LiveIntervalAnalysis.cpp

  // Filter the list of operand indexes that are to be folded. Abort if
  // any operand will prevent folding.
  unsigned MRInfo = 0;
  SmallVector<unsigned, 2> FoldOps;
  if (FilterFoldedOps(MI, Ops, MRInfo, FoldOps))
    return false;

  // It's only legal to remat for a use, not a def.
  if (ReMat && (MRInfo & VirtRegMap::isMod))
    return false;

  return tii_->canFoldMemoryOperand(MI, FoldOps);
}

bool LiveIntervals::intervalIsInOneMBB(const LiveInterval &li) const {
  SmallPtrSet<MachineBasicBlock*, 4> MBBs;
  for (LiveInterval::Ranges::const_iterator
         I = li.ranges.begin(), E = li.ranges.end(); I != E; ++I) {
    std::vector<IdxMBBPair>::const_iterator II =
      std::lower_bound(Idx2MBBMap.begin(), Idx2MBBMap.end(), I->start);
    if (II == Idx2MBBMap.end())
      continue;
    if (I->end > II->first)  // crossing a MBB.
      return false;
    MBBs.insert(II->second);
    if (MBBs.size() > 1)
      return false;
  }
  return true;
}

/// rewriteImplicitOps - Rewrite implicit use operands of MI (i.e. uses of
/// interval on to-be re-materialized operands of MI) with new register.
void LiveIntervals::rewriteImplicitOps(const LiveInterval &li,
                                       MachineInstr *MI, unsigned NewVReg,
                                       VirtRegMap &vrm) {
  // There is an implicit use. That means one of the other operand is
  // being remat'ed and the remat'ed instruction has li.reg as an
  // use operand. Make sure we rewrite that as well.
  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
    MachineOperand &MO = MI->getOperand(i);
    if (!MO.isRegister())
      continue;
    unsigned Reg = MO.getReg();
    if (Reg == 0 || TargetRegisterInfo::isPhysicalRegister(Reg))
      continue;
    if (!vrm.isReMaterialized(Reg))
      continue;
    MachineInstr *ReMatMI = vrm.getReMaterializedMI(Reg);
    MachineOperand *UseMO = ReMatMI->findRegisterUseOperand(li.reg);
    if (UseMO)
      UseMO->setReg(NewVReg);
  }
}

/// rewriteInstructionForSpills, rewriteInstructionsForSpills - Helper functions
/// for addIntervalsForSpills to rewrite uses / defs for the given live range.
bool LiveIntervals::
rewriteInstructionForSpills(const LiveInterval &li, const VNInfo *VNI,
                 bool TrySplit, unsigned index, unsigned end,  MachineInstr *MI,
                 MachineInstr *ReMatOrigDefMI, MachineInstr *ReMatDefMI,
                 unsigned Slot, int LdSlot,
                 bool isLoad, bool isLoadSS, bool DefIsReMat, bool CanDelete,
                 VirtRegMap &vrm,
                 const TargetRegisterClass* rc,
                 SmallVector<int, 4> &ReMatIds,
                 const MachineLoopInfo *loopInfo,
                 unsigned &NewVReg, unsigned ImpUse, bool &HasDef, bool &HasUse,
                 std::map<unsigned,unsigned> &MBBVRegsMap,
                 std::vector<LiveInterval*> &NewLIs, float &SSWeight) {
  MachineBasicBlock *MBB = MI->getParent();
  unsigned loopDepth = loopInfo->getLoopDepth(MBB);
  bool CanFold = false;
 RestartInstruction:
  for (unsigned i = 0; i != MI->getNumOperands(); ++i) {
    MachineOperand& mop = MI->getOperand(i);
    if (!mop.isRegister())
      continue;
    unsigned Reg = mop.getReg();
    unsigned RegI = Reg;
    if (Reg == 0 || TargetRegisterInfo::isPhysicalRegister(Reg))
      continue;
    if (Reg != li.reg)
      continue;

    bool TryFold = !DefIsReMat;
    bool FoldSS = true; // Default behavior unless it's a remat.
    int FoldSlot = Slot;
    if (DefIsReMat) {
      // If this is the rematerializable definition MI itself and
      // all of its uses are rematerialized, simply delete it.
      if (MI == ReMatOrigDefMI && CanDelete) {
        DOUT << "\t\t\t\tErasing re-materlizable def: ";
        DOUT << MI << '\n';
        RemoveMachineInstrFromMaps(MI);
        vrm.RemoveMachineInstrFromMaps(MI);
        MI->eraseFromParent();
        break;
      }

      // If def for this use can't be rematerialized, then try folding.
      // If def is rematerializable and it's a load, also try folding.
      TryFold = !ReMatDefMI || (ReMatDefMI && (MI == ReMatOrigDefMI || isLoad));
      if (isLoad) {
        // Try fold loads (from stack slot, constant pool, etc.) into uses.
        FoldSS = isLoadSS;
        FoldSlot = LdSlot;
      }
    }

    // Scan all of the operands of this instruction rewriting operands
    // to use NewVReg instead of li.reg as appropriate.  We do this for
    // two reasons:
    //
    //   1. If the instr reads the same spilled vreg multiple times, we
    //      want to reuse the NewVReg.
    //   2. If the instr is a two-addr instruction, we are required to
    //      keep the src/dst regs pinned.
    //
    // Keep track of whether we replace a use and/or def so that we can
    // create the spill interval with the appropriate range. 

