StackSlotColoring.cpp revision b4093593a76c81520893762e237f55d86f6b5191 
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/MachineRegisterInfo.h"
22#include "llvm/CodeGen/PseudoSourceValue.h"
23#include "llvm/Support/CommandLine.h"
24#include "llvm/Support/Compiler.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/SmallVector.h"
30#include "llvm/ADT/Statistic.h"
31#include <vector>
32using namespace llvm;
33
34static cl::opt<bool>
35DisableSharing("no-stack-slot-sharing",
36             cl::init(false), cl::Hidden,
37             cl::desc("Suppress slot sharing during stack coloring"));
38
39static cl::opt<bool>
40ColorWithRegsOpt("color-ss-with-regs",
41                 cl::init(false), cl::Hidden,
42                 cl::desc("Color stack slots with free registers"));
43
44
45static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
46
47STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
48STATISTIC(NumRegRepl,    "Number of stack slot refs replaced with reg refs");
49STATISTIC(NumLoadElim,   "Number of loads eliminated");
50STATISTIC(NumStoreElim,  "Number of stores eliminated");
51STATISTIC(NumDead,       "Number of trivially dead stack accesses eliminated");
52
53namespace {
54  class VISIBILITY_HIDDEN StackSlotColoring : public MachineFunctionPass {
55    bool ColorWithRegs;
56    LiveStacks* LS;
57    VirtRegMap* VRM;
58    MachineFrameInfo *MFI;
59    MachineRegisterInfo *MRI;
60    const TargetInstrInfo  *TII;
61    const TargetRegisterInfo *TRI;
62    const MachineLoopInfo *loopInfo;
63
64    // SSIntervals - Spill slot intervals.
65    std::vector<LiveInterval*> SSIntervals;
66
67    // SSRefs - Keep a list of frame index references for each spill slot.
68    SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
69
70    // OrigAlignments - Alignments of stack objects before coloring.
71    SmallVector<unsigned, 16> OrigAlignments;
72
73    // OrigSizes - Sizess of stack objects before coloring.
74    SmallVector<unsigned, 16> OrigSizes;
75
76    // AllColors - If index is set, it's a spill slot, i.e. color.
77    // FIXME: This assumes PEI locate spill slot with smaller indices
78    // closest to stack pointer / frame pointer. Therefore, smaller
79    // index == better color.
80    BitVector AllColors;
81
82    // NextColor - Next "color" that's not yet used.
83    int NextColor;
84
85    // UsedColors - "Colors" that have been assigned.
86    BitVector UsedColors;
87
88    // Assignments - Color to intervals mapping.
89    SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
90
91  public:
92    static char ID; // Pass identification
93    StackSlotColoring() :
94      MachineFunctionPass(&ID), ColorWithRegs(false), NextColor(-1) {}
95    StackSlotColoring(bool RegColor) :
96      MachineFunctionPass(&ID), ColorWithRegs(RegColor), NextColor(-1) {}
97
98    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
99      AU.addRequired<LiveStacks>();
100      AU.addRequired<VirtRegMap>();
101      AU.addPreserved<VirtRegMap>();
102      AU.addRequired<MachineLoopInfo>();
103      AU.addPreserved<MachineLoopInfo>();
104      AU.addPreservedID(MachineDominatorsID);
105      MachineFunctionPass::getAnalysisUsage(AU);
106    }
107
108    virtual bool runOnMachineFunction(MachineFunction &MF);
109    virtual const char* getPassName() const {
110      return "Stack Slot Coloring";
111    }
112
113  private:
114    void InitializeSlots();
115    void ScanForSpillSlotRefs(MachineFunction &MF);
116    bool OverlapWithAssignments(LiveInterval *li, int Color) const;
117    int ColorSlot(LiveInterval *li);
118    bool ColorSlots(MachineFunction &MF);
119    bool ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
120                                SmallVector<SmallVector<int, 4>, 16> &RevMap,
121                                BitVector &SlotIsReg);
122    void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
123                            MachineFunction &MF);
124    bool PropagateBackward(MachineBasicBlock::iterator MII,
125                           MachineBasicBlock *MBB,
126                           unsigned OldReg, unsigned NewReg);
127    bool PropagateForward(MachineBasicBlock::iterator MII,
128                          MachineBasicBlock *MBB,
129                          unsigned OldReg, unsigned NewReg);
130    void UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
131                                    unsigned Reg, const TargetRegisterClass *RC,
132                                    MachineFunction &MF);
133    bool AllMemRefsCanBeUnfolded(int SS);
134    bool RemoveDeadStores(MachineBasicBlock* MBB);
135  };
136} // end anonymous namespace
137
138char StackSlotColoring::ID = 0;
139
140static RegisterPass<StackSlotColoring>
141X("stack-slot-coloring", "Stack Slot Coloring");
142
143FunctionPass *llvm::createStackSlotColoringPass(bool RegColor) {
144  return new StackSlotColoring(RegColor);
145}
146
147namespace {
148  // IntervalSorter - Comparison predicate that sort live intervals by
149  // their weight.
