llvm-mirror/include/llvm/CodeGen/ScheduleDAGInstrs.h

//==- ScheduleDAGInstrs.h - MachineInstr Scheduling --------------*- C++ -*-==//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the ScheduleDAGInstrs class, which implements
// scheduling for a MachineInstr-based dependency graph.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_SCHEDULEDAGINSTRS_H
#define LLVM_CODEGEN_SCHEDULEDAGINSTRS_H

#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SparseMultiSet.h"
#include "llvm/ADT/SparseSet.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/TargetSchedule.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include <list>

namespace llvm {
  class MachineFrameInfo;
  class MachineLoopInfo;
  class MachineDominatorTree;
  class RegPressureTracker;
  class PressureDiffs;

  /// An individual mapping from virtual register number to SUnit.
  struct VReg2SUnit {
    unsigned VirtReg;
    LaneBitmask LaneMask;
    SUnit *SU;

    VReg2SUnit(unsigned VReg, LaneBitmask LaneMask, SUnit *SU)
      : VirtReg(VReg), LaneMask(LaneMask), SU(SU) {}

    unsigned getSparseSetIndex() const {
      return TargetRegisterInfo::virtReg2Index(VirtReg);
    }
  };

  /// Mapping from virtual register to SUnit including an operand index.
  struct VReg2SUnitOperIdx : public VReg2SUnit {
    unsigned OperandIndex;

    VReg2SUnitOperIdx(unsigned VReg, LaneBitmask LaneMask,
                      unsigned OperandIndex, SUnit *SU)
      : VReg2SUnit(VReg, LaneMask, SU), OperandIndex(OperandIndex) {}
  };

  /// Record a physical register access.
  /// For non-data-dependent uses, OpIdx == -1.
  struct PhysRegSUOper {
    SUnit *SU;
    int OpIdx;
    unsigned Reg;

    PhysRegSUOper(SUnit *su, int op, unsigned R): SU(su), OpIdx(op), Reg(R) {}

    unsigned getSparseSetIndex() const { return Reg; }
  };

  /// Use a SparseMultiSet to track physical registers. Storage is only
  /// allocated once for the pass. It can be cleared in constant time and reused
  /// without any frees.
  typedef SparseMultiSet<PhysRegSUOper, llvm::identity<unsigned>, uint16_t>
  Reg2SUnitsMap;

  /// Use SparseSet as a SparseMap by relying on the fact that it never
  /// compares ValueT's, only unsigned keys. This allows the set to be cleared
  /// between scheduling regions in constant time as long as ValueT does not
  /// require a destructor.
  typedef SparseSet<VReg2SUnit, VirtReg2IndexFunctor> VReg2SUnitMap;

  /// Track local uses of virtual registers. These uses are gathered by the DAG
  /// builder and may be consulted by the scheduler to avoid iterating an entire
  /// vreg use list.
  typedef SparseMultiSet<VReg2SUnit, VirtReg2IndexFunctor> VReg2SUnitMultiMap;

  typedef SparseMultiSet<VReg2SUnitOperIdx, VirtReg2IndexFunctor>
    VReg2SUnitOperIdxMultiMap;

  typedef PointerUnion<const Value *, const PseudoSourceValue *> ValueType;
  struct UnderlyingObject : PointerIntPair<ValueType, 1, bool> {
    UnderlyingObject(ValueType V, bool MayAlias)
        : PointerIntPair<ValueType, 1, bool>(V, MayAlias) {}
    ValueType getValue() const { return getPointer(); }
    bool mayAlias() const { return getInt(); }
  };
  typedef SmallVector<UnderlyingObject, 4> UnderlyingObjectsVector;

  /// ScheduleDAGInstrs - A ScheduleDAG subclass for scheduling lists of
  /// MachineInstrs.
  class ScheduleDAGInstrs : public ScheduleDAG {
  protected:
    const MachineLoopInfo *MLI;
    const MachineFrameInfo &MFI;

    /// TargetSchedModel provides an interface to the machine model.
    TargetSchedModel SchedModel;

    /// True if the DAG builder should remove kill flags (in preparation for
    /// rescheduling).
    bool RemoveKillFlags;

    /// The standard DAG builder does not normally include terminators as DAG
    /// nodes because it does not create the necessary dependencies to prevent
    /// reordering. A specialized scheduler can override
    /// TargetInstrInfo::isSchedulingBoundary then enable this flag to indicate
    /// it has taken responsibility for scheduling the terminator correctly.
    bool CanHandleTerminators;

    /// Whether lane masks should get tracked.
    bool TrackLaneMasks;

    /// State specific to the current scheduling region.
    /// ------------------------------------------------

    /// The block in which to insert instructions
    MachineBasicBlock *BB;

