bpred_unit.hh revision 5999
1768SN/A/* 21762SN/A * Copyright (c) 2004-2005 The Regents of The University of Michigan 3768SN/A * All rights reserved. 4768SN/A * 5768SN/A * Redistribution and use in source and binary forms, with or without 6768SN/A * modification, are permitted provided that the following conditions are 7768SN/A * met: redistributions of source code must retain the above copyright 8768SN/A * notice, this list of conditions and the following disclaimer; 9768SN/A * redistributions in binary form must reproduce the above copyright 10768SN/A * notice, this list of conditions and the following disclaimer in the 11768SN/A * documentation and/or other materials provided with the distribution; 12768SN/A * neither the name of the copyright holders nor the names of its 13768SN/A * contributors may be used to endorse or promote products derived from 14768SN/A * this software without specific prior written permission. 15768SN/A * 16768SN/A * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17768SN/A * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18768SN/A * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19768SN/A * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20768SN/A * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21768SN/A * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22768SN/A * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23768SN/A * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24768SN/A * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25768SN/A * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26768SN/A * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 272665SN/A * 282665SN/A * Authors: Kevin Lim 292665SN/A */ 302665SN/A 31768SN/A#ifndef __CPU_O3_BPRED_UNIT_HH__ 32768SN/A#define __CPU_O3_BPRED_UNIT_HH__ 331722SN/A 341722SN/A#include "base/statistics.hh" 35768SN/A#include "cpu/inst_seq.hh" 36768SN/A 371401SN/A#include "cpu/o3/2bit_local_pred.hh" 381401SN/A#include "cpu/o3/btb.hh" 39768SN/A#include "cpu/o3/ras.hh" 403540Sgblack@eecs.umich.edu#include "cpu/o3/tournament_pred.hh" 419338SAndreas.Sandberg@arm.com 425443Sgblack@eecs.umich.edu#include "sim/host.hh" 438229Snate@binkert.org 445392Sgblack@eecs.umich.edu#include <list> 454762Snate@binkert.org 46932SN/Aclass DerivO3CPUParams; 47768SN/A 481722SN/A/** 49885SN/A * Basically a wrapper class to hold both the branch predictor 50885SN/A * and the BTB. 51768SN/A */ 522542SN/Atemplate<class Impl> 53768SN/Aclass BPredUnit 54809SN/A{ 55773SN/A private: 56773SN/A typedef typename Impl::DynInstPtr DynInstPtr; 57768SN/A 585392Sgblack@eecs.umich.edu enum PredType { 595606Snate@binkert.org Local, 601854SN/A Tournament 615392Sgblack@eecs.umich.edu }; 625606Snate@binkert.org 635606Snate@binkert.org PredType predictor; 645392Sgblack@eecs.umich.edu 655392Sgblack@eecs.umich.edu public: 665392Sgblack@eecs.umich.edu 671854SN/A /** 685392Sgblack@eecs.umich.edu * @param params The params object, that has the size of the BP and BTB. 695392Sgblack@eecs.umich.edu */ 705392Sgblack@eecs.umich.edu BPredUnit(DerivO3CPUParams *params); 711817SN/A 72771SN/A /** 73885SN/A * Registers statistics. 74803SN/A */ 75885SN/A void regStats(); 76885SN/A 77803SN/A void switchOut(); 78885SN/A 79885SN/A void takeOverFrom(); 80803SN/A 81885SN/A /** 82885SN/A * Predicts whether or not the instruction is a taken branch, and the 83803SN/A * target of the branch if it is taken. 84769SN/A * @param inst The branch instruction. 85885SN/A * @param PC The predicted PC is passed back through this parameter. 86885SN/A * @param tid The thread id. 87885SN/A * @return Returns if the branch is taken or not. 88885SN/A */ 89777SN/A bool predict(DynInstPtr &inst, Addr &PC, unsigned tid); 90777SN/A 91885SN/A // @todo: Rename this function. 92775SN/A void BPUncond(void * &bp_history); 93775SN/A 941817SN/A /** 955443Sgblack@eecs.umich.edu * Tells the branch predictor to commit any updates until the given 96773SN/A * sequence number. 975606Snate@binkert.org * @param done_sn The sequence number to commit any older updates up until. 985392Sgblack@eecs.umich.edu * @param tid The thread id. 995392Sgblack@eecs.umich.edu */ 100773SN/A void update(const InstSeqNum &done_sn, unsigned tid); 101885SN/A 102885SN/A /** 103885SN/A * Squashes all outstanding updates until a given sequence number. 104885SN/A * @param squashed_sn The sequence number to squash any younger updates up 1051817SN/A * until. 106771SN/A * @param tid The thread id. 107768SN/A */ 108891SN/A void squash(const InstSeqNum &squashed_sn, unsigned tid); 109891SN/A 110891SN/A /** 111891SN/A * Squashes all outstanding updates until a given sequence number, and 1121634SN/A * corrects that sn's update with the proper address and taken/not taken. 113775SN/A * @param squashed_sn The sequence number to squash any younger updates up 1142539SN/A * until. 1154762Snate@binkert.org * @param corr_target The correct branch target. 116885SN/A * @param actually_taken The correct branch direction. 