text: //===-- RegisterPressure.h - Dynamic Register Pressure -*- C++ -*-------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the RegisterPressure class which can be used to track
  // MachineInstr level register pressure.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_CODEGEN_REGISTERPRESSURE_H
  #define LLVM_CODEGEN_REGISTERPRESSURE_H
  
  #include "llvm/ADT/SparseSet.h"
  #include "llvm/CodeGen/SlotIndexes.h"
  #include "llvm/Target/TargetRegisterInfo.h"
  
  namespace llvm {
  
  class LiveIntervals;
  class LiveRange;
  class RegisterClassInfo;
  class MachineInstr;
  
  /// Base class for register pressure results.
  struct RegisterPressure {
    /// Map of max reg pressure indexed by pressure set ID, not class ID.
    std::vector<unsigned> MaxSetPressure;
  
    /// List of live in virtual registers or physical register units.
    SmallVector<unsigned,8> LiveInRegs;
    SmallVector<unsigned,8> LiveOutRegs;
  
    /// Increase register pressure for each pressure set impacted by this register
    /// class. Normally called by RegPressureTracker, but may be called manually
    /// to account for live through (global liveness).
    ///
    /// \param Reg is either a virtual register number or register unit number.
    void increase(unsigned Reg, const TargetRegisterInfo *TRI,
                  const MachineRegisterInfo *MRI);
  
    /// Decrease register pressure for each pressure set impacted by this register
    /// class. This is only useful to account for spilling or rematerialization.
    ///
    /// \param Reg is either a virtual register number or register unit number.
    void decrease(unsigned Reg, const TargetRegisterInfo *TRI,
                  const MachineRegisterInfo *MRI);
  
    void dump(const TargetRegisterInfo *TRI) const;
  };
  
  /// RegisterPressure computed within a region of instructions delimited by
  /// TopIdx and BottomIdx.  During pressure computation, the maximum pressure per
  /// register pressure set is increased. Once pressure within a region is fully
  /// computed, the live-in and live-out sets are recorded.
  ///
  /// This is preferable to RegionPressure when LiveIntervals are available,
  /// because delimiting regions by SlotIndex is more robust and convenient than
  /// holding block iterators. The block contents can change without invalidating
  /// the pressure result.
  struct IntervalPressure : RegisterPressure {
    /// Record the boundary of the region being tracked.
    SlotIndex TopIdx;
    SlotIndex BottomIdx;
  
    void reset();
  
    void openTop(SlotIndex NextTop);
  
    void openBottom(SlotIndex PrevBottom);
  };
  
  /// RegisterPressure computed within a region of instructions delimited by
  /// TopPos and BottomPos. This is a less precise version of IntervalPressure for
  /// use when LiveIntervals are unavailable.
  struct RegionPressure : RegisterPressure {
    /// Record the boundary of the region being tracked.
    MachineBasicBlock::const_iterator TopPos;
    MachineBasicBlock::const_iterator BottomPos;
  
    void reset();
  
    void openTop(MachineBasicBlock::const_iterator PrevTop);
  
    void openBottom(MachineBasicBlock::const_iterator PrevBottom);
  };
  
  /// Capture a change in pressure for a single pressure set. UnitInc may be
  /// expressed in terms of upward or downward pressure depending on the client
  /// and will be dynamically adjusted for current liveness.
  ///
  /// Pressure increments are tiny, typically 1-2 units, and this is only for
  /// heuristics, so we don't check UnitInc overflow. Instead, we may have a
  /// higher level assert that pressure is consistent within a region. We also
  /// effectively ignore dead defs which don't affect heuristics much.
  class PressureChange {
    uint16_t PSetID; // ID+1. 0=Invalid.
    int16_t  UnitInc;
  public:
    PressureChange(): PSetID(0), UnitInc(0) {}
    PressureChange(unsigned id): PSetID(id+1), UnitInc(0) {
      assert(id < UINT16_MAX && "PSetID overflow.");
    }
  
    bool isValid() const { return PSetID > 0; }
  
    unsigned getPSet() const {
      assert(isValid() && "invalid PressureChange");
      return PSetID - 1;
    }
    // If PSetID is invalid, return UINT16_MAX to give it lowest priority.
    unsigned getPSetOrMax() const { return (PSetID - 1) & UINT16_MAX; }
  
    int getUnitInc() const { return UnitInc; }
  
    void setUnitInc(int Inc) { UnitInc = Inc; }
  
    bool operator==(const PressureChange &RHS) const {
      return PSetID == RHS.PSetID && UnitInc == RHS.UnitInc;
    }
  };
  
  template <> struct isPodLike<PressureChange> {
     static const bool value = true;
  };
  
