StackSlotColoring.cpp revision 203954 
1//===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the stack slot coloring pass.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "stackcoloring"
15#include "VirtRegMap.h"
16#include "llvm/CodeGen/Passes.h"
17#include "llvm/CodeGen/LiveIntervalAnalysis.h"
18#include "llvm/CodeGen/LiveStackAnalysis.h"
19#include "llvm/CodeGen/MachineFrameInfo.h"
20#include "llvm/CodeGen/MachineLoopInfo.h"
21#include "llvm/CodeGen/MachineMemOperand.h"
22#include "llvm/CodeGen/MachineRegisterInfo.h"
23#include "llvm/CodeGen/PseudoSourceValue.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Support/Debug.h"
26#include "llvm/Target/TargetInstrInfo.h"
27#include "llvm/Target/TargetMachine.h"
28#include "llvm/ADT/BitVector.h"
29#include "llvm/ADT/SmallSet.h"
30#include "llvm/ADT/SmallVector.h"
31#include "llvm/ADT/Statistic.h"
32#include <vector>
33using namespace llvm;
34
35static cl::opt<bool>
36DisableSharing("no-stack-slot-sharing",
37             cl::init(false), cl::Hidden,
38             cl::desc("Suppress slot sharing during stack coloring"));
39
40static cl::opt<bool>
41ColorWithRegsOpt("color-ss-with-regs",
42                 cl::init(false), cl::Hidden,
43                 cl::desc("Color stack slots with free registers"));
44
45
46static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
47
48STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
49STATISTIC(NumRegRepl,    "Number of stack slot refs replaced with reg refs");
50STATISTIC(NumLoadElim,   "Number of loads eliminated");
51STATISTIC(NumStoreElim,  "Number of stores eliminated");
52STATISTIC(NumDead,       "Number of trivially dead stack accesses eliminated");
53
54namespace {
55  class StackSlotColoring : public MachineFunctionPass {
56    bool ColorWithRegs;
57    LiveStacks* LS;
58    VirtRegMap* VRM;
59    MachineFrameInfo *MFI;
60    MachineRegisterInfo *MRI;
61    const TargetInstrInfo  *TII;
62    const TargetRegisterInfo *TRI;
63    const MachineLoopInfo *loopInfo;
64
65    // SSIntervals - Spill slot intervals.
66    std::vector<LiveInterval*> SSIntervals;
67
68    // SSRefs - Keep a list of frame index references for each spill slot.
69    SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
70
71    // OrigAlignments - Alignments of stack objects before coloring.
72    SmallVector<unsigned, 16> OrigAlignments;
73
74    // OrigSizes - Sizess of stack objects before coloring.
75    SmallVector<unsigned, 16> OrigSizes;
76
77    // AllColors - If index is set, it's a spill slot, i.e. color.
78    // FIXME: This assumes PEI locate spill slot with smaller indices
79    // closest to stack pointer / frame pointer. Therefore, smaller
80    // index == better color.
81    BitVector AllColors;
82
83    // NextColor - Next "color" that's not yet used.
84    int NextColor;
85
86    // UsedColors - "Colors" that have been assigned.
87    BitVector UsedColors;
88
89    // Assignments - Color to intervals mapping.
