LiveIntervalAnalysis.cpp

//===-- LiveIntervalAnalysis.cpp - Live Interval Analysis -----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LiveInterval analysis pass which is used
// by the Linear Scan Register allocator. This pass linearizes the
// basic blocks of the function in DFS order and uses the
// LiveVariables pass to conservatively compute live intervals for
// each virtual and physical register.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "liveintervals"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "VirtRegMap.h"
#include "llvm/Value.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
#include <cmath>
using namespace llvm;

// Hidden options for help debugging.
static cl::opt<bool> DisableReMat("disable-rematerialization", 
                                  cl::init(false), cl::Hidden);

static cl::opt<bool> SplitAtBB("split-intervals-at-bb", 
                               cl::init(true), cl::Hidden);
static cl::opt<int> SplitLimit("split-limit",
                               cl::init(-1), cl::Hidden);

static cl::opt<bool> EnableAggressiveRemat("aggressive-remat", cl::Hidden);

static cl::opt<bool> EnableFastSpilling("fast-spill",
                                        cl::init(false), cl::Hidden);

STATISTIC(numIntervals, "Number of original intervals");
STATISTIC(numIntervalsAfter, "Number of intervals after coalescing");
STATISTIC(numFolds    , "Number of loads/stores folded into instructions");
STATISTIC(numSplits   , "Number of intervals split");

char LiveIntervals::ID = 0;
static RegisterPass<LiveIntervals> X("liveintervals", "Live Interval Analysis");

void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.addRequired<AliasAnalysis>();
  AU.addPreserved<AliasAnalysis>();
  AU.addPreserved<LiveVariables>();
  AU.addRequired<LiveVariables>();
  AU.addPreservedID(MachineLoopInfoID);
  AU.addPreservedID(MachineDominatorsID);
  
  if (!StrongPHIElim) {
    AU.addPreservedID(PHIEliminationID);
    AU.addRequiredID(PHIEliminationID);
  }
  
  AU.addRequiredID(TwoAddressInstructionPassID);
  MachineFunctionPass::getAnalysisUsage(AU);
}

void LiveIntervals::releaseMemory() {
  // Free the live intervals themselves.
  for (DenseMap<unsigned, LiveInterval*>::iterator I = r2iMap_.begin(),
       E = r2iMap_.end(); I != E; ++I)
    delete I->second;
  
  MBB2IdxMap.clear();
  Idx2MBBMap.clear();
  mi2iMap_.clear();
  i2miMap_.clear();
  r2iMap_.clear();
  // Release VNInfo memroy regions after all VNInfo objects are dtor'd.
  VNInfoAllocator.Reset();
  while (!ClonedMIs.empty()) {
    MachineInstr *MI = ClonedMIs.back();
    ClonedMIs.pop_back();
    mf_->DeleteMachineInstr(MI);
  }
}

void LiveIntervals::computeNumbering() {
  Index2MiMap OldI2MI = i2miMap_;
  std::vector<IdxMBBPair> OldI2MBB = Idx2MBBMap;
  
  Idx2MBBMap.clear();
  MBB2IdxMap.clear();
  mi2iMap_.clear();
  i2miMap_.clear();
  
  FunctionSize = 0;
  
  // Number MachineInstrs and MachineBasicBlocks.
  // Initialize MBB indexes to a sentinal.
  MBB2IdxMap.resize(mf_->getNumBlockIDs(), std::make_pair(~0U,~0U));
  
  unsigned MIIndex = 0;
  for (MachineFunction::iterator MBB = mf_->begin(), E = mf_->end();
       MBB != E; ++MBB) {
    unsigned StartIdx = MIIndex;

    // Insert an empty slot at the beginning of each block.
    MIIndex += InstrSlots::NUM;
    i2miMap_.push_back(0);

    for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
         I != E; ++I) {
      bool inserted = mi2iMap_.insert(std::make_pair(I, MIIndex)).second;
      assert(inserted && "multiple MachineInstr -> index mappings");
      i2miMap_.push_back(I);
      MIIndex += InstrSlots::NUM;
      FunctionSize++;
      
      // Insert max(1, numdefs) empty slots after every instruction.
      unsigned Slots = I->getDesc().getNumDefs();
      if (Slots == 0)
        Slots = 1;
      MIIndex += InstrSlots::NUM * Slots;
      while (Slots--)
        i2miMap_.push_back(0);
    }
    
    // Set the MBB2IdxMap entry for this MBB.
    MBB2IdxMap[MBB->getNumber()] = std::make_pair(StartIdx, MIIndex - 1);
    Idx2MBBMap.push_back(std::make_pair(StartIdx, MBB));
  }
  std::sort(Idx2MBBMap.begin(), Idx2MBBMap.end(), Idx2MBBCompare());
  
  if (!OldI2MI.empty())
    for (iterator OI = begin(), OE = end(); OI != OE; ++OI) {
      for (LiveInterval::iterator LI = OI->second->begin(),
           LE = OI->second->end(); LI != LE; ++LI) {
        
