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Diffstat (limited to 'src/cpu/tournament_pred.cc')
| -rw-r--r-- | src/cpu/tournament_pred.cc | 297 |
1 files changed, 297 insertions, 0 deletions
diff --git a/src/cpu/tournament_pred.cc b/src/cpu/tournament_pred.cc new file mode 100644 index 000000000..ffb941c77 --- /dev/null +++ b/src/cpu/tournament_pred.cc @@ -0,0 +1,297 @@ +/* + * Copyright (c) 2004-2006 The Regents of The University of Michigan + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer; + * redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution; + * neither the name of the copyright holders nor the names of its + * contributors may be used to endorse or promote products derived from + * this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + * + * Authors: Kevin Lim + */ + +#include "base/intmath.hh" +#include "cpu/o3/tournament_pred.hh" + +TournamentBP::TournamentBP(unsigned _localPredictorSize, + unsigned _localCtrBits, + unsigned _localHistoryTableSize, + unsigned _localHistoryBits, + unsigned _globalPredictorSize, + unsigned _globalCtrBits, + unsigned _globalHistoryBits, + unsigned _choicePredictorSize, + unsigned _choiceCtrBits, + unsigned _instShiftAmt) + : localPredictorSize(_localPredictorSize), + localCtrBits(_localCtrBits), + localHistoryTableSize(_localHistoryTableSize), + localHistoryBits(_localHistoryBits), + globalPredictorSize(_globalPredictorSize), + globalCtrBits(_globalCtrBits), + globalHistoryBits(_globalHistoryBits), + choicePredictorSize(_globalPredictorSize), + choiceCtrBits(_choiceCtrBits), + instShiftAmt(_instShiftAmt) +{ + if (!isPowerOf2(localPredictorSize)) { + fatal("Invalid local predictor size!\n"); + } + + //Setup the array of counters for the local predictor + localCtrs.resize(localPredictorSize); + + for (int i = 0; i < localPredictorSize; ++i) + localCtrs[i].setBits(localCtrBits); + + localPredictorMask = floorPow2(localPredictorSize) - 1; + + if (!isPowerOf2(localHistoryTableSize)) { + fatal("Invalid local history table size!\n"); + } + + //Setup the history table for the local table + localHistoryTable.resize(localHistoryTableSize); + + for (int i = 0; i < localHistoryTableSize; ++i) + localHistoryTable[i] = 0; + + // Setup the local history mask + localHistoryMask = (1 << localHistoryBits) - 1; + + if (!isPowerOf2(globalPredictorSize)) { + fatal("Invalid global predictor size!\n"); + } + + //Setup the array of counters for the global predictor + globalCtrs.resize(globalPredictorSize); + + for (int i = 0; i < globalPredictorSize; ++i) + globalCtrs[i].setBits(globalCtrBits); + + //Clear the global history + globalHistory = 0; + // Setup the global history mask + globalHistoryMask = (1 << globalHistoryBits) - 1; + + if (!isPowerOf2(choicePredictorSize)) { + fatal("Invalid choice predictor size!\n"); + } + + //Setup the array of counters for the choice predictor + choiceCtrs.resize(choicePredictorSize); + + for (int i = 0; i < choicePredictorSize; ++i) + choiceCtrs[i].setBits(choiceCtrBits); + + // @todo: Allow for different thresholds between the predictors. + threshold = (1 << (localCtrBits - 1)) - 1; + threshold = threshold / 2; +} + +inline +unsigned +TournamentBP::calcLocHistIdx(Addr &branch_addr) +{ + // Get low order bits after removing instruction offset. + return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1); +} + +inline +void +TournamentBP::updateGlobalHistTaken() +{ + globalHistory = (globalHistory << 1) | 1; + globalHistory = globalHistory & globalHistoryMask; +} + +inline +void +TournamentBP::updateGlobalHistNotTaken() +{ + globalHistory = (globalHistory << 1); + globalHistory = globalHistory & globalHistoryMask; +} + +inline +void +TournamentBP::updateLocalHistTaken(unsigned local_history_idx) +{ + localHistoryTable[local_history_idx] = + (localHistoryTable[local_history_idx] << 1) | 1; +} + +inline +void +TournamentBP::updateLocalHistNotTaken(unsigned local_history_idx) +{ + localHistoryTable[local_history_idx] = + (localHistoryTable[local_history_idx] << 1); +} + +bool +TournamentBP::lookup(Addr &branch_addr, void * &bp_history) +{ + bool local_prediction; + unsigned local_history_idx; + unsigned local_predictor_idx; + + bool global_prediction; + bool choice_prediction; + + //Lookup in the local predictor