lib/CodeGen/LiveIntervalAnalysis.cpp

//===-- LiveIntervalAnalysis.cpp - Live Interval Analysis -----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LiveInterval analysis pass which is used
// by the Linear Scan Register allocator. This pass linearizes the
// basic blocks of the function in DFS order and uses the
// LiveVariables pass to conservatively compute live intervals for
// each virtual and physical register.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "liveintervals"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "VirtRegMap.h"
#include "llvm/Value.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/ProcessImplicitDefs.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
#include <limits>
#include <cmath>
using namespace llvm;

// Hidden options for help debugging.
static cl::opt<bool> DisableReMat("disable-rematerialization",
                                  cl::init(false), cl::Hidden);

STATISTIC(numIntervals , "Number of original intervals");

char LiveIntervals::ID = 0;
INITIALIZE_PASS_BEGIN(LiveIntervals, "liveintervals",
                "Live Interval Analysis", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveVariables)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_DEPENDENCY(PHIElimination)
INITIALIZE_PASS_DEPENDENCY(TwoAddressInstructionPass)
INITIALIZE_PASS_DEPENDENCY(ProcessImplicitDefs)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(LiveIntervals, "liveintervals",
                "Live Interval Analysis", false, false)

void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesCFG();
  AU.addRequired<AliasAnalysis>();
  AU.addPreserved<AliasAnalysis>();
  AU.addRequired<LiveVariables>();
  AU.addPreserved<LiveVariables>();
  AU.addRequired<MachineLoopInfo>();
  AU.addPreserved<MachineLoopInfo>();
  AU.addPreservedID(MachineDominatorsID);

  if (!StrongPHIElim) {
    AU.addPreservedID(PHIEliminationID);
    AU.addRequiredID(PHIEliminationID);
  }

  AU.addRequiredID(TwoAddressInstructionPassID);
  AU.addPreserved<ProcessImplicitDefs>();
  AU.addRequired<ProcessImplicitDefs>();
  AU.addPreserved<SlotIndexes>();
  AU.addRequiredTransitive<SlotIndexes>();
  MachineFunctionPass::getAnalysisUsage(AU);
}

void LiveIntervals::releaseMemory() {
  // Free the live intervals themselves.
  for (DenseMap<unsigned, LiveInterval*>::iterator I = r2iMap_.begin(),
       E = r2iMap_.end(); I != E; ++I)
    delete I->second;

  r2iMap_.clear();

  // Release VNInfo memory regions, VNInfo objects don't need to be dtor'd.
  VNInfoAllocator.Reset();
  while (!CloneMIs.empty()) {
    MachineInstr *MI = CloneMIs.back();
    CloneMIs.pop_back();
    mf_->DeleteMachineInstr(MI);
  }
}

/// runOnMachineFunction - Register allocate the whole function
///
bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
  mf_ = &fn;
  mri_ = &mf_->getRegInfo();
  tm_ = &fn.getTarget();
  tri_ = tm_->getRegisterInfo();
  tii_ = tm_->getInstrInfo();
  aa_ = &getAnalysis<AliasAnalysis>();
  lv_ = &getAnalysis<LiveVariables>();
  indexes_ = &getAnalysis<SlotIndexes>();
  allocatableRegs_ = tri_->getAllocatableSet(fn);

  computeIntervals();

  numIntervals += getNumIntervals();

  DEBUG(dump());
  return true;
}

/// print - Implement the dump method.
void LiveIntervals::print(raw_ostream &OS, const Module* ) const {
  OS << "********** INTERVALS **********\n";
  for (const_iterator I = begin(), E = end(); I != E; ++I) {
    I->second->print(OS, tri_);
    OS << "\n";
  }

  printInstrs(OS);
}

void LiveIntervals::printInstrs(raw_ostream &OS) const {
  OS << "********** MACHINEINSTRS **********\n";
  mf_->print(OS, indexes_);
}

void LiveIntervals::dumpInstrs() const {
  printInstrs(dbgs());
}

static
bool MultipleDefsBySameMI(const MachineInstr &MI, unsigned MOIdx) {
  unsigned Reg = MI.getOperand(MOIdx).getReg();
  for (unsigned i = MOIdx+1, e = MI.getNumOperands(); i < e; ++i) {
    const MachineOperand &MO = MI.getOperand(i);
    if (!MO.isReg())
      continue;
    if (MO.getReg() == Reg && MO.isDef()) {
      assert(MI.getOperand(MOIdx).getSubReg() != MO.getSubReg() &&
             MI.getOperand(MOIdx).getSubReg() &&
             (MO.getSubReg() || MO.isImplicit()));
      return true;
    }
  }
  return false;
}