        // Remap the start index of the live range to the corresponding new
        // number, or our best guess at what it _should_ correspond to if the
        // original instruction has been erased.  This is either the following
        // instruction or its predecessor.
        unsigned index = LI->start / InstrSlots::NUM;
        unsigned offset = LI->start % InstrSlots::NUM;
        if (offset == InstrSlots::LOAD) {
          std::vector<IdxMBBPair>::const_iterator I =
                  std::lower_bound(OldI2MBB.begin(), OldI2MBB.end(), LI->start);
          // Take the pair containing the index
          std::vector<IdxMBBPair>::const_iterator J =
                    (I == OldI2MBB.end() && OldI2MBB.size()>0) ? (I-1): I;
          
          LI->start = getMBBStartIdx(J->second);
        } else {
          LI->start = mi2iMap_[OldI2MI[index]] + offset;
        }
        
        // Remap the ending index in the same way that we remapped the start,
        // except for the final step where we always map to the immediately
        // following instruction.
        index = (LI->end - 1) / InstrSlots::NUM;
        offset  = LI->end % InstrSlots::NUM;
        if (offset == InstrSlots::LOAD) {
          // VReg dies at end of block.
          std::vector<IdxMBBPair>::const_iterator I =
                  std::lower_bound(OldI2MBB.begin(), OldI2MBB.end(), LI->end);
          --I;
          
          LI->end = getMBBEndIdx(I->second) + 1;
        } else {
          unsigned idx = index;
          while (index < OldI2MI.size() && !OldI2MI[index]) ++index;
          
          if (index != OldI2MI.size())
            LI->end = mi2iMap_[OldI2MI[index]] + (idx == index ? offset : 0);
          else
            LI->end = InstrSlots::NUM * i2miMap_.size();
        }
      }
      
      for (LiveInterval::vni_iterator VNI = OI->second->vni_begin(),
           VNE = OI->second->vni_end(); VNI != VNE; ++VNI) { 
        VNInfo* vni = *VNI;
        
        // Remap the VNInfo def index, which works the same as the
        // start indices above. VN's with special sentinel defs
        // don't need to be remapped.
        if (vni->def != ~0U && vni->def != ~1U) {
          unsigned index = vni->def / InstrSlots::NUM;
          unsigned offset = vni->def % InstrSlots::NUM;
          if (offset == InstrSlots::LOAD) {
            std::vector<IdxMBBPair>::const_iterator I =
                  std::lower_bound(OldI2MBB.begin(), OldI2MBB.end(), vni->def);
            // Take the pair containing the index
            std::vector<IdxMBBPair>::const_iterator J =
                    (I == OldI2MBB.end() && OldI2MBB.size()>0) ? (I-1): I;
          
            vni->def = getMBBStartIdx(J->second);
          } else {
            vni->def = mi2iMap_[OldI2MI[index]] + offset;
          }
        }
        
        // Remap the VNInfo kill indices, which works the same as
        // the end indices above.
        for (size_t i = 0; i < vni->kills.size(); ++i) {
          // PHI kills don't need to be remapped.
          if (!vni->kills[i]) continue;
          
          unsigned index = (vni->kills[i]-1) / InstrSlots::NUM;
          unsigned offset = vni->kills[i] % InstrSlots::NUM;
          if (offset == InstrSlots::LOAD) {
            std::vector<IdxMBBPair>::const_iterator I =
             std::lower_bound(OldI2MBB.begin(), OldI2MBB.end(), vni->kills[i]);
            --I;

            vni->kills[i] = getMBBEndIdx(I->second);
          } else {
            unsigned idx = index;
            while (index < OldI2MI.size() && !OldI2MI[index]) ++index;
            
            if (index != OldI2MI.size())
              vni->kills[i] = mi2iMap_[OldI2MI[index]] + 
                              (idx == index ? offset : 0);
            else
              vni->kills[i] = InstrSlots::NUM * i2miMap_.size();
          }
        }
      }
    }
}

/// runOnMachineFunction - Register allocate the whole function
///
bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
  mf_ = &fn;
  mri_ = &mf_->getRegInfo();
  tm_ = &fn.getTarget();
  tri_ = tm_->getRegisterInfo();
  tii_ = tm_->getInstrInfo();
  aa_ = &getAnalysis<AliasAnalysis>();
  lv_ = &getAnalysis<LiveVariables>();
  allocatableRegs_ = tri_->getAllocatableSet(fn);

  computeNumbering();
  computeIntervals();

  numIntervals += getNumIntervals();

