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   DOUT << "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   DOUT << '\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   DOUT << "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         DOUT << "Assigning fi#" << RSS << " to " << TRI->getName(Reg) << '\n';
 276         ColoredRegs.push_back(Reg);
 277         SlotMapping[RSS] = Reg;
 278         SlotIsReg.set(RSS);
 279         Changed = true;
 280       }
 281     }
 282
 283     // Register and its sub-registers are no longer free.
 284     while (!ColoredRegs.empty()) {
 285       unsigned Reg = ColoredRegs.back();
 286       ColoredRegs.pop_back();
 287       VRM->setRegisterUsed(Reg);
 288       // If reg is a callee-saved register, it will have to be spilled in
 289       // the prologue.
 290       MRI->setPhysRegUsed(Reg);
 291       for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
 292         VRM->setRegisterUsed(*AS);
 293         MRI->setPhysRegUsed(*AS);
 294       }
 295     }
 296     // This spill slot is dead after the rewrites
 297     if (AllColored) {
 298       MFI->RemoveStackObject(SS);
 299       ++NumEliminated;
 300     }
 301   }
 302   DOUT << '\n';
 303
 304   return Changed;
 305 }
 306
 307 /// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
 308 ///
 309 int StackSlotColoring::ColorSlot(LiveInterval *li) {
 310   int Color = -1;
 311   bool Share = false;
 312   if (!DisableSharing) {
 313     // Check if it's possible to reuse any of the used colors.
 314     Color = UsedColors.find_first();
 315     while (Color != -1) {
 316       if (!OverlapWithAssignments(li, Color)) {
 317         Share = true;
 318         ++NumEliminated;
 319         break;
 320       }
 321       Color = UsedColors.find_next(Color);
 322     }
 323   }
 324
 325   // Assign it to the first available color (assumed to be the best) if it's
 326   // not possible to share a used color with other objects.
 327   if (!Share) {
 328     assert(NextColor != -1 && "No more spill slots?");
 329     Color = NextColor;
 330     UsedColors.set(Color);
 331     NextColor = AllColors.find_next(NextColor);
 332   }
 333
 334   // Record the assignment.
 335   Assignments[Color].push_back(li);
 336   int FI = li->getStackSlotIndex();
 337   DOUT << "Assigning fi#" << FI << " to fi#" << Color << "\n";
 338
 339   // Change size and alignment of the allocated slot. If there are multiple
 340   // objects sharing the same slot, then make sure the size and alignment
 341   // are large enough for all.
 342   unsigned Align = OrigAlignments[FI];
 343   if (!Share || Align > MFI->getObjectAlignment(Color))
 344     MFI->setObjectAlignment(Color, Align);
 345   int64_t Size = OrigSizes[FI];
 346   if (!Share || Size > MFI->getObjectSize(Color))
 347     MFI->setObjectSize(Color, Size);
 348   return Color;
 349 }
 350
 351 /// Colorslots - Color all spill stack slots and rewrite all frameindex machine
 352 /// operands in the function.
 353 bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
 354   unsigned NumObjs = MFI->getObjectIndexEnd();
 355   SmallVector<int, 16> SlotMapping(NumObjs, -1);
 356   SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
 357   SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
 358   BitVector SlotIsReg(NumObjs);
 359   BitVector UsedColors(NumObjs);
 360
 361   DOUT << "Color spill slot intervals:\n";
 362   bool Changed = false;
 363   for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
 364     LiveInterval *li = SSIntervals[i];
 365     int SS = li->getStackSlotIndex();
 366     int NewSS = ColorSlot(li);
 367     assert(NewSS >= 0 && "Stack coloring failed?");
 368     SlotMapping[SS] = NewSS;
 369     RevMap[NewSS].push_back(SS);
 370     SlotWeights[NewSS] += li->weight;
 371     UsedColors.set(NewSS);
 372     Changed |= (SS != NewSS);
 373   }
 374
 375   DOUT << "\nSpill slots after coloring:\n";
 376   for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
 377     LiveInterval *li = SSIntervals[i];
 378     int SS = li->getStackSlotIndex();
 379     li->weight = SlotWeights[SS];
 380   }
 381   // Sort them by new weight.
 382   std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
 383
 384 #ifndef NDEBUG
 385   for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
 386     DEBUG(SSIntervals[i]->dump());
 387   DOUT << '\n';
 388 #endif
 389
 390   // Can we "color" a stack slot with a unused register?
 391   Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
 392
 393   if (!Changed)
 394     return false;
 395
 396   // Rewrite all MO_FrameIndex operands.
