llvm/lib/CodeGen/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.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/MachineScheduler.h"
#include "llvm/ADT/PriorityQueue.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/ScheduleDFS.h"
#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GraphWriter.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include <queue>

using namespace llvm;

#define DEBUG_TYPE "misched"

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"));
cl::opt<bool>
DumpCriticalPathLength("misched-dcpl", cl::Hidden,
                       cl::desc("Print critical path length to stdout"));
}

#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));

static cl::opt<std::string> SchedOnlyFunc("misched-only-func", cl::Hidden,
  cl::desc("Only schedule this function"));
static cl::opt<unsigned> SchedOnlyBlock("misched-only-block", cl::Hidden,
  cl::desc("Only schedule this MBB#"));
#else
static bool ViewMISchedDAGs = false;
#endif // NDEBUG

static cl::opt<bool> EnableRegPressure("misched-regpressure", cl::Hidden,
  cl::desc("Enable register pressure scheduling."), cl::init(true));

static cl::opt<bool> EnableCyclicPath("misched-cyclicpath", cl::Hidden,
  cl::desc("Enable cyclic critical path analysis."), cl::init(true));

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

// Experimental heuristics
static cl::opt<bool> EnableMacroFusion("misched-fusion", cl::Hidden,
  cl::desc("Enable scheduling for macro fusion."), cl::init(true));

static cl::opt<bool> VerifyScheduling("verify-misched", cl::Hidden,
  cl::desc("Verify machine instrs before and after machine scheduling"));

// DAG subtrees must have at least this many nodes.
static const unsigned MinSubtreeSize = 8;

// Pin the vtables to this file.
void MachineSchedStrategy::anchor() {}
void ScheduleDAGMutation::anchor() {}

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

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

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

namespace {
/// Base class for a machine scheduler class that can run at any point.
class MachineSchedulerBase : public MachineSchedContext,
                             public MachineFunctionPass {
public:
  MachineSchedulerBase(char &ID): MachineFunctionPass(ID) {}

  void print(raw_ostream &O, const Module* = nullptr) const override;

protected:
  void scheduleRegions(ScheduleDAGInstrs &Scheduler);
};

/// MachineScheduler runs after coalescing and before register allocation.
class MachineScheduler : public MachineSchedulerBase {
public:
  MachineScheduler();

  void getAnalysisUsage(AnalysisUsage &AU) const override;

  bool runOnMachineFunction(MachineFunction&) override;

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

protected:
  ScheduleDAGInstrs *createMachineScheduler();
};

/// PostMachineScheduler runs after shortly before code emission.
class PostMachineScheduler : public MachineSchedulerBase {
public:
  PostMachineScheduler();

  void getAnalysisUsage(AnalysisUsage &AU) const override;

  bool runOnMachineFunction(MachineFunction&) override;

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

protected:
  ScheduleDAGInstrs *createPostMachineScheduler();
};
} // namespace

char MachineScheduler::ID = 0;

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

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

MachineScheduler::MachineScheduler()
: MachineSchedulerBase(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);
}

char PostMachineScheduler::ID = 0;

char &llvm::PostMachineSchedulerID = PostMachineScheduler::ID;

INITIALIZE_PASS(PostMachineScheduler, "postmisched",
                "PostRA Machine Instruction Scheduler", false, false)

PostMachineScheduler::PostMachineScheduler()
: MachineSchedulerBase(ID) {
  initializePostMachineSchedulerPass(*PassRegistry::getPassRegistry());
}

void PostMachineScheduler::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesCFG();
  AU.addRequiredID(MachineDominatorsID);
  AU.addRequired<MachineLoopInfo>();
  AU.addRequired<TargetPassConfig>();
  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 nullptr;
}

/// 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 *createGenericSchedLive(MachineSchedContext *C);
static ScheduleDAGInstrs *createGenericSchedPostRA(MachineSchedContext *C);

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

/// Non-const version.
static MachineBasicBlock::iterator
priorNonDebug(MachineBasicBlock::iterator I,
              MachineBasicBlock::const_iterator Beg) {
  return const_cast<MachineInstr*>(
    &*priorNonDebug(MachineBasicBlock::const_iterator(I), Beg));
}

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

/// Non-const version.
static MachineBasicBlock::iterator
nextIfDebug(MachineBasicBlock::iterator I,
            MachineBasicBlock::const_iterator End) {
  // Cast the return value to nonconst MachineInstr, then cast to an
  // instr_iterator, which does not check for null, finally return a
  // bundle_iterator.
  return MachineBasicBlock::instr_iterator(
    const_cast<MachineInstr*>(
      &*nextIfDebug(MachineBasicBlock::const_iterator(I), End)));
}

/// Instantiate a ScheduleDAGInstrs that will be owned by the caller.
ScheduleDAGInstrs *MachineScheduler::createMachineScheduler() {
  // Select the scheduler, or set the default.
  MachineSchedRegistry::ScheduleDAGCtor Ctor = MachineSchedOpt;
  if (Ctor != useDefaultMachineSched)
    return Ctor(this);

  // Get the default scheduler set by the target for this function.
  ScheduleDAGInstrs *Scheduler = PassConfig->createMachineScheduler(this);
  if (Scheduler)
    return Scheduler;

  // Default to GenericScheduler.
  return createGenericSchedLive(this);
}

/// Instantiate a ScheduleDAGInstrs for PostRA scheduling that will be owned by
/// the caller. We don't have a command line option to override the postRA
/// scheduler. The Target must configure it.
ScheduleDAGInstrs *PostMachineScheduler::createPostMachineScheduler() {
  // Get the postRA scheduler set by the target for this function.
  ScheduleDAGInstrs *Scheduler = PassConfig->createPostMachineScheduler(this);
  if (Scheduler)
    return Scheduler;

  // Default to GenericScheduler.
  return createGenericSchedPostRA(this);
}

/// 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>();

  if (VerifyScheduling) {
    DEBUG(LIS->dump());
    MF->verify(this, "Before machine scheduling.");
  }
  RegClassInfo->runOnMachineFunction(*MF);

  // Instantiate the selected scheduler for this target, function, and
  // optimization level.
  std::unique_ptr<ScheduleDAGInstrs> Scheduler(createMachineScheduler());
  scheduleRegions(*Scheduler);

  DEBUG(LIS->dump());
  if (VerifyScheduling)
    MF->verify(this, "After machine scheduling.");
  return true;
}

bool PostMachineScheduler::runOnMachineFunction(MachineFunction &mf) {
  if (skipOptnoneFunction(*mf.getFunction()))
    return false;

  const TargetSubtargetInfo &ST =
    mf.getTarget().getSubtarget<TargetSubtargetInfo>();
  if (!ST.enablePostMachineScheduler()) {
    DEBUG(dbgs() << "Subtarget disables post-MI-sched.\n");
    return false;
  }
  DEBUG(dbgs() << "Before post-MI-sched:\n"; mf.print(dbgs()));

  // Initialize the context of the pass.
  MF = &mf;
  PassConfig = &getAnalysis<TargetPassConfig>();

  if (VerifyScheduling)
    MF->verify(this, "Before post machine scheduling.");

  // Instantiate the selected scheduler for this target, function, and
  // optimization level.
  std::unique_ptr<ScheduleDAGInstrs> Scheduler(createPostMachineScheduler());
  scheduleRegions(*Scheduler);

  if (VerifyScheduling)
    MF->verify(this, "After post machine scheduling.");
  return true;
}

/// Return true of the given instruction should not be included in a scheduling
/// region.
///
/// MachineScheduler does not currently support scheduling across calls. To
/// handle calls, the DAG builder needs to be modified to create register
/// anti/output dependencies on the registers clobbered by the call's regmask
/// operand. In PreRA scheduling, the stack pointer adjustment already prevents
/// scheduling across calls. In PostRA scheduling, we need the isCall to enforce
/// the boundary, but there would be no benefit to postRA scheduling across
/// calls this late anyway.
static bool isSchedBoundary(MachineBasicBlock::iterator MI,
                            MachineBasicBlock *MBB,
                            MachineFunction *MF,
                            const TargetInstrInfo *TII,
                            bool IsPostRA) {
  return MI->isCall() || TII->isSchedulingBoundary(MI, MBB, *MF);
}

/// Main driver for both MachineScheduler and PostMachineScheduler.
void MachineSchedulerBase::scheduleRegions(ScheduleDAGInstrs &Scheduler) {
  const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
  bool IsPostRA = Scheduler.isPostRA();

  // 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);

#ifndef NDEBUG
    if (SchedOnlyFunc.getNumOccurrences() && SchedOnlyFunc != MF->getName())
      continue;
    if (SchedOnlyBlock.getNumOccurrences()
        && (int)SchedOnlyBlock != MBB->getNumber())
      continue;
#endif

    // 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.
    //
    // MBB::size() uses instr_iterator to count. Here we need a bundle to count
    // as a single instruction.
    unsigned RemainingInstrs = std::distance(MBB->begin(), MBB->end());
    for(MachineBasicBlock::iterator RegionEnd = MBB->end();
        RegionEnd != MBB->begin(); RegionEnd = Scheduler.begin()) {

      // Avoid decrementing RegionEnd for blocks with no terminator.
      if (RegionEnd != MBB->end() ||
          isSchedBoundary(std::prev(RegionEnd), MBB, MF, TII, IsPostRA)) {
        --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.
      unsigned NumRegionInstrs = 0;
      MachineBasicBlock::iterator I = RegionEnd;
      for(;I != MBB->begin(); --I, --RemainingInstrs) {
        if (isSchedBoundary(std::prev(I), MBB, MF, TII, IsPostRA))
          break;
        if (!I->isDebugValue())
          ++NumRegionInstrs;
      }
      // 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, NumRegionInstrs);

      // Skip empty scheduling regions (0 or 1 schedulable instructions).
      if (I == RegionEnd || I == std::prev(RegionEnd)) {
        // Close the current region. Bundle the terminator if needed.
        // This invalidates 'RegionEnd' and 'I'.
        Scheduler.exitRegion();
        continue;
      }
      DEBUG(dbgs() << "********** " << ((Scheduler.isPostRA()) ? "PostRA " : "")
            << "MI Scheduling **********\n");
      DEBUG(dbgs() << MF->getName()
            << ":BB#" << MBB->getNumber() << " " << MBB->getName()
            << "\n  From: " << *I << "    To: ";
            if (RegionEnd != MBB->end()) dbgs() << *RegionEnd;
            else dbgs() << "End";
            dbgs() << " RegionInstrs: " << NumRegionInstrs
            << " Remaining: " << RemainingInstrs << "\n");
      if (DumpCriticalPathLength) {
        errs() << MF->getName();
        errs() << ":BB# " << MBB->getNumber();
        errs() << " " << MBB->getName() << " \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();
    if (Scheduler.isPostRA()) {
      // FIXME: Ideally, no further passes should rely on kill flags. However,
      // thumb2 size reduction is currently an exception.
      Scheduler.fixupKills(MBB);
    }
  }
  Scheduler.finalizeSchedule();
}

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

LLVM_DUMP_METHOD
void ReadyQueue::dump() {
  dbgs() << Name << ": ";
  for (unsigned i = 0, e = Queue.size(); i < e; ++i)
    dbgs() << Queue[i]->NodeNum << " ";
  dbgs() << "\n";
}

//===----------------------------------------------------------------------===//
// ScheduleDAGMI - Basic machine instruction scheduling. This is
// independent of PreRA/PostRA scheduling and involves no extra book-keeping for
// virtual registers.
// ===----------------------------------------------------------------------===/

// Provide a vtable anchor.
ScheduleDAGMI::~ScheduleDAGMI() {
}

bool ScheduleDAGMI::canAddEdge(SUnit *SuccSU, SUnit *PredSU) {
  return SuccSU == &ExitSU || !Topo.IsReachable(PredSU, SuccSU);
}

bool ScheduleDAGMI::addEdge(SUnit *SuccSU, const SDep &PredDep) {
  if (SuccSU != &ExitSU) {
    // 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(nullptr);
  }
#endif
  // SU->TopReadyCycle was set to CurrCycle when it was scheduled. However,
  // CurrCycle may have advanced since then.
  if (SuccSU->TopReadyCycle < SU->TopReadyCycle + SuccEdge->getLatency())
    SuccSU->TopReadyCycle = SU->TopReadyCycle + SuccEdge->getLatency();

  --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(nullptr);
  }
#endif
  // SU->BotReadyCycle was set to CurrCycle when it was scheduled. However,
  // CurrCycle may have advanced since then.
  if (PredSU->BotReadyCycle < SU->BotReadyCycle + PredEdge->getLatency())
    PredSU->BotReadyCycle = SU->BotReadyCycle + PredEdge->getLatency();

  --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);
  }
}

/// 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 regioninstrs)
{
  ScheduleDAGInstrs::enterRegion(bb, begin, end, regioninstrs);

  SchedImpl->initPolicy(begin, end, regioninstrs);
}

/// This is normally called from the main scheduler loop but may also be invoked
/// by the scheduling strategy to perform additional code motion.
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
  if (LIS)
    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;
}

/// Per-region scheduling driver, called back from
/// MachineScheduler::runOnMachineFunction. This is a simplified driver that
/// does not consider liveness or register pressure. It is useful for PostRA
/// scheduling and potentially other custom schedulers.
void ScheduleDAGMI::schedule() {
  // Build the DAG.
  buildSchedGraph(AA);

  Topo.InitDAGTopologicalSorting();

  postprocessDAG();

  SmallVector<SUnit*, 8> TopRoots, BotRoots;
  findRootsAndBiasEdges(TopRoots, BotRoots);

  // Initialize the strategy before modifying the DAG.
  // This may initialize a DFSResult to be used for queue priority.
  SchedImpl->initialize(this);

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

  // Initialize ready queues now that the DAG and priority data are finalized.
  initQueues(TopRoots, BotRoots);

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

    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);
    }
    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);
        moveInstruction(MI, CurrentBottom);
        CurrentBottom = MI;
      }
    }
    // Notify the scheduling strategy before updating the DAG.
    // This sets the scheduled node's ReadyCycle to CurrCycle. When updateQueues
    // runs, it can then use the accurate ReadyCycle time to determine whether
    // newly released nodes can move to the readyQ.
    SchedImpl->schedNode(SU, IsTopNode);

