src/cpu/ozone/null_predictor.hh

/*
 * Copyright (c) 2006 The Regents of The University of Michigan
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Kevin Lim
 */

#ifndef __CPU_OZONE_NULL_PREDICTOR_HH__
#define __CPU_OZONE_NULL_PREDICTOR_HH__

#include "base/types.hh"
#include "cpu/inst_seq.hh"

template <class Impl>
class NullPredictor
{
  public:
    typedef typename Impl::Params Params;
    typedef typename Impl::DynInstPtr DynInstPtr;

    NullPredictor(Params *p) { }

    struct BPredInfo {
        BPredInfo()
            : PC(0), nextPC(0)
        { }

        BPredInfo(const Addr &pc, const Addr &next_pc)
            : PC(pc), nextPC(next_pc)
        { }

        Addr PC;
        Addr nextPC;
    };

    BPredInfo lookup(Addr &PC) { return BPredInfo(PC, PC+4); }

    void undo(BPredInfo &bp_info) { return; }

    /**
     * Predicts whether or not the instruction is a taken branch, and the
     * target of the branch if it is taken.
     * @param inst The branch instruction.
     * @param PC The predicted PC is passed back through this parameter.
     * @param tid The thread id.
     * @return Returns if the branch is taken or not.
     */
    bool predict(DynInstPtr &inst, Addr &PC, ThreadID tid)
    { return false; }

    /**
     * Tells the branch predictor to commit any updates until the given
     * sequence number.
     * @param done_sn The sequence number to commit any older updates up until.
     * @param tid The thread id.
     */
    void update(const InstSeqNum &done_sn, ThreadID tid) { }

    /**
     * Squashes all outstanding updates until a given sequence number.
     * @param squashed_sn The sequence number to squash any younger updates up
     * until.
     * @param tid The thread id.
     */
    void squash(const InstSeqNum &squashed_sn, ThreadID tid) { }

    /**
     * Squashes all outstanding updates until a given sequence number, and
     * corrects that sn's update with the proper address and taken/not taken.
     * @param squashed_sn The sequence number to squash any younger updates up
     * until.
     * @param corr_target The correct branch target.
     * @param actually_taken The correct branch direction.
     * @param tid The thread id.
     */
    void squash(const InstSeqNum &squashed_sn, const Addr &corr_target,
                bool actually_taken, ThreadID tid)
    { }

};

#endif // __CPU_OZONE_NULL_PREDICTOR_HH__