llvm.org GIT mirror llvm / eaa7353 lib / CodeGen / StackSlotColoring.cpp
eaa7353

Tree @eaa7353 (Download .tar.gz)

StackSlotColoring.cpp @eaa7353raw · 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
//===- StackSlotColoring.cpp - Stack slot coloring pass. ------------------===//
//
//                     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 stack slot coloring pass.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveStacks.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <vector>

using namespace llvm;

#define DEBUG_TYPE "stack-slot-coloring"

static cl::opt<bool>
DisableSharing("no-stack-slot-sharing",
             cl::init(false), cl::Hidden,
             cl::desc("Suppress slot sharing during stack coloring"));

static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);

STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
STATISTIC(NumDead,       "Number of trivially dead stack accesses eliminated");

namespace {

  class StackSlotColoring : public MachineFunctionPass {
    LiveStacks* LS;
    MachineFrameInfo *MFI;
    const TargetInstrInfo  *TII;
    const MachineBlockFrequencyInfo *MBFI;

    // SSIntervals - Spill slot intervals.
    std::vector<LiveInterval*> SSIntervals;

    // SSRefs - Keep a list of MachineMemOperands for each spill slot.
    // MachineMemOperands can be shared between instructions, so we need
    // to be careful that renames like [FI0, FI1] -> [FI1, FI2] do not
    // become FI0 -> FI1 -> FI2.
    SmallVector<SmallVector<MachineMemOperand *, 8>, 16> SSRefs;

    // OrigAlignments - Alignments of stack objects before coloring.
    SmallVector<unsigned, 16> OrigAlignments;

    // OrigSizes - Sizess of stack objects before coloring.
    SmallVector<unsigned, 16> OrigSizes;

    // AllColors - If index is set, it's a spill slot, i.e. color.
    // FIXME: This assumes PEI locate spill slot with smaller indices
    // closest to stack pointer / frame pointer. Therefore, smaller
    // index == better color. This is per stack ID.
    SmallVector<BitVector, 2> AllColors;

    // NextColor - Next "color" that's not yet used. This is per stack ID.
    SmallVector<int, 2> NextColors = { -1 };

    // UsedColors - "Colors" that have been assigned. This is per stack ID
    SmallVector<BitVector, 2> UsedColors;

    // Assignments - Color to intervals mapping.
    SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;

  public:
    static char ID; // Pass identification

    StackSlotColoring() : MachineFunctionPass(ID) {
      initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
    }

    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.setPreservesCFG();
      AU.addRequired<SlotIndexes>();
      AU.addPreserved<SlotIndexes>();
      AU.addRequired<LiveStacks>();
      AU.addRequired<MachineBlockFrequencyInfo>();
      AU.addPreserved<MachineBlockFrequencyInfo>();
      AU.addPreservedID(MachineDominatorsID);
      MachineFunctionPass::getAnalysisUsage(AU);
    }

    bool runOnMachineFunction(MachineFunction &MF) override;

  private:
    void InitializeSlots();
    void ScanForSpillSlotRefs(MachineFunction &MF);
    bool OverlapWithAssignments(LiveInterval *li, int Color) const;
    int ColorSlot(LiveInterval *li);
    bool ColorSlots(MachineFunction &MF);
    void RewriteInstruction(MachineInstr &MI, SmallVectorImpl<int> &SlotMapping,
                            MachineFunction &MF);
    bool RemoveDeadStores(MachineBasicBlock* MBB);
  };

} // end anonymous namespace

char StackSlotColoring::ID = 0;

char &llvm::StackSlotColoringID = StackSlotColoring::ID;

INITIALIZE_PASS_BEGIN(StackSlotColoring, DEBUG_TYPE,
                "Stack Slot Coloring", false, false)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_DEPENDENCY(LiveStacks)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_END(StackSlotColoring, DEBUG_TYPE,
                "Stack Slot Coloring", false, false)

namespace {

// IntervalSorter - Comparison predicate that sort live intervals by
// their weight.
struct IntervalSorter {
  bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
    return LHS->weight > RHS->weight;
  }
};

