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      1 //===-- StackColoring.cpp -------------------------------------------------===//
      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 pass implements the stack-coloring optimization that looks for
     11 // lifetime markers machine instructions (LIFESTART_BEGIN and LIFESTART_END),
     12 // which represent the possible lifetime of stack slots. It attempts to
     13 // merge disjoint stack slots and reduce the used stack space.
     14 // NOTE: This pass is not StackSlotColoring, which optimizes spill slots.
     15 //
     16 // TODO: In the future we plan to improve stack coloring in the following ways:
     17 // 1. Allow merging multiple small slots into a single larger slot at different
     18 //    offsets.
     19 // 2. Merge this pass with StackSlotColoring and allow merging of allocas with
     20 //    spill slots.
     21 //
     22 //===----------------------------------------------------------------------===//
     23 
     24 #define DEBUG_TYPE "stackcoloring"
     25 #include "MachineTraceMetrics.h"
     26 #include "llvm/Function.h"
     27 #include "llvm/Module.h"
     28 #include "llvm/ADT/BitVector.h"
     29 #include "llvm/Analysis/Dominators.h"
     30 #include "llvm/Analysis/ValueTracking.h"
     31 #include "llvm/ADT/DepthFirstIterator.h"
     32 #include "llvm/ADT/PostOrderIterator.h"
     33 #include "llvm/ADT/SetVector.h"
     34 #include "llvm/ADT/SmallPtrSet.h"
     35 #include "llvm/ADT/SparseSet.h"
     36 #include "llvm/ADT/Statistic.h"
     37 #include "llvm/CodeGen/LiveInterval.h"
     38 #include "llvm/CodeGen/MachineLoopInfo.h"
     39 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
     40 #include "llvm/CodeGen/MachineDominators.h"
     41 #include "llvm/CodeGen/MachineBasicBlock.h"
     42 #include "llvm/CodeGen/MachineFunctionPass.h"
     43 #include "llvm/CodeGen/MachineLoopInfo.h"
     44 #include "llvm/CodeGen/MachineModuleInfo.h"
     45 #include "llvm/CodeGen/MachineRegisterInfo.h"
     46 #include "llvm/CodeGen/MachineFrameInfo.h"
     47 #include "llvm/CodeGen/MachineMemOperand.h"
     48 #include "llvm/CodeGen/Passes.h"
     49 #include "llvm/CodeGen/SlotIndexes.h"
     50 #include "llvm/DebugInfo.h"
     51 #include "llvm/MC/MCInstrItineraries.h"
     52 #include "llvm/Target/TargetInstrInfo.h"
     53 #include "llvm/Target/TargetRegisterInfo.h"
     54 #include "llvm/Support/CommandLine.h"
     55 #include "llvm/Support/Debug.h"
     56 #include "llvm/Support/raw_ostream.h"
     57 
     58 using namespace llvm;
     59 
     60 static cl::opt<bool>
     61 DisableColoring("no-stack-coloring",
     62                cl::init(true), cl::Hidden,
     63                cl::desc("Suppress stack coloring"));
     64 
     65 STATISTIC(NumMarkerSeen,  "Number of life markers found.");
     66 STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots.");
     67 STATISTIC(StackSlotMerged, "Number of stack slot merged.");
     68 
     69 //===----------------------------------------------------------------------===//
     70 //                           StackColoring Pass
     71 //===----------------------------------------------------------------------===//
     72 
     73 namespace {
     74 /// StackColoring - A machine pass for merging disjoint stack allocations,
     75 /// marked by the LIFETIME_START and LIFETIME_END pseudo instructions.
     76 class StackColoring : public MachineFunctionPass {
     77   MachineFrameInfo *MFI;
     78   MachineFunction *MF;
     79 
     80   /// A class representing liveness information for a single basic block.
     81   /// Each bit in the BitVector represents the liveness property
     82   /// for a different stack slot.
     83   struct BlockLifetimeInfo {
     84     /// Which slots BEGINs in each basic block.