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

  placeDebugValues();

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

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

void ScheduleDAGMI::
findRootsAndBiasEdges(SmallVectorImpl<SUnit*> &TopRoots,
                      SmallVectorImpl<SUnit*> &BotRoots) {
  for (std::vector<SUnit>::iterator
         I = SUnits.begin(), E = SUnits.end(); I != E; ++I) {
    SUnit *SU = &(*I);
    assert(!SU->isBoundaryNode() && "Boundary node should not be in SUnits");

    // Order predecessors so DFSResult follows the critical path.
    SU->biasCriticalPath();

    // A SUnit is ready to top schedule if it has no predecessors.
    if (!I->NumPredsLeft)
      TopRoots.push_back(SU);
    // A SUnit is ready to bottom schedule if it has no successors.
    if (!I->NumSuccsLeft)
      BotRoots.push_back(SU);
  }
  ExitSU.biasCriticalPath();
}

/// Identify DAG roots and setup scheduler queues.
void ScheduleDAGMI::initQueues(ArrayRef<SUnit*> TopRoots,
                               ArrayRef<SUnit*> BotRoots) {
  NextClusterSucc = nullptr;
  NextClusterPred = nullptr;

  // Release all DAG roots for scheduling, not including EntrySU/ExitSU.
  //
  // Nodes with unreleased weak edges can still be roots.
  // Release top roots in forward order.
  for (SmallVectorImpl<SUnit*>::const_iterator
         I = TopRoots.begin(), E = TopRoots.end(); I != E; ++I) {
    SchedImpl->releaseTopNode(*I);
  }
  // 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);
  }

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

  SchedImpl->registerRoots();

  // Advance past initial DebugValues.
  CurrentTop = nextIfDebug(RegionBegin, RegionEnd);
  CurrentBottom = RegionEnd;
}

/// 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;
}

/// 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 = *std::prev(DI);
    MachineInstr *DbgValue = P.first;
    MachineBasicBlock::iterator OrigPrevMI = P.second;
    if (&*RegionBegin == DbgValue)
      ++RegionBegin;
    BB->splice(++OrigPrevMI, BB, DbgValue);
    if (OrigPrevMI == std::prev(RegionEnd))
      RegionEnd = DbgValue;
  }
  DbgValues.clear();
  FirstDbgValue = nullptr;
}

#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

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

ScheduleDAGMILive::~ScheduleDAGMILive() {
  delete DFSResult;
}

/// 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 ScheduleDAGMILive::enterRegion(MachineBasicBlock *bb,
                                MachineBasicBlock::iterator begin,
                                MachineBasicBlock::iterator end,
                                unsigned regioninstrs)
{
  // ScheduleDAGMI initializes SchedImpl's per-region policy.
  ScheduleDAGMI::enterRegion(bb, begin, end, regioninstrs);

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

  SUPressureDiffs.clear();

  ShouldTrackPressure = SchedImpl->shouldTrackPressure();
}

// Setup the register pressure trackers for the top scheduled top and bottom
// scheduled regions.
void ScheduleDAGMILive::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.dump());

  // 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();

  BotRPTracker.initLiveThru(RPTracker);
  if (!BotRPTracker.getLiveThru().empty()) {
    TopRPTracker.initLiveThru(BotRPTracker.getLiveThru());
    DEBUG(dbgs() << "Live Thru: ";
          dumpRegSetPressure(BotRPTracker.getLiveThru(), TRI));
  };

  // For each live out vreg reduce the pressure change associated with other
  // uses of the same vreg below the live-out reaching def.
  updatePressureDiffs(RPTracker.getPressure().LiveOutRegs);

  // Account for liveness generated by the region boundary.
  if (LiveRegionEnd != RegionEnd) {
    SmallVector<unsigned, 8> LiveUses;
    BotRPTracker.recede(&LiveUses);
    updatePressureDiffs(LiveUses);
  }

  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();
  const std::vector<unsigned> &RegionPressure =
    RPTracker.getPressure().MaxSetPressure;
  for (unsigned i = 0, e = RegionPressure.size(); i < e; ++i) {
    unsigned Limit = RegClassInfo->getRegPressureSetLimit(i);
    if (RegionPressure[i] > Limit) {
      DEBUG(dbgs() << TRI->getRegPressureSetName(i)
            << " Limit " << Limit
            << " Actual " << RegionPressure[i] << "\n");
      RegionCriticalPSets.push_back(PressureChange(i));
    }
  }
  DEBUG(dbgs() << "Excess PSets: ";
        for (unsigned i = 0, e = RegionCriticalPSets.size(); i != e; ++i)
          dbgs() << TRI->getRegPressureSetName(
            RegionCriticalPSets[i].getPSet()) << " ";
        dbgs() << "\n");
}

void ScheduleDAGMILive::
updateScheduledPressure(const SUnit *SU,
                        const std::vector<unsigned> &NewMaxPressure) {
  const PressureDiff &PDiff = getPressureDiff(SU);
  unsigned CritIdx = 0, CritEnd = RegionCriticalPSets.size();
  for (PressureDiff::const_iterator I = PDiff.begin(), E = PDiff.end();
       I != E; ++I) {
    if (!I->isValid())
      break;
    unsigned ID = I->getPSet();
    while (CritIdx != CritEnd && RegionCriticalPSets[CritIdx].getPSet() < ID)
      ++CritIdx;
    if (CritIdx != CritEnd && RegionCriticalPSets[CritIdx].getPSet() == ID) {
      if ((int)NewMaxPressure[ID] > RegionCriticalPSets[CritIdx].getUnitInc()
          && NewMaxPressure[ID] <= INT16_MAX)
        RegionCriticalPSets[CritIdx].setUnitInc(NewMaxPressure[ID]);
    }
    unsigned Limit = RegClassInfo->getRegPressureSetLimit(ID);
    if (NewMaxPressure[ID] >= Limit - 2) {
      DEBUG(dbgs() << "  " << TRI->getRegPressureSetName(ID) << ": "
            << NewMaxPressure[ID] << " > " << Limit << "(+ "
            << BotRPTracker.getLiveThru()[ID] << " livethru)\n");
    }
  }
}

/// Update the PressureDiff array for liveness after scheduling this
/// instruction.
void ScheduleDAGMILive::updatePressureDiffs(ArrayRef<unsigned> LiveUses) {
  for (unsigned LUIdx = 0, LUEnd = LiveUses.size(); LUIdx != LUEnd; ++LUIdx) {
    /// FIXME: Currently assuming single-use physregs.
    unsigned Reg = LiveUses[LUIdx];
    DEBUG(dbgs() << "  LiveReg: " << PrintVRegOrUnit(Reg, TRI) << "\n");
    if (!TRI->isVirtualRegister(Reg))
      continue;

    // This may be called before CurrentBottom has been initialized. However,
    // BotRPTracker must have a valid position. We want the value live into the
    // instruction or live out of the block, so ask for the previous
    // instruction's live-out.
    const LiveInterval &LI = LIS->getInterval(Reg);
    VNInfo *VNI;
    MachineBasicBlock::const_iterator I =
      nextIfDebug(BotRPTracker.getPos(), BB->end());
    if (I == BB->end())
      VNI = LI.getVNInfoBefore(LIS->getMBBEndIdx(BB));
    else {
      LiveQueryResult LRQ = LI.Query(LIS->getInstructionIndex(I));
      VNI = LRQ.valueIn();
    }
    // RegisterPressureTracker guarantees that readsReg is true for LiveUses.
    assert(VNI && "No live value at use.");
    for (VReg2UseMap::iterator
           UI = VRegUses.find(Reg); UI != VRegUses.end(); ++UI) {
      SUnit *SU = UI->SU;
      DEBUG(dbgs() << "  UpdateRegP: SU(" << SU->NodeNum << ") "
            << *SU->getInstr());
      // If this use comes before the reaching def, it cannot be a last use, so
      // descrease its pressure change.
      if (!SU->isScheduled && SU != &ExitSU) {
        LiveQueryResult LRQ
          = LI.Query(LIS->getInstructionIndex(SU->getInstr()));
        if (LRQ.valueIn() == VNI)
          getPressureDiff(SU).addPressureChange(Reg, true, &MRI);
      }
    }
  }
}

/// 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
/// ScheduleDAGMILive then it will want to override this virtual method in order
/// to update any specialized state.
void ScheduleDAGMILive::schedule() {
  buildDAGWithRegPressure();

  Topo.InitDAGTopologicalSorting();

  postprocessDAG();

  SmallVector<SUnit*, 8> TopRoots, BotRoots;
  findRootsAndBiasEdges(TopRoots, BotRoots);

  // Initialize the strategy before modifying the DAG.
  // This may initialize a DFSResult to be used for queue priority.
  SchedImpl->initialize(this);

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

  // Initialize ready queues now that the DAG and priority data are finalized.
  initQueues(TopRoots, BotRoots);

  if (ShouldTrackPressure) {
    assert(TopRPTracker.getPos() == RegionBegin && "bad initial Top tracker");
    TopRPTracker.setPos(CurrentTop);
  }

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

    scheduleMI(SU, IsTopNode);

    updateQueues(SU, IsTopNode);

    if (DFSResult) {
      unsigned SubtreeID = DFSResult->getSubtreeID(SU);
      if (!ScheduledTrees.test(SubtreeID)) {
        ScheduledTrees.set(SubtreeID);
        DFSResult->scheduleTree(SubtreeID);
        SchedImpl->scheduleTree(SubtreeID);
      }
    }

    // Notify the scheduling strategy after updating the DAG.
    SchedImpl->schedNode(SU, IsTopNode);
  }
  assert(CurrentTop == CurrentBottom && "Nonempty unscheduled zone.");

  placeDebugValues();

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

/// Build the DAG and setup three register pressure trackers.
void ScheduleDAGMILive::buildDAGWithRegPressure() {
  if (!ShouldTrackPressure) {
    RPTracker.reset();
    RegionCriticalPSets.clear();
    buildSchedGraph(AA);
    return;
  }

  // Initialize the register pressure tracker used by buildSchedGraph.
  RPTracker.init(&MF, RegClassInfo, LIS, BB, LiveRegionEnd,
                 /*TrackUntiedDefs=*/true);

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

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

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

void ScheduleDAGMILive::computeDFSResult() {
  if (!DFSResult)
    DFSResult = new SchedDFSResult(/*BottomU*/true, MinSubtreeSize);
  DFSResult->clear();
  ScheduledTrees.clear();
  DFSResult->resize(SUnits.size());
  DFSResult->compute(SUnits);
  ScheduledTrees.resize(DFSResult->getNumSubtrees());
}

/// Compute the max cyclic critical path through the DAG. The scheduling DAG
/// only provides the critical path for single block loops. To handle loops that
/// span blocks, we could use the vreg path latencies provided by
/// MachineTraceMetrics instead. However, MachineTraceMetrics is not currently
/// available for use in the scheduler.
///
/// The cyclic path estimation identifies a def-use pair that crosses the back
/// edge and considers the depth and height of the nodes. For example, consider
/// the following instruction sequence where each instruction has unit latency
/// and defines an epomymous virtual register:
///
/// a->b(a,c)->c(b)->d(c)->exit
///
/// The cyclic critical path is a two cycles: b->c->b
/// The acyclic critical path is four cycles: a->b->c->d->exit
/// LiveOutHeight = height(c) = len(c->d->exit) = 2
/// LiveOutDepth = depth(c) + 1 = len(a->b->c) + 1 = 3
/// LiveInHeight = height(b) + 1 = len(b->c->d->exit) + 1 = 4
/// LiveInDepth = depth(b) = len(a->b) = 1
///
/// LiveOutDepth - LiveInDepth = 3 - 1 = 2
/// LiveInHeight - LiveOutHeight = 4 - 2 = 2
/// CyclicCriticalPath = min(2, 2) = 2
///
/// This could be relevant to PostRA scheduling, but is currently implemented
/// assuming LiveIntervals.
unsigned ScheduleDAGMILive::computeCyclicCriticalPath() {
  // This only applies to single block loop.
  if (!BB->isSuccessor(BB))
    return 0;

  unsigned MaxCyclicLatency = 0;
  // Visit each live out vreg def to find def/use pairs that cross iterations.
  ArrayRef<unsigned> LiveOuts = RPTracker.getPressure().LiveOutRegs;
  for (ArrayRef<unsigned>::iterator RI = LiveOuts.begin(), RE = LiveOuts.end();
       RI != RE; ++RI) {
    unsigned Reg = *RI;
    if (!TRI->isVirtualRegister(Reg))
        continue;
    const LiveInterval &LI = LIS->getInterval(Reg);
    const VNInfo *DefVNI = LI.getVNInfoBefore(LIS->getMBBEndIdx(BB));
    if (!DefVNI)
      continue;

    MachineInstr *DefMI = LIS->getInstructionFromIndex(DefVNI->def);
    const SUnit *DefSU = getSUnit(DefMI);
    if (!DefSU)
      continue;

    unsigned LiveOutHeight = DefSU->getHeight();
    unsigned LiveOutDepth = DefSU->getDepth() + DefSU->Latency;
    // Visit all local users of the vreg def.
    for (VReg2UseMap::iterator
           UI = VRegUses.find(Reg); UI != VRegUses.end(); ++UI) {
      if (UI->SU == &ExitSU)
        continue;

      // Only consider uses of the phi.
      LiveQueryResult LRQ =
        LI.Query(LIS->getInstructionIndex(UI->SU->getInstr()));
      if (!LRQ.valueIn()->isPHIDef())
        continue;

      // Assume that a path spanning two iterations is a cycle, which could
      // overestimate in strange cases. This allows cyclic latency to be
      // estimated as the minimum slack of the vreg's depth or height.
      unsigned CyclicLatency = 0;
      if (LiveOutDepth > UI->SU->getDepth())
        CyclicLatency = LiveOutDepth - UI->SU->getDepth();

      unsigned LiveInHeight = UI->SU->getHeight() + DefSU->Latency;
      if (LiveInHeight > LiveOutHeight) {
        if (LiveInHeight - LiveOutHeight < CyclicLatency)
          CyclicLatency = LiveInHeight - LiveOutHeight;
      }
      else
        CyclicLatency = 0;

