bpred_unit.hh revision 2292
16313Sgblack@eecs.umich.edu/* 26313Sgblack@eecs.umich.edu * Copyright (c) 2004-2005 The Regents of The University of Michigan 36313Sgblack@eecs.umich.edu * All rights reserved. 46313Sgblack@eecs.umich.edu * 56313Sgblack@eecs.umich.edu * Redistribution and use in source and binary forms, with or without 66313Sgblack@eecs.umich.edu * modification, are permitted provided that the following conditions are 76313Sgblack@eecs.umich.edu * met: redistributions of source code must retain the above copyright 86313Sgblack@eecs.umich.edu * notice, this list of conditions and the following disclaimer; 96313Sgblack@eecs.umich.edu * redistributions in binary form must reproduce the above copyright 106313Sgblack@eecs.umich.edu * notice, this list of conditions and the following disclaimer in the 116313Sgblack@eecs.umich.edu * documentation and/or other materials provided with the distribution; 126313Sgblack@eecs.umich.edu * neither the name of the copyright holders nor the names of its 136313Sgblack@eecs.umich.edu * contributors may be used to endorse or promote products derived from 146313Sgblack@eecs.umich.edu * this software without specific prior written permission. 156313Sgblack@eecs.umich.edu * 166313Sgblack@eecs.umich.edu * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 176313Sgblack@eecs.umich.edu * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 186313Sgblack@eecs.umich.edu * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 196313Sgblack@eecs.umich.edu * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 206313Sgblack@eecs.umich.edu * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 216313Sgblack@eecs.umich.edu * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 226313Sgblack@eecs.umich.edu * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 236313Sgblack@eecs.umich.edu * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 246313Sgblack@eecs.umich.edu * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 256313Sgblack@eecs.umich.edu * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 266313Sgblack@eecs.umich.edu * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 276313Sgblack@eecs.umich.edu */ 286313Sgblack@eecs.umich.edu 296313Sgblack@eecs.umich.edu#ifndef __CPU_O3_BPRED_UNIT_HH__ 306313Sgblack@eecs.umich.edu#define __CPU_O3_BPRED_UNIT_HH__ 316313Sgblack@eecs.umich.edu 326313Sgblack@eecs.umich.edu// For Addr type. 336313Sgblack@eecs.umich.edu#include "arch/isa_traits.hh" 346334Sgblack@eecs.umich.edu#include "base/statistics.hh" 356334Sgblack@eecs.umich.edu#include "cpu/inst_seq.hh" 366334Sgblack@eecs.umich.edu 376334Sgblack@eecs.umich.edu#include "cpu/o3/2bit_local_pred.hh" 386334Sgblack@eecs.umich.edu#include "cpu/o3/btb.hh" 396313Sgblack@eecs.umich.edu#include "cpu/o3/ras.hh" 406334Sgblack@eecs.umich.edu#include "cpu/o3/tournament_pred.hh" 417878Sgblack@eecs.umich.edu 426313Sgblack@eecs.umich.edu#include <list> 436334Sgblack@eecs.umich.edu 446313Sgblack@eecs.umich.edu/** 456313Sgblack@eecs.umich.edu * Basically a wrapper class to hold both the branch predictor 466334Sgblack@eecs.umich.edu * and the BTB. Right now I'm unsure of the implementation; it would 476313Sgblack@eecs.umich.edu * be nicer to have something closer to the CPUPolicy or the Impl where 486313Sgblack@eecs.umich.edu * this is just typedefs, but it forces the upper level stages to be 496313Sgblack@eecs.umich.edu * aware of the constructors of the BP and the BTB. The nicer thing 506313Sgblack@eecs.umich.edu * to do is have this templated on the Impl, accept the usual Params 516313Sgblack@eecs.umich.edu * object, and be able to call the constructors on the BP and BTB. 526334Sgblack@eecs.umich.edu */ 536334Sgblack@eecs.umich.edutemplate<class Impl> 546334Sgblack@eecs.umich.educlass TwobitBPredUnit 556334Sgblack@eecs.umich.edu{ 566313Sgblack@eecs.umich.edu public: 578181Sksewell@umich.edu typedef typename Impl::Params Params; 588181Sksewell@umich.edu typedef typename Impl::DynInstPtr DynInstPtr; 598181Sksewell@umich.edu 608181Sksewell@umich.edu /** 616334Sgblack@eecs.umich.edu * @param params The params object, that has the size of the BP and BTB. 626334Sgblack@eecs.umich.edu */ 636334Sgblack@eecs.umich.edu TwobitBPredUnit(Params *params); 646334Sgblack@eecs.umich.edu 656334Sgblack@eecs.umich.edu /** 666334Sgblack@eecs.umich.edu * Registers statistics. 