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//===- RegisterPressure.h - Dynamic Register Pressure -----------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// 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/ArrayRef.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/ADT/SparseSet.h"

#include "llvm/CodeGen/MachineBasicBlock.h"

#include "llvm/CodeGen/SlotIndexes.h"

#include "llvm/CodeGen/TargetRegisterInfo.h"

#include "llvm/MC/LaneBitmask.h"

#include <cassert>

#include <cstdint>

#include <cstdlib>

#include <limits>

#include <vector>

namespace llvm {

class LiveIntervals;

class MachineFunction;

class MachineInstr;

class MachineRegisterInfo;

class RegisterClassInfo;

struct RegisterMaskPair {

  Register RegUnit; ///< Virtual register or register unit.

  LaneBitmask LaneMask;

  RegisterMaskPair(Register RegUnit, LaneBitmask LaneMask)

      : RegUnit(RegUnit), LaneMask(LaneMask) {}

};

/// 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<RegisterMaskPair,8> LiveInRegs;

  SmallVector<RegisterMaskPair,8> LiveOutRegs;

  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 = 0; // ID+1. 0=Invalid.

  int16_t UnitInc = 0;

public:

  PressureChange() = default;

  PressureChange(unsigned id): PSetID(id + 1) {

    assert(id < std::numeric_limits<uint16_t>::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) & std::numeric_limits<uint16_t>::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;

  }

  void dump() const;

};

/// 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];

  using iterator = PressureChange *;

  iterator nonconst_begin() { return &PressureChanges[0]; }

  iterator nonconst_end() { return &PressureChanges[MaxPSets]; }

public:

  using const_iterator = const PressureChange *;

  const_iterator begin() const { return &PressureChanges[0]; }

  const_iterator end() const { return &PressureChanges[MaxPSets]; }

  void addPressureChange(Register RegUnit, bool IsDec,

                         const MachineRegisterInfo *MRI);

  void dump(const TargetRegisterInfo &TRI) const;

};

/// List of registers defined and used by a machine instruction.

class RegisterOperands {

public:

  /// List of virtual registers and register units read by the instruction.

  SmallVector<RegisterMaskPair, 8> Uses;

  /// List of virtual registers and register units defined by the

  /// instruction which are not dead.

  SmallVector<RegisterMaskPair, 8> Defs;

  /// List of virtual registers and register units defined by the

  /// instruction but dead.

  SmallVector<RegisterMaskPair, 8> DeadDefs;

  /// Analyze the given instruction \p MI and fill in the Uses, Defs and

  /// DeadDefs list based on the MachineOperand flags.

  void collect(const MachineInstr &MI, const TargetRegisterInfo &TRI,

               const MachineRegisterInfo &MRI, bool TrackLaneMasks,

               bool IgnoreDead);

  /// Use liveness information to find dead defs not marked with a dead flag

  /// and move them to the DeadDefs vector.

  void detectDeadDefs(const MachineInstr &MI, const LiveIntervals &LIS);

  /// Use liveness information to find out which uses/defs are partially

  /// undefined/dead and adjust the RegisterMaskPairs accordingly.

  /// If \p AddFlagsMI is given then missing read-undef and dead flags will be

  /// added to the instruction.

  void adjustLaneLiveness(const LiveIntervals &LIS,

                          const MachineRegisterInfo &MRI, SlotIndex Pos,

                          MachineInstr *AddFlagsMI = nullptr);

};

/// Array of PressureDiffs.

class PressureDiffs {

  PressureDiff *PDiffArray = nullptr;

  unsigned Size = 0;

  unsigned Max = 0;

public:

  PressureDiffs() = default;

  ~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);

  }

  /// Record pressure difference induced by the given operand list to

  /// node with index \p Idx.

  void addInstruction(unsigned Idx, const RegisterOperands &RegOpers,

                      const MachineRegisterInfo &MRI);

};

/// 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() = default;

  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);

  }

  void dump() const;

};

/// A set of live virtual registers and physical register units.

///

/// This is a wrapper around a SparseSet which deals with mapping register unit

/// and virtual register indexes to an index usable by the sparse set.

class LiveRegSet {

private:

  struct IndexMaskPair {

    unsigned Index;

    LaneBitmask LaneMask;

    IndexMaskPair(unsigned Index, LaneBitmask LaneMask)

        : Index(Index), LaneMask(LaneMask) {}

    unsigned getSparseSetIndex() const {

      return Index;

    }

  };

  using RegSet = SparseSet<IndexMaskPair>;

  RegSet Regs;

  unsigned NumRegUnits;

  unsigned getSparseIndexFromReg(Register Reg) const {

    if (Reg.isVirtual())

      return Register::virtReg2Index(Reg) + NumRegUnits;

    assert(Reg < NumRegUnits);

    return Reg;

  }

  Register getRegFromSparseIndex(unsigned SparseIndex) const {

    if (SparseIndex >= NumRegUnits)

      return Register::index2VirtReg(SparseIndex - NumRegUnits);

    return Register(SparseIndex);

  }

public:

  void clear();

  void init(const MachineRegisterInfo &MRI);

  LaneBitmask contains(Register Reg) const {

    unsigned SparseIndex = getSparseIndexFromReg(Reg);

    RegSet::const_iterator I = Regs.find(SparseIndex);

    if (I == Regs.end())

      return LaneBitmask::getNone();

    return I->LaneMask;

  }

  /// Mark the \p Pair.LaneMask lanes of \p Pair.Reg as live.

