LiveIntervalAnalysis.cpp

    if (!MO.isReg() || !MO.isUse())
      continue;
    unsigned Reg = MO.getReg();
    if (Reg == 0 || Reg == li.reg)
      continue;

    if (TargetRegisterInfo::isPhysicalRegister(Reg) &&
        !allocatableRegs_[Reg])
      continue;
    RegOp = MO.getReg();
    break; // Found vreg operand - leave the loop.
  }
  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,
                                       SlotIndex UseIdx) const {
  VNInfo *UValNo = li.getVNInfoAt(UseIdx);
  return UValNo && UValNo == li.getVNInfoAt(getInstructionIndex(MI));
}

/// 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,
                                  const SmallVectorImpl<LiveInterval*> *SpillIs,
                                  bool &isLoad) {
  if (DisableReMat)
    return false;

  if (!tii_->isTriviallyReMaterializable(MI, aa_))
    return false;

  // Target-specific code can mark an instruction as being rematerializable
  // if it has one virtual reg use, though it had better be something like
  // a PIC base register which is likely to be live everywhere.
  unsigned ImpUse = getReMatImplicitUse(li, MI);
  if (ImpUse) {
    const LiveInterval &ImpLi = getInterval(ImpUse);
    for (MachineRegisterInfo::use_nodbg_iterator
           ri = mri_->use_nodbg_begin(li.reg), re = mri_->use_nodbg_end();
         ri != re; ++ri) {
      MachineInstr *UseMI = &*ri;
      SlotIndex UseIdx = getInstructionIndex(UseMI);
      if (li.getVNInfoAt(UseIdx) != 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.
    if (SpillIs)
      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,
                                  const 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;
    if (VNI->isUnused())
      continue; // Dead val#.
    // Is the def for the val# rematerializable?
    MachineInstr *ReMatDefMI = getInstructionFromIndex(VNI->def);
    if (!ReMatDefMI)
      return false;
    bool DefIsLoad = false;
    if (!ReMatDefMI ||
        !isReMaterializable(li, VNI, ReMatDefMI, SpillIs, DefIsLoad))
      return false;
    isLoad |= DefIsLoad;
  }
  return true;
}

MachineBasicBlock*
LiveIntervals::intervalIsInOneMBB(const LiveInterval &LI) const {
  // A local live range must be fully contained inside the block, meaning it is
  // defined and killed at instructions, not at block boundaries. It is not
  // live in or or out of any block.
  //
  // It is technically possible to have a PHI-defined live range identical to a
  // single block, but we are going to return false in that case.

  SlotIndex Start = LI.beginIndex();
  if (Start.isBlock())
    return NULL;

  SlotIndex Stop = LI.endIndex();
  if (Stop.isBlock())
    return NULL;

  // getMBBFromIndex doesn't need to search the MBB table when both indexes
  // belong to proper instructions.
  MachineBasicBlock *MBB1 = indexes_->getMBBFromIndex(Start);
  MachineBasicBlock *MBB2 = indexes_->getMBBFromIndex(Stop);
  return MBB1 == MBB2 ? MBB1 : NULL;
}

float
LiveIntervals::getSpillWeight(bool isDef, bool isUse, unsigned loopDepth) {
  // Limit the loop depth ridiculousness.
  if (loopDepth > 200)
    loopDepth = 200;

  // The loop depth is used to roughly estimate the number of times the
  // instruction is executed. Something like 10^d is simple, but will quickly
  // overflow a float. This expression behaves like 10^d for small d, but is
  // more tempered for large d. At d=200 we get 6.7e33 which leaves a bit of
  // headroom before overflow.
  // By the way, powf() might be unavailable here. For consistency,
  // We may take pow(double,double).
  float lc = std::pow(1 + (100.0 / (loopDepth + 10)), (double)loopDepth);

  return (isDef + isUse) * lc;
}

LiveRange LiveIntervals::addLiveRangeToEndOfBlock(unsigned reg,
                                                  MachineInstr* startInst) {
  LiveInterval& Interval = getOrCreateInterval(reg);
  VNInfo* VN = Interval.getNextValue(
    SlotIndex(getInstructionIndex(startInst).getRegSlot()),
    getVNInfoAllocator());
  VN->setHasPHIKill(true);
  LiveRange LR(
     SlotIndex(getInstructionIndex(startInst).getRegSlot()),
     getMBBEndIdx(startInst->getParent()), VN);
  Interval.addRange(LR);

  return LR;
}


//===----------------------------------------------------------------------===//
//                          Register mask functions
//===----------------------------------------------------------------------===//

bool LiveIntervals::checkRegMaskInterference(LiveInterval &LI,
                                             BitVector &UsableRegs) {
  if (LI.empty())
    return false;

  // We are going to enumerate all the register mask slots contained in LI.
  // Start with a binary search of RegMaskSlots to find a starting point.
  LiveInterval::iterator LiveI = LI.begin(), LiveE = LI.end();
  ArrayRef<SlotIndex> Slots = getRegMaskSlots();
  ArrayRef<SlotIndex>::iterator SlotI =
    std::lower_bound(Slots.begin(), Slots.end(), LiveI->start);
  ArrayRef<SlotIndex>::iterator SlotE = Slots.end();

  // No slots in range, LI begins after the last call.
  if (SlotI == SlotE)
    return false;

  bool Found = false;
  for (;;) {
    assert(*SlotI >= LiveI->start);
    // Loop over all slots overlapping this segment.
    while (*SlotI < LiveI->end) {
      // *SlotI overlaps LI. Collect mask bits.
      if (!Found) {
        // This is the first overlap. Initialize UsableRegs to all ones.
        UsableRegs.clear();
        UsableRegs.resize(tri_->getNumRegs(), true);
        Found = true;
      }
      // Remove usable registers clobbered by this mask.
      UsableRegs.clearBitsNotInMask(RegMaskBits[SlotI-Slots.begin()]);
      if (++SlotI == SlotE)
        return Found;
    }
    // *SlotI is beyond the current LI segment.
    LiveI = LI.advanceTo(LiveI, *SlotI);
    if (LiveI == LiveE)
      return Found;
    // Advance SlotI until it overlaps.
    while (*SlotI < LiveI->start)
      if (++SlotI == SlotE)
        return Found;
  }
}