      DEBUG(dbgs() << "Cyclic Path: SU(" << DefSU->NodeNum << ") -> SU("
            << UI->SU->NodeNum << ") = " << CyclicLatency << "c\n");
      if (CyclicLatency > MaxCyclicLatency)
        MaxCyclicLatency = CyclicLatency;
    }
  }
  DEBUG(dbgs() << "Cyclic Critical Path: " << MaxCyclicLatency << "c\n");
  return MaxCyclicLatency;
}

/// Move an instruction and update register pressure.
void ScheduleDAGMILive::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);
    }

    if (ShouldTrackPressure) {
      // Update top scheduled pressure.
      TopRPTracker.advance();
      assert(TopRPTracker.getPos() == CurrentTop && "out of sync");
      updateScheduledPressure(SU, 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;
    }
    if (ShouldTrackPressure) {
      // Update bottom scheduled pressure.
      SmallVector<unsigned, 8> LiveUses;
      BotRPTracker.recede(&LiveUses);
      assert(BotRPTracker.getPos() == CurrentBottom && "out of sync");
      updateScheduledPressure(SU, BotRPTracker.getPressure().MaxSetPressure);
      updatePressureDiffs(LiveUses);
    }
  }
}

//===----------------------------------------------------------------------===//
// LoadClusterMutation - DAG post-processing to cluster loads.
//===----------------------------------------------------------------------===//

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) {}

    bool operator<(const LoadInfo &RHS) const {
      return std::tie(BaseReg, Offset) < std::tie(RHS.BaseReg, RHS.Offset);
    }
  };

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

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

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());
  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->shouldClusterLoads(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);
}

//===----------------------------------------------------------------------===//
// MacroFusion - DAG post-processing to encourage fusion of macro ops.
//===----------------------------------------------------------------------===//

namespace {
/// \brief Post-process the DAG to create cluster edges between instructions
/// that may be fused by the processor into a single operation.
class MacroFusion : public ScheduleDAGMutation {
  const TargetInstrInfo *TII;
public:
  MacroFusion(const TargetInstrInfo *tii): TII(tii) {}

  void apply(ScheduleDAGMI *DAG) override;
};
} // anonymous

/// \brief Callback from DAG postProcessing to create cluster edges to encourage
/// fused operations.
void MacroFusion::apply(ScheduleDAGMI *DAG) {
  // For now, assume targets can only fuse with the branch.
  MachineInstr *Branch = DAG->ExitSU.getInstr();
  if (!Branch)
    return;

  for (unsigned Idx = DAG->SUnits.size(); Idx > 0;) {
    SUnit *SU = &DAG->SUnits[--Idx];
    if (!TII->shouldScheduleAdjacent(SU->getInstr(), Branch))
      continue;

    // Create a single weak edge from SU to ExitSU. The only effect is to cause
    // bottom-up scheduling to heavily prioritize the clustered SU.  There is no
    // need to copy predecessor edges from ExitSU to SU, since top-down
    // scheduling cannot prioritize ExitSU anyway. To defer top-down scheduling
    // of SU, we could create an artificial edge from the deepest root, but it
    // hasn't been needed yet.
    bool Success = DAG->addEdge(&DAG->ExitSU, SDep(SU, SDep::Cluster));
    (void)Success;
    assert(Success && "No DAG nodes should be reachable from ExitSU");

    DEBUG(dbgs() << "Macro Fuse SU(" << SU->NodeNum << ")\n");
    break;
  }
}

//===----------------------------------------------------------------------===//
// CopyConstrain - DAG post-processing to encourage copy elimination.
//===----------------------------------------------------------------------===//

namespace {
/// \brief Post-process the DAG to create weak edges from all uses of a copy to
/// the one use that defines the copy's source vreg, most likely an induction
/// variable increment.
class CopyConstrain : public ScheduleDAGMutation {
  // Transient state.
  SlotIndex RegionBeginIdx;
  // RegionEndIdx is the slot index of the last non-debug instruction in the
  // scheduling region. So we may have RegionBeginIdx == RegionEndIdx.
  SlotIndex RegionEndIdx;
public:
  CopyConstrain(const TargetInstrInfo *, const TargetRegisterInfo *) {}

  void apply(ScheduleDAGMI *DAG) override;

protected:
  void constrainLocalCopy(SUnit *CopySU, ScheduleDAGMILive *DAG);
};
} // anonymous

/// constrainLocalCopy handles two possibilities:
/// 1) Local src:
/// I0:     = dst
/// I1: src = ...
/// I2:     = dst
/// I3: dst = src (copy)
/// (create pred->succ edges I0->I1, I2->I1)
///
/// 2) Local copy:
/// I0: dst = src (copy)
/// I1:     = dst
/// I2: src = ...
/// I3:     = dst
/// (create pred->succ edges I1->I2, I3->I2)
///
/// Although the MachineScheduler is currently constrained to single blocks,
/// this algorithm should handle extended blocks. An EBB is a set of
/// contiguously numbered blocks such that the previous block in the EBB is
/// always the single predecessor.
void CopyConstrain::constrainLocalCopy(SUnit *CopySU, ScheduleDAGMILive *DAG) {
  LiveIntervals *LIS = DAG->getLIS();
  MachineInstr *Copy = CopySU->getInstr();

  // Check for pure vreg copies.
  unsigned SrcReg = Copy->getOperand(1).getReg();
  if (!TargetRegisterInfo::isVirtualRegister(SrcReg))
    return;

  unsigned DstReg = Copy->getOperand(0).getReg();
  if (!TargetRegisterInfo::isVirtualRegister(DstReg))
    return;

  // Check if either the dest or source is local. If it's live across a back
  // edge, it's not local. Note that if both vregs are live across the back
  // edge, we cannot successfully contrain the copy without cyclic scheduling.
  // If both the copy's source and dest are local live intervals, then we
  // should treat the dest as the global for the purpose of adding
  // constraints. This adds edges from source's other uses to the copy.
  unsigned LocalReg = SrcReg;
  unsigned GlobalReg = DstReg;
  LiveInterval *LocalLI = &LIS->getInterval(LocalReg);
  if (!LocalLI->isLocal(RegionBeginIdx, RegionEndIdx)) {
    LocalReg = DstReg;
    GlobalReg = SrcReg;
    LocalLI = &LIS->getInterval(LocalReg);
    if (!LocalLI->isLocal(RegionBeginIdx, RegionEndIdx))
      return;
  }
  LiveInterval *GlobalLI = &LIS->getInterval(GlobalReg);

  // Find the global segment after the start of the local LI.
  LiveInterval::iterator GlobalSegment = GlobalLI->find(LocalLI->beginIndex());
  // If GlobalLI does not overlap LocalLI->start, then a copy directly feeds a
  // local live range. We could create edges from other global uses to the local
  // start, but the coalescer should have already eliminated these cases, so
  // don't bother dealing with it.
  if (GlobalSegment == GlobalLI->end())
    return;

  // If GlobalSegment is killed at the LocalLI->start, the call to find()
  // returned the next global segment. But if GlobalSegment overlaps with
  // LocalLI->start, then advance to the next segement. If a hole in GlobalLI
  // exists in LocalLI's vicinity, GlobalSegment will be the end of the hole.
  if (GlobalSegment->contains(LocalLI->beginIndex()))
    ++GlobalSegment;

  if (GlobalSegment == GlobalLI->end())
    return;

  // Check if GlobalLI contains a hole in the vicinity of LocalLI.
  if (GlobalSegment != GlobalLI->begin()) {
    // Two address defs have no hole.
    if (SlotIndex::isSameInstr(std::prev(GlobalSegment)->end,
                               GlobalSegment->start)) {
      return;
    }
    // If the prior global segment may be defined by the same two-address
    // instruction that also defines LocalLI, then can't make a hole here.
    if (SlotIndex::isSameInstr(std::prev(GlobalSegment)->start,
                               LocalLI->beginIndex())) {
      return;
    }
    // If GlobalLI has a prior segment, it must be live into the EBB. Otherwise
    // it would be a disconnected component in the live range.
    assert(std::prev(GlobalSegment)->start < LocalLI->beginIndex() &&
           "Disconnected LRG within the scheduling region.");
  }
  MachineInstr *GlobalDef = LIS->getInstructionFromIndex(GlobalSegment->start);
  if (!GlobalDef)
    return;

  SUnit *GlobalSU = DAG->getSUnit(GlobalDef);
  if (!GlobalSU)
    return;

  // GlobalDef is the bottom of the GlobalLI hole. Open the hole by
  // constraining the uses of the last local def to precede GlobalDef.
  SmallVector<SUnit*,8> LocalUses;
  const VNInfo *LastLocalVN = LocalLI->getVNInfoBefore(LocalLI->endIndex());
  MachineInstr *LastLocalDef = LIS->getInstructionFromIndex(LastLocalVN->def);
  SUnit *LastLocalSU = DAG->getSUnit(LastLocalDef);
  for (SUnit::const_succ_iterator
         I = LastLocalSU->Succs.begin(), E = LastLocalSU->Succs.end();
       I != E; ++I) {
    if (I->getKind() != SDep::Data || I->getReg() != LocalReg)
      continue;
    if (I->getSUnit() == GlobalSU)
      continue;
    if (!DAG->canAddEdge(GlobalSU, I->getSUnit()))
      return;
    LocalUses.push_back(I->getSUnit());
  }
  // Open the top of the GlobalLI hole by constraining any earlier global uses
  // to precede the start of LocalLI.
  SmallVector<SUnit*,8> GlobalUses;
  MachineInstr *FirstLocalDef =
    LIS->getInstructionFromIndex(LocalLI->beginIndex());
  SUnit *FirstLocalSU = DAG->getSUnit(FirstLocalDef);
  for (SUnit::const_pred_iterator
         I = GlobalSU->Preds.begin(), E = GlobalSU->Preds.end(); I != E; ++I) {
    if (I->getKind() != SDep::Anti || I->getReg() != GlobalReg)
      continue;
    if (I->getSUnit() == FirstLocalSU)
      continue;
    if (!DAG->canAddEdge(FirstLocalSU, I->getSUnit()))
      return;
    GlobalUses.push_back(I->getSUnit());
  }
  DEBUG(dbgs() << "Constraining copy SU(" << CopySU->NodeNum << ")\n");
  // Add the weak edges.
  for (SmallVectorImpl<SUnit*>::const_iterator
         I = LocalUses.begin(), E = LocalUses.end(); I != E; ++I) {
    DEBUG(dbgs() << "  Local use SU(" << (*I)->NodeNum << ") -> SU("
          << GlobalSU->NodeNum << ")\n");
    DAG->addEdge(GlobalSU, SDep(*I, SDep::Weak));
  }
  for (SmallVectorImpl<SUnit*>::const_iterator
         I = GlobalUses.begin(), E = GlobalUses.end(); I != E; ++I) {
    DEBUG(dbgs() << "  Global use SU(" << (*I)->NodeNum << ") -> SU("
          << FirstLocalSU->NodeNum << ")\n");
    DAG->addEdge(FirstLocalSU, SDep(*I, SDep::Weak));
  }
}

/// \brief Callback from DAG postProcessing to create weak edges to encourage
/// copy elimination.
void CopyConstrain::apply(ScheduleDAGMI *DAG) {
  assert(DAG->hasVRegLiveness() && "Expect VRegs with LiveIntervals");

  MachineBasicBlock::iterator FirstPos = nextIfDebug(DAG->begin(), DAG->end());
  if (FirstPos == DAG->end())
    return;
  RegionBeginIdx = DAG->getLIS()->getInstructionIndex(&*FirstPos);
  RegionEndIdx = DAG->getLIS()->getInstructionIndex(
    &*priorNonDebug(DAG->end(), DAG->begin()));

  for (unsigned Idx = 0, End = DAG->SUnits.size(); Idx != End; ++Idx) {
    SUnit *SU = &DAG->SUnits[Idx];
    if (!SU->getInstr()->isCopy())
      continue;

    constrainLocalCopy(SU, static_cast<ScheduleDAGMILive*>(DAG));
  }
}

//===----------------------------------------------------------------------===//
// MachineSchedStrategy helpers used by GenericScheduler, GenericPostScheduler
// and possibly other custom schedulers.
//===----------------------------------------------------------------------===//

static const unsigned InvalidCycle = ~0U;

SchedBoundary::~SchedBoundary() { delete HazardRec; }

void SchedBoundary::reset() {
  // A new HazardRec is created for each DAG and owned by SchedBoundary.
  // Destroying and reconstructing it is very expensive though. So keep
  // invalid, placeholder HazardRecs.
  if (HazardRec && HazardRec->isEnabled()) {
    delete HazardRec;
    HazardRec = nullptr;
  }
  Available.clear();
  Pending.clear();
  CheckPending = false;
  NextSUs.clear();
  CurrCycle = 0;
  CurrMOps = 0;
  MinReadyCycle = UINT_MAX;
  ExpectedLatency = 0;
  DependentLatency = 0;
  RetiredMOps = 0;
  MaxExecutedResCount = 0;
  ZoneCritResIdx = 0;
  IsResourceLimited = false;
  ReservedCycles.clear();
#ifndef NDEBUG
  // Track the maximum number of stall cycles that could arise either from the
  // latency of a DAG edge or the number of cycles that a processor resource is
  // reserved (SchedBoundary::ReservedCycles).
  MaxObservedStall = 0;
#endif
  // Reserve a zero-count for invalid CritResIdx.
  ExecutedResCounts.resize(1);
  assert(!ExecutedResCounts[0] && "nonzero count for bad resource");
}

void SchedRemainder::
init(ScheduleDAGMI *DAG, const TargetSchedModel *SchedModel) {
  reset();
  if (!SchedModel->hasInstrSchedModel())
    return;
  RemainingCounts.resize(SchedModel->getNumProcResourceKinds());
  for (std::vector<SUnit>::iterator
         I = DAG->SUnits.begin(), E = DAG->SUnits.end(); I != E; ++I) {
    const MCSchedClassDesc *SC = DAG->getSchedClass(&*I);
    RemIssueCount += SchedModel->getNumMicroOps(I->getInstr(), SC)
      * SchedModel->getMicroOpFactor();
    for (TargetSchedModel::ProcResIter
           PI = SchedModel->getWriteProcResBegin(SC),
           PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
      unsigned PIdx = PI->ProcResourceIdx;
      unsigned Factor = SchedModel->getResourceFactor(PIdx);
      RemainingCounts[PIdx] += (Factor * PI->Cycles);
    }
  }
}

void SchedBoundary::
init(ScheduleDAGMI *dag, const TargetSchedModel *smodel, SchedRemainder *rem) {
  reset();
  DAG = dag;
  SchedModel = smodel;
  Rem = rem;
  if (SchedModel->hasInstrSchedModel()) {
    ExecutedResCounts.resize(SchedModel->getNumProcResourceKinds());
    ReservedCycles.resize(SchedModel->getNumProcResourceKinds(), InvalidCycle);
  }
}

