tournament.cc revision 8463
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" 326226Snate@binkert.org#include "cpu/pred/tournament.hh" 336184SN/A 346184SN/ATournamentBP::TournamentBP(unsigned _localPredictorSize, 356184SN/A unsigned _localCtrBits, 366184SN/A unsigned _localHistoryTableSize, 376184SN/A unsigned _localHistoryBits, 386184SN/A unsigned _globalPredictorSize, 398463SMrinmoy.Ghosh@arm.com unsigned _globalHistoryBits, 406184SN/A unsigned _globalCtrBits, 416184SN/A unsigned _choicePredictorSize, 426184SN/A unsigned _choiceCtrBits, 436184SN/A unsigned _instShiftAmt) 446184SN/A : localPredictorSize(_localPredictorSize), 456184SN/A localCtrBits(_localCtrBits), 466184SN/A localHistoryTableSize(_localHistoryTableSize), 476184SN/A localHistoryBits(_localHistoryBits), 486184SN/A globalPredictorSize(_globalPredictorSize), 496184SN/A globalCtrBits(_globalCtrBits), 506184SN/A globalHistoryBits(_globalHistoryBits), 516184SN/A choicePredictorSize(_globalPredictorSize), 526184SN/A choiceCtrBits(_choiceCtrBits), 536184SN/A instShiftAmt(_instShiftAmt) 546184SN/A{ 556184SN/A if (!isPowerOf2(localPredictorSize)) { 566184SN/A fatal("Invalid local predictor size!\n"); 576184SN/A } 586184SN/A 596184SN/A //Setup the array of counters for the local predictor 606184SN/A localCtrs.resize(localPredictorSize); 616184SN/A 626184SN/A for (int i = 0; i < localPredictorSize; ++i) 636184SN/A localCtrs[i].setBits(localCtrBits); 646184SN/A 656184SN/A localPredictorMask = floorPow2(localPredictorSize) - 1; 666184SN/A 676184SN/A if (!isPowerOf2(localHistoryTableSize)) { 686184SN/A fatal("Invalid local history table size!\n"); 696184SN/A } 706184SN/A 716184SN/A //Setup the history table for the local table 726184SN/A localHistoryTable.resize(localHistoryTableSize); 736184SN/A 746184SN/A for (int i = 0; i < localHistoryTableSize; ++i) 756184SN/A localHistoryTable[i] = 0; 766184SN/A 776184SN/A // Setup the local history mask 786184SN/A localHistoryMask = (1 << localHistoryBits) - 1; 796184SN/A 806184SN/A if (!isPowerOf2(globalPredictorSize)) { 816184SN/A fatal("Invalid global predictor size!\n"); 826184SN/A } 836184SN/A 846184SN/A //Setup the array of counters for the global predictor 856184SN/A globalCtrs.resize(globalPredictorSize); 866184SN/A 876184SN/A for (int i = 0; i < globalPredictorSize; ++i) 886184SN/A globalCtrs[i].setBits(globalCtrBits); 896184SN/A 906184SN/A //Clear the global history 916184SN/A globalHistory = 0; 926184SN/A // Setup the global history mask 936184SN/A globalHistoryMask = (1 << globalHistoryBits) - 1; 946184SN/A 956184SN/A if (!isPowerOf2(choicePredictorSize)) { 966184SN/A fatal("Invalid choice predictor size!\n"); 976184SN/A } 986184SN/A 996184SN/A //Setup the array of counters for the choice predictor 1006184SN/A choiceCtrs.resize(choicePredictorSize); 1016184SN/A 1026184SN/A for (int i = 0; i < choicePredictorSize; ++i) 1036184SN/A choiceCtrs[i].setBits(choiceCtrBits); 1046184SN/A 1056184SN/A // @todo: Allow for different thresholds between the predictors. 1066184SN/A threshold = (1 << (localCtrBits - 1)) - 1; 1076184SN/A} 1086184SN/A 1096184SN/Ainline 1106184SN/Aunsigned 1116184SN/ATournamentBP::calcLocHistIdx(Addr &branch_addr) 1126184SN/A{ 1136184SN/A // Get low order bits after removing instruction offset. 1146184SN/A return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1); 1156184SN/A} 1166184SN/A 1176184SN/Ainline 1186184SN/Avoid 1196184SN/ATournamentBP::updateGlobalHistTaken() 1206184SN/A{ 1216184SN/A globalHistory = (globalHistory << 1) | 1; 1226184SN/A globalHistory = globalHistory & globalHistoryMask; 1236184SN/A} 1246184SN/A 1256184SN/Ainline 1266184SN/Avoid 1276184SN/ATournamentBP::updateGlobalHistNotTaken() 1286184SN/A{ 1296184SN/A globalHistory = (globalHistory << 1); 1306184SN/A globalHistory = globalHistory & globalHistoryMask; 1316184SN/A} 1326184SN/A 1336184SN/Ainline 1346184SN/Avoid 1356184SN/ATournamentBP::updateLocalHistTaken(unsigned