/// isPartialRedef - Return true if the specified def at the specific index is
/// partially re-defining the specified live interval. A common case of this is
/// a definition of the sub-register.
bool LiveIntervals::isPartialRedef(SlotIndex MIIdx, MachineOperand &MO,
                                   LiveInterval &interval) {
  if (!MO.getSubReg() || MO.isEarlyClobber())
    return false;

  SlotIndex RedefIndex = MIIdx.getRegSlot();
  const LiveRange *OldLR =
    interval.getLiveRangeContaining(RedefIndex.getRegSlot(true));
  MachineInstr *DefMI = getInstructionFromIndex(OldLR->valno->def);
  if (DefMI != 0) {
    return DefMI->findRegisterDefOperandIdx(interval.reg) != -1;
  }
  return false;
}

void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
                                             MachineBasicBlock::iterator mi,
                                             SlotIndex MIIdx,
                                             MachineOperand& MO,
                                             unsigned MOIdx,
                                             LiveInterval &interval) {
  DEBUG(dbgs() << "\t\tregister: " << PrintReg(interval.reg, tri_));

  // Virtual registers may be defined multiple times (due to phi
  // elimination and 2-addr elimination).  Much of what we do only has to be
  // done once for the vreg.  We use an empty interval to detect the first
  // time we see a vreg.
  LiveVariables::VarInfo& vi = lv_->getVarInfo(interval.reg);
  if (interval.empty()) {
    // Get the Idx of the defining instructions.
    SlotIndex defIndex = MIIdx.getRegSlot();
    // Earlyclobbers move back one, so that they overlap the live range
    // of inputs.
    if (MO.isEarlyClobber())
      defIndex = MIIdx.getRegSlot(true);

    // Make sure the first definition is not a partial redefinition. Add an
    // <imp-def> of the full register.
    // FIXME: LiveIntervals shouldn't modify the code like this.  Whoever
    // created the machine instruction should annotate it with <undef> flags
    // as needed.  Then we can simply assert here.  The REG_SEQUENCE lowering
    // is the main suspect.
    if (MO.getSubReg()) {
      mi->addRegisterDefined(interval.reg);
      // Mark all defs of interval.reg on this instruction as reading <undef>.
      for (unsigned i = MOIdx, e = mi->getNumOperands(); i != e; ++i) {
        MachineOperand &MO2 = mi->getOperand(i);
        if (MO2.isReg() && MO2.getReg() == interval.reg && MO2.getSubReg())
          MO2.setIsUndef();
      }
    }

    MachineInstr *CopyMI = NULL;
    if (mi->isCopyLike()) {
      CopyMI = mi;
    }

    VNInfo *ValNo = interval.getNextValue(defIndex, CopyMI, VNInfoAllocator);
    assert(ValNo->id == 0 && "First value in interval is not 0?");

    // Loop over all of the blocks that the vreg is defined in.  There are
    // two cases we have to handle here.  The most common case is a vreg
    // whose lifetime is contained within a basic block.  In this case there
    // will be a single kill, in MBB, which comes after the definition.
    if (vi.Kills.size() == 1 && vi.Kills[0]->getParent() == mbb) {
      // FIXME: what about dead vars?
      SlotIndex killIdx;
      if (vi.Kills[0] != mi)
        killIdx = getInstructionIndex(vi.Kills[0]).getRegSlot();
      else
        killIdx = defIndex.getDeadSlot();

      // If the kill happens after the definition, we have an intra-block
      // live range.
      if (killIdx > defIndex) {
        assert(vi.AliveBlocks.empty() &&
               "Shouldn't be alive across any blocks!");
        LiveRange LR(defIndex, killIdx, ValNo);
        interval.addRange(LR);
        DEBUG(dbgs() << " +" << LR << "\n");
        return;
      }
    }

    // The other case we handle is when a virtual register lives to the end
    // of the defining block, potentially live across some blocks, then is
    // live into some number of blocks, but gets killed.  Start by adding a
    // range that goes from this definition to the end of the defining block.
    LiveRange NewLR(defIndex, getMBBEndIdx(mbb), ValNo);
    DEBUG(dbgs() << " +" << NewLR);
    interval.addRange(NewLR);

    bool PHIJoin = lv_->isPHIJoin(interval.reg);

    if (PHIJoin) {
      // A phi join register is killed at the end of the MBB and revived as a new
      // valno in the killing blocks.
      assert(vi.AliveBlocks.empty() && "Phi join can't pass through blocks");
      DEBUG(dbgs() << " phi-join");
      ValNo->setHasPHIKill(true);
    } else {
      // Iterate over all of the blocks that the variable is completely
      // live in, adding [insrtIndex(begin), instrIndex(end)+4) to the
      // live interval.
      for (SparseBitVector<>::iterator I = vi.AliveBlocks.begin(),
               E = vi.AliveBlocks.end(); I != E; ++I) {
        MachineBasicBlock *aliveBlock = mf_->getBlockNumbered(*I);
        LiveRange LR(getMBBStartIdx(aliveBlock), getMBBEndIdx(aliveBlock), ValNo);
        interval.addRange(LR);
        DEBUG(dbgs() << " +" << LR);
      }
    }

