lib/CodeGen/StackSlotColoring.cpp

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