MachineScheduler.cpp

//===- MachineScheduler.cpp - Machine Instruction Scheduler ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// MachineScheduler schedules machine instructions after phi elimination. It
// preserves LiveIntervals so it can be invoked before register allocation.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "misched"

#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineScheduler.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/ScheduleDAGILP.h"
#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
#include "llvm/Analysis/AliasAnalysis.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/OwningPtr.h"
#include "llvm/ADT/PriorityQueue.h"

#include <queue>

using namespace llvm;

namespace llvm {
cl::opt<bool> ForceTopDown("misched-topdown", cl::Hidden,
                           cl::desc("Force top-down list scheduling"));
cl::opt<bool> ForceBottomUp("misched-bottomup", cl::Hidden,
                            cl::desc("Force bottom-up list scheduling"));
}

#ifndef NDEBUG
static cl::opt<bool> ViewMISchedDAGs("view-misched-dags", cl::Hidden,
  cl::desc("Pop up a window to show MISched dags after they are processed"));

static cl::opt<unsigned> MISchedCutoff("misched-cutoff", cl::Hidden,
  cl::desc("Stop scheduling after N instructions"), cl::init(~0U));
#else
static bool ViewMISchedDAGs = false;
#endif // NDEBUG

// Threshold to very roughly model an out-of-order processor's instruction
// buffers. If the actual value of this threshold matters much in practice, then
// it can be specified by the machine model. For now, it's an experimental
// tuning knob to determine when and if it matters.
static cl::opt<unsigned> ILPWindow("ilp-window", cl::Hidden,
  cl::desc("Allow expected latency to exceed the critical path by N cycles "
           "before attempting to balance ILP"),
  cl::init(10U));

// Experimental heuristics
static cl::opt<bool> EnableLoadCluster("misched-cluster", cl::Hidden,
  cl::desc("Enable load clustering."));

//===----------------------------------------------------------------------===//
// Machine Instruction Scheduling Pass and Registry
//===----------------------------------------------------------------------===//

MachineSchedContext::MachineSchedContext():
    MF(0), MLI(0), MDT(0), PassConfig(0), AA(0), LIS(0) {
  RegClassInfo = new RegisterClassInfo();
}

MachineSchedContext::~MachineSchedContext() {
  delete RegClassInfo;
}

namespace {
/// MachineScheduler runs after coalescing and before register allocation.
class MachineScheduler : public MachineSchedContext,
                         public MachineFunctionPass {
public:
  MachineScheduler();

  virtual void getAnalysisUsage(AnalysisUsage &AU) const;

  virtual void releaseMemory() {}

  virtual bool runOnMachineFunction(MachineFunction&);

  virtual void print(raw_ostream &O, const Module* = 0) const;

  static char ID; // Class identification, replacement for typeinfo
};
} // namespace

char MachineScheduler::ID = 0;

char &llvm::MachineSchedulerID = MachineScheduler::ID;

INITIALIZE_PASS_BEGIN(MachineScheduler, "misched",
                      "Machine Instruction Scheduler", false, false)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(MachineScheduler, "misched",
                    "Machine Instruction Scheduler", false, false)

MachineScheduler::MachineScheduler()
: MachineFunctionPass(ID) {
  initializeMachineSchedulerPass(*PassRegistry::getPassRegistry());
}

void MachineScheduler::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesCFG();
  AU.addRequiredID(MachineDominatorsID);
  AU.addRequired<MachineLoopInfo>();
  AU.addRequired<AliasAnalysis>();
  AU.addRequired<TargetPassConfig>();
  AU.addRequired<SlotIndexes>();
  AU.addPreserved<SlotIndexes>();
  AU.addRequired<LiveIntervals>();
  AU.addPreserved<LiveIntervals>();
  MachineFunctionPass::getAnalysisUsage(AU);
}

MachinePassRegistry MachineSchedRegistry::Registry;

/// A dummy default scheduler factory indicates whether the scheduler
/// is overridden on the command line.
static ScheduleDAGInstrs *useDefaultMachineSched(MachineSchedContext *C) {
  return 0;
}

/// MachineSchedOpt allows command line selection of the scheduler.
static cl::opt<MachineSchedRegistry::ScheduleDAGCtor, false,
               RegisterPassParser<MachineSchedRegistry> >
MachineSchedOpt("misched",
                cl::init(&useDefaultMachineSched), cl::Hidden,
                cl::desc("Machine instruction scheduler to use"));

static MachineSchedRegistry
DefaultSchedRegistry("default", "Use the target's default scheduler choice.",
                     useDefaultMachineSched);

/// Forward declare the standard machine scheduler. This will be used as the
/// default scheduler if the target does not set a default.
static ScheduleDAGInstrs *createConvergingSched(MachineSchedContext *C);


