LiveIntervalAnalysis.cpp

    bool HasUse = false;
    bool CanFold = rewriteInstructionForSpills(li, TrySplit, I->valno->id,
                                index, end, MI, ReMatOrigDefMI, ReMatDefMI,
                                Slot, LdSlot, isLoad, isLoadSS, DefIsReMat,
                                CanDelete, vrm, RegMap, rc, ReMatIds, NewVReg,
                                HasDef, HasUse, loopInfo, MBBVRegsMap, NewLIs);
    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.
    unsigned MBBId = MBB->getNumber();
    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 = findDefinedVNInfo(li, 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->getBasicBlock());
    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;
}


std::vector<LiveInterval*> LiveIntervals::
addIntervalsForSpills(const LiveInterval &li,
                      const LoopInfo *loopInfo, VirtRegMap &vrm) {
  // Since this is called after the analysis is done we don't know if
  // LiveVariables is available
  lv_ = getAnalysisToUpdate<LiveVariables>();

  assert(li.weight != HUGE_VALF &&
         "attempt to spill already spilled interval!");

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

  // 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;
  SSARegMap *RegMap = mf_->getSSARegMap();
  const TargetRegisterClass* rc = RegMap->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);
    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->getInstrDescriptor()->Flags & M_LOAD_FLAG));
    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, RegMap, rc, ReMatIds, loopInfo,
                             SpillMBBs, SpillIdxes, RestoreMBBs, RestoreIdxes,
                             MBBVRegsMap, NewLIs);
      } else {
        rewriteInstructionsForSpills(li, false, I, NULL, 0,
                             Slot, 0, false, false, false,
                             false, vrm, RegMap, rc, ReMatIds, loopInfo,
                             SpillMBBs, SpillIdxes, RestoreMBBs, RestoreIdxes,
                             MBBVRegsMap, NewLIs);
      }
      IsFirstRange = false;
    }
    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);
    if (ReMatDefMI && isReMaterializable(li, VNI, ReMatDefMI)) {
      // 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. vrm must
      // delete these!
      ReMatDefs[VN] = ReMatDefMI = ReMatDefMI->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->getInstrDescriptor()->Flags & M_LOAD_FLAG));
    rewriteInstructionsForSpills(li, TrySplit, I, ReMatOrigDefMI, ReMatDefMI,
                               Slot, LdSlot, isLoad, isLoadSS, DefIsReMat,
                               CanDelete, vrm, RegMap, rc, ReMatIds, loopInfo,
                               SpillMBBs, SpillIdxes, RestoreMBBs, RestoreIdxes,
                               MBBVRegsMap, NewLIs);
  }

  // Insert spills / restores if we are splitting.
  if (!TrySplit)
    return NewLIs;

  SmallPtrSet<LiveInterval*, 4> AddedKill;
  SmallVector<unsigned, 2> Ops;
  if (NeedStackSlot) {
    int Id = SpillMBBs.find_first();
    while (Id != -1) {
      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));
          }
        }

        // Else tell the spiller to issue a spill.
        if (!Folded) {
          LiveRange *LR = &nI.ranges[nI.ranges.size()-1];
          bool isKill = LR->end == getStoreIndex(index);
          vrm.addSpillPoint(VReg, isKill, MI);
          if (isKill)
            AddedKill.insert(&nI);
        }
      }
      Id = SpillMBBs.find_next(Id);
    }
  }

  int Id = RestoreMBBs.find_first();
  while (Id != -1) {
    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);
      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 (!vrm.isReMaterialized(VReg))
          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->getInstrDescriptor()->Flags & M_LOAD_FLAG))
            Folded = tryFoldMemoryOperand(MI, vrm, ReMatDefMI, index,
                                          Ops, isLoadSS, LdSlot, VReg);
        }
      }
      // 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);
    }
    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 /= LI->getSize();
      if (!AddedKill.count(LI)) {
        LiveRange *LR = &LI->ranges[LI->ranges.size()-1];
        MachineInstr *LastUse = getInstructionFromIndex(getBaseIndex(LR->end));
        int UseIdx = LastUse->findRegisterUseOperandIdx(LI->reg);
        assert(UseIdx != -1);
        if (LastUse->getInstrDescriptor()->
            getOperandConstraint(UseIdx, TOI::TIED_TO) == -1) {
          LastUse->getOperand(UseIdx).setIsKill();
          vrm.addKillPoint(LI->reg, &LastUse->getOperand(UseIdx));
        }
      }
      RetNewLIs.push_back(LI);
    }
  }

  return RetNewLIs;
}