117885SN/A * @param tid The thread id. 1182539SN/A */ 119885SN/A void squash(const InstSeqNum &squashed_sn, const Addr &corr_target, 1204762Snate@binkert.org bool actually_taken, unsigned tid); 1214762Snate@binkert.org 1224762Snate@binkert.org /** 1234762Snate@binkert.org * @param bp_history Pointer to the history object. The predictor 1244762Snate@binkert.org * will need to update any state and delete the object. 1254762Snate@binkert.org */ 1264762Snate@binkert.org void BPSquash(void *bp_history); 127768SN/A 1283349SN/A /** 1293349SN/A * Looks up a given PC in the BP to see if it is taken or not taken. 130768SN/A * @param inst_PC The PC to look up. 131885SN/A * @param bp_history Pointer that will be set to an object that 132885SN/A * has the branch predictor state associated with the lookup. 133885SN/A * @return Whether the branch is taken or not taken. 134885SN/A */ 135777SN/A bool BPLookup(Addr &inst_PC, void * &bp_history); 136885SN/A 137885SN/A /** 138885SN/A * Looks up a given PC in the BTB to see if a matching entry exists. 139885SN/A * @param inst_PC The PC to look up. 140885SN/A * @return Whether the BTB contains the given PC. 141777SN/A */ 142777SN/A bool BTBValid(Addr &inst_PC) 143885SN/A { return BTB.valid(inst_PC, 0); } 144885SN/A 145885SN/A /** 146885SN/A * Looks up a given PC in the BTB to get the predicted target. 147768SN/A * @param inst_PC The PC to look up. 148885SN/A * @return The address of the target of the branch. 149885SN/A */ 150885SN/A Addr BTBLookup(Addr &inst_PC) 151885SN/A { return BTB.lookup(inst_PC, 0); } 152885SN/A 153885SN/A /** 154768SN/A * Updates the BP with taken/not taken information. 155909SN/A * @param inst_PC The branch's PC that will be updated. 156768SN/A * @param taken Whether the branch was taken or not taken. 157768SN/A * @param bp_history Pointer to the branch predictor state that is 1581401SN/A * associated with the branch lookup that is being updated. 159 * @todo Make this update flexible enough to handle a global predictor. 160 */ 161 void BPUpdate(Addr &inst_PC, bool taken, void *bp_history); 162 163 /** 164 * Updates the BTB with the target of a branch. 165 * @param inst_PC The branch's PC that will be updated. 166 * @param target_PC The branch's target that will be added to the BTB. 167 */ 168 void BTBUpdate(Addr &inst_PC, Addr &target_PC) 169 { BTB.update(inst_PC, target_PC,0); } 170 171 void dump(); 172 173 private: 174 struct PredictorHistory { 175 /** 176 * Makes a predictor history struct that contains any 177 * information needed to update the predictor, BTB, and RAS. 178 */ 179 PredictorHistory(const InstSeqNum &seq_num, const Addr &inst_PC, 180 const bool pred_taken, void *bp_history, 181 const unsigned _tid) 182 : seqNum(seq_num), PC(inst_PC), RASTarget(0), 183 RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0), 184 wasCall(0), bpHistory(bp_history) 185 { } 186 187 /** The sequence number for the predictor history entry. */ 188 InstSeqNum seqNum; 189 190 /** The PC associated with the sequence number. */ 191 Addr PC; 192 193 /** The RAS target (only valid if a return). */ 194 Addr RASTarget; 195 196 /** The RAS index of the instruction (only valid if a call). */ 197 unsigned RASIndex; 198 199 /** The thread id. */ 200 unsigned tid; 201 202 /** Whether or not it was predicted taken. */ 203 bool predTaken; 204 205 /** Whether or not the RAS was used. */ 206 bool usedRAS; 207 208 /** Whether or not the instruction was a call. */ 209 bool wasCall; 210 211 /** Pointer to the history object passed back from the branch 212 * predictor. It is used to update or restore state of the 213 * branch predictor. 214 */ 215 void *bpHistory; 216 }; 217 218 typedef std::list<PredictorHistory> History; 219 220 /** 221 * The per-thread predictor history. This is used to update the predictor 222 * as instructions are committed, or restore it to the proper state after 223 * a squash. 224 */ 225 History predHist[Impl::MaxThreads]; 226 227 /** The local branch predictor. */ 228 LocalBP *localBP; 229 230 /** The tournament branch predictor. */ 231 TournamentBP *tournamentBP; 232 233 /** The BTB. */ 234 DefaultBTB BTB; 235 236 /** The per-thread return address stack. */ 237 ReturnAddrStack RAS[Impl::MaxThreads]; 238 239 /** Stat for number of BP lookups. */ 240 Stats::Scalar lookups; 241 /** Stat for number of conditional branches predicted. */ 242 Stats::Scalar condPredicted; 243 /** Stat for number of conditional branches predicted incorrectly. */ 244 Stats::Scalar condIncorrect; 245 /** Stat for number of BTB lookups. */ 246 Stats::Scalar BTBLookups; 247 /** Stat for number of BTB hits. */ 248 Stats::Scalar BTBHits; 249 /** Stat for number of times the BTB is correct. */ 250 Stats::Scalar BTBCorrect; 251 /** Stat for number of times the RAS is used to get a target. */ 252 Stats::Scalar usedRAS; 253 /** Stat for number of times the RAS is incorrect. */ 254 Stats::Scalar RASIncorrect; 255}; 256 257#endif // __CPU_O3_BPRED_UNIT_HH__ 258