/// Compute the stall cycles based on this SUnit's ready time. Heuristics treat
/// these "soft stalls" differently than the hard stall cycles based on CPU
/// resources and computed by checkHazard(). A fully in-order model
/// (MicroOpBufferSize==0) will not make use of this since instructions are not
/// available for scheduling until they are ready. However, a weaker in-order
/// model may use this for heuristics. For example, if a processor has in-order
/// behavior when reading certain resources, this may come into play.
unsigned SchedBoundary::getLatencyStallCycles(SUnit *SU) {
  if (!SU->isUnbuffered)
    return 0;

  unsigned ReadyCycle = (isTop() ? SU->TopReadyCycle : SU->BotReadyCycle);
  if (ReadyCycle > CurrCycle)
    return ReadyCycle - CurrCycle;
  return 0;
}

/// Compute the next cycle at which the given processor resource can be
/// scheduled.
unsigned SchedBoundary::
getNextResourceCycle(unsigned PIdx, unsigned Cycles) {
  unsigned NextUnreserved = ReservedCycles[PIdx];
  // If this resource has never been used, always return cycle zero.
  if (NextUnreserved == InvalidCycle)
    return 0;
  // For bottom-up scheduling add the cycles needed for the current operation.
  if (!isTop())
    NextUnreserved += Cycles;
  return NextUnreserved;
}

/// Does this SU have a hazard within the current instruction group.
///
/// The scheduler supports two modes of hazard recognition. The first is the
/// ScheduleHazardRecognizer API. It is a fully general hazard recognizer that
/// supports highly complicated in-order reservation tables
/// (ScoreboardHazardRecognizer) and arbitraty target-specific logic.
///
/// The second is a streamlined mechanism that checks for hazards based on
/// simple counters that the scheduler itself maintains. It explicitly checks
/// for instruction dispatch limitations, including the number of micro-ops that
/// can dispatch per cycle.
///
/// TODO: Also check whether the SU must start a new group.
bool SchedBoundary::checkHazard(SUnit *SU) {
  if (HazardRec->isEnabled()
      && HazardRec->getHazardType(SU) != ScheduleHazardRecognizer::NoHazard) {
    return true;
  }
  unsigned uops = SchedModel->getNumMicroOps(SU->getInstr());
  if ((CurrMOps > 0) && (CurrMOps + uops > SchedModel->getIssueWidth())) {
    DEBUG(dbgs() << "  SU(" << SU->NodeNum << ") uops="
          << SchedModel->getNumMicroOps(SU->getInstr()) << '\n');
    return true;
  }
  if (SchedModel->hasInstrSchedModel() && SU->hasReservedResource) {
    const MCSchedClassDesc *SC = DAG->getSchedClass(SU);
    for (TargetSchedModel::ProcResIter
           PI = SchedModel->getWriteProcResBegin(SC),
           PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
      unsigned NRCycle = getNextResourceCycle(PI->ProcResourceIdx, PI->Cycles);
      if (NRCycle > CurrCycle) {
#ifndef NDEBUG
        MaxObservedStall = std::max(PI->Cycles, MaxObservedStall);
#endif
        DEBUG(dbgs() << "  SU(" << SU->NodeNum << ") "
              << SchedModel->getResourceName(PI->ProcResourceIdx)
              << "=" << NRCycle << "c\n");
        return true;
      }
    }
  }
  return false;
}

// Find the unscheduled node in ReadySUs with the highest latency.
unsigned SchedBoundary::
findMaxLatency(ArrayRef<SUnit*> ReadySUs) {
  SUnit *LateSU = nullptr;
  unsigned RemLatency = 0;
  for (ArrayRef<SUnit*>::iterator I = ReadySUs.begin(), E = ReadySUs.end();
       I != E; ++I) {
    unsigned L = getUnscheduledLatency(*I);
    if (L > RemLatency) {
      RemLatency = L;
      LateSU = *I;
    }
  }
  if (LateSU) {
    DEBUG(dbgs() << Available.getName() << " RemLatency SU("
          << LateSU->NodeNum << ") " << RemLatency << "c\n");
  }
  return RemLatency;
}

// Count resources in this zone and the remaining unscheduled
// instruction. Return the max count, scaled. Set OtherCritIdx to the critical
// resource index, or zero if the zone is issue limited.
unsigned SchedBoundary::
getOtherResourceCount(unsigned &OtherCritIdx) {
  OtherCritIdx = 0;
  if (!SchedModel->hasInstrSchedModel())
    return 0;

  unsigned OtherCritCount = Rem->RemIssueCount
    + (RetiredMOps * SchedModel->getMicroOpFactor());
  DEBUG(dbgs() << "  " << Available.getName() << " + Remain MOps: "
        << OtherCritCount / SchedModel->getMicroOpFactor() << '\n');
  for (unsigned PIdx = 1, PEnd = SchedModel->getNumProcResourceKinds();
       PIdx != PEnd; ++PIdx) {
    unsigned OtherCount = getResourceCount(PIdx) + Rem->RemainingCounts[PIdx];
    if (OtherCount > OtherCritCount) {
      OtherCritCount = OtherCount;
      OtherCritIdx = PIdx;
    }
  }
  if (OtherCritIdx) {
    DEBUG(dbgs() << "  " << Available.getName() << " + Remain CritRes: "
          << OtherCritCount / SchedModel->getResourceFactor(OtherCritIdx)
          << " " << SchedModel->getResourceName(OtherCritIdx) << "\n");
  }
  return OtherCritCount;
}

void SchedBoundary::releaseNode(SUnit *SU, unsigned ReadyCycle) {
  assert(SU->getInstr() && "Scheduled SUnit must have instr");

#ifndef NDEBUG
  // ReadyCycle was been bumped up to the CurrCycle when this node was
  // scheduled, but CurrCycle may have been eagerly advanced immediately after
  // scheduling, so may now be greater than ReadyCycle.
  if (ReadyCycle > CurrCycle)
    MaxObservedStall = std::max(ReadyCycle - CurrCycle, MaxObservedStall);
#endif

  if (ReadyCycle < MinReadyCycle)
    MinReadyCycle = ReadyCycle;

  // Check for interlocks first. For the purpose of other heuristics, an
  // instruction that cannot issue appears as if it's not in the ReadyQueue.
  bool IsBuffered = SchedModel->getMicroOpBufferSize() != 0;
  if ((!IsBuffered && ReadyCycle > CurrCycle) || checkHazard(SU))
    Pending.push(SU);
  else
    Available.push(SU);

  // Record this node as an immediate dependent of the scheduled node.
  NextSUs.insert(SU);
}

void SchedBoundary::releaseTopNode(SUnit *SU) {
  if (SU->isScheduled)
    return;

  releaseNode(SU, SU->TopReadyCycle);
}

void SchedBoundary::releaseBottomNode(SUnit *SU) {
  if (SU->isScheduled)
    return;

  releaseNode(SU, SU->BotReadyCycle);
}

/// Move the boundary of scheduled code by one cycle.
void SchedBoundary::bumpCycle(unsigned NextCycle) {
  if (SchedModel->getMicroOpBufferSize() == 0) {
    assert(MinReadyCycle < UINT_MAX && "MinReadyCycle uninitialized");
    if (MinReadyCycle > NextCycle)
      NextCycle = MinReadyCycle;
  }
  // Update the current micro-ops, which will issue in the next cycle.
  unsigned DecMOps = SchedModel->getIssueWidth() * (NextCycle - CurrCycle);
  CurrMOps = (CurrMOps <= DecMOps) ? 0 : CurrMOps - DecMOps;

  // Decrement DependentLatency based on the next cycle.
  if ((NextCycle - CurrCycle) > DependentLatency)
    DependentLatency = 0;
  else
    DependentLatency -= (NextCycle - CurrCycle);

  if (!HazardRec->isEnabled()) {
    // Bypass HazardRec virtual calls.
    CurrCycle = NextCycle;
  }
  else {
    // Bypass getHazardType calls in case of long latency.
    for (; CurrCycle != NextCycle; ++CurrCycle) {
      if (isTop())
        HazardRec->AdvanceCycle();
      else
        HazardRec->RecedeCycle();
    }
  }
  CheckPending = true;
  unsigned LFactor = SchedModel->getLatencyFactor();
  IsResourceLimited =
    (int)(getCriticalCount() - (getScheduledLatency() * LFactor))
    > (int)LFactor;

  DEBUG(dbgs() << "Cycle: " << CurrCycle << ' ' << Available.getName() << '\n');
}

void SchedBoundary::incExecutedResources(unsigned PIdx, unsigned Count) {
  ExecutedResCounts[PIdx] += Count;
  if (ExecutedResCounts[PIdx] > MaxExecutedResCount)
    MaxExecutedResCount = ExecutedResCounts[PIdx];
}

/// Add the given processor resource to this scheduled zone.
///
/// \param Cycles indicates the number of consecutive (non-pipelined) cycles
/// during which this resource is consumed.
///
/// \return the next cycle at which the instruction may execute without
/// oversubscribing resources.
unsigned SchedBoundary::
countResource(unsigned PIdx, unsigned Cycles, unsigned NextCycle) {
  unsigned Factor = SchedModel->getResourceFactor(PIdx);
  unsigned Count = Factor * Cycles;
  DEBUG(dbgs() << "  " << SchedModel->getResourceName(PIdx)
        << " +" << Cycles << "x" << Factor << "u\n");

  // Update Executed resources counts.
  incExecutedResources(PIdx, Count);
  assert(Rem->RemainingCounts[PIdx] >= Count && "resource double counted");
  Rem->RemainingCounts[PIdx] -= Count;

  // Check if this resource exceeds the current critical resource. If so, it
  // becomes the critical resource.
  if (ZoneCritResIdx != PIdx && (getResourceCount(PIdx) > getCriticalCount())) {
    ZoneCritResIdx = PIdx;
    DEBUG(dbgs() << "  *** Critical resource "
          << SchedModel->getResourceName(PIdx) << ": "
          << getResourceCount(PIdx) / SchedModel->getLatencyFactor() << "c\n");
  }
  // For reserved resources, record the highest cycle using the resource.
  unsigned NextAvailable = getNextResourceCycle(PIdx, Cycles);
  if (NextAvailable > CurrCycle) {
    DEBUG(dbgs() << "  Resource conflict: "
          << SchedModel->getProcResource(PIdx)->Name << " reserved until @"
          << NextAvailable << "\n");
  }
  return NextAvailable;
}

/// Move the boundary of scheduled code by one SUnit.
void SchedBoundary::bumpNode(SUnit *SU) {
  // Update the reservation table.
  if (HazardRec->isEnabled()) {
    if (!isTop() && SU->isCall) {
      // Calls are scheduled with their preceding instructions. For bottom-up
      // scheduling, clear the pipeline state before emitting.
      HazardRec->Reset();
    }
    HazardRec->EmitInstruction(SU);
  }
  // checkHazard should prevent scheduling multiple instructions per cycle that
  // exceed the issue width.
  const MCSchedClassDesc *SC = DAG->getSchedClass(SU);
  unsigned IncMOps = SchedModel->getNumMicroOps(SU->getInstr());
  assert(
      (CurrMOps == 0 || (CurrMOps + IncMOps) <= SchedModel->getIssueWidth()) &&
      "Cannot schedule this instruction's MicroOps in the current cycle.");

  unsigned ReadyCycle = (isTop() ? SU->TopReadyCycle : SU->BotReadyCycle);
  DEBUG(dbgs() << "  Ready @" << ReadyCycle << "c\n");

  unsigned NextCycle = CurrCycle;
  switch (SchedModel->getMicroOpBufferSize()) {
  case 0:
    assert(ReadyCycle <= CurrCycle && "Broken PendingQueue");
    break;
  case 1:
    if (ReadyCycle > NextCycle) {
      NextCycle = ReadyCycle;
      DEBUG(dbgs() << "  *** Stall until: " << ReadyCycle << "\n");
    }
    break;
  default:
    // We don't currently model the OOO reorder buffer, so consider all
    // scheduled MOps to be "retired". We do loosely model in-order resource
    // latency. If this instruction uses an in-order resource, account for any
    // likely stall cycles.
    if (SU->isUnbuffered && ReadyCycle > NextCycle)
      NextCycle = ReadyCycle;
    break;
  }
  RetiredMOps += IncMOps;

  // Update resource counts and critical resource.
  if (SchedModel->hasInstrSchedModel()) {
    unsigned DecRemIssue = IncMOps * SchedModel->getMicroOpFactor();
    assert(Rem->RemIssueCount >= DecRemIssue && "MOps double counted");
    Rem->RemIssueCount -= DecRemIssue;
    if (ZoneCritResIdx) {
      // Scale scheduled micro-ops for comparing with the critical resource.
      unsigned ScaledMOps =
        RetiredMOps * SchedModel->getMicroOpFactor();