  /// List of PressureChanges in order of increasing, unique PSetID.
  ///
  /// Use a small fixed number, because we can fit more PressureChanges in an
  /// empty SmallVector than ever need to be tracked per register class. If more
  /// PSets are affected, then we only track the most constrained.
  class PressureDiff {
    // The initial design was for MaxPSets=4, but that requires PSet partitions,
    // which are not yet implemented. (PSet partitions are equivalent PSets given
    // the register classes actually in use within the scheduling region.)
    enum { MaxPSets = 16 };
  
    PressureChange PressureChanges[MaxPSets];
  public:
    typedef PressureChange* iterator;
    typedef const PressureChange* const_iterator;
    iterator begin() { return &PressureChanges[0]; }
    iterator end() { return &PressureChanges[MaxPSets]; }
    const_iterator begin() const { return &PressureChanges[0]; }
    const_iterator end() const { return &PressureChanges[MaxPSets]; }
  
    void addPressureChange(unsigned RegUnit, bool IsDec,
                           const MachineRegisterInfo *MRI);
  };
  
  /// Array of PressureDiffs.
  class PressureDiffs {
    PressureDiff *PDiffArray;
    unsigned Size;
    unsigned Max;
  public:
    PressureDiffs(): PDiffArray(0), Size(0), Max(0) {}
    ~PressureDiffs() { free(PDiffArray); }
  
    void clear() { Size = 0; }
  
    void init(unsigned N);
  
    PressureDiff &operator[](unsigned Idx) {
      assert(Idx < Size && "PressureDiff index out of bounds");
      return PDiffArray[Idx];
    }
    const PressureDiff &operator[](unsigned Idx) const {
      return const_cast<PressureDiffs*>(this)->operator[](Idx);
    }
  };
  
  /// Store the effects of a change in pressure on things that MI scheduler cares
  /// about.
  ///
  /// Excess records the value of the largest difference in register units beyond
  /// the target's pressure limits across the affected pressure sets, where
  /// largest is defined as the absolute value of the difference. Negative
  /// ExcessUnits indicates a reduction in pressure that had already exceeded the
  /// target's limits.
  ///
  /// CriticalMax records the largest increase in the tracker's max pressure that
  /// exceeds the critical limit for some pressure set determined by the client.
  ///
  /// CurrentMax records the largest increase in the tracker's max pressure that
  /// exceeds the current limit for some pressure set determined by the client.
  struct RegPressureDelta {
    PressureChange Excess;
    PressureChange CriticalMax;
    PressureChange CurrentMax;
  
    RegPressureDelta() {}
  
    bool operator==(const RegPressureDelta &RHS) const {
      return Excess == RHS.Excess && CriticalMax == RHS.CriticalMax
        && CurrentMax == RHS.CurrentMax;
    }
    bool operator!=(const RegPressureDelta &RHS) const {
      return !operator==(RHS);
    }
  };
  
  /// \brief A set of live virtual registers and physical register units.
  ///
  /// Virtual and physical register numbers require separate sparse sets, but most
  /// of the RegisterPressureTracker handles them uniformly.
  struct LiveRegSet {
    SparseSet<unsigned> PhysRegs;
    SparseSet<unsigned, VirtReg2IndexFunctor> VirtRegs;
  
    bool contains(unsigned Reg) const {
      if (TargetRegisterInfo::isVirtualRegister(Reg))
        return VirtRegs.count(Reg);
      return PhysRegs.count(Reg);
    }
  
    bool insert(unsigned Reg) {
      if (TargetRegisterInfo::isVirtualRegister(Reg))
        return VirtRegs.insert(Reg).second;
      return PhysRegs.insert(Reg).second;
    }
  
    bool erase(unsigned Reg) {
      if (TargetRegisterInfo::isVirtualRegister(Reg))
        return VirtRegs.erase(Reg);
      return PhysRegs.erase(Reg);
    }
  };
  
