i < e; ++i) {
    unsigned POld = OldMaxPressureVec[i];
    unsigned PNew = NewMaxPressureVec[i];
    if (PNew == POld) // No change in this set in the common case.
      continue;

    if (!Delta.CriticalMax.isValid()) {
      while (CritIdx != CritEnd && CriticalPSets[CritIdx].getPSet() < i)
        ++CritIdx;

      if (CritIdx != CritEnd && CriticalPSets[CritIdx].getPSet() == i) {
        int PDiff = (int)PNew - (int)CriticalPSets[CritIdx].getUnitInc();
        if (PDiff > 0) {
          Delta.CriticalMax = PressureChange(i);
          Delta.CriticalMax.setUnitInc(PDiff);
        }
      }
    }
    // Find the first increase above MaxPressureLimit.
    // (Ignores negative MDiff).
    if (!Delta.CurrentMax.isValid() && PNew > MaxPressureLimit[i]) {
      Delta.CurrentMax = PressureChange(i);
      Delta.CurrentMax.setUnitInc(PNew - POld);
      if (CritIdx == CritEnd || Delta.CriticalMax.isValid())
        break;
    }
  }
}

/// Record the upward impact of a single instruction on current register
/// pressure. Unlike the advance/recede pressure tracking interface, this does
/// not discover live in/outs.
///
/// This is intended for speculative queries. It leaves pressure inconsistent
/// with the current position, so must be restored by the caller.
void RegPressureTracker::bumpUpwardPressure(const MachineInstr *MI) {
  assert(!MI->isDebugValue() && "Expect a nondebug instruction.");

  // Account for register pressure similar to RegPressureTracker::recede().
  RegisterOperands RegOpers(TRI, MRI, /*IgnoreDead=*/true);
  collectOperands(MI, RegOpers);

  // Boost max pressure for all dead defs together.
  // Since CurrSetPressure and MaxSetPressure
  increaseRegPressure(RegOpers.DeadDefs);
  decreaseRegPressure(RegOpers.DeadDefs);

  // Kill liveness at live defs.
  for (unsigned i = 0, e = RegOpers.Defs.size(); i < e; ++i) {
    unsigned Reg = RegOpers.Defs[i];
    bool DeadDef = false;
    if (RequireIntervals) {
      const LiveRange *LR = getLiveRange(Reg);
      if (LR) {
        SlotIndex SlotIdx = LIS->getInstructionIndex(MI);
        LiveQueryResult LRQ = LR->Query(SlotIdx);
        DeadDef = LRQ.isDeadDef();
      }
    }
    if (!DeadDef) {
      if (!containsReg(RegOpers.Uses, Reg))
        decreaseRegPressure(Reg);
    }
  }
  // Generate liveness for uses.
  for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
    unsigned Reg = RegOpers.Uses[i];
    if (!LiveRegs.contains(Reg))
      increaseRegPressure(Reg);
  }
}

/// Consider the pressure increase caused by traversing this instruction
/// bottom-up. Find the pressure set with the most change beyond its pressure
/// limit based on the tracker's current pressure, and return the change in
/// number of register units of that pressure set introduced by this
/// instruction.
///
/// This assumes that the current LiveOut set is sufficient.
///
/// FIXME: This is expensive for an on-the-fly query. We need to cache the
/// result per-SUnit with enough information to adjust for the current
/// scheduling position. But this works as a proof of concept.
void RegPressureTracker::
getMaxUpwardPressureDelta(const MachineInstr *MI, PressureDiff *PDiff,
                          RegPressureDelta &Delta,
                          ArrayRef<PressureChange> CriticalPSets,
                          ArrayRef<unsigned> MaxPressureLimit) {
  // Snapshot Pressure.
  // FIXME: The snapshot heap space should persist. But I'm planning to
  // summarize the pressure effect so we don't need to snapshot at all.
  std::vector<unsigned> SavedPressure = CurrSetPressure;
  std::vector<unsigned> SavedMaxPressure = P.MaxSetPressure;

  bumpUpwardPressure(MI);

  computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, RCI,
                             LiveThruPressure);
  computeMaxPressureDelta(SavedMaxPressure, P.MaxSetPressure, CriticalPSets,
                          MaxPressureLimit, Delta);
  assert(Delta.CriticalMax.getUnitInc() >= 0 &&
         Delta.CurrentMax.getUnitInc() >= 0 && "cannot decrease max pressure");

  // Restore the tracker's state.
  P.MaxSetPressure.swap(SavedMaxPressure);
  CurrSetPressure.swap(SavedPressure);

#ifndef NDEBUG
  if (!PDiff)
    return;

