2bit_local.cc revision 11783
16184SN/A/* 26184SN/A * Copyright (c) 2004-2006 The Regents of The University of Michigan 36184SN/A * All rights reserved. 46184SN/A * 56184SN/A * Redistribution and use in source and binary forms, with or without 66184SN/A * modification, are permitted provided that the following conditions are 76184SN/A * met: redistributions of source code must retain the above copyright 86184SN/A * notice, this list of conditions and the following disclaimer; 96184SN/A * redistributions in binary form must reproduce the above copyright 106184SN/A * notice, this list of conditions and the following disclaimer in the 116184SN/A * documentation and/or other materials provided with the distribution; 126184SN/A * neither the name of the copyright holders nor the names of its 136184SN/A * contributors may be used to endorse or promote products derived from 146184SN/A * this software without specific prior written permission. 156184SN/A * 166184SN/A * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 176184SN/A * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 186184SN/A * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 196184SN/A * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 206184SN/A * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 216184SN/A * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 226184SN/A * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 236184SN/A * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 246184SN/A * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 256184SN/A * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 266184SN/A * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 276184SN/A * 286184SN/A * Authors: Kevin Lim 296184SN/A */ 306184SN/A 316184SN/A#include "base/intmath.hh" 326184SN/A#include "base/misc.hh" 336184SN/A#include "base/trace.hh" 346226Snate@binkert.org#include "cpu/pred/2bit_local.hh" 358232Snate@binkert.org#include "debug/Fetch.hh" 366184SN/A 3710785Sgope@wisc.eduLocalBP::LocalBP(const LocalBPParams *params) 389480Snilay@cs.wisc.edu : BPredUnit(params), 399480Snilay@cs.wisc.edu localPredictorSize(params->localPredictorSize), 4010785Sgope@wisc.edu localCtrBits(params->localCtrBits) 416184SN/A{ 426184SN/A if (!isPowerOf2(localPredictorSize)) { 436184SN/A fatal("Invalid local predictor size!\n"); 446184SN/A } 456184SN/A 466184SN/A localPredictorSets = localPredictorSize / localCtrBits; 476184SN/A 486184SN/A if (!isPowerOf2(localPredictorSets)) { 496184SN/A fatal("Invalid number of local predictor sets! Check localCtrBits.\n"); 506184SN/A } 516184SN/A 526184SN/A // Setup the index mask. 536184SN/A indexMask = localPredictorSets - 1; 546184SN/A 559480Snilay@cs.wisc.edu DPRINTF(Fetch, "index mask: %#x\n", indexMask); 566184SN/A 576184SN/A // Setup the array of counters for the local predictor. 586184SN/A localCtrs.resize(localPredictorSets); 596184SN/A 606227Snate@binkert.org for (unsigned i = 0; i < localPredictorSets; ++i) 619480Snilay@cs.wisc.edu localCtrs[i].setBits(localCtrBits); 626184SN/A 639480Snilay@cs.wisc.edu DPRINTF(Fetch, "local predictor size: %i\n", 646184SN/A localPredictorSize); 656184SN/A 669480Snilay@cs.wisc.edu DPRINTF(Fetch, "local counter bits: %i\n", localCtrBits); 676184SN/A 689480Snilay@cs.wisc.edu DPRINTF(Fetch, "instruction shift amount: %i\n", 696184SN/A instShiftAmt); 706184SN/A} 716184SN/A 726184SN/Avoid 736184SN/ALocalBP::reset() 746184SN/A{ 756227Snate@binkert.org for (unsigned i = 0; i < localPredictorSets; ++i) { 766184SN/A localCtrs[i].reset(); 776184SN/A } 786184SN/A} 796184SN/A 808842Smrinmoy.ghosh@arm.comvoid 8111434Smitch.hayenga@arm.comLocalBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history) 828842Smrinmoy.ghosh@arm.com{ 838842Smrinmoy.ghosh@arm.com// Place holder for a function that is called to update predictor history when 848842Smrinmoy.ghosh@arm.com// a BTB entry is invalid or not found. 