StackSlotColoring.cpp revision 224145 
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/Function.h"
17#include "llvm/Module.h"
18#include "llvm/CodeGen/Passes.h"
19#include "llvm/CodeGen/LiveIntervalAnalysis.h"
20#include "llvm/CodeGen/LiveStackAnalysis.h"
21#include "llvm/CodeGen/MachineFrameInfo.h"
22#include "llvm/CodeGen/MachineInstrBuilder.h"
23#include "llvm/CodeGen/MachineLoopInfo.h"
24#include "llvm/CodeGen/MachineMemOperand.h"
25#include "llvm/CodeGen/MachineRegisterInfo.h"
26#include "llvm/CodeGen/PseudoSourceValue.h"
27#include "llvm/Support/CommandLine.h"
28#include "llvm/Support/Debug.h"
29#include "llvm/Target/TargetInstrInfo.h"
30#include "llvm/Target/TargetMachine.h"
31#include "llvm/ADT/BitVector.h"
32#include "llvm/ADT/SmallSet.h"
33#include "llvm/ADT/SmallVector.h"
34#include "llvm/ADT/Statistic.h"
35#include <vector>
36using namespace llvm;
37
38static cl::opt<bool>
39DisableSharing("no-stack-slot-sharing",
40             cl::init(false), cl::Hidden,
41             cl::desc("Suppress slot sharing during stack coloring"));
42
43static cl::opt<bool>
44ColorWithRegsOpt("color-ss-with-regs",
45                 cl::init(false), cl::Hidden,
46                 cl::desc("Color stack slots with free registers"));
47
48
49static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
50
51STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
52STATISTIC(NumRegRepl,    "Number of stack slot refs replaced with reg refs");
53STATISTIC(NumLoadElim,   "Number of loads eliminated");
54STATISTIC(NumStoreElim,  "Number of stores eliminated");
55STATISTIC(NumDead,       "Number of trivially dead stack accesses eliminated");
56
57namespace {
58  class StackSlotColoring : public MachineFunctionPass {
59    bool ColorWithRegs;
60    LiveStacks* LS;
61    VirtRegMap* VRM;
62    MachineFrameInfo *MFI;
63    MachineRegisterInfo *MRI;
64    const TargetInstrInfo  *TII;
65    const TargetRegisterInfo *TRI;
66    const MachineLoopInfo *loopInfo;
67
68    // SSIntervals - Spill slot intervals.
69    std::vector<LiveInterval*> SSIntervals;
70
71    // SSRefs - Keep a list of frame index references for each spill slot.
72    SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
73
74    // OrigAlignments - Alignments of stack objects before coloring.
75    SmallVector<unsigned, 16> OrigAlignments;
76
77    // OrigSizes - Sizess of stack objects before coloring.
78    SmallVector<unsigned, 16> OrigSizes;
79
80    // AllColors - If index is set, it's a spill slot, i.e. color.
81    // FIXME: This assumes PEI locate spill slot with smaller indices
82    // closest to stack pointer / frame pointer. Therefore, smaller
83    // index == better color.
84    BitVector AllColors;
85
86    // NextColor - Next "color" that's not yet used.
87    int NextColor;
88
89    // UsedColors - "Colors" that have been assigned.
90    BitVector UsedColors;
91
92    // Assignments - Color to intervals mapping.