150  struct IntervalSorter {
151    bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
152      return LHS->weight > RHS->weight;
153    }
154  };
155}
156
157/// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
158/// references and update spill slot weights.
159void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
160  SSRefs.resize(MFI->getObjectIndexEnd());
161
162  // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
163  for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
164       MBBI != E; ++MBBI) {
165    MachineBasicBlock *MBB = &*MBBI;
166    unsigned loopDepth = loopInfo->getLoopDepth(MBB);
167    for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
168         MII != EE; ++MII) {
169      MachineInstr *MI = &*MII;
170      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
171        MachineOperand &MO = MI->getOperand(i);
172        if (!MO.isFI())
173          continue;
174        int FI = MO.getIndex();
175        if (FI < 0)
176          continue;
177        if (!LS->hasInterval(FI))
178          continue;
179        LiveInterval &li = LS->getInterval(FI);
180        li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
181        SSRefs[FI].push_back(MI);
182      }
183    }
184  }
185}
186
187/// InitializeSlots - Process all spill stack slot liveintervals and add them
188/// to a sorted (by weight) list.
189void StackSlotColoring::InitializeSlots() {
190  int LastFI = MFI->getObjectIndexEnd();
191  OrigAlignments.resize(LastFI);
192  OrigSizes.resize(LastFI);
193  AllColors.resize(LastFI);
194  UsedColors.resize(LastFI);
195  Assignments.resize(LastFI);
196
197  // Gather all spill slots into a list.
198  DOUT << "Spill slot intervals:\n";
199  for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
200    LiveInterval &li = i->second;
201    DEBUG(li.dump());
202    int FI = li.getStackSlotIndex();
203    if (MFI->isDeadObjectIndex(FI))
204      continue;
205    SSIntervals.push_back(&li);
206    OrigAlignments[FI] = MFI->getObjectAlignment(FI);
207    OrigSizes[FI]      = MFI->getObjectSize(FI);
208    AllColors.set(FI);
209  }
210  DOUT << '\n';
211
212  // Sort them by weight.
213  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
214
215  // Get first "color".
216  NextColor = AllColors.find_first();
217}
218
219/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
220/// LiveIntervals that have already been assigned to the specified color.
221bool
222StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
223  const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
224  for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
225    LiveInterval *OtherLI = OtherLIs[i];
226    if (OtherLI->overlaps(*li))
227      return true;
228  }
229  return false;
230}
231
232/// ColorSlotsWithFreeRegs - If there are any free registers available, try
233/// replacing spill slots references with registers instead.
