C++ MachineBasicBlock::SkipPHIsAndLabels方法代码示例

/// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in
/// predecessor basic blocks.
///
bool PHIElimination::EliminatePHINodes(MachineFunction &MF,
                                             MachineBasicBlock &MBB) {
  if (MBB.empty() || !MBB.front().isPHI())
    return false;   // Quick exit for basic blocks without PHIs.

  // Get an iterator to the first instruction after the last PHI node (this may
  // also be the end of the basic block).
  MachineBasicBlock::iterator AfterPHIsIt = MBB.SkipPHIsAndLabels(MBB.begin());

  while (MBB.front().isPHI())
    LowerAtomicPHINode(MBB, AfterPHIsIt);

  return true;
}

SlotIndex SplitEditor::leaveIntvAtTop(MachineBasicBlock &MBB) {
  assert(OpenIdx && "openIntv not called before leaveIntvAtTop");
  SlotIndex Start = LIS.getMBBStartIdx(&MBB);
  DEBUG(dbgs() << "    leaveIntvAtTop BB#" << MBB.getNumber() << ", " << Start);

  VNInfo *ParentVNI = Edit->getParent().getVNInfoAt(Start);
  if (!ParentVNI) {
    DEBUG(dbgs() << ": not live\n");
    return Start;
  }

  VNInfo *VNI = defFromParent(0, ParentVNI, Start, MBB,
                              MBB.SkipPHIsAndLabels(MBB.begin()));
  RegAssign.insert(Start, VNI->def, OpenIdx);
  DEBUG(dump());
  return VNI->def;
}

/// hoistSpill - Given a sibling copy that defines a value to be spilled, insert
/// a spill at a better location.
bool InlineSpiller::hoistSpill(LiveInterval &SpillLI, MachineInstr *CopyMI) {
  SlotIndex Idx = LIS.getInstructionIndex(CopyMI);
  VNInfo *VNI = SpillLI.getVNInfoAt(Idx.getRegSlot());
  assert(VNI && VNI->def == Idx.getRegSlot() && "Not defined by copy");
  SibValueMap::iterator I = SibValues.find(VNI);
  if (I == SibValues.end())
    return false;

  const SibValueInfo &SVI = I->second;

  // Let the normal folding code deal with the boring case.
  if (!SVI.AllDefsAreReloads && SVI.SpillVNI == VNI)
    return false;

  // SpillReg may have been deleted by remat and DCE.
  if (!LIS.hasInterval(SVI.SpillReg)) {
    DEBUG(dbgs() << "Stale interval: " << PrintReg(SVI.SpillReg) << '\n');
    SibValues.erase(I);
    return false;
  }

  LiveInterval &SibLI = LIS.getInterval(SVI.SpillReg);
  if (!SibLI.containsValue(SVI.SpillVNI)) {
    DEBUG(dbgs() << "Stale value: " << PrintReg(SVI.SpillReg) << '\n');
    SibValues.erase(I);
    return false;
  }

  // Conservatively extend the stack slot range to the range of the original
  // value. We may be able to do better with stack slot coloring by being more
  // careful here.
  assert(StackInt && "No stack slot assigned yet.");
  LiveInterval &OrigLI = LIS.getInterval(Original);
  VNInfo *OrigVNI = OrigLI.getVNInfoAt(Idx);
  StackInt->MergeValueInAsValue(OrigLI, OrigVNI, StackInt->getValNumInfo(0));
  DEBUG(dbgs() << "\tmerged orig valno " << OrigVNI->id << ": "
               << *StackInt << '\n');

  // Already spilled everywhere.
  if (SVI.AllDefsAreReloads) {
    DEBUG(dbgs() << "\tno spill needed: " << SVI);
    ++NumOmitReloadSpill;
    return true;
  }
  // We are going to spill SVI.SpillVNI immediately after its def, so clear out
  // any later spills of the same value.
  eliminateRedundantSpills(SibLI, SVI.SpillVNI);

  MachineBasicBlock *MBB = LIS.getMBBFromIndex(SVI.SpillVNI->def);
  MachineBasicBlock::iterator MII;
  if (SVI.SpillVNI->isPHIDef())
    MII = MBB->SkipPHIsAndLabels(MBB->begin());
  else {
    MachineInstr *DefMI = LIS.getInstructionFromIndex(SVI.SpillVNI->def);
    assert(DefMI && "Defining instruction disappeared");
    MII = DefMI;
    ++MII;
  }
  // Insert spill without kill flag immediately after def.
  TII.storeRegToStackSlot(*MBB, MII, SVI.SpillReg, false, StackSlot,
                          MRI.getRegClass(SVI.SpillReg), &TRI);
  --MII; // Point to store instruction.
  LIS.InsertMachineInstrInMaps(MII);
  DEBUG(dbgs() << "\thoisted: " << SVI.SpillVNI->def << '\t' << *MII);

  ++NumSpills;
  ++NumHoists;
  return true;
}