93    SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
94
95  public:
96    static char ID; // Pass identification
97    StackSlotColoring() :
98      MachineFunctionPass(ID), ColorWithRegs(false), NextColor(-1) {
99        initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
100      }
101    StackSlotColoring(bool RegColor) :
102      MachineFunctionPass(ID), ColorWithRegs(RegColor), NextColor(-1) {
103        initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
104      }
105
106    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
107      AU.setPreservesCFG();
108      AU.addRequired<SlotIndexes>();
109      AU.addPreserved<SlotIndexes>();
110      AU.addRequired<LiveStacks>();
111      AU.addRequired<VirtRegMap>();
112      AU.addPreserved<VirtRegMap>();
113      AU.addRequired<MachineLoopInfo>();
114      AU.addPreserved<MachineLoopInfo>();
115      AU.addPreservedID(MachineDominatorsID);
116      MachineFunctionPass::getAnalysisUsage(AU);
117    }
118
119    virtual bool runOnMachineFunction(MachineFunction &MF);
120    virtual const char* getPassName() const {
121      return "Stack Slot Coloring";
122    }
123
124  private:
125    void InitializeSlots();
126    void ScanForSpillSlotRefs(MachineFunction &MF);
127    bool OverlapWithAssignments(LiveInterval *li, int Color) const;
128    int ColorSlot(LiveInterval *li);
129    bool ColorSlots(MachineFunction &MF);
130    bool ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
131                                SmallVector<SmallVector<int, 4>, 16> &RevMap,
132                                BitVector &SlotIsReg);
133    void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
134                            MachineFunction &MF);
135    bool PropagateBackward(MachineBasicBlock::iterator MII,
136                           MachineBasicBlock *MBB,
137                           unsigned OldReg, unsigned NewReg);
138    bool PropagateForward(MachineBasicBlock::iterator MII,
139                          MachineBasicBlock *MBB,
140                          unsigned OldReg, unsigned NewReg);
141    void UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
142                                    unsigned Reg, const TargetRegisterClass *RC,
143                                    SmallSet<unsigned, 4> &Defs,
144                                    MachineFunction &MF);
145    bool AllMemRefsCanBeUnfolded(int SS);
146    bool RemoveDeadStores(MachineBasicBlock* MBB);
147  };
148} // end anonymous namespace
149
150char StackSlotColoring::ID = 0;
151
152INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
153                "Stack Slot Coloring", false, false)
154INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
155INITIALIZE_PASS_DEPENDENCY(LiveStacks)
156INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
157INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
158INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
159                "Stack Slot Coloring", false, false)
160
161FunctionPass *llvm::createStackSlotColoringPass(bool RegColor) {
162  return new StackSlotColoring(RegColor);
163}
164
165namespace {
166  // IntervalSorter - Comparison predicate that sort live intervals by
167  // their weight.
168  struct IntervalSorter {
169    bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
170      return LHS->weight > RHS->weight;
171    }
172  };
173}
174
175/// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
176/// references and update spill slot weights.
177void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
178  SSRefs.resize(MFI->getObjectIndexEnd());
179
180  // FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
181  for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
182       MBBI != E; ++MBBI) {
183    MachineBasicBlock *MBB = &*MBBI;
184    unsigned loopDepth = loopInfo->getLoopDepth(MBB);
185    for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
186         MII != EE; ++MII) {
187      MachineInstr *MI = &*MII;
188      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
189        MachineOperand &MO = MI->getOperand(i);
190        if (!MO.isFI())
191          continue;
192        int FI = MO.getIndex();
193        if (FI < 0)
194          continue;
195        if (!LS->hasInterval(FI))
196          continue;
197        LiveInterval &li = LS->getInterval(FI);
198        if (!MI->isDebugValue())
199          li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
200        SSRefs[FI].push_back(MI);
201      }
202    }
203  }
204}
205
206/// InitializeSlots - Process all spill stack slot liveintervals and add them
207/// to a sorted (by weight) list.
208void StackSlotColoring::InitializeSlots() {
209  int LastFI = MFI->getObjectIndexEnd();
210  OrigAlignments.resize(LastFI);
211  OrigSizes.resize(LastFI);
212  AllColors.resize(LastFI);
213  UsedColors.resize(LastFI);
214  Assignments.resize(LastFI);
215
216  // Gather all spill slots into a list.
217  DEBUG(dbgs() << "Spill slot intervals:\n");
218  for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
219    LiveInterval &li = i->second;
220    DEBUG(li.dump());
221    int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
222    if (MFI->isDeadObjectIndex(FI))
223      continue;
224    SSIntervals.push_back(&li);
225    OrigAlignments[FI] = MFI->getObjectAlignment(FI);
226    OrigSizes[FI]      = MFI->getObjectSize(FI);
227    AllColors.set(FI);
228  }
229  DEBUG(dbgs() << '\n');
230
231  // Sort them by weight.
232  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
233
234  // Get first "color".
235  NextColor = AllColors.find_first();
236}
237
238/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
239/// LiveIntervals that have already been assigned to the specified color.
240bool
241StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
242  const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
243  for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
244    LiveInterval *OtherLI = OtherLIs[i];
245    if (OtherLI->overlaps(*li))
246      return true;
247  }
248  return false;
249}
250
251/// ColorSlotsWithFreeRegs - If there are any free registers available, try
252/// replacing spill slots references with registers instead.