/// Decrement this iterator until reaching the top or a non-debug instr.
static MachineBasicBlock::iterator
priorNonDebug(MachineBasicBlock::iterator I, MachineBasicBlock::iterator Beg) {
  assert(I != Beg && "reached the top of the region, cannot decrement");
  while (--I != Beg) {
    if (!I->isDebugValue())
      break;
  }
  return I;
}

/// If this iterator is a debug value, increment until reaching the End or a
/// non-debug instruction.
static MachineBasicBlock::iterator
nextIfDebug(MachineBasicBlock::iterator I, MachineBasicBlock::iterator End) {
  for(; I != End; ++I) {
    if (!I->isDebugValue())
      break;
  }
  return I;
}

/// Top-level MachineScheduler pass driver.
///
/// Visit blocks in function order. Divide each block into scheduling regions
/// and visit them bottom-up. Visiting regions bottom-up is not required, but is
/// consistent with the DAG builder, which traverses the interior of the
/// scheduling regions bottom-up.
///
/// This design avoids exposing scheduling boundaries to the DAG builder,
/// simplifying the DAG builder's support for "special" target instructions.
/// At the same time the design allows target schedulers to operate across
/// scheduling boundaries, for example to bundle the boudary instructions
/// without reordering them. This creates complexity, because the target
/// scheduler must update the RegionBegin and RegionEnd positions cached by
/// ScheduleDAGInstrs whenever adding or removing instructions. A much simpler
/// design would be to split blocks at scheduling boundaries, but LLVM has a
/// general bias against block splitting purely for implementation simplicity.
bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
  DEBUG(dbgs() << "Before MISsched:\n"; mf.print(dbgs()));

  // Initialize the context of the pass.
  MF = &mf;
  MLI = &getAnalysis<MachineLoopInfo>();
  MDT = &getAnalysis<MachineDominatorTree>();
  PassConfig = &getAnalysis<TargetPassConfig>();
  AA = &getAnalysis<AliasAnalysis>();

  LIS = &getAnalysis<LiveIntervals>();
  const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();

  RegClassInfo->runOnMachineFunction(*MF);

  // Select the scheduler, or set the default.
  MachineSchedRegistry::ScheduleDAGCtor Ctor = MachineSchedOpt;
  if (Ctor == useDefaultMachineSched) {
    // Get the default scheduler set by the target.
    Ctor = MachineSchedRegistry::getDefault();
    if (!Ctor) {
      Ctor = createConvergingSched;
      MachineSchedRegistry::setDefault(Ctor);
    }
  }
  // Instantiate the selected scheduler.
  OwningPtr<ScheduleDAGInstrs> Scheduler(Ctor(this));

  // Visit all machine basic blocks.
  //
  // TODO: Visit blocks in global postorder or postorder within the bottom-up
  // loop tree. Then we can optionally compute global RegPressure.
  for (MachineFunction::iterator MBB = MF->begin(), MBBEnd = MF->end();
       MBB != MBBEnd; ++MBB) {

    Scheduler->startBlock(MBB);

    // Break the block into scheduling regions [I, RegionEnd), and schedule each
    // region as soon as it is discovered. RegionEnd points the scheduling
    // boundary at the bottom of the region. The DAG does not include RegionEnd,
    // but the region does (i.e. the next RegionEnd is above the previous
    // RegionBegin). If the current block has no terminator then RegionEnd ==
    // MBB->end() for the bottom region.
    //
    // The Scheduler may insert instructions during either schedule() or
    // exitRegion(), even for empty regions. So the local iterators 'I' and
    // 'RegionEnd' are invalid across these calls.
    unsigned RemainingInstrs = MBB->size();
    for(MachineBasicBlock::iterator RegionEnd = MBB->end();
        RegionEnd != MBB->begin(); RegionEnd = Scheduler->begin()) {

      // Avoid decrementing RegionEnd for blocks with no terminator.
      if (RegionEnd != MBB->end()
          || TII->isSchedulingBoundary(llvm::prior(RegionEnd), MBB, *MF)) {
        --RegionEnd;
        // Count the boundary instruction.
        --RemainingInstrs;
      }

      // The next region starts above the previous region. Look backward in the
      // instruction stream until we find the nearest boundary.
      MachineBasicBlock::iterator I = RegionEnd;
      for(;I != MBB->begin(); --I, --RemainingInstrs) {
        if (TII->isSchedulingBoundary(llvm::prior(I), MBB, *MF))
          break;
      }
      // Notify the scheduler of the region, even if we may skip scheduling
      // it. Perhaps it still needs to be bundled.
      Scheduler->enterRegion(MBB, I, RegionEnd, RemainingInstrs);