    HasUse = mop.isUse();
    HasDef = mop.isDef();
    SmallVector<unsigned, 2> Ops;
    Ops.push_back(i);
    for (unsigned j = i+1, e = MI->getNumOperands(); j != e; ++j) {
      const MachineOperand &MOj = MI->getOperand(j);
      if (!MOj.isRegister())
        continue;
      unsigned RegJ = MOj.getReg();
      if (RegJ == 0 || TargetRegisterInfo::isPhysicalRegister(RegJ))
        continue;
      if (RegJ == RegI) {
        Ops.push_back(j);
        HasUse |= MOj.isUse();
        HasDef |= MOj.isDef();
      }
    }

    if (HasUse && !li.liveAt(getUseIndex(index)))
      // Must be defined by an implicit def. It should not be spilled. Note,
      // this is for correctness reason. e.g.
      // 8   %reg1024<def> = IMPLICIT_DEF
      // 12  %reg1024<def> = INSERT_SUBREG %reg1024<kill>, %reg1025, 2
      // The live range [12, 14) are not part of the r1024 live interval since
      // it's defined by an implicit def. It will not conflicts with live
      // interval of r1025. Now suppose both registers are spilled, you can
      // easily see a situation where both registers are reloaded before
      // the INSERT_SUBREG and both target registers that would overlap.
      HasUse = false;

    // Update stack slot spill weight if we are splitting.
    float Weight = getSpillWeight(HasDef, HasUse, loopDepth);
      if (!TrySplit)
      SSWeight += Weight;

    if (!TryFold)
      CanFold = false;
    else {
      // Do not fold load / store here if we are splitting. We'll find an
      // optimal point to insert a load / store later.
      if (!TrySplit) {
        if (tryFoldMemoryOperand(MI, vrm, ReMatDefMI, index,
                                 Ops, FoldSS, FoldSlot, Reg)) {
          // Folding the load/store can completely change the instruction in
          // unpredictable ways, rescan it from the beginning.
          HasUse = false;
          HasDef = false;
          CanFold = false;
          if (isRemoved(MI)) {
            SSWeight -= Weight;
            break;
          }
          goto RestartInstruction;
        }
      } else {
        // We'll try to fold it later if it's profitable.
        CanFold = canFoldMemoryOperand(MI, Ops, DefIsReMat);
      }
    }

    // Create a new virtual register for the spill interval.
    bool CreatedNewVReg = false;
    if (NewVReg == 0) {
      NewVReg = mri_->createVirtualRegister(rc);
      vrm.grow();
      CreatedNewVReg = true;
    }
    mop.setReg(NewVReg);
    if (mop.isImplicit())
      rewriteImplicitOps(li, MI, NewVReg, vrm);

    // Reuse NewVReg for other reads.
    for (unsigned j = 0, e = Ops.size(); j != e; ++j) {
      MachineOperand &mopj = MI->getOperand(Ops[j]);
      mopj.setReg(NewVReg);
      if (mopj.isImplicit())
        rewriteImplicitOps(li, MI, NewVReg, vrm);
    }
            
    if (CreatedNewVReg) {
      if (DefIsReMat) {
        vrm.setVirtIsReMaterialized(NewVReg, ReMatDefMI/*, CanDelete*/);
        if (ReMatIds[VNI->id] == VirtRegMap::MAX_STACK_SLOT) {
          // Each valnum may have its own remat id.
          ReMatIds[VNI->id] = vrm.assignVirtReMatId(NewVReg);
        } else {
          vrm.assignVirtReMatId(NewVReg, ReMatIds[VNI->id]);
        }
        if (!CanDelete || (HasUse && HasDef)) {
          // If this is a two-addr instruction then its use operands are
          // rematerializable but its def is not. It should be assigned a
          // stack slot.
          vrm.assignVirt2StackSlot(NewVReg, Slot);
        }
      } else {
        vrm.assignVirt2StackSlot(NewVReg, Slot);
      }
    } else if (HasUse && HasDef &&
               vrm.getStackSlot(NewVReg) == VirtRegMap::NO_STACK_SLOT) {
      // If this interval hasn't been assigned a stack slot (because earlier
      // def is a deleted remat def), do it now.
      assert(Slot != VirtRegMap::NO_STACK_SLOT);
      vrm.assignVirt2StackSlot(NewVReg, Slot);
    }

    // Re-matting an instruction with virtual register use. Add the
    // register as an implicit use on the use MI.
    if (DefIsReMat && ImpUse)
      MI->addOperand(MachineOperand::CreateReg(ImpUse, false, true));

    // create a new register interval for this spill / remat.
    LiveInterval &nI = getOrCreateInterval(NewVReg);
    if (CreatedNewVReg) {
      NewLIs.push_back(&nI);
      MBBVRegsMap.insert(std::make_pair(MI->getParent()->getNumber(), NewVReg));
      if (TrySplit)
        vrm.setIsSplitFromReg(NewVReg, li.reg);
    }

    if (HasUse) {
      if (CreatedNewVReg) {
        LiveRange LR(getLoadIndex(index), getUseIndex(index)+1,
                     nI.getNextValue(~0U, 0, VNInfoAllocator));
        DOUT << " +" << LR;
        nI.addRange(LR);
      } else {
        // Extend the split live interval to this def / use.
        unsigned End = getUseIndex(index)+1;
        LiveRange LR(nI.ranges[nI.ranges.size()-1].end, End,
                     nI.getValNumInfo(nI.getNumValNums()-1));
        DOUT << " +" << LR;
        nI.addRange(LR);
      }
    }
    if (HasDef) {
      LiveRange LR(getDefIndex(index), getStoreIndex(index),
                   nI.getNextValue(~0U, 0, VNInfoAllocator));
      DOUT << " +" << LR;
      nI.addRange(LR);
    }