234bool
235StackSlotColoring::ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
236                                   SmallVector<SmallVector<int, 4>, 16> &RevMap,
237                                   BitVector &SlotIsReg) {
238  if (!(ColorWithRegs || ColorWithRegsOpt) || !VRM->HasUnusedRegisters())
239    return false;
240
241  bool Changed = false;
242  DOUT << "Assigning unused registers to spill slots:\n";
243  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
244    LiveInterval *li = SSIntervals[i];
245    int SS = li->getStackSlotIndex();
246    if (!UsedColors[SS] || li->weight < 20)
247      // If the weight is < 20, i.e. two references in a loop with depth 1,
248      // don't bother with it.
249      continue;
250
251    // These slots allow to share the same registers.
252    bool AllColored = true;
253    SmallVector<unsigned, 4> ColoredRegs;
254    for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
255      int RSS = RevMap[SS][j];
256      const TargetRegisterClass *RC = LS->getIntervalRegClass(RSS);
257      // If it's not colored to another stack slot, try coloring it
258      // to a "free" register.
259      if (!RC) {
260        AllColored = false;
261        continue;
262      }
263      unsigned Reg = VRM->getFirstUnusedRegister(RC);
264      if (!Reg) {
265        AllColored = false;
266        continue;
267      }
268      if (!AllMemRefsCanBeUnfolded(RSS)) {
269        AllColored = false;
270        continue;
271      } else {
272        DOUT << "Assigning fi#" << RSS << " to " << TRI->getName(Reg) << '\n';
273        ColoredRegs.push_back(Reg);
274        SlotMapping[RSS] = Reg;
275        SlotIsReg.set(RSS);
276        Changed = true;
277      }
278    }
279
280    // Register and its sub-registers are no longer free.
281    while (!ColoredRegs.empty()) {
282      unsigned Reg = ColoredRegs.back();
283      ColoredRegs.pop_back();
284      VRM->setRegisterUsed(Reg);
285      // If reg is a callee-saved register, it will have to be spilled in
286      // the prologue.
287      MRI->setPhysRegUsed(Reg);
288      for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
289        VRM->setRegisterUsed(*AS);
290        MRI->setPhysRegUsed(*AS);
291      }
292    }
293    // This spill slot is dead after the rewrites
294    if (AllColored) {
295      MFI->RemoveStackObject(SS);
296      ++NumEliminated;
297    }
298  }
299  DOUT << '\n';
300
301  return Changed;
302}
303
304/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
305///
306int StackSlotColoring::ColorSlot(LiveInterval *li) {
307  int Color = -1;
308  bool Share = false;
309  if (!DisableSharing) {
310    // Check if it's possible to reuse any of the used colors.
311    Color = UsedColors.find_first();
312    while (Color != -1) {
313      if (!OverlapWithAssignments(li, Color)) {
314        Share = true;
315        ++NumEliminated;
316        break;
317      }
318      Color = UsedColors.find_next(Color);
319    }
320  }
321
322  // Assign it to the first available color (assumed to be the best) if it's
323  // not possible to share a used color with other objects.
324  if (!Share) {
325    assert(NextColor != -1 && "No more spill slots?");
326    Color = NextColor;
327    UsedColors.set(Color);
328    NextColor = AllColors.find_next(NextColor);
329  }
330
331  // Record the assignment.
332  Assignments[Color].push_back(li);
333  int FI = li->getStackSlotIndex();
334  DOUT << "Assigning fi#" << FI << " to fi#" << Color << "\n";
335
336  // Change size and alignment of the allocated slot. If there are multiple
337  // objects sharing the same slot, then make sure the size and alignment
338  // are large enough for all.
339  unsigned Align = OrigAlignments[FI];
340  if (!Share || Align > MFI->getObjectAlignment(Color))
341    MFI->setObjectAlignment(Color, Align);
342  int64_t Size = OrigSizes[FI];
343  if (!Share || Size > MFI->getObjectSize(Color))
344    MFI->setObjectSize(Color, Size);
345  return Color;
346}
347
348/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
349/// operands in the function.
350bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
351  unsigned NumObjs = MFI->getObjectIndexEnd();
352  SmallVector<int, 16> SlotMapping(NumObjs, -1);
353  SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
354  SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
355  BitVector SlotIsReg(NumObjs);
356  BitVector UsedColors(NumObjs);
357
358  DOUT << "Color spill slot intervals:\n";
359  bool Changed = false;
360  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
361    LiveInterval *li = SSIntervals[i];
362    int SS = li->getStackSlotIndex();
363    int NewSS = ColorSlot(li);
364    assert(NewSS >= 0 && "Stack coloring failed?");
365    SlotMapping[SS] = NewSS;
366    RevMap[NewSS].push_back(SS);
367    SlotWeights[NewSS] += li->weight;
368    UsedColors.set(NewSS);
369    Changed |= (SS != NewSS);
370  }
371
372  DOUT << "\nSpill slots after coloring:\n";
373  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
374    LiveInterval *li = SSIntervals[i];
375    int SS = li->getStackSlotIndex();
376    li->weight = SlotWeights[SS];
377  }
378  // Sort them by new weight.
379  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
380
381#ifndef NDEBUG
382  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
383    DEBUG(SSIntervals[i]->dump());
384  DOUT << '\n';
385#endif
386
387  // Can we "color" a stack slot with a unused register?
388  Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
389
390  if (!Changed)
391    return false;
392
393  // Rewrite all MO_FrameIndex operands.
394  for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
395    bool isReg = SlotIsReg[SS];
396    int NewFI = SlotMapping[SS];
397    if (NewFI == -1 || (NewFI == (int)SS && !isReg))
398      continue;
399
400    SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
401    for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
402      if (!isReg)
403        RewriteInstruction(RefMIs[i], SS, NewFI, MF);
404      else {
405        // Rewrite to use a register instead.
406        const TargetRegisterClass *RC = LS->getIntervalRegClass(SS);
407        UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, RC, MF);
408      }
409  }
410
411  // Delete unused stack slots.
412  while (NextColor != -1) {
413    DOUT << "Removing unused stack object fi#" << NextColor << "\n";
414    MFI->RemoveStackObject(NextColor);
415    NextColor = AllColors.find_next(NextColor);
416  }
417
418  return true;
419}
420
421/// AllMemRefsCanBeUnfolded - Return true if all references of the specified
422/// spill slot index can be unfolded.
423bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
424  SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
425  for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
426    MachineInstr *MI = RefMIs[i];
427    if (TII->isLoadFromStackSlot(MI, SS) ||
428        TII->isStoreToStackSlot(MI, SS))
429      // Restore and spill will become copies.
430      return true;
431    if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
432      return false;
433    for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
434      MachineOperand &MO = MI->getOperand(j);
435      if (MO.isFI() && MO.getIndex() != SS)
436        // If it uses another frameindex, we can, currently* unfold it.
437        return false;
438    }
439  }
440  return true;
441}
442
443/// RewriteInstruction - Rewrite specified instruction by replacing references
444/// to old frame index with new one.
445void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
446                                           int NewFI, MachineFunction &MF) {
447  for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
448    MachineOperand &MO = MI->getOperand(i);
449    if (!MO.isFI())
450      continue;
451    int FI = MO.getIndex();
452    if (FI != OldFI)
453      continue;
454    MO.setIndex(NewFI);
455  }
456
457  // Update the MachineMemOperand for the new memory location.
458  // FIXME: We need a better method of managing these too.
459  SmallVector<MachineMemOperand, 2> MMOs(MI->memoperands_begin(),
460                                         MI->memoperands_end());
461  MI->clearMemOperands(MF);
462  const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
463  for (unsigned i = 0, ee = MMOs.size(); i != ee; ++i) {
464    if (MMOs[i].getValue() != OldSV)
465      MI->addMemOperand(MF, MMOs[i]);
466    else {
467      MachineMemOperand MMO(PseudoSourceValue::getFixedStack(NewFI),
468                            MMOs[i].getFlags(), MMOs[i].getOffset(),
469                            MMOs[i].getSize(),  MMOs[i].getAlignment());
470      MI->addMemOperand(MF, MMO);
471    }
472  }
473}
474
475/// PropagateBackward - Traverse backward and look for the definition of
476/// OldReg. If it can successfully update all of the references with NewReg,
477/// do so and return true.
