2bit_local_pred.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 90 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 __CPU_O3_CPU_2BIT_LOCAL_PRED_HH__
#define __CPU_O3_CPU_2BIT_LOCAL_PRED_HH__

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

class DefaultBP
{
  public:
    /**
     * Default branch predictor constructor.
     */
    DefaultBP(unsigned localPredictorSize, unsigned localCtrBits,
              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, bool taken);

  private:

    /** Returns the taken/not taken prediction given the value of the
     *  counter.
     */
    inline bool getPrediction(uint8_t &count);

    /** Calculates the local index based on the PC. */
    inline unsigned getLocalIndex(Addr &PC);

    /** Array of counters that make up the local predictor. */
    SatCounter *localCtrs;

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

    /** Number of bits of the local predictor's counters. */
    unsigned localCtrBits;
    
    /** Number of bits to shift the PC when calculating index. */
    unsigned instShiftAmt;
    
    /** Mask to get index bits. */
    unsigned indexMask;
};

#endif // __CPU_O3_CPU_2BIT_LOCAL_PRED_HH__