src/cpu/o3/2bit_local_pred.hh

   1 /*
   2  * Copyright (c) 2004-2005 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Kevin Lim
  29  */
  30
  31 #ifndef __CPU_O3_CPU_2BIT_LOCAL_PRED_HH__
  32 #define __CPU_O3_CPU_2BIT_LOCAL_PRED_HH__
  33
  34 // For Addr type.
  35 #include "arch/isa_traits.hh"
  36 #include "cpu/o3/sat_counter.hh"
  37
  38 class DefaultBP
  39 {
  40   public:
  41     /**
  42      * Default branch predictor constructor.
  43      */
  44     DefaultBP(unsigned localPredictorSize, unsigned localCtrBits,
  45               unsigned instShiftAmt);
  46
  47     /**
  48      * Looks up the given address in the branch predictor and returns
  49      * a true/false value as to whether it is taken.
  50      * @param branch_addr The address of the branch to look up.
  51      * @return Whether or not the branch is taken.
  52      */
  53     bool lookup(Addr &branch_addr);
  54
  55     /**
  56      * Updates the branch predictor with the actual result of a branch.
  57      * @param branch_addr The address of the branch to update.
  58      * @param taken Whether or not the branch was taken.
  59      */
  60     void update(Addr &branch_addr, bool taken);
  61
  62   private:
  63
  64     /** Returns the taken/not taken prediction given the value of the
  65      *  counter.
  66      */
  67     inline bool getPrediction(uint8_t &count);
  68
  69     /** Calculates the local index based on the PC. */
  70     inline unsigned getLocalIndex(Addr &PC);
  71
  72     /** Array of counters that make up the local predictor. */
  73     SatCounter *localCtrs;
  74
  75     /** Size of the local predictor. */
  76     unsigned localPredictorSize;
  77
  78     /** Number of bits of the local predictor's counters. */
  79     unsigned localCtrBits;
  80
  81     /** Number of bits to shift the PC when calculating index. */
  82     unsigned instShiftAmt;
  83
  84     /** Mask to get index bits. */
  85     unsigned indexMask;
  86 };
  87
  88 #endif // __CPU_O3_CPU_2BIT_LOCAL_PRED_HH__