llvm-project/llvm/lib/CodeGen/CriticalAntiDepBreaker.h

//=- llvm/CodeGen/CriticalAntiDepBreaker.h - Anti-Dep Support -*- 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 CriticalAntiDepBreaker class, which
// implements register anti-dependence breaking along a blocks
// critical path during post-RA scheduler.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_CRITICALANTIDEPBREAKER_H
#define LLVM_CODEGEN_CRITICALANTIDEPBREAKER_H

#include "AntiDepBreaker.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallSet.h"

namespace llvm {
  class CriticalAntiDepBreaker : public AntiDepBreaker {
    MachineFunction& MF;
    MachineRegisterInfo &MRI;
    const TargetRegisterInfo *TRI;

    /// AllocatableSet - 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;

    /// Classes - 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.
    const TargetRegisterClass *
      Classes[TargetRegisterInfo::FirstVirtualRegister];

    /// RegRegs - Map registers to all their references within a live range.
    std::multimap<unsigned, MachineOperand *> RegRefs;

    /// KillIndices - The index of the most recent kill (proceding bottom-up),
    /// or ~0u if the register is not live.
    unsigned KillIndices[TargetRegisterInfo::FirstVirtualRegister];

    /// DefIndices - The index of the most recent complete def (proceding bottom
    /// up), or ~0u if the register is live.
    unsigned DefIndices[TargetRegisterInfo::FirstVirtualRegister];

    /// KeepRegs - A set of registers which are live and cannot be changed to
    /// break anti-dependencies.
    SmallSet<unsigned, 4> KeepRegs;

  public:
    CriticalAntiDepBreaker(MachineFunction& MFi);
    ~CriticalAntiDepBreaker();
    
    /// GetMaxTrials - Critical path anti-dependence breaking requires
    /// only a single pass
    unsigned GetMaxTrials() { return 1; }

    /// NeedCandidates - Candidates not needed.
    bool NeedCandidates() { return false; }

    /// Start - Initialize anti-dep breaking for a new basic block.
    void StartBlock(MachineBasicBlock *BB);

    /// BreakAntiDependencies - Identifiy anti-dependencies along the critical path
    /// of the ScheduleDAG and break them by renaming registers.
    ///
    unsigned BreakAntiDependencies(std::vector<SUnit>& SUnits,
                                   CandidateMap& Candidates,
                                   MachineBasicBlock::iterator& Begin,
                                   MachineBasicBlock::iterator& End,
                                   unsigned InsertPosIndex);

    /// Observe - Update liveness information to account for the current
    /// instruction, which will not be scheduled.
    ///
    void Observe(MachineInstr *MI, unsigned Count, unsigned InsertPosIndex);

    /// Finish - Finish anti-dep breaking for a basic block.
    void FinishBlock();

  private:
    void PrescanInstruction(MachineInstr *MI);
    void ScanInstruction(MachineInstr *MI, unsigned Count);
    unsigned findSuitableFreeRegister(unsigned AntiDepReg,
                                      unsigned LastNewReg,
                                      const TargetRegisterClass *);
  };
}

#endif