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