bpred_unit.hh

来自「linux下基于c++的处理器仿真平台。具有处理器流水线」· HH 代码 · 共 138 行

/*
 * Copyright (c) 2004, 2005
 * The Regents of The University of Michigan
 * All Rights Reserved
 *
 * This code is part of the M5 simulator, developed by Nathan Binkert,
 * Erik Hallnor, Steve Raasch, and Steve Reinhardt, with contributions
 * from Ron Dreslinski, Dave Greene, Lisa Hsu, Kevin Lim, Ali Saidi, 
 * and Andrew Schultz.
 *
 * Permission is granted to use, copy, create derivative works and
 * redistribute this software and such derivative works for any
 * purpose, so long as the copyright notice above, this grant of
 * permission, and the disclaimer below appear in all copies made; and
 * so long as the name of The University of Michigan is not used in
 * any advertising or publicity pertaining to the use or distribution
 * of this software without specific, written prior authorization.
 *
 * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION FROM THE
 * UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY PURPOSE, AND
 * WITHOUT WARRANTY BY THE UNIVERSITY OF MICHIGAN OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE. THE REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE
 * LIABLE FOR ANY DAMAGES, INCLUDING DIRECT, SPECIAL, INDIRECT,
 * INCIDENTAL, OR CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM
 * ARISING OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
 * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGES.
 */


#ifndef __BPRED_UNIT_HH__
#define __BPRED_UNIT_HH__

// For Addr type.
#include "arch/alpha/isa_traits.hh"
#include "base/statistics.hh"
#include "cpu/inst_seq.hh"

#include "cpu/o3/2bit_local_pred.hh"
#include "cpu/o3/tournament_pred.hh"
#include "cpu/o3/btb.hh"
#include "cpu/o3/ras.hh"

#include <list>

/**
 * Basically a wrapper class to hold both the branch predictor
 * and the BTB.  Right now I'm unsure of the implementation; it would
 * be nicer to have something closer to the CPUPolicy or the Impl where
 * this is just typedefs, but it forces the upper level stages to be
 * aware of the constructors of the BP and the BTB.  The nicer thing
 * to do is have this templated on the Impl, accept the usual Params
 * object, and be able to call the constructors on the BP and BTB.
 */
template<class Impl>
class TwobitBPredUnit
{
  public:
    typedef typename Impl::Params Params;
    typedef typename Impl::DynInstPtr DynInstPtr;
    
    TwobitBPredUnit(Params &params);

    void regStats();

    bool predict(DynInstPtr &inst, Addr &PC);

    void update(const InstSeqNum &done_sn);

    void squash(const InstSeqNum &squashed_sn);

    void squash(const InstSeqNum &squashed_sn, const Addr &corr_target, 
                bool actually_taken);
    
    bool BPLookup(Addr &inst_PC)
    { return BP.lookup(inst_PC); }
    
    bool BTBValid(Addr &inst_PC)
    { return BTB.valid(inst_PC); }
    
    Addr BTBLookup(Addr &inst_PC)
    { return BTB.lookup(inst_PC); }

    // Will want to include global history.
    void BPUpdate(Addr &inst_PC, bool taken)
    { BP.update(inst_PC, taken); }
    
    void BTBUpdate(Addr &inst_PC, Addr &target_PC)
    { BTB.update(inst_PC, target_PC); }
    
  private:
    struct PredictorHistory {
        PredictorHistory(const InstSeqNum &seq_num, const Addr &inst_PC,
                         const bool pred_taken)
            : seqNum(seq_num), PC(inst_PC), predTaken(pred_taken),
              globalHistory(0), usedRAS(0), wasCall(0), RASIndex(0),
              RASTarget(0)
        { }

        InstSeqNum seqNum;

        Addr PC;

        bool predTaken;

        unsigned globalHistory;

        bool usedRAS;

        bool wasCall;

        unsigned RASIndex;

        Addr RASTarget;
    };

    std::list<PredictorHistory> predHist;
  
    DefaultBP BP;

    DefaultBTB BTB;

    ReturnAddrStack RAS;

    Stats::Scalar<> lookups;
    Stats::Scalar<> condPredicted;
    Stats::Scalar<> condIncorrect;
    Stats::Scalar<> BTBLookups;
    Stats::Scalar<> BTBHits;
    Stats::Scalar<> BTBCorrect;
    Stats::Scalar<> usedRAS;
    Stats::Scalar<> RASIncorrect;
};

#endif // __BPRED_UNIT_HH__