     85     BitVector Begin;
     86     /// Which slots ENDs in each basic block.
     87     BitVector End;
     88     /// Which slots are marked as LIVE_IN, coming into each basic block.
     89     BitVector LiveIn;
     90     /// Which slots are marked as LIVE_OUT, coming out of each basic block.
     91     BitVector LiveOut;
     92   };
     93 
     94   /// Maps active slots (per bit) for each basic block.
     95   DenseMap<MachineBasicBlock*, BlockLifetimeInfo> BlockLiveness;
     96 
     97   /// Maps serial numbers to basic blocks.
     98   DenseMap<MachineBasicBlock*, int> BasicBlocks;
     99   /// Maps basic blocks to a serial number.
    100   SmallVector<MachineBasicBlock*, 8> BasicBlockNumbering;
    101 
    102   /// Maps liveness intervals for each slot.
    103   SmallVector<LiveInterval*, 16> Intervals;
    104   /// VNInfo is used for the construction of LiveIntervals.
    105   VNInfo::Allocator VNInfoAllocator;
    106   /// SlotIndex analysis object.
    107   SlotIndexes* Indexes;
    108 
    109   /// The list of lifetime markers found. These markers are to be removed
    110   /// once the coloring is done.
    111   SmallVector<MachineInstr*, 8> Markers;
    112 
    113   /// SlotSizeSorter - A Sort utility for arranging stack slots according
    114   /// to their size.
    115   struct SlotSizeSorter {
    116     MachineFrameInfo *MFI;
    117     SlotSizeSorter(MachineFrameInfo *mfi) : MFI(mfi) { }
    118     bool operator()(int LHS, int RHS) {
    119       // We use -1 to denote a uninteresting slot. Place these slots at the end.
    120       if (LHS == -1) return false;
    121       if (RHS == -1) return true;
    122       // Sort according to size.
    123       return MFI->getObjectSize(LHS) > MFI->getObjectSize(RHS);
    124   }
    125 };
    126 
    127 public:
    128   static char ID;
    129   StackColoring() : MachineFunctionPass(ID) {
    130     initializeStackColoringPass(*PassRegistry::getPassRegistry());
    131   }
    132   void getAnalysisUsage(AnalysisUsage &AU) const;
    133   bool runOnMachineFunction(MachineFunction &MF);
    134 
    135 private:
    136   /// Debug.
    137   void dump();
    138 
    139   /// Removes all of the lifetime marker instructions from the function.
    140   /// \returns true if any markers were removed.
    141   bool removeAllMarkers();
    142 
    143   /// Scan the machine function and find all of the lifetime markers.
    144   /// Record the findings in the BEGIN and END vectors.
    145   /// \returns the number of markers found.
    146   unsigned collectMarkers(unsigned NumSlot);
    147 
    148   /// Perform the dataflow calculation and calculate the lifetime for each of
    149   /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and
    150   /// LifetimeLIVE_OUT maps that represent which stack slots are live coming
    151   /// in and out blocks.
    152   void calculateLocalLiveness();
    153 
    154   /// Construct the LiveIntervals for the slots.
    155   void calculateLiveIntervals(unsigned NumSlots);
    156 
    157   /// Go over the machine function and change instructions which use stack
    158   /// slots to use the joint slots.
    159   void remapInstructions(DenseMap<int, int> &SlotRemap);
    160 
    161   /// Map entries which point to other entries to their destination.
    162   ///   A->B->C becomes A->C.
