2bit_local.cc revision 8232
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 376184SN/ALocalBP::LocalBP(unsigned _localPredictorSize, 386184SN/A unsigned _localCtrBits, 396184SN/A unsigned _instShiftAmt) 406184SN/A : localPredictorSize(_localPredictorSize), 416184SN/A localCtrBits(_localCtrBits), 426184SN/A instShiftAmt(_instShiftAmt) 436184SN/A{ 446184SN/A if (!isPowerOf2(localPredictorSize)) { 456184SN/A fatal("Invalid local predictor size!\n"); 466184SN/A } 476184SN/A 486184SN/A localPredictorSets = localPredictorSize / localCtrBits; 496184SN/A 506184SN/A if (!isPowerOf2(localPredictorSets)) { 516184SN/A fatal("Invalid number of local predictor sets! Check localCtrBits.\n"); 526184SN/A } 536184SN/A 546184SN/A // Setup the index mask. 556184SN/A indexMask = localPredictorSets - 1; 566184SN/A 576184SN/A DPRINTF(Fetch, "Branch predictor: index mask: %#x\n", indexMask); 586184SN/A 596184SN/A // Setup the array of counters for the local predictor. 606184SN/A localCtrs.resize(localPredictorSets); 616184SN/A 626227Snate@binkert.org for (unsigned i = 0; i < localPredictorSets; ++i) 636184SN/A localCtrs[i].setBits(_localCtrBits); 646184SN/A 656184SN/A DPRINTF(Fetch, "Branch predictor: local predictor size: %i\n", 666184SN/A localPredictorSize); 676184SN/A 686184SN/A DPRINTF(Fetch, "Branch predictor: local counter bits: %i\n", localCtrBits); 696184SN/A 706184SN/A DPRINTF(Fetch, "Branch predictor: instruction shift amount: %i\n", 716184SN/A instShiftAmt); 726184SN/A} 736184SN/A 746184SN/Avoid 756184SN/ALocalBP::reset() 766184SN/A{ 776227Snate@binkert.org for (unsigned i = 0; i < localPredictorSets; ++i) { 786184SN/A localCtrs[i].reset(); 796184SN/A } 806184SN/A} 816184SN/A 826184SN/Abool 836184SN/ALocalBP::lookup(Addr &branch_addr, void * &bp_history) 846184SN/A{ 856184SN/A bool taken; 866184SN/A uint8_t counter_val; 876184SN/A unsigned local_predictor_idx = getLocalIndex(branch_addr); 886184SN/A 896184SN/A DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n", 906184SN/A local_predictor_idx); 916184SN/A 926184SN/A counter_val = localCtrs[local_predictor_idx].read(); 936184SN/A 946184SN/A DPRINTF(Fetch, "Branch predictor: prediction is %i.\n", 956184SN/A (int)counter_val); 966184SN/A 976184SN/A taken = getPrediction(counter_val); 986184SN/A 996184SN/A#if 0 1006184SN/A // Speculative update. 1016184SN/A if (taken) { 1026184SN/A DPRINTF(Fetch, "Branch predictor: Branch updated as taken.\n"); 1036184SN/A localCtrs[local_predictor_idx].increment(); 1046184SN/A } else { 1056184SN/A DPRINTF(Fetch, "Branch predictor: Branch updated as not taken.\n"); 1066184SN/A localCtrs[local_predictor_idx].decrement(); 1076184SN/A } 1086184SN/A#endif 1096184SN/A 1106184SN/A return taken; 1116184SN/A} 1126184SN/A 1136184SN/Avoid 1146184SN/ALocalBP::update(Addr &branch_addr, bool taken, void *bp_history) 1156184SN/A{ 1166184SN/A assert(bp_history == NULL); 1176184SN/A unsigned local_predictor_idx; 1186184SN/A 1196184SN/A // Update the local predictor. 1206184SN/A local_predictor_idx = getLocalIndex(branch_addr); 1216184SN/A 1226184SN/A DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n", 1236184SN/A local_predictor_idx); 1246184SN/A 1256184SN/A if (taken) { 1266184SN/A DPRINTF(Fetch, "Branch predictor: Branch updated as taken.\n"); 1276184SN/A localCtrs[local_predictor_idx].increment(); 1286184SN/A } else { 1296184SN/A DPRINTF(Fetch, "Branch predictor: Branch updated as not taken.\n"); 1306184SN/A localCtrs[local_predictor_idx].decrement(); 1316184SN/A } 1326184SN/A} 1336184SN/A 1346184SN/Ainline 1356184SN/Abool 1366184SN/ALocalBP::getPrediction(uint8_t &count) 1376184SN/A{ 1386184SN/A // Get the MSB of the count 1396184SN/A return (count >> (localCtrBits - 1)); 1406184SN/A} 1416184SN/A 1426184SN/Ainline 1436184SN/Aunsigned 1446184SN/ALocalBP::getLocalIndex(Addr &branch_addr) 1456184SN/A{ 1466184SN/A return (branch_addr >> instShiftAmt) & indexMask; 1476184SN/A} 148