src/cpu/o3/2bit_local_pred.hh

   1 /*
   2  * Copyright (c) 2004-2006 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_2BIT_LOCAL_PRED_HH__
  32 #define __CPU_O3_2BIT_LOCAL_PRED_HH__
  33
  34 // For Addr type.
  35 #include "arch/isa_traits.hh"
  36 #include "cpu/o3/sat_counter.hh"
  37
  38 #include <vector>
  39
  40 /**
  41  * Implements a local predictor that uses the PC to index into a table of
  42  * counters.  Note that any time a pointer to the bp_history is given, it
  43  * should be NULL using this predictor because it does not have any branch
  44  * predictor state that needs to be recorded or updated; the update can be
  45  * determined solely by the branch being taken or not taken.
  46  */
  47 class LocalBP
  48 {
  49   public:
  50     /**
  51      * Default branch predictor constructor.
  52      * @param localPredictorSize Size of the local predictor.
  53      * @param localCtrBits Number of bits per counter.
  54      * @param instShiftAmt Offset amount for instructions to ignore alignment.
  55      */
  56     LocalBP(unsigned localPredictorSize, unsigned localCtrBits,
  57             unsigned instShiftAmt);
  58
  59     /**
  60      * Looks up the given address in the branch predictor and returns
  61      * a true/false value as to whether it is taken.
  62      * @param branch_addr The address of the branch to look up.
  63      * @param bp_history Pointer to any bp history state.
  64      * @return Whether or not the branch is taken.
  65      */
  66     bool lookup(Addr &branch_addr, void * &bp_history);
  67
  68     /**
  69      * Updates the branch predictor with the actual result of a branch.
  70      * @param branch_addr The address of the branch to update.
  71      * @param taken Whether or not the branch was taken.
  72      */
  73     void update(Addr &branch_addr, bool taken, void *bp_history);
  74
  75     void squash(void *bp_history)
  76     { assert(bp_history == NULL); }
  77
  78     void reset();
  79
  80   private:
  81     /**
  82      *  Returns the taken/not taken prediction given the value of the
  83      *  counter.
  84      *  @param count The value of the counter.
  85      *  @return The prediction based on the counter value.
  86      */
  87     inline bool getPrediction(uint8_t &count);
  88
  89     /** Calculates the local index based on the PC. */
  90     inline unsigned getLocalIndex(Addr &PC);
  91
  92     /** Array of counters that make up the local predictor. */
  93     std::vector<SatCounter> localCtrs;
  94
  95     /** Size of the local predictor. */
  96     unsigned localPredictorSize;
  97
  98     /** Number of sets. */
  99     unsigned localPredictorSets;
 100
 101     /** Number of bits of the local predictor's counters. */
 102     unsigned localCtrBits;
 103
 104     /** Number of bits to shift the PC when calculating index. */
 105     unsigned instShiftAmt;
 106
 107     /** Mask to get index bits. */
 108     unsigned indexMask;
 109 };
 110
 111 #endif // __CPU_O3_2BIT_LOCAL_PRED_HH__