    163    void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots);
    164 };
    165 } // end anonymous namespace
    166 
    167 char StackColoring::ID = 0;
    168 char &llvm::StackColoringID = StackColoring::ID;
    169 
    170 INITIALIZE_PASS_BEGIN(StackColoring,
    171                    "stack-coloring", "Merge disjoint stack slots", false, false)
    172 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
    173 INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
    174 INITIALIZE_PASS_END(StackColoring,
    175                    "stack-coloring", "Merge disjoint stack slots", false, false)
    176 
    177 void StackColoring::getAnalysisUsage(AnalysisUsage &AU) const {
    178   AU.addRequired<MachineDominatorTree>();
    179   AU.addPreserved<MachineDominatorTree>();
    180   AU.addRequired<SlotIndexes>();
    181   MachineFunctionPass::getAnalysisUsage(AU);
    182 }
    183 
    184 void StackColoring::dump() {
    185   for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
    186        FI != FE; ++FI) {
    187     unsigned Num = BasicBlocks[*FI];
    188     DEBUG(dbgs()<<"Inspecting block #"<<Num<<" ["<<FI->getName()<<"]\n");
    189     Num = 0;
    190     DEBUG(dbgs()<<"BEGIN  : {");
    191     for (unsigned i=0; i < BlockLiveness[*FI].Begin.size(); ++i)
    192       DEBUG(dbgs()<<BlockLiveness[*FI].Begin.test(i)<<" ");
    193     DEBUG(dbgs()<<"}\n");
    194 
    195     DEBUG(dbgs()<<"END    : {");
    196     for (unsigned i=0; i < BlockLiveness[*FI].End.size(); ++i)
    197       DEBUG(dbgs()<<BlockLiveness[*FI].End.test(i)<<" ");
    198 
    199     DEBUG(dbgs()<<"}\n");
    200 
    201     DEBUG(dbgs()<<"LIVE_IN: {");
    202     for (unsigned i=0; i < BlockLiveness[*FI].LiveIn.size(); ++i)
    203       DEBUG(dbgs()<<BlockLiveness[*FI].LiveIn.test(i)<<" ");
    204 
    205     DEBUG(dbgs()<<"}\n");
    206     DEBUG(dbgs()<<"LIVEOUT: {");
    207     for (unsigned i=0; i < BlockLiveness[*FI].LiveOut.size(); ++i)
    208       DEBUG(dbgs()<<BlockLiveness[*FI].LiveOut.test(i)<<" ");
    209     DEBUG(dbgs()<<"}\n");
    210   }
    211 }
    212 
    213 unsigned StackColoring::collectMarkers(unsigned NumSlot) {
    214   unsigned MarkersFound = 0;
    215   // Scan the function to find all lifetime markers.
    216   // NOTE: We use the a reverse-post-order iteration to ensure that we obtain a
    217   // deterministic numbering, and because we'll need a post-order iteration
    218   // later for solving the liveness dataflow problem.
    219   for (df_iterator<MachineFunction*> FI = df_begin(MF), FE = df_end(MF);
    220        FI != FE; ++FI) {
    221 
    222     // Assign a serial number to this basic block.
    223     BasicBlocks[*FI] = BasicBlockNumbering.size();
    224     BasicBlockNumbering.push_back(*FI);
    225 
    226     BlockLiveness[*FI].Begin.resize(NumSlot);
    227     BlockLiveness[*FI].End.resize(NumSlot);
    228 
    229     for (MachineBasicBlock::iterator BI = (*FI)->begin(), BE = (*FI)->end();
    230          BI != BE; ++BI) {
    231 
    232       if (BI->getOpcode() != TargetOpcode::LIFETIME_START &&
    233           BI->getOpcode() != TargetOpcode::LIFETIME_END)
    234         continue;
    235 
    236       Markers.push_back(BI);
    237 
    238       bool IsStart = BI->getOpcode() == TargetOpcode::LIFETIME_START;
    239       MachineOperand &MI = BI->getOperand(0);
    240       unsigned Slot = MI.getIndex();
    241 
    242       MarkersFound++;
    243 
    244       const Value *Allocation = MFI->getObjectAllocation(Slot);
    245       if (Allocation) {
    246         DEBUG(dbgs()<<"Found lifetime marker for allocation: "<<
    247               Allocation->getName()<<"\n");
    248       }
    249 
    250       if (IsStart) {
    251         BlockLiveness[*FI].Begin.set(Slot);
    252       } else {
    253         if (BlockLiveness[*FI].Begin.test(Slot)) {
    254           // Allocas that start and end within a single block are handled
    255           // specially when computing the LiveIntervals to avoid pessimizing
    256           // the liveness propagation.