local_history_idx) 1366184SN/A{ 1376184SN/A localHistoryTable[local_history_idx] = 1386184SN/A (localHistoryTable[local_history_idx] << 1) | 1; 1396184SN/A} 1406184SN/A 1416184SN/Ainline 1426184SN/Avoid 1436184SN/ATournamentBP::updateLocalHistNotTaken(unsigned local_history_idx) 1446184SN/A{ 1456184SN/A localHistoryTable[local_history_idx] = 1466184SN/A (localHistoryTable[local_history_idx] << 1); 1476184SN/A} 1486184SN/A 1496184SN/Abool 1506184SN/ATournamentBP::lookup(Addr &branch_addr, void * &bp_history) 1516184SN/A{ 1526184SN/A bool local_prediction; 1536184SN/A unsigned local_history_idx; 1546184SN/A unsigned local_predictor_idx; 1556184SN/A 1566184SN/A bool global_prediction; 1576184SN/A bool choice_prediction; 1586184SN/A 1596184SN/A //Lookup in the local predictor to get its branch prediction 1606184SN/A local_history_idx = calcLocHistIdx(branch_addr); 1616184SN/A local_predictor_idx = localHistoryTable[local_history_idx] 1626184SN/A & localPredictorMask; 1636184SN/A local_prediction = localCtrs[local_predictor_idx].read() > threshold; 1646184SN/A 1656184SN/A //Lookup in the global predictor to get its branch prediction 1666184SN/A global_prediction = globalCtrs[globalHistory].read() > threshold; 1676184SN/A 1686184SN/A //Lookup in the choice predictor to see which one to use 1696184SN/A choice_prediction = choiceCtrs[globalHistory].read() > threshold; 1706184SN/A 1716184SN/A // Create BPHistory and pass it back to be recorded. 1726184SN/A BPHistory *history = new BPHistory; 1736184SN/A history->globalHistory = globalHistory; 1746184SN/A history->localPredTaken = local_prediction; 1756184SN/A history->globalPredTaken = global_prediction; 1766184SN/A history->globalUsed = choice_prediction; 1776184SN/A bp_history = (void *)history; 1786184SN/A 1796184SN/A assert(globalHistory < globalPredictorSize && 1806184SN/A local_history_idx < localHistoryTableSize && 1816184SN/A local_predictor_idx < localPredictorSize); 1826184SN/A 1836184SN/A // Commented code is for doing speculative update of counters and 1846184SN/A // all histories. 1856184SN/A if (choice_prediction) { 1866184SN/A if (global_prediction) { 1876184SN/A// updateHistoriesTaken(local_history_idx); 1886184SN/A// globalCtrs[globalHistory].increment(); 1896184SN/A// localCtrs[local_history_idx].increment(); 1906184SN/A updateGlobalHistTaken(); 1916184SN/A return true; 1926184SN/A } else { 1936184SN/A// updateHistoriesNotTaken(local_history_idx); 1946184SN/A// globalCtrs[globalHistory].decrement(); 1956184SN/A// localCtrs[local_history_idx].decrement(); 1966184SN/A updateGlobalHistNotTaken(); 1976184SN/A return false; 1986184SN/A } 1996184SN/A } else { 2006184SN/A if (local_prediction) { 2016184SN/A// updateHistoriesTaken(local_history_idx); 2026184SN/A// globalCtrs[globalHistory].increment(); 2036184SN/A// localCtrs[local_history_idx].increment(); 2046184SN/A updateGlobalHistTaken(); 2056184SN/A return true; 2066184SN/A } else { 2076184SN/A// updateHistoriesNotTaken(local_history_idx); 2086184SN/A// globalCtrs[globalHistory].decrement(); 2096184SN/A// localCtrs[local_history_idx].decrement(); 2106184SN/A updateGlobalHistNotTaken(); 2116184SN/A return false; 2126184SN/A } 2136184SN/A } 2146184SN/A} 2156184SN/A 2166184SN/Avoid 2176184SN/ATournamentBP::uncondBr(void * &bp_history) 2186184SN/A{ 2196184SN/A // Create BPHistory and pass it back to be recorded. 2206184SN/A BPHistory *history = new BPHistory; 2216184SN/A history->globalHistory = globalHistory; 2226184SN/A history->localPredTaken = true; 2236184SN/A history->globalPredTaken = true; 2246184SN/A bp_history = static_cast<void *>(history); 2256184SN/A 2266184SN/A updateGlobalHistTaken(); 2276184SN/A} 2286184SN/A 2296184SN/Avoid 2306184SN/ATournamentBP::update(Addr &branch_addr, bool taken, void *bp_history) 2316184SN/A{ 2326184SN/A unsigned local_history_idx; 2336184SN/A unsigned local_predictor_idx; 2346184SN/A unsigned local_predictor_hist; 2356184SN/A 2366184SN/A // Get the local predictor's current prediction 2376184SN/A local_history_idx = calcLocHistIdx(branch_addr); 2386184SN/A local_predictor_hist = localHistoryTable[local_history_idx]; 2396184SN/A local_predictor_idx = local_predictor_hist & localPredictorMask; 2406184SN/A 2416184SN/A // Update the choice predictor to tell it which one was correct if 2426184SN/A // there was a prediction. 