      // Skip empty scheduling regions (0 or 1 schedulable instructions).
      if (I == RegionEnd || I == llvm::prior(RegionEnd)) {
        // Close the current region. Bundle the terminator if needed.
        // This invalidates 'RegionEnd' and 'I'.
        Scheduler->exitRegion();
        continue;
      }
      DEBUG(dbgs() << "********** MI Scheduling **********\n");
      DEBUG(dbgs() << MF->getName()
            << ":BB#" << MBB->getNumber() << "\n  From: " << *I << "    To: ";
            if (RegionEnd != MBB->end()) dbgs() << *RegionEnd;
            else dbgs() << "End";
            dbgs() << " Remaining: " << RemainingInstrs << "\n");

      // Schedule a region: possibly reorder instructions.
      // This invalidates 'RegionEnd' and 'I'.
      Scheduler->schedule();

      // Close the current region.
      Scheduler->exitRegion();

      // Scheduling has invalidated the current iterator 'I'. Ask the
      // scheduler for the top of it's scheduled region.
      RegionEnd = Scheduler->begin();
    }
    assert(RemainingInstrs == 0 && "Instruction count mismatch!");
    Scheduler->finishBlock();
  }
  Scheduler->finalizeSchedule();
  DEBUG(LIS->print(dbgs()));
  return true;
}

void MachineScheduler::print(raw_ostream &O, const Module* m) const {
  // unimplemented
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void ReadyQueue::dump() {
  dbgs() << Name << ": ";
  for (unsigned i = 0, e = Queue.size(); i < e; ++i)
    dbgs() << Queue[i]->NodeNum << " ";
  dbgs() << "\n";
}
#endif

//===----------------------------------------------------------------------===//
// ScheduleDAGMI - Base class for MachineInstr scheduling with LiveIntervals
// preservation.
//===----------------------------------------------------------------------===//

bool ScheduleDAGMI::addEdge(SUnit *SuccSU, const SDep &PredDep) {
  // Do not use WillCreateCycle, it assumes SD scheduling.
  // If Pred is reachable from Succ, then the edge creates a cycle.
  if (Topo.IsReachable(PredDep.getSUnit(), SuccSU))
    return false;
  Topo.AddPred(SuccSU, PredDep.getSUnit());
  SuccSU->addPred(PredDep, /*Required=*/!PredDep.isArtificial());
  // Return true regardless of whether a new edge needed to be inserted.
  return true;
}

/// ReleaseSucc - Decrement the NumPredsLeft count of a successor. When
/// NumPredsLeft reaches zero, release the successor node.
///
/// FIXME: Adjust SuccSU height based on MinLatency.
void ScheduleDAGMI::releaseSucc(SUnit *SU, SDep *SuccEdge) {
  SUnit *SuccSU = SuccEdge->getSUnit();

  if (SuccEdge->isWeak()) {
    --SuccSU->WeakPredsLeft;
    if (SuccEdge->isCluster())
      NextClusterSucc = SuccSU;
    return;
  }
#ifndef NDEBUG
  if (SuccSU->NumPredsLeft == 0) {
    dbgs() << "*** Scheduling failed! ***\n";
    SuccSU->dump(this);
    dbgs() << " has been released too many times!\n";
    llvm_unreachable(0);
  }
#endif
  --SuccSU->NumPredsLeft;
  if (SuccSU->NumPredsLeft == 0 && SuccSU != &ExitSU)
    SchedImpl->releaseTopNode(SuccSU);
}

/// releaseSuccessors - Call releaseSucc on each of SU's successors.
void ScheduleDAGMI::releaseSuccessors(SUnit *SU) {
  for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
       I != E; ++I) {
    releaseSucc(SU, &*I);
  }
}

/// ReleasePred - Decrement the NumSuccsLeft count of a predecessor. When
/// NumSuccsLeft reaches zero, release the predecessor node.
///
/// FIXME: Adjust PredSU height based on MinLatency.
void ScheduleDAGMI::releasePred(SUnit *SU, SDep *PredEdge) {
  SUnit *PredSU = PredEdge->getSUnit();

  if (PredEdge->isWeak()) {
    --PredSU->WeakSuccsLeft;
    if (PredEdge->isCluster())
      NextClusterPred = PredSU;
    return;
  }
#ifndef NDEBUG
  if (PredSU->NumSuccsLeft == 0) {
    dbgs() << "*** Scheduling failed! ***\n";
    PredSU->dump(this);
    dbgs() << " has been released too many times!\n";
    llvm_unreachable(0);
  }
#endif
  --PredSU->NumSuccsLeft;
  if (PredSU->NumSuccsLeft == 0 && PredSU != &EntrySU)
    SchedImpl->releaseBottomNode(PredSU);
}