    DOUT << "\t\t\t\tAdded new interval: ";
    nI.print(DOUT, tri_);
    DOUT << '\n';
  }
  return CanFold;
}
bool LiveIntervals::anyKillInMBBAfterIdx(const LiveInterval &li,
                                   const VNInfo *VNI,
                                   MachineBasicBlock *MBB, unsigned Idx) const {
  unsigned End = getMBBEndIdx(MBB);
  for (unsigned j = 0, ee = VNI->kills.size(); j != ee; ++j) {
    unsigned KillIdx = VNI->kills[j];
    if (KillIdx > Idx && KillIdx < End)
      return true;
  }
  return false;
}

/// RewriteInfo - Keep track of machine instrs that will be rewritten
/// during spilling.
namespace {
  struct RewriteInfo {
    unsigned Index;
    MachineInstr *MI;
    bool HasUse;
    bool HasDef;
    RewriteInfo(unsigned i, MachineInstr *mi, bool u, bool d)
      : Index(i), MI(mi), HasUse(u), HasDef(d) {}
  };

  struct RewriteInfoCompare {
    bool operator()(const RewriteInfo &LHS, const RewriteInfo &RHS) const {
      return LHS.Index < RHS.Index;
    }
  };
}

void LiveIntervals::
rewriteInstructionsForSpills(const LiveInterval &li, bool TrySplit,
                    LiveInterval::Ranges::const_iterator &I,
                    MachineInstr *ReMatOrigDefMI, MachineInstr *ReMatDefMI,
                    unsigned Slot, int LdSlot,
                    bool isLoad, bool isLoadSS, bool DefIsReMat, bool CanDelete,
                    VirtRegMap &vrm,
                    const TargetRegisterClass* rc,
                    SmallVector<int, 4> &ReMatIds,
                    const MachineLoopInfo *loopInfo,
                    BitVector &SpillMBBs,
                    std::map<unsigned, std::vector<SRInfo> > &SpillIdxes,
                    BitVector &RestoreMBBs,
                    std::map<unsigned, std::vector<SRInfo> > &RestoreIdxes,
                    std::map<unsigned,unsigned> &MBBVRegsMap,
                    std::vector<LiveInterval*> &NewLIs, float &SSWeight) {
  bool AllCanFold = true;
  unsigned NewVReg = 0;
  unsigned start = getBaseIndex(I->start);
  unsigned end = getBaseIndex(I->end-1) + InstrSlots::NUM;

  // First collect all the def / use in this live range that will be rewritten.
  // Make sure they are sorted according to instruction index.
  std::vector<RewriteInfo> RewriteMIs;
  for (MachineRegisterInfo::reg_iterator ri = mri_->reg_begin(li.reg),
         re = mri_->reg_end(); ri != re; ) {
    MachineInstr *MI = &*ri;
    MachineOperand &O = ri.getOperand();
    ++ri;
    assert(!O.isImplicit() && "Spilling register that's used as implicit use?");
    unsigned index = getInstructionIndex(MI);
    if (index < start || index >= end)
      continue;
    if (O.isUse() && !li.liveAt(getUseIndex(index)))
      // Must be defined by an implicit def. It should not be spilled. Note,
      // this is for correctness reason. e.g.
      // 8   %reg1024<def> = IMPLICIT_DEF
      // 12  %reg1024<def> = INSERT_SUBREG %reg1024<kill>, %reg1025, 2
      // The live range [12, 14) are not part of the r1024 live interval since
      // it's defined by an implicit def. It will not conflicts with live
      // interval of r1025. Now suppose both registers are spilled, you can
      // easily see a situation where both registers are reloaded before
      // the INSERT_SUBREG and both target registers that would overlap.
      continue;
    RewriteMIs.push_back(RewriteInfo(index, MI, O.isUse(), O.isDef()));
  }
  std::sort(RewriteMIs.begin(), RewriteMIs.end(), RewriteInfoCompare());

  unsigned ImpUse = DefIsReMat ? getReMatImplicitUse(li, ReMatDefMI) : 0;
  // Now rewrite the defs and uses.
  for (unsigned i = 0, e = RewriteMIs.size(); i != e; ) {
    RewriteInfo &rwi = RewriteMIs[i];
    ++i;
    unsigned index = rwi.Index;
    bool MIHasUse = rwi.HasUse;
    bool MIHasDef = rwi.HasDef;
    MachineInstr *MI = rwi.MI;
    // If MI def and/or use the same register multiple times, then there
    // are multiple entries.
    unsigned NumUses = MIHasUse;
    while (i != e && RewriteMIs[i].MI == MI) {
      assert(RewriteMIs[i].Index == index);
      bool isUse = RewriteMIs[i].HasUse;
      if (isUse) ++NumUses;
      MIHasUse |= isUse;
      MIHasDef |= RewriteMIs[i].HasDef;
      ++i;
    }
    MachineBasicBlock *MBB = MI->getParent();