  DOUT << "********** INTERVALS **********\n";
  for (iterator I = begin(), E = end(); I != E; ++I) {
    I->second->print(DOUT, tri_);
    DOUT << "\n";
  }

  numIntervalsAfter += getNumIntervals();
  DEBUG(dump());
  return true;
}

/// print - Implement the dump method.
void LiveIntervals::print(std::ostream &O, const Module* ) const {
  O << "********** INTERVALS **********\n";
  for (const_iterator I = begin(), E = end(); I != E; ++I) {
    I->second->print(O, tri_);
    O << "\n";
  }

  O << "********** MACHINEINSTRS **********\n";
  for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
       mbbi != mbbe; ++mbbi) {
    O << ((Value*)mbbi->getBasicBlock())->getName() << ":\n";
    for (MachineBasicBlock::iterator mii = mbbi->begin(),
           mie = mbbi->end(); mii != mie; ++mii) {
      O << getInstructionIndex(mii) << '\t' << *mii;
    }
  }
}

/// conflictsWithPhysRegDef - Returns true if the specified register
/// is defined during the duration of the specified interval.
bool LiveIntervals::conflictsWithPhysRegDef(const LiveInterval &li,
                                            VirtRegMap &vrm, unsigned reg) {
  for (LiveInterval::Ranges::const_iterator
         I = li.ranges.begin(), E = li.ranges.end(); I != E; ++I) {
    for (unsigned index = getBaseIndex(I->start),
           end = getBaseIndex(I->end-1) + InstrSlots::NUM; index != end;
         index += InstrSlots::NUM) {
      // skip deleted instructions
      while (index != end && !getInstructionFromIndex(index))
        index += InstrSlots::NUM;
      if (index == end) break;

      MachineInstr *MI = getInstructionFromIndex(index);
      unsigned SrcReg, DstReg;
      if (tii_->isMoveInstr(*MI, SrcReg, DstReg))
        if (SrcReg == li.reg || DstReg == li.reg)
          continue;
      for (unsigned i = 0; i != MI->getNumOperands(); ++i) {
        MachineOperand& mop = MI->getOperand(i);
        if (!mop.isReg())
          continue;
        unsigned PhysReg = mop.getReg();
        if (PhysReg == 0 || PhysReg == li.reg)
          continue;
        if (TargetRegisterInfo::isVirtualRegister(PhysReg)) {
          if (!vrm.hasPhys(PhysReg))
            continue;
          PhysReg = vrm.getPhys(PhysReg);
        }
        if (PhysReg && tri_->regsOverlap(PhysReg, reg))
          return true;
      }
    }
  }

  return false;
}

void LiveIntervals::printRegName(unsigned reg) const {
  if (TargetRegisterInfo::isPhysicalRegister(reg))
    cerr << tri_->getName(reg);
  else
    cerr << "%reg" << reg;
}

void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
                                             MachineBasicBlock::iterator mi,
                                             unsigned MIIdx, MachineOperand& MO,
                                             unsigned MOIdx,
                                             LiveInterval &interval) {
  DOUT << "\t\tregister: "; DEBUG(printRegName(interval.reg));
  LiveVariables::VarInfo& vi = lv_->getVarInfo(interval.reg);

  if (mi->getOpcode() == TargetInstrInfo::IMPLICIT_DEF) {
    DOUT << "is a implicit_def\n";
    return;
  }

  // Virtual registers may be defined multiple times (due to phi
  // elimination and 2-addr elimination).  Much of what we do only has to be
  // done once for the vreg.  We use an empty interval to detect the first
  // time we see a vreg.
  if (interval.empty()) {
    // Get the Idx of the defining instructions.
    unsigned defIndex = getDefIndex(MIIdx);
    // Earlyclobbers move back one.
    if (MO.isEarlyClobber())
      defIndex = getUseIndex(MIIdx);
    VNInfo *ValNo;
    MachineInstr *CopyMI = NULL;
    unsigned SrcReg, DstReg;
    if (mi->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG ||
        mi->getOpcode() == TargetInstrInfo::INSERT_SUBREG ||
        tii_->isMoveInstr(*mi, SrcReg, DstReg))
      CopyMI = mi;
    ValNo = interval.getNextValue(defIndex, CopyMI, VNInfoAllocator);

    assert(ValNo->id == 0 && "First value in interval is not 0?");

    // Loop over all of the blocks that the vreg is defined in.  There are
    // two cases we have to handle here.  The most common case is a vreg
    // whose lifetime is contained within a basic block.  In this case there
    // will be a single kill, in MBB, which comes after the definition.
    if (vi.Kills.size() == 1 && vi.Kills[0]->getParent() == mbb) {
      // FIXME: what about dead vars?
      unsigned killIdx;
      if (vi.Kills[0] != mi)
        killIdx = getUseIndex(getInstructionIndex(vi.Kills[0]))+1;
      else
        killIdx = defIndex+1;