      // If scaled micro-ops are now more than the previous critical resource by
      // a full cycle, then micro-ops issue becomes critical.
      if ((int)(ScaledMOps - getResourceCount(ZoneCritResIdx))
          >= (int)SchedModel->getLatencyFactor()) {
        ZoneCritResIdx = 0;
        DEBUG(dbgs() << "  *** Critical resource NumMicroOps: "
              << ScaledMOps / SchedModel->getLatencyFactor() << "c\n");
      }
    }
    for (TargetSchedModel::ProcResIter
           PI = SchedModel->getWriteProcResBegin(SC),
           PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
      unsigned RCycle =
        countResource(PI->ProcResourceIdx, PI->Cycles, NextCycle);
      if (RCycle > NextCycle)
        NextCycle = RCycle;
    }
    if (SU->hasReservedResource) {
      // For reserved resources, record the highest cycle using the resource.
      // For top-down scheduling, this is the cycle in which we schedule this
      // instruction plus the number of cycles the operations reserves the
      // resource. For bottom-up is it simply the instruction's cycle.
      for (TargetSchedModel::ProcResIter
             PI = SchedModel->getWriteProcResBegin(SC),
             PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
        unsigned PIdx = PI->ProcResourceIdx;
        if (SchedModel->getProcResource(PIdx)->BufferSize == 0) {
          if (isTop()) {
            ReservedCycles[PIdx] =
              std::max(getNextResourceCycle(PIdx, 0), NextCycle + PI->Cycles);
          }
          else
            ReservedCycles[PIdx] = NextCycle;
        }
      }
    }
  }
  // Update ExpectedLatency and DependentLatency.
  unsigned &TopLatency = isTop() ? ExpectedLatency : DependentLatency;
  unsigned &BotLatency = isTop() ? DependentLatency : ExpectedLatency;
  if (SU->getDepth() > TopLatency) {
    TopLatency = SU->getDepth();
    DEBUG(dbgs() << "  " << Available.getName()
          << " TopLatency SU(" << SU->NodeNum << ") " << TopLatency << "c\n");
  }
  if (SU->getHeight() > BotLatency) {
    BotLatency = SU->getHeight();
    DEBUG(dbgs() << "  " << Available.getName()
          << " BotLatency SU(" << SU->NodeNum << ") " << BotLatency << "c\n");
  }
  // If we stall for any reason, bump the cycle.
  if (NextCycle > CurrCycle) {
    bumpCycle(NextCycle);
  }
  else {
    // After updating ZoneCritResIdx and ExpectedLatency, check if we're
    // resource limited. If a stall occurred, bumpCycle does this.
    unsigned LFactor = SchedModel->getLatencyFactor();
    IsResourceLimited =
      (int)(getCriticalCount() - (getScheduledLatency() * LFactor))
      > (int)LFactor;
  }
  // Update CurrMOps after calling bumpCycle to handle stalls, since bumpCycle
  // resets CurrMOps. Loop to handle instructions with more MOps than issue in
  // one cycle.  Since we commonly reach the max MOps here, opportunistically
  // bump the cycle to avoid uselessly checking everything in the readyQ.
  CurrMOps += IncMOps;
  while (CurrMOps >= SchedModel->getIssueWidth()) {
    DEBUG(dbgs() << "  *** Max MOps " << CurrMOps
          << " at cycle " << CurrCycle << '\n');
    bumpCycle(++NextCycle);
  }
  DEBUG(dumpScheduledState());
}

/// Release pending ready nodes in to the available queue. This makes them
/// visible to heuristics.
void SchedBoundary::releasePending() {
  // If the available queue is empty, it is safe to reset MinReadyCycle.
  if (Available.empty())
    MinReadyCycle = UINT_MAX;

  // Check to see if any of the pending instructions are ready to issue.  If
  // so, add them to the available queue.
  bool IsBuffered = SchedModel->getMicroOpBufferSize() != 0;
  for (unsigned i = 0, e = Pending.size(); i != e; ++i) {
    SUnit *SU = *(Pending.begin()+i);
    unsigned ReadyCycle = isTop() ? SU->TopReadyCycle : SU->BotReadyCycle;

    if (ReadyCycle < MinReadyCycle)
      MinReadyCycle = ReadyCycle;

    if (!IsBuffered && ReadyCycle > CurrCycle)
      continue;

    if (checkHazard(SU))
      continue;

    Available.push(SU);
    Pending.remove(Pending.begin()+i);
    --i; --e;
  }
  DEBUG(if (!Pending.empty()) Pending.dump());
  CheckPending = false;
}

/// Remove SU from the ready set for this boundary.
void SchedBoundary::removeReady(SUnit *SU) {
  if (Available.isInQueue(SU))
    Available.remove(Available.find(SU));
  else {
    assert(Pending.isInQueue(SU) && "bad ready count");
    Pending.remove(Pending.find(SU));
  }
}

/// If this queue only has one ready candidate, return it. As a side effect,
/// defer any nodes that now hit a hazard, and advance the cycle until at least
/// one node is ready. If multiple instructions are ready, return NULL.
SUnit *SchedBoundary::pickOnlyChoice() {
  if (CheckPending)
    releasePending();

  if (CurrMOps > 0) {
    // Defer any ready instrs that now have a hazard.
    for (ReadyQueue::iterator I = Available.begin(); I != Available.end();) {
      if (checkHazard(*I)) {
        Pending.push(*I);
        I = Available.remove(I);
        continue;
      }
      ++I;
    }
  }
  for (unsigned i = 0; Available.empty(); ++i) {
//  FIXME: Re-enable assert once PR20057 is resolved.
//    assert(i <= (HazardRec->getMaxLookAhead() + MaxObservedStall) &&
//           "permanent hazard");
    (void)i;
    bumpCycle(CurrCycle + 1);
    releasePending();
  }
  if (Available.size() == 1)
    return *Available.begin();
  return nullptr;
}

#ifndef NDEBUG
// This is useful information to dump after bumpNode.
// Note that the Queue contents are more useful before pickNodeFromQueue.
void SchedBoundary::dumpScheduledState() {
  unsigned ResFactor;
  unsigned ResCount;
  if (ZoneCritResIdx) {
    ResFactor = SchedModel->getResourceFactor(ZoneCritResIdx);
    ResCount = getResourceCount(ZoneCritResIdx);
  }
  else {
    ResFactor = SchedModel->getMicroOpFactor();
    ResCount = RetiredMOps * SchedModel->getMicroOpFactor();
  }
  unsigned LFactor = SchedModel->getLatencyFactor();
  dbgs() << Available.getName() << " @" << CurrCycle << "c\n"
         << "  Retired: " << RetiredMOps;
  dbgs() << "\n  Executed: " << getExecutedCount() / LFactor << "c";
  dbgs() << "\n  Critical: " << ResCount / LFactor << "c, "
         << ResCount / ResFactor << " "
         << SchedModel->getResourceName(ZoneCritResIdx)
         << "\n  ExpectedLatency: " << ExpectedLatency << "c\n"
         << (IsResourceLimited ? "  - Resource" : "  - Latency")
         << " limited.\n";
}
#endif

//===----------------------------------------------------------------------===//
// GenericScheduler - Generic implementation of MachineSchedStrategy.
//===----------------------------------------------------------------------===//

void GenericSchedulerBase::SchedCandidate::
initResourceDelta(const ScheduleDAGMI *DAG,
                  const TargetSchedModel *SchedModel) {
  if (!Policy.ReduceResIdx && !Policy.DemandResIdx)
    return;

  const MCSchedClassDesc *SC = DAG->getSchedClass(SU);
  for (TargetSchedModel::ProcResIter
         PI = SchedModel->getWriteProcResBegin(SC),
         PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
    if (PI->ProcResourceIdx == Policy.ReduceResIdx)
      ResDelta.CritResources += PI->Cycles;
    if (PI->ProcResourceIdx == Policy.DemandResIdx)
      ResDelta.DemandedResources += PI->Cycles;
  }
}

/// Set the CandPolicy given a scheduling zone given the current resources and
/// latencies inside and outside the zone.
void GenericSchedulerBase::setPolicy(CandPolicy &Policy,
                                     bool IsPostRA,
                                     SchedBoundary &CurrZone,
                                     SchedBoundary *OtherZone) {
  // Apply preemptive heuristics based on the the total latency and resources
  // inside and outside this zone. Potential stalls should be considered before
  // following this policy.

  // Compute remaining latency. We need this both to determine whether the
  // overall schedule has become latency-limited and whether the instructions
  // outside this zone are resource or latency limited.
  //
  // The "dependent" latency is updated incrementally during scheduling as the
  // max height/depth of scheduled nodes minus the cycles since it was
  // scheduled:
  //   DLat = max (N.depth - (CurrCycle - N.ReadyCycle) for N in Zone
  //
  // The "independent" latency is the max ready queue depth:
  //   ILat = max N.depth for N in Available|Pending
  //
  // RemainingLatency is the greater of independent and dependent latency.
  unsigned RemLatency = CurrZone.getDependentLatency();
  RemLatency = std::max(RemLatency,
                        CurrZone.findMaxLatency(CurrZone.Available.elements()));
  RemLatency = std::max(RemLatency,
                        CurrZone.findMaxLatency(CurrZone.Pending.elements()));

  // Compute the critical resource outside the zone.
  unsigned OtherCritIdx = 0;
  unsigned OtherCount =
    OtherZone ? OtherZone->getOtherResourceCount(OtherCritIdx) : 0;

  bool OtherResLimited = false;
  if (SchedModel->hasInstrSchedModel()) {
    unsigned LFactor = SchedModel->getLatencyFactor();
    OtherResLimited = (int)(OtherCount - (RemLatency * LFactor)) > (int)LFactor;
  }
  // Schedule aggressively for latency in PostRA mode. We don't check for
  // acyclic latency during PostRA, and highly out-of-order processors will
  // skip PostRA scheduling.
  if (!OtherResLimited) {
    if (IsPostRA || (RemLatency + CurrZone.getCurrCycle() > Rem.CriticalPath)) {
      Policy.ReduceLatency |= true;
      DEBUG(dbgs() << "  " << CurrZone.Available.getName()
            << " RemainingLatency " << RemLatency << " + "
            << CurrZone.getCurrCycle() << "c > CritPath "
            << Rem.CriticalPath << "\n");
    }
  }
  // If the same resource is limiting inside and outside the zone, do nothing.
  if (CurrZone.getZoneCritResIdx() == OtherCritIdx)
    return;

  DEBUG(
    if (CurrZone.isResourceLimited()) {
      dbgs() << "  " << CurrZone.Available.getName() << " ResourceLimited: "
             << SchedModel->getResourceName(CurrZone.getZoneCritResIdx())
             << "\n";
    }
    if (OtherResLimited)
      dbgs() << "  RemainingLimit: "
             << SchedModel->getResourceName(OtherCritIdx) << "\n";
    if (!CurrZone.isResourceLimited() && !OtherResLimited)
      dbgs() << "  Latency limited both directions.\n");

  if (CurrZone.isResourceLimited() && !Policy.ReduceResIdx)
    Policy.ReduceResIdx = CurrZone.getZoneCritResIdx();

  if (OtherResLimited)
    Policy.DemandResIdx = OtherCritIdx;
}

#ifndef NDEBUG
const char *GenericSchedulerBase::getReasonStr(
  GenericSchedulerBase::CandReason Reason) {
  switch (Reason) {
  case NoCand:         return "NOCAND    ";
  case PhysRegCopy:    return "PREG-COPY";
  case RegExcess:      return "REG-EXCESS";
  case RegCritical:    return "REG-CRIT  ";
  case Stall:          return "STALL     ";
  case Cluster:        return "CLUSTER   ";
  case Weak:           return "WEAK      ";
  case RegMax:         return "REG-MAX   ";
  case ResourceReduce: return "RES-REDUCE";
  case ResourceDemand: return "RES-DEMAND";
  case TopDepthReduce: return "TOP-DEPTH ";
  case TopPathReduce:  return "TOP-PATH  ";
  case BotHeightReduce:return "BOT-HEIGHT";
  case BotPathReduce:  return "BOT-PATH  ";
  case NextDefUse:     return "DEF-USE   ";
  case NodeOrder:      return "ORDER     ";
  };
  llvm_unreachable("Unknown reason!");
}

void GenericSchedulerBase::traceCandidate(const SchedCandidate &Cand) {
  PressureChange P;
  unsigned ResIdx = 0;
  unsigned Latency = 0;
  switch (Cand.Reason) {
  default:
    break;
  case RegExcess:
    P = Cand.RPDelta.Excess;
    break;
  case RegCritical:
    P = Cand.RPDelta.CriticalMax;
    break;
  case RegMax:
    P = Cand.RPDelta.CurrentMax;
    break;
  case ResourceReduce:
    ResIdx = Cand.Policy.ReduceResIdx;
    break;
  case ResourceDemand:
    ResIdx = Cand.Policy.DemandResIdx;
    break;
  case TopDepthReduce:
    Latency = Cand.SU->getDepth();
    break;
  case TopPathReduce:
    Latency = Cand.SU->getHeight();
    break;
  case BotHeightReduce:
    Latency = Cand.SU->getHeight();
    break;
  case BotPathReduce:
    Latency = Cand.SU->getDepth();
    break;
  }
  dbgs() << "  SU(" << Cand.SU->NodeNum << ") " << getReasonStr(Cand.Reason);
  if (P.isValid())
    dbgs() << " " << TRI->getRegPressureSetName(P.getPSet())
           << ":" << P.getUnitInc() << " ";
  else
    dbgs() << "      ";
  if (ResIdx)
    dbgs() << " " << SchedModel->getProcResource(ResIdx)->Name << " ";
  else
    dbgs() << "         ";
  if (Latency)
    dbgs() << " " << Latency << " cycles ";
  else
    dbgs() << "          ";
  dbgs() << '\n';
}
#endif