    if (ImpUse && MI != ReMatDefMI) {
      // Re-matting an instruction with virtual register use. Update the
      // register interval's spill weight to HUGE_VALF to prevent it from
      // being spilled.
      LiveInterval &ImpLi = getInterval(ImpUse);
      ImpLi.weight = HUGE_VALF;
    }

    unsigned MBBId = MBB->getNumber();
    unsigned ThisVReg = 0;
    if (TrySplit) {
      std::map<unsigned,unsigned>::const_iterator NVI = MBBVRegsMap.find(MBBId);
      if (NVI != MBBVRegsMap.end()) {
        ThisVReg = NVI->second;
        // One common case:
        // x = use
        // ...
        // ...
        // def = ...
        //     = use
        // It's better to start a new interval to avoid artifically
        // extend the new interval.
        if (MIHasDef && !MIHasUse) {
          MBBVRegsMap.erase(MBB->getNumber());
          ThisVReg = 0;
        }
      }
    }

    bool IsNew = ThisVReg == 0;
    if (IsNew) {
      // This ends the previous live interval. If all of its def / use
      // can be folded, give it a low spill weight.
      if (NewVReg && TrySplit && AllCanFold) {
        LiveInterval &nI = getOrCreateInterval(NewVReg);
        nI.weight /= 10.0F;
      }
      AllCanFold = true;
    }
    NewVReg = ThisVReg;

    bool HasDef = false;
    bool HasUse = false;
    bool CanFold = rewriteInstructionForSpills(li, I->valno, TrySplit,
                         index, end, MI, ReMatOrigDefMI, ReMatDefMI,
                         Slot, LdSlot, isLoad, isLoadSS, DefIsReMat,
                         CanDelete, vrm, rc, ReMatIds, loopInfo, NewVReg,
                         ImpUse, HasDef, HasUse, MBBVRegsMap, NewLIs, SSWeight);
    if (!HasDef && !HasUse)
      continue;

    AllCanFold &= CanFold;

    // Update weight of spill interval.
    LiveInterval &nI = getOrCreateInterval(NewVReg);
    if (!TrySplit) {
      // The spill weight is now infinity as it cannot be spilled again.
      nI.weight = HUGE_VALF;
      continue;
    }

    // Keep track of the last def and first use in each MBB.
    if (HasDef) {
      if (MI != ReMatOrigDefMI || !CanDelete) {
        bool HasKill = false;
        if (!HasUse)
          HasKill = anyKillInMBBAfterIdx(li, I->valno, MBB, getDefIndex(index));
        else {
          // If this is a two-address code, then this index starts a new VNInfo.
          const VNInfo *VNI = li.findDefinedVNInfo(getDefIndex(index));
          if (VNI)
            HasKill = anyKillInMBBAfterIdx(li, VNI, MBB, getDefIndex(index));
        }
        std::map<unsigned, std::vector<SRInfo> >::iterator SII =
          SpillIdxes.find(MBBId);
        if (!HasKill) {
          if (SII == SpillIdxes.end()) {
            std::vector<SRInfo> S;
            S.push_back(SRInfo(index, NewVReg, true));
            SpillIdxes.insert(std::make_pair(MBBId, S));
          } else if (SII->second.back().vreg != NewVReg) {
            SII->second.push_back(SRInfo(index, NewVReg, true));
          } else if ((int)index > SII->second.back().index) {
            // If there is an earlier def and this is a two-address
            // instruction, then it's not possible to fold the store (which
            // would also fold the load).
            SRInfo &Info = SII->second.back();
            Info.index = index;
            Info.canFold = !HasUse;
          }
          SpillMBBs.set(MBBId);
        } else if (SII != SpillIdxes.end() &&
                   SII->second.back().vreg == NewVReg &&
                   (int)index > SII->second.back().index) {
          // There is an earlier def that's not killed (must be two-address).
          // The spill is no longer needed.
          SII->second.pop_back();
          if (SII->second.empty()) {
            SpillIdxes.erase(MBBId);
            SpillMBBs.reset(MBBId);
          }
        }
      }
    }

    if (HasUse) {
      std::map<unsigned, std::vector<SRInfo> >::iterator SII =
        SpillIdxes.find(MBBId);
      if (SII != SpillIdxes.end() &&
          SII->second.back().vreg == NewVReg &&
          (int)index > SII->second.back().index)
        // Use(s) following the last def, it's not safe to fold the spill.
        SII->second.back().canFold = false;
      std::map<unsigned, std::vector<SRInfo> >::iterator RII =
        RestoreIdxes.find(MBBId);
      if (RII != RestoreIdxes.end() && RII->second.back().vreg == NewVReg)
        // If we are splitting live intervals, only fold if it's the first
        // use and there isn't another use later in the MBB.
        RII->second.back().canFold = false;
      else if (IsNew) {
        // Only need a reload if there isn't an earlier def / use.
        if (RII == RestoreIdxes.end()) {
          std::vector<SRInfo> Infos;
          Infos.push_back(SRInfo(index, NewVReg, true));
          RestoreIdxes.insert(std::make_pair(MBBId, Infos));
        } else {
          RII->second.push_back(SRInfo(index, NewVReg, true));
        }
        RestoreMBBs.set(MBBId);
      }
    }