      // If the kill happens after the definition, we have an intra-block
      // live range.
      if (killIdx > defIndex) {
        assert(vi.AliveBlocks.none() &&
               "Shouldn't be alive across any blocks!");
        LiveRange LR(defIndex, killIdx, ValNo);
        interval.addRange(LR);
        DOUT << " +" << LR << "\n";
        interval.addKill(ValNo, killIdx);
        return;
      }
    }

    // The other case we handle is when a virtual register lives to the end
    // of the defining block, potentially live across some blocks, then is
    // live into some number of blocks, but gets killed.  Start by adding a
    // range that goes from this definition to the end of the defining block.
    LiveRange NewLR(defIndex, getMBBEndIdx(mbb)+1, ValNo);
    DOUT << " +" << NewLR;
    interval.addRange(NewLR);

    // Iterate over all of the blocks that the variable is completely
    // live in, adding [insrtIndex(begin), instrIndex(end)+4) to the
    // live interval.
    for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
      if (vi.AliveBlocks[i]) {
        LiveRange LR(getMBBStartIdx(i),
                     getMBBEndIdx(i)+1,  // MBB ends at -1.
                     ValNo);
        interval.addRange(LR);
        DOUT << " +" << LR;
      }
    }

    // Finally, this virtual register is live from the start of any killing
    // block to the 'use' slot of the killing instruction.
    for (unsigned i = 0, e = vi.Kills.size(); i != e; ++i) {
      MachineInstr *Kill = vi.Kills[i];
      unsigned killIdx = getUseIndex(getInstructionIndex(Kill))+1;
      LiveRange LR(getMBBStartIdx(Kill->getParent()),
                   killIdx, ValNo);
      interval.addRange(LR);
      interval.addKill(ValNo, killIdx);
      DOUT << " +" << LR;
    }

  } else {
    // If this is the second time we see a virtual register definition, it
    // must be due to phi elimination or two addr elimination.  If this is
    // the result of two address elimination, then the vreg is one of the
    // def-and-use register operand.
    if (mi->isRegReDefinedByTwoAddr(interval.reg, MOIdx)) {
      // If this is a two-address definition, then we have already processed
      // the live range.  The only problem is that we didn't realize there
      // are actually two values in the live interval.  Because of this we
      // need to take the LiveRegion that defines this register and split it
      // into two values.
      assert(interval.containsOneValue());
      unsigned DefIndex = getDefIndex(interval.getValNumInfo(0)->def);
      unsigned RedefIndex = getDefIndex(MIIdx);
      // Earlyclobbers move back one.
      if (MO.isEarlyClobber())
        RedefIndex = getUseIndex(MIIdx);

      const LiveRange *OldLR = interval.getLiveRangeContaining(RedefIndex-1);
      VNInfo *OldValNo = OldLR->valno;

      // Delete the initial value, which should be short and continuous,
      // because the 2-addr copy must be in the same MBB as the redef.
      interval.removeRange(DefIndex, RedefIndex);

      // Two-address vregs should always only be redefined once.  This means
      // that at this point, there should be exactly one value number in it.
      assert(interval.containsOneValue() && "Unexpected 2-addr liveint!");

      // The new value number (#1) is defined by the instruction we claimed
      // defined value #0.
      VNInfo *ValNo = interval.getNextValue(OldValNo->def, OldValNo->copy,
                                            VNInfoAllocator);
      
      // Value#0 is now defined by the 2-addr instruction.
      OldValNo->def  = RedefIndex;
      OldValNo->copy = 0;
      
      // Add the new live interval which replaces the range for the input copy.
      LiveRange LR(DefIndex, RedefIndex, ValNo);
      DOUT << " replace range with " << LR;
      interval.addRange(LR);
      interval.addKill(ValNo, RedefIndex);

      // If this redefinition is dead, we need to add a dummy unit live
      // range covering the def slot.
      if (MO.isDead())
        interval.addRange(LiveRange(RedefIndex, RedefIndex+1, OldValNo));

      DOUT << " RESULT: ";
      interval.print(DOUT, tri_);

    } else {
      // Otherwise, this must be because of phi elimination.  If this is the
      // first redefinition of the vreg that we have seen, go back and change
      // the live range in the PHI block to be a different value number.
      if (interval.containsOneValue()) {
        assert(vi.Kills.size() == 1 &&
               "PHI elimination vreg should have one kill, the PHI itself!");

        // Remove the old range that we now know has an incorrect number.
        VNInfo *VNI = interval.getValNumInfo(0);
        MachineInstr *Killer = vi.Kills[0];
        unsigned Start = getMBBStartIdx(Killer->getParent());
        unsigned End = getUseIndex(getInstructionIndex(Killer))+1;
        DOUT << " Removing [" << Start << "," << End << "] from: ";
        interval.print(DOUT, tri_); DOUT << "\n";
        interval.removeRange(Start, End);
        VNI->hasPHIKill = true;
        DOUT << " RESULT: "; interval.print(DOUT, tri_);