/// Return true if this heuristic determines order.
static bool tryLess(int TryVal, int CandVal,
                    GenericSchedulerBase::SchedCandidate &TryCand,
                    GenericSchedulerBase::SchedCandidate &Cand,
                    GenericSchedulerBase::CandReason Reason) {
  if (TryVal < CandVal) {
    TryCand.Reason = Reason;
    return true;
  }
  if (TryVal > CandVal) {
    if (Cand.Reason > Reason)
      Cand.Reason = Reason;
    return true;
  }
  Cand.setRepeat(Reason);
  return false;
}

static bool tryGreater(int TryVal, int CandVal,
                       GenericSchedulerBase::SchedCandidate &TryCand,
                       GenericSchedulerBase::SchedCandidate &Cand,
                       GenericSchedulerBase::CandReason Reason) {
  if (TryVal > CandVal) {
    TryCand.Reason = Reason;
    return true;
  }
  if (TryVal < CandVal) {
    if (Cand.Reason > Reason)
      Cand.Reason = Reason;
    return true;
  }
  Cand.setRepeat(Reason);
  return false;
}

static bool tryLatency(GenericSchedulerBase::SchedCandidate &TryCand,
                       GenericSchedulerBase::SchedCandidate &Cand,
                       SchedBoundary &Zone) {
  if (Zone.isTop()) {
    if (Cand.SU->getDepth() > Zone.getScheduledLatency()) {
      if (tryLess(TryCand.SU->getDepth(), Cand.SU->getDepth(),
                  TryCand, Cand, GenericSchedulerBase::TopDepthReduce))
        return true;
    }
    if (tryGreater(TryCand.SU->getHeight(), Cand.SU->getHeight(),
                   TryCand, Cand, GenericSchedulerBase::TopPathReduce))
      return true;
  }
  else {
    if (Cand.SU->getHeight() > Zone.getScheduledLatency()) {
      if (tryLess(TryCand.SU->getHeight(), Cand.SU->getHeight(),
                  TryCand, Cand, GenericSchedulerBase::BotHeightReduce))
        return true;
    }
    if (tryGreater(TryCand.SU->getDepth(), Cand.SU->getDepth(),
                   TryCand, Cand, GenericSchedulerBase::BotPathReduce))
      return true;
  }
  return false;
}

static void tracePick(const GenericSchedulerBase::SchedCandidate &Cand,
                      bool IsTop) {
  DEBUG(dbgs() << "Pick " << (IsTop ? "Top " : "Bot ")
        << GenericSchedulerBase::getReasonStr(Cand.Reason) << '\n');
}

void GenericScheduler::initialize(ScheduleDAGMI *dag) {
  assert(dag->hasVRegLiveness() &&
         "(PreRA)GenericScheduler needs vreg liveness");
  DAG = static_cast<ScheduleDAGMILive*>(dag);
  SchedModel = DAG->getSchedModel();
  TRI = DAG->TRI;

  Rem.init(DAG, SchedModel);
  Top.init(DAG, SchedModel, &Rem);
  Bot.init(DAG, SchedModel, &Rem);

  // Initialize resource counts.

  // Initialize the HazardRecognizers. If itineraries don't exist, are empty, or
  // are disabled, then these HazardRecs will be disabled.
  const InstrItineraryData *Itin = SchedModel->getInstrItineraries();
  if (!Top.HazardRec) {
    Top.HazardRec =
        DAG->MF.getSubtarget().getInstrInfo()->CreateTargetMIHazardRecognizer(
            Itin, DAG);
  }
  if (!Bot.HazardRec) {
    Bot.HazardRec =
        DAG->MF.getSubtarget().getInstrInfo()->CreateTargetMIHazardRecognizer(
            Itin, DAG);
  }
}

/// Initialize the per-region scheduling policy.
void GenericScheduler::initPolicy(MachineBasicBlock::iterator Begin,
                                  MachineBasicBlock::iterator End,
                                  unsigned NumRegionInstrs) {
  const MachineFunction &MF = *Begin->getParent()->getParent();
  const TargetLowering *TLI = MF.getSubtarget().getTargetLowering();

  // Avoid setting up the register pressure tracker for small regions to save
  // compile time. As a rough heuristic, only track pressure when the number of
  // schedulable instructions exceeds half the integer register file.
  RegionPolicy.ShouldTrackPressure = true;
  for (unsigned VT = MVT::i32; VT > (unsigned)MVT::i1; --VT) {
    MVT::SimpleValueType LegalIntVT = (MVT::SimpleValueType)VT;
    if (TLI->isTypeLegal(LegalIntVT)) {
      unsigned NIntRegs = Context->RegClassInfo->getNumAllocatableRegs(
        TLI->getRegClassFor(LegalIntVT));
      RegionPolicy.ShouldTrackPressure = NumRegionInstrs > (NIntRegs / 2);
    }
  }

  // For generic targets, we default to bottom-up, because it's simpler and more
  // compile-time optimizations have been implemented in that direction.
  RegionPolicy.OnlyBottomUp = true;

  // Allow the subtarget to override default policy.
  MF.getSubtarget().overrideSchedPolicy(RegionPolicy, Begin, End,
                                        NumRegionInstrs);

  // After subtarget overrides, apply command line options.
  if (!EnableRegPressure)
    RegionPolicy.ShouldTrackPressure = false;

  // Check -misched-topdown/bottomup can force or unforce scheduling direction.
  // e.g. -misched-bottomup=false allows scheduling in both directions.
  assert((!ForceTopDown || !ForceBottomUp) &&
         "-misched-topdown incompatible with -misched-bottomup");
  if (ForceBottomUp.getNumOccurrences() > 0) {
    RegionPolicy.OnlyBottomUp = ForceBottomUp;
    if (RegionPolicy.OnlyBottomUp)
      RegionPolicy.OnlyTopDown = false;
  }
  if (ForceTopDown.getNumOccurrences() > 0) {
    RegionPolicy.OnlyTopDown = ForceTopDown;
    if (RegionPolicy.OnlyTopDown)
      RegionPolicy.OnlyBottomUp = false;
  }
}

/// Set IsAcyclicLatencyLimited if the acyclic path is longer than the cyclic
/// critical path by more cycles than it takes to drain the instruction buffer.
/// We estimate an upper bounds on in-flight instructions as:
///
/// CyclesPerIteration = max( CyclicPath, Loop-Resource-Height )
/// InFlightIterations = AcyclicPath / CyclesPerIteration
/// InFlightResources = InFlightIterations * LoopResources
///
/// TODO: Check execution resources in addition to IssueCount.
void GenericScheduler::checkAcyclicLatency() {
  if (Rem.CyclicCritPath == 0 || Rem.CyclicCritPath >= Rem.CriticalPath)
    return;

  // Scaled number of cycles per loop iteration.
  unsigned IterCount =
    std::max(Rem.CyclicCritPath * SchedModel->getLatencyFactor(),
             Rem.RemIssueCount);
  // Scaled acyclic critical path.
  unsigned AcyclicCount = Rem.CriticalPath * SchedModel->getLatencyFactor();
  // InFlightCount = (AcyclicPath / IterCycles) * InstrPerLoop
  unsigned InFlightCount =
    (AcyclicCount * Rem.RemIssueCount + IterCount-1) / IterCount;
  unsigned BufferLimit =
    SchedModel->getMicroOpBufferSize() * SchedModel->getMicroOpFactor();

  Rem.IsAcyclicLatencyLimited = InFlightCount > BufferLimit;

  DEBUG(dbgs() << "IssueCycles="
        << Rem.RemIssueCount / SchedModel->getLatencyFactor() << "c "
        << "IterCycles=" << IterCount / SchedModel->getLatencyFactor()
        << "c NumIters=" << (AcyclicCount + IterCount-1) / IterCount
        << " InFlight=" << InFlightCount / SchedModel->getMicroOpFactor()
        << "m BufferLim=" << SchedModel->getMicroOpBufferSize() << "m\n";
        if (Rem.IsAcyclicLatencyLimited)
          dbgs() << "  ACYCLIC LATENCY LIMIT\n");
}

void GenericScheduler::registerRoots() {
  Rem.CriticalPath = DAG->ExitSU.getDepth();

  // Some roots may not feed into ExitSU. Check all of them in case.
  for (std::vector<SUnit*>::const_iterator
         I = Bot.Available.begin(), E = Bot.Available.end(); I != E; ++I) {
    if ((*I)->getDepth() > Rem.CriticalPath)
      Rem.CriticalPath = (*I)->getDepth();
  }
  DEBUG(dbgs() << "Critical Path(GS-RR ): " << Rem.CriticalPath << '\n');
  if (DumpCriticalPathLength) {
    errs() << "Critical Path(GS-RR ): " << Rem.CriticalPath << " \n";
  }

  if (EnableCyclicPath) {
    Rem.CyclicCritPath = DAG->computeCyclicCriticalPath();
    checkAcyclicLatency();
  }
}

static bool tryPressure(const PressureChange &TryP,
                        const PressureChange &CandP,
                        GenericSchedulerBase::SchedCandidate &TryCand,
                        GenericSchedulerBase::SchedCandidate &Cand,
                        GenericSchedulerBase::CandReason Reason) {
  int TryRank = TryP.getPSetOrMax();
  int CandRank = CandP.getPSetOrMax();
  // If both candidates affect the same set, go with the smallest increase.
  if (TryRank == CandRank) {
    return tryLess(TryP.getUnitInc(), CandP.getUnitInc(), TryCand, Cand,
                   Reason);
  }
  // If one candidate decreases and the other increases, go with it.
  // Invalid candidates have UnitInc==0.
  if (tryGreater(TryP.getUnitInc() < 0, CandP.getUnitInc() < 0, TryCand, Cand,
                 Reason)) {
    return true;
  }
  // If the candidates are decreasing pressure, reverse priority.
  if (TryP.getUnitInc() < 0)
    std::swap(TryRank, CandRank);
  return tryGreater(TryRank, CandRank, TryCand, Cand, Reason);
}

static unsigned getWeakLeft(const SUnit *SU, bool isTop) {
  return (isTop) ? SU->WeakPredsLeft : SU->WeakSuccsLeft;
}

/// Minimize physical register live ranges. Regalloc wants them adjacent to
/// their physreg def/use.
///
/// FIXME: This is an unnecessary check on the critical path. Most are root/leaf
/// copies which can be prescheduled. The rest (e.g. x86 MUL) could be bundled
/// with the operation that produces or consumes the physreg. We'll do this when
/// regalloc has support for parallel copies.
static int biasPhysRegCopy(const SUnit *SU, bool isTop) {
  const MachineInstr *MI = SU->getInstr();
  if (!MI->isCopy())
    return 0;

  unsigned ScheduledOper = isTop ? 1 : 0;
  unsigned UnscheduledOper = isTop ? 0 : 1;
  // If we have already scheduled the physreg produce/consumer, immediately
  // schedule the copy.
  if (TargetRegisterInfo::isPhysicalRegister(
        MI->getOperand(ScheduledOper).getReg()))
    return 1;
  // If the physreg is at the boundary, defer it. Otherwise schedule it
  // immediately to free the dependent. We can hoist the copy later.
  bool AtBoundary = isTop ? !SU->NumSuccsLeft : !SU->NumPredsLeft;
  if (TargetRegisterInfo::isPhysicalRegister(
        MI->getOperand(UnscheduledOper).getReg()))
    return AtBoundary ? -1 : 1;
  return 0;
}

/// Apply a set of heursitics to a new candidate. Heuristics are currently
/// hierarchical. This may be more efficient than a graduated cost model because
/// we don't need to evaluate all aspects of the model for each node in the
/// queue. But it's really done to make the heuristics easier to debug and
/// statistically analyze.
///
/// \param Cand provides the policy and current best candidate.
/// \param TryCand refers to the next SUnit candidate, otherwise uninitialized.
/// \param Zone describes the scheduled zone that we are extending.
/// \param RPTracker describes reg pressure within the scheduled zone.
/// \param TempTracker is a scratch pressure tracker to reuse in queries.
void GenericScheduler::tryCandidate(SchedCandidate &Cand,
                                    SchedCandidate &TryCand,
                                    SchedBoundary &Zone,
                                    const RegPressureTracker &RPTracker,
                                    RegPressureTracker &TempTracker) {

  if (DAG->isTrackingPressure()) {
    // Always initialize TryCand's RPDelta.
    if (Zone.isTop()) {
      TempTracker.getMaxDownwardPressureDelta(
        TryCand.SU->getInstr(),
        TryCand.RPDelta,
        DAG->getRegionCriticalPSets(),
        DAG->getRegPressure().MaxSetPressure);
    }
    else {
      if (VerifyScheduling) {
        TempTracker.getMaxUpwardPressureDelta(
          TryCand.SU->getInstr(),
          &DAG->getPressureDiff(TryCand.SU),
          TryCand.RPDelta,
          DAG->getRegionCriticalPSets(),
          DAG->getRegPressure().MaxSetPressure);
      }
      else {
        RPTracker.getUpwardPressureDelta(
          TryCand.SU->getInstr(),
          DAG->getPressureDiff(TryCand.SU),
          TryCand.RPDelta,
          DAG->getRegionCriticalPSets(),
          DAG->getRegPressure().MaxSetPressure);
      }
    }
  }
  DEBUG(if (TryCand.RPDelta.Excess.isValid())
          dbgs() << "  SU(" << TryCand.SU->NodeNum << ") "
                 << TRI->getRegPressureSetName(TryCand.RPDelta.Excess.getPSet())
                 << ":" << TryCand.RPDelta.Excess.getUnitInc() << "\n");

  // Initialize the candidate if needed.
  if (!Cand.isValid()) {
    TryCand.Reason = NodeOrder;
    return;
  }

  if (tryGreater(biasPhysRegCopy(TryCand.SU, Zone.isTop()),
                 biasPhysRegCopy(Cand.SU, Zone.isTop()),
                 TryCand, Cand, PhysRegCopy))
    return;

  // Avoid exceeding the target's limit. If signed PSetID is negative, it is
  // invalid; convert it to INT_MAX to give it lowest priority.
  if (DAG->isTrackingPressure() && tryPressure(TryCand.RPDelta.Excess,
                                               Cand.RPDelta.Excess,
                                               TryCand, Cand, RegExcess))
    return;