90    SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
91
92  public:
93    static char ID; // Pass identification
94    StackSlotColoring() :
95      MachineFunctionPass(&ID), ColorWithRegs(false), NextColor(-1) {}
96    StackSlotColoring(bool RegColor) :
97      MachineFunctionPass(&ID), ColorWithRegs(RegColor), NextColor(-1) {}
98
99    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
100      AU.setPreservesCFG();
101      AU.addRequired<SlotIndexes>();
102      AU.addPreserved<SlotIndexes>();
103      AU.addRequired<LiveStacks>();
104      AU.addRequired<VirtRegMap>();
105      AU.addPreserved<VirtRegMap>();
106      AU.addRequired<MachineLoopInfo>();
107      AU.addPreserved<MachineLoopInfo>();
108      AU.addPreservedID(MachineDominatorsID);
109      MachineFunctionPass::getAnalysisUsage(AU);
110    }
111
112    virtual bool runOnMachineFunction(MachineFunction &MF);
113    virtual const char* getPassName() const {
114      return "Stack Slot Coloring";
115    }
116
117  private:
118    void InitializeSlots();
119    void ScanForSpillSlotRefs(MachineFunction &MF);
120    bool OverlapWithAssignments(LiveInterval *li, int Color) const;
121    int ColorSlot(LiveInterval *li);
122    bool ColorSlots(MachineFunction &MF);
123    bool ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
124                                SmallVector<SmallVector<int, 4>, 16> &RevMap,
125                                BitVector &SlotIsReg);
126    void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
127                            MachineFunction &MF);
128    bool PropagateBackward(MachineBasicBlock::iterator MII,
129                           MachineBasicBlock *MBB,
130                           unsigned OldReg, unsigned NewReg);
131    bool PropagateForward(MachineBasicBlock::iterator MII,
132                          MachineBasicBlock *MBB,
133                          unsigned OldReg, unsigned NewReg);
134    void UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
135                                    unsigned Reg, const TargetRegisterClass *RC,
136                                    SmallSet<unsigned, 4> &Defs,
137                                    MachineFunction &MF);
138    bool AllMemRefsCanBeUnfolded(int SS);
139    bool RemoveDeadStores(MachineBasicBlock* MBB);
140  };
141} // end anonymous namespace
142
143char StackSlotColoring::ID = 0;
144
145static RegisterPass<StackSlotColoring>
146X("stack-slot-coloring", "Stack Slot Coloring");
147
148FunctionPass *llvm::createStackSlotColoringPass(bool RegColor) {
149  return new StackSlotColoring(RegColor);
150}
151
152namespace {
153  // IntervalSorter - Comparison predicate that sort live intervals by
154  // their weight.
155  struct IntervalSorter {
156    bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
157      return LHS->weight > RHS->weight;
158    }
159  };
160}
161
162/// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
163/// references and update spill slot weights.
164void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
165  SSRefs.resize(MFI->getObjectIndexEnd());
166
167  // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
168  for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
169       MBBI != E; ++MBBI) {
170    MachineBasicBlock *MBB = &*MBBI;
171    unsigned loopDepth = loopInfo->getLoopDepth(MBB);
172    for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
173         MII != EE; ++MII) {
174      MachineInstr *MI = &*MII;
175      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
176        MachineOperand &MO = MI->getOperand(i);
177        if (!MO.isFI())
178          continue;
179        int FI = MO.getIndex();
180        if (FI < 0)
181          continue;
182        if (!LS->hasInterval(FI))
183          continue;
184        LiveInterval &li = LS->getInterval(FI);
185        li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
186        SSRefs[FI].push_back(MI);
187      }
188    }
189  }
190}
191
192/// InitializeSlots - Process all spill stack slot liveintervals and add them
193/// to a sorted (by weight) list.
194void StackSlotColoring::InitializeSlots() {
195  int LastFI = MFI->getObjectIndexEnd();
196  OrigAlignments.resize(LastFI);
197  OrigSizes.resize(LastFI);
198  AllColors.resize(LastFI);
199  UsedColors.resize(LastFI);
200  Assignments.resize(LastFI);
201
202  // Gather all spill slots into a list.
203  DEBUG(dbgs() << "Spill slot intervals:\n");
204  for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
205    LiveInterval &li = i->second;
206    DEBUG(li.dump());
207    int FI = li.getStackSlotIndex();
208    if (MFI->isDeadObjectIndex(FI))
209      continue;
210    SSIntervals.push_back(&li);
211    OrigAlignments[FI] = MFI->getObjectAlignment(FI);
212    OrigSizes[FI]      = MFI->getObjectSize(FI);
213    AllColors.set(FI);
214  }
215  DEBUG(dbgs() << '\n');
216
217  // Sort them by weight.
218  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
219
220  // Get first "color".
221  NextColor = AllColors.find_first();
222}
223
224/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
225/// LiveIntervals that have already been assigned to the specified color.
226bool
227StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
228  const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
229  for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
230    LiveInterval *OtherLI = OtherLIs[i];
231    if (OtherLI->overlaps(*li))
232      return true;
233  }
234  return false;
235}
236
237/// ColorSlotsWithFreeRegs - If there are any free registers available, try
238/// replacing spill slots references with registers instead.