    // Update spill weight.
    unsigned loopDepth = loopInfo->getLoopDepth(MBB);
    nI.weight += getSpillWeight(HasDef, HasUse, loopDepth);
  }

  if (NewVReg && TrySplit && AllCanFold) {
    // If all of its def / use can be folded, give it a low spill weight.
    LiveInterval &nI = getOrCreateInterval(NewVReg);
    nI.weight /= 10.0F;
  }
}

bool LiveIntervals::alsoFoldARestore(int Id, int index, unsigned vr,
                        BitVector &RestoreMBBs,
                        std::map<unsigned,std::vector<SRInfo> > &RestoreIdxes) {
  if (!RestoreMBBs[Id])
    return false;
  std::vector<SRInfo> &Restores = RestoreIdxes[Id];
  for (unsigned i = 0, e = Restores.size(); i != e; ++i)
    if (Restores[i].index == index &&
        Restores[i].vreg == vr &&
        Restores[i].canFold)
      return true;
  return false;
}

void LiveIntervals::eraseRestoreInfo(int Id, int index, unsigned vr,
                        BitVector &RestoreMBBs,
                        std::map<unsigned,std::vector<SRInfo> > &RestoreIdxes) {
  if (!RestoreMBBs[Id])
    return;
  std::vector<SRInfo> &Restores = RestoreIdxes[Id];
  for (unsigned i = 0, e = Restores.size(); i != e; ++i)
    if (Restores[i].index == index && Restores[i].vreg)
      Restores[i].index = -1;
}

/// handleSpilledImpDefs - Remove IMPLICIT_DEF instructions which are being
/// spilled and create empty intervals for their uses.
void
LiveIntervals::handleSpilledImpDefs(const LiveInterval &li, VirtRegMap &vrm,
                                    const TargetRegisterClass* rc,
                                    std::vector<LiveInterval*> &NewLIs) {
  for (MachineRegisterInfo::reg_iterator ri = mri_->reg_begin(li.reg),
         re = mri_->reg_end(); ri != re; ) {
    MachineOperand &O = ri.getOperand();
    MachineInstr *MI = &*ri;
    ++ri;
    if (O.isDef()) {
      assert(MI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF &&
             "Register def was not rewritten?");
      RemoveMachineInstrFromMaps(MI);
      vrm.RemoveMachineInstrFromMaps(MI);
      MI->eraseFromParent();
    } else {
      // This must be an use of an implicit_def so it's not part of the live
      // interval. Create a new empty live interval for it.
      // FIXME: Can we simply erase some of the instructions? e.g. Stores?
      unsigned NewVReg = mri_->createVirtualRegister(rc);
      vrm.grow();
      vrm.setIsImplicitlyDefined(NewVReg);
      NewLIs.push_back(&getOrCreateInterval(NewVReg));
      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
        MachineOperand &MO = MI->getOperand(i);
        if (MO.isReg() && MO.getReg() == li.reg)
          MO.setReg(NewVReg);
      }
    }
  }
}


std::vector<LiveInterval*> LiveIntervals::
addIntervalsForSpills(const LiveInterval &li,
                      const MachineLoopInfo *loopInfo, VirtRegMap &vrm,
                      float &SSWeight) {
  assert(li.weight != HUGE_VALF &&
         "attempt to spill already spilled interval!");

  DOUT << "\t\t\t\tadding intervals for spills for interval: ";
  li.print(DOUT, tri_);
  DOUT << '\n';

  // Spill slot weight.
  SSWeight = 0.0f;

  // Each bit specify whether it a spill is required in the MBB.
  BitVector SpillMBBs(mf_->getNumBlockIDs());
  std::map<unsigned, std::vector<SRInfo> > SpillIdxes;
  BitVector RestoreMBBs(mf_->getNumBlockIDs());
  std::map<unsigned, std::vector<SRInfo> > RestoreIdxes;
  std::map<unsigned,unsigned> MBBVRegsMap;
  std::vector<LiveInterval*> NewLIs;
  const TargetRegisterClass* rc = mri_->getRegClass(li.reg);

  unsigned NumValNums = li.getNumValNums();
  SmallVector<MachineInstr*, 4> ReMatDefs;
  ReMatDefs.resize(NumValNums, NULL);
  SmallVector<MachineInstr*, 4> ReMatOrigDefs;
  ReMatOrigDefs.resize(NumValNums, NULL);
  SmallVector<int, 4> ReMatIds;
  ReMatIds.resize(NumValNums, VirtRegMap::MAX_STACK_SLOT);
  BitVector ReMatDelete(NumValNums);
  unsigned Slot = VirtRegMap::MAX_STACK_SLOT;