858842Smrinmoy.ghosh@arm.com} 868842Smrinmoy.ghosh@arm.com 878842Smrinmoy.ghosh@arm.com 886184SN/Abool 8911434Smitch.hayenga@arm.comLocalBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history) 906184SN/A{ 916184SN/A bool taken; 926184SN/A uint8_t counter_val; 936184SN/A unsigned local_predictor_idx = getLocalIndex(branch_addr); 946184SN/A 959480Snilay@cs.wisc.edu DPRINTF(Fetch, "Looking up index %#x\n", 966184SN/A local_predictor_idx); 976184SN/A 986184SN/A counter_val = localCtrs[local_predictor_idx].read(); 996184SN/A 1009480Snilay@cs.wisc.edu DPRINTF(Fetch, "prediction is %i.\n", 1016184SN/A (int)counter_val); 1026184SN/A 1036184SN/A taken = getPrediction(counter_val); 1046184SN/A 1056184SN/A#if 0 1066184SN/A // Speculative update. 1076184SN/A if (taken) { 1089480Snilay@cs.wisc.edu DPRINTF(Fetch, "Branch updated as taken.\n"); 1096184SN/A localCtrs[local_predictor_idx].increment(); 1106184SN/A } else { 1119480Snilay@cs.wisc.edu DPRINTF(Fetch, "Branch updated as not taken.\n"); 1126184SN/A localCtrs[local_predictor_idx].decrement(); 1136184SN/A } 1146184SN/A#endif 1156184SN/A 1166184SN/A return taken; 1176184SN/A} 1186184SN/A 1196184SN/Avoid 12011434Smitch.hayenga@arm.comLocalBP::update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history, 12111434Smitch.hayenga@arm.com bool squashed) 1226184SN/A{ 1236184SN/A assert(bp_history == NULL); 1246184SN/A unsigned local_predictor_idx; 1256184SN/A 12611783Sarthur.perais@inria.fr // No state to restore, and we do not update on the wrong 12711783Sarthur.perais@inria.fr // path. 12811783Sarthur.perais@inria.fr if (squashed) { 12911783Sarthur.perais@inria.fr return; 13011783Sarthur.perais@inria.fr } 13111783Sarthur.perais@inria.fr 1326184SN/A // Update the local predictor. 1336184SN/A local_predictor_idx = getLocalIndex(branch_addr); 1346184SN/A 1359480Snilay@cs.wisc.edu DPRINTF(Fetch, "Looking up index %#x\n", local_predictor_idx); 1366184SN/A 1376184SN/A if (taken) { 1389480Snilay@cs.wisc.edu DPRINTF(Fetch, "Branch updated as taken.\n"); 1396184SN/A localCtrs[local_predictor_idx].increment(); 1406184SN/A } else { 1419480Snilay@cs.wisc.edu DPRINTF(Fetch, "Branch updated as not taken.\n"); 1426184SN/A localCtrs[local_predictor_idx].decrement(); 1436184SN/A } 1446184SN/A} 1456184SN/A 1466184SN/Ainline 1476184SN/Abool 1486184SN/ALocalBP::getPrediction(uint8_t &count) 1496184SN/A{ 1506184SN/A // Get the MSB of the count 1516184SN/A return (count >> (localCtrBits - 1)); 1526184SN/A} 1536184SN/A 1546184SN/Ainline 1556184SN/Aunsigned 1566184SN/ALocalBP::getLocalIndex(Addr &branch_addr) 1576184SN/A{ 1586184SN/A return (branch_addr >> instShiftAmt) & indexMask; 1596184SN/A} 1609480Snilay@cs.wisc.edu 1619480Snilay@cs.wisc.eduvoid 16211434Smitch.hayenga@arm.comLocalBP::uncondBranch(ThreadID tid, Addr pc, void *&bp_history) 1639480Snilay@cs.wisc.edu{ 1649480Snilay@cs.wisc.edu} 16510785Sgope@wisc.edu 16610785Sgope@wisc.eduLocalBP* 16710785Sgope@wisc.eduLocalBPParams::create() 16810785Sgope@wisc.edu{ 16910785Sgope@wisc.edu return new LocalBP(this); 17010785Sgope@wisc.edu} 171