/// releasePredecessors - Call releasePred on each of SU's predecessors.
void ScheduleDAGMI::releasePredecessors(SUnit *SU) {
  for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
       I != E; ++I) {
    releasePred(SU, &*I);
  }
}

void ScheduleDAGMI::moveInstruction(MachineInstr *MI,
                                    MachineBasicBlock::iterator InsertPos) {
  // Advance RegionBegin if the first instruction moves down.
  if (&*RegionBegin == MI)
    ++RegionBegin;

  // Update the instruction stream.
  BB->splice(InsertPos, BB, MI);

  // Update LiveIntervals
  LIS->handleMove(MI, /*UpdateFlags=*/true);

  // Recede RegionBegin if an instruction moves above the first.
  if (RegionBegin == InsertPos)
    RegionBegin = MI;
}

bool ScheduleDAGMI::checkSchedLimit() {
#ifndef NDEBUG
  if (NumInstrsScheduled == MISchedCutoff && MISchedCutoff != ~0U) {
    CurrentTop = CurrentBottom;
    return false;
  }
  ++NumInstrsScheduled;
#endif
  return true;
}

/// enterRegion - Called back from MachineScheduler::runOnMachineFunction after
/// crossing a scheduling boundary. [begin, end) includes all instructions in
/// the region, including the boundary itself and single-instruction regions
/// that don't get scheduled.
void ScheduleDAGMI::enterRegion(MachineBasicBlock *bb,
                                MachineBasicBlock::iterator begin,
                                MachineBasicBlock::iterator end,
                                unsigned endcount)
{
  ScheduleDAGInstrs::enterRegion(bb, begin, end, endcount);

  // For convenience remember the end of the liveness region.
  LiveRegionEnd =
    (RegionEnd == bb->end()) ? RegionEnd : llvm::next(RegionEnd);
}

// Setup the register pressure trackers for the top scheduled top and bottom
// scheduled regions.
void ScheduleDAGMI::initRegPressure() {
  TopRPTracker.init(&MF, RegClassInfo, LIS, BB, RegionBegin);
  BotRPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd);

  // Close the RPTracker to finalize live ins.
  RPTracker.closeRegion();

  DEBUG(RPTracker.getPressure().dump(TRI));

  // Initialize the live ins and live outs.
  TopRPTracker.addLiveRegs(RPTracker.getPressure().LiveInRegs);
  BotRPTracker.addLiveRegs(RPTracker.getPressure().LiveOutRegs);

  // Close one end of the tracker so we can call
  // getMaxUpward/DownwardPressureDelta before advancing across any
  // instructions. This converts currently live regs into live ins/outs.
  TopRPTracker.closeTop();
  BotRPTracker.closeBottom();

  // Account for liveness generated by the region boundary.
  if (LiveRegionEnd != RegionEnd)
    BotRPTracker.recede();

  assert(BotRPTracker.getPos() == RegionEnd && "Can't find the region bottom");

  // Cache the list of excess pressure sets in this region. This will also track
  // the max pressure in the scheduled code for these sets.
  RegionCriticalPSets.clear();
  std::vector<unsigned> RegionPressure = RPTracker.getPressure().MaxSetPressure;
  for (unsigned i = 0, e = RegionPressure.size(); i < e; ++i) {
    unsigned Limit = TRI->getRegPressureSetLimit(i);
    DEBUG(dbgs() << TRI->getRegPressureSetName(i)
          << "Limit " << Limit
          << " Actual " << RegionPressure[i] << "\n");
    if (RegionPressure[i] > Limit)
      RegionCriticalPSets.push_back(PressureElement(i, 0));
  }
  DEBUG(dbgs() << "Excess PSets: ";
        for (unsigned i = 0, e = RegionCriticalPSets.size(); i != e; ++i)
          dbgs() << TRI->getRegPressureSetName(
            RegionCriticalPSets[i].PSetID) << " ";
        dbgs() << "\n");
}

// FIXME: When the pressure tracker deals in pressure differences then we won't
// iterate over all RegionCriticalPSets[i].
void ScheduleDAGMI::
updateScheduledPressure(std::vector<unsigned> NewMaxPressure) {
  for (unsigned i = 0, e = RegionCriticalPSets.size(); i < e; ++i) {
    unsigned ID = RegionCriticalPSets[i].PSetID;
    int &MaxUnits = RegionCriticalPSets[i].UnitIncrease;
    if ((int)NewMaxPressure[ID] > MaxUnits)
      MaxUnits = NewMaxPressure[ID];
  }
}

/// schedule - Called back from MachineScheduler::runOnMachineFunction
/// after setting up the current scheduling region. [RegionBegin, RegionEnd)
/// only includes instructions that have DAG nodes, not scheduling boundaries.
///
/// This is a skeletal driver, with all the functionality pushed into helpers,
/// so that it can be easilly extended by experimental schedulers. Generally,
/// implementing MachineSchedStrategy should be sufficient to implement a new
/// scheduling algorithm. However, if a scheduler further subclasses
/// ScheduleDAGMI then it will want to override this virtual method in order to
/// update any specialized state.
void ScheduleDAGMI::schedule() {
  buildDAGWithRegPressure();

