2bit_local.cc revision 13626
12440SN/A/* 22440SN/A * Copyright (c) 2004-2006 The Regents of The University of Michigan 32440SN/A * All rights reserved. 42440SN/A * 52440SN/A * Redistribution and use in source and binary forms, with or without 62440SN/A * modification, are permitted provided that the following conditions are 72440SN/A * met: redistributions of source code must retain the above copyright 82440SN/A * notice, this list of conditions and the following disclaimer; 92440SN/A * redistributions in binary form must reproduce the above copyright 102440SN/A * notice, this list of conditions and the following disclaimer in the 112440SN/A * documentation and/or other materials provided with the distribution; 122440SN/A * neither the name of the copyright holders nor the names of its 132440SN/A * contributors may be used to endorse or promote products derived from 142440SN/A * this software without specific prior written permission. 152440SN/A * 162440SN/A * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 172440SN/A * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 182440SN/A * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 192440SN/A * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 202440SN/A * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 212440SN/A * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 222440SN/A * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 232440SN/A * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 242440SN/A * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 252440SN/A * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 262440SN/A * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 272665SN/A * 282665SN/A * Authors: Kevin Lim 292440SN/A */ 302440SN/A 316329Sgblack@eecs.umich.edu#include "cpu/pred/2bit_local.hh" 326329Sgblack@eecs.umich.edu 332440SN/A#include "base/intmath.hh" 348961Sgblack@eecs.umich.edu#include "base/logging.hh" 356327SN/A#include "base/trace.hh" 366329Sgblack@eecs.umich.edu#include "debug/Fetch.hh" 372440SN/A 385569SN/ALocalBP::LocalBP(const LocalBPParams *params) 392972SN/A : BPredUnit(params), 406329Sgblack@eecs.umich.edu localPredictorSize(params->localPredictorSize), 416329Sgblack@eecs.umich.edu localCtrBits(params->localCtrBits) 426327SN/A{ 439046SAli.Saidi@ARM.com if (!isPowerOf2(localPredictorSize)) { 449046SAli.Saidi@ARM.com fatal("Invalid local predictor size!\n"); 459046SAli.Saidi@ARM.com } 466329Sgblack@eecs.umich.edu 476329Sgblack@eecs.umich.edu localPredictorSets = localPredictorSize / localCtrBits; 486327SN/A 496329Sgblack@eecs.umich.edu if (!isPowerOf2(localPredictorSets)) { 506329Sgblack@eecs.umich.edu fatal("Invalid number of local predictor sets! Check localCtrBits.\n"); 516329Sgblack@eecs.umich.edu } 526327SN/A 536329Sgblack@eecs.umich.edu // Setup the index mask. 546329Sgblack@eecs.umich.edu indexMask = localPredictorSets - 1; 556327SN/A 566329Sgblack@eecs.umich.edu DPRINTF(Fetch, "index mask: %#x\n", indexMask); 576329Sgblack@eecs.umich.edu 586329Sgblack@eecs.umich.edu // Setup the array of counters for the local predictor. 