    257           BlockLiveness[*FI].Begin.reset(Slot);
    258         } else {
    259           BlockLiveness[*FI].End.set(Slot);
    260         }
    261       }
    262     }
    263   }
    264 
    265   // Update statistics.
    266   NumMarkerSeen += MarkersFound;
    267   return MarkersFound;
    268 }
    269 
    270 void StackColoring::calculateLocalLiveness() {
    271   // Perform a standard reverse dataflow computation to solve for
    272   // global liveness.  The BEGIN set here is equivalent to KILL in the standard
    273   // formulation, and END is equivalent to GEN.  The result of this computation
    274   // is a map from blocks to bitvectors where the bitvectors represent which
    275   // allocas are live in/out of that block.
    276   SmallPtrSet<MachineBasicBlock*, 8> BBSet(BasicBlockNumbering.begin(),
    277                                            BasicBlockNumbering.end());
    278   unsigned NumSSMIters = 0;
    279   bool changed = true;
    280   while (changed) {
    281     changed = false;
    282     ++NumSSMIters;
    283 
    284     SmallPtrSet<MachineBasicBlock*, 8> NextBBSet;
    285 
    286     for (SmallVector<MachineBasicBlock*, 8>::iterator
    287          PI = BasicBlockNumbering.begin(), PE = BasicBlockNumbering.end();
    288          PI != PE; ++PI) {
    289 
    290       MachineBasicBlock *BB = *PI;
    291       if (!BBSet.count(BB)) continue;
    292 
    293       BitVector LocalLiveIn;
    294       BitVector LocalLiveOut;
    295 
    296       // Forward propagation from begins to ends.
    297       for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
    298            PE = BB->pred_end(); PI != PE; ++PI)
    299         LocalLiveIn |= BlockLiveness[*PI].LiveOut;
    300       LocalLiveIn |= BlockLiveness[BB].End;
    301       LocalLiveIn.reset(BlockLiveness[BB].Begin);
    302 
    303       // Reverse propagation from ends to begins.
    304       for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
    305            SE = BB->succ_end(); SI != SE; ++SI)
    306         LocalLiveOut |= BlockLiveness[*SI].LiveIn;
    307       LocalLiveOut |= BlockLiveness[BB].Begin;
    308       LocalLiveOut.reset(BlockLiveness[BB].End);
    309 
    310       LocalLiveIn |= LocalLiveOut;
    311       LocalLiveOut |= LocalLiveIn;
    312 
    313       // After adopting the live bits, we need to turn-off the bits which
    314       // are de-activated in this block.
    315       LocalLiveOut.reset(BlockLiveness[BB].End);
    316       LocalLiveIn.reset(BlockLiveness[BB].Begin);
    317 
    318       // If we have both BEGIN and END markers in the same basic block then
    319       // we know that the BEGIN marker comes after the END, because we already
    320       // handle the case where the BEGIN comes before the END when collecting
    321       // the markers (and building the BEGIN/END vectore).
    322       // Want to enable the LIVE_IN and LIVE_OUT of slots that have both
    323       // BEGIN and END because it means that the value lives before and after
    324       // this basic block.
    325       BitVector LocalEndBegin = BlockLiveness[BB].End;
    326       LocalEndBegin &= BlockLiveness[BB].Begin;
    327       LocalLiveIn |= LocalEndBegin;
    328       LocalLiveOut |= LocalEndBegin;
    329 
    330       if (LocalLiveIn.test(BlockLiveness[BB].LiveIn)) {
    331         changed = true;
    332         BlockLiveness[BB].LiveIn |= LocalLiveIn;
    333 
    334         for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
    335              PE = BB->pred_end(); PI != PE; ++PI)
    336           NextBBSet.insert(*PI);
    337       }
    338 
    339       if (LocalLiveOut.test(BlockLiveness[BB].LiveOut)) {
    340         changed = true;
    341         BlockLiveness[BB].LiveOut |= LocalLiveOut;
    342 
    343         for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
    344              SE = BB->succ_end(); SI != SE; ++SI)
    345           NextBBSet.insert(*SI);
    346       }
    347     }
    348 
    349     BBSet = NextBBSet;
    350   }// while changed.