  /// Returns the previously live lanes of \p Pair.Reg.

  LaneBitmask insert(RegisterMaskPair Pair) {

    unsigned SparseIndex = getSparseIndexFromReg(Pair.RegUnit);

    auto InsertRes = Regs.insert(IndexMaskPair(SparseIndex, Pair.LaneMask));

    if (!InsertRes.second) {

      LaneBitmask PrevMask = InsertRes.first->LaneMask;

      InsertRes.first->LaneMask |= Pair.LaneMask;

      return PrevMask;

    }

    return LaneBitmask::getNone();

  }

  /// Clears the \p Pair.LaneMask lanes of \p Pair.Reg (mark them as dead).

  /// Returns the previously live lanes of \p Pair.Reg.

  LaneBitmask erase(RegisterMaskPair Pair) {

    unsigned SparseIndex = getSparseIndexFromReg(Pair.RegUnit);

    RegSet::iterator I = Regs.find(SparseIndex);

    if (I == Regs.end())

      return LaneBitmask::getNone();

    LaneBitmask PrevMask = I->LaneMask;

    I->LaneMask &= ~Pair.LaneMask;

    return PrevMask;

  }

  size_t size() const {

    return Regs.size();

  }

  template<typename ContainerT>

  void appendTo(ContainerT &To) const {

    for (const IndexMaskPair &P : Regs) {

      Register Reg = getRegFromSparseIndex(P.Index);

      if (P.LaneMask.any())

        To.push_back(RegisterMaskPair(Reg, P.LaneMask));

    }

  }

};

/// 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 = nullptr;

  const TargetRegisterInfo *TRI = nullptr;

  const RegisterClassInfo *RCI = nullptr;

  const MachineRegisterInfo *MRI;

  const LiveIntervals *LIS = nullptr;

  /// We currently only allow pressure tracking within a block.

  const MachineBasicBlock *MBB = nullptr;

  /// 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 = false;

  /// True if lanemasks should be tracked.

  bool TrackLaneMasks = false;

  /// 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<Register, VirtReg2IndexFunctor> UntiedDefs;

  /// Live-through pressure.

  std::vector<unsigned> LiveThruPressure;

public:

  RegPressureTracker(IntervalPressure &rp) : P(rp), RequireIntervals(true) {}

  RegPressureTracker(RegionPressure &rp) : P(rp), RequireIntervals(false) {}

  void reset();

  void init(const MachineFunction *mf, const RegisterClassInfo *rci,

            const LiveIntervals *lis, const MachineBasicBlock *mbb,

            MachineBasicBlock::const_iterator pos,

            bool TrackLaneMasks, bool TrackUntiedDefs);

  /// 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<RegisterMaskPair> 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; }

  /// Recede across the previous instruction.

  void recede(SmallVectorImpl<RegisterMaskPair> *LiveUses = nullptr);

  /// Recede across the previous instruction.

  /// This "low-level" variant assumes that recedeSkipDebugValues() was

  /// called previously and takes precomputed RegisterOperands for the

  /// instruction.

  void recede(const RegisterOperands &RegOpers,

              SmallVectorImpl<RegisterMaskPair> *LiveUses = nullptr);

  /// Recede until we find an instruction which is not a DebugValue.

  void recedeSkipDebugValues();

  /// Advance across the current instruction.

  void advance();

  /// Advance across the current instruction.

  /// This is a "low-level" variant of advance() which takes precomputed

  /// RegisterOperands of the instruction.

  void advance(const RegisterOperands &RegOpers);

  /// 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 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.

  const std::vector<unsigned> &getRegSetPressureAtPos() const {

    return CurrSetPressure;

  }

  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, nullptr, 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(Register VirtReg) const {

    return UntiedDefs.count(VirtReg);

  }

  void dump() const;

  void increaseRegPressure(Register RegUnit, LaneBitmask PreviousMask,

                           LaneBitmask NewMask);

  void decreaseRegPressure(Register RegUnit, LaneBitmask PreviousMask,

                           LaneBitmask NewMask);

protected:

  /// Add Reg to the live out set and increase max pressure.

  void discoverLiveOut(RegisterMaskPair Pair);

  /// Add Reg to the live in set and increase max pressure.

  void discoverLiveIn(RegisterMaskPair Pair);

  /// Get the SlotIndex for the first nondebug instruction including or

  /// after the current position.

  SlotIndex getCurrSlot() const;

  void bumpDeadDefs(ArrayRef<RegisterMaskPair> DeadDefs);

  void bumpUpwardPressure(const MachineInstr *MI);

  void bumpDownwardPressure(const MachineInstr *MI);

  void discoverLiveInOrOut(RegisterMaskPair Pair,

                           SmallVectorImpl<RegisterMaskPair> &LiveInOrOut);

  LaneBitmask getLastUsedLanes(Register RegUnit, SlotIndex Pos) const;

  LaneBitmask getLiveLanesAt(Register RegUnit, SlotIndex Pos) const;

  LaneBitmask getLiveThroughAt(Register RegUnit, SlotIndex Pos) const;

};

void dumpRegSetPressure(ArrayRef<unsigned> SetPressure,

                        const TargetRegisterInfo *TRI);

} // end namespace llvm

#endif // LLVM_CODEGEN_REGISTERPRESSURE_H