} // end anonymous namespace

/// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
/// references and update spill slot weights.
void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
  SSRefs.resize(MFI->getObjectIndexEnd());

  // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
  for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
       MBBI != E; ++MBBI) {
    MachineBasicBlock *MBB = &*MBBI;
    for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
         MII != EE; ++MII) {
      MachineInstr &MI = *MII;
      for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
        MachineOperand &MO = MI.getOperand(i);
        if (!MO.isFI())
          continue;
        int FI = MO.getIndex();
        if (FI < 0)
          continue;
        if (!LS->hasInterval(FI))
          continue;
        LiveInterval &li = LS->getInterval(FI);
        if (!MI.isDebugValue())
          li.weight += LiveIntervals::getSpillWeight(false, true, MBFI, MI);
      }
      for (MachineInstr::mmo_iterator MMOI = MI.memoperands_begin(),
                                      EE = MI.memoperands_end();
           MMOI != EE; ++MMOI) {
        MachineMemOperand *MMO = *MMOI;
        if (const FixedStackPseudoSourceValue *FSV =
            dyn_cast_or_null<FixedStackPseudoSourceValue>(
                MMO->getPseudoValue())) {
          int FI = FSV->getFrameIndex();
          if (FI >= 0)
            SSRefs[FI].push_back(MMO);
        }
      }
    }
  }
}

/// InitializeSlots - Process all spill stack slot liveintervals and add them
/// to a sorted (by weight) list.
void StackSlotColoring::InitializeSlots() {
  int LastFI = MFI->getObjectIndexEnd();

  // There is always at least one stack ID.
  AllColors.resize(1);
  UsedColors.resize(1);

  OrigAlignments.resize(LastFI);
  OrigSizes.resize(LastFI);
  AllColors[0].resize(LastFI);
  UsedColors[0].resize(LastFI);
  Assignments.resize(LastFI);

  using Pair = std::iterator_traits<LiveStacks::iterator>::value_type;

  SmallVector<Pair *, 16> Intervals;

  Intervals.reserve(LS->getNumIntervals());
  for (auto &I : *LS)
    Intervals.push_back(&I);
  llvm::sort(Intervals,
             [](Pair *LHS, Pair *RHS) { return LHS->first < RHS->first; });

  // Gather all spill slots into a list.
  LLVM_DEBUG(dbgs() << "Spill slot intervals:\n");
  for (auto *I : Intervals) {
    LiveInterval &li = I->second;
    LLVM_DEBUG(li.dump());
    int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
    if (MFI->isDeadObjectIndex(FI))
      continue;

    SSIntervals.push_back(&li);
    OrigAlignments[FI] = MFI->getObjectAlignment(FI);
    OrigSizes[FI]      = MFI->getObjectSize(FI);

    auto StackID = MFI->getStackID(FI);
    if (StackID != 0) {
      AllColors.resize(StackID + 1);
      UsedColors.resize(StackID + 1);
      AllColors[StackID].resize(LastFI);
      UsedColors[StackID].resize(LastFI);
    }

    AllColors[StackID].set(FI);
  }
  LLVM_DEBUG(dbgs() << '\n');

  // Sort them by weight.
  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());

  NextColors.resize(AllColors.size());

  // Get first "color".
  for (unsigned I = 0, E = AllColors.size(); I != E; ++I)
    NextColors[I] = AllColors[I].find_first();
}

/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
/// LiveIntervals that have already been assigned to the specified color.
bool
StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
  const SmallVectorImpl<LiveInterval *> &OtherLIs = Assignments[Color];
  for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
    LiveInterval *OtherLI = OtherLIs[i];
    if (OtherLI->overlaps(*li))
      return true;
  }
  return false;
}

