src/cpu/inorder/resources/bpred_unit.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  *          Korey Sewell
  30  */
  31
  32 #ifndef __CPU_INORDER_BPRED_UNIT_HH__
  33 #define __CPU_INORDER_BPRED_UNIT_HH__
  34
  35 #include <list>
  36
  37 #include "arch/isa_traits.hh"
  38 #include "base/statistics.hh"
  39 #include "cpu/inst_seq.hh"
  40 #include "cpu/inorder/inorder_dyn_inst.hh"
  41 #include "cpu/inorder/pipeline_traits.hh"
  42 #include "cpu/inorder/resource.hh"
  43 #include "cpu/pred/2bit_local.hh"
  44 #include "cpu/pred/btb.hh"
  45 #include "cpu/pred/ras.hh"
  46 #include "cpu/pred/tournament.hh"
  47 #include "params/InOrderCPU.hh"
  48
  49 /**
  50  * Basically a wrapper class to hold both the branch predictor
  51  * and the BTB.
  52  */
  53 class BPredUnit
  54 {
  55   private:
  56
  57     enum PredType {
  58         Local,
  59         Tournament
  60     };
  61
  62     PredType predictor;
  63
  64   public:
  65
  66     /**
  67      * @param params The params object, that has the size of the BP and BTB.
  68      */
  69     BPredUnit(Resource *_res, ThePipeline::Params *params);
  70
  71     std::string name();
  72
  73     /**
  74      * Registers statistics.
  75      */
  76     void regStats();
  77
  78     void switchOut();
  79
  80     void takeOverFrom();
  81
  82     /**
  83      * Predicts whether or not the instruction is a taken branch, and the
  84      * target of the branch if it is taken.
  85      * @param inst The branch instruction.
  86      * @param PC The predicted PC is passed back through this parameter.
  87      * @param tid The thread id.
  88      * @return Returns if the branch is taken or not.
  89      */
  90     bool predict(ThePipeline::DynInstPtr &inst, Addr &PC, ThreadID tid);
  91
  92     // @todo: Rename this function.
  93     void BPUncond(void * &bp_history);
  94
  95     /**
  96      * Tells the branch predictor to commit any updates until the given
  97      * sequence number.
  98      * @param done_sn The sequence number to commit any older updates up until.
  99      * @param tid The thread id.
 100      */
 101     void update(const InstSeqNum &done_sn, ThreadID tid);
 102
 103     /**
 104      * Squashes all outstanding updates until a given sequence number.
 105      * @param squashed_sn The sequence number to squash any younger updates up
 106      * until.
 107      * @param tid The thread id.
 108      */
 109     void squash(const InstSeqNum &squashed_sn, ThreadID tid);
 110
 111     /**
 112      * Squashes all outstanding updates until a given sequence number, and
 113      * corrects that sn's update with the proper address and taken/not taken.
 114      * @param squashed_sn The sequence number to squash any younger updates up
 115      * until.
 116      * @param corr_target The correct branch target.
 117      * @param actually_taken The correct branch direction.
 118      * @param tid The thread id.
 119      */
 120     void squash(const InstSeqNum &squashed_sn, const Addr &corr_target,
 121                 bool actually_taken, ThreadID tid);
 122
 123     /**
 124      * @param bp_history Pointer to the history object.  The predictor
 125      * will need to update any state and delete the object.
 126      */
 127     void BPSquash(void *bp_history);
 128
 129     /**
 130      * Looks up a given PC in the BP to see if it is taken or not taken.
 131      * @param inst_PC The PC to look up.
 132      * @param bp_history Pointer that will be set to an object that
 133      * has the branch predictor state associated with the lookup.
 134      * @return Whether the branch is taken or not taken.
 135      */
 136     bool BPLookup(Addr &inst_PC, void * &bp_history);
 137
 138     /**
 139      * Looks up a given PC in the BTB to see if a matching entry exists.
 140      * @param inst_PC The PC to look up.
 141      * @return Whether the BTB contains the given PC.
 142      */
 143     bool BTBValid(Addr &inst_PC)
 144     { return BTB.valid(inst_PC, 0); }
 145
 146     /**
 147      * Looks up a given PC in the BTB to get the predicted target.
