Spiller.cpp

//===-- llvm/CodeGen/Spiller.cpp -  Spiller -------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "spiller"
#include "Spiller.h"

#include <algorithm>
using namespace llvm;

STATISTIC(NumDSE     , "Number of dead stores elided");
STATISTIC(NumDSS     , "Number of dead spill slots removed");
STATISTIC(NumCommutes, "Number of instructions commuted");
STATISTIC(NumDRM     , "Number of re-materializable defs elided");
STATISTIC(NumStores  , "Number of stores added");
STATISTIC(NumPSpills , "Number of physical register spills");
STATISTIC(NumOmitted , "Number of reloads omited");
STATISTIC(NumCopified, "Number of available reloads turned into copies");
STATISTIC(NumReMats  , "Number of re-materialization");
STATISTIC(NumLoads   , "Number of loads added");
STATISTIC(NumReused  , "Number of values reused");
STATISTIC(NumDCE     , "Number of copies elided");

namespace {
  enum SpillerName { simple, local };
}

static cl::opt<SpillerName>
SpillerOpt("spiller",
           cl::desc("Spiller to use: (default: local)"),
           cl::Prefix,
           cl::values(clEnumVal(simple, "simple spiller"),
                      clEnumVal(local,  "local spiller"),
                      clEnumValEnd),
           cl::init(local));

// ****************************** //
// Simple Spiller Implementation  //
// ****************************** //

Spiller::~Spiller() {}

bool SimpleSpiller::runOnMachineFunction(MachineFunction &MF, VirtRegMap &VRM) {
  DOUT << "********** REWRITE MACHINE CODE **********\n";
  DOUT << "********** Function: " << MF.getFunction()->getName() << '\n';
  const TargetMachine &TM = MF.getTarget();
  const TargetInstrInfo &TII = *TM.getInstrInfo();
  const TargetRegisterInfo &TRI = *TM.getRegisterInfo();


  // LoadedRegs - Keep track of which vregs are loaded, so that we only load
  // each vreg once (in the case where a spilled vreg is used by multiple
  // operands).  This is always smaller than the number of operands to the
  // current machine instr, so it should be small.
  std::vector<unsigned> LoadedRegs;

  for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
       MBBI != E; ++MBBI) {
    DOUT << MBBI->getBasicBlock()->getName() << ":\n";
    MachineBasicBlock &MBB = *MBBI;
    for (MachineBasicBlock::iterator MII = MBB.begin(), E = MBB.end();
         MII != E; ++MII) {
      MachineInstr &MI = *MII;
      for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
        MachineOperand &MO = MI.getOperand(i);
        if (MO.isReg() && MO.getReg()) {
          if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
            unsigned VirtReg = MO.getReg();
            unsigned SubIdx = MO.getSubReg();
            unsigned PhysReg = VRM.getPhys(VirtReg);
            unsigned RReg = SubIdx ? TRI.getSubReg(PhysReg, SubIdx) : PhysReg;
            if (!VRM.isAssignedReg(VirtReg)) {
              int StackSlot = VRM.getStackSlot(VirtReg);
              const TargetRegisterClass* RC = 
                                           MF.getRegInfo().getRegClass(VirtReg);
              
              if (MO.isUse() &&
                  std::find(LoadedRegs.begin(), LoadedRegs.end(), VirtReg)
                           == LoadedRegs.end()) {
                TII.loadRegFromStackSlot(MBB, &MI, PhysReg, StackSlot, RC);
                MachineInstr *LoadMI = prior(MII);
                VRM.addSpillSlotUse(StackSlot, LoadMI);
                LoadedRegs.push_back(VirtReg);
                ++NumLoads;
                DOUT << '\t' << *LoadMI;
              }

              if (MO.isDef()) {
                TII.storeRegToStackSlot(MBB, next(MII), PhysReg, true,   
                                        StackSlot, RC);
                MachineInstr *StoreMI = next(MII);
                VRM.addSpillSlotUse(StackSlot, StoreMI);
                ++NumStores;
              }
            }
            MF.getRegInfo().setPhysRegUsed(RReg);
            MI.getOperand(i).setReg(RReg);
          } else {
            MF.getRegInfo().setPhysRegUsed(MO.getReg());
          }
        }
      }

      DOUT << '\t' << MI;
      LoadedRegs.clear();
    }
  }
  return true;
}

// ****************** //
// Utility Functions  //
// ****************** //

/// InvalidateKill - A MI that defines the specified register is being deleted,
/// invalidate the register kill information.
static void InvalidateKill(unsigned Reg, BitVector &RegKills,
                           std::vector<MachineOperand*> &KillOps) {
  if (RegKills[Reg]) {
    KillOps[Reg]->setIsKill(false);
    KillOps[Reg] = NULL;
    RegKills.reset(Reg);
  }
}

/// findSinglePredSuccessor - Return via reference a vector of machine basic
/// blocks each of which is a successor of the specified BB and has no other
/// predecessor.
static void findSinglePredSuccessor(MachineBasicBlock *MBB,
                                   SmallVectorImpl<MachineBasicBlock *> &Succs) {
  for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
         SE = MBB->succ_end(); SI != SE; ++SI) {
    MachineBasicBlock *SuccMBB = *SI;
    if (SuccMBB->pred_size() == 1)
      Succs.push_back(SuccMBB);
  }
}

/// InvalidateKills - MI is going to be deleted. If any of its operands are
/// marked kill, then invalidate the information.
static void InvalidateKills(MachineInstr &MI, BitVector &RegKills,
                            std::vector<MachineOperand*> &KillOps,
                            SmallVector<unsigned, 2> *KillRegs = NULL) {
  for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
    MachineOperand &MO = MI.getOperand(i);
    if (!MO.isReg() || !MO.isUse() || !MO.isKill())
      continue;
    unsigned Reg = MO.getReg();
    if (TargetRegisterInfo::isVirtualRegister(Reg))
      continue;
    if (KillRegs)
      KillRegs->push_back(Reg);
    assert(Reg < KillOps.size());
    if (KillOps[Reg] == &MO) {
      RegKills.reset(Reg);
      KillOps[Reg] = NULL;
    }
  }
}

/// InvalidateRegDef - If the def operand of the specified def MI is now dead
/// (since it's spill instruction is removed), mark it isDead. Also checks if
/// the def MI has other definition operands that are not dead. Returns it by
/// reference.
static bool InvalidateRegDef(MachineBasicBlock::iterator I,
                             MachineInstr &NewDef, unsigned Reg,
                             bool &HasLiveDef) {
  // Due to remat, it's possible this reg isn't being reused. That is,
  // the def of this reg (by prev MI) is now dead.
  MachineInstr *DefMI = I;
  MachineOperand *DefOp = NULL;
  for (unsigned i = 0, e = DefMI->getNumOperands(); i != e; ++i) {
    MachineOperand &MO = DefMI->getOperand(i);
    if (MO.isReg() && MO.isDef()) {
      if (MO.getReg() == Reg)
        DefOp = &MO;
      else if (!MO.isDead())
        HasLiveDef = true;
    }
  }
  if (!DefOp)
    return false;

  bool FoundUse = false, Done = false;
  MachineBasicBlock::iterator E = &NewDef;
  ++I; ++E;
  for (; !Done && I != E; ++I) {
    MachineInstr *NMI = I;
    for (unsigned j = 0, ee = NMI->getNumOperands(); j != ee; ++j) {
      MachineOperand &MO = NMI->getOperand(j);
      if (!MO.isReg() || MO.getReg() != Reg)
        continue;
      if (MO.isUse())
        FoundUse = true;
      Done = true; // Stop after scanning all the operands of this MI.