  // Spilling a split live interval. It cannot be split any further. Also,
  // it's also guaranteed to be a single val# / range interval.
  if (vrm.getPreSplitReg(li.reg)) {
    vrm.setIsSplitFromReg(li.reg, 0);
    // Unset the split kill marker on the last use.
    unsigned KillIdx = vrm.getKillPoint(li.reg);
    if (KillIdx) {
      MachineInstr *KillMI = getInstructionFromIndex(KillIdx);
      assert(KillMI && "Last use disappeared?");
      int KillOp = KillMI->findRegisterUseOperandIdx(li.reg, true);
      assert(KillOp != -1 && "Last use disappeared?");
      KillMI->getOperand(KillOp).setIsKill(false);
    }
    vrm.removeKillPoint(li.reg);
    bool DefIsReMat = vrm.isReMaterialized(li.reg);
    Slot = vrm.getStackSlot(li.reg);
    assert(Slot != VirtRegMap::MAX_STACK_SLOT);
    MachineInstr *ReMatDefMI = DefIsReMat ?
      vrm.getReMaterializedMI(li.reg) : NULL;
    int LdSlot = 0;
    bool isLoadSS = DefIsReMat && tii_->isLoadFromStackSlot(ReMatDefMI, LdSlot);
    bool isLoad = isLoadSS ||
      (DefIsReMat && (ReMatDefMI->getDesc().isSimpleLoad()));
    bool IsFirstRange = true;
    for (LiveInterval::Ranges::const_iterator
           I = li.ranges.begin(), E = li.ranges.end(); I != E; ++I) {
      // If this is a split live interval with multiple ranges, it means there
      // are two-address instructions that re-defined the value. Only the
      // first def can be rematerialized!
      if (IsFirstRange) {
        // Note ReMatOrigDefMI has already been deleted.
        rewriteInstructionsForSpills(li, false, I, NULL, ReMatDefMI,
                             Slot, LdSlot, isLoad, isLoadSS, DefIsReMat,
                             false, vrm, rc, ReMatIds, loopInfo,
                             SpillMBBs, SpillIdxes, RestoreMBBs, RestoreIdxes,
                             MBBVRegsMap, NewLIs, SSWeight);
      } else {
        rewriteInstructionsForSpills(li, false, I, NULL, 0,
                             Slot, 0, false, false, false,
                             false, vrm, rc, ReMatIds, loopInfo,
                             SpillMBBs, SpillIdxes, RestoreMBBs, RestoreIdxes,
                             MBBVRegsMap, NewLIs, SSWeight);
      }
      IsFirstRange = false;
    }

    SSWeight = 0.0f;  // Already accounted for when split.
    handleSpilledImpDefs(li, vrm, rc, NewLIs);
    return NewLIs;
  }

  bool TrySplit = SplitAtBB && !intervalIsInOneMBB(li);
  if (SplitLimit != -1 && (int)numSplits >= SplitLimit)
    TrySplit = false;
  if (TrySplit)
    ++numSplits;
  bool NeedStackSlot = false;
  for (LiveInterval::const_vni_iterator i = li.vni_begin(), e = li.vni_end();
       i != e; ++i) {
    const VNInfo *VNI = *i;
    unsigned VN = VNI->id;
    unsigned DefIdx = VNI->def;
    if (DefIdx == ~1U)
      continue; // Dead val#.
    // Is the def for the val# rematerializable?
    MachineInstr *ReMatDefMI = (DefIdx == ~0u)
      ? 0 : getInstructionFromIndex(DefIdx);
    bool dummy;
    if (ReMatDefMI && isReMaterializable(li, VNI, ReMatDefMI, dummy)) {
      // Remember how to remat the def of this val#.
      ReMatOrigDefs[VN] = ReMatDefMI;
      // Original def may be modified so we have to make a copy here.
      MachineInstr *Clone = mf_->CloneMachineInstr(ReMatDefMI);
      ClonedMIs.push_back(Clone);
      ReMatDefs[VN] = Clone;

      bool CanDelete = true;
      if (VNI->hasPHIKill) {
        // A kill is a phi node, not all of its uses can be rematerialized.
        // It must not be deleted.
        CanDelete = false;
        // Need a stack slot if there is any live range where uses cannot be
        // rematerialized.
        NeedStackSlot = true;
      }
      if (CanDelete)
        ReMatDelete.set(VN);
    } else {
      // Need a stack slot if there is any live range where uses cannot be
      // rematerialized.
      NeedStackSlot = true;
    }
  }

  // One stack slot per live interval.
  if (NeedStackSlot && vrm.getPreSplitReg(li.reg) == 0)
    Slot = vrm.assignVirt2StackSlot(li.reg);

  // Create new intervals and rewrite defs and uses.
  for (LiveInterval::Ranges::const_iterator
         I = li.ranges.begin(), E = li.ranges.end(); I != E; ++I) {
    MachineInstr *ReMatDefMI = ReMatDefs[I->valno->id];
    MachineInstr *ReMatOrigDefMI = ReMatOrigDefs[I->valno->id];
    bool DefIsReMat = ReMatDefMI != NULL;
    bool CanDelete = ReMatDelete[I->valno->id];
    int LdSlot = 0;
    bool isLoadSS = DefIsReMat && tii_->isLoadFromStackSlot(ReMatDefMI, LdSlot);
    bool isLoad = isLoadSS ||
      (DefIsReMat && ReMatDefMI->getDesc().isSimpleLoad());
    rewriteInstructionsForSpills(li, TrySplit, I, ReMatOrigDefMI, ReMatDefMI,
                               Slot, LdSlot, isLoad, isLoadSS, DefIsReMat,
                               CanDelete, vrm, rc, ReMatIds, loopInfo,
                               SpillMBBs, SpillIdxes, RestoreMBBs, RestoreIdxes,
                               MBBVRegsMap, NewLIs, SSWeight);
  }

  // Insert spills / restores if we are splitting.
  if (!TrySplit) {
    handleSpilledImpDefs(li, vrm, rc, NewLIs);
    return NewLIs;
  }