239bool
240StackSlotColoring::ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
241                                   SmallVector<SmallVector<int, 4>, 16> &RevMap,
242                                   BitVector &SlotIsReg) {
243  if (!(ColorWithRegs || ColorWithRegsOpt) || !VRM->HasUnusedRegisters())
244    return false;
245
246  bool Changed = false;
247  DEBUG(dbgs() << "Assigning unused registers to spill slots:\n");
248  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
249    LiveInterval *li = SSIntervals[i];
250    int SS = li->getStackSlotIndex();
251    if (!UsedColors[SS] || li->weight < 20)
252      // If the weight is < 20, i.e. two references in a loop with depth 1,
253      // don't bother with it.
254      continue;
255
256    // These slots allow to share the same registers.
257    bool AllColored = true;
258    SmallVector<unsigned, 4> ColoredRegs;
259    for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
260      int RSS = RevMap[SS][j];
261      const TargetRegisterClass *RC = LS->getIntervalRegClass(RSS);
262      // If it's not colored to another stack slot, try coloring it
263      // to a "free" register.
264      if (!RC) {
265        AllColored = false;
266        continue;
267      }
268      unsigned Reg = VRM->getFirstUnusedRegister(RC);
269      if (!Reg) {
270        AllColored = false;
271        continue;
272      }
273      if (!AllMemRefsCanBeUnfolded(RSS)) {
274        AllColored = false;
275        continue;
276      } else {
277        DEBUG(dbgs() << "Assigning fi#" << RSS << " to "
278                     << TRI->getName(Reg) << '\n');
279        ColoredRegs.push_back(Reg);
280        SlotMapping[RSS] = Reg;
281        SlotIsReg.set(RSS);
282        Changed = true;
283      }
284    }
285
286    // Register and its sub-registers are no longer free.
287    while (!ColoredRegs.empty()) {
288      unsigned Reg = ColoredRegs.back();
289      ColoredRegs.pop_back();
290      VRM->setRegisterUsed(Reg);
291      // If reg is a callee-saved register, it will have to be spilled in
292      // the prologue.
293      MRI->setPhysRegUsed(Reg);
294      for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
295        VRM->setRegisterUsed(*AS);
296        MRI->setPhysRegUsed(*AS);
297      }
298    }
299    // This spill slot is dead after the rewrites
300    if (AllColored) {
301      MFI->RemoveStackObject(SS);
302      ++NumEliminated;
303    }
304  }
305  DEBUG(dbgs() << '\n');
306
307  return Changed;
308}
309
310/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
311///
312int StackSlotColoring::ColorSlot(LiveInterval *li) {
313  int Color = -1;
314  bool Share = false;
315  if (!DisableSharing) {
316    // Check if it's possible to reuse any of the used colors.
317    Color = UsedColors.find_first();
318    while (Color != -1) {
319      if (!OverlapWithAssignments(li, Color)) {
320        Share = true;
321        ++NumEliminated;
322        break;
323      }
324      Color = UsedColors.find_next(Color);
325    }
326  }
327
328  // Assign it to the first available color (assumed to be the best) if it's
329  // not possible to share a used color with other objects.
330  if (!Share) {
331    assert(NextColor != -1 && "No more spill slots?");
332    Color = NextColor;
333    UsedColors.set(Color);
334    NextColor = AllColors.find_next(NextColor);
335  }
336
337  // Record the assignment.
338  Assignments[Color].push_back(li);
339  int FI = li->getStackSlotIndex();
340  DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
341
342  // Change size and alignment of the allocated slot. If there are multiple
343  // objects sharing the same slot, then make sure the size and alignment
344  // are large enough for all.
345  unsigned Align = OrigAlignments[FI];
346  if (!Share || Align > MFI->getObjectAlignment(Color))
347    MFI->setObjectAlignment(Color, Align);
348  int64_t Size = OrigSizes[FI];
349  if (!Share || Size > MFI->getObjectSize(Color))
350    MFI->setObjectSize(Color, Size);
351  return Color;
352}
353
354/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
355/// operands in the function.
356bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
357  unsigned NumObjs = MFI->getObjectIndexEnd();
358  SmallVector<int, 16> SlotMapping(NumObjs, -1);
359  SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
360  SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
361  BitVector SlotIsReg(NumObjs);
362  BitVector UsedColors(NumObjs);
363
364  DEBUG(dbgs() << "Color spill slot intervals:\n");
365  bool Changed = false;
366  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
367    LiveInterval *li = SSIntervals[i];
368    int SS = li->getStackSlotIndex();
369    int NewSS = ColorSlot(li);
370    assert(NewSS >= 0 && "Stack coloring failed?");
371    SlotMapping[SS] = NewSS;
372    RevMap[NewSS].push_back(SS);
373    SlotWeights[NewSS] += li->weight;
374    UsedColors.set(NewSS);
375    Changed |= (SS != NewSS);
376  }
377
378  DEBUG(dbgs() << "\nSpill slots after coloring:\n");
379  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
380    LiveInterval *li = SSIntervals[i];
381    int SS = li->getStackSlotIndex();
382    li->weight = SlotWeights[SS];
383  }
384  // Sort them by new weight.
385  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
386
387#ifndef NDEBUG
388  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
389    DEBUG(SSIntervals[i]->dump());
390  DEBUG(dbgs() << '\n');
391#endif
392
393  // Can we "color" a stack slot with a unused register?
394  Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
395
396  if (!Changed)
397    return false;
398
399  // Rewrite all MO_FrameIndex operands.
400  SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
401  for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
402    bool isReg = SlotIsReg[SS];
403    int NewFI = SlotMapping[SS];
404    if (NewFI == -1 || (NewFI == (int)SS && !isReg))
405      continue;
406
407    const TargetRegisterClass *RC = LS->getIntervalRegClass(SS);
408    SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
409    for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
410      if (!isReg)
411        RewriteInstruction(RefMIs[i], SS, NewFI, MF);
412      else {
413        // Rewrite to use a register instead.
414        unsigned MBBId = RefMIs[i]->getParent()->getNumber();
415        SmallSet<unsigned, 4> &Defs = NewDefs[MBBId];
416        UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, RC, Defs, MF);
417      }
418  }
419
420  // Delete unused stack slots.
421  while (NextColor != -1) {
422    DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
423    MFI->RemoveStackObject(NextColor);
424    NextColor = AllColors.find_next(NextColor);
425  }
426
427  return true;
428}
429
430/// AllMemRefsCanBeUnfolded - Return true if all references of the specified
431/// spill slot index can be unfolded.
432bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
433  SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
434  for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
435    MachineInstr *MI = RefMIs[i];
436    if (TII->isLoadFromStackSlot(MI, SS) ||
437        TII->isStoreToStackSlot(MI, SS))
438      // Restore and spill will become copies.
439      return true;
440    if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
441      return false;
442    for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
443      MachineOperand &MO = MI->getOperand(j);
444      if (MO.isFI() && MO.getIndex() != SS)
445        // If it uses another frameindex, we can, currently* unfold it.
446        return false;
447    }
448  }
449  return true;
450}
451
452/// RewriteInstruction - Rewrite specified instruction by replacing references
453/// to old frame index with new one.
454void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
455                                           int NewFI, MachineFunction &MF) {
456  // Update the operands.
457  for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
458    MachineOperand &MO = MI->getOperand(i);
459    if (!MO.isFI())
460      continue;
461    int FI = MO.getIndex();
462    if (FI != OldFI)
463      continue;
464    MO.setIndex(NewFI);
465  }
466
467  // Update the memory references. This changes the MachineMemOperands
468  // directly. They may be in use by multiple instructions, however all
469  // instructions using OldFI are being rewritten to use NewFI.
470  const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
471  const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
472  for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
473       E = MI->memoperands_end(); I != E; ++I)
474    if ((*I)->getValue() == OldSV)
475      (*I)->setValue(NewSV);
476}
477
478/// PropagateBackward - Traverse backward and look for the definition of
479/// OldReg. If it can successfully update all of the references with NewReg,
480/// do so and return true.
481bool StackSlotColoring::PropagateBackward(MachineBasicBlock::iterator MII,
482                                          MachineBasicBlock *MBB,
483                                          unsigned OldReg, unsigned NewReg) {
484  if (MII == MBB->begin())
485    return false;
486
487  SmallVector<MachineOperand*, 4> Uses;
488  SmallVector<MachineOperand*, 4> Refs;
489  while (--MII != MBB->begin()) {
490    bool FoundDef = false;  // Not counting 2address def.