    // Finally, this virtual register is live from the start of any killing
    // block to the 'use' slot of the killing instruction.
    for (unsigned i = 0, e = vi.Kills.size(); i != e; ++i) {
      MachineInstr *Kill = vi.Kills[i];
      SlotIndex Start = getMBBStartIdx(Kill->getParent());
      SlotIndex killIdx = getInstructionIndex(Kill).getRegSlot();

      // Create interval with one of a NEW value number.  Note that this value
      // number isn't actually defined by an instruction, weird huh? :)
      if (PHIJoin) {
        assert(getInstructionFromIndex(Start) == 0 &&
               "PHI def index points at actual instruction.");
        ValNo = interval.getNextValue(Start, 0, VNInfoAllocator);
        ValNo->setIsPHIDef(true);
      }
      LiveRange LR(Start, killIdx, ValNo);
      interval.addRange(LR);
      DEBUG(dbgs() << " +" << LR);
    }

  } else {
    if (MultipleDefsBySameMI(*mi, MOIdx))
      // Multiple defs of the same virtual register by the same instruction.
      // e.g. %reg1031:5<def>, %reg1031:6<def> = VLD1q16 %reg1024<kill>, ...
      // This is likely due to elimination of REG_SEQUENCE instructions. Return
      // here since there is nothing to do.
      return;

    // If this is the second time we see a virtual register definition, it
    // must be due to phi elimination or two addr elimination.  If this is
    // the result of two address elimination, then the vreg is one of the
    // def-and-use register operand.

    // It may also be partial redef like this:
    // 80  %reg1041:6<def> = VSHRNv4i16 %reg1034<kill>, 12, pred:14, pred:%reg0
    // 120 %reg1041:5<def> = VSHRNv4i16 %reg1039<kill>, 12, pred:14, pred:%reg0
    bool PartReDef = isPartialRedef(MIIdx, MO, interval);
    if (PartReDef || mi->isRegTiedToUseOperand(MOIdx)) {
      // If this is a two-address definition, then we have already processed
      // the live range.  The only problem is that we didn't realize there
      // are actually two values in the live interval.  Because of this we
      // need to take the LiveRegion that defines this register and split it
      // into two values.
      SlotIndex RedefIndex = MIIdx.getRegSlot();
      if (MO.isEarlyClobber())
        RedefIndex = MIIdx.getRegSlot(true);

      const LiveRange *OldLR =
        interval.getLiveRangeContaining(RedefIndex.getRegSlot(true));
      VNInfo *OldValNo = OldLR->valno;
      SlotIndex DefIndex = OldValNo->def.getRegSlot();

      // Delete the previous value, which should be short and continuous,
      // because the 2-addr copy must be in the same MBB as the redef.
      interval.removeRange(DefIndex, RedefIndex);

      // The new value number (#1) is defined by the instruction we claimed
      // defined value #0.
      VNInfo *ValNo = interval.createValueCopy(OldValNo, VNInfoAllocator);

      // Value#0 is now defined by the 2-addr instruction.
      OldValNo->def  = RedefIndex;
      OldValNo->setCopy(0);

      // A re-def may be a copy. e.g. %reg1030:6<def> = VMOVD %reg1026, ...
      if (PartReDef && mi->isCopyLike())
        OldValNo->setCopy(&*mi);

      // Add the new live interval which replaces the range for the input copy.
      LiveRange LR(DefIndex, RedefIndex, ValNo);
      DEBUG(dbgs() << " replace range with " << LR);
      interval.addRange(LR);

      // If this redefinition is dead, we need to add a dummy unit live
      // range covering the def slot.
      if (MO.isDead())
        interval.addRange(LiveRange(RedefIndex, RedefIndex.getDeadSlot(),
                                    OldValNo));

      DEBUG({
          dbgs() << " RESULT: ";
          interval.print(dbgs(), tri_);
        });
    } else if (lv_->isPHIJoin(interval.reg)) {
      // In the case of PHI elimination, each variable definition is only
      // live until the end of the block.  We've already taken care of the
      // rest of the live range.