    351 }
    352 
    353 void StackColoring::calculateLiveIntervals(unsigned NumSlots) {
    354   SmallVector<SlotIndex, 16> Starts;
    355   SmallVector<SlotIndex, 16> Finishes;
    356 
    357   // For each block, find which slots are active within this block
    358   // and update the live intervals.
    359   for (MachineFunction::iterator MBB = MF->begin(), MBBe = MF->end();
    360        MBB != MBBe; ++MBB) {
    361     Starts.clear();
    362     Starts.resize(NumSlots);
    363     Finishes.clear();
    364     Finishes.resize(NumSlots);
    365 
    366     // Create the interval for the basic blocks with lifetime markers in them.
    367     for (SmallVector<MachineInstr*, 8>::iterator it = Markers.begin(),
    368          e = Markers.end(); it != e; ++it) {
    369       MachineInstr *MI = *it;
    370       if (MI->getParent() != MBB)
    371         continue;
    372 
    373       assert((MI->getOpcode() == TargetOpcode::LIFETIME_START ||
    374               MI->getOpcode() == TargetOpcode::LIFETIME_END) &&
    375              "Invalid Lifetime marker");
    376 
    377       bool IsStart = MI->getOpcode() == TargetOpcode::LIFETIME_START;
    378       MachineOperand &Mo = MI->getOperand(0);
    379       int Slot = Mo.getIndex();
    380       assert(Slot >= 0 && "Invalid slot");
    381 
    382       SlotIndex ThisIndex = Indexes->getInstructionIndex(MI);
    383 
    384       if (IsStart) {
    385         if (!Starts[Slot].isValid() || Starts[Slot] > ThisIndex)
    386           Starts[Slot] = ThisIndex;
    387       } else {
    388         if (!Finishes[Slot].isValid() || Finishes[Slot] < ThisIndex)
    389           Finishes[Slot] = ThisIndex;
    390       }
    391     }
    392 
    393     // Create the interval of the blocks that we previously found to be 'alive'.
    394     BitVector Alive = BlockLiveness[MBB].LiveIn;
    395     Alive |= BlockLiveness[MBB].LiveOut;
    396 
    397     if (Alive.any()) {
    398       for (int pos = Alive.find_first(); pos != -1;
    399            pos = Alive.find_next(pos)) {
    400         if (!Starts[pos].isValid())
    401           Starts[pos] = Indexes->getMBBStartIdx(MBB);
    402         if (!Finishes[pos].isValid())
    403           Finishes[pos] = Indexes->getMBBEndIdx(MBB);
    404       }
    405     }
    406 
    407     for (unsigned i = 0; i < NumSlots; ++i) {
    408       assert(Starts[i].isValid() == Finishes[i].isValid() && "Unmatched range");
    409       if (!Starts[i].isValid())
    410         continue;
    411 
    412       assert(Starts[i] && Finishes[i] && "Invalid interval");
    413       VNInfo *ValNum = Intervals[i]->getValNumInfo(0);
    414       SlotIndex S = Starts[i];
    415       SlotIndex F = Finishes[i];
    416       if (S < F) {
    417         // We have a single consecutive region.
    418         Intervals[i]->addRange(LiveRange(S, F, ValNum));
    419       } else {
    420         // We have two non consecutive regions. This happens when
    421         // LIFETIME_START appears after the LIFETIME_END marker.