    /// The beginning of the range to be scheduled.
    MachineBasicBlock::iterator RegionBegin;

    /// The end of the range to be scheduled.
    MachineBasicBlock::iterator RegionEnd;

    /// Instructions in this region (distance(RegionBegin, RegionEnd)).
    unsigned NumRegionInstrs;

    /// After calling BuildSchedGraph, each machine instruction in the current
    /// scheduling region is mapped to an SUnit.
    DenseMap<MachineInstr*, SUnit*> MISUnitMap;

    /// State internal to DAG building.
    /// -------------------------------

    /// Defs, Uses - Remember where defs and uses of each register are as we
    /// iterate upward through the instructions. This is allocated here instead
    /// of inside BuildSchedGraph to avoid the need for it to be initialized and
    /// destructed for each block.
    Reg2SUnitsMap Defs;
    Reg2SUnitsMap Uses;

    /// Tracks the last instruction(s) in this region defining each virtual
    /// register. There may be multiple current definitions for a register with
    /// disjunct lanemasks.
    VReg2SUnitMultiMap CurrentVRegDefs;
    /// Tracks the last instructions in this region using each virtual register.
    VReg2SUnitOperIdxMultiMap CurrentVRegUses;

    AliasAnalysis *AAForDep;

    /// Remember a generic side-effecting instruction as we proceed.
    /// No other SU ever gets scheduled around it (except in the special
    /// case of a huge region that gets reduced).
    SUnit *BarrierChain;

  public:

    /// A list of SUnits, used in Value2SUsMap, during DAG construction.
    /// Note: to gain speed it might be worth investigating an optimized
    /// implementation of this data structure, such as a singly linked list
    /// with a memory pool (SmallVector was tried but slow and SparseSet is not
    /// applicable).
    typedef std::list<SUnit *> SUList;
  protected:
    /// A map from ValueType to SUList, used during DAG construction,
    /// as a means of remembering which SUs depend on which memory
    /// locations.
    class Value2SUsMap;

    /// Remove in FIFO order some SUs from huge maps.
    void reduceHugeMemNodeMaps(Value2SUsMap &stores,
                               Value2SUsMap &loads, unsigned N);

    /// Add a chain edge between SUa and SUb, but only if both AliasAnalysis
    /// and Target fail to deny the dependency.
    void addChainDependency(SUnit *SUa, SUnit *SUb,
                            unsigned Latency = 0);

    /// Add dependencies as needed from all SUs in list to SU.
    void addChainDependencies(SUnit *SU, SUList &sus, unsigned Latency) {
      for (auto *su : sus)
        addChainDependency(SU, su, Latency);
    }

    /// Add dependencies as needed from all SUs in map, to SU.
    void addChainDependencies(SUnit *SU, Value2SUsMap &Val2SUsMap);

    /// Add dependencies as needed to SU, from all SUs mapped to V.
    void addChainDependencies(SUnit *SU, Value2SUsMap &Val2SUsMap,
                              ValueType V);

    /// Add barrier chain edges from all SUs in map, and then clear
    /// the map. This is equivalent to insertBarrierChain(), but
    /// optimized for the common case where the new BarrierChain (a
    /// global memory object) has a higher NodeNum than all SUs in
    /// map. It is assumed BarrierChain has been set before calling
    /// this.
    void addBarrierChain(Value2SUsMap &map);

    /// Insert a barrier chain in a huge region, far below current
    /// SU. Add barrier chain edges from all SUs in map with higher
    /// NodeNums than this new BarrierChain, and remove them from
    /// map. It is assumed BarrierChain has been set before calling
    /// this.
    void insertBarrierChain(Value2SUsMap &map);

    /// For an unanalyzable memory access, this Value is used in maps.
    UndefValue *UnknownValue;

    /// DbgValues - Remember instruction that precedes DBG_VALUE.
    /// These are generated by buildSchedGraph but persist so they can be
    /// referenced when emitting the final schedule.
    typedef std::vector<std::pair<MachineInstr *, MachineInstr *> >
      DbgValueVector;
    DbgValueVector DbgValues;
    MachineInstr *FirstDbgValue;

    /// Set of live physical registers for updating kill flags.
    BitVector LiveRegs;

  public:
    explicit ScheduleDAGInstrs(MachineFunction &mf,
                               const MachineLoopInfo *mli,
                               bool RemoveKillFlags = false);

    ~ScheduleDAGInstrs() override {}

    /// \brief Get the machine model for instruction scheduling.
    const TargetSchedModel *getSchedModel() const { return &SchedModel; }

