LLVM Exercise VII

So why does the code produced in the last exercise contain the labels .LBB0_2 and .LBB0_3 but no .LBB0_1?

Well that is because I have added a code generation pass that deletes useless jumps like:

    	JNC .LBB0_1
    .LBB0_1:

Code snippets:

void HP41MCODEPassConfig::addPreEmitPass() {
    addPass(new RemoveUselessJMP()); }

...

bool RemoveUselessJMP::runOnMachineBasicBlock(
    MachineBasicBlock &MBB, MachineBasicBlock &MBBN) {
  bool Modified = false;

  MachineBasicBlock::iterator I = MBB.end();
  if (I != MBB.begin())
    I--;
  else
    return Modified;

  if (I->getOpcode() == HP41MCODE::JNC &&
        I->getOperand(0).getMBB() == &MBBN) {
    MBB.erase(I);
    Modified = true;
  }

  return Modified;
}

bool RemoveUselessJMP::runOnMachineFunction(MachineFunction &MF) {
  bool Modified = false;
  MachineFunction::iterator FJ = MF.begin();
  if (FJ != MF.end())
    FJ++;
  if (FJ == MF.end())
    return Modified;
  for (MachineFunction::iterator FI = MF.begin(),
       FE = MF.end(); FJ != FE; ++FI, ++FJ)
    Modified |= runOnMachineBasicBlock(*FI, *FJ);
 
  return Modified;
}