  /// Track the current register pressure at some position in the instruction
  /// stream, and remember the high water mark within the region traversed. This
  /// does not automatically consider live-through ranges. The client may
  /// independently adjust for global liveness.
  ///
  /// Each RegPressureTracker only works within a MachineBasicBlock. Pressure can
  /// be tracked across a larger region by storing a RegisterPressure result at
  /// each block boundary and explicitly adjusting pressure to account for block
  /// live-in and live-out register sets.
  ///
  /// RegPressureTracker holds a reference to a RegisterPressure result that it
  /// computes incrementally. During downward tracking, P.BottomIdx or P.BottomPos
  /// is invalid until it reaches the end of the block or closeRegion() is
  /// explicitly called. Similarly, P.TopIdx is invalid during upward
  /// tracking. Changing direction has the side effect of closing region, and
  /// traversing past TopIdx or BottomIdx reopens it.
  class RegPressureTracker {
    const MachineFunction     *MF;
    const TargetRegisterInfo  *TRI;
    const RegisterClassInfo   *RCI;
    const MachineRegisterInfo *MRI;
    const LiveIntervals       *LIS;
  
    /// We currently only allow pressure tracking within a block.
    const MachineBasicBlock *MBB;
  
    /// Track the max pressure within the region traversed so far.
    RegisterPressure &P;
  
    /// Run in two modes dependending on whether constructed with IntervalPressure
    /// or RegisterPressure. If requireIntervals is false, LIS are ignored.
    bool RequireIntervals;
  
    /// True if UntiedDefs will be populated.
    bool TrackUntiedDefs;
  
    /// Register pressure corresponds to liveness before this instruction
    /// iterator. It may point to the end of the block or a DebugValue rather than
    /// an instruction.
    MachineBasicBlock::const_iterator CurrPos;
  
    /// Pressure map indexed by pressure set ID, not class ID.
    std::vector<unsigned> CurrSetPressure;
  
    /// Set of live registers.
    LiveRegSet LiveRegs;
  
    /// Set of vreg defs that start a live range.
    SparseSet<unsigned, VirtReg2IndexFunctor> UntiedDefs;
    /// Live-through pressure.
    std::vector<unsigned> LiveThruPressure;
  
  public:
    RegPressureTracker(IntervalPressure &rp) :
      MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(true),
      TrackUntiedDefs(false) {}
  
    RegPressureTracker(RegionPressure &rp) :
      MF(0), TRI(0), RCI(0), LIS(0), MBB(0), P(rp), RequireIntervals(false),
      TrackUntiedDefs(false) {}
  
    void reset();
  
    void init(const MachineFunction *mf, const RegisterClassInfo *rci,
              const LiveIntervals *lis, const MachineBasicBlock *mbb,
              MachineBasicBlock::const_iterator pos,
              bool ShouldTrackUntiedDefs = false);
  
    /// Force liveness of virtual registers or physical register
    /// units. Particularly useful to initialize the livein/out state of the
    /// tracker before the first call to advance/recede.
    void addLiveRegs(ArrayRef<unsigned> Regs);
  
    /// Get the MI position corresponding to this register pressure.
    MachineBasicBlock::const_iterator getPos() const { return CurrPos; }
  
    // Reset the MI position corresponding to the register pressure. This allows
    // schedulers to move instructions above the RegPressureTracker's
    // CurrPos. Since the pressure is computed before CurrPos, the iterator
    // position changes while pressure does not.
    void setPos(MachineBasicBlock::const_iterator Pos) { CurrPos = Pos; }
  
    /// \brief Get the SlotIndex for the first nondebug instruction including or
    /// after the current position.
    SlotIndex getCurrSlot() const;
  
    /// Recede across the previous instruction.
    bool recede(SmallVectorImpl<unsigned> *LiveUses = 0, PressureDiff *PDiff = 0);
  
    /// Advance across the current instruction.
    bool advance();
  
    /// Finalize the region boundaries and recored live ins and live outs.
    void closeRegion();
  
    /// Initialize the LiveThru pressure set based on the untied defs found in
    /// RPTracker.
    void initLiveThru(const RegPressureTracker &RPTracker);
  
    /// Copy an existing live thru pressure result.
    void initLiveThru(ArrayRef<unsigned> PressureSet) {
      LiveThruPressure.assign(PressureSet.begin(), PressureSet.end());
    }
  