  Topo.InitDAGTopologicalSorting();

  postprocessDAG();

  DEBUG(for (unsigned su = 0, e = SUnits.size(); su != e; ++su)
          SUnits[su].dumpAll(this));

  if (ViewMISchedDAGs) viewGraph();

  initQueues();

  bool IsTopNode = false;
  while (SUnit *SU = SchedImpl->pickNode(IsTopNode)) {
    assert(!SU->isScheduled && "Node already scheduled");
    if (!checkSchedLimit())
      break;

    scheduleMI(SU, IsTopNode);

    updateQueues(SU, IsTopNode);
  }
  assert(CurrentTop == CurrentBottom && "Nonempty unscheduled zone.");

  placeDebugValues();

  DEBUG({
      unsigned BBNum = top()->getParent()->getNumber();
      dbgs() << "*** Final schedule for BB#" << BBNum << " ***\n";
      dumpSchedule();
      dbgs() << '\n';
    });
}

/// Build the DAG and setup three register pressure trackers.
void ScheduleDAGMI::buildDAGWithRegPressure() {
  // Initialize the register pressure tracker used by buildSchedGraph.
  RPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd);

  // Account for liveness generate by the region boundary.
  if (LiveRegionEnd != RegionEnd)
    RPTracker.recede();

  // Build the DAG, and compute current register pressure.
  buildSchedGraph(AA, &RPTracker);
  if (ViewMISchedDAGs) viewGraph();

  // Initialize top/bottom trackers after computing region pressure.
  initRegPressure();
}

/// Apply each ScheduleDAGMutation step in order.
void ScheduleDAGMI::postprocessDAG() {
  for (unsigned i = 0, e = Mutations.size(); i < e; ++i) {
    Mutations[i]->apply(this);
  }
}

// Release all DAG roots for scheduling.
//
// Nodes with unreleased weak edges can still be roots.
void ScheduleDAGMI::releaseRoots() {
  SmallVector<SUnit*, 16> BotRoots;

  for (std::vector<SUnit>::iterator
         I = SUnits.begin(), E = SUnits.end(); I != E; ++I) {
    SUnit *SU = &(*I);
    // A SUnit is ready to top schedule if it has no predecessors.
    if (!I->NumPredsLeft && SU != &EntrySU)
      SchedImpl->releaseTopNode(SU);
    // A SUnit is ready to bottom schedule if it has no successors.
    if (!I->NumSuccsLeft && SU != &ExitSU)
      BotRoots.push_back(SU);
  }
  // Release bottom roots in reverse order so the higher priority nodes appear
  // first. This is more natural and slightly more efficient.
  for (SmallVectorImpl<SUnit*>::const_reverse_iterator
         I = BotRoots.rbegin(), E = BotRoots.rend(); I != E; ++I)
    SchedImpl->releaseBottomNode(*I);
}

/// Identify DAG roots and setup scheduler queues.
void ScheduleDAGMI::initQueues() {
  NextClusterSucc = NULL;
  NextClusterPred = NULL;

  // Initialize the strategy before modifying the DAG.
  SchedImpl->initialize(this);

  // Release all DAG roots for scheduling, not including EntrySU/ExitSU.
  releaseRoots();

  releaseSuccessors(&EntrySU);
  releasePredecessors(&ExitSU);

  SchedImpl->registerRoots();

  CurrentTop = nextIfDebug(RegionBegin, RegionEnd);
  CurrentBottom = RegionEnd;
}

/// Move an instruction and update register pressure.
void ScheduleDAGMI::scheduleMI(SUnit *SU, bool IsTopNode) {
  // Move the instruction to its new location in the instruction stream.
  MachineInstr *MI = SU->getInstr();

  if (IsTopNode) {
    assert(SU->isTopReady() && "node still has unscheduled dependencies");
    if (&*CurrentTop == MI)
      CurrentTop = nextIfDebug(++CurrentTop, CurrentBottom);
    else {
      moveInstruction(MI, CurrentTop);
      TopRPTracker.setPos(MI);
    }

