RegAllocFast.cpp

      MO.setReg(DestPhysReg);  // Assign the output register
      UsedInInstr.set(DestPhysReg);
    }

    // If this instruction defines any registers that are immediately dead,
    // kill them now.
    //
    for (unsigned i = 0, e = DeadDefs.size(); i != e; ++i) {
      unsigned VirtReg = DeadDefs[i];
      unsigned PhysReg = VirtReg;
      if (TargetRegisterInfo::isVirtualRegister(VirtReg)) {
        unsigned &PhysRegSlot = getVirt2PhysRegMapSlot(VirtReg);
        PhysReg = PhysRegSlot;
        assert(PhysReg != 0);
        PhysRegSlot = 0;
      } else if (PhysRegsUsed[PhysReg] == -2) {
        // Unallocatable register dead, ignore.
        continue;
      } else if (!PhysReg)
        continue;

      DEBUG(dbgs()  << "  Register " << TRI->getName(PhysReg)
                    << " [%reg" << VirtReg
                    << "] is never used, removing it from live set\n");
      removePhysReg(PhysReg);
      for (const unsigned *AliasSet = TRI->getAliasSet(PhysReg);
           *AliasSet; ++AliasSet) {
        if (PhysRegsUsed[*AliasSet] != -2) {
          DEBUG(dbgs()  << "  Register " << TRI->getName(*AliasSet)
                        << " [%reg" << *AliasSet
                        << "] is never used, removing it from live set\n");
          removePhysReg(*AliasSet);
        }
      }
    }

    // Finally, if this is a noop copy instruction, zap it.  (Except that if
    // the copy is dead, it must be kept to avoid messing up liveness info for
    // the register scavenger.  See pr4100.)
    if (TII->isMoveInstr(*MI, SrcCopyReg, DstCopyReg,
                         SrcCopySubReg, DstCopySubReg) &&
        SrcCopyReg == DstCopyReg && DeadDefs.empty())
      MBB.erase(MI);
  }

  MachineBasicBlock::iterator MI = MBB.getFirstTerminator();

  // Spill all physical registers holding virtual registers now.
  for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i)
    if (PhysRegsUsed[i] != -1 && PhysRegsUsed[i] != -2) {
      if (unsigned VirtReg = PhysRegsUsed[i])
        spillVirtReg(MBB, MI, VirtReg, i);
      else
        removePhysReg(i);
    }
}

/// runOnMachineFunction - Register allocate the whole function
///
bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
  DEBUG(dbgs() << "Machine Function\n");
  MF = &Fn;
  TM = &Fn.getTarget();
  TRI = TM->getRegisterInfo();
  TII = TM->getInstrInfo();

  PhysRegsUsed.assign(TRI->getNumRegs(), -1);
  UsedInInstr.resize(TRI->getNumRegs());

  // At various places we want to efficiently check to see whether a register
  // is allocatable.  To handle this, we mark all unallocatable registers as
  // being pinned down, permanently.
  {
    BitVector Allocable = TRI->getAllocatableSet(Fn);
    for (unsigned i = 0, e = Allocable.size(); i != e; ++i)
      if (!Allocable[i])
        PhysRegsUsed[i] = -2;  // Mark the reg unallocable.
  }

  // initialize the virtual->physical register map to have a 'null'
  // mapping for all virtual registers
  unsigned LastVirtReg = MF->getRegInfo().getLastVirtReg();
  StackSlotForVirtReg.grow(LastVirtReg);
  Virt2PhysRegMap.grow(LastVirtReg);
  Virt2LastUseMap.grow(LastVirtReg);
  VirtRegModified.resize(LastVirtReg+1 -
                         TargetRegisterInfo::FirstVirtualRegister);
  UsedInMultipleBlocks.resize(LastVirtReg+1 -
                              TargetRegisterInfo::FirstVirtualRegister);

  // Loop over all of the basic blocks, eliminating virtual register references
  for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
       MBB != MBBe; ++MBB)
    AllocateBasicBlock(*MBB);

  StackSlotForVirtReg.clear();
  PhysRegsUsed.clear();
  VirtRegModified.clear();
  UsedInMultipleBlocks.clear();
  Virt2PhysRegMap.clear();
  Virt2LastUseMap.clear();
  return true;
}

FunctionPass *llvm::createFastRegisterAllocator() {
  return new RAFast();
}