bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
  bool AnyChanges = false;
  MRI = &MF.getRegInfo();
  TRI = MF.getTarget().getRegisterInfo();
  TII = MF.getTarget().getInstrInfo();

  // Treat reserved registers as always live.
  BitVector ReservedRegs = TRI->getReservedRegs(MF);

  // Loop over all instructions in all blocks, from bottom to top, so that it's
  // more likely that chains of dependent but ultimately dead instructions will
  // be cleaned up.
  for (MachineFunction::reverse_iterator I = MF.rbegin(), E = MF.rend();
       I != E; ++I) {
    MachineBasicBlock *MBB = &*I;

    // Start out assuming that reserved registers are live out of this block.
    LivePhysRegs = ReservedRegs;

    // Also add any explicit live-out physregs for this block.
    if (!MBB->empty() && MBB->back().getDesc().isReturn())
      for (MachineRegisterInfo::liveout_iterator LOI = MRI->liveout_begin(),
           LOE = MRI->liveout_end(); LOI != LOE; ++LOI) {
        unsigned Reg = *LOI;
        if (TargetRegisterInfo::isPhysicalRegister(Reg))
          LivePhysRegs.set(Reg);
      }

    // FIXME: Add live-ins from sucessors to LivePhysRegs. Normally, physregs
    // are not live across blocks, but some targets (x86) can have flags live
    // out of a block.

    // Now scan the instructions and delete dead ones, tracking physreg
    // liveness as we go.
    for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
         MIE = MBB->rend(); MII != MIE; ) {
      MachineInstr *MI = &*MII;

      // If the instruction is dead, delete it!
      if (isDead(MI)) {
        DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);
        // It is possible that some DBG_VALUE instructions refer to this
        // instruction.  Examine each def operand for such references;
        // if found, mark the DBG_VALUE as undef (but don't delete it).
        for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
          const MachineOperand &MO = MI->getOperand(i);
          if (!MO.isReg() || !MO.isDef())
            continue;
          unsigned Reg = MO.getReg();
          if (!TargetRegisterInfo::isVirtualRegister(Reg))
            continue;
          MachineRegisterInfo::use_iterator nextI;
          for (MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg),
               E = MRI->use_end(); I!=E; I=nextI) {
            nextI = llvm::next(I);  // I is invalidated by the setReg
            MachineOperand& Use = I.getOperand();
            MachineInstr *UseMI = Use.getParent();
            if (UseMI==MI)
              continue;
            assert(Use.isDebug());
            UseMI->getOperand(0).setReg(0U);
          }
        }
        AnyChanges = true;
        MI->eraseFromParent();
        ++NumDeletes;
        MIE = MBB->rend();
        // MII is now pointing to the next instruction to process,
        // so don't increment it.
        continue;
      }

      // Record the physreg defs.
      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
        const MachineOperand &MO = MI->getOperand(i);
        if (MO.isReg() && MO.isDef()) {
          unsigned Reg = MO.getReg();
          if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg)) {
            LivePhysRegs.reset(Reg);
            // Check the subreg set, not the alias set, because a def
            // of a super-register may still be partially live after
            // this def.
            for (const unsigned *SubRegs = TRI->getSubRegisters(Reg);
                 *SubRegs; ++SubRegs)
              LivePhysRegs.reset(*SubRegs);
          }
        }
      }
      // Record the physreg uses, after the defs, in case a physreg is
      // both defined and used in the same instruction.
      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
        const MachineOperand &MO = MI->getOperand(i);
        if (MO.isReg() && MO.isUse()) {
          unsigned Reg = MO.getReg();
          if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg)) {
            LivePhysRegs.set(Reg);
            for (const unsigned *AliasSet = TRI->getAliasSet(Reg);
                 *AliasSet; ++AliasSet)
              LivePhysRegs.set(*AliasSet);
          }
        }
      }

      // We didn't delete the current instruction, so increment MII to
      // the next one.
      ++MII;
    }
  }

  LivePhysRegs.clear();
  return AnyChanges;
}
bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
    if (skipOptnoneFunction(*MF.getFunction()))
        return false;

    bool AnyChanges = false;
    MRI = &MF.getRegInfo();
    TRI = MF.getSubtarget().getRegisterInfo();
    TII = MF.getSubtarget().getInstrInfo();

    // Loop over all instructions in all blocks, from bottom to top, so that it's
    // more likely that chains of dependent but ultimately dead instructions will
    // be cleaned up.
    for (MachineFunction::reverse_iterator I = MF.rbegin(), E = MF.rend();
            I != E; ++I) {
        MachineBasicBlock *MBB = &*I;

        // Start out assuming that reserved registers are live out of this block.
        LivePhysRegs = MRI->getReservedRegs();

        // Add live-ins from sucessors to LivePhysRegs. Normally, physregs are not
        // live across blocks, but some targets (x86) can have flags live out of a
        // block.
        for (MachineBasicBlock::succ_iterator S = MBB->succ_begin(),
                E = MBB->succ_end(); S != E; S++)
            for (MachineBasicBlock::livein_iterator LI = (*S)->livein_begin();
                    LI != (*S)->livein_end(); LI++)
                LivePhysRegs.set(*LI);

        // Now scan the instructions and delete dead ones, tracking physreg
        // liveness as we go.
        for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
                MIE = MBB->rend(); MII != MIE; ) {
            MachineInstr *MI = &*MII;

            // If the instruction is dead, delete it!
            if (isDead(MI)) {
                DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);
                // It is possible that some DBG_VALUE instructions refer to this
                // instruction.  They get marked as undef and will be deleted
                // in the live debug variable analysis.
                MI->eraseFromParentAndMarkDBGValuesForRemoval();
                AnyChanges = true;
                ++NumDeletes;
                MIE = MBB->rend();
                // MII is now pointing to the next instruction to process,
                // so don't increment it.
                continue;
            }

            // Record the physreg defs.
            for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
                const MachineOperand &MO = MI->getOperand(i);
                if (MO.isReg() && MO.isDef()) {
                    unsigned Reg = MO.getReg();
                    if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
                        // Check the subreg set, not the alias set, because a def
                        // of a super-register may still be partially live after
                        // this def.
                        for (MCSubRegIterator SR(Reg, TRI,/*IncludeSelf=*/true);
                                SR.isValid(); ++SR)
                            LivePhysRegs.reset(*SR);
                    }
                } else if (MO.isRegMask()) {
                    // Register mask of preserved registers. All clobbers are dead.
                    LivePhysRegs.clearBitsNotInMask(MO.getRegMask());
                }
            }
            // Record the physreg uses, after the defs, in case a physreg is
            // both defined and used in the same instruction.
            for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
                const MachineOperand &MO = MI->getOperand(i);
                if (MO.isReg() && MO.isUse()) {
                    unsigned Reg = MO.getReg();
                    if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
                        for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
                            LivePhysRegs.set(*AI);
                    }
                }
            }

            // We didn't delete the current instruction, so increment MII to
            // the next one.
            ++MII;
        }
    }

    LivePhysRegs.clear();
    return AnyChanges;
}