    422         SlotIndex NewStart = Indexes->getMBBStartIdx(MBB);
    423         SlotIndex NewFin = Indexes->getMBBEndIdx(MBB);
    424         Intervals[i]->addRange(LiveRange(NewStart, F, ValNum));
    425         Intervals[i]->addRange(LiveRange(S, NewFin, ValNum));
    426       }
    427     }
    428   }
    429 }
    430 
    431 bool StackColoring::removeAllMarkers() {
    432   unsigned Count = 0;
    433   for (unsigned i = 0; i < Markers.size(); ++i) {
    434     Markers[i]->eraseFromParent();
    435     Count++;
    436   }
    437   Markers.clear();
    438 
    439   DEBUG(dbgs()<<"Removed "<<Count<<" markers.\n");
    440   return Count;
    441 }
    442 
    443 void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
    444   unsigned FixedInstr = 0;
    445   unsigned FixedMemOp = 0;
    446   unsigned FixedDbg = 0;
    447   MachineModuleInfo *MMI = &MF->getMMI();
    448 
    449   // Remap debug information that refers to stack slots.
    450   MachineModuleInfo::VariableDbgInfoMapTy &VMap = MMI->getVariableDbgInfo();
    451   for (MachineModuleInfo::VariableDbgInfoMapTy::iterator VI = VMap.begin(),
    452        VE = VMap.end(); VI != VE; ++VI) {
    453     const MDNode *Var = VI->first;
    454     if (!Var) continue;
    455     std::pair<unsigned, DebugLoc> &VP = VI->second;
    456     if (SlotRemap.count(VP.first)) {
    457       DEBUG(dbgs()<<"Remapping debug info for ["<<Var->getName()<<"].\n");
    458       VP.first = SlotRemap[VP.first];
    459       FixedDbg++;
    460     }
    461   }
    462 
    463   // Keep a list of *allocas* which need to be remapped.
    464   DenseMap<const Value*, const Value*> Allocas;
    465   for (DenseMap<int, int>::iterator it = SlotRemap.begin(),
    466        e = SlotRemap.end(); it != e; ++it) {
    467     const Value *From = MFI->getObjectAllocation(it->first);
    468     const Value *To = MFI->getObjectAllocation(it->second);
    469     assert(To && From && "Invalid allocation object");
    470     Allocas[From] = To;
    471   }
    472 
    473   // Remap all instructions to the new stack slots.
    474   MachineFunction::iterator BB, BBE;
    475   MachineBasicBlock::iterator I, IE;
    476   for (BB = MF->begin(), BBE = MF->end(); BB != BBE; ++BB)
    477     for (I = BB->begin(), IE = BB->end(); I != IE; ++I) {
    478 
    479       // Skip lifetime markers. We'll remove them soon.
    480       if (I->getOpcode() == TargetOpcode::LIFETIME_START ||
    481           I->getOpcode() == TargetOpcode::LIFETIME_END)
    482         continue;
    483 
    484       // Update the MachineMemOperand to use the new alloca.
    485       for (MachineInstr::mmo_iterator MM = I->memoperands_begin(),
    486            E = I->memoperands_end(); MM != E; ++MM) {
    487         MachineMemOperand *MMO = *MM;
    488 
    489         const Value *V = MMO->getValue();
    490 
    491         if (!V)
    492           continue;
    493 
    494         // Climb up and find the original alloca.
    495         V = GetUnderlyingObject(V);
    496         // If we did not find one, or if the one that we found is not in our
    497         // map, then move on.
    498         if (!V || !Allocas.count(V))
    499           continue;
    500 
    501         MMO->setValue(Allocas[V]);
    502         FixedMemOp++;
    503       }
    504 
    505       // Update all of the machine instruction operands.
    506       for (unsigned i = 0 ; i <  I->getNumOperands(); ++i) {
    507         MachineOperand &MO = I->getOperand(i);
    508 
    509         if (!MO.isFI())
    510           continue;
    511         int FromSlot = MO.getIndex();
    512 
    513         // Don't touch arguments.