    /// \brief Resolve and cache a resolved scheduling class for an SUnit.
    const MCSchedClassDesc *getSchedClass(SUnit *SU) const {
      if (!SU->SchedClass && SchedModel.hasInstrSchedModel())
        SU->SchedClass = SchedModel.resolveSchedClass(SU->getInstr());
      return SU->SchedClass;
    }

    /// begin - Return an iterator to the top of the current scheduling region.
    MachineBasicBlock::iterator begin() const { return RegionBegin; }

    /// end - Return an iterator to the bottom of the current scheduling region.
    MachineBasicBlock::iterator end() const { return RegionEnd; }

    /// newSUnit - Creates a new SUnit and return a ptr to it.
    SUnit *newSUnit(MachineInstr *MI);

    /// getSUnit - Return an existing SUnit for this MI, or NULL.
    SUnit *getSUnit(MachineInstr *MI) const;

    /// startBlock - Prepare to perform scheduling in the given block.
    virtual void startBlock(MachineBasicBlock *BB);

    /// finishBlock - Clean up after scheduling in the given block.
    virtual void finishBlock();

    /// Initialize the scheduler state for the next scheduling region.
    virtual void enterRegion(MachineBasicBlock *bb,
                             MachineBasicBlock::iterator begin,
                             MachineBasicBlock::iterator end,
                             unsigned regioninstrs);

    /// Notify that the scheduler has finished scheduling the current region.
    virtual void exitRegion();

    /// buildSchedGraph - Build SUnits from the MachineBasicBlock that we are
    /// input.
    void buildSchedGraph(AliasAnalysis *AA,
                         RegPressureTracker *RPTracker = nullptr,
                         PressureDiffs *PDiffs = nullptr,
                         LiveIntervals *LIS = nullptr,
                         bool TrackLaneMasks = false);

    /// addSchedBarrierDeps - Add dependencies from instructions in the current
    /// list of instructions being scheduled to scheduling barrier. We want to
    /// make sure instructions which define registers that are either used by
    /// the terminator or are live-out are properly scheduled. This is
    /// especially important when the definition latency of the return value(s)
    /// are too high to be hidden by the branch or when the liveout registers
    /// used by instructions in the fallthrough block.
    void addSchedBarrierDeps();

    /// schedule - Order nodes according to selected style, filling
    /// in the Sequence member.
    ///
    /// Typically, a scheduling algorithm will implement schedule() without
    /// overriding enterRegion() or exitRegion().
    virtual void schedule() = 0;

    /// finalizeSchedule - Allow targets to perform final scheduling actions at
    /// the level of the whole MachineFunction. By default does nothing.
    virtual void finalizeSchedule() {}

    void dumpNode(const SUnit *SU) const override;

    /// Return a label for a DAG node that points to an instruction.
    std::string getGraphNodeLabel(const SUnit *SU) const override;

    /// Return a label for the region of code covered by the DAG.
    std::string getDAGName() const override;

    /// \brief Fix register kill flags that scheduling has made invalid.
    void fixupKills(MachineBasicBlock *MBB);
  protected:
    void initSUnits();
    void addPhysRegDataDeps(SUnit *SU, unsigned OperIdx);
    void addPhysRegDeps(SUnit *SU, unsigned OperIdx);
    void addVRegDefDeps(SUnit *SU, unsigned OperIdx);
    void addVRegUseDeps(SUnit *SU, unsigned OperIdx);

    /// \brief PostRA helper for rewriting kill flags.
    void startBlockForKills(MachineBasicBlock *BB);

    /// \brief Toggle a register operand kill flag.
    ///
    /// Other adjustments may be made to the instruction if necessary. Return
    /// true if the operand has been deleted, false if not.
    bool toggleKillFlag(MachineInstr *MI, MachineOperand &MO);

    /// Returns a mask for which lanes get read/written by the given (register)
    /// machine operand.
    LaneBitmask getLaneMaskForMO(const MachineOperand &MO) const;
  };

  /// newSUnit - Creates a new SUnit and return a ptr to it.
  inline SUnit *ScheduleDAGInstrs::newSUnit(MachineInstr *MI) {
#ifndef NDEBUG
    const SUnit *Addr = SUnits.empty() ? nullptr : &SUnits[0];
#endif
    SUnits.emplace_back(MI, (unsigned)SUnits.size());
    assert((Addr == nullptr || Addr == &SUnits[0]) &&
           "SUnits std::vector reallocated on the fly!");
    return &SUnits.back();
  }

  /// getSUnit - Return an existing SUnit for this MI, or NULL.
  inline SUnit *ScheduleDAGInstrs::getSUnit(MachineInstr *MI) const {
    DenseMap<MachineInstr*, SUnit*>::const_iterator I = MISUnitMap.find(MI);
    if (I == MISUnitMap.end())
      return nullptr;
    return I->second;
  }
} // namespace llvm

#endif