478bool StackSlotColoring::PropagateBackward(MachineBasicBlock::iterator MII,
479                                          MachineBasicBlock *MBB,
480                                          unsigned OldReg, unsigned NewReg) {
481  if (MII == MBB->begin())
482    return false;
483
484  SmallVector<MachineOperand*, 4> Refs;
485  while (--MII != MBB->begin()) {
486    bool FoundDef = false;  // Not counting 2address def.
487    bool FoundUse = false;
488    bool FoundKill = false;
489    const TargetInstrDesc &TID = MII->getDesc();
490    for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
491      MachineOperand &MO = MII->getOperand(i);
492      if (!MO.isReg())
493        continue;
494      unsigned Reg = MO.getReg();
495      if (Reg == 0)
496        continue;
497      if (Reg == OldReg) {
498        const TargetRegisterClass *RC = getInstrOperandRegClass(TRI, TID, i);
499        if (RC && !RC->contains(NewReg))
500          return false;
501
502        if (MO.isUse()) {
503          FoundUse = true;
504          if (MO.isKill())
505            FoundKill = true;
506          Refs.push_back(&MO);
507        } else {
508          Refs.push_back(&MO);
509          if (!MII->isRegTiedToUseOperand(i))
510            FoundDef = true;
511        }
512      } else if (TRI->regsOverlap(Reg, NewReg)) {
513        return false;
514      } else if (TRI->regsOverlap(Reg, OldReg)) {
515        if (!MO.isUse() || !MO.isKill())
516          return false;
517      }
518    }
519    if (FoundDef) {
520      for (unsigned i = 0, e = Refs.size(); i != e; ++i)
521        Refs[i]->setReg(NewReg);
522      return true;
523    }
524  }
525  return false;
526}
527
528/// PropagateForward - Traverse forward and look for the kill of OldReg. If
529/// it can successfully update all of the uses with NewReg, do so and
530/// return true.
531bool StackSlotColoring::PropagateForward(MachineBasicBlock::iterator MII,
532                                         MachineBasicBlock *MBB,
533                                         unsigned OldReg, unsigned NewReg) {
534  if (MII == MBB->end())
535    return false;
536
537  SmallVector<MachineOperand*, 4> Uses;
538  while (++MII != MBB->end()) {
539    bool FoundUse = false;
540    bool FoundKill = false;
541    const TargetInstrDesc &TID = MII->getDesc();
542    for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
543      MachineOperand &MO = MII->getOperand(i);
544      if (!MO.isReg())
545        continue;
546      unsigned Reg = MO.getReg();
547      if (Reg == 0)
548        continue;
549      if (Reg == OldReg) {
550        if (MO.isDef())
551          return false;
552
553        const TargetRegisterClass *RC = getInstrOperandRegClass(TRI, TID, i);
554        if (RC && !RC->contains(NewReg))
555          return false;
556        FoundUse = true;
557        if (MO.isKill())
558          FoundKill = true;
559        Uses.push_back(&MO);
560      } else if (TRI->regsOverlap(Reg, NewReg) ||
561                 TRI->regsOverlap(Reg, OldReg))
562        return false;
563    }
564    if (FoundKill) {
565      for (unsigned i = 0, e = Uses.size(); i != e; ++i)
566        Uses[i]->setReg(NewReg);
567      return true;
568    }
569  }
570  return false;
571}
572
573/// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
574/// folded memory references and replacing those references with register
575/// references instead.