491
492    Uses.clear();
493    const TargetInstrDesc &TID = MII->getDesc();
494    for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
495      MachineOperand &MO = MII->getOperand(i);
496      if (!MO.isReg())
497        continue;
498      unsigned Reg = MO.getReg();
499      if (Reg == 0)
500        continue;
501      if (Reg == OldReg) {
502        if (MO.isImplicit())
503          return false;
504
505        // Abort the use is actually a sub-register def. We don't have enough
506        // information to figure out if it is really legal.
507        if (MO.getSubReg() || MII->isExtractSubreg() ||
508            MII->isInsertSubreg() || MII->isSubregToReg())
509          return false;
510
511        const TargetRegisterClass *RC = TID.OpInfo[i].getRegClass(TRI);
512        if (RC && !RC->contains(NewReg))
513          return false;
514
515        if (MO.isUse()) {
516          Uses.push_back(&MO);
517        } else {
518          Refs.push_back(&MO);
519          if (!MII->isRegTiedToUseOperand(i))
520            FoundDef = true;
521        }
522      } else if (TRI->regsOverlap(Reg, NewReg)) {
523        return false;
524      } else if (TRI->regsOverlap(Reg, OldReg)) {
525        if (!MO.isUse() || !MO.isKill())
526          return false;
527      }
528    }
529
530    if (FoundDef) {
531      // Found non-two-address def. Stop here.
532      for (unsigned i = 0, e = Refs.size(); i != e; ++i)
533        Refs[i]->setReg(NewReg);
534      return true;
535    }
536
537    // Two-address uses must be updated as well.
538    for (unsigned i = 0, e = Uses.size(); i != e; ++i)
539      Refs.push_back(Uses[i]);
540  }
541  return false;
542}
543
544/// PropagateForward - Traverse forward and look for the kill of OldReg. If
545/// it can successfully update all of the uses with NewReg, do so and
546/// return true.
547bool StackSlotColoring::PropagateForward(MachineBasicBlock::iterator MII,
548                                         MachineBasicBlock *MBB,
549                                         unsigned OldReg, unsigned NewReg) {
550  if (MII == MBB->end())
551    return false;
552
553  SmallVector<MachineOperand*, 4> Uses;
554  while (++MII != MBB->end()) {
555    bool FoundKill = false;
556    const TargetInstrDesc &TID = MII->getDesc();
557    for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
558      MachineOperand &MO = MII->getOperand(i);
559      if (!MO.isReg())
560        continue;
561      unsigned Reg = MO.getReg();
562      if (Reg == 0)
563        continue;
564      if (Reg == OldReg) {
565        if (MO.isDef() || MO.isImplicit())
566          return false;
567
568        // Abort the use is actually a sub-register use. We don't have enough
569        // information to figure out if it is really legal.
570        if (MO.getSubReg() || MII->isExtractSubreg())
571          return false;
572
573        const TargetRegisterClass *RC = TID.OpInfo[i].getRegClass(TRI);
574        if (RC && !RC->contains(NewReg))
575          return false;
576        if (MO.isKill())
577          FoundKill = true;
578
579        Uses.push_back(&MO);
580      } else if (TRI->regsOverlap(Reg, NewReg) ||
581                 TRI->regsOverlap(Reg, OldReg))
582        return false;
583    }
584    if (FoundKill) {
585      for (unsigned i = 0, e = Uses.size(); i != e; ++i)
586        Uses[i]->setReg(NewReg);
587      return true;
588    }
589  }
590  return false;
591}
592
593/// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
594/// folded memory references and replacing those references with register
595/// references instead.
596void
597StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
598                                               unsigned Reg,
599                                               const TargetRegisterClass *RC,
600                                               SmallSet<unsigned, 4> &Defs,
601                                               MachineFunction &MF) {
602  MachineBasicBlock *MBB = MI->getParent();
603  if (unsigned DstReg = TII->isLoadFromStackSlot(MI, OldFI)) {
604    if (PropagateForward(MI, MBB, DstReg, Reg)) {
605      DEBUG(dbgs() << "Eliminated load: ");
606      DEBUG(MI->dump());
607      ++NumLoadElim;
608    } else {
609      TII->copyRegToReg(*MBB, MI, DstReg, Reg, RC, RC);
610      ++NumRegRepl;
611    }
612
613    if (!Defs.count(Reg)) {
614      // If this is the first use of Reg in this MBB and it wasn't previously
615      // defined in MBB, add it to livein.