  SmallPtrSet<LiveInterval*, 4> AddedKill;
  SmallVector<unsigned, 2> Ops;
  if (NeedStackSlot) {
    int Id = SpillMBBs.find_first();
    while (Id != -1) {
      MachineBasicBlock *MBB = mf_->getBlockNumbered(Id);
      unsigned loopDepth = loopInfo->getLoopDepth(MBB);
      std::vector<SRInfo> &spills = SpillIdxes[Id];
      for (unsigned i = 0, e = spills.size(); i != e; ++i) {
        int index = spills[i].index;
        unsigned VReg = spills[i].vreg;
        LiveInterval &nI = getOrCreateInterval(VReg);
        bool isReMat = vrm.isReMaterialized(VReg);
        MachineInstr *MI = getInstructionFromIndex(index);
        bool CanFold = false;
        bool FoundUse = false;
        Ops.clear();
        if (spills[i].canFold) {
          CanFold = true;
          for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
            MachineOperand &MO = MI->getOperand(j);
            if (!MO.isRegister() || MO.getReg() != VReg)
              continue;

            Ops.push_back(j);
            if (MO.isDef())
              continue;
            if (isReMat || 
                (!FoundUse && !alsoFoldARestore(Id, index, VReg,
                                                RestoreMBBs, RestoreIdxes))) {
              // MI has two-address uses of the same register. If the use
              // isn't the first and only use in the BB, then we can't fold
              // it. FIXME: Move this to rewriteInstructionsForSpills.
              CanFold = false;
              break;
            }
            FoundUse = true;
          }
        }
        // Fold the store into the def if possible.
        bool Folded = false;
        if (CanFold && !Ops.empty()) {
          if (tryFoldMemoryOperand(MI, vrm, NULL, index, Ops, true, Slot,VReg)){
            Folded = true;
            if (FoundUse > 0) {
              // Also folded uses, do not issue a load.
              eraseRestoreInfo(Id, index, VReg, RestoreMBBs, RestoreIdxes);
              nI.removeRange(getLoadIndex(index), getUseIndex(index)+1);
            }
            nI.removeRange(getDefIndex(index), getStoreIndex(index));
          }
        }

        // Otherwise tell the spiller to issue a spill.
        if (!Folded) {
          LiveRange *LR = &nI.ranges[nI.ranges.size()-1];
          bool isKill = LR->end == getStoreIndex(index);
          if (!MI->registerDefIsDead(nI.reg))
            // No need to spill a dead def.
            vrm.addSpillPoint(VReg, isKill, MI);
          if (isKill)
            AddedKill.insert(&nI);
        }

        // Update spill slot weight.
        if (!isReMat)
          SSWeight += getSpillWeight(true, false, loopDepth);
      }
      Id = SpillMBBs.find_next(Id);
    }
  }

  int Id = RestoreMBBs.find_first();
  while (Id != -1) {
    MachineBasicBlock *MBB = mf_->getBlockNumbered(Id);
    unsigned loopDepth = loopInfo->getLoopDepth(MBB);

    std::vector<SRInfo> &restores = RestoreIdxes[Id];
    for (unsigned i = 0, e = restores.size(); i != e; ++i) {
      int index = restores[i].index;
      if (index == -1)
        continue;
      unsigned VReg = restores[i].vreg;
      LiveInterval &nI = getOrCreateInterval(VReg);
      bool isReMat = vrm.isReMaterialized(VReg);
      MachineInstr *MI = getInstructionFromIndex(index);
      bool CanFold = false;
      Ops.clear();
      if (restores[i].canFold) {
        CanFold = true;
        for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
          MachineOperand &MO = MI->getOperand(j);
          if (!MO.isRegister() || MO.getReg() != VReg)
            continue;

          if (MO.isDef()) {
            // If this restore were to be folded, it would have been folded
            // already.
            CanFold = false;
            break;
          }
          Ops.push_back(j);
        }
      }

      // Fold the load into the use if possible.
      bool Folded = false;
      if (CanFold && !Ops.empty()) {
        if (!isReMat)
          Folded = tryFoldMemoryOperand(MI, vrm, NULL,index,Ops,true,Slot,VReg);
        else {
          MachineInstr *ReMatDefMI = vrm.getReMaterializedMI(VReg);
          int LdSlot = 0;
          bool isLoadSS = tii_->isLoadFromStackSlot(ReMatDefMI, LdSlot);
          // If the rematerializable def is a load, also try to fold it.
          if (isLoadSS || ReMatDefMI->getDesc().isSimpleLoad())
            Folded = tryFoldMemoryOperand(MI, vrm, ReMatDefMI, index,
                                          Ops, isLoadSS, LdSlot, VReg);
          unsigned ImpUse = getReMatImplicitUse(li, ReMatDefMI);
          if (ImpUse) {
            // Re-matting an instruction with virtual register use. Add the
            // register as an implicit use on the use MI and update the register
            // interval's spill weight to HUGE_VALF to prevent it from being
            // spilled.
            LiveInterval &ImpLi = getInterval(ImpUse);
            ImpLi.weight = HUGE_VALF;
            MI->addOperand(MachineOperand::CreateReg(ImpUse, false, true));
          }
        }
      }
      // If folding is not possible / failed, then tell the spiller to issue a
      // load / rematerialization for us.
      if (Folded)
        nI.removeRange(getLoadIndex(index), getUseIndex(index)+1);
      else
        vrm.addRestorePoint(VReg, MI);

      // Update spill slot weight.
      if (!isReMat)
        SSWeight += getSpillWeight(false, true, loopDepth);
    }
    Id = RestoreMBBs.find_next(Id);
  }