    // Update top scheduled pressure.
    TopRPTracker.advance();
    assert(TopRPTracker.getPos() == CurrentTop && "out of sync");
    updateScheduledPressure(TopRPTracker.getPressure().MaxSetPressure);
  }
  else {
    assert(SU->isBottomReady() && "node still has unscheduled dependencies");
    MachineBasicBlock::iterator priorII =
      priorNonDebug(CurrentBottom, CurrentTop);
    if (&*priorII == MI)
      CurrentBottom = priorII;
    else {
      if (&*CurrentTop == MI) {
        CurrentTop = nextIfDebug(++CurrentTop, priorII);
        TopRPTracker.setPos(CurrentTop);
      }
      moveInstruction(MI, CurrentBottom);
      CurrentBottom = MI;
    }
    // Update bottom scheduled pressure.
    BotRPTracker.recede();
    assert(BotRPTracker.getPos() == CurrentBottom && "out of sync");
    updateScheduledPressure(BotRPTracker.getPressure().MaxSetPressure);
  }
}

/// Update scheduler queues after scheduling an instruction.
void ScheduleDAGMI::updateQueues(SUnit *SU, bool IsTopNode) {
  // Release dependent instructions for scheduling.
  if (IsTopNode)
    releaseSuccessors(SU);
  else
    releasePredecessors(SU);

  SU->isScheduled = true;

  // Notify the scheduling strategy after updating the DAG.
  SchedImpl->schedNode(SU, IsTopNode);
}

/// Reinsert any remaining debug_values, just like the PostRA scheduler.
void ScheduleDAGMI::placeDebugValues() {
  // If first instruction was a DBG_VALUE then put it back.
  if (FirstDbgValue) {
    BB->splice(RegionBegin, BB, FirstDbgValue);
    RegionBegin = FirstDbgValue;
  }

  for (std::vector<std::pair<MachineInstr *, MachineInstr *> >::iterator
         DI = DbgValues.end(), DE = DbgValues.begin(); DI != DE; --DI) {
    std::pair<MachineInstr *, MachineInstr *> P = *prior(DI);
    MachineInstr *DbgValue = P.first;
    MachineBasicBlock::iterator OrigPrevMI = P.second;
    BB->splice(++OrigPrevMI, BB, DbgValue);
    if (OrigPrevMI == llvm::prior(RegionEnd))
      RegionEnd = DbgValue;
  }
  DbgValues.clear();
  FirstDbgValue = NULL;
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void ScheduleDAGMI::dumpSchedule() const {
  for (MachineBasicBlock::iterator MI = begin(), ME = end(); MI != ME; ++MI) {
    if (SUnit *SU = getSUnit(&(*MI)))
      SU->dump(this);
    else
      dbgs() << "Missing SUnit\n";
  }
}
#endif

namespace {
/// \brief Post-process the DAG to create cluster edges between neighboring
/// loads.
class LoadClusterMutation : public ScheduleDAGMutation {
  struct LoadInfo {
    SUnit *SU;
    unsigned BaseReg;
    unsigned Offset;
    LoadInfo(SUnit *su, unsigned reg, unsigned ofs)
      : SU(su), BaseReg(reg), Offset(ofs) {}
  };
  static bool LoadInfoLess(const LoadClusterMutation::LoadInfo &LHS,
                           const LoadClusterMutation::LoadInfo &RHS);

  const TargetInstrInfo *TII;
  const TargetRegisterInfo *TRI;
public:
  LoadClusterMutation(const TargetInstrInfo *tii,
                      const TargetRegisterInfo *tri)
    : TII(tii), TRI(tri) {}

  virtual void apply(ScheduleDAGMI *DAG);
protected:
  void clusterNeighboringLoads(ArrayRef<SUnit*> Loads, ScheduleDAGMI *DAG);
};
} // anonymous

bool LoadClusterMutation::LoadInfoLess(
  const LoadClusterMutation::LoadInfo &LHS,
  const LoadClusterMutation::LoadInfo &RHS) {
  if (LHS.BaseReg != RHS.BaseReg)
    return LHS.BaseReg < RHS.BaseReg;
  return LHS.Offset < RHS.Offset;
}

void LoadClusterMutation::clusterNeighboringLoads(ArrayRef<SUnit*> Loads,
                                                  ScheduleDAGMI *DAG) {
  SmallVector<LoadClusterMutation::LoadInfo,32> LoadRecords;
  for (unsigned Idx = 0, End = Loads.size(); Idx != End; ++Idx) {
    SUnit *SU = Loads[Idx];
    unsigned BaseReg;
    unsigned Offset;
    if (TII->getLdStBaseRegImmOfs(SU->getInstr(), BaseReg, Offset, TRI))
      LoadRecords.push_back(LoadInfo(SU, BaseReg, Offset));
  }
  if (LoadRecords.size() < 2)
    return;
  std::sort(LoadRecords.begin(), LoadRecords.end(), LoadInfoLess);
  unsigned ClusterLength = 1;
  for (unsigned Idx = 0, End = LoadRecords.size(); Idx < (End - 1); ++Idx) {
    if (LoadRecords[Idx].BaseReg != LoadRecords[Idx+1].BaseReg) {
      ClusterLength = 1;
      continue;
    }