to get its branch prediction + local_history_idx = calcLocHistIdx(branch_addr); + local_predictor_idx = localHistoryTable[local_history_idx] + & localPredictorMask; + local_prediction = localCtrs[local_predictor_idx].read() > threshold; + + //Lookup in the global predictor to get its branch prediction + global_prediction = globalCtrs[globalHistory].read() > threshold; + + //Lookup in the choice predictor to see which one to use + choice_prediction = choiceCtrs[globalHistory].read() > threshold; + + // Create BPHistory and pass it back to be recorded. + BPHistory *history = new BPHistory; + history->globalHistory = globalHistory; + history->localPredTaken = local_prediction; + history->globalPredTaken = global_prediction; + history->globalUsed = choice_prediction; + bp_history = (void *)history; + + assert(globalHistory < globalPredictorSize && + local_history_idx < localHistoryTableSize && + local_predictor_idx < localPredictorSize); + + // Commented code is for doing speculative update of counters and + // all histories. + if (choice_prediction) { + if (global_prediction) { +// updateHistoriesTaken(local_history_idx); +// globalCtrs[globalHistory].increment(); +// localCtrs[local_history_idx].increment(); + updateGlobalHistTaken(); + return true; + } else { +// updateHistoriesNotTaken(local_history_idx); +// globalCtrs[globalHistory].decrement(); +// localCtrs[local_history_idx].decrement(); + updateGlobalHistNotTaken(); + return false; + } + } else { + if (local_prediction) { +// updateHistoriesTaken(local_history_idx); +// globalCtrs[globalHistory].increment(); +// localCtrs[local_history_idx].increment(); + updateGlobalHistTaken(); + return true; + } else { +// updateHistoriesNotTaken(local_history_idx); +// globalCtrs[globalHistory].decrement(); +// localCtrs[local_history_idx].decrement(); + updateGlobalHistNotTaken(); + return false; + } + } +} + +void +TournamentBP::uncondBr(void * &bp_history) +{ + // Create BPHistory and pass it back to be recorded. + BPHistory *history = new BPHistory; + history->globalHistory = globalHistory; + history->localPredTaken = true; + history->globalPredTaken = true; + bp_history = static_cast<void *>(history); + + updateGlobalHistTaken(); +} + +void +TournamentBP::update(Addr &branch_addr, bool taken, void *bp_history) +{ + unsigned local_history_idx; + unsigned local_predictor_idx; + unsigned local_predictor_hist; + + // Get the local predictor's current prediction + local_history_idx = calcLocHistIdx(branch_addr); + local_predictor_hist = localHistoryTable[local_history_idx]; + local_predictor_idx = local_predictor_hist & localPredictorMask; + + // Update the choice predictor to tell it which one was correct if + // there was a prediction. + if (bp_history) { + BPHistory *history = static_cast<BPHistory *>(bp_history); + if (history->localPredTaken != history->globalPredTaken) { + // If the local prediction matches the actual outcome, + // decerement the counter. Otherwise increment the + // counter. + if (history->localPredTaken == taken) { + choiceCtrs[globalHistory].decrement(); + } else if (history->globalPredTaken == taken){ + choiceCtrs[globalHistory].increment(); + } + } + + // We're done with this history, now delete it. + delete history; + } + + assert(globalHistory < globalPredictorSize && + local_history_idx < localHistoryTableSize && + local_predictor_idx < localPredictorSize); + + // Update the counters and local history with the proper + // resolution of the branch. Global history is updated + // speculatively and restored upon squash() calls, so it does not + // need to be updated. + if (taken) { + localCtrs[local_predictor_idx].increment(); + globalCtrs[globalHistory].increment(); + + updateLocalHistTaken(local_history_idx); + } else { + localCtrs[local_predictor_idx].decrement(); + globalCtrs[globalHistory].decrement(); + + updateLocalHistNotTaken(local_history_idx); + } +} + +void +TournamentBP::squash(void *bp_history) +{ + BPHistory *history = static_cast<BPHistory *>(bp_history); + + // Restore global history to state prior to this branch. + globalHistory = history->globalHistory; + + // Delete this BPHistory now that we're done with it. + delete history; +} + +#ifdef DEBUG +int +TournamentBP::BPHistory::newCount = 0; +#endif |