  // Check if the alternate algorithm yields the same result.
  RegPressureDelta Delta2;
  getUpwardPressureDelta(MI, *PDiff, Delta2, CriticalPSets, MaxPressureLimit);
  if (Delta != Delta2) {
    dbgs() << "DELTA: " << *MI;
    if (Delta.Excess.isValid())
      dbgs() << "Excess1 " << TRI->getRegPressureSetName(Delta.Excess.getPSet())
             << " " << Delta.Excess.getUnitInc() << "\n";
    if (Delta.CriticalMax.isValid())
      dbgs() << "Critic1 " << TRI->getRegPressureSetName(Delta.CriticalMax.getPSet())
             << " " << Delta.CriticalMax.getUnitInc() << "\n";
    if (Delta.CurrentMax.isValid())
      dbgs() << "CurrMx1 " << TRI->getRegPressureSetName(Delta.CurrentMax.getPSet())
             << " " << Delta.CurrentMax.getUnitInc() << "\n";
    if (Delta2.Excess.isValid())
      dbgs() << "Excess2 " << TRI->getRegPressureSetName(Delta2.Excess.getPSet())
             << " " << Delta2.Excess.getUnitInc() << "\n";
    if (Delta2.CriticalMax.isValid())
      dbgs() << "Critic2 " << TRI->getRegPressureSetName(Delta2.CriticalMax.getPSet())
             << " " << Delta2.CriticalMax.getUnitInc() << "\n";
    if (Delta2.CurrentMax.isValid())
      dbgs() << "CurrMx2 " << TRI->getRegPressureSetName(Delta2.CurrentMax.getPSet())
             << " " << Delta2.CurrentMax.getUnitInc() << "\n";
    llvm_unreachable("RegP Delta Mismatch");
  }
#endif
}

/// This is a prototype of the fast version of querying register pressure that
/// does not directly depend on current liveness. It's still slow because we
/// recompute pressure change on-the-fly. This implementation only exists to
/// prove correctness.
///
/// @param Delta captures information needed for heuristics.
///
/// @param CriticalPSets Are the pressure sets that are known to exceed some
/// limit within the region, not necessarily at the current position.
///
/// @param MaxPressureLimit Is the max pressure within the region, not
/// necessarily at the current position.
void RegPressureTracker::
getUpwardPressureDelta(const MachineInstr *MI, /*const*/ PressureDiff &PDiff,
                       RegPressureDelta &Delta,
                       ArrayRef<PressureChange> CriticalPSets,
                       ArrayRef<unsigned> MaxPressureLimit) const {
  unsigned CritIdx = 0, CritEnd = CriticalPSets.size();
  for (PressureDiff::const_iterator
         PDiffI = PDiff.begin(), PDiffE = PDiff.end();
       PDiffI != PDiffE && PDiffI->isValid(); ++PDiffI) {

    unsigned PSetID = PDiffI->getPSet();
    unsigned Limit = RCI->getRegPressureSetLimit(PSetID);
    if (!LiveThruPressure.empty())
      Limit += LiveThruPressure[PSetID];

    unsigned POld = CurrSetPressure[PSetID];
    unsigned MOld = P.MaxSetPressure[PSetID];
    unsigned MNew = MOld;
    // Ignore DeadDefs here because they aren't captured by PressureChange.
    unsigned PNew = POld + PDiffI->getUnitInc();
    assert((PDiffI->getUnitInc() >= 0) == (PNew >= POld) && "PSet overflow");
    if (PNew > MOld)
      MNew = PNew;
    // Check if current pressure has exceeded the limit.
    if (!Delta.Excess.isValid()) {
      unsigned ExcessInc = 0;
      if (PNew > Limit)
        ExcessInc = POld > Limit ? PNew - POld : PNew - Limit;
      else if (POld > Limit)
        ExcessInc = Limit - POld;
      if (ExcessInc) {
        Delta.Excess = PressureChange(PSetID);
        Delta.Excess.setUnitInc(ExcessInc);
      }
    }
    // Check if max pressure has exceeded a critical pressure set max.
    if (MNew == MOld)
      continue;
    if (!Delta.CriticalMax.isValid()) {
      while (CritIdx != CritEnd && CriticalPSets[CritIdx].getPSet() < PSetID)
        ++CritIdx;

      if (CritIdx != CritEnd && CriticalPSets[CritIdx].getPSet() == PSetID) {
        int CritInc = (int)MNew - (int)CriticalPSets[CritIdx].getUnitInc();
        if (CritInc > 0 && CritInc <= INT16_MAX) {
          Delta.CriticalMax = PressureChange(PSetID);
          Delta.CriticalMax.setUnitInc(CritInc);
        }
      }
    }
    // Check if max pressure has exceeded the current max.
    if (!Delta.CurrentMax.isValid() && MNew > MaxPressureLimit[PSetID]) {
      Delta.CurrentMax = PressureChange(PSetID);
      Delta.CurrentMax.setUnitInc(MNew - MOld);
    }
  }
}