253bool
254StackSlotColoring::ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
255                                   SmallVector<SmallVector<int, 4>, 16> &RevMap,
256                                   BitVector &SlotIsReg) {
257  if (!(ColorWithRegs || ColorWithRegsOpt) || !VRM->HasUnusedRegisters())
258    return false;
259
260  bool Changed = false;
261  DEBUG(dbgs() << "Assigning unused registers to spill slots:\n");
262  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
263    LiveInterval *li = SSIntervals[i];
264    int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
265    if (!UsedColors[SS] || li->weight < 20)
266      // If the weight is < 20, i.e. two references in a loop with depth 1,
267      // don't bother with it.
268      continue;
269
270    // These slots allow to share the same registers.
271    bool AllColored = true;
272    SmallVector<unsigned, 4> ColoredRegs;
273    for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
274      int RSS = RevMap[SS][j];
275      const TargetRegisterClass *RC = LS->getIntervalRegClass(RSS);
276      // If it's not colored to another stack slot, try coloring it
277      // to a "free" register.
278      if (!RC) {
279        AllColored = false;
280        continue;
281      }
282      unsigned Reg = VRM->getFirstUnusedRegister(RC);
283      if (!Reg) {
284        AllColored = false;
285        continue;
286      }
287      if (!AllMemRefsCanBeUnfolded(RSS)) {
288        AllColored = false;
289        continue;
290      } else {
291        DEBUG(dbgs() << "Assigning fi#" << RSS << " to "
292                     << TRI->getName(Reg) << '\n');
293        ColoredRegs.push_back(Reg);
294        SlotMapping[RSS] = Reg;
295        SlotIsReg.set(RSS);
296        Changed = true;
297      }
298    }
299
300    // Register and its sub-registers are no longer free.
301    while (!ColoredRegs.empty()) {
302      unsigned Reg = ColoredRegs.back();
303      ColoredRegs.pop_back();
304      VRM->setRegisterUsed(Reg);
305      // If reg is a callee-saved register, it will have to be spilled in
306      // the prologue.
307      MRI->setPhysRegUsed(Reg);
308      for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
309        VRM->setRegisterUsed(*AS);
310        MRI->setPhysRegUsed(*AS);
311      }
312    }
313    // This spill slot is dead after the rewrites
314    if (AllColored) {
315      MFI->RemoveStackObject(SS);
316      ++NumEliminated;
317    }
318  }
319  DEBUG(dbgs() << '\n');
320
321  return Changed;
322}
323
324/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
325///
326int StackSlotColoring::ColorSlot(LiveInterval *li) {
327  int Color = -1;
328  bool Share = false;
329  if (!DisableSharing) {
330    // Check if it's possible to reuse any of the used colors.
331    Color = UsedColors.find_first();
332    while (Color != -1) {
333      if (!OverlapWithAssignments(li, Color)) {
334        Share = true;
335        ++NumEliminated;
336        break;
337      }
338      Color = UsedColors.find_next(Color);
339    }
340  }
341
342  // Assign it to the first available color (assumed to be the best) if it's
343  // not possible to share a used color with other objects.
344  if (!Share) {
345    assert(NextColor != -1 && "No more spill slots?");
346    Color = NextColor;
347    UsedColors.set(Color);
348    NextColor = AllColors.find_next(NextColor);
349  }
350
351  // Record the assignment.
352  Assignments[Color].push_back(li);
353  int FI = TargetRegisterInfo::stackSlot2Index(li->reg);
354  DEBUG(dbgs() << "Assigning fi#" << FI << " to fi#" << Color << "\n");
355
356  // Change size and alignment of the allocated slot. If there are multiple
357  // objects sharing the same slot, then make sure the size and alignment
358  // are large enough for all.
359  unsigned Align = OrigAlignments[FI];
360  if (!Share || Align > MFI->getObjectAlignment(Color))
361    MFI->setObjectAlignment(Color, Align);
362  int64_t Size = OrigSizes[FI];
363  if (!Share || Size > MFI->getObjectSize(Color))
364    MFI->setObjectSize(Color, Size);
365  return Color;
366}
367
368/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
369/// operands in the function.
370bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
371  unsigned NumObjs = MFI->getObjectIndexEnd();
372  SmallVector<int, 16> SlotMapping(NumObjs, -1);
373  SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
374  SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
375  BitVector SlotIsReg(NumObjs);
376  BitVector UsedColors(NumObjs);
377
378  DEBUG(dbgs() << "Color spill slot intervals:\n");
379  bool Changed = false;
380  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
381    LiveInterval *li = SSIntervals[i];
382    int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
383    int NewSS = ColorSlot(li);
384    assert(NewSS >= 0 && "Stack coloring failed?");
385    SlotMapping[SS] = NewSS;
386    RevMap[NewSS].push_back(SS);
387    SlotWeights[NewSS] += li->weight;
388    UsedColors.set(NewSS);
389    Changed |= (SS != NewSS);
390  }
391
392  DEBUG(dbgs() << "\nSpill slots after coloring:\n");
393  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
394    LiveInterval *li = SSIntervals[i];
395    int SS = TargetRegisterInfo::stackSlot2Index(li->reg);
396    li->weight = SlotWeights[SS];
397  }
398  // Sort them by new weight.
399  std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
400
401#ifndef NDEBUG
402  for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
403    DEBUG(SSIntervals[i]->dump());
404  DEBUG(dbgs() << '\n');
405#endif
406
407  // Can we "color" a stack slot with a unused register?
408  Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
409
410  if (!Changed)
411    return false;
412
413  // Rewrite all MO_FrameIndex operands.
414  SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
415  for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
416    bool isReg = SlotIsReg[SS];
417    int NewFI = SlotMapping[SS];
418    if (NewFI == -1 || (NewFI == (int)SS && !isReg))
419      continue;
420
421    const TargetRegisterClass *RC = LS->getIntervalRegClass(SS);
422    SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
423    for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
424      if (!isReg)
425        RewriteInstruction(RefMIs[i], SS, NewFI, MF);
426      else {
427        // Rewrite to use a register instead.
428        unsigned MBBId = RefMIs[i]->getParent()->getNumber();
429        SmallSet<unsigned, 4> &Defs = NewDefs[MBBId];
430        UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, RC, Defs, MF);
431      }
432  }
433
434  // Delete unused stack slots.
435  while (NextColor != -1) {
436    DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
437    MFI->RemoveStackObject(NextColor);
438    NextColor = AllColors.find_next(NextColor);
439  }
440
441  return true;
442}
443
444/// AllMemRefsCanBeUnfolded - Return true if all references of the specified
445/// spill slot index can be unfolded.
446bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
447  SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
448  for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
449    MachineInstr *MI = RefMIs[i];
450    if (TII->isLoadFromStackSlot(MI, SS) ||
451        TII->isStoreToStackSlot(MI, SS))
452      // Restore and spill will become copies.
453      return true;
454    if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
455      return false;
456    for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
457      MachineOperand &MO = MI->getOperand(j);
458      if (MO.isFI() && MO.getIndex() != SS)
459        // If it uses another frameindex, we can, currently* unfold it.
460        return false;
461    }
462  }
463  return true;
464}
465
466/// RewriteInstruction - Rewrite specified instruction by replacing references
467/// to old frame index with new one.
468void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
469                                           int NewFI, MachineFunction &MF) {
470  // Update the operands.
471  for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
472    MachineOperand &MO = MI->getOperand(i);
473    if (!MO.isFI())
474      continue;
475    int FI = MO.getIndex();
476    if (FI != OldFI)
477      continue;
478    MO.setIndex(NewFI);
479  }
480
481  // Update the memory references. This changes the MachineMemOperands
482  // directly. They may be in use by multiple instructions, however all
483  // instructions using OldFI are being rewritten to use NewFI.
484  const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
485  const Value *NewSV = PseudoSourceValue::getFixedStack(NewFI);
486  for (MachineInstr::mmo_iterator I = MI->memoperands_begin(),
487       E = MI->memoperands_end(); I != E; ++I)
488    if ((*I)->getValue() == OldSV)
489      (*I)->setValue(NewSV);
490}
491
492/// PropagateBackward - Traverse backward and look for the definition of
493/// OldReg. If it can successfully update all of the references with NewReg,
494/// do so and return true.
495bool StackSlotColoring::PropagateBackward(MachineBasicBlock::iterator MII,
496                                          MachineBasicBlock *MBB,
497                                          unsigned OldReg, unsigned NewReg) {
498  if (MII == MBB->begin())
499    return false;
500
501  SmallVector<MachineOperand*, 4> Uses;
502  SmallVector<MachineOperand*, 4> Refs;
503  while (--MII != MBB->begin()) {
504    bool FoundDef = false;  // Not counting 2address def.