      SlotIndex defIndex = MIIdx.getRegSlot();
      if (MO.isEarlyClobber())
        defIndex = MIIdx.getRegSlot(true);

      VNInfo *ValNo;
      MachineInstr *CopyMI = NULL;
      if (mi->isCopyLike())
        CopyMI = mi;
      ValNo = interval.getNextValue(defIndex, CopyMI, VNInfoAllocator);

      SlotIndex killIndex = getMBBEndIdx(mbb);
      LiveRange LR(defIndex, killIndex, ValNo);
      interval.addRange(LR);
      ValNo->setHasPHIKill(true);
      DEBUG(dbgs() << " phi-join +" << LR);
    } else {
      llvm_unreachable("Multiply defined register");
    }
  }

  DEBUG(dbgs() << '\n');
}

void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock *MBB,
                                              MachineBasicBlock::iterator mi,
                                              SlotIndex MIIdx,
                                              MachineOperand& MO,
                                              LiveInterval &interval,
                                              MachineInstr *CopyMI) {
  // A physical register cannot be live across basic block, so its
  // lifetime must end somewhere in its defining basic block.
  DEBUG(dbgs() << "\t\tregister: " << PrintReg(interval.reg, tri_));

  SlotIndex baseIndex = MIIdx;
  SlotIndex start = baseIndex.getRegSlot();
  // Earlyclobbers move back one.
  if (MO.isEarlyClobber())
    start = MIIdx.getRegSlot(true);
  SlotIndex end = start;

  // If it is not used after definition, it is considered dead at
  // the instruction defining it. Hence its interval is:
  // [defSlot(def), defSlot(def)+1)
  // For earlyclobbers, the defSlot was pushed back one; the extra
  // advance below compensates.
  if (MO.isDead()) {
    DEBUG(dbgs() << " dead");
    end = start.getDeadSlot();
    goto exit;
  }

  // If it is not dead on definition, it must be killed by a
  // subsequent instruction. Hence its interval is:
  // [defSlot(def), useSlot(kill)+1)
  baseIndex = baseIndex.getNextIndex();
  while (++mi != MBB->end()) {

    if (mi->isDebugValue())
      continue;
    if (getInstructionFromIndex(baseIndex) == 0)
      baseIndex = indexes_->getNextNonNullIndex(baseIndex);

    if (mi->killsRegister(interval.reg, tri_)) {
      DEBUG(dbgs() << " killed");
      end = baseIndex.getRegSlot();
      goto exit;
    } else {
      int DefIdx = mi->findRegisterDefOperandIdx(interval.reg,false,false,tri_);
      if (DefIdx != -1) {
        if (mi->isRegTiedToUseOperand(DefIdx)) {
          // Two-address instruction.
          end = baseIndex.getRegSlot();
        } else {
          // Another instruction redefines the register before it is ever read.
          // Then the register is essentially dead at the instruction that
          // defines it. Hence its interval is:
          // [defSlot(def), defSlot(def)+1)
          DEBUG(dbgs() << " dead");
          end = start.getDeadSlot();
        }
        goto exit;
      }
    }

    baseIndex = baseIndex.getNextIndex();
  }

  // The only case we should have a dead physreg here without a killing or
  // instruction where we know it's dead is if it is live-in to the function
  // and never used. Another possible case is the implicit use of the
  // physical register has been deleted by two-address pass.
  end = start.getDeadSlot();

exit:
  assert(start < end && "did not find end of interval?");

  // Already exists? Extend old live interval.
  VNInfo *ValNo = interval.getVNInfoAt(start);
  bool Extend = ValNo != 0;
  if (!Extend)
    ValNo = interval.getNextValue(start, CopyMI, VNInfoAllocator);
  if (Extend && MO.isEarlyClobber())
    ValNo->setHasRedefByEC(true);
  LiveRange LR(start, end, ValNo);
  interval.addRange(LR);
  DEBUG(dbgs() << " +" << LR << '\n');
}

void LiveIntervals::handleRegisterDef(MachineBasicBlock *MBB,
                                      MachineBasicBlock::iterator MI,
                                      SlotIndex MIIdx,
                                      MachineOperand& MO,
                                      unsigned MOIdx) {
  if (TargetRegisterInfo::isVirtualRegister(MO.getReg()))
    handleVirtualRegisterDef(MBB, MI, MIIdx, MO, MOIdx,
                             getOrCreateInterval(MO.getReg()));
  else {
    MachineInstr *CopyMI = NULL;
    if (MI->isCopyLike())
      CopyMI = MI;
    handlePhysicalRegisterDef(MBB, MI, MIIdx, MO,
                              getOrCreateInterval(MO.getReg()), CopyMI);
  }
}

void LiveIntervals::handleLiveInRegister(MachineBasicBlock *MBB,
                                         SlotIndex MIIdx,
                                         LiveInterval &interval, bool isAlias) {
  DEBUG(dbgs() << "\t\tlivein register: " << PrintReg(interval.reg, tri_));

  // Look for kills, if it reaches a def before it's killed, then it shouldn't
  // be considered a livein.
  MachineBasicBlock::iterator mi = MBB->begin();
  MachineBasicBlock::iterator E = MBB->end();
  // Skip over DBG_VALUE at the start of the MBB.
  if (mi != E && mi->isDebugValue()) {
    while (++mi != E && mi->isDebugValue())
      ;
    if (mi == E)
      // MBB is empty except for DBG_VALUE's.
      return;
  }