    ArrayRef<unsigned> getLiveThru() const { return LiveThruPressure; }
  
    /// Get the resulting register pressure over the traversed region.
    /// This result is complete if either advance() or recede() has returned true,
    /// or if closeRegion() was explicitly invoked.
    RegisterPressure &getPressure() { return P; }
    const RegisterPressure &getPressure() const { return P; }
  
    /// Get the register set pressure at the current position, which may be less
    /// than the pressure across the traversed region.
    std::vector<unsigned> &getRegSetPressureAtPos() { return CurrSetPressure; }
  
    void discoverLiveOut(unsigned Reg);
    void discoverLiveIn(unsigned Reg);
  
    bool isTopClosed() const;
    bool isBottomClosed() const;
  
    void closeTop();
    void closeBottom();
  
    /// Consider the pressure increase caused by traversing this instruction
    /// bottom-up. Find the pressure set with the most change beyond its pressure
    /// limit based on the tracker's current pressure, and record the number of
    /// excess register units of that pressure set introduced by this instruction.
    void getMaxUpwardPressureDelta(const MachineInstr *MI,
                                   PressureDiff *PDiff,
                                   RegPressureDelta &Delta,
                                   ArrayRef<PressureChange> CriticalPSets,
                                   ArrayRef<unsigned> MaxPressureLimit);
  
    void getUpwardPressureDelta(const MachineInstr *MI,
                                /*const*/ PressureDiff &PDiff,
                                RegPressureDelta &Delta,
                                ArrayRef<PressureChange> CriticalPSets,
                                ArrayRef<unsigned> MaxPressureLimit) const;
  
    /// Consider the pressure increase caused by traversing this instruction
    /// top-down. Find the pressure set with the most change beyond its pressure
    /// limit based on the tracker's current pressure, and record the number of
    /// excess register units of that pressure set introduced by this instruction.
    void getMaxDownwardPressureDelta(const MachineInstr *MI,
                                     RegPressureDelta &Delta,
                                     ArrayRef<PressureChange> CriticalPSets,
                                     ArrayRef<unsigned> MaxPressureLimit);
  
    /// Find the pressure set with the most change beyond its pressure limit after
    /// traversing this instruction either upward or downward depending on the
    /// closed end of the current region.
    void getMaxPressureDelta(const MachineInstr *MI,
                             RegPressureDelta &Delta,
                             ArrayRef<PressureChange> CriticalPSets,
                             ArrayRef<unsigned> MaxPressureLimit) {
      if (isTopClosed())
        return getMaxDownwardPressureDelta(MI, Delta, CriticalPSets,
                                           MaxPressureLimit);
  
      assert(isBottomClosed() && "Uninitialized pressure tracker");
      return getMaxUpwardPressureDelta(MI, 0, Delta, CriticalPSets,
                                       MaxPressureLimit);
    }
  
    /// Get the pressure of each PSet after traversing this instruction bottom-up.
    void getUpwardPressure(const MachineInstr *MI,
                           std::vector<unsigned> &PressureResult,
                           std::vector<unsigned> &MaxPressureResult);
  
    /// Get the pressure of each PSet after traversing this instruction top-down.
    void getDownwardPressure(const MachineInstr *MI,
                             std::vector<unsigned> &PressureResult,
                             std::vector<unsigned> &MaxPressureResult);
  
    void getPressureAfterInst(const MachineInstr *MI,
                              std::vector<unsigned> &PressureResult,
                              std::vector<unsigned> &MaxPressureResult) {
      if (isTopClosed())
        return getUpwardPressure(MI, PressureResult, MaxPressureResult);
  
      assert(isBottomClosed() && "Uninitialized pressure tracker");
      return getDownwardPressure(MI, PressureResult, MaxPressureResult);
    }
  
    bool hasUntiedDef(unsigned VirtReg) const {
      return UntiedDefs.count(VirtReg);
    }
  
    void dump() const;
  
  protected:
    const LiveRange *getLiveRange(unsigned Reg) const;
  
    void increaseRegPressure(ArrayRef<unsigned> Regs);
    void decreaseRegPressure(ArrayRef<unsigned> Regs);
  
    void bumpUpwardPressure(const MachineInstr *MI);
    void bumpDownwardPressure(const MachineInstr *MI);
  };
  
  #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
  void dumpRegSetPressure(ArrayRef<unsigned> SetPressure,
                          const TargetRegisterInfo *TRI);
  #endif
  } // end namespace llvm
  
  #endif
  