616      MBB->addLiveIn(Reg);
617      Defs.insert(Reg);
618    }
619  } else if (unsigned SrcReg = TII->isStoreToStackSlot(MI, OldFI)) {
620    if (MI->killsRegister(SrcReg) && PropagateBackward(MI, MBB, SrcReg, Reg)) {
621      DEBUG(dbgs() << "Eliminated store: ");
622      DEBUG(MI->dump());
623      ++NumStoreElim;
624    } else {
625      TII->copyRegToReg(*MBB, MI, Reg, SrcReg, RC, RC);
626      ++NumRegRepl;
627    }
628
629    // Remember reg has been defined in MBB.
630    Defs.insert(Reg);
631  } else {
632    SmallVector<MachineInstr*, 4> NewMIs;
633    bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
634    Success = Success; // Silence compiler warning.
635    assert(Success && "Failed to unfold!");
636    MachineInstr *NewMI = NewMIs[0];
637    MBB->insert(MI, NewMI);
638    ++NumRegRepl;
639
640    if (NewMI->readsRegister(Reg)) {
641      if (!Defs.count(Reg))
642        // If this is the first use of Reg in this MBB and it wasn't previously
643        // defined in MBB, add it to livein.
644        MBB->addLiveIn(Reg);
645      Defs.insert(Reg);
646    }
647  }
648  MBB->erase(MI);
649}
650
651/// RemoveDeadStores - Scan through a basic block and look for loads followed
652/// by stores.  If they're both using the same stack slot, then the store is
653/// definitely dead.  This could obviously be much more aggressive (consider
654/// pairs with instructions between them), but such extensions might have a
655/// considerable compile time impact.
656bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
657  // FIXME: This could be much more aggressive, but we need to investigate
658  // the compile time impact of doing so.
659  bool changed = false;
660
661  SmallVector<MachineInstr*, 4> toErase;
662
663  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
664       I != E; ++I) {
665    if (DCELimit != -1 && (int)NumDead >= DCELimit)
666      break;
667
668    MachineBasicBlock::iterator NextMI = llvm::next(I);
669    if (NextMI == MBB->end()) continue;
670
671    int FirstSS, SecondSS;
672    unsigned LoadReg = 0;
673    unsigned StoreReg = 0;
674    if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
675    if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
676    if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
677
678    ++NumDead;
679    changed = true;
680
681    if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
682      ++NumDead;
683      toErase.push_back(I);
684    }
685
686    toErase.push_back(NextMI);
687    ++I;
688  }
689
690  for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
691       E = toErase.end(); I != E; ++I)
692    (*I)->eraseFromParent();
693
694  return changed;
695}
696
697
698bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
699  DEBUG(dbgs() << "********** Stack Slot Coloring **********\n");
700
701  MFI = MF.getFrameInfo();
702  MRI = &MF.getRegInfo();
703  TII = MF.getTarget().getInstrInfo();
704  TRI = MF.getTarget().getRegisterInfo();
705  LS = &getAnalysis<LiveStacks>();
706  VRM = &getAnalysis<VirtRegMap>();
707  loopInfo = &getAnalysis<MachineLoopInfo>();
708
709  bool Changed = false;
710
711  unsigned NumSlots = LS->getNumIntervals();
712  if (NumSlots < 2) {
713    if (NumSlots == 0 || !VRM->HasUnusedRegisters())
714      // Nothing to do!
715      return false;
716  }
717
718  // Gather spill slot references
719  ScanForSpillSlotRefs(MF);
720  InitializeSlots();
721  Changed = ColorSlots(MF);
722
723  NextColor = -1;
724  SSIntervals.clear();
725  for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
726    SSRefs[i].clear();
727  SSRefs.clear();
728  OrigAlignments.clear();
729  OrigSizes.clear();
730  AllColors.clear();
731  UsedColors.clear();
732  for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
733    Assignments[i].clear();
734  Assignments.clear();
735
736  if (Changed) {
737    for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
738      Changed |= RemoveDeadStores(I);
739  }
740
741  return Changed;
742}
743