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/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>
  36 using namespace llvm;
  37
  38 static cl::opt<bool>
  39 DisableSharing("no-stack-slot-sharing",
  40              cl::init(false), cl::Hidden,
  41              cl::desc("Suppress slot sharing during stack coloring"));
  42
  43 static cl::opt<bool>
  44 ColorWithRegsOpt("color-ss-with-regs",
  45                  cl::init(false), cl::Hidden,
  46                  cl::desc("Color stack slots with free registers"));
  47
  48
  49 static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
  50
  51 STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
  52 STATISTIC(NumRegRepl,    "Number of stack slot refs replaced with reg refs");
  53 STATISTIC(NumLoadElim,   "Number of loads eliminated");
  54 STATISTIC(NumStoreElim,  "Number of stores eliminated");
  55 STATISTIC(NumDead,       "Number of trivially dead stack accesses eliminated");
  56
  57 namespace {
  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
 150 char StackSlotColoring::ID = 0;
 151
 152 INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
 153                 "Stack Slot Coloring", false, false)
 154 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
 155 INITIALIZE_PASS_DEPENDENCY(LiveStacks)
 156 INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
 157 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
 158 INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
 159                 "Stack Slot Coloring", false, false)
 160
 161 FunctionPass *llvm::createStackSlotColoringPass(bool RegColor) {
 162   return new StackSlotColoring(RegColor);
 163 }
 164
 165 namespace {
 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.
 177 void 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.
 208 void 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.
 240 bool
 241 StackSlotColoring::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.
 253 bool
 254 StackSlotColoring::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 ///
 326 int 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.
 370 bool 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.
 446 bool 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.
 468 void 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.
 495 bool 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.
 560 bool 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.
 609 void
 610 StackSlotColoring::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.
 671 bool 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
 713 bool 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 }