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/*
* 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__
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