676334Sgblack@eecs.umich.edu */ 686334Sgblack@eecs.umich.edu void regStats(); 696334Sgblack@eecs.umich.edu 706334Sgblack@eecs.umich.edu /** 716313Sgblack@eecs.umich.edu * Predicts whether or not the instruction is a taken branch, and the 728181Sksewell@umich.edu * target of the branch if it is taken. 736313Sgblack@eecs.umich.edu * @param inst The branch instruction. 748181Sksewell@umich.edu * @param PC The predicted PC is passed back through this parameter. 756334Sgblack@eecs.umich.edu * @param tid The thread id. 768181Sksewell@umich.edu * @return Returns if the branch is taken or not. 776334Sgblack@eecs.umich.edu */ 786334Sgblack@eecs.umich.edu bool predict(DynInstPtr &inst, Addr &PC, unsigned tid); 796334Sgblack@eecs.umich.edu 806334Sgblack@eecs.umich.edu /** 816334Sgblack@eecs.umich.edu * Tells the branch predictor to commit any updates until the given 826334Sgblack@eecs.umich.edu * sequence number. 836334Sgblack@eecs.umich.edu * @param done_sn The sequence number to commit any older updates up until. 846334Sgblack@eecs.umich.edu * @param tid The thread id. 856334Sgblack@eecs.umich.edu */ 866334Sgblack@eecs.umich.edu void update(const InstSeqNum &done_sn, unsigned tid); 876334Sgblack@eecs.umich.edu 886334Sgblack@eecs.umich.edu /** 896334Sgblack@eecs.umich.edu * Squashes all outstanding updates until a given sequence number. 906334Sgblack@eecs.umich.edu * @param squashed_sn The sequence number to squash any younger updates up 916334Sgblack@eecs.umich.edu * until. 926334Sgblack@eecs.umich.edu * @param tid The thread id. 936334Sgblack@eecs.umich.edu */ 946334Sgblack@eecs.umich.edu void squash(const InstSeqNum &squashed_sn, unsigned tid); 956334Sgblack@eecs.umich.edu 966334Sgblack@eecs.umich.edu /** 976334Sgblack@eecs.umich.edu * Squashes all outstanding updates until a given sequence number, and 986334Sgblack@eecs.umich.edu * corrects that sn's update with the proper address and taken/not taken. 996334Sgblack@eecs.umich.edu * @param squashed_sn The sequence number to squash any younger updates up 1006334Sgblack@eecs.umich.edu * until. 1016334Sgblack@eecs.umich.edu * @param corr_target The correct branch target. 1026334Sgblack@eecs.umich.edu * @param actually_taken The correct branch direction. 1036334Sgblack@eecs.umich.edu * @param tid The thread id. 1046334Sgblack@eecs.umich.edu */ 1056334Sgblack@eecs.umich.edu void squash(const InstSeqNum &squashed_sn, const Addr &corr_target, 1066334Sgblack@eecs.umich.edu bool actually_taken, unsigned tid); 1076334Sgblack@eecs.umich.edu 1086334Sgblack@eecs.umich.edu /** 1096334Sgblack@eecs.umich.edu * Looks up a given PC in the BP to see if it is taken or not taken. 1106334Sgblack@eecs.umich.edu * @param inst_PC The PC to look up. 1116334Sgblack@eecs.umich.edu * @return Whether the branch is taken or not taken. 1126334Sgblack@eecs.umich.edu */ 1136334Sgblack@eecs.umich.edu bool BPLookup(Addr &inst_PC) 1146334Sgblack@eecs.umich.edu { return BP.lookup(inst_PC); } 1156334Sgblack@eecs.umich.edu 1166334Sgblack@eecs.umich.edu /** 1176334Sgblack@eecs.umich.edu * Looks up a given PC in the BTB to see if a matching entry exists. 1186334Sgblack@eecs.umich.edu * @param inst_PC The PC to look up. 1196334Sgblack@eecs.umich.edu * @return Whether the BTB contains the given PC. 1206334Sgblack@eecs.umich.edu */ 1216313Sgblack@eecs.umich.edu bool BTBValid(Addr &inst_PC) 1226334Sgblack@eecs.umich.edu { return BTB.valid(inst_PC, 0); } 1236334Sgblack@eecs.umich.edu 1246334Sgblack@eecs.umich.edu /** 1256334Sgblack@eecs.umich.edu * Looks up a given PC in the BTB to get the predicted target. 1266334Sgblack@eecs.umich.edu * @param inst_PC The PC to look up. 1276313Sgblack@eecs.umich.edu * @return The address of the target of the branch. 1286334Sgblack@eecs.umich.edu */ 1296334Sgblack@eecs.umich.edu Addr BTBLookup(Addr &inst_PC) 1306334Sgblack@eecs.umich.edu { return BTB.lookup(inst_PC, 0); } 1316313Sgblack@eecs.umich.edu 1326334Sgblack@eecs.umich.edu /** 1336334Sgblack@eecs.umich.edu * Updates the BP with taken/not taken information. 