505
506    Uses.clear();
507    const MCInstrDesc &MCID = MII->getDesc();
508    for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
509      MachineOperand &MO = MII->getOperand(i);
510      if (!MO.isReg())
511        continue;
512      unsigned Reg = MO.getReg();
513      if (Reg == 0)
514        continue;
515      if (Reg == OldReg) {
516        if (MO.isImplicit())
517          return false;
518
519        // Abort the use is actually a sub-register def. We don't have enough
520        // information to figure out if it is really legal.
521        if (MO.getSubReg() || MII->isSubregToReg())
522          return false;
523
524        const TargetRegisterClass *RC = TII->getRegClass(MCID, i, TRI);
525        if (RC && !RC->contains(NewReg))
526          return false;
527
528        if (MO.isUse()) {
529          Uses.push_back(&MO);
530        } else {
531          Refs.push_back(&MO);
532          if (!MII->isRegTiedToUseOperand(i))
533            FoundDef = true;
534        }
535      } else if (TRI->regsOverlap(Reg, NewReg)) {
536        return false;
537      } else if (TRI->regsOverlap(Reg, OldReg)) {
538        if (!MO.isUse() || !MO.isKill())
539          return false;
540      }
541    }
542
543    if (FoundDef) {
544      // Found non-two-address def. Stop here.
545      for (unsigned i = 0, e = Refs.size(); i != e; ++i)
546        Refs[i]->setReg(NewReg);
547      return true;
548    }
549
550    // Two-address uses must be updated as well.
551    for (unsigned i = 0, e = Uses.size(); i != e; ++i)
552      Refs.push_back(Uses[i]);
553  }
554  return false;
555}
556
557/// PropagateForward - Traverse forward and look for the kill of OldReg. If
558/// it can successfully update all of the uses with NewReg, do so and
559/// return true.
560bool StackSlotColoring::PropagateForward(MachineBasicBlock::iterator MII,
561                                         MachineBasicBlock *MBB,
562                                         unsigned OldReg, unsigned NewReg) {
563  if (MII == MBB->end())
564    return false;
565
566  SmallVector<MachineOperand*, 4> Uses;
567  while (++MII != MBB->end()) {
568    bool FoundKill = false;
569    const MCInstrDesc &MCID = MII->getDesc();
570    for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
571      MachineOperand &MO = MII->getOperand(i);
572      if (!MO.isReg())
573        continue;
574      unsigned Reg = MO.getReg();
575      if (Reg == 0)
576        continue;
577      if (Reg == OldReg) {
578        if (MO.isDef() || MO.isImplicit())
579          return false;
580
581        // Abort the use is actually a sub-register use. We don't have enough
582        // information to figure out if it is really legal.
583        if (MO.getSubReg())
584          return false;
585
586        const TargetRegisterClass *RC = TII->getRegClass(MCID, i, TRI);
587        if (RC && !RC->contains(NewReg))
588          return false;
589        if (MO.isKill())
590          FoundKill = true;
591
592        Uses.push_back(&MO);
593      } else if (TRI->regsOverlap(Reg, NewReg) ||
594                 TRI->regsOverlap(Reg, OldReg))
595        return false;
596    }
597    if (FoundKill) {
598      for (unsigned i = 0, e = Uses.size(); i != e; ++i)
599        Uses[i]->setReg(NewReg);
600      return true;
601    }
602  }
603  return false;
604}
605
606/// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
607/// folded memory references and replacing those references with register
608/// references instead.
609void
610StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
611                                               unsigned Reg,
612                                               const TargetRegisterClass *RC,
613                                               SmallSet<unsigned, 4> &Defs,
614                                               MachineFunction &MF) {
615  MachineBasicBlock *MBB = MI->getParent();
616  if (unsigned DstReg = TII->isLoadFromStackSlot(MI, OldFI)) {
617    if (PropagateForward(MI, MBB, DstReg, Reg)) {
618      DEBUG(dbgs() << "Eliminated load: ");
619      DEBUG(MI->dump());
620      ++NumLoadElim;
621    } else {
622      BuildMI(*MBB, MI, MI->getDebugLoc(), TII->get(TargetOpcode::COPY),
623              DstReg).addReg(Reg);
624      ++NumRegRepl;
625    }
626
627    if (!Defs.count(Reg)) {
628      // If this is the first use of Reg in this MBB and it wasn't previously
629      // defined in MBB, add it to livein.