        // Replace the interval with one of a NEW value number.  Note that this
        // value number isn't actually defined by an instruction, weird huh? :)
        LiveRange LR(Start, End, interval.getNextValue(~0, 0, VNInfoAllocator));
        DOUT << " replace range with " << LR;
        interval.addRange(LR);
        interval.addKill(LR.valno, End);
        DOUT << " RESULT: "; interval.print(DOUT, tri_);
      }

      // In the case of PHI elimination, each variable definition is only
      // live until the end of the block.  We've already taken care of the
      // rest of the live range.
      unsigned defIndex = getDefIndex(MIIdx);
      // Earlyclobbers move back one.
      if (MO.isEarlyClobber())
        defIndex = getUseIndex(MIIdx);
      
      VNInfo *ValNo;
      MachineInstr *CopyMI = NULL;
      unsigned SrcReg, DstReg;
      if (mi->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG ||
          mi->getOpcode() == TargetInstrInfo::INSERT_SUBREG ||
          tii_->isMoveInstr(*mi, SrcReg, DstReg))
        CopyMI = mi;
      ValNo = interval.getNextValue(defIndex, CopyMI, VNInfoAllocator);
      
      unsigned killIndex = getMBBEndIdx(mbb) + 1;
      LiveRange LR(defIndex, killIndex, ValNo);
      interval.addRange(LR);
      interval.addKill(ValNo, killIndex);
      ValNo->hasPHIKill = true;
      DOUT << " +" << LR;
    }
  }

  DOUT << '\n';
}

void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock *MBB,
                                              MachineBasicBlock::iterator mi,
                                              unsigned MIIdx,
                                              MachineOperand& MO,
                                              LiveInterval &interval,
                                              MachineInstr *CopyMI) {
  // A physical register cannot be live across basic block, so its
  // lifetime must end somewhere in its defining basic block.
  DOUT << "\t\tregister: "; DEBUG(printRegName(interval.reg));

  unsigned baseIndex = MIIdx;
  unsigned start = getDefIndex(baseIndex);
  // Earlyclobbers move back one.
  if (MO.isEarlyClobber())
    start = getUseIndex(MIIdx);
  unsigned end = start;

  // If it is not used after definition, it is considered dead at
  // the instruction defining it. Hence its interval is:
  // [defSlot(def), defSlot(def)+1)
  if (MO.isDead()) {
    DOUT << " dead";
    end = start + 1;
    goto exit;
  }

  // If it is not dead on definition, it must be killed by a
  // subsequent instruction. Hence its interval is:
  // [defSlot(def), useSlot(kill)+1)
  baseIndex += InstrSlots::NUM;
  while (++mi != MBB->end()) {
    while (baseIndex / InstrSlots::NUM < i2miMap_.size() &&
           getInstructionFromIndex(baseIndex) == 0)
      baseIndex += InstrSlots::NUM;
    if (mi->killsRegister(interval.reg, tri_)) {
      DOUT << " killed";
      end = getUseIndex(baseIndex) + 1;
      goto exit;
    } else if (mi->modifiesRegister(interval.reg, tri_)) {
      // Another instruction redefines the register before it is ever read.
      // Then the register is essentially dead at the instruction that defines
      // it. Hence its interval is:
      // [defSlot(def), defSlot(def)+1)
      DOUT << " dead";
      end = start + 1;
      goto exit;
    }
    
    baseIndex += InstrSlots::NUM;
  }
  
  // The only case we should have a dead physreg here without a killing or
  // instruction where we know it's dead is if it is live-in to the function
  // and never used.
  assert(!CopyMI && "physreg was not killed in defining block!");
  end = start + 1;

exit:
  assert(start < end && "did not find end of interval?");

  // Already exists? Extend old live interval.
  LiveInterval::iterator OldLR = interval.FindLiveRangeContaining(start);
  VNInfo *ValNo = (OldLR != interval.end())
    ? OldLR->valno : interval.getNextValue(start, CopyMI, VNInfoAllocator);
  LiveRange LR(start, end, ValNo);
  interval.addRange(LR);
  interval.addKill(LR.valno, end);
  DOUT << " +" << LR << '\n';
}

void LiveIntervals::handleRegisterDef(MachineBasicBlock *MBB,
                                      MachineBasicBlock::iterator MI,
                                      unsigned MIIdx,
                                      MachineOperand& MO,
                                      unsigned MOIdx) {
  if (TargetRegisterInfo::isVirtualRegister(MO.getReg()))
    handleVirtualRegisterDef(MBB, MI, MIIdx, MO, MOIdx,
                             getOrCreateInterval(MO.getReg()));
  else if (allocatableRegs_[MO.getReg()]) {
    MachineInstr *CopyMI = NULL;
    unsigned SrcReg, DstReg;
    if (MI->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG ||
        MI->getOpcode() == TargetInstrInfo::INSERT_SUBREG ||
        tii_->isMoveInstr(*MI, SrcReg, DstReg))
      CopyMI = MI;
    handlePhysicalRegisterDef(MBB, MI, MIIdx, MO, 
                              getOrCreateInterval(MO.getReg()), CopyMI);
    // Def of a register also defines its sub-registers.
    for (const unsigned* AS = tri_->getSubRegisters(MO.getReg()); *AS; ++AS)
      // If MI also modifies the sub-register explicitly, avoid processing it
      // more than once. Do not pass in TRI here so it checks for exact match.
      if (!MI->modifiesRegister(*AS))
        handlePhysicalRegisterDef(MBB, MI, MIIdx, MO, 
                                  getOrCreateInterval(*AS), 0);
  }
}

