C++ iterator::isUnconditionalBranch方法代码示例

/// True if this BB has only one unconditional jump.
bool TailDuplicator::isSimpleBB(MachineBasicBlock *TailBB) {
  if (TailBB->succ_size() != 1)
    return false;
  if (TailBB->pred_empty())
    return false;
  MachineBasicBlock::iterator I = TailBB->getFirstNonDebugInstr();
  if (I == TailBB->end())
    return true;
  return I->isUnconditionalBranch();
}

/// isSimpleBB - True if this BB has only one unconditional jump.
bool
TailDuplicatePass::isSimpleBB(MachineBasicBlock *TailBB) {
  if (TailBB->succ_size() != 1)
    return false;
  if (TailBB->pred_empty())
    return false;
  MachineBasicBlock::iterator I = TailBB->begin();
  MachineBasicBlock::iterator E = TailBB->end();
  while (I != E && I->isDebugValue())
    ++I;
  if (I == E)
    return true;
  return I->isUnconditionalBranch();
}

bool BranchRelaxation::relaxBranchInstructions() {
  bool Changed = false;

  // Relaxing branches involves creating new basic blocks, so re-eval
  // end() for termination.
  for (MachineFunction::iterator I = MF->begin(); I != MF->end(); ++I) {
    MachineBasicBlock &MBB = *I;

    // Empty block?
    MachineBasicBlock::iterator Last = MBB.getLastNonDebugInstr();
    if (Last == MBB.end())
      continue;

    // Expand the unconditional branch first if necessary. If there is a
    // conditional branch, this will end up changing the branch destination of
    // it to be over the newly inserted indirect branch block, which may avoid
    // the need to try expanding the conditional branch first, saving an extra
    // jump.
    if (Last->isUnconditionalBranch()) {
      // Unconditional branch destination might be unanalyzable, assume these
      // are OK.
      if (MachineBasicBlock *DestBB = TII->getBranchDestBlock(*Last)) {
        if (!isBlockInRange(*Last, *DestBB)) {
          fixupUnconditionalBranch(*Last);
          ++NumUnconditionalRelaxed;
          Changed = true;
        }
      }
    }

    // Loop over the conditional branches.
    MachineBasicBlock::iterator Next;
    for (MachineBasicBlock::iterator J = MBB.getFirstTerminator();
         J != MBB.end(); J = Next) {
      Next = std::next(J);
      MachineInstr &MI = *J;

      if (MI.isConditionalBranch()) {
        MachineBasicBlock *DestBB = TII->getBranchDestBlock(MI);
        if (!isBlockInRange(MI, *DestBB)) {
          if (Next != MBB.end() && Next->isConditionalBranch()) {
            // If there are multiple conditional branches, this isn't an
            // analyzable block. Split later terminators into a new block so
            // each one will be analyzable.

            splitBlockBeforeInstr(*Next, DestBB);
          } else {
            fixupConditionalBranch(MI);
            ++NumConditionalRelaxed;
          }

          Changed = true;

          // This may have modified all of the terminators, so start over.
          Next = MBB.getFirstTerminator();
        }
      }
    }
  }

  return Changed;
}

bool PatmosInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,
                                    MachineBasicBlock *&TBB,
                                    MachineBasicBlock *&FBB,
                                    SmallVectorImpl<MachineOperand> &Cond,
                                    bool AllowModify) const {
  // If the client does not want to only simplify the branch,
  // the output arguments must be initialized.
  assert(AllowModify || (TBB==0 && FBB==0 && Cond.size()==0));

  // Start from the bottom of the block and work up, examining the
  // terminator instructions.
  MachineBasicBlock::iterator I = MBB.end();

  while (I != MBB.begin()) {
    --I;

    if (I->isDebugValue() || I->isPseudo())
      continue;

    // Working from the bottom, when we see a non-terminator inst, we're done.
    if (!isUnpredicatedTerminator(I))
      break;

    // A terminator that isn't a (direct) branch can't easily be handled
    // by this analysis.
    if (!I->isBranch() || I->isIndirectBranch())
      return true;

    // Handle Unconditional branches
    if (!isPredicated(I)) {
      // fix instruction, if necessary
      if (!I->isUnconditionalBranch()) fixOpcodeForGuard(I);
      // TBB is used to indicate the unconditional destination.
      TBB = getBranchTarget(I);
      if (AllowModify) {
        // If the block has any instructions after an uncond branch, delete them.
        while (llvm::next(I) != MBB.end())
          llvm::next(I)->eraseFromParent();
      }
      continue;
    }

    // Handle conditional branches
    if (isPredicated(I)) {
      // fix instruction, if necessary
      if (!I->isConditionalBranch()) fixOpcodeForGuard(I);
      // we only treat the first conditional branch in a row
      if (Cond.size() > 0)
        return true;
      // Get branch condition
      int i = I->findFirstPredOperandIdx();
      assert(i != -1 );
      Cond.push_back(I->getOperand(i));   // reg
      Cond.push_back(I->getOperand(i+1)); // flag
      // We've processed an unconditional branch before,
      // the unconditional target goes to FBB now
      if (TBB) FBB = TBB;
      // target of conditional branch goes to TBB
      TBB = getBranchTarget(I);
      continue;
    }
    // we explicitly leave or continue.
    llvm_unreachable("AnalyzeBranch error.");
  }
  // left the loop? then we're done
  return false;
}