1346313Sgblack@eecs.umich.edu * @param inst_PC The branch's PC that will be updated. 1356334Sgblack@eecs.umich.edu * @param taken Whether the branch was taken or not taken. 1366334Sgblack@eecs.umich.edu * @todo Make this update flexible enough to handle a global predictor. 1376334Sgblack@eecs.umich.edu */ 1386334Sgblack@eecs.umich.edu void BPUpdate(Addr &inst_PC, bool taken) 1396334Sgblack@eecs.umich.edu { BP.update(inst_PC, taken); } 1406334Sgblack@eecs.umich.edu 1416334Sgblack@eecs.umich.edu /** 1426334Sgblack@eecs.umich.edu * Updates the BTB with the target of a branch. 1436334Sgblack@eecs.umich.edu * @param inst_PC The branch's PC that will be updated. 1446334Sgblack@eecs.umich.edu * @param target_PC The branch's target that will be added to the BTB. 1456334Sgblack@eecs.umich.edu */ 1466806Sgblack@eecs.umich.edu void BTBUpdate(Addr &inst_PC, Addr &target_PC) 1476334Sgblack@eecs.umich.edu { BTB.update(inst_PC, target_PC,0); } 1486334Sgblack@eecs.umich.edu 1496334Sgblack@eecs.umich.edu private: 1506806Sgblack@eecs.umich.edu struct PredictorHistory { 1516334Sgblack@eecs.umich.edu /** 1526334Sgblack@eecs.umich.edu * Makes a predictor history struct that contains a sequence number, 1536334Sgblack@eecs.umich.edu * the PC of its instruction, and whether or not it was predicted 1546334Sgblack@eecs.umich.edu * taken. 1556334Sgblack@eecs.umich.edu */ 1566334Sgblack@eecs.umich.edu PredictorHistory(const InstSeqNum &seq_num, const Addr &inst_PC, 1576334Sgblack@eecs.umich.edu const bool pred_taken, const unsigned _tid) 1586313Sgblack@eecs.umich.edu : seqNum(seq_num), PC(inst_PC), RASTarget(0), globalHistory(0), 1596313Sgblack@eecs.umich.edu RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0), 1606313Sgblack@eecs.umich.edu wasCall(0) 1616313Sgblack@eecs.umich.edu { } 1626313Sgblack@eecs.umich.edu 1636313Sgblack@eecs.umich.edu /** The sequence number for the predictor history entry. */ 1646313Sgblack@eecs.umich.edu InstSeqNum seqNum; 1656313Sgblack@eecs.umich.edu 1666313Sgblack@eecs.umich.edu /** The PC associated with the sequence number. */ 1676313Sgblack@eecs.umich.edu Addr PC; 1686313Sgblack@eecs.umich.edu 1696313Sgblack@eecs.umich.edu /** The RAS target (only valid if a return). */ 1706313Sgblack@eecs.umich.edu Addr RASTarget; 1716678Sgblack@eecs.umich.edu 1726678Sgblack@eecs.umich.edu /** The global history at the time this entry was created. */ 1736678Sgblack@eecs.umich.edu unsigned globalHistory; 1746678Sgblack@eecs.umich.edu 1756678Sgblack@eecs.umich.edu /** The RAS index of the instruction (only valid if a call). */ 1766313Sgblack@eecs.umich.edu unsigned RASIndex; 1776313Sgblack@eecs.umich.edu 1786313Sgblack@eecs.umich.edu /** The thread id. */ 1796313Sgblack@eecs.umich.edu unsigned tid; 180 181 /** Whether or not it was predicted taken. */ 182 bool predTaken; 183 184 /** Whether or not the RAS was used. */ 185 bool usedRAS; 186 187 /** Whether or not the instruction was a call. */ 188 bool wasCall; 189 }; 190 191 typedef std::list<PredictorHistory> History; 192 193 /** 194 * The per-thread predictor history. This is used to update the predictor 195 * as instructions are committed, or restore it to the proper state after 196 * a squash. 197 */ 198 History predHist[Impl::MaxThreads]; 199 200 /** The branch predictor. */ 201 DefaultBP BP; 202 203 /** The BTB. */ 204 DefaultBTB BTB; 205 206 /** The per-thread return address stack. */ 207 ReturnAddrStack RAS[Impl::MaxThreads]; 208 209 /** Stat for number of BP lookups. */ 210 Stats::Scalar<> lookups; 211 /** Stat for number of conditional branches predicted. */ 212 Stats::Scalar<> condPredicted; 213 /** Stat for number of conditional branches predicted incorrectly. */ 214 Stats::Scalar<> condIncorrect; 215 /** Stat for number of BTB lookups. */ 216 Stats::Scalar<> BTBLookups; 217 /** Stat for number of BTB hits. */ 218 Stats::Scalar<> BTBHits; 219 /** Stat for number of times the BTB is correct. */ 220 Stats::Scalar<> BTBCorrect; 221 /** Stat for number of times the RAS is used to get a target. */ 222 Stats::Scalar<> usedRAS; 223 /** Stat for number of times the RAS is incorrect. */ 224 Stats::Scalar<> RASIncorrect; 225}; 226 227#endif // __CPU_O3_BPRED_UNIT_HH__ 228