void LiveIntervals::handleLiveInRegister(MachineBasicBlock *MBB,
                                         unsigned MIIdx,
                                         LiveInterval &interval, bool isAlias) {
  DOUT << "\t\tlivein register: "; DEBUG(printRegName(interval.reg));

  // Look for kills, if it reaches a def before it's killed, then it shouldn't
  // be considered a livein.
  MachineBasicBlock::iterator mi = MBB->begin();
  unsigned baseIndex = MIIdx;
  unsigned start = baseIndex;
  while (baseIndex / InstrSlots::NUM < i2miMap_.size() && 
         getInstructionFromIndex(baseIndex) == 0)
    baseIndex += InstrSlots::NUM;
  unsigned end = baseIndex;
  
  while (mi != MBB->end()) {
    if (mi->killsRegister(interval.reg, tri_)) {
      DOUT << " killed";
      end = getUseIndex(baseIndex) + 1;
      goto exit;
    } else if (mi->modifiesRegister(interval.reg, tri_)) {
      // Another instruction redefines the register before it is ever read.
      // Then the register is essentially dead at the instruction that defines
      // it. Hence its interval is:
      // [defSlot(def), defSlot(def)+1)
      DOUT << " dead";
      end = getDefIndex(start) + 1;
      goto exit;
    }

    baseIndex += InstrSlots::NUM;
    while (baseIndex / InstrSlots::NUM < i2miMap_.size() && 
           getInstructionFromIndex(baseIndex) == 0)
      baseIndex += InstrSlots::NUM;
    ++mi;
  }

exit:
  // Live-in register might not be used at all.
  if (end == MIIdx) {
    if (isAlias) {
      DOUT << " dead";
      end = getDefIndex(MIIdx) + 1;
    } else {
      DOUT << " live through";
      end = baseIndex;
    }
  }

  LiveRange LR(start, end, interval.getNextValue(~0U, 0, VNInfoAllocator));
  interval.addRange(LR);
  interval.addKill(LR.valno, end);
  DOUT << " +" << LR << '\n';
}

/// computeIntervals - computes the live intervals for virtual
/// registers. for some ordering of the machine instructions [1,N] a
/// live interval is an interval [i, j) where 1 <= i <= j < N for
/// which a variable is live
void LiveIntervals::computeIntervals() { 

  DOUT << "********** COMPUTING LIVE INTERVALS **********\n"
       << "********** Function: "
       << ((Value*)mf_->getFunction())->getName() << '\n';
  
  for (MachineFunction::iterator MBBI = mf_->begin(), E = mf_->end();
       MBBI != E; ++MBBI) {
    MachineBasicBlock *MBB = MBBI;
    // Track the index of the current machine instr.
    unsigned MIIndex = getMBBStartIdx(MBB);
    DOUT << ((Value*)MBB->getBasicBlock())->getName() << ":\n";

    MachineBasicBlock::iterator MI = MBB->begin(), miEnd = MBB->end();

    // Create intervals for live-ins to this BB first.
    for (MachineBasicBlock::const_livein_iterator LI = MBB->livein_begin(),
           LE = MBB->livein_end(); LI != LE; ++LI) {
      handleLiveInRegister(MBB, MIIndex, getOrCreateInterval(*LI));
      // Multiple live-ins can alias the same register.
      for (const unsigned* AS = tri_->getSubRegisters(*LI); *AS; ++AS)
        if (!hasInterval(*AS))
          handleLiveInRegister(MBB, MIIndex, getOrCreateInterval(*AS),
                               true);
    }
    
    // Skip over empty initial indices.
    while (MIIndex / InstrSlots::NUM < i2miMap_.size() &&
           getInstructionFromIndex(MIIndex) == 0)
      MIIndex += InstrSlots::NUM;
    
    for (; MI != miEnd; ++MI) {
      DOUT << MIIndex << "\t" << *MI;

      // Handle defs.
      for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
        MachineOperand &MO = MI->getOperand(i);
        // handle register defs - build intervals
        if (MO.isReg() && MO.getReg() && MO.isDef()) {
          handleRegisterDef(MBB, MI, MIIndex, MO, i);
        }
      }