    514         if (FromSlot<0)
    515           continue;
    516 
    517         // Only look at mapped slots.
    518         if (!SlotRemap.count(FromSlot))
    519           continue;
    520 
    521         // In a debug build, check that the instruction that we are modifying is
    522         // inside the expected live range. If the instruction is not inside
    523         // the calculated range then it means that the alloca usage moved
    524         // outside of the lifetime markers.
    525 #ifndef NDEBUG
    526         SlotIndex Index = Indexes->getInstructionIndex(I);
    527         LiveInterval* Interval = Intervals[FromSlot];
    528         assert(Interval->find(Index) != Interval->end() &&
    529                "Found instruction usage outside of live range.");
    530 #endif
    531 
    532         // Fix the machine instructions.
    533         int ToSlot = SlotRemap[FromSlot];
    534         MO.setIndex(ToSlot);
    535         FixedInstr++;
    536       }
    537     }
    538 
    539   DEBUG(dbgs()<<"Fixed "<<FixedMemOp<<" machine memory operands.\n");
    540   DEBUG(dbgs()<<"Fixed "<<FixedDbg<<" debug locations.\n");
    541   DEBUG(dbgs()<<"Fixed "<<FixedInstr<<" machine instructions.\n");
    542 }
    543 
    544 void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap,
    545                                    unsigned NumSlots) {
    546   // Expunge slot remap map.
    547   for (unsigned i=0; i < NumSlots; ++i) {
    548     // If we are remapping i
    549     if (SlotRemap.count(i)) {
    550       int Target = SlotRemap[i];
    551       // As long as our target is mapped to something else, follow it.
    552       while (SlotRemap.count(Target)) {
    553         Target = SlotRemap[Target];
    554         SlotRemap[i] = Target;
    555       }
    556     }
    557   }
    558 }
    559 
    560 bool StackColoring::runOnMachineFunction(MachineFunction &Func) {
    561   DEBUG(dbgs() << "********** Stack Coloring **********\n"
    562                << "********** Function: "
    563                << ((const Value*)Func.getFunction())->getName() << '\n');
    564   MF = &Func;
    565   MFI = MF->getFrameInfo();
    566   Indexes = &getAnalysis<SlotIndexes>();
    567   BlockLiveness.clear();
    568   BasicBlocks.clear();
    569   BasicBlockNumbering.clear();
    570   Markers.clear();
    571   Intervals.clear();
    572   VNInfoAllocator.Reset();
    573 
    574   unsigned NumSlots = MFI->getObjectIndexEnd();
    575 
    576   // If there are no stack slots then there are no markers to remove.
    577   if (!NumSlots)
    578     return false;
    579 
    580   SmallVector<int, 8> SortedSlots;
    581 
    582   SortedSlots.reserve(NumSlots);
    583   Intervals.reserve(NumSlots);
    584 
    585   unsigned NumMarkers = collectMarkers(NumSlots);
    586 
    587   unsigned TotalSize = 0;
    588   DEBUG(dbgs()<<"Found "<<NumMarkers<<" markers and "<<NumSlots<<" slots\n");
    589   DEBUG(dbgs()<<"Slot structure:\n");
    590 
    591   for (int i=0; i < MFI->getObjectIndexEnd(); ++i) {
    592     DEBUG(dbgs()<<"Slot #"<<i<<" - "<<MFI->getObjectSize(i)<<" bytes.\n");
    593     TotalSize += MFI->getObjectSize(i);
    594   }
    595 
    596   DEBUG(dbgs()<<"Total Stack size: "<<TotalSize<<" bytes\n\n");
    597 
    598   // Don't continue because there are not enough lifetime markers, or the
    599   // stack or too small, or we are told not to optimize the slots.
    600   if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) {
    601     DEBUG(dbgs()<<"Will not try to merge slots.\n");
    602     return removeAllMarkers();
    603   }
    604 
    605   for (unsigned i=0; i < NumSlots; ++i) {
    606     LiveInterval *LI = new LiveInterval(i, 0);
    607     Intervals.push_back(LI);
    608     LI->getNextValue(Indexes->getZeroIndex(), VNInfoAllocator);
    609     SortedSlots.push_back(i);
    610   }
    611 
    612   // Calculate the liveness of each block.