 148      * @param inst_PC The PC to look up.
 149      * @return The address of the target of the branch.
 150      */
 151     Addr BTBLookup(Addr &inst_PC)
 152     { return BTB.lookup(inst_PC, 0); }
 153
 154     /**
 155      * Updates the BP with taken/not taken information.
 156      * @param inst_PC The branch's PC that will be updated.
 157      * @param taken Whether the branch was taken or not taken.
 158      * @param bp_history Pointer to the branch predictor state that is
 159      * associated with the branch lookup that is being updated.
 160      * @todo Make this update flexible enough to handle a global predictor.
 161      */
 162     void BPUpdate(Addr &inst_PC, bool taken, void *bp_history);
 163
 164     /**
 165      * Updates the BTB with the target of a branch.
 166      * @param inst_PC The branch's PC that will be updated.
 167      * @param target_PC The branch's target that will be added to the BTB.
 168      */
 169     void BTBUpdate(Addr &inst_PC, Addr &target_PC)
 170     { BTB.update(inst_PC, target_PC,0); }
 171
 172     void dump();
 173
 174   private:
 175     Resource *res;
 176
 177     struct PredictorHistory {
 178         /**
 179          * Makes a predictor history struct that contains any
 180          * information needed to update the predictor, BTB, and RAS.
 181          */
 182         PredictorHistory(const InstSeqNum &seq_num, const Addr &inst_PC,
 183                          bool pred_taken, void *bp_history,
 184                          ThreadID _tid)
 185             : seqNum(seq_num), PC(inst_PC), RASTarget(0),
 186               RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0),
 187               wasCall(0), bpHistory(bp_history)
 188         { }
 189
 190         /** The sequence number for the predictor history entry. */
 191         InstSeqNum seqNum;
 192
 193         /** The PC associated with the sequence number. */
 194         Addr PC;
 195
 196         /** The RAS target (only valid if a return). */
 197         Addr RASTarget;
 198
 199         /** The RAS index of the instruction (only valid if a call). */
 200         unsigned RASIndex;
 201
 202         /** The thread id. */
 203         ThreadID tid;
 204
 205         /** Whether or not it was predicted taken. */
 206         bool predTaken;
 207
 208         /** Whether or not the RAS was used. */
 209         bool usedRAS;
 210
 211         /** Whether or not the instruction was a call. */
 212         bool wasCall;
 213
 214         /** Pointer to the history object passed back from the branch
 215          * predictor.  It is used to update or restore state of the
 216          * branch predictor.
 217          */
 218         void *bpHistory;
 219     };
 220
 221     typedef std::list<PredictorHistory> History;
 222
 223     /**
 224      * The per-thread predictor history. This is used to update the predictor
 225      * as instructions are committed, or restore it to the proper state after
 226      * a squash.
 227      */
 228     History predHist[ThePipeline::MaxThreads];
 229
 230     /** The local branch predictor. */
 231     LocalBP *localBP;
 232
 233     /** The tournament branch predictor. */
 234     TournamentBP *tournamentBP;
 235
 236     /** The BTB. */
 237     DefaultBTB BTB;
 238
 239     /** The per-thread return address stack. */
 240     ReturnAddrStack RAS[ThePipeline::MaxThreads];
 241
 242     /** Stat for number of BP lookups. */
 243     Stats::Scalar lookups;
 244     /** Stat for number of conditional branches predicted. */
 245     Stats::Scalar condPredicted;
 246     /** Stat for number of conditional branches predicted incorrectly. */
 247     Stats::Scalar condIncorrect;
 248     /** Stat for number of BTB lookups. */
 249     Stats::Scalar BTBLookups;
 250     /** Stat for number of BTB hits. */
 251     Stats::Scalar BTBHits;
 252     /** Stat for number of times the BTB is correct. */
 253     Stats::Scalar BTBCorrect;
 254     /** Stat for number of times the RAS is used to get a target. */
 255     Stats::Scalar usedRAS;
 256     /** Stat for number of times the RAS is incorrect. */
 257     Stats::Scalar RASIncorrect;
 258 };
 259
 260 #endif // __CPU_INORDER_BPRED_UNIT_HH__