  SlotIndex baseIndex = MIIdx;
  SlotIndex start = baseIndex;
  if (getInstructionFromIndex(baseIndex) == 0)
    baseIndex = indexes_->getNextNonNullIndex(baseIndex);

  SlotIndex end = baseIndex;
  bool SeenDefUse = false;

  while (mi != E) {
    if (mi->killsRegister(interval.reg, tri_)) {
      DEBUG(dbgs() << " killed");
      end = baseIndex.getRegSlot();
      SeenDefUse = true;
      break;
    } else if (mi->definesRegister(interval.reg, tri_)) {
      // Another instruction redefines the register before it is ever read.
      // Then the register is essentially dead at the instruction that defines
      // it. Hence its interval is:
      // [defSlot(def), defSlot(def)+1)
      DEBUG(dbgs() << " dead");
      end = start.getDeadSlot();
      SeenDefUse = true;
      break;
    }

    while (++mi != E && mi->isDebugValue())
      // Skip over DBG_VALUE.
      ;
    if (mi != E)
      baseIndex = indexes_->getNextNonNullIndex(baseIndex);
  }

  // Live-in register might not be used at all.
  if (!SeenDefUse) {
    if (isAlias) {
      DEBUG(dbgs() << " dead");
      end = MIIdx.getDeadSlot();
    } else {
      DEBUG(dbgs() << " live through");
      end = getMBBEndIdx(MBB);
    }
  }

  SlotIndex defIdx = getMBBStartIdx(MBB);
  assert(getInstructionFromIndex(defIdx) == 0 &&
         "PHI def index points at actual instruction.");
  VNInfo *vni =
    interval.getNextValue(defIdx, 0, VNInfoAllocator);
  vni->setIsPHIDef(true);
  LiveRange LR(start, end, vni);

  interval.addRange(LR);
  DEBUG(dbgs() << " +" << LR << '\n');
}

/// computeIntervals - computes the live intervals for virtual
/// registers. for some ordering of the machine instructions [1,N] a
/// live interval is an interval [i, j) where 1 <= i <= j < N for
/// which a variable is live
void LiveIntervals::computeIntervals() {
  DEBUG(dbgs() << "********** COMPUTING LIVE INTERVALS **********\n"
               << "********** Function: "
               << ((Value*)mf_->getFunction())->getName() << '\n');

  SmallVector<unsigned, 8> UndefUses;
  for (MachineFunction::iterator MBBI = mf_->begin(), E = mf_->end();
       MBBI != E; ++MBBI) {
    MachineBasicBlock *MBB = MBBI;
    if (MBB->empty())
      continue;

    // Track the index of the current machine instr.
    SlotIndex MIIndex = getMBBStartIdx(MBB);
    DEBUG(dbgs() << "BB#" << MBB->getNumber()
          << ":\t\t# derived from " << MBB->getName() << "\n");

    // Create intervals for live-ins to this BB first.
    for (MachineBasicBlock::livein_iterator LI = MBB->livein_begin(),
           LE = MBB->livein_end(); LI != LE; ++LI) {
      handleLiveInRegister(MBB, MIIndex, getOrCreateInterval(*LI));
      // Multiple live-ins can alias the same register.
      for (const unsigned* AS = tri_->getSubRegisters(*LI); *AS; ++AS)
        if (!hasInterval(*AS))
          handleLiveInRegister(MBB, MIIndex, getOrCreateInterval(*AS),
                               true);
    }

    // Skip over empty initial indices.
    if (getInstructionFromIndex(MIIndex) == 0)
      MIIndex = indexes_->getNextNonNullIndex(MIIndex);

    for (MachineBasicBlock::iterator MI = MBB->begin(), miEnd = MBB->end();
         MI != miEnd; ++MI) {
      DEBUG(dbgs() << MIIndex << "\t" << *MI);
      if (MI->isDebugValue())
        continue;

      // Handle defs.
      for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
        MachineOperand &MO = MI->getOperand(i);
        if (!MO.isReg() || !MO.getReg())
          continue;

        // handle register defs - build intervals
        if (MO.isDef())
          handleRegisterDef(MBB, MI, MIIndex, MO, i);
        else if (MO.isUndef())
          UndefUses.push_back(MO.getReg());
      }

      // Move to the next instr slot.
      MIIndex = indexes_->getNextNonNullIndex(MIIndex);
    }
  }

  // Create empty intervals for registers defined by implicit_def's (except
  // for those implicit_def that define values which are liveout of their
  // blocks.
  for (unsigned i = 0, e = UndefUses.size(); i != e; ++i) {
    unsigned UndefReg = UndefUses[i];
    (void)getOrCreateInterval(UndefReg);
  }
}