 397   SmallVector<SmallSet<unsigned, 4>, 4> NewDefs(MF.getNumBlockIDs());
 398   for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
 399     bool isReg = SlotIsReg[SS];
 400     int NewFI = SlotMapping[SS];
 401     if (NewFI == -1 || (NewFI == (int)SS && !isReg))
 402       continue;
 403
 404     const TargetRegisterClass *RC = LS->getIntervalRegClass(SS);
 405     SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
 406     for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
 407       if (!isReg)
 408         RewriteInstruction(RefMIs[i], SS, NewFI, MF);
 409       else {
 410         // Rewrite to use a register instead.
 411         unsigned MBBId = RefMIs[i]->getParent()->getNumber();
 412         SmallSet<unsigned, 4> &Defs = NewDefs[MBBId];
 413         UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, RC, Defs, MF);
 414       }
 415   }
 416
 417   // Delete unused stack slots.
 418   while (NextColor != -1) {
 419     DOUT << "Removing unused stack object fi#" << NextColor << "\n";
 420     MFI->RemoveStackObject(NextColor);
 421     NextColor = AllColors.find_next(NextColor);
 422   }
 423
 424   return true;
 425 }
 426
 427 /// AllMemRefsCanBeUnfolded - Return true if all references of the specified
 428 /// spill slot index can be unfolded.
 429 bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
 430   SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
 431   for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
 432     MachineInstr *MI = RefMIs[i];
 433     if (TII->isLoadFromStackSlot(MI, SS) ||
 434         TII->isStoreToStackSlot(MI, SS))
 435       // Restore and spill will become copies.
 436       return true;
 437     if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
 438       return false;
 439     for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
 440       MachineOperand &MO = MI->getOperand(j);
 441       if (MO.isFI() && MO.getIndex() != SS)
 442         // If it uses another frameindex, we can, currently* unfold it.
 443         return false;
 444     }
 445   }
 446   return true;
 447 }
 448
 449 /// RewriteInstruction - Rewrite specified instruction by replacing references
 450 /// to old frame index with new one.
 451 void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
 452                                            int NewFI, MachineFunction &MF) {
 453   for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
 454     MachineOperand &MO = MI->getOperand(i);
 455     if (!MO.isFI())
 456       continue;
 457     int FI = MO.getIndex();
 458     if (FI != OldFI)
 459       continue;
 460     MO.setIndex(NewFI);
 461   }
 462
 463   // Update the MachineMemOperand for the new memory location.
 464   // FIXME: We need a better method of managing these too.
 465   SmallVector<MachineMemOperand, 2> MMOs(MI->memoperands_begin(),
 466                                          MI->memoperands_end());
 467   MI->clearMemOperands(MF);
 468   const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
 469   for (unsigned i = 0, ee = MMOs.size(); i != ee; ++i) {
 470     if (MMOs[i].getValue() != OldSV)
 471       MI->addMemOperand(MF, MMOs[i]);
 472     else {
 473       MachineMemOperand MMO(PseudoSourceValue::getFixedStack(NewFI),
 474                             MMOs[i].getFlags(), MMOs[i].getOffset(),
 475                             MMOs[i].getSize(),  MMOs[i].getAlignment());
 476       MI->addMemOperand(MF, MMO);
 477     }
 478   }
 479 }
 480
 481 /// PropagateBackward - Traverse backward and look for the definition of
 482 /// OldReg. If it can successfully update all of the references with NewReg,
 483 /// do so and return true.
 484 bool StackSlotColoring::PropagateBackward(MachineBasicBlock::iterator MII,
 485                                           MachineBasicBlock *MBB,
 486                                           unsigned OldReg, unsigned NewReg) {
 487   if (MII == MBB->begin())
 488     return false;
 489
 490   SmallVector<MachineOperand*, 4> Uses;
 491   SmallVector<MachineOperand*, 4> Refs;
 492   while (--MII != MBB->begin()) {
 493     bool FoundDef = false;  // Not counting 2address def.
 494
 495     Uses.clear();
 496     const TargetInstrDesc &TID = MII->getDesc();
 497     for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
 498       MachineOperand &MO = MII->getOperand(i);
 499       if (!MO.isReg())
 500         continue;
 501       unsigned Reg = MO.getReg();
 502       if (Reg == 0)
 503         continue;
 504       if (Reg == OldReg) {
 505         if (MO.isImplicit())
 506           return false;
 507
 508         // Abort the use is actually a sub-register def. We don't have enough
 509         // information to figure out if it is really legal.