/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
int StackSlotColoring::ColorSlot(LiveInterval *li) {
  int Color = -1;
  bool Share = false;
  int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
  uint8_t StackID = MFI->getStackID(FI);

  if (!DisableSharing) {

    // Check if it's possible to reuse any of the used colors.
    Color = UsedColors[StackID].find_first();
    while (Color != -1) {
      if (!OverlapWithAssignments(li, Color)) {
        Share = true;
        ++NumEliminated;
        break;
      }
      Color = UsedColors[StackID].find_next(Color);
    }
  }

  if (Color != -1 && MFI->getStackID(Color) != MFI->getStackID(FI)) {
    LLVM_DEBUG(dbgs() << "cannot share FIs with different stack IDs\n");
    Share = false;
  }

  // Assign it to the first available color (assumed to be the best) if it's
  // not possible to share a used color with other objects.
  if (!Share) {
    assert(NextColors[StackID] != -1 && "No more spill slots?");
    Color = NextColors[StackID];
    UsedColors[StackID].set(Color);
    NextColors[StackID] = AllColors[StackID].find_next(NextColors[StackID]);
  }

  assert(MFI->getStackID(Color) == MFI->getStackID(FI));

  // Record the assignment.
  Assignments[Color].push_back(li);
  LLVM_DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");

  // Change size and alignment of the allocated slot. If there are multiple
  // objects sharing the same slot, then make sure the size and alignment
  // are large enough for all.
  unsigned Align = OrigAlignments[FI];
  if (!Share || Align > MFI->getObjectAlignment(Color))
    MFI->setObjectAlignment(Color, Align);
  int64_t Size = OrigSizes[FI];
  if (!Share || Size > MFI->getObjectSize(Color))
    MFI->setObjectSize(Color, Size);
  return Color;
}

/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
/// operands in the function.
bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
  unsigned NumObjs = MFI->getObjectIndexEnd();
  SmallVector<int, 16> SlotMapping(NumObjs, -1);
  SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
  SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
  BitVector UsedColors(NumObjs);

  LLVM_DEBUG(dbgs() << "Color spill slot intervals:\n");
  bool Changed = false;
  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
    LiveInterval *li = SSIntervals[i];
    int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
    int NewSS = ColorSlot(li);
    assert(NewSS >= 0 && "Stack coloring failed?");
    SlotMapping[SS] = NewSS;
    RevMap[NewSS].push_back(SS);
    SlotWeights[NewSS] += li->weight;
    UsedColors.set(NewSS);
    Changed |= (SS != NewSS);
  }

  LLVM_DEBUG(dbgs() << "\nSpill slots after coloring:\n");
  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
    LiveInterval *li = SSIntervals[i];
    int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
    li->weight = SlotWeights[SS];
  }
  // Sort them by new weight.
  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());

#ifndef NDEBUG
  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
    LLVM_DEBUG(SSIntervals[i]->dump());
  LLVM_DEBUG(dbgs() << '\n');
#endif

  if (!Changed)
    return false;

  // Rewrite all MachineMemOperands.
  for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
    int NewFI = SlotMapping[SS];
    if (NewFI == -1 || (NewFI == (int)SS))
      continue;

    const PseudoSourceValue *NewSV = MF.getPSVManager().getFixedStack(NewFI);
    SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
    for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i)
      RefMMOs[i]->setValue(NewSV);
  }

  // Rewrite all MO_FrameIndex operands.  Look for dead stores.
  for (MachineBasicBlock &MBB : MF) {
    for (MachineInstr &MI : MBB)
      RewriteInstruction(MI, SlotMapping, MF);
    RemoveDeadStores(&MBB);
  }

  // Delete unused stack slots.
  for (int StackID = 0, E = AllColors.size(); StackID != E; ++StackID) {
    int NextColor = NextColors[StackID];
    while (NextColor != -1) {
      LLVM_DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
      MFI->RemoveStackObject(NextColor);
      NextColor = AllColors[StackID].find_next(NextColor);
    }
  }

  return true;
}

/// RewriteInstruction - Rewrite specified instruction by replacing references
/// to old frame index with new one.
void StackSlotColoring::RewriteInstruction(MachineInstr &MI,
                                           SmallVectorImpl<int> &SlotMapping,
                                           MachineFunction &MF) {
  // Update the operands.
  for (unsigned i = 0, ee = MI.getNumOperands(); i != ee; ++i) {
    MachineOperand &MO = MI.getOperand(i);
    if (!MO.isFI())
      continue;
    int OldFI = MO.getIndex();
    if (OldFI < 0)
      continue;
    int NewFI = SlotMapping[OldFI];
    if (NewFI == -1 || NewFI == OldFI)
      continue;

    assert(MFI->getStackID(OldFI) == MFI->getStackID(NewFI));
    MO.setIndex(NewFI);
  }