LiveInterval* LiveIntervals::createInterval(unsigned reg) {
  float Weight = TargetRegisterInfo::isPhysicalRegister(reg) ? HUGE_VALF : 0.0F;
  return new LiveInterval(reg, Weight);
}

/// dupInterval - Duplicate a live interval. The caller is responsible for
/// managing the allocated memory.
LiveInterval* LiveIntervals::dupInterval(LiveInterval *li) {
  LiveInterval *NewLI = createInterval(li->reg);
  NewLI->Copy(*li, mri_, getVNInfoAllocator());
  return NewLI;
}

/// shrinkToUses - After removing some uses of a register, shrink its live
/// range to just the remaining uses. This method does not compute reaching
/// defs for new uses, and it doesn't remove dead defs.
bool LiveIntervals::shrinkToUses(LiveInterval *li,
                                 SmallVectorImpl<MachineInstr*> *dead) {
  DEBUG(dbgs() << "Shrink: " << *li << '\n');
  assert(TargetRegisterInfo::isVirtualRegister(li->reg)
         && "Can't only shrink physical registers");
  // Find all the values used, including PHI kills.
  SmallVector<std::pair<SlotIndex, VNInfo*>, 16> WorkList;

  // Blocks that have already been added to WorkList as live-out.
  SmallPtrSet<MachineBasicBlock*, 16> LiveOut;

  // Visit all instructions reading li->reg.
  for (MachineRegisterInfo::reg_iterator I = mri_->reg_begin(li->reg);
       MachineInstr *UseMI = I.skipInstruction();) {
    if (UseMI->isDebugValue() || !UseMI->readsVirtualRegister(li->reg))
      continue;
    SlotIndex Idx = getInstructionIndex(UseMI).getRegSlot(true);
    VNInfo *VNI = li->getVNInfoAt(Idx);
    if (!VNI) {
      // This shouldn't happen: readsVirtualRegister returns true, but there is
      // no live value. It is likely caused by a target getting <undef> flags
      // wrong.
      DEBUG(dbgs() << Idx << '\t' << *UseMI
                   << "Warning: Instr claims to read non-existent value in "
                    << *li << '\n');
      continue;
    }
    if (VNI->def == Idx) {
      // Special case: An early-clobber tied operand reads and writes the
      // register one slot early.
      Idx = Idx.getPrevSlot();
      VNI = li->getVNInfoAt(Idx);
      assert(VNI && "Early-clobber tied value not available");
    }
    WorkList.push_back(std::make_pair(Idx, VNI));
  }

  // Create a new live interval with only minimal live segments per def.
  LiveInterval NewLI(li->reg, 0);
  for (LiveInterval::vni_iterator I = li->vni_begin(), E = li->vni_end();
       I != E; ++I) {
    VNInfo *VNI = *I;
    if (VNI->isUnused())
      continue;
    NewLI.addRange(LiveRange(VNI->def, VNI->def.getNextSlot(), VNI));

    // A use tied to an early-clobber def ends at the load slot and isn't caught
    // above. Catch it here instead. This probably only ever happens for inline
    // assembly.
    if (VNI->def.isEarlyClobber())
      if (VNInfo *UVNI = li->getVNInfoBefore(VNI->def))
        WorkList.push_back(std::make_pair(VNI->def.getPrevSlot(), UVNI));
  }

  // Keep track of the PHIs that are in use.
  SmallPtrSet<VNInfo*, 8> UsedPHIs;

  // Extend intervals to reach all uses in WorkList.
  while (!WorkList.empty()) {
    SlotIndex Idx = WorkList.back().first;
    VNInfo *VNI = WorkList.back().second;
    WorkList.pop_back();
    const MachineBasicBlock *MBB = getMBBFromIndex(Idx);
    SlotIndex BlockStart = getMBBStartIdx(MBB);

    // Extend the live range for VNI to be live at Idx.
    if (VNInfo *ExtVNI = NewLI.extendInBlock(BlockStart, Idx.getNextSlot())) {
      (void)ExtVNI;
      assert(ExtVNI == VNI && "Unexpected existing value number");
      // Is this a PHIDef we haven't seen before?
      if (!VNI->isPHIDef() || VNI->def != BlockStart || !UsedPHIs.insert(VNI))
        continue;
      // The PHI is live, make sure the predecessors are live-out.
      for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
           PE = MBB->pred_end(); PI != PE; ++PI) {
        if (!LiveOut.insert(*PI))
          continue;
        SlotIndex Stop = getMBBEndIdx(*PI).getPrevSlot();
        // A predecessor is not required to have a live-out value for a PHI.
        if (VNInfo *PVNI = li->getVNInfoAt(Stop))
          WorkList.push_back(std::make_pair(Stop, PVNI));
      }
      continue;
    }

    // VNI is live-in to MBB.
    DEBUG(dbgs() << " live-in at " << BlockStart << '\n');
    NewLI.addRange(LiveRange(BlockStart, Idx.getNextSlot(), VNI));

