C++ const_iterator::isBarrier方法代码示例

/// isBlockOnlyReachableByFallthough - Return true if the basic block has
/// exactly one predecessor and the control transfer mechanism between
/// the predecessor and this block is a fall-through.
///
/// This overrides AsmPrinter's implementation to handle delay slots.
bool SparcAsmPrinter::
isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) const {
  // If this is a landing pad, it isn't a fall through.  If it has no preds,
  // then nothing falls through to it.
  if (MBB->isLandingPad() || MBB->pred_empty())
    return false;
  
  // If there isn't exactly one predecessor, it can't be a fall through.
  MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(), PI2 = PI;
  ++PI2;
  if (PI2 != MBB->pred_end())
    return false;
  
  // The predecessor has to be immediately before this block.
  const MachineBasicBlock *Pred = *PI;
  
  if (!Pred->isLayoutSuccessor(MBB))
    return false;
  
  // Check if the last terminator is an unconditional branch.
  MachineBasicBlock::const_iterator I = Pred->end();
  while (I != Pred->begin() && !(--I)->isTerminator())
    ; // Noop
  return I == Pred->end() || !I->isBarrier();
}

// KLUDGE: HexagonInstrInfo::AnalyzeBranch may be unable to recognize
// that a block can never fall-through.
bool HexagonEarlyIfConversion::hasUncondBranch(const MachineBasicBlock *B)
      const {
  MachineBasicBlock::const_iterator I = B->getFirstTerminator(), E = B->end();
  while (I != E) {
    if (I->isBarrier())
      return true;
    ++I;
  }
  return false;
}

void llvm::guessSuccessors(const MachineBasicBlock &MBB,
                           SmallVectorImpl<MachineBasicBlock*> &Result,
                           bool &IsFallthrough) {
  SmallPtrSet<MachineBasicBlock*,8> Seen;

  for (const MachineInstr &MI : MBB) {
    if (MI.isPHI())
      continue;
    for (const MachineOperand &MO : MI.operands()) {
      if (!MO.isMBB())
        continue;
      MachineBasicBlock *Succ = MO.getMBB();
      auto RP = Seen.insert(Succ);
      if (RP.second)
        Result.push_back(Succ);
    }
  }
  MachineBasicBlock::const_iterator I = MBB.getLastNonDebugInstr();
  IsFallthrough = I == MBB.end() || !I->isBarrier();
}

bool PatmosAsmPrinter::
isBlockOnlyReachableByFallthrough(const MachineBasicBlock *MBB) const {
  // If this is a landing pad, it isn't a fall through.  If it has no preds,
  // then nothing falls through to it.
  if (MBB->isLandingPad() || MBB->pred_empty() || MBB->hasAddressTaken())
    return false;

  // If there isn't exactly one predecessor, it can't be a fall through.
  MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(), PI2 = PI;
  if (++PI2 != MBB->pred_end())
    return false;

  // The predecessor has to be immediately before this block.
  const MachineBasicBlock *Pred = *PI;

  if (!Pred->isLayoutSuccessor(MBB))
    return false;

  // if the block starts a new cache block, do not fall through (we need to
  // insert cache stuff, even if we only reach this block from a jump from the
  // previous block, and we need the label).
  if (isFStart(MBB))
    return false;

  // If the block is completely empty, then it definitely does fall through.
  if (Pred->empty())
    return true;


  // Here is the difference to the AsmPrinter method;
  // We do not check properties of all terminator instructions
  // (delay slot instructions do not have to be terminators),
  // but instead check if the *last terminator* is an
  // unconditional branch (no barrier)
  MachineBasicBlock::const_iterator I = Pred->end();
  // find last terminator
  while (I != Pred->begin() && !(--I)->isTerminator()) ;
  return I == Pred->end() || !I->isBarrier();
}

/// isBlockOnlyReachableByFallthough - Return true if the basic block has
/// exactly one predecessor and the control transfer mechanism between
/// the predecessor and this block is a fall-through.
// FIXME: could the overridden cases be handled in AnalyzeBranch?
bool OR1KAsmPrinter::isBlockOnlyReachableByFallthrough(const MachineBasicBlock*
                                                       MBB) const {
  // The predecessor has to be immediately before this block.
  const MachineBasicBlock *Pred = *MBB->pred_begin();

  // If the predecessor is a switch statement, assume a jump table
  // implementation, so it is not a fall through.
  if (const BasicBlock *bb = Pred->getBasicBlock())
    if (isa<SwitchInst>(bb->getTerminator()))
      return false;

  // Check default implementation
  if (!AsmPrinter::isBlockOnlyReachableByFallthrough(MBB))
    return false;

  // Otherwise, check the last instruction.
  // Check if the last terminator is an unconditional branch.
  MachineBasicBlock::const_iterator I = Pred->end();
  while (I != Pred->begin() && !(--I)->isTerminator()) ;

  return !I->isBarrier();
}

/// isBlockOnlyReachableByFallthough - Return true if the basic block has
/// exactly one predecessor and the control transfer mechanism between
/// the predecessor and this block is a fall-through.
bool MipsAsmPrinter::isBlockOnlyReachableByFallthrough(const MachineBasicBlock*
                                                       MBB) const {
  // The predecessor has to be immediately before this block.
  const MachineBasicBlock *Pred = *MBB->pred_begin();

  // If the predecessor is a switch statement, assume a jump table
  // implementation, so it is not a fall through.
  if (const BasicBlock *bb = Pred->getBasicBlock())
    if (isa<SwitchInst>(bb->getTerminator()))
      return false;

  // If this is a landing pad, it isn't a fall through.  If it has no preds,
  // then nothing falls through to it.
  if (MBB->isEHPad() || MBB->pred_empty())
    return false;

  // If there isn't exactly one predecessor, it can't be a fall through.
  MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(), PI2 = PI;
  ++PI2;

  if (PI2 != MBB->pred_end())
    return false;

  // The predecessor has to be immediately before this block.
  if (!Pred->isLayoutSuccessor(MBB))
    return false;

  // If the block is completely empty, then it definitely does fall through.
  if (Pred->empty())
    return true;

  // Otherwise, check the last instruction.
  // Check if the last terminator is an unconditional branch.
  MachineBasicBlock::const_iterator I = Pred->end();
  while (I != Pred->begin() && !(--I)->isTerminator()) ;

  return !I->isBarrier();
}