C++ iterator::advanceTo方法代码示例

void UserValue::computeIntervals(MachineRegisterInfo &MRI,
                                 const TargetRegisterInfo &TRI,
                                 LiveIntervals &LIS, LexicalScopes &LS) {
  SmallVector<std::pair<SlotIndex, unsigned>, 16> Defs;

  // Collect all defs to be extended (Skipping undefs).
  for (LocMap::const_iterator I = locInts.begin(); I.valid(); ++I)
    if (I.value() != UndefLocNo)
      Defs.push_back(std::make_pair(I.start(), I.value()));

  // Extend all defs, and possibly add new ones along the way.
  for (unsigned i = 0; i != Defs.size(); ++i) {
    SlotIndex Idx = Defs[i].first;
    unsigned LocNo = Defs[i].second;
    const MachineOperand &Loc = locations[LocNo];

    if (!Loc.isReg()) {
      extendDef(Idx, LocNo, nullptr, nullptr, nullptr, LIS);
      continue;
    }

    // Register locations are constrained to where the register value is live.
    if (TargetRegisterInfo::isVirtualRegister(Loc.getReg())) {
      LiveInterval *LI = nullptr;
      const VNInfo *VNI = nullptr;
      if (LIS.hasInterval(Loc.getReg())) {
        LI = &LIS.getInterval(Loc.getReg());
        VNI = LI->getVNInfoAt(Idx);
      }
      SmallVector<SlotIndex, 16> Kills;
      extendDef(Idx, LocNo, LI, VNI, &Kills, LIS);
      if (LI)
        addDefsFromCopies(LI, LocNo, Kills, Defs, MRI, LIS);
      continue;
    }

    // For physregs, use the live range of the first regunit as a guide.
    unsigned Unit = *MCRegUnitIterator(Loc.getReg(), &TRI);
    LiveRange *LR = &LIS.getRegUnit(Unit);
    const VNInfo *VNI = LR->getVNInfoAt(Idx);
    // Don't track copies from physregs, it is too expensive.
    extendDef(Idx, LocNo, LR, VNI, nullptr, LIS);
  }

  // Erase all the undefs.
  for (LocMap::iterator I = locInts.begin(); I.valid();)
    if (I.value() == UndefLocNo)
      I.erase();
    else
      ++I;

  // The computed intervals may extend beyond the range of the debug
  // location's lexical scope. In this case, splitting of an interval
  // can result in an interval outside of the scope being created,
  // causing extra unnecessary DBG_VALUEs to be emitted. To prevent
  // this, trim the intervals to the lexical scope.

  LexicalScope *Scope = LS.findLexicalScope(dl);
  if (!Scope)
    return;

  SlotIndex PrevEnd;
  LocMap::iterator I = locInts.begin();

  // Iterate over the lexical scope ranges. Each time round the loop
  // we check the intervals for overlap with the end of the previous
  // range and the start of the next. The first range is handled as
  // a special case where there is no PrevEnd.
  for (const InsnRange &Range : Scope->getRanges()) {
    SlotIndex RStart = LIS.getInstructionIndex(*Range.first);
    SlotIndex REnd = LIS.getInstructionIndex(*Range.second);

    // At the start of each iteration I has been advanced so that
    // I.stop() >= PrevEnd. Check for overlap.
    if (PrevEnd && I.start() < PrevEnd) {
      SlotIndex IStop = I.stop();
      unsigned LocNo = I.value();

      // Stop overlaps previous end - trim the end of the interval to
      // the scope range.
      I.setStopUnchecked(PrevEnd);
      ++I;

      // If the interval also overlaps the start of the "next" (i.e.
      // current) range create a new interval for the remainder (which
      // may be further trimmed).
      if (RStart < IStop)
        I.insert(RStart, IStop, LocNo);
    }

    // Advance I so that I.stop() >= RStart, and check for overlap.
    I.advanceTo(RStart);
    if (!I.valid())
      return;

    if (I.start() < RStart) {
      // Interval start overlaps range - trim to the scope range.
      I.setStartUnchecked(RStart);
      // Remember that this interval was trimmed.
      trimmedDefs.insert(RStart);
//.........这里部分代码省略.........