576void StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
577                                                  unsigned Reg,
578                                                  const TargetRegisterClass *RC,
579                                                  MachineFunction &MF) {
580  MachineBasicBlock *MBB = MI->getParent();
581  if (unsigned DstReg = TII->isLoadFromStackSlot(MI, OldFI)) {
582    if (PropagateForward(MI, MBB, DstReg, Reg)) {
583      DOUT << "Eliminated load: ";
584      DEBUG(MI->dump());
585      ++NumLoadElim;
586    } else {
587      TII->copyRegToReg(*MBB, MI, DstReg, Reg, RC, RC);
588      ++NumRegRepl;
589    }
590  } else if (unsigned SrcReg = TII->isStoreToStackSlot(MI, OldFI)) {
591    if (MI->killsRegister(SrcReg) && PropagateBackward(MI, MBB, SrcReg, Reg)) {
592      DOUT << "Eliminated store: ";
593      DEBUG(MI->dump());
594      ++NumStoreElim;
595    } else {
596      TII->copyRegToReg(*MBB, MI, Reg, SrcReg, RC, RC);
597      ++NumRegRepl;
598    }
599  } else {
600    SmallVector<MachineInstr*, 4> NewMIs;
601    bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
602    assert(Success && "Failed to unfold!");
603    MBB->insert(MI, NewMIs[0]);
604    ++NumRegRepl;
605  }
606  MBB->erase(MI);
607}
608
609/// RemoveDeadStores - Scan through a basic block and look for loads followed
610/// by stores.  If they're both using the same stack slot, then the store is
611/// definitely dead.  This could obviously be much more aggressive (consider
612/// pairs with instructions between them), but such extensions might have a
613/// considerable compile time impact.
614bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
615  // FIXME: This could be much more aggressive, but we need to investigate
616  // the compile time impact of doing so.
617  bool changed = false;
618
619  SmallVector<MachineInstr*, 4> toErase;
620
621  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
622       I != E; ++I) {
623    if (DCELimit != -1 && (int)NumDead >= DCELimit)
624      break;
625
626    MachineBasicBlock::iterator NextMI = next(I);
627    if (NextMI == MBB->end()) continue;
628
629    int FirstSS, SecondSS;
630    unsigned LoadReg = 0;
631    unsigned StoreReg = 0;
632    if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
633    if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
634    if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
635
636    ++NumDead;
637    changed = true;
638
639    if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
640      ++NumDead;
641      toErase.push_back(I);
642    }
643
644    toErase.push_back(NextMI);
645    ++I;
646  }
647
648  for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
649       E = toErase.end(); I != E; ++I)
650    (*I)->eraseFromParent();
651
652  return changed;
653}
654
655
656bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
657  DOUT << "********** Stack Slot Coloring **********\n";
658
659  MFI = MF.getFrameInfo();
660  MRI = &MF.getRegInfo();
661  TII = MF.getTarget().getInstrInfo();
662  TRI = MF.getTarget().getRegisterInfo();
663  LS = &getAnalysis<LiveStacks>();
664  VRM = &getAnalysis<VirtRegMap>();
665  loopInfo = &getAnalysis<MachineLoopInfo>();
666
667  bool Changed = false;
668
669  unsigned NumSlots = LS->getNumIntervals();
670  if (NumSlots < 2) {
671    if (NumSlots == 0 || !VRM->HasUnusedRegisters())
672      // Nothing to do!
673      return false;
674  }
675
676  // Gather spill slot references
677  ScanForSpillSlotRefs(MF);
678  InitializeSlots();
679  Changed = ColorSlots(MF);
680
681  NextColor = -1;
682  SSIntervals.clear();
683  for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
684    SSRefs[i].clear();
685  SSRefs.clear();
686  OrigAlignments.clear();
687  OrigSizes.clear();
688  AllColors.clear();
689  UsedColors.clear();
690  for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
691    Assignments[i].clear();
692  Assignments.clear();
693
694  if (Changed) {
695    for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
696      Changed |= RemoveDeadStores(I);
697  }
698
699  return Changed;
700}
701