  // The MachineMemOperands have already been updated.
}

/// RemoveDeadStores - Scan through a basic block and look for loads followed
/// by stores.  If they're both using the same stack slot, then the store is
/// definitely dead.  This could obviously be much more aggressive (consider
/// pairs with instructions between them), but such extensions might have a
/// considerable compile time impact.
bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
  // FIXME: This could be much more aggressive, but we need to investigate
  // the compile time impact of doing so.
  bool changed = false;

  SmallVector<MachineInstr*, 4> toErase;

  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
       I != E; ++I) {
    if (DCELimit != -1 && (int)NumDead >= DCELimit)
      break;
    int FirstSS, SecondSS;
    if (TII->isStackSlotCopy(*I, FirstSS, SecondSS) && FirstSS == SecondSS &&
        FirstSS != -1) {
      ++NumDead;
      changed = true;
      toErase.push_back(&*I);
      continue;
    }

    MachineBasicBlock::iterator NextMI = std::next(I);
    MachineBasicBlock::iterator ProbableLoadMI = I;

    unsigned LoadReg = 0;
    unsigned StoreReg = 0;
    unsigned LoadSize = 0;
    unsigned StoreSize = 0;
    if (!(LoadReg = TII->isLoadFromStackSlot(*I, FirstSS, LoadSize)))
      continue;
    // Skip the ...pseudo debugging... instructions between a load and store.
    while ((NextMI != E) && NextMI->isDebugInstr()) {
      ++NextMI;
      ++I;
    }
    if (NextMI == E) continue;
    if (!(StoreReg = TII->isStoreToStackSlot(*NextMI, SecondSS, StoreSize)))
      continue;
    if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1 ||
        LoadSize != StoreSize)
      continue;

    ++NumDead;
    changed = true;

    if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) {
      ++NumDead;
      toErase.push_back(&*ProbableLoadMI);
    }

    toErase.push_back(&*NextMI);
    ++I;
  }

  for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(),
       E = toErase.end(); I != E; ++I)
    (*I)->eraseFromParent();

  return changed;
}

bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
  LLVM_DEBUG({
    dbgs() << "********** Stack Slot Coloring **********\n"
           << "********** Function: " << MF.getName() << '\n';
  });

  if (skipFunction(MF.getFunction()))
    return false;

  MFI = &MF.getFrameInfo();
  TII = MF.getSubtarget().getInstrInfo();
  LS = &getAnalysis<LiveStacks>();
  MBFI = &getAnalysis<MachineBlockFrequencyInfo>();

  bool Changed = false;

  unsigned NumSlots = LS->getNumIntervals();
  if (NumSlots == 0)
    // Nothing to do!
    return false;

  // If there are calls to setjmp or sigsetjmp, don't perform stack slot
  // coloring. The stack could be modified before the longjmp is executed,
  // resulting in the wrong value being used afterwards. (See
  // <rdar://problem/8007500>.)
  if (MF.exposesReturnsTwice())
    return false;

  // Gather spill slot references
  ScanForSpillSlotRefs(MF);
  InitializeSlots();
  Changed = ColorSlots(MF);

  for (int &Next : NextColors)
    Next = -1;

  SSIntervals.clear();
  for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
    SSRefs[i].clear();
  SSRefs.clear();
  OrigAlignments.clear();
  OrigSizes.clear();
  AllColors.clear();
  UsedColors.clear();
  for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
    Assignments[i].clear();
  Assignments.clear();

  return Changed;
}