    // Make sure VNI is live-out from the predecessors.
    for (MachineBasicBlock::const_pred_iterator PI = MBB->pred_begin(),
         PE = MBB->pred_end(); PI != PE; ++PI) {
      if (!LiveOut.insert(*PI))
        continue;
      SlotIndex Stop = getMBBEndIdx(*PI).getPrevSlot();
      assert(li->getVNInfoAt(Stop) == VNI && "Wrong value out of predecessor");
      WorkList.push_back(std::make_pair(Stop, VNI));
    }
  }

  // Handle dead values.
  bool CanSeparate = false;
  for (LiveInterval::vni_iterator I = li->vni_begin(), E = li->vni_end();
       I != E; ++I) {
    VNInfo *VNI = *I;
    if (VNI->isUnused())
      continue;
    LiveInterval::iterator LII = NewLI.FindLiveRangeContaining(VNI->def);
    assert(LII != NewLI.end() && "Missing live range for PHI");
    if (LII->end != VNI->def.getNextSlot())
      continue;
    if (VNI->isPHIDef()) {
      // This is a dead PHI. Remove it.
      VNI->setIsUnused(true);
      NewLI.removeRange(*LII);
      DEBUG(dbgs() << "Dead PHI at " << VNI->def << " may separate interval\n");
      CanSeparate = true;
    } else {
      // This is a dead def. Make sure the instruction knows.
      MachineInstr *MI = getInstructionFromIndex(VNI->def);
      assert(MI && "No instruction defining live value");
      MI->addRegisterDead(li->reg, tri_);
      if (dead && MI->allDefsAreDead()) {
        DEBUG(dbgs() << "All defs dead: " << VNI->def << '\t' << *MI);
        dead->push_back(MI);
      }
    }
  }

  // Move the trimmed ranges back.
  li->ranges.swap(NewLI.ranges);
  DEBUG(dbgs() << "Shrunk: " << *li << '\n');
  return CanSeparate;
}


//===----------------------------------------------------------------------===//
// Register allocator hooks.
//

MachineBasicBlock::iterator
LiveIntervals::getLastSplitPoint(const LiveInterval &li,
                                 MachineBasicBlock *mbb) const {
  const MachineBasicBlock *lpad = mbb->getLandingPadSuccessor();

  // If li is not live into a landing pad, we can insert spill code before the
  // first terminator.
  if (!lpad || !isLiveInToMBB(li, lpad))
    return mbb->getFirstTerminator();

  // When there is a landing pad, spill code must go before the call instruction
  // that can throw.
  MachineBasicBlock::iterator I = mbb->end(), B = mbb->begin();
  while (I != B) {
    --I;
    if (I->getDesc().isCall())
      return I;
  }
  // The block contains no calls that can throw, so use the first terminator.
  return mbb->getFirstTerminator();
}

void LiveIntervals::addKillFlags() {
  for (iterator I = begin(), E = end(); I != E; ++I) {
    unsigned Reg = I->first;
    if (TargetRegisterInfo::isPhysicalRegister(Reg))
      continue;
    if (mri_->reg_nodbg_empty(Reg))
      continue;
    LiveInterval *LI = I->second;

    // Every instruction that kills Reg corresponds to a live range end point.
    for (LiveInterval::iterator RI = LI->begin(), RE = LI->end(); RI != RE;
         ++RI) {
      // A block index indicates an MBB edge.
      if (RI->end.isBlock())
        continue;
      MachineInstr *MI = getInstructionFromIndex(RI->end);
      if (!MI)
        continue;
      MI->addRegisterKilled(Reg, NULL);
    }
  }
}

/// getReMatImplicitUse - If the remat definition MI has one (for now, we only
/// allow one) virtual register operand, then its uses are implicitly using
/// the register. Returns the virtual register.
unsigned LiveIntervals::getReMatImplicitUse(const LiveInterval &li,
                                            MachineInstr *MI) const {
  unsigned RegOp = 0;
  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
    MachineOperand &MO = MI->getOperand(i);
    if (!MO.isReg() || !MO.isUse())
      continue;
    unsigned Reg = MO.getReg();
    if (Reg == 0 || Reg == li.reg)
      continue;

    if (TargetRegisterInfo::isPhysicalRegister(Reg) &&
        !allocatableRegs_[Reg])
      continue;
    // FIXME: For now, only remat MI with at most one register operand.
    assert(!RegOp &&
           "Can't rematerialize instruction with multiple register operand!");
    RegOp = MO.getReg();
#ifndef NDEBUG
    break;
#endif
  }
  return RegOp;
}

