gem5/cpu/o3/tournament_pred.hh

/*
 * Copyright (c) 2004-2005 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.
 */

#ifndef __CPU_O3_CPU_TOURNAMENT_PRED_HH__
#define __CPU_O3_CPU_TOURNAMENT_PRED_HH__

// For Addr type.
#include "arch/isa_traits.hh"
#include "cpu/o3/sat_counter.hh"

class TournamentBP
{
  public:
    /**
     * Default branch predictor constructor.
     */
    TournamentBP(unsigned local_predictor_size,
                 unsigned local_ctr_bits,
                 unsigned local_history_table_size,
                 unsigned local_history_bits,
                 unsigned global_predictor_size,
                 unsigned global_history_bits,
                 unsigned global_ctr_bits,
                 unsigned choice_predictor_size,
                 unsigned choice_ctr_bits,
                 unsigned instShiftAmt);

    /**
     * Looks up the given address in the branch predictor and returns
     * a true/false value as to whether it is taken.
     * @param branch_addr The address of the branch to look up.
     * @return Whether or not the branch is taken.
     */
    bool lookup(Addr &branch_addr);

    /**
     * Updates the branch predictor with the actual result of a branch.
     * @param branch_addr The address of the branch to update.
     * @param taken Whether or not the branch was taken.
     */
    void update(Addr &branch_addr, unsigned global_history, bool taken);

    inline unsigned readGlobalHist() { return globalHistory; }

  private:

    inline bool getPrediction(uint8_t &count);

    inline unsigned calcLocHistIdx(Addr &branch_addr);

    inline void updateHistoriesTaken(unsigned local_history_idx);

    inline void updateHistoriesNotTaken(unsigned local_history_idx);

    /** Local counters. */
    SatCounter *localCtrs;

    /** Size of the local predictor. */
    unsigned localPredictorSize;

    /** Number of bits of the local predictor's counters. */
    unsigned localCtrBits;

    /** Array of local history table entries. */
    unsigned *localHistoryTable;

    /** Size of the local history table. */
    unsigned localHistoryTableSize;

    /** Number of bits for each entry of the local history table.
     *  @todo Doesn't this come from the size of the local predictor?
     */
    unsigned localHistoryBits;

    /** Mask to get the proper local history. */
    unsigned localHistoryMask;


    /** Array of counters that make up the global predictor. */
    SatCounter *globalCtrs;

    /** Size of the global predictor. */
    unsigned globalPredictorSize;

    /** Number of bits of the global predictor's counters. */
    unsigned globalCtrBits;

    /** Global history register. */
    unsigned globalHistory;

    /** Number of bits for the global history. */
    unsigned globalHistoryBits;

    /** Mask to get the proper global history. */
    unsigned globalHistoryMask;


    /** Array of counters that make up the choice predictor. */
    SatCounter *choiceCtrs;

    /** Size of the choice predictor (identical to the global predictor). */
    unsigned choicePredictorSize;

    /** Number of bits of the choice predictor's counters. */
    unsigned choiceCtrBits;

    /** Number of bits to shift the instruction over to get rid of the word
     *  offset.
     */
    unsigned instShiftAmt;

    /** Threshold for the counter value; above the threshold is taken,
     *  equal to or below the threshold is not taken.
     */
    unsigned threshold;
};

#endif // __CPU_O3_CPU_TOURNAMENT_PRED_HH__