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-rw-r--r--cpu/o3/tournament_pred.cc255
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diff --git a/cpu/o3/tournament_pred.cc b/cpu/o3/tournament_pred.cc
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--- a/cpu/o3/tournament_pred.cc
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-/*
- * Copyright (c) 2004-2005 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.
- */
-
-#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)
-{
- //Should do checks here to make sure sizes are correct (powers of 2)
-
- //Setup the array of counters for the local predictor
- localCtrs.resize(localPredictorSize);
-
- for (int i = 0; i < localPredictorSize; ++i)
- localCtrs[i].setBits(localCtrBits);
-
- //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;
-
- //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;
-
- //Setup the array of counters for the choice predictor
- choiceCtrs.resize(choicePredictorSize);
-
- for (int i = 0; i < choicePredictorSize; ++i)
- choiceCtrs[i].setBits(choiceCtrBits);
-
- threshold = (1 << (localCtrBits - 1)) - 1;
- threshold = threshold / 2;
-}
-
-inline
-unsigned
-TournamentBP::calcLocHistIdx(Addr &branch_addr)
-{
- return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
-}
-
-inline
-void
-TournamentBP::updateHistoriesTaken(unsigned local_history_idx)
-{
- globalHistory = (globalHistory << 1) | 1;
- globalHistory = globalHistory & globalHistoryMask;
-
- localHistoryTable[local_history_idx] =
- (localHistoryTable[local_history_idx] << 1) | 1;
-}
-
-inline
-void
-TournamentBP::updateHistoriesNotTaken(unsigned local_history_idx)
-{
- globalHistory = (globalHistory << 1);
- globalHistory = globalHistory & globalHistoryMask;
-
- localHistoryTable[local_history_idx] =
- (localHistoryTable[local_history_idx] << 1);
-}
-
-bool
-TournamentBP::lookup(Addr &branch_addr)
-{
- uint8_t local_prediction;
- unsigned local_history_idx;
- unsigned local_predictor_idx;
-
- uint8_t global_prediction;
- uint8_t 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]
- & localHistoryMask;
- local_prediction = localCtrs[local_predictor_idx].read();
-
- //Lookup in the global predictor to get its branch prediction
- global_prediction = globalCtrs[globalHistory].read();
-
- //Lookup in the choice predictor to see which one to use
- choice_prediction = choiceCtrs[globalHistory].read();
-
- //@todo Put a threshold value in for the three predictors that can
- // be set through the constructor (so this isn't hard coded).
- //Also should put some of this code into functions.
- if (choice_prediction > threshold) {
- if (global_prediction > threshold) {
- updateHistoriesTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].increment();
- localCtrs[local_history_idx].increment();
-
- return true;
- } else {
- updateHistoriesNotTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].decrement();
- localCtrs[local_history_idx].decrement();
-
- return false;
- }
- } else {
- if (local_prediction > threshold) {
- updateHistoriesTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].increment();
- localCtrs[local_history_idx].increment();
-
- return true;
- } else {
- updateHistoriesNotTaken(local_history_idx);
-
- assert(globalHistory < globalPredictorSize &&
- local_history_idx < localPredictorSize);
-
- globalCtrs[globalHistory].decrement();
- localCtrs[local_history_idx].decrement();
-
- return false;
- }
- }
-}
-
-// Update the branch predictor if it predicted a branch wrong.
-void
-TournamentBP::update(Addr &branch_addr, unsigned correct_gh, bool taken)
-{
-
- uint8_t local_prediction;
- unsigned local_history_idx;
- unsigned local_predictor_idx;
- bool local_pred_taken;
-
- uint8_t global_prediction;
- bool global_pred_taken;
-
- // Load the correct global history into the register.
- globalHistory = correct_gh;
-
- // Get the local predictor's current prediction, remove the incorrect
- // update, and update the local predictor
- local_history_idx = calcLocHistIdx(branch_addr);
- local_predictor_idx = localHistoryTable[local_history_idx];
- local_predictor_idx = (local_predictor_idx >> 1) & localHistoryMask;
-
- local_prediction = localCtrs[local_predictor_idx].read();
- local_pred_taken = local_prediction > threshold;
-
- //Get the global predictor's current prediction, and update the
- //global predictor
- global_prediction = globalCtrs[globalHistory].read();
- global_pred_taken = global_prediction > threshold;
-
- //Update the choice predictor to tell it which one was correct
- if (local_pred_taken != global_pred_taken) {
- //If the local prediction matches the actual outcome, decerement
- //the counter. Otherwise increment the counter.
- if (local_pred_taken == taken) {
- choiceCtrs[globalHistory].decrement();
- } else {
- choiceCtrs[globalHistory].increment();
- }
- }
-
- if (taken) {
- assert(globalHistory < globalPredictorSize &&
- local_predictor_idx < localPredictorSize);
-
- localCtrs[local_predictor_idx].increment();
- globalCtrs[globalHistory].increment();
-
- globalHistory = (globalHistory << 1) | 1;
- globalHistory = globalHistory & globalHistoryMask;
-
- localHistoryTable[local_history_idx] |= 1;
- } else {
- assert(globalHistory < globalPredictorSize &&
- local_predictor_idx < localPredictorSize);
-
- localCtrs[local_predictor_idx].decrement();
- globalCtrs[globalHistory].decrement();
-
- globalHistory = (globalHistory << 1);
- globalHistory = globalHistory & globalHistoryMask;
-
- localHistoryTable[local_history_idx] &= ~1;
- }
-}
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