StrongPHIElimination.cpp

        phis.push_back(BI);
  }
  
  for (std::vector<MachineInstr*>::iterator I = phis.begin(), E = phis.end();
       I != E; ) {
    MachineInstr* PInstr = *(I++);
    
    // If this is a dead PHI node, then remove it from LiveIntervals.
    unsigned DestReg = PInstr->getOperand(0).getReg();
    LiveInterval& PI = LI.getInterval(DestReg);
    if (PInstr->registerDefIsDead(DestReg)) {
      if (PI.containsOneValue()) {
        LI.removeInterval(DestReg);
      } else {
        unsigned idx = LI.getDefIndex(LI.getInstructionIndex(PInstr));
        PI.removeRange(*PI.getLiveRangeContaining(idx), true);
      }
    } else {
      // Trim live intervals of input registers.  They are no longer live into
      // this block if they died after the PHI.  If they lived after it, don't
      // trim them because they might have other legitimate uses.
      for (unsigned i = 1; i < PInstr->getNumOperands(); i += 2) {
        unsigned reg = PInstr->getOperand(i).getReg();
        
        MachineBasicBlock* MBB = PInstr->getOperand(i+1).getMBB();
        LiveInterval& InputI = LI.getInterval(reg);
        if (MBB != PInstr->getParent() &&
            InputI.liveAt(LI.getMBBStartIdx(PInstr->getParent())) &&
            InputI.expiredAt(LI.getInstructionIndex(PInstr) + 
                             LiveIntervals::InstrSlots::NUM))
          InputI.removeRange(LI.getMBBStartIdx(PInstr->getParent()),
                             LI.getInstructionIndex(PInstr),
                             true);
      }
      
      // If the PHI is not dead, then the valno defined by the PHI
      // now has an unknown def.
      unsigned idx = LI.getDefIndex(LI.getInstructionIndex(PInstr));
      const LiveRange* PLR = PI.getLiveRangeContaining(idx);
      PLR->valno->def = ~0U;
      LiveRange R (LI.getMBBStartIdx(PInstr->getParent()),
                   PLR->start, PLR->valno);
      PI.addRange(R);
    }
    
    LI.RemoveMachineInstrFromMaps(PInstr);
    PInstr->eraseFromParent();
  }
  
  LI.computeNumbering();
  
  return true;
}