2436184SN/A if (bp_history) { 2446184SN/A BPHistory *history = static_cast<BPHistory *>(bp_history); 2456184SN/A if (history->localPredTaken != history->globalPredTaken) { 2466184SN/A // If the local prediction matches the actual outcome, 2476184SN/A // decerement the counter. Otherwise increment the 2486184SN/A // counter. 2496184SN/A if (history->localPredTaken == taken) { 2508463SMrinmoy.Ghosh@arm.com choiceCtrs[history->globalHistory].decrement(); 2516184SN/A } else if (history->globalPredTaken == taken){ 2528463SMrinmoy.Ghosh@arm.com choiceCtrs[history->globalHistory].increment(); 2536184SN/A } 2548463SMrinmoy.Ghosh@arm.com 2556184SN/A } 2566184SN/A 2578463SMrinmoy.Ghosh@arm.com // Update the counters and local history with the proper 2588463SMrinmoy.Ghosh@arm.com // resolution of the branch. Global history is updated 2598463SMrinmoy.Ghosh@arm.com // speculatively and restored upon squash() calls, so it does not 2608463SMrinmoy.Ghosh@arm.com // need to be updated. 2618463SMrinmoy.Ghosh@arm.com if (taken) { 2628463SMrinmoy.Ghosh@arm.com localCtrs[local_predictor_idx].increment(); 2638463SMrinmoy.Ghosh@arm.com globalCtrs[history->globalHistory].increment(); 2648463SMrinmoy.Ghosh@arm.com 2658463SMrinmoy.Ghosh@arm.com updateLocalHistTaken(local_history_idx); 2668463SMrinmoy.Ghosh@arm.com } else { 2678463SMrinmoy.Ghosh@arm.com localCtrs[local_predictor_idx].decrement(); 2688463SMrinmoy.Ghosh@arm.com globalCtrs[history->globalHistory].decrement(); 2698463SMrinmoy.Ghosh@arm.com 2708463SMrinmoy.Ghosh@arm.com updateLocalHistNotTaken(local_history_idx); 2718463SMrinmoy.Ghosh@arm.com } 2728463SMrinmoy.Ghosh@arm.com 2738463SMrinmoy.Ghosh@arm.com bool mispredict = false; 2748463SMrinmoy.Ghosh@arm.com 2758463SMrinmoy.Ghosh@arm.com //global predictor used and mispredicted 2768463SMrinmoy.Ghosh@arm.com if (history->globalUsed && history->globalPredTaken != taken) 2778463SMrinmoy.Ghosh@arm.com mispredict = true; 2788463SMrinmoy.Ghosh@arm.com //local predictor used and mispredicted 2798463SMrinmoy.Ghosh@arm.com else if (!history->globalUsed && history->localPredTaken != taken) 2808463SMrinmoy.Ghosh@arm.com mispredict = true; 2818463SMrinmoy.Ghosh@arm.com 2828463SMrinmoy.Ghosh@arm.com if (mispredict) { 2838463SMrinmoy.Ghosh@arm.com if (taken) { 2848463SMrinmoy.Ghosh@arm.com globalHistory = globalHistory | 1; 2858463SMrinmoy.Ghosh@arm.com } else { 2868463SMrinmoy.Ghosh@arm.com unsigned mask = globalHistoryMask - 1; 2878463SMrinmoy.Ghosh@arm.com globalHistory = globalHistory & mask; 2888463SMrinmoy.Ghosh@arm.com } 2898463SMrinmoy.Ghosh@arm.com 2908463SMrinmoy.Ghosh@arm.com } 2916184SN/A // We're done with this history, now delete it. 2926184SN/A delete history; 2936184SN/A } 2946184SN/A 2956184SN/A assert(globalHistory < globalPredictorSize && 2966184SN/A local_history_idx < localHistoryTableSize && 2976184SN/A local_predictor_idx < localPredictorSize); 2986184SN/A 2996184SN/A 3006184SN/A} 3016184SN/A 3026184SN/Avoid 3036184SN/ATournamentBP::squash(void *bp_history) 3046184SN/A{ 3056184SN/A BPHistory *history = static_cast<BPHistory *>(bp_history); 3066184SN/A 3076184SN/A // Restore global history to state prior to this branch. 3086184SN/A globalHistory = history->globalHistory; 3096184SN/A 3106184SN/A // Delete this BPHistory now that we're done with it. 3116184SN/A delete history; 3126184SN/A} 3136184SN/A 3146184SN/A#ifdef DEBUG 3156184SN/Aint 3166184SN/ATournamentBP::BPHistory::newCount = 0; 3176184SN/A#endif 318