      // Skip over the empty slots after each instruction.
      unsigned Slots = MI->getDesc().getNumDefs();
      if (Slots == 0)
        Slots = 1;
      MIIndex += InstrSlots::NUM * Slots;
      
      // Skip over empty indices.
      while (MIIndex / InstrSlots::NUM < i2miMap_.size() &&
             getInstructionFromIndex(MIIndex) == 0)
        MIIndex += InstrSlots::NUM;
    }
  }
}

bool LiveIntervals::findLiveInMBBs(const LiveRange &LR,
                              SmallVectorImpl<MachineBasicBlock*> &MBBs) const {
  std::vector<IdxMBBPair>::const_iterator I =
    std::lower_bound(Idx2MBBMap.begin(), Idx2MBBMap.end(), LR.start);

  bool ResVal = false;
  while (I != Idx2MBBMap.end()) {
    if (LR.end <= I->first)
      break;
    MBBs.push_back(I->second);
    ResVal = true;
    ++I;
  }
  return ResVal;
}

LiveInterval* LiveIntervals::createInterval(unsigned reg) {
  float Weight = TargetRegisterInfo::isPhysicalRegister(reg) ?
                       HUGE_VALF : 0.0F;
  return new LiveInterval(reg, Weight);
}

/// getVNInfoSourceReg - Helper function that parses the specified VNInfo
/// copy field and returns the source register that defines it.
unsigned LiveIntervals::getVNInfoSourceReg(const VNInfo *VNI) const {
  if (!VNI->copy)
    return 0;

  if (VNI->copy->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG)
    return VNI->copy->getOperand(1).getReg();
  if (VNI->copy->getOpcode() == TargetInstrInfo::INSERT_SUBREG)
    return VNI->copy->getOperand(2).getReg();
  unsigned SrcReg, DstReg;
  if (tii_->isMoveInstr(*VNI->copy, SrcReg, DstReg))
    return SrcReg;
  assert(0 && "Unrecognized copy instruction!");
  return 0;
}

//===----------------------------------------------------------------------===//
// Register allocator hooks.
//

/// getReMatImplicitUse - If the remat definition MI has one (for now, we only
/// allow one) virtual register operand, then its uses are implicitly using
/// the register. Returns the virtual register.
unsigned LiveIntervals::getReMatImplicitUse(const LiveInterval &li,
                                            MachineInstr *MI) const {
  unsigned RegOp = 0;
  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
    MachineOperand &MO = MI->getOperand(i);
    if (!MO.isReg() || !MO.isUse())
      continue;
    unsigned Reg = MO.getReg();
    if (Reg == 0 || Reg == li.reg)
      continue;
    // FIXME: For now, only remat MI with at most one register operand.
    assert(!RegOp &&
           "Can't rematerialize instruction with multiple register operand!");
    RegOp = MO.getReg();
#ifndef NDEBUG
    break;
#endif
  }
  return RegOp;
}

/// isValNoAvailableAt - Return true if the val# of the specified interval
/// which reaches the given instruction also reaches the specified use index.
bool LiveIntervals::isValNoAvailableAt(const LiveInterval &li, MachineInstr *MI,
                                       unsigned UseIdx) const {
  unsigned Index = getInstructionIndex(MI);  
  VNInfo *ValNo = li.FindLiveRangeContaining(Index)->valno;
  LiveInterval::const_iterator UI = li.FindLiveRangeContaining(UseIdx);
  return UI != li.end() && UI->valno == ValNo;
}

/// isReMaterializable - Returns true if the definition MI of the specified
/// val# of the specified interval is re-materializable.
bool LiveIntervals::isReMaterializable(const LiveInterval &li,
                                       const VNInfo *ValNo, MachineInstr *MI,
                                       SmallVectorImpl<LiveInterval*> &SpillIs,
                                       bool &isLoad) {
  if (DisableReMat)
    return false;

  if (MI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF)
    return true;

  int FrameIdx = 0;
  if (tii_->isLoadFromStackSlot(MI, FrameIdx) &&
      mf_->getFrameInfo()->isImmutableObjectIndex(FrameIdx))
    // FIXME: Let target specific isReallyTriviallyReMaterializable determines
    // this but remember this is not safe to fold into a two-address
    // instruction.
    // This is a load from fixed stack slot. It can be rematerialized.
    return true;

  // If the target-specific rules don't identify an instruction as
  // being trivially rematerializable, use some target-independent
  // rules.
  if (!MI->getDesc().isRematerializable() ||
      !tii_->isTriviallyReMaterializable(MI)) {
    if (!EnableAggressiveRemat)
      return false;

    // If the instruction accesses memory but the memoperands have been lost,
    // we can't analyze it.
    const TargetInstrDesc &TID = MI->getDesc();
    if ((TID.mayLoad() || TID.mayStore()) && MI->memoperands_empty())
      return false;

    // Avoid instructions obviously unsafe for remat.
    if (TID.hasUnmodeledSideEffects() || TID.isNotDuplicable())
      return false;