  // Avoid increasing the max critical pressure in the scheduled region.
  if (DAG->isTrackingPressure() && tryPressure(TryCand.RPDelta.CriticalMax,
                                               Cand.RPDelta.CriticalMax,
                                               TryCand, Cand, RegCritical))
    return;

  // For loops that are acyclic path limited, aggressively schedule for latency.
  // This can result in very long dependence chains scheduled in sequence, so
  // once every cycle (when CurrMOps == 0), switch to normal heuristics.
  if (Rem.IsAcyclicLatencyLimited && !Zone.getCurrMOps()
      && tryLatency(TryCand, Cand, Zone))
    return;

  // Prioritize instructions that read unbuffered resources by stall cycles.
  if (tryLess(Zone.getLatencyStallCycles(TryCand.SU),
              Zone.getLatencyStallCycles(Cand.SU), TryCand, Cand, Stall))
    return;

  // Keep clustered nodes together to encourage downstream peephole
  // optimizations which may reduce resource requirements.
  //
  // This is a best effort to set things up for a post-RA pass. Optimizations
  // like generating loads of multiple registers should ideally be done within
  // the scheduler pass by combining the loads during DAG postprocessing.
  const SUnit *NextClusterSU =
    Zone.isTop() ? DAG->getNextClusterSucc() : DAG->getNextClusterPred();
  if (tryGreater(TryCand.SU == NextClusterSU, Cand.SU == NextClusterSU,
                 TryCand, Cand, Cluster))
    return;

  // Weak edges are for clustering and other constraints.
  if (tryLess(getWeakLeft(TryCand.SU, Zone.isTop()),
              getWeakLeft(Cand.SU, Zone.isTop()),
              TryCand, Cand, Weak)) {
    return;
  }
  // Avoid increasing the max pressure of the entire region.
  if (DAG->isTrackingPressure() && tryPressure(TryCand.RPDelta.CurrentMax,
                                               Cand.RPDelta.CurrentMax,
                                               TryCand, Cand, RegMax))
    return;

  // Avoid critical resource consumption and balance the schedule.
  TryCand.initResourceDelta(DAG, SchedModel);
  if (tryLess(TryCand.ResDelta.CritResources, Cand.ResDelta.CritResources,
              TryCand, Cand, ResourceReduce))
    return;
  if (tryGreater(TryCand.ResDelta.DemandedResources,
                 Cand.ResDelta.DemandedResources,
                 TryCand, Cand, ResourceDemand))
    return;

  // Avoid serializing long latency dependence chains.
  // For acyclic path limited loops, latency was already checked above.
  if (Cand.Policy.ReduceLatency && !Rem.IsAcyclicLatencyLimited
      && tryLatency(TryCand, Cand, Zone)) {
    return;
  }

  // Prefer immediate defs/users of the last scheduled instruction. This is a
  // local pressure avoidance strategy that also makes the machine code
  // readable.
  if (tryGreater(Zone.isNextSU(TryCand.SU), Zone.isNextSU(Cand.SU),
                 TryCand, Cand, NextDefUse))
    return;

  // Fall through to original instruction order.
  if ((Zone.isTop() && TryCand.SU->NodeNum < Cand.SU->NodeNum)
      || (!Zone.isTop() && TryCand.SU->NodeNum > Cand.SU->NodeNum)) {
    TryCand.Reason = NodeOrder;
  }
}

/// Pick the best candidate from the queue.
///
/// TODO: getMaxPressureDelta results can be mostly cached for each SUnit during
/// DAG building. To adjust for the current scheduling location we need to
/// maintain the number of vreg uses remaining to be top-scheduled.
void GenericScheduler::pickNodeFromQueue(SchedBoundary &Zone,
                                         const RegPressureTracker &RPTracker,
                                         SchedCandidate &Cand) {
  ReadyQueue &Q = Zone.Available;

  DEBUG(Q.dump());

  // getMaxPressureDelta temporarily modifies the tracker.
  RegPressureTracker &TempTracker = const_cast<RegPressureTracker&>(RPTracker);

  for (ReadyQueue::iterator I = Q.begin(), E = Q.end(); I != E; ++I) {

    SchedCandidate TryCand(Cand.Policy);
    TryCand.SU = *I;
    tryCandidate(Cand, TryCand, Zone, RPTracker, TempTracker);
    if (TryCand.Reason != NoCand) {
      // Initialize resource delta if needed in case future heuristics query it.
      if (TryCand.ResDelta == SchedResourceDelta())
        TryCand.initResourceDelta(DAG, SchedModel);
      Cand.setBest(TryCand);
      DEBUG(traceCandidate(Cand));
    }
  }
}

/// Pick the best candidate node from either the top or bottom queue.
SUnit *GenericScheduler::pickNodeBidirectional(bool &IsTopNode) {
  // Schedule as far as possible in the direction of no choice. This is most
  // efficient, but also provides the best heuristics for CriticalPSets.
  if (SUnit *SU = Bot.pickOnlyChoice()) {
    IsTopNode = false;
    DEBUG(dbgs() << "Pick Bot NOCAND\n");
    return SU;
  }
  if (SUnit *SU = Top.pickOnlyChoice()) {
    IsTopNode = true;
    DEBUG(dbgs() << "Pick Top NOCAND\n");
    return SU;
  }
  CandPolicy NoPolicy;
  SchedCandidate BotCand(NoPolicy);
  SchedCandidate TopCand(NoPolicy);
  // Set the bottom-up policy based on the state of the current bottom zone and
  // the instructions outside the zone, including the top zone.
  setPolicy(BotCand.Policy, /*IsPostRA=*/false, Bot, &Top);
  // Set the top-down policy based on the state of the current top zone and
  // the instructions outside the zone, including the bottom zone.
  setPolicy(TopCand.Policy, /*IsPostRA=*/false, Top, &Bot);

  // Prefer bottom scheduling when heuristics are silent.
  pickNodeFromQueue(Bot, DAG->getBotRPTracker(), BotCand);
  assert(BotCand.Reason != NoCand && "failed to find the first candidate");

  // If either Q has a single candidate that provides the least increase in
  // Excess pressure, we can immediately schedule from that Q.
  //
  // RegionCriticalPSets summarizes the pressure within the scheduled region and
  // affects picking from either Q. If scheduling in one direction must
  // increase pressure for one of the excess PSets, then schedule in that
  // direction first to provide more freedom in the other direction.
  if ((BotCand.Reason == RegExcess && !BotCand.isRepeat(RegExcess))
      || (BotCand.Reason == RegCritical
          && !BotCand.isRepeat(RegCritical)))
  {
    IsTopNode = false;
    tracePick(BotCand, IsTopNode);
    return BotCand.SU;
  }
  // Check if the top Q has a better candidate.
  pickNodeFromQueue(Top, DAG->getTopRPTracker(), TopCand);
  assert(TopCand.Reason != NoCand && "failed to find the first candidate");

  // Choose the queue with the most important (lowest enum) reason.
  if (TopCand.Reason < BotCand.Reason) {
    IsTopNode = true;
    tracePick(TopCand, IsTopNode);
    return TopCand.SU;
  }
  // Otherwise prefer the bottom candidate, in node order if all else failed.
  IsTopNode = false;
  tracePick(BotCand, IsTopNode);
  return BotCand.SU;
}

/// Pick the best node to balance the schedule. Implements MachineSchedStrategy.
SUnit *GenericScheduler::pickNode(bool &IsTopNode) {
  if (DAG->top() == DAG->bottom()) {
    assert(Top.Available.empty() && Top.Pending.empty() &&
           Bot.Available.empty() && Bot.Pending.empty() && "ReadyQ garbage");
    return nullptr;
  }
  SUnit *SU;
  do {
    if (RegionPolicy.OnlyTopDown) {
      SU = Top.pickOnlyChoice();
      if (!SU) {
        CandPolicy NoPolicy;
        SchedCandidate TopCand(NoPolicy);
        pickNodeFromQueue(Top, DAG->getTopRPTracker(), TopCand);
        assert(TopCand.Reason != NoCand && "failed to find a candidate");
        tracePick(TopCand, true);
        SU = TopCand.SU;
      }
      IsTopNode = true;
    }
    else if (RegionPolicy.OnlyBottomUp) {
      SU = Bot.pickOnlyChoice();
      if (!SU) {
        CandPolicy NoPolicy;
        SchedCandidate BotCand(NoPolicy);
        pickNodeFromQueue(Bot, DAG->getBotRPTracker(), BotCand);
        assert(BotCand.Reason != NoCand && "failed to find a candidate");
        tracePick(BotCand, false);
        SU = BotCand.SU;
      }
      IsTopNode = false;
    }
    else {
      SU = pickNodeBidirectional(IsTopNode);
    }
  } while (SU->isScheduled);

  if (SU->isTopReady())
    Top.removeReady(SU);
  if (SU->isBottomReady())
    Bot.removeReady(SU);

  DEBUG(dbgs() << "Scheduling SU(" << SU->NodeNum << ") " << *SU->getInstr());
  return SU;
}

void GenericScheduler::reschedulePhysRegCopies(SUnit *SU, bool isTop) {

  MachineBasicBlock::iterator InsertPos = SU->getInstr();
  if (!isTop)
    ++InsertPos;
  SmallVectorImpl<SDep> &Deps = isTop ? SU->Preds : SU->Succs;

  // Find already scheduled copies with a single physreg dependence and move
  // them just above the scheduled instruction.
  for (SmallVectorImpl<SDep>::iterator I = Deps.begin(), E = Deps.end();
       I != E; ++I) {
    if (I->getKind() != SDep::Data || !TRI->isPhysicalRegister(I->getReg()))
      continue;
    SUnit *DepSU = I->getSUnit();
    if (isTop ? DepSU->Succs.size() > 1 : DepSU->Preds.size() > 1)
      continue;
    MachineInstr *Copy = DepSU->getInstr();
    if (!Copy->isCopy())
      continue;
    DEBUG(dbgs() << "  Rescheduling physreg copy ";
          I->getSUnit()->dump(DAG));
    DAG->moveInstruction(Copy, InsertPos);
  }
}

/// Update the scheduler's state after scheduling a node. This is the same node
/// that was just returned by pickNode(). However, ScheduleDAGMILive needs to
/// update it's state based on the current cycle before MachineSchedStrategy
/// does.
///
/// FIXME: Eventually, we may bundle physreg copies rather than rescheduling
/// them here. See comments in biasPhysRegCopy.
void GenericScheduler::schedNode(SUnit *SU, bool IsTopNode) {
  if (IsTopNode) {
    SU->TopReadyCycle = std::max(SU->TopReadyCycle, Top.getCurrCycle());
    Top.bumpNode(SU);
    if (SU->hasPhysRegUses)
      reschedulePhysRegCopies(SU, true);
  }
  else {
    SU->BotReadyCycle = std::max(SU->BotReadyCycle, Bot.getCurrCycle());
    Bot.bumpNode(SU);
    if (SU->hasPhysRegDefs)
      reschedulePhysRegCopies(SU, false);
  }
}

/// Create the standard converging machine scheduler. This will be used as the
/// default scheduler if the target does not set a default.
static ScheduleDAGInstrs *createGenericSchedLive(MachineSchedContext *C) {
  ScheduleDAGMILive *DAG = new ScheduleDAGMILive(C, make_unique<GenericScheduler>(C));
  // Register DAG post-processors.
  //
  // FIXME: extend the mutation API to allow earlier mutations to instantiate
  // data and pass it to later mutations. Have a single mutation that gathers
  // the interesting nodes in one pass.
  DAG->addMutation(make_unique<CopyConstrain>(DAG->TII, DAG->TRI));
  if (EnableLoadCluster && DAG->TII->enableClusterLoads())
    DAG->addMutation(make_unique<LoadClusterMutation>(DAG->TII, DAG->TRI));
  if (EnableMacroFusion)
    DAG->addMutation(make_unique<MacroFusion>(DAG->TII));
  return DAG;
}

static MachineSchedRegistry
GenericSchedRegistry("converge", "Standard converging scheduler.",
                     createGenericSchedLive);

//===----------------------------------------------------------------------===//
// PostGenericScheduler - Generic PostRA implementation of MachineSchedStrategy.
//===----------------------------------------------------------------------===//

void PostGenericScheduler::initialize(ScheduleDAGMI *Dag) {
  DAG = Dag;
  SchedModel = DAG->getSchedModel();
  TRI = DAG->TRI;

  Rem.init(DAG, SchedModel);
  Top.init(DAG, SchedModel, &Rem);
  BotRoots.clear();

  // Initialize the HazardRecognizers. If itineraries don't exist, are empty,
  // or are disabled, then these HazardRecs will be disabled.
  const InstrItineraryData *Itin = SchedModel->getInstrItineraries();
  if (!Top.HazardRec) {
    Top.HazardRec =
        DAG->MF.getSubtarget().getInstrInfo()->CreateTargetMIHazardRecognizer(
            Itin, DAG);
  }
}


void PostGenericScheduler::registerRoots() {
  Rem.CriticalPath = DAG->ExitSU.getDepth();

  // Some roots may not feed into ExitSU. Check all of them in case.
  for (SmallVectorImpl<SUnit*>::const_iterator
         I = BotRoots.begin(), E = BotRoots.end(); I != E; ++I) {
    if ((*I)->getDepth() > Rem.CriticalPath)
      Rem.CriticalPath = (*I)->getDepth();
  }
  DEBUG(dbgs() << "Critical Path: (PGS-RR) " << Rem.CriticalPath << '\n');
  if (DumpCriticalPathLength) {
    errs() << "Critical Path(PGS-RR ): " << Rem.CriticalPath << " \n";
  }
}

/// Apply a set of heursitics to a new candidate for PostRA scheduling.
///
/// \param Cand provides the policy and current best candidate.
/// \param TryCand refers to the next SUnit candidate, otherwise uninitialized.
void PostGenericScheduler::tryCandidate(SchedCandidate &Cand,
                                        SchedCandidate &TryCand) {

  // Initialize the candidate if needed.
  if (!Cand.isValid()) {
    TryCand.Reason = NodeOrder;
    return;
  }