    613   calculateLocalLiveness();
    614 
    615   // Propagate the liveness information.
    616   calculateLiveIntervals(NumSlots);
    617 
    618   // Maps old slots to new slots.
    619   DenseMap<int, int> SlotRemap;
    620   unsigned RemovedSlots = 0;
    621   unsigned ReducedSize = 0;
    622 
    623   // Do not bother looking at empty intervals.
    624   for (unsigned I = 0; I < NumSlots; ++I) {
    625     if (Intervals[SortedSlots[I]]->empty())
    626       SortedSlots[I] = -1;
    627   }
    628 
    629   // This is a simple greedy algorithm for merging allocas. First, sort the
    630   // slots, placing the largest slots first. Next, perform an n^2 scan and look
    631   // for disjoint slots. When you find disjoint slots, merge the samller one
    632   // into the bigger one and update the live interval. Remove the small alloca
    633   // and continue.
    634 
    635   // Sort the slots according to their size. Place unused slots at the end.
    636   std::sort(SortedSlots.begin(), SortedSlots.end(), SlotSizeSorter(MFI));
    637 
    638   bool Chanded = true;
    639   while (Chanded) {
    640     Chanded = false;
    641     for (unsigned I = 0; I < NumSlots; ++I) {
    642       if (SortedSlots[I] == -1)
    643         continue;
    644 
    645       for (unsigned J=I+1; J < NumSlots; ++J) {
    646         if (SortedSlots[J] == -1)
    647           continue;
    648 
    649         int FirstSlot = SortedSlots[I];
    650         int SecondSlot = SortedSlots[J];
    651         LiveInterval *First = Intervals[FirstSlot];
    652         LiveInterval *Second = Intervals[SecondSlot];
    653         assert (!First->empty() && !Second->empty() && "Found an empty range");
    654 
    655         // Merge disjoint slots.
    656         if (!First->overlaps(*Second)) {
    657           Chanded = true;
    658           First->MergeRangesInAsValue(*Second, First->getValNumInfo(0));
    659           SlotRemap[SecondSlot] = FirstSlot;
    660           SortedSlots[J] = -1;
    661           DEBUG(dbgs()<<"Merging #"<<FirstSlot<<" and slots #"<<
    662                 SecondSlot<<" together.\n");
    663           unsigned MaxAlignment = std::max(MFI->getObjectAlignment(FirstSlot),
    664                                            MFI->getObjectAlignment(SecondSlot));
    665 
    666           assert(MFI->getObjectSize(FirstSlot) >=
    667                  MFI->getObjectSize(SecondSlot) &&
    668                  "Merging a small object into a larger one");
    669 
    670           RemovedSlots+=1;
    671           ReducedSize += MFI->getObjectSize(SecondSlot);
    672           MFI->setObjectAlignment(FirstSlot, MaxAlignment);
    673           MFI->RemoveStackObject(SecondSlot);
    674         }
    675       }
    676     }
    677   }// While changed.
    678 
    679   // Record statistics.
    680   StackSpaceSaved += ReducedSize;
    681   StackSlotMerged += RemovedSlots;
    682   DEBUG(dbgs()<<"Merge "<<RemovedSlots<<" slots. Saved "<<
    683         ReducedSize<<" bytes\n");
    684 
    685   // Scan the entire function and update all machine operands that use frame
    686   // indices to use the remapped frame index.
    687   expungeSlotMap(SlotRemap, NumSlots);
    688   remapInstructions(SlotRemap);
    689 
    690   // Release the intervals.
    691   for (unsigned I = 0; I < NumSlots; ++I) {
    692     delete Intervals[I];
    693   }
    694 
    695   return removeAllMarkers();
    696 }
    697