    SUnit *SUa = LoadRecords[Idx].SU;
    SUnit *SUb = LoadRecords[Idx+1].SU;
    if (TII->shouldScheduleLoadsNear(SUa->getInstr(), SUb->getInstr(),
                                     ClusterLength)
        && DAG->addEdge(SUb, SDep(SUa, SDep::Cluster))) {

      DEBUG(dbgs() << "Cluster loads SU(" << SUa->NodeNum << ") - SU("
            << SUb->NodeNum << ")\n");
      // Copy successor edges from SUa to SUb. Interleaving computation
      // dependent on SUa can prevent load combining due to register reuse.
      // Predecessor edges do not need to be copied from SUb to SUa since nearby
      // loads should have effectively the same inputs.
      for (SUnit::const_succ_iterator
             SI = SUa->Succs.begin(), SE = SUa->Succs.end(); SI != SE; ++SI) {
        if (SI->getSUnit() == SUb)
          continue;
        DEBUG(dbgs() << "  Copy Succ SU(" << SI->getSUnit()->NodeNum << ")\n");
        DAG->addEdge(SI->getSUnit(), SDep(SUb, SDep::Artificial));
      }
      ++ClusterLength;
    }
    else
      ClusterLength = 1;
  }
}

/// \brief Callback from DAG postProcessing to create cluster edges for loads.
void LoadClusterMutation::apply(ScheduleDAGMI *DAG) {
  // Map DAG NodeNum to store chain ID.
  DenseMap<unsigned, unsigned> StoreChainIDs;
  // Map each store chain to a set of dependent loads.
  SmallVector<SmallVector<SUnit*,4>, 32> StoreChainDependents;
  for (unsigned Idx = 0, End = DAG->SUnits.size(); Idx != End; ++Idx) {
    SUnit *SU = &DAG->SUnits[Idx];
    if (!SU->getInstr()->mayLoad())
      continue;
    unsigned ChainPredID = DAG->SUnits.size();
    for (SUnit::const_pred_iterator
           PI = SU->Preds.begin(), PE = SU->Preds.end(); PI != PE; ++PI) {
      if (PI->isCtrl()) {
        ChainPredID = PI->getSUnit()->NodeNum;
        break;
      }
    }
    // Check if this chain-like pred has been seen
    // before. ChainPredID==MaxNodeID for loads at the top of the schedule.
    unsigned NumChains = StoreChainDependents.size();
    std::pair<DenseMap<unsigned, unsigned>::iterator, bool> Result =
      StoreChainIDs.insert(std::make_pair(ChainPredID, NumChains));
    if (Result.second)
      StoreChainDependents.resize(NumChains + 1);
    StoreChainDependents[Result.first->second].push_back(SU);
  }
  // Iterate over the store chains.
  for (unsigned Idx = 0, End = StoreChainDependents.size(); Idx != End; ++Idx)
    clusterNeighboringLoads(StoreChainDependents[Idx], DAG);
}

//===----------------------------------------------------------------------===//
// ConvergingScheduler - Implementation of the standard MachineSchedStrategy.
//===----------------------------------------------------------------------===//

namespace {
/// ConvergingScheduler shrinks the unscheduled zone using heuristics to balance
/// the schedule.
class ConvergingScheduler : public MachineSchedStrategy {
public:
  /// Represent the type of SchedCandidate found within a single queue.
  /// pickNodeBidirectional depends on these listed by decreasing priority.
  enum CandReason {
    NoCand, SingleExcess, SingleCritical, Cluster,
    ResourceReduce, ResourceDemand, BotHeightReduce, BotPathReduce,
    TopDepthReduce, TopPathReduce, SingleMax, MultiPressure, NextDefUse,
    NodeOrder};

#ifndef NDEBUG
  static const char *getReasonStr(ConvergingScheduler::CandReason Reason);
#endif

  /// Policy for scheduling the next instruction in the candidate's zone.
  struct CandPolicy {
    bool ReduceLatency;
    unsigned ReduceResIdx;
    unsigned DemandResIdx;

    CandPolicy(): ReduceLatency(false), ReduceResIdx(0), DemandResIdx(0) {}
  };

  /// Status of an instruction's critical resource consumption.
  struct SchedResourceDelta {
    // Count critical resources in the scheduled region required by SU.
    unsigned CritResources;

    // Count critical resources from another region consumed by SU.
    unsigned DemandedResources;

    SchedResourceDelta(): CritResources(0), DemandedResources(0) {}

    bool operator==(const SchedResourceDelta &RHS) const {
      return CritResources == RHS.CritResources
        && DemandedResources == RHS.DemandedResources;
    }
    bool operator!=(const SchedResourceDelta &RHS) const {
      return !operator==(RHS);
    }
  };