/// isValNoAvailableAt - Return true if the val# of the specified interval
/// which reaches the given instruction also reaches the specified use index.
bool LiveIntervals::isValNoAvailableAt(const LiveInterval &li, MachineInstr *MI,
                                       SlotIndex UseIdx) const {
  VNInfo *UValNo = li.getVNInfoAt(UseIdx);
  return UValNo && UValNo == li.getVNInfoAt(getInstructionIndex(MI));
}

/// isReMaterializable - Returns true if the definition MI of the specified
/// val# of the specified interval is re-materializable.
bool
LiveIntervals::isReMaterializable(const LiveInterval &li,
                                  const VNInfo *ValNo, MachineInstr *MI,
                                  const SmallVectorImpl<LiveInterval*> *SpillIs,
                                  bool &isLoad) {
  if (DisableReMat)
    return false;

  if (!tii_->isTriviallyReMaterializable(MI, aa_))
    return false;

  // Target-specific code can mark an instruction as being rematerializable
  // if it has one virtual reg use, though it had better be something like
  // a PIC base register which is likely to be live everywhere.
  unsigned ImpUse = getReMatImplicitUse(li, MI);
  if (ImpUse) {
    const LiveInterval &ImpLi = getInterval(ImpUse);
    for (MachineRegisterInfo::use_nodbg_iterator
           ri = mri_->use_nodbg_begin(li.reg), re = mri_->use_nodbg_end();
         ri != re; ++ri) {
      MachineInstr *UseMI = &*ri;
      SlotIndex UseIdx = getInstructionIndex(UseMI);
      if (li.getVNInfoAt(UseIdx) != ValNo)
        continue;
      if (!isValNoAvailableAt(ImpLi, MI, UseIdx))
        return false;
    }

    // If a register operand of the re-materialized instruction is going to
    // be spilled next, then it's not legal to re-materialize this instruction.
    if (SpillIs)
      for (unsigned i = 0, e = SpillIs->size(); i != e; ++i)
        if (ImpUse == (*SpillIs)[i]->reg)
          return false;
  }
  return true;
}

/// isReMaterializable - Returns true if every definition of MI of every
/// val# of the specified interval is re-materializable.
bool
LiveIntervals::isReMaterializable(const LiveInterval &li,
                                  const SmallVectorImpl<LiveInterval*> *SpillIs,
                                  bool &isLoad) {
  isLoad = false;
  for (LiveInterval::const_vni_iterator i = li.vni_begin(), e = li.vni_end();
       i != e; ++i) {
    const VNInfo *VNI = *i;
    if (VNI->isUnused())
      continue; // Dead val#.
    // Is the def for the val# rematerializable?
    MachineInstr *ReMatDefMI = getInstructionFromIndex(VNI->def);
    if (!ReMatDefMI)
      return false;
    bool DefIsLoad = false;
    if (!ReMatDefMI ||
        !isReMaterializable(li, VNI, ReMatDefMI, SpillIs, DefIsLoad))
      return false;
    isLoad |= DefIsLoad;
  }
  return true;
}

bool LiveIntervals::intervalIsInOneMBB(const LiveInterval &li) const {
  LiveInterval::Ranges::const_iterator itr = li.ranges.begin();

  MachineBasicBlock *mbb =  indexes_->getMBBCoveringRange(itr->start, itr->end);

  if (mbb == 0)
    return false;

  for (++itr; itr != li.ranges.end(); ++itr) {
    MachineBasicBlock *mbb2 =
      indexes_->getMBBCoveringRange(itr->start, itr->end);

    if (mbb2 != mbb)
      return false;
  }

  return true;
}

float
LiveIntervals::getSpillWeight(bool isDef, bool isUse, unsigned loopDepth) {
  // Limit the loop depth ridiculousness.
  if (loopDepth > 200)
    loopDepth = 200;

  // The loop depth is used to roughly estimate the number of times the
  // instruction is executed. Something like 10^d is simple, but will quickly
  // overflow a float. This expression behaves like 10^d for small d, but is
  // more tempered for large d. At d=200 we get 6.7e33 which leaves a bit of
  // headroom before overflow.
  // By the way, powf() might be unavailable here. For consistency,
  // We may take pow(double,double).
  float lc = std::pow(1 + (100.0 / (loopDepth + 10)), (double)loopDepth);

  return (isDef + isUse) * lc;
}

LiveRange LiveIntervals::addLiveRangeToEndOfBlock(unsigned reg,
                                                  MachineInstr* startInst) {
  LiveInterval& Interval = getOrCreateInterval(reg);
  VNInfo* VN = Interval.getNextValue(
    SlotIndex(getInstructionIndex(startInst).getRegSlot()),
    startInst, getVNInfoAllocator());
  VN->setHasPHIKill(true);
  LiveRange LR(
     SlotIndex(getInstructionIndex(startInst).getRegSlot()),
     getMBBEndIdx(startInst->getParent()), VN);
  Interval.addRange(LR);

  return LR;
}