630      MBB->addLiveIn(Reg);
631      Defs.insert(Reg);
632    }
633  } else if (unsigned SrcReg = TII->isStoreToStackSlot(MI, OldFI)) {
634    if (MI->killsRegister(SrcReg) && PropagateBackward(MI, MBB, SrcReg, Reg)) {
635      DEBUG(dbgs() << "Eliminated store: ");
636      DEBUG(MI->dump());
637      ++NumStoreElim;
638    } else {
639      BuildMI(*MBB, MI, MI->getDebugLoc(), TII->get(TargetOpcode::COPY), Reg)
640        .addReg(SrcReg);
641      ++NumRegRepl;
642    }
643
644    // Remember reg has been defined in MBB.
645    Defs.insert(Reg);
646  } else {
647    SmallVector<MachineInstr*, 4> NewMIs;
648    bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
649    (void)Success; // Silence compiler warning.
650    assert(Success && "Failed to unfold!");
651    MachineInstr *NewMI = NewMIs[0];
652    MBB->insert(MI, NewMI);
653    ++NumRegRepl;
654
655    if (NewMI->readsRegister(Reg)) {
656      if (!Defs.count(Reg))
657        // If this is the first use of Reg in this MBB and it wasn't previously
658        // defined in MBB, add it to livein.
659        MBB->addLiveIn(Reg);
660      Defs.insert(Reg);
661    }
662  }
663  MBB->erase(MI);
664}
665
666/// RemoveDeadStores - Scan through a basic block and look for loads followed
667/// by stores.  If they're both using the same stack slot, then the store is
668/// definitely dead.  This could obviously be much more aggressive (consider
669/// pairs with instructions between them), but such extensions might have a
670/// considerable compile time impact.
671bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
672  // FIXME: This could be much more aggressive, but we need to investigate
673  // the compile time impact of doing so.
674  bool changed = false;
675
676  SmallVector<MachineInstr*, 4> toErase;
677
678  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
679       I != E; ++I) {
680    if (DCELimit != -1 && (int)NumDead >= DCELimit)
681      break;
682
683    MachineBasicBlock::iterator NextMI = llvm::next(I);
684    if (NextMI == MBB->end()) continue;
685
686    int FirstSS, SecondSS;
687    unsigned LoadReg = 0;
688    unsigned StoreReg = 0;
689    if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
690    if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
691    if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
692
693    ++NumDead;
694    changed = true;
695
696    if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
697      ++NumDead;
698      toErase.push_back(I);
699    }
700
701    toErase.push_back(NextMI);
702    ++I;
703  }
704
705  for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
706       E = toErase.end(); I != E; ++I)
707    (*I)->eraseFromParent();
708
709  return changed;
710}
711
712
713bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
714  DEBUG({
715      dbgs() << "********** Stack Slot Coloring **********\n"
716             << "********** Function: "
717             << MF.getFunction()->getName() << '\n';
718    });
719
720  MFI = MF.getFrameInfo();
721  MRI = &MF.getRegInfo();
722  TII = MF.getTarget().getInstrInfo();
723  TRI = MF.getTarget().getRegisterInfo();
724  LS = &getAnalysis<LiveStacks>();
725  VRM = &getAnalysis<VirtRegMap>();
726  loopInfo = &getAnalysis<MachineLoopInfo>();
727
728  bool Changed = false;
729
730  unsigned NumSlots = LS->getNumIntervals();
731  if (NumSlots < 2) {
732    if (NumSlots == 0 || !VRM->HasUnusedRegisters())
733      // Nothing to do!
734      return false;
735  }
736
737  // If there are calls to setjmp or sigsetjmp, don't perform stack slot
738  // coloring. The stack could be modified before the longjmp is executed,
739  // resulting in the wrong value being used afterwards. (See
740  // <rdar://problem/8007500>.)
741  if (MF.callsSetJmp())
742    return false;
743
744  // Gather spill slot references
745  ScanForSpillSlotRefs(MF);
746  InitializeSlots();
747  Changed = ColorSlots(MF);
748
749  NextColor = -1;
750  SSIntervals.clear();
751  for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
752    SSRefs[i].clear();
753  SSRefs.clear();
754  OrigAlignments.clear();
755  OrigSizes.clear();
756  AllColors.clear();
757  UsedColors.clear();
758  for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
759    Assignments[i].clear();
760  Assignments.clear();
761
762  if (Changed) {
763    for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
764      Changed |= RemoveDeadStores(I);
765  }
766
767  return Changed;
768}
769