  /// Store the state used by ConvergingScheduler heuristics, required for the
  /// lifetime of one invocation of pickNode().
  struct SchedCandidate {
    CandPolicy Policy;

    // The best SUnit candidate.
    SUnit *SU;

    // The reason for this candidate.
    CandReason Reason;

    // Register pressure values for the best candidate.
    RegPressureDelta RPDelta;

    // Critical resource consumption of the best candidate.
    SchedResourceDelta ResDelta;

    SchedCandidate(const CandPolicy &policy)
    : Policy(policy), SU(NULL), Reason(NoCand) {}

    bool isValid() const { return SU; }

    // Copy the status of another candidate without changing policy.
    void setBest(SchedCandidate &Best) {
      assert(Best.Reason != NoCand && "uninitialized Sched candidate");
      SU = Best.SU;
      Reason = Best.Reason;
      RPDelta = Best.RPDelta;
      ResDelta = Best.ResDelta;
    }

    void initResourceDelta(const ScheduleDAGMI *DAG,
                           const TargetSchedModel *SchedModel);
  };

  /// Summarize the unscheduled region.
  struct SchedRemainder {
    // Critical path through the DAG in expected latency.
    unsigned CriticalPath;

    // Unscheduled resources
    SmallVector<unsigned, 16> RemainingCounts;
    // Critical resource for the unscheduled zone.
    unsigned CritResIdx;
    // Number of micro-ops left to schedule.
    unsigned RemainingMicroOps;
    // Is the unscheduled zone resource limited.
    bool IsResourceLimited;

    unsigned MaxRemainingCount;

    void reset() {
      CriticalPath = 0;
      RemainingCounts.clear();
      CritResIdx = 0;
      RemainingMicroOps = 0;
      IsResourceLimited = false;
      MaxRemainingCount = 0;
    }

    SchedRemainder() { reset(); }

    void init(ScheduleDAGMI *DAG, const TargetSchedModel *SchedModel);
  };

  /// Each Scheduling boundary is associated with ready queues. It tracks the
  /// current cycle in the direction of movement, and maintains the state
  /// of "hazards" and other interlocks at the current cycle.
  struct SchedBoundary {
    ScheduleDAGMI *DAG;
    const TargetSchedModel *SchedModel;
    SchedRemainder *Rem;

    ReadyQueue Available;
    ReadyQueue Pending;
    bool CheckPending;

    // For heuristics, keep a list of the nodes that immediately depend on the
    // most recently scheduled node.
    SmallPtrSet<const SUnit*, 8> NextSUs;

    ScheduleHazardRecognizer *HazardRec;

    unsigned CurrCycle;
    unsigned IssueCount;

    /// MinReadyCycle - Cycle of the soonest available instruction.
    unsigned MinReadyCycle;

    // The expected latency of the critical path in this scheduled zone.
    unsigned ExpectedLatency;

    // Resources used in the scheduled zone beyond this boundary.
    SmallVector<unsigned, 16> ResourceCounts;

    // Cache the critical resources ID in this scheduled zone.
    unsigned CritResIdx;

    // Is the scheduled region resource limited vs. latency limited.
    bool IsResourceLimited;

    unsigned ExpectedCount;

    // Policy flag: attempt to find ILP until expected latency is covered.
    bool ShouldIncreaseILP;

#ifndef NDEBUG
    // Remember the greatest min operand latency.
    unsigned MaxMinLatency;
#endif

    void reset() {
      Available.clear();
      Pending.clear();
      CheckPending = false;
      NextSUs.clear();
      HazardRec = 0;
      CurrCycle = 0;
      IssueCount = 0;
      MinReadyCycle = UINT_MAX;
      ExpectedLatency = 0;
      ResourceCounts.resize(1);
      assert(!ResourceCounts[0] && "nonzero count for bad resource");
      CritResIdx = 0;
      IsResourceLimited = false;
      ExpectedCount = 0;
      ShouldIncreaseILP = false;
#ifndef NDEBUG
      MaxMinLatency = 0;
#endif
      // Reserve a zero-count for invalid CritResIdx.
      ResourceCounts.resize(1);
    }

    /// Pending queues extend the ready queues with the same ID and the
    /// PendingFlag set.
    SchedBoundary(unsigned ID, const Twine &Name):
      DAG(0), SchedModel(0), Rem(0), Available(ID, Name+".A"),
      Pending(ID << ConvergingScheduler::LogMaxQID, Name+".P") {
      reset();
    }

    ~SchedBoundary() { delete HazardRec; }

    void init(ScheduleDAGMI *dag, const TargetSchedModel *smodel,
              SchedRemainder *rem);

    bool isTop() const {
      return Available.getID() == ConvergingScheduler::TopQID;