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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 VRegMaskOrUnit {
   Register RegUnit; ///< Virtual register or register unit.
   LaneBitmask LaneMask;
 
   VRegMaskOrUnit(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<VRegMaskOrUnit, 8> LiveInRegs;
   SmallVector<VRegMaskOrUnit, 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<VRegMaskOrUnit, 8> Uses;
   /// List of virtual registers and register units defined by the
   /// instruction which are not dead.
   SmallVector<VRegMaskOrUnit, 8> Defs;
   /// List of virtual registers and register units defined by the
   /// instruction but dead.
   SmallVector<VRegMaskOrUnit, 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 VRegMaskOrUnits 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 &operator=(const PressureDiffs &other) = delete;
   PressureDiffs(const PressureDiffs &other) = delete;
   ~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 = 0u;
 
   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(VRegMaskOrUnit 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(VRegMaskOrUnit 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();
   }
 
   void appendTo(SmallVectorImpl<VRegMaskOrUnit> &To) const {
     for (const IndexMaskPair &P : Regs) {
       Register Reg = getRegFromSparseIndex(P.Index);
       if (P.LaneMask.any())
         To.emplace_back(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 = nullptr;
   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<VRegMaskOrUnit> 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<VRegMaskOrUnit> *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<VRegMaskOrUnit> *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(VRegMaskOrUnit Pair);
   /// Add Reg to the live in set and increase max pressure.
   void discoverLiveIn(VRegMaskOrUnit Pair);
 
   /// Get the SlotIndex for the first nondebug instruction including or
   /// after the current position.
   SlotIndex getCurrSlot() const;
 
   void bumpDeadDefs(ArrayRef<VRegMaskOrUnit> DeadDefs);
 
   void bumpUpwardPressure(const MachineInstr *MI);
   void bumpDownwardPressure(const MachineInstr *MI);
 
   void discoverLiveInOrOut(VRegMaskOrUnit Pair,
                            SmallVectorImpl<VRegMaskOrUnit> &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

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