  // Finalize intervals: add kills, finalize spill weights, and filter out
  // dead intervals.
  std::vector<LiveInterval*> RetNewLIs;
  for (unsigned i = 0, e = NewLIs.size(); i != e; ++i) {
    LiveInterval *LI = NewLIs[i];
    if (!LI->empty()) {
      LI->weight /= InstrSlots::NUM * getApproximateInstructionCount(*LI);
      if (!AddedKill.count(LI)) {
        LiveRange *LR = &LI->ranges[LI->ranges.size()-1];
        unsigned LastUseIdx = getBaseIndex(LR->end);
        MachineInstr *LastUse = getInstructionFromIndex(LastUseIdx);
        int UseIdx = LastUse->findRegisterUseOperandIdx(LI->reg, false);
        assert(UseIdx != -1);
        if (LastUse->getOperand(UseIdx).isImplicit() ||
            LastUse->getDesc().getOperandConstraint(UseIdx,TOI::TIED_TO) == -1){
          LastUse->getOperand(UseIdx).setIsKill();
          vrm.addKillPoint(LI->reg, LastUseIdx);
        }
      }
      RetNewLIs.push_back(LI);
    }
  }

  handleSpilledImpDefs(li, vrm, rc, RetNewLIs);
  return RetNewLIs;
}

/// hasAllocatableSuperReg - Return true if the specified physical register has
/// any super register that's allocatable.
bool LiveIntervals::hasAllocatableSuperReg(unsigned Reg) const {
  for (const unsigned* AS = tri_->getSuperRegisters(Reg); *AS; ++AS)
    if (allocatableRegs_[*AS] && hasInterval(*AS))
      return true;
  return false;
}

/// getRepresentativeReg - Find the largest super register of the specified
/// physical register.
unsigned LiveIntervals::getRepresentativeReg(unsigned Reg) const {
  // Find the largest super-register that is allocatable. 
  unsigned BestReg = Reg;
  for (const unsigned* AS = tri_->getSuperRegisters(Reg); *AS; ++AS) {
    unsigned SuperReg = *AS;
    if (!hasAllocatableSuperReg(SuperReg) && hasInterval(SuperReg)) {
      BestReg = SuperReg;
      break;
    }
  }
  return BestReg;
}

/// getNumConflictsWithPhysReg - Return the number of uses and defs of the
/// specified interval that conflicts with the specified physical register.
unsigned LiveIntervals::getNumConflictsWithPhysReg(const LiveInterval &li,
                                                   unsigned PhysReg) const {
  unsigned NumConflicts = 0;
  const LiveInterval &pli = getInterval(getRepresentativeReg(PhysReg));
  for (MachineRegisterInfo::reg_iterator I = mri_->reg_begin(li.reg),
         E = mri_->reg_end(); I != E; ++I) {
    MachineOperand &O = I.getOperand();
    MachineInstr *MI = O.getParent();
    unsigned Index = getInstructionIndex(MI);
    if (pli.liveAt(Index))
      ++NumConflicts;
  }
  return NumConflicts;
}

/// spillPhysRegAroundRegDefsUses - Spill the specified physical register
/// around all defs and uses of the specified interval.
void LiveIntervals::spillPhysRegAroundRegDefsUses(const LiveInterval &li,
                                            unsigned PhysReg, VirtRegMap &vrm) {
  unsigned SpillReg = getRepresentativeReg(PhysReg);

  for (const unsigned *AS = tri_->getAliasSet(PhysReg); *AS; ++AS)
    // If there are registers which alias PhysReg, but which are not a
    // sub-register of the chosen representative super register. Assert
    // since we can't handle it yet.
    assert(*AS == SpillReg || !allocatableRegs_[*AS] ||
           tri_->isSuperRegister(*AS, SpillReg));

  LiveInterval &pli = getInterval(SpillReg);
  SmallPtrSet<MachineInstr*, 8> SeenMIs;
  for (MachineRegisterInfo::reg_iterator I = mri_->reg_begin(li.reg),
         E = mri_->reg_end(); I != E; ++I) {
    MachineOperand &O = I.getOperand();
    MachineInstr *MI = O.getParent();
    if (SeenMIs.count(MI))
      continue;
    SeenMIs.insert(MI);
    unsigned Index = getInstructionIndex(MI);
    if (pli.liveAt(Index)) {
      vrm.addEmergencySpill(SpillReg, MI);
      pli.removeRange(getLoadIndex(Index), getStoreIndex(Index)+1);
      for (const unsigned* AS = tri_->getSubRegisters(SpillReg); *AS; ++AS) {
        if (!hasInterval(*AS))
          continue;
        LiveInterval &spli = getInterval(*AS);
        if (spli.liveAt(Index))
          spli.removeRange(getLoadIndex(Index), getStoreIndex(Index)+1);
      }
    }
  }
}

LiveRange LiveIntervals::addLiveRangeToEndOfBlock(unsigned reg,
                                                   MachineInstr* startInst) {
  LiveInterval& Interval = getOrCreateInterval(reg);
  VNInfo* VN = Interval.getNextValue(
            getInstructionIndex(startInst) + InstrSlots::DEF,
            startInst, getVNInfoAllocator());
  VN->hasPHIKill = true;
  VN->kills.push_back(getMBBEndIdx(startInst->getParent()));
  LiveRange LR(getInstructionIndex(startInst) + InstrSlots::DEF,
               getMBBEndIdx(startInst->getParent()) + 1, VN);
  Interval.addRange(LR);
  
  return LR;
}