src/cpu/pred/2bit_local.hh

   1 /*
   2  * Copyright (c) 2011, 2014 ARM Limited
   3  * All rights reserved
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   9  * licensed hereunder.  You may use the software subject to the license
  10  * terms below provided that you ensure that this notice is replicated
  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Copyright (c) 2004-2006 The Regents of The University of Michigan
  15  * All rights reserved.
  16  *
  17  * Redistribution and use in source and binary forms, with or without
  18  * modification, are permitted provided that the following conditions are
  19  * met: redistributions of source code must retain the above copyright
  20  * notice, this list of conditions and the following disclaimer;
  21  * redistributions in binary form must reproduce the above copyright
  22  * notice, this list of conditions and the following disclaimer in the
  23  * documentation and/or other materials provided with the distribution;
  24  * neither the name of the copyright holders nor the names of its
  25  * contributors may be used to endorse or promote products derived from
  26  * this software without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  29  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  30  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  31  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  32  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  33  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  34  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  35  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  36  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  37  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  38  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  39  *
  40  * Authors: Kevin Lim
  41  *          Timothy M. Jones
  42  */
  43
  44 #ifndef __CPU_PRED_2BIT_LOCAL_PRED_HH__
  45 #define __CPU_PRED_2BIT_LOCAL_PRED_HH__
  46
  47 #include <vector>
  48
  49 #include "base/types.hh"
  50 #include "cpu/pred/bpred_unit.hh"
  51 #include "cpu/pred/sat_counter.hh"
  52
  53 /**
  54  * Implements a local predictor that uses the PC to index into a table of
  55  * counters.  Note that any time a pointer to the bp_history is given, it
  56  * should be NULL using this predictor because it does not have any branch
  57  * predictor state that needs to be recorded or updated; the update can be
  58  * determined solely by the branch being taken or not taken.
  59  */
  60 class LocalBP : public BPredUnit
  61 {
  62   public:
  63     /**
  64      * Default branch predictor constructor.
  65      */
  66     LocalBP(const Params *params);
  67
  68     virtual void uncondBranch(void * &bp_history);
  69
  70     /**
  71      * Looks up the given address in the branch predictor and returns
  72      * a true/false value as to whether it is taken.
  73      * @param branch_addr The address of the branch to look up.
  74      * @param bp_history Pointer to any bp history state.
  75      * @return Whether or not the branch is taken.
  76      */
  77     bool lookup(Addr branch_addr, void * &bp_history);
  78
  79     /**
  80      * Updates the branch predictor to Not Taken if a BTB entry is
  81      * invalid or not found.
  82      * @param branch_addr The address of the branch to look up.
  83      * @param bp_history Pointer to any bp history state.
  84      * @return Whether or not the branch is taken.
  85      */
  86     void btbUpdate(Addr branch_addr, void * &bp_history);
  87
  88     /**
  89      * Updates the branch predictor with the actual result of a branch.
  90      * @param branch_addr The address of the branch to update.
  91      * @param taken Whether or not the branch was taken.
  92      */
  93     void update(Addr branch_addr, bool taken, void *bp_history, bool squashed);
  94
  95     void retireSquashed(void *bp_history)
  96     { assert(bp_history == NULL); }
  97
  98     void squash(void *bp_history)
  99     { assert(bp_history == NULL); }
 100
 101     void reset();
 102
 103   private:
 104     /**
 105      *  Returns the taken/not taken prediction given the value of the
 106      *  counter.
 107      *  @param count The value of the counter.
 108      *  @return The prediction based on the counter value.
 109      */
 110     inline bool getPrediction(uint8_t &count);
 111
 112     /** Calculates the local index based on the PC. */
 113     inline unsigned getLocalIndex(Addr &PC);
 114
 115     /** Array of counters that make up the local predictor. */
 116     std::vector<SatCounter> localCtrs;
 117
 118     /** Size of the local predictor. */
 119     unsigned localPredictorSize;
 120
 121     /** Number of sets. */
 122     unsigned localPredictorSets;
 123
 124     /** Number of bits of the local predictor's counters. */
 125     unsigned localCtrBits;
 126
 127     /** Number of bits to shift the PC when calculating index. */
 128     unsigned instShiftAmt;
 129
 130     /** Mask to get index bits. */
 131     unsigned indexMask;
 132 };
 133
 134 #endif // __CPU_PRED_2BIT_LOCAL_PRED_HH__