    // If the instruction accesses memory and the memory could be non-constant,
    // assume the instruction is not rematerializable.
    for (std::list<MachineMemOperand>::const_iterator
           I = MI->memoperands_begin(), E = MI->memoperands_end(); I != E; ++I){
      const MachineMemOperand &MMO = *I;
      if (MMO.isVolatile() || MMO.isStore())
        return false;
      const Value *V = MMO.getValue();
      if (!V)
        return false;
      if (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V)) {
        if (!PSV->isConstant(mf_->getFrameInfo()))
          return false;
      } else if (!aa_->pointsToConstantMemory(V))
        return false;
    }

    // If any of the registers accessed are non-constant, conservatively assume
    // the instruction is not rematerializable.
    unsigned ImpUse = 0;
    for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
      const MachineOperand &MO = MI->getOperand(i);
      if (MO.isReg()) {
        unsigned Reg = MO.getReg();
        if (Reg == 0)
          continue;
        if (TargetRegisterInfo::isPhysicalRegister(Reg))
          return false;

        // Only allow one def, and that in the first operand.
        if (MO.isDef() != (i == 0))
          return false;

        // Only allow constant-valued registers.
        bool IsLiveIn = mri_->isLiveIn(Reg);
        MachineRegisterInfo::def_iterator I = mri_->def_begin(Reg),
                                          E = mri_->def_end();

        // For the def, it should be the only def.
        if (MO.isDef() && (next(I) != E || IsLiveIn))
          return false;

        if (MO.isUse()) {
          // Only allow one use other register use, as that's all the
          // remat mechanisms support currently.
          if (Reg != li.reg) {
            if (ImpUse == 0)
              ImpUse = Reg;
            else if (Reg != ImpUse)
              return false;
          }
          // For uses, there should be only one associate def.
          if (I != E && (next(I) != E || IsLiveIn))
            return false;
        }
      }
    }
  }

  unsigned ImpUse = getReMatImplicitUse(li, MI);
  if (ImpUse) {
    const LiveInterval &ImpLi = getInterval(ImpUse);
    for (MachineRegisterInfo::use_iterator ri = mri_->use_begin(li.reg),
           re = mri_->use_end(); ri != re; ++ri) {
      MachineInstr *UseMI = &*ri;
      unsigned UseIdx = getInstructionIndex(UseMI);
      if (li.FindLiveRangeContaining(UseIdx)->valno != ValNo)
        continue;
      if (!isValNoAvailableAt(ImpLi, MI, UseIdx))
        return false;
    }

    // If a register operand of the re-materialized instruction is going to
    // be spilled next, then it's not legal to re-materialize this instruction.
    for (unsigned i = 0, e = SpillIs.size(); i != e; ++i)
      if (ImpUse == SpillIs[i]->reg)
        return false;
  }
  return true;
}

/// isReMaterializable - Returns true if every definition of MI of every
/// val# of the specified interval is re-materializable.
bool LiveIntervals::isReMaterializable(const LiveInterval &li,
                                       SmallVectorImpl<LiveInterval*> &SpillIs,
                                       bool &isLoad) {
  isLoad = false;
  for (LiveInterval::const_vni_iterator i = li.vni_begin(), e = li.vni_end();
       i != e; ++i) {
    const VNInfo *VNI = *i;
    unsigned DefIdx = VNI->def;
    if (DefIdx == ~1U)
      continue; // Dead val#.
    // Is the def for the val# rematerializable?
    if (DefIdx == ~0u)
      return false;
    MachineInstr *ReMatDefMI = getInstructionFromIndex(DefIdx);
    bool DefIsLoad = false;
    if (!ReMatDefMI ||
        !isReMaterializable(li, VNI, ReMatDefMI, SpillIs, DefIsLoad))
      return false;
    isLoad |= DefIsLoad;
  }
  return true;
}

/// FilterFoldedOps - Filter out two-address use operands. Return
/// true if it finds any issue with the operands that ought to prevent
/// folding.
static bool FilterFoldedOps(MachineInstr *MI,
                            SmallVector<unsigned, 2> &Ops,
                            unsigned &MRInfo,
                            SmallVector<unsigned, 2> &FoldOps) {
  const TargetInstrDesc &TID = MI->getDesc();

  MRInfo = 0;
  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
    unsigned OpIdx = Ops[i];
    MachineOperand &MO = MI->getOperand(OpIdx);
    // FIXME: fold subreg use.
    if (MO.getSubReg())
      return true;
    if (MO.isDef())
      MRInfo |= (unsigned)VirtRegMap::isMod;
    else {
      // Filter out two-address use operand(s).
      if (!MO.isImplicit() &&
          TID.getOperandConstraint(OpIdx, TOI::TIED_TO) != -1) {
        MRInfo = VirtRegMap::isModRef;
        continue;
      }