/// Helper to find a vreg use between two indices [PriorUseIdx, NextUseIdx).
static bool findUseBetween(unsigned Reg,
                           SlotIndex PriorUseIdx, SlotIndex NextUseIdx,
                           const MachineRegisterInfo *MRI,
                           const LiveIntervals *LIS) {
  for (MachineRegisterInfo::use_nodbg_iterator
         UI = MRI->use_nodbg_begin(Reg), UE = MRI->use_nodbg_end();
         UI != UE; UI.skipInstruction()) {
      const MachineInstr* MI = &*UI;
      if (MI->isDebugValue())
        continue;
      SlotIndex InstSlot = LIS->getInstructionIndex(MI).getRegSlot();
      if (InstSlot >= PriorUseIdx && InstSlot < NextUseIdx)
        return true;
  }
  return false;
}

/// Record the downward impact of a single instruction on current register
/// pressure. Unlike the advance/recede pressure tracking interface, this does
/// not discover live in/outs.
///
/// This is intended for speculative queries. It leaves pressure inconsistent
/// with the current position, so must be restored by the caller.
void RegPressureTracker::bumpDownwardPressure(const MachineInstr *MI) {
  assert(!MI->isDebugValue() && "Expect a nondebug instruction.");

  // Account for register pressure similar to RegPressureTracker::recede().
  RegisterOperands RegOpers(TRI, MRI);
  collectOperands(MI, RegOpers);

  // Kill liveness at last uses. Assume allocatable physregs are single-use
  // rather than checking LiveIntervals.
  SlotIndex SlotIdx;
  if (RequireIntervals)
    SlotIdx = LIS->getInstructionIndex(MI).getRegSlot();

  for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
    unsigned Reg = RegOpers.Uses[i];
    if (RequireIntervals) {
      // FIXME: allow the caller to pass in the list of vreg uses that remain
      // to be bottom-scheduled to avoid searching uses at each query.
      SlotIndex CurrIdx = getCurrSlot();
      const LiveRange *LR = getLiveRange(Reg);
      if (LR) {
        LiveQueryResult LRQ = LR->Query(SlotIdx);
        if (LRQ.isKill() && !findUseBetween(Reg, CurrIdx, SlotIdx, MRI, LIS)) {
          decreaseRegPressure(Reg);
        }
      }
    }
    else if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
      // Allocatable physregs are always single-use before register rewriting.
      decreaseRegPressure(Reg);
    }
  }

  // Generate liveness for defs.
  increaseRegPressure(RegOpers.Defs);

  // Boost pressure for all dead defs together.
  increaseRegPressure(RegOpers.DeadDefs);
  decreaseRegPressure(RegOpers.DeadDefs);
}

/// Consider the pressure increase caused by traversing this instruction
/// top-down. Find the register class with the most change in its pressure limit
/// based on the tracker's current pressure, and return the number of excess
/// register units of that pressure set introduced by this instruction.
///
/// This assumes that the current LiveIn set is sufficient.
void RegPressureTracker::
getMaxDownwardPressureDelta(const MachineInstr *MI, RegPressureDelta &Delta,
                            ArrayRef<PressureChange> CriticalPSets,
                            ArrayRef<unsigned> MaxPressureLimit) {
  // Snapshot Pressure.
  std::vector<unsigned> SavedPressure = CurrSetPressure;
  std::vector<unsigned> SavedMaxPressure = P.MaxSetPressure;

  bumpDownwardPressure(MI);

  computeExcessPressureDelta(SavedPressure, CurrSetPressure, Delta, RCI,
                             LiveThruPressure);
  computeMaxPressureDelta(SavedMaxPressure, P.MaxSetPressure, CriticalPSets,
                          MaxPressureLimit, Delta);
  assert(Delta.CriticalMax.getUnitInc() >= 0 &&
         Delta.CurrentMax.getUnitInc() >= 0 && "cannot decrease max pressure");

  // Restore the tracker's state.
  P.MaxSetPressure.swap(SavedMaxPressure);
  CurrSetPressure.swap(SavedPressure);
}

/// Get the pressure of each PSet after traversing this instruction bottom-up.
void RegPressureTracker::
getUpwardPressure(const MachineInstr *MI,
                  std::vector<unsigned> &PressureResult,
                  std::vector<unsigned> &MaxPressureResult) {
  // Snapshot pressure.
  PressureResult = CurrSetPressure;
  MaxPressureResult = P.MaxSetPressure;

  bumpUpwardPressure(MI);

  // Current pressure becomes the result. Restore current pressure.
  P.MaxSetPressure.swap(MaxPressureResult);
  CurrSetPressure.swap(PressureResult);
}

/// Get the pressure of each PSet after traversing this instruction top-down.
void RegPressureTracker::
getDownwardPressure(const MachineInstr *MI,
                    std::vector<unsigned> &PressureResult,
                    std::vector<unsigned> &MaxPressureResult) {
  // Snapshot pressure.
  PressureResult = CurrSetPressure;
  MaxPressureResult = P.MaxSetPressure;

  bumpDownwardPressure(MI);

  // Current pressure becomes the result. Restore current pressure.
  P.MaxSetPressure.swap(MaxPressureResult);
  CurrSetPressure.swap(PressureResult);
}