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Diffstat (limited to 'src/cpu/o3/tournament_pred.hh')
| -rw-r--r-- | src/cpu/o3/tournament_pred.hh | 218 |
1 files changed, 218 insertions, 0 deletions
diff --git a/src/cpu/o3/tournament_pred.hh b/src/cpu/o3/tournament_pred.hh new file mode 100644 index 000000000..92402adc6 --- /dev/null +++ b/src/cpu/o3/tournament_pred.hh @@ -0,0 +1,218 @@ +/* + * 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 + */ + +#ifndef __CPU_O3_TOURNAMENT_PRED_HH__ +#define __CPU_O3_TOURNAMENT_PRED_HH__ + +// For Addr type. +#include "arch/isa_traits.hh" +#include "cpu/o3/sat_counter.hh" +#include <vector> + +/** + * Implements a tournament branch predictor, hopefully identical to the one + * used in the 21264. It has a local predictor, which uses a local history + * table to index into a table of counters, and a global predictor, which + * uses a global history to index into a table of counters. A choice + * predictor chooses between the two. Only the global history register + * is speculatively updated, the rest are updated upon branches committing + * or misspeculating. + */ +class TournamentBP +{ + public: + /** + * Default branch predictor constructor. + */ + TournamentBP(unsigned localPredictorSize, + unsigned localCtrBits, + unsigned localHistoryTableSize, + unsigned localHistoryBits, + unsigned globalPredictorSize, + unsigned globalHistoryBits, + unsigned globalCtrBits, + unsigned choicePredictorSize, + unsigned choiceCtrBits, + unsigned instShiftAmt); + + /** + * Looks up the given address in the branch predictor and returns + * a true/false value as to whether it is taken. Also creates a + * BPHistory object to store any state it will need on squash/update. + * @param branch_addr The address of the branch to look up. + * @param bp_history Pointer that will be set to the BPHistory object. + * @return Whether or not the branch is taken. + */ + bool lookup(Addr &branch_addr, void * &bp_history); + + /** + * Records that there was an unconditional branch, and modifies + * the bp history to point to an object that has the previous + * global history stored in it. + * @param bp_history Pointer that will be set to the BPHistory object. + */ + void uncondBr(void * &bp_history); + + /** + * Updates the branch predictor with the actual result of a branch. + * @param branch_addr The address of the branch to update. + * @param taken Whether or not the branch was taken. + * @param bp_history Pointer to the BPHistory object that was created + * when the branch was predicted. + */ + void update(Addr &branch_addr, bool taken, void *bp_history); + + /** + * Restores the global branch history on a squash. + * @param bp_history Pointer to the BPHistory object that has the + * previous global branch history in it. + */ + void squash(void *bp_history); + + /** Returns the global history. */ + inline unsigned readGlobalHist() { return globalHistory; } + + private: + /** + * Returns if the branch should be taken or not, given a counter + * value. + * @param count The counter value. + */ + inline bool getPrediction(uint8_t &count); + + /** + * Returns the local history index, given a branch address. + * @param branch_addr The branch's PC address. + */ + inline unsigned calcLocHistIdx(Addr &branch_addr); + + /** Updates global history as taken. */ + inline void updateGlobalHistTaken(); + + /** Updates global history as not taken. */ + inline void updateGlobalHistNotTaken(); + + /** + * Updates local histories as taken. + * @param local_history_idx The local history table entry that + * will be updated. + */ + inline void updateLocalHistTaken(unsigned local_history_idx); + + /** + * Updates local histories as not taken. + * @param local_history_idx The local history table entry that + * will be updated. + */ + inline void updateLocalHistNotTaken(unsigned local_history_idx); + + /** + * The branch history information that is created upon predicting + * a branch. It will be passed back upon updating and squashing, + * when the BP can use this information to update/restore its + * state properly. + */ + struct BPHistory { +#ifdef DEBUG + BPHistory() + { newCount++; } + ~BPHistory() + { newCount--; } + + static int newCount; +#endif + unsigned globalHistory; + bool localPredTaken; + bool globalPredTaken; + bool globalUsed; + }; + + /** Local counters. */ + std::vector<SatCounter> localCtrs; + + /** Size of the local predictor. */ + unsigned localPredictorSize; + + /** Number of bits of the local predictor's counters. */ + unsigned localCtrBits; + + /** Array of local history table entries. */ + std::vector<unsigned> localHistoryTable; + + /** Size of the local history table. */ + unsigned localHistoryTableSize; + + /** Number of bits for each entry of the local history table. + * @todo Doesn't this come from the size of the local predictor? + */ + unsigned localHistoryBits; + + /** Mask to get the proper local history. */ + unsigned localHistoryMask; + + /** Array of counters that make up the global predictor. */ + std::vector<SatCounter> globalCtrs; + + /** Size of the global predictor. */ + unsigned globalPredictorSize; + + /** Number of bits of the global predictor's counters. */ + unsigned globalCtrBits; + + /** Global history register. */ + unsigned globalHistory; + + /** Number of bits for the global history. */ + unsigned globalHistoryBits; + + /** Mask to get the proper global history. */ + unsigned globalHistoryMask; + + /** Array of counters that make up the choice predictor. */ + std::vector<SatCounter> choiceCtrs; + + /** Size of the choice predictor (identical to the global predictor). */ + unsigned choicePredictorSize; + + /** Number of bits of the choice predictor's counters. */ + unsigned choiceCtrBits; + + /** Number of bits to shift the instruction over to get rid of the word + * offset. + */ + unsigned instShiftAmt; + + /** Threshold for the counter value; above the threshold is taken, + * equal to or below the threshold is not taken. + */ + unsigned threshold; +}; + +#endif // __CPU_O3_TOURNAMENT_PRED_HH__ |