596329Sgblack@eecs.umich.edu localCtrs.resize(localPredictorSets); 606329Sgblack@eecs.umich.edu 616329Sgblack@eecs.umich.edu for (unsigned i = 0; i < localPredictorSets; ++i) 626321SN/A localCtrs[i].setBits(localCtrBits); 636329Sgblack@eecs.umich.edu 646329Sgblack@eecs.umich.edu DPRINTF(Fetch, "local predictor size: %i\n", 656329Sgblack@eecs.umich.edu localPredictorSize); 666329Sgblack@eecs.umich.edu 676329Sgblack@eecs.umich.edu DPRINTF(Fetch, "local counter bits: %i\n", localCtrBits); 686329Sgblack@eecs.umich.edu 697699Sgblack@eecs.umich.edu DPRINTF(Fetch, "instruction shift amount: %i\n", 707699Sgblack@eecs.umich.edu instShiftAmt); 716329Sgblack@eecs.umich.edu} 725569SN/A 736329Sgblack@eecs.umich.eduvoid 746329Sgblack@eecs.umich.eduLocalBP::reset() 756329Sgblack@eecs.umich.edu{ 766329Sgblack@eecs.umich.edu for (unsigned i = 0; i < localPredictorSets; ++i) { 776329Sgblack@eecs.umich.edu localCtrs[i].reset(); 786329Sgblack@eecs.umich.edu } 796329Sgblack@eecs.umich.edu} 806329Sgblack@eecs.umich.edu 816329Sgblack@eecs.umich.eduvoid 826329Sgblack@eecs.umich.eduLocalBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history) 836329Sgblack@eecs.umich.edu{ 846329Sgblack@eecs.umich.edu// Place holder for a function that is called to update predictor history when 856329Sgblack@eecs.umich.edu// a BTB entry is invalid or not found. 866329Sgblack@eecs.umich.edu} 876329Sgblack@eecs.umich.edu 886329Sgblack@eecs.umich.edu 896329Sgblack@eecs.umich.edubool 906329Sgblack@eecs.umich.eduLocalBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history) 917699Sgblack@eecs.umich.edu{ 926329Sgblack@eecs.umich.edu bool taken; 936329Sgblack@eecs.umich.edu uint8_t counter_val; 946329Sgblack@eecs.umich.edu unsigned local_predictor_idx = getLocalIndex(branch_addr); 956329Sgblack@eecs.umich.edu 966329Sgblack@eecs.umich.edu DPRINTF(Fetch, "Looking up index %#x\n", 976329Sgblack@eecs.umich.edu local_predictor_idx); 987699Sgblack@eecs.umich.edu 996329Sgblack@eecs.umich.edu counter_val = localCtrs[local_predictor_idx].read(); 1006329Sgblack@eecs.umich.edu 1016329Sgblack@eecs.umich.edu DPRINTF(Fetch, "prediction is %i.\n", 1026329Sgblack@eecs.umich.edu (int)counter_val); 1036329Sgblack@eecs.umich.edu 1046329Sgblack@eecs.umich.edu taken = getPrediction(counter_val); 1056329Sgblack@eecs.umich.edu 1066329Sgblack@eecs.umich.edu#if 0 1077649Sminkyu.jeong@arm.com // Speculative update. 1087649Sminkyu.jeong@arm.com if (taken) { 1096329Sgblack@eecs.umich.edu DPRINTF(Fetch, "Branch updated as taken.\n"); 1105569SN/A localCtrs[local_predictor_idx].increment(); 1112440SN/A } else { 1122440SN/A DPRINTF(Fetch, "Branch updated as not taken.\n"); 1135569SN/A localCtrs[local_predictor_idx].decrement(); 114 } 115#endif 116 117 return taken; 118} 119 120void 121LocalBP::update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history, 122 bool squashed, const StaticInstPtr & inst, Addr corrTarget) 123{ 124 assert(bp_history == NULL); 125 unsigned local_predictor_idx; 126 127 // No state to restore, and we do not update on the wrong 128 // path. 129 if (squashed) { 130 return; 131 } 132 133 // Update the local predictor. 134 local_predictor_idx = getLocalIndex(branch_addr); 135 136 DPRINTF(Fetch, "Looking up index %#x\n", local_predictor_idx); 137 138 if (taken) { 139 DPRINTF(Fetch, "Branch updated as taken.\n"); 140 localCtrs[local_predictor_idx].increment(); 141 } else { 142 DPRINTF(Fetch, "Branch updated as not taken.\n"); 143 localCtrs[local_predictor_idx].decrement(); 144 } 145} 146 147inline 148bool 149LocalBP::getPrediction(uint8_t &count) 150{ 151 // Get the MSB of the count 152 return (count >> (localCtrBits - 1)); 153} 154 155inline 156unsigned 157LocalBP::getLocalIndex(Addr &branch_addr) 158{ 159 return (branch_addr >> instShiftAmt) & indexMask; 160} 161 162void 163LocalBP::uncondBranch(ThreadID tid, Addr pc, void *&bp_history) 164{ 165} 166 167LocalBP* 168LocalBPParams::create() 169{ 170 return new LocalBP(this); 171} 172