 510         if (MO.getSubReg() ||
 511             TID.getOpcode() == TargetInstrInfo::EXTRACT_SUBREG ||
 512             TID.getOpcode() == TargetInstrInfo::INSERT_SUBREG ||
 513             TID.getOpcode() == TargetInstrInfo::SUBREG_TO_REG)
 514           return false;
 515
 516         const TargetRegisterClass *RC = TID.OpInfo[i].getRegClass(TRI);
 517         if (RC && !RC->contains(NewReg))
 518           return false;
 519
 520         if (MO.isUse()) {
 521           Uses.push_back(&MO);
 522         } else {
 523           Refs.push_back(&MO);
 524           if (!MII->isRegTiedToUseOperand(i))
 525             FoundDef = true;
 526         }
 527       } else if (TRI->regsOverlap(Reg, NewReg)) {
 528         return false;
 529       } else if (TRI->regsOverlap(Reg, OldReg)) {
 530         if (!MO.isUse() || !MO.isKill())
 531           return false;
 532       }
 533     }
 534
 535     if (FoundDef) {
 536       // Found non-two-address def. Stop here.
 537       for (unsigned i = 0, e = Refs.size(); i != e; ++i)
 538         Refs[i]->setReg(NewReg);
 539       return true;
 540     }
 541
 542     // Two-address uses must be updated as well.
 543     for (unsigned i = 0, e = Uses.size(); i != e; ++i)
 544       Refs.push_back(Uses[i]);
 545   }
 546   return false;
 547 }
 548
 549 /// PropagateForward - Traverse forward and look for the kill of OldReg. If
 550 /// it can successfully update all of the uses with NewReg, do so and
 551 /// return true.
 552 bool StackSlotColoring::PropagateForward(MachineBasicBlock::iterator MII,
 553                                          MachineBasicBlock *MBB,
 554                                          unsigned OldReg, unsigned NewReg) {
 555   if (MII == MBB->end())
 556     return false;
 557
 558   SmallVector<MachineOperand*, 4> Uses;
 559   while (++MII != MBB->end()) {
 560     bool FoundUse = false;
 561     bool FoundKill = false;
 562     const TargetInstrDesc &TID = MII->getDesc();
 563     for (unsigned i = 0, e = MII->getNumOperands(); i != e; ++i) {
 564       MachineOperand &MO = MII->getOperand(i);
 565       if (!MO.isReg())
 566         continue;
 567       unsigned Reg = MO.getReg();
 568       if (Reg == 0)
 569         continue;
 570       if (Reg == OldReg) {
 571         if (MO.isDef() || MO.isImplicit())
 572           return false;
 573
 574         // Abort the use is actually a sub-register use. We don't have enough
 575         // information to figure out if it is really legal.
 576         if (MO.getSubReg() ||
 577             TID.getOpcode() == TargetInstrInfo::EXTRACT_SUBREG)
 578           return false;
 579
 580         const TargetRegisterClass *RC = TID.OpInfo[i].getRegClass(TRI);
 581         if (RC && !RC->contains(NewReg))
 582           return false;
 583         FoundUse = true;
 584         if (MO.isKill())
 585           FoundKill = true;
 586
 587         Uses.push_back(&MO);
 588       } else if (TRI->regsOverlap(Reg, NewReg) ||
 589                  TRI->regsOverlap(Reg, OldReg))
 590         return false;
 591     }
 592     if (FoundKill) {
 593       for (unsigned i = 0, e = Uses.size(); i != e; ++i)
 594         Uses[i]->setReg(NewReg);
 595       return true;
 596     }
 597   }
 598   return false;
 599 }
 600
 601 /// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
 602 /// folded memory references and replacing those references with register
 603 /// references instead.
 604 void
 605 StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
 606                                                unsigned Reg,
 607                                                const TargetRegisterClass *RC,
 608                                                SmallSet<unsigned, 4> &Defs,
 609                                                MachineFunction &MF) {
 610   MachineBasicBlock *MBB = MI->getParent();
 611   if (unsigned DstReg = TII->isLoadFromStackSlot(MI, OldFI)) {
 612     if (PropagateForward(MI, MBB, DstReg, Reg)) {
 613       DOUT << "Eliminated load: ";
 614       DEBUG(MI->dump());
 615       ++NumLoadElim;
 616     } else {
 617       TII->copyRegToReg(*MBB, MI, DstReg, Reg, RC, RC);
 618       ++NumRegRepl;
 619     }
 620
 621     if (!Defs.count(Reg)) {
 622       // If this is the first use of Reg in this MBB and it wasn't previously
 623       // defined in MBB, add it to livein.
