text: //===- llvm/CodeGen/CriticalAntiDepBreaker.h - Anti-Dep Support -*- 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 implements the CriticalAntiDepBreaker class, which
  // implements register anti-dependence breaking along a blocks
  // critical path during post-RA scheduler.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_LIB_CODEGEN_CRITICALANTIDEPBREAKER_H
  #define LLVM_LIB_CODEGEN_CRITICALANTIDEPBREAKER_H
  
  #include "llvm/ADT/BitVector.h"
  #include "llvm/CodeGen/AntiDepBreaker.h"
  #include "llvm/Support/Compiler.h"
  #include <map>
  #include <vector>
  
  namespace llvm {
  
  class MachineBasicBlock;
  class MachineFunction;
  class MachineInstr;
  class MachineOperand;
  class MachineRegisterInfo;
  class RegisterClassInfo;
  class TargetInstrInfo;
  class TargetRegisterClass;
  class TargetRegisterInfo;
  
  class LLVM_LIBRARY_VISIBILITY CriticalAntiDepBreaker : public AntiDepBreaker {
      MachineFunction& MF;
      MachineRegisterInfo &MRI;
      const TargetInstrInfo *TII;
      const TargetRegisterInfo *TRI;
      const RegisterClassInfo &RegClassInfo;
  
      /// The set of allocatable registers.
      /// We'll be ignoring anti-dependencies on non-allocatable registers,
      /// because they may not be safe to break.
      const BitVector AllocatableSet;
  
      /// For live regs that are only used in one register class in a
      /// live range, the register class. If the register is not live, the
      /// corresponding value is null. If the register is live but used in
      /// multiple register classes, the corresponding value is -1 casted to a
      /// pointer.
      std::vector<const TargetRegisterClass *> Classes;
  
      /// Map registers to all their references within a live range.
      std::multimap<unsigned, MachineOperand *> RegRefs;
  
      using RegRefIter =
          std::multimap<unsigned, MachineOperand *>::const_iterator;
  
      /// The index of the most recent kill (proceeding bottom-up),
      /// or ~0u if the register is not live.
      std::vector<unsigned> KillIndices;
  
      /// The index of the most recent complete def (proceeding
      /// bottom up), or ~0u if the register is live.
      std::vector<unsigned> DefIndices;
  
      /// A set of registers which are live and cannot be changed to
      /// break anti-dependencies.
      BitVector KeepRegs;
  
    public:
      CriticalAntiDepBreaker(MachineFunction& MFi, const RegisterClassInfo &RCI);
      ~CriticalAntiDepBreaker() override;
  
      /// Initialize anti-dep breaking for a new basic block.
      void StartBlock(MachineBasicBlock *BB) override;
  
      /// Identifiy anti-dependencies along the critical path
      /// of the ScheduleDAG and break them by renaming registers.
      unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits,
                                     MachineBasicBlock::iterator Begin,
                                     MachineBasicBlock::iterator End,
                                     unsigned InsertPosIndex,
                                     DbgValueVector &DbgValues) override;
  
      /// Update liveness information to account for the current
      /// instruction, which will not be scheduled.
      void Observe(MachineInstr &MI, unsigned Count,
                   unsigned InsertPosIndex) override;
  
      /// Finish anti-dep breaking for a basic block.
      void FinishBlock() override;
  
    private:
      void PrescanInstruction(MachineInstr &MI);
      void ScanInstruction(MachineInstr &MI, unsigned Count);
      bool isNewRegClobberedByRefs(RegRefIter RegRefBegin,
                                   RegRefIter RegRefEnd,
                                   unsigned NewReg);
      unsigned findSuitableFreeRegister(RegRefIter RegRefBegin,
                                        RegRefIter RegRefEnd,
                                        unsigned AntiDepReg,
                                        unsigned LastNewReg,
                                        const TargetRegisterClass *RC,
                                        SmallVectorImpl<unsigned> &Forbid);
    };
  
  } // end namespace llvm
  
  #endif // LLVM_LIB_CODEGEN_CRITICALANTIDEPBREAKER_H
  