RegAllocFast.cpp

    // Kill dead defs after the scan to ensure that multiple defs of the same
    // register are allocated identically. We didn't need to do this for uses
    // because we are crerating our own kill flags, and they are always at the
    // last use.
    for (unsigned i = 0, e = VirtDead.size(); i != e; ++i)
      killVirtReg(VirtDead[i]);
    VirtDead.clear();

    MRI->addPhysRegsUsed(UsedInInstr);

    if (CopyDst && CopyDst == CopySrc && CopyDstSub == CopySrcSub) {
      DEBUG(dbgs() << "-- coalescing: " << *MI);
      Coalesced.push_back(MI);
    } else {
      DEBUG(dbgs() << "<< " << *MI);
    }
  }

  // Spill all physical registers holding virtual registers now.
  DEBUG(dbgs() << "Spilling live registers at end of block.\n");
  spillAll(MBB->getFirstTerminator());

  // Erase all the coalesced copies. We are delaying it until now because
  // LiveVirtRegs might refer to the instrs.
  for (unsigned i = 0, e = Coalesced.size(); i != e; ++i)
    MBB->erase(Coalesced[i]);
  NumCopies += Coalesced.size();

  DEBUG(MBB->dump());
}

/// runOnMachineFunction - Register allocate the whole function
///
bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
  DEBUG(dbgs() << "********** FAST REGISTER ALLOCATION **********\n"
               << "********** Function: "
               << ((Value*)Fn.getFunction())->getName() << '\n');
  MF = &Fn;
  MRI = &MF->getRegInfo();
  TM = &Fn.getTarget();
  TRI = TM->getRegisterInfo();
  TII = TM->getInstrInfo();

  UsedInInstr.resize(TRI->getNumRegs());
  Allocatable = TRI->getAllocatableSet(*MF);

  // initialize the virtual->physical register map to have a 'null'
  // mapping for all virtual registers
  StackSlotForVirtReg.resize(MRI->getNumVirtRegs());

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

  // Make sure the set of used physregs is closed under subreg operations.
  MRI->closePhysRegsUsed(*TRI);

  // Add the clobber lists for all the instructions we skipped earlier.
  for (SmallPtrSet<const TargetInstrDesc*, 4>::const_iterator
       I = SkippedInstrs.begin(), E = SkippedInstrs.end(); I != E; ++I)
    if (const unsigned *Defs = (*I)->getImplicitDefs())
      while (*Defs)
        MRI->setPhysRegUsed(*Defs++);

  SkippedInstrs.clear();
  StackSlotForVirtReg.clear();
  LiveDbgValueMap.clear();
  return true;
}

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