 624       MBB->addLiveIn(Reg);
 625       Defs.insert(Reg);
 626     }
 627   } else if (unsigned SrcReg = TII->isStoreToStackSlot(MI, OldFI)) {
 628     if (MI->killsRegister(SrcReg) && PropagateBackward(MI, MBB, SrcReg, Reg)) {
 629       DOUT << "Eliminated store: ";
 630       DEBUG(MI->dump());
 631       ++NumStoreElim;
 632     } else {
 633       TII->copyRegToReg(*MBB, MI, Reg, SrcReg, RC, RC);
 634       ++NumRegRepl;
 635     }
 636
 637     // Remember reg has been defined in MBB.
 638     Defs.insert(Reg);
 639   } else {
 640     SmallVector<MachineInstr*, 4> NewMIs;
 641     bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
 642     Success = Success; // Silence compiler warning.
 643     assert(Success && "Failed to unfold!");
 644     MachineInstr *NewMI = NewMIs[0];
 645     MBB->insert(MI, NewMI);
 646     ++NumRegRepl;
 647
 648     if (NewMI->readsRegister(Reg)) {
 649       if (!Defs.count(Reg))
 650         // If this is the first use of Reg in this MBB and it wasn't previously
 651         // defined in MBB, add it to livein.
 652         MBB->addLiveIn(Reg);
 653       Defs.insert(Reg);
 654     }
 655   }
 656   MBB->erase(MI);
 657 }
 658
 659 /// RemoveDeadStores - Scan through a basic block and look for loads followed
 660 /// by stores.  If they're both using the same stack slot, then the store is
 661 /// definitely dead.  This could obviously be much more aggressive (consider
 662 /// pairs with instructions between them), but such extensions might have a
 663 /// considerable compile time impact.
 664 bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
 665   // FIXME: This could be much more aggressive, but we need to investigate
 666   // the compile time impact of doing so.
 667   bool changed = false;
 668
 669   SmallVector<MachineInstr*, 4> toErase;
 670
 671   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
 672        I != E; ++I) {
 673     if (DCELimit != -1 && (int)NumDead >= DCELimit)
 674       break;
 675
 676     MachineBasicBlock::iterator NextMI = next(I);
 677     if (NextMI == MBB->end()) continue;
 678
 679     int FirstSS, SecondSS;
 680     unsigned LoadReg = 0;
 681     unsigned StoreReg = 0;
 682     if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
 683     if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
 684     if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
 685
 686     ++NumDead;
 687     changed = true;
 688
 689     if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
 690       ++NumDead;
 691       toErase.push_back(I);
 692     }
 693
 694     toErase.push_back(NextMI);
 695     ++I;
 696   }
 697
 698   for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
 699        E = toErase.end(); I != E; ++I)
 700     (*I)->eraseFromParent();
 701
 702   return changed;
 703 }
 704
 705
 706 bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
 707   DOUT << "********** Stack Slot Coloring **********\n";
 708
 709   MFI = MF.getFrameInfo();
 710   MRI = &MF.getRegInfo();
 711   TII = MF.getTarget().getInstrInfo();
 712   TRI = MF.getTarget().getRegisterInfo();
 713   LS = &getAnalysis<LiveStacks>();
 714   VRM = &getAnalysis<VirtRegMap>();
 715   loopInfo = &getAnalysis<MachineLoopInfo>();
 716
 717   bool Changed = false;
 718
 719   unsigned NumSlots = LS->getNumIntervals();
 720   if (NumSlots < 2) {
 721     if (NumSlots == 0 || !VRM->HasUnusedRegisters())
 722       // Nothing to do!
 723       return false;
 724   }
 725
 726   // Gather spill slot references
 727   ScanForSpillSlotRefs(MF);
 728   InitializeSlots();
 729   Changed = ColorSlots(MF);
 730
 731   NextColor = -1;
 732   SSIntervals.clear();
 733   for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
 734     SSRefs[i].clear();
 735   SSRefs.clear();
 736   OrigAlignments.clear();
 737   OrigSizes.clear();
 738   AllColors.clear();
 739   UsedColors.clear();
 740   for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
 741     Assignments[i].clear();
 742   Assignments.clear();
 743
 744   if (Changed) {
 745     for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
 746       Changed |= RemoveDeadStores(I);
 747   }
 748
 749   return Changed;
 750 }