PreAllocSplitting.cpp

      if (LI->liveAt(BarrierIdx) && !Barrier->readsRegister(Reg))
        // Virtual register live interval is intercepted by the barrier. We
        // should split and shrink wrap its interval if possible.
        Intervals.push_back(LI);
    }
  }

  // Process the affected live intervals.
  bool Change = false;
  while (!Intervals.empty()) {
    if (PreSplitLimit != -1 && (int)NumSplits == PreSplitLimit)
      break;
    LiveInterval *LI = Intervals.back();
    Intervals.pop_back();
    Change |= SplitRegLiveInterval(LI);
  }

  return Change;
}

bool PreAllocSplitting::createsNewJoin(LiveRange* LR,
                                       MachineBasicBlock* DefMBB,
                                       MachineBasicBlock* BarrierMBB) {
  if (DefMBB == BarrierMBB)
    return false;
  
  if (LR->valno->hasPHIKill)
    return false;
  
  unsigned MBBEnd = LIs->getMBBEndIdx(BarrierMBB);
  if (LR->end < MBBEnd)
    return false;
  
  MachineLoopInfo& MLI = getAnalysis<MachineLoopInfo>();
  if (MLI.getLoopFor(DefMBB) != MLI.getLoopFor(BarrierMBB))
    return true;
  
  MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
  SmallPtrSet<MachineBasicBlock*, 4> Visited;
  typedef std::pair<MachineBasicBlock*,
                    MachineBasicBlock::succ_iterator> ItPair;
  SmallVector<ItPair, 4> Stack;
  Stack.push_back(std::make_pair(BarrierMBB, BarrierMBB->succ_begin()));
  
  while (!Stack.empty()) {
    ItPair P = Stack.back();
    Stack.pop_back();
    
    MachineBasicBlock* PredMBB = P.first;
    MachineBasicBlock::succ_iterator S = P.second;
    
    if (S == PredMBB->succ_end())
      continue;
    else if (Visited.count(*S)) {
      Stack.push_back(std::make_pair(PredMBB, ++S));
      continue;
    } else
      Stack.push_back(std::make_pair(PredMBB, S+1));
    
    MachineBasicBlock* MBB = *S;
    Visited.insert(MBB);
    
    if (MBB == BarrierMBB)
      return true;
    
    MachineDomTreeNode* DefMDTN = MDT.getNode(DefMBB);
    MachineDomTreeNode* BarrierMDTN = MDT.getNode(BarrierMBB);
    MachineDomTreeNode* MDTN = MDT.getNode(MBB)->getIDom();
    while (MDTN) {
      if (MDTN == DefMDTN)
        return true;
      else if (MDTN == BarrierMDTN)
        break;
      MDTN = MDTN->getIDom();
    }
    
    MBBEnd = LIs->getMBBEndIdx(MBB);
    if (LR->end > MBBEnd)
      Stack.push_back(std::make_pair(MBB, MBB->succ_begin()));
  }
  
  return false;
} 
  

bool PreAllocSplitting::runOnMachineFunction(MachineFunction &MF) {
  CurrMF = &MF;
  TM     = &MF.getTarget();
  TII    = TM->getInstrInfo();
  MFI    = MF.getFrameInfo();
  MRI    = &MF.getRegInfo();
  LIs    = &getAnalysis<LiveIntervals>();
  LSs    = &getAnalysis<LiveStacks>();

  bool MadeChange = false;

  // Make sure blocks are numbered in order.
  MF.RenumberBlocks();

#if 1
  // FIXME: Go top down.
  MachineBasicBlock *Entry = MF.begin();
  SmallPtrSet<MachineBasicBlock*,16> Visited;

  for (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*,16> >
         DFI = df_ext_begin(Entry, Visited), E = df_ext_end(Entry, Visited);
       DFI != E; ++DFI) {
    BarrierMBB = *DFI;
    for (MachineBasicBlock::iterator I = BarrierMBB->begin(),
           E = BarrierMBB->end(); I != E; ++I) {
      Barrier = &*I;
      const TargetRegisterClass **BarrierRCs =
        Barrier->getDesc().getRegClassBarriers();
      if (!BarrierRCs)
        continue;
      BarrierIdx = LIs->getInstructionIndex(Barrier);
      MadeChange |= SplitRegLiveIntervals(BarrierRCs);
    }
  }
#else
  for (MachineFunction::reverse_iterator I = MF.rbegin(), E = MF.rend();
       I != E; ++I) {
    BarrierMBB = &*I;
    for (MachineBasicBlock::reverse_iterator II = BarrierMBB->rbegin(),
           EE = BarrierMBB->rend(); II != EE; ++II) {
      Barrier = &*II;
      const TargetRegisterClass **BarrierRCs =
        Barrier->getDesc().getRegClassBarriers();
      if (!BarrierRCs)
        continue;
      BarrierIdx = LIs->getInstructionIndex(Barrier);
      MadeChange |= SplitRegLiveIntervals(BarrierRCs);
    }
  }
#endif

  return MadeChange;
}