  // Prioritize instructions that read unbuffered resources by stall cycles.
  if (tryLess(Top.getLatencyStallCycles(TryCand.SU),
              Top.getLatencyStallCycles(Cand.SU), TryCand, Cand, Stall))
    return;

  // Avoid critical resource consumption and balance the schedule.
  if (tryLess(TryCand.ResDelta.CritResources, Cand.ResDelta.CritResources,
              TryCand, Cand, ResourceReduce))
    return;
  if (tryGreater(TryCand.ResDelta.DemandedResources,
                 Cand.ResDelta.DemandedResources,
                 TryCand, Cand, ResourceDemand))
    return;

  // Avoid serializing long latency dependence chains.
  if (Cand.Policy.ReduceLatency && tryLatency(TryCand, Cand, Top)) {
    return;
  }

  // Fall through to original instruction order.
  if (TryCand.SU->NodeNum < Cand.SU->NodeNum)
    TryCand.Reason = NodeOrder;
}

void PostGenericScheduler::pickNodeFromQueue(SchedCandidate &Cand) {
  ReadyQueue &Q = Top.Available;

  DEBUG(Q.dump());

  for (ReadyQueue::iterator I = Q.begin(), E = Q.end(); I != E; ++I) {
    SchedCandidate TryCand(Cand.Policy);
    TryCand.SU = *I;
    TryCand.initResourceDelta(DAG, SchedModel);
    tryCandidate(Cand, TryCand);
    if (TryCand.Reason != NoCand) {
      Cand.setBest(TryCand);
      DEBUG(traceCandidate(Cand));
    }
  }
}

/// Pick the next node to schedule.
SUnit *PostGenericScheduler::pickNode(bool &IsTopNode) {
  if (DAG->top() == DAG->bottom()) {
    assert(Top.Available.empty() && Top.Pending.empty() && "ReadyQ garbage");
    return nullptr;
  }
  SUnit *SU;
  do {
    SU = Top.pickOnlyChoice();
    if (!SU) {
      CandPolicy NoPolicy;
      SchedCandidate TopCand(NoPolicy);
      // Set the top-down policy based on the state of the current top zone and
      // the instructions outside the zone, including the bottom zone.
      setPolicy(TopCand.Policy, /*IsPostRA=*/true, Top, nullptr);
      pickNodeFromQueue(TopCand);
      assert(TopCand.Reason != NoCand && "failed to find a candidate");
      tracePick(TopCand, true);
      SU = TopCand.SU;
    }
  } while (SU->isScheduled);

  IsTopNode = true;
  Top.removeReady(SU);

  DEBUG(dbgs() << "Scheduling SU(" << SU->NodeNum << ") " << *SU->getInstr());
  return SU;
}

/// Called after ScheduleDAGMI has scheduled an instruction and updated
/// scheduled/remaining flags in the DAG nodes.
void PostGenericScheduler::schedNode(SUnit *SU, bool IsTopNode) {
  SU->TopReadyCycle = std::max(SU->TopReadyCycle, Top.getCurrCycle());
  Top.bumpNode(SU);
}

/// Create a generic scheduler with no vreg liveness or DAG mutation passes.
static ScheduleDAGInstrs *createGenericSchedPostRA(MachineSchedContext *C) {
  return new ScheduleDAGMI(C, make_unique<PostGenericScheduler>(C), /*IsPostRA=*/true);
}

//===----------------------------------------------------------------------===//
// ILP Scheduler. Currently for experimental analysis of heuristics.
//===----------------------------------------------------------------------===//

namespace {
/// \brief Order nodes by the ILP metric.
struct ILPOrder {
  const SchedDFSResult *DFSResult;
  const BitVector *ScheduledTrees;
  bool MaximizeILP;

  ILPOrder(bool MaxILP)
    : DFSResult(nullptr), ScheduledTrees(nullptr), MaximizeILP(MaxILP) {}

  /// \brief Apply a less-than relation on node priority.
  ///
  /// (Return true if A comes after B in the Q.)
  bool operator()(const SUnit *A, const SUnit *B) const {
    unsigned SchedTreeA = DFSResult->getSubtreeID(A);
    unsigned SchedTreeB = DFSResult->getSubtreeID(B);
    if (SchedTreeA != SchedTreeB) {
      // Unscheduled trees have lower priority.
      if (ScheduledTrees->test(SchedTreeA) != ScheduledTrees->test(SchedTreeB))
        return ScheduledTrees->test(SchedTreeB);

      // Trees with shallower connections have have lower priority.
      if (DFSResult->getSubtreeLevel(SchedTreeA)
          != DFSResult->getSubtreeLevel(SchedTreeB)) {
        return DFSResult->getSubtreeLevel(SchedTreeA)
          < DFSResult->getSubtreeLevel(SchedTreeB);
      }
    }
    if (MaximizeILP)
      return DFSResult->getILP(A) < DFSResult->getILP(B);
    else
      return DFSResult->getILP(A) > DFSResult->getILP(B);
  }
};

/// \brief Schedule based on the ILP metric.
class ILPScheduler : public MachineSchedStrategy {
  ScheduleDAGMILive *DAG;
  ILPOrder Cmp;

  std::vector<SUnit*> ReadyQ;
public:
  ILPScheduler(bool MaximizeILP): DAG(nullptr), Cmp(MaximizeILP) {}

  void initialize(ScheduleDAGMI *dag) override {
    assert(dag->hasVRegLiveness() && "ILPScheduler needs vreg liveness");
    DAG = static_cast<ScheduleDAGMILive*>(dag);
    DAG->computeDFSResult();
    Cmp.DFSResult = DAG->getDFSResult();
    Cmp.ScheduledTrees = &DAG->getScheduledTrees();
    ReadyQ.clear();
  }

  void registerRoots() override {
    // Restore the heap in ReadyQ with the updated DFS results.
    std::make_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
  }

  /// Implement MachineSchedStrategy interface.
  /// -----------------------------------------

  /// Callback to select the highest priority node from the ready Q.
  SUnit *pickNode(bool &IsTopNode) override {
    if (ReadyQ.empty()) return nullptr;
    std::pop_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
    SUnit *SU = ReadyQ.back();
    ReadyQ.pop_back();
    IsTopNode = false;
    DEBUG(dbgs() << "Pick node " << "SU(" << SU->NodeNum << ") "
          << " ILP: " << DAG->getDFSResult()->getILP(SU)
          << " Tree: " << DAG->getDFSResult()->getSubtreeID(SU) << " @"
          << DAG->getDFSResult()->getSubtreeLevel(
            DAG->getDFSResult()->getSubtreeID(SU)) << '\n'
          << "Scheduling " << *SU->getInstr());
    return SU;
  }

  /// \brief Scheduler callback to notify that a new subtree is scheduled.
  void scheduleTree(unsigned SubtreeID) override {
    std::make_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
  }

  /// Callback after a node is scheduled. Mark a newly scheduled tree, notify
  /// DFSResults, and resort the priority Q.
  void schedNode(SUnit *SU, bool IsTopNode) override {
    assert(!IsTopNode && "SchedDFSResult needs bottom-up");
  }

  void releaseTopNode(SUnit *) override { /*only called for top roots*/ }

  void releaseBottomNode(SUnit *SU) override {
    ReadyQ.push_back(SU);
    std::push_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
  }
};
} // namespace

static ScheduleDAGInstrs *createILPMaxScheduler(MachineSchedContext *C) {
  return new ScheduleDAGMILive(C, make_unique<ILPScheduler>(true));
}
static ScheduleDAGInstrs *createILPMinScheduler(MachineSchedContext *C) {
  return new ScheduleDAGMILive(C, make_unique<ILPScheduler>(false));
}
static MachineSchedRegistry ILPMaxRegistry(
  "ilpmax", "Schedule bottom-up for max ILP", createILPMaxScheduler);
static MachineSchedRegistry ILPMinRegistry(
  "ilpmin", "Schedule bottom-up for min ILP", createILPMinScheduler);

//===----------------------------------------------------------------------===//
// Machine Instruction Shuffler for Correctness Testing
//===----------------------------------------------------------------------===//

#ifndef NDEBUG
namespace {
/// Apply a less-than relation on the node order, which corresponds to the
/// instruction order prior to scheduling. IsReverse implements greater-than.
template<bool IsReverse>
struct SUnitOrder {
  bool operator()(SUnit *A, SUnit *B) const {
    if (IsReverse)
      return A->NodeNum > B->NodeNum;
    else
      return A->NodeNum < B->NodeNum;
  }
};

/// Reorder instructions as much as possible.
class InstructionShuffler : public MachineSchedStrategy {
  bool IsAlternating;
  bool IsTopDown;

  // Using a less-than relation (SUnitOrder<false>) for the TopQ priority
  // gives nodes with a higher number higher priority causing the latest
  // instructions to be scheduled first.
  PriorityQueue<SUnit*, std::vector<SUnit*>, SUnitOrder<false> >
    TopQ;
  // When scheduling bottom-up, use greater-than as the queue priority.
  PriorityQueue<SUnit*, std::vector<SUnit*>, SUnitOrder<true> >
    BottomQ;
public:
  InstructionShuffler(bool alternate, bool topdown)
    : IsAlternating(alternate), IsTopDown(topdown) {}

  void initialize(ScheduleDAGMI*) override {
    TopQ.clear();
    BottomQ.clear();
  }

  /// Implement MachineSchedStrategy interface.
  /// -----------------------------------------

  SUnit *pickNode(bool &IsTopNode) override {
    SUnit *SU;
    if (IsTopDown) {
      do {
        if (TopQ.empty()) return nullptr;
        SU = TopQ.top();
        TopQ.pop();
      } while (SU->isScheduled);
      IsTopNode = true;
    }
    else {
      do {
        if (BottomQ.empty()) return nullptr;
        SU = BottomQ.top();
        BottomQ.pop();
      } while (SU->isScheduled);
      IsTopNode = false;
    }
    if (IsAlternating)
      IsTopDown = !IsTopDown;
    return SU;
  }

  void schedNode(SUnit *SU, bool IsTopNode) override {}

  void releaseTopNode(SUnit *SU) override {
    TopQ.push(SU);
  }
  void releaseBottomNode(SUnit *SU) override {
    BottomQ.push(SU);
  }
};
} // namespace

static ScheduleDAGInstrs *createInstructionShuffler(MachineSchedContext *C) {
  bool Alternate = !ForceTopDown && !ForceBottomUp;
  bool TopDown = !ForceBottomUp;
  assert((TopDown || !ForceTopDown) &&
         "-misched-topdown incompatible with -misched-bottomup");
  return new ScheduleDAGMILive(C, make_unique<InstructionShuffler>(Alternate, TopDown));
}
static MachineSchedRegistry ShufflerRegistry(
  "shuffle", "Shuffle machine instructions alternating directions",
  createInstructionShuffler);
#endif // !NDEBUG

//===----------------------------------------------------------------------===//
// GraphWriter support for ScheduleDAGMILive.
//===----------------------------------------------------------------------===//

#ifndef NDEBUG
namespace llvm {

template<> struct GraphTraits<
  ScheduleDAGMI*> : public GraphTraits<ScheduleDAG*> {};

template<>
struct DOTGraphTraits<ScheduleDAGMI*> : public DefaultDOTGraphTraits {

  DOTGraphTraits (bool isSimple=false) : DefaultDOTGraphTraits(isSimple) {}

  static std::string getGraphName(const ScheduleDAG *G) {
    return G->MF.getName();
  }

  static bool renderGraphFromBottomUp() {
    return true;
  }

  static bool isNodeHidden(const SUnit *Node) {
    return (Node->Preds.size() > 10 || Node->Succs.size() > 10);
  }

  static bool hasNodeAddressLabel(const SUnit *Node,
                                  const ScheduleDAG *Graph) {
    return false;
  }

  /// If you want to override the dot attributes printed for a particular
  /// edge, override this method.
  static std::string getEdgeAttributes(const SUnit *Node,
                                       SUnitIterator EI,
                                       const ScheduleDAG *Graph) {
    if (EI.isArtificialDep())
      return "color=cyan,style=dashed";
    if (EI.isCtrlDep())
      return "color=blue,style=dashed";
    return "";
  }

  static std::string getNodeLabel(const SUnit *SU, const ScheduleDAG *G) {
    std::string Str;
    raw_string_ostream SS(Str);
    const ScheduleDAGMI *DAG = static_cast<const ScheduleDAGMI*>(G);
    const SchedDFSResult *DFS = DAG->hasVRegLiveness() ?
      static_cast<const ScheduleDAGMILive*>(G)->getDFSResult() : nullptr;
    SS << "SU:" << SU->NodeNum;
    if (DFS)
      SS << " I:" << DFS->getNumInstrs(SU);
    return SS.str();
  }
  static std::string getNodeDescription(const SUnit *SU, const ScheduleDAG *G) {
    return G->getGraphNodeLabel(SU);
  }

  static std::string getNodeAttributes(const SUnit *N, const ScheduleDAG *G) {
    std::string Str("shape=Mrecord");
    const ScheduleDAGMI *DAG = static_cast<const ScheduleDAGMI*>(G);
    const SchedDFSResult *DFS = DAG->hasVRegLiveness() ?
      static_cast<const ScheduleDAGMILive*>(G)->getDFSResult() : nullptr;
    if (DFS) {
      Str += ",style=filled,fillcolor=\"#";
      Str += DOT::getColorString(DFS->getSubtreeID(N));
      Str += '"';
    }
    return Str;
  }
};
} // namespace llvm
#endif // NDEBUG

/// viewGraph - Pop up a ghostview window with the reachable parts of the DAG
/// rendered using 'dot'.
///
void ScheduleDAGMI::viewGraph(const Twine &Name, const Twine &Title) {
#ifndef NDEBUG
  ViewGraph(this, Name, false, Title);
#else
  errs() << "ScheduleDAGMI::viewGraph is only available in debug builds on "
         << "systems with Graphviz or gv!\n";
#endif  // NDEBUG
}

/// Out-of-line implementation with no arguments is handy for gdb.
void ScheduleDAGMI::viewGraph() {
  viewGraph(getDAGName(), "Scheduling-Units Graph for " + getDAGName());
}