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/*
* Copyright (c) 2011, 2014 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* 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
* Timothy M. Jones
* Nilay Vaish
*/
#ifndef __CPU_PRED_TOURNAMENT_PRED_HH__
#define __CPU_PRED_TOURNAMENT_PRED_HH__
#include <vector>
#include "base/types.hh"
#include "cpu/pred/bpred_unit.hh"
#include "cpu/pred/sat_counter.hh"
/**
* 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 BPredUnit
{
public:
/**
* Default branch predictor constructor.
*/
TournamentBP(const Params *params);
/**
* 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 uncondBranch(void * &bp_history);
/**
* Updates the branch predictor to Not Taken if a BTB entry is
* invalid or not found.
* @param branch_addr The address of the branch to look up.
* @param bp_history Pointer to any bp history state.
* @return Whether or not the branch is taken.
*/
void btbUpdate(Addr branch_addr, 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.
* @param squashed is set when this function is called during a squash
* operation.
*/
void update(Addr branch_addr, bool taken, void *bp_history, bool squashed);
void retireSquashed(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;
unsigned localHistory;
bool localPredTaken;
bool globalPredTaken;
bool globalUsed;
};
/** Flag for invalid predictor index */
static const int invalidPredictorIndex = -1;
/** Local counters. */
std::vector<SatCounter> localCtrs;
/** Number of counters in the local predictor. */
unsigned localPredictorSize;
/** Mask to truncate values stored in the local history table. */
unsigned localPredictorMask;
/** Number of bits of the local predictor's counters. */
unsigned localCtrBits;
/** Array of local history table entries. */
std::vector<unsigned> localHistoryTable;
/** Number of entries in the local history table. */
unsigned localHistoryTableSize;
/** Number of bits for each entry of the local history table. */
unsigned localHistoryBits;
/** Array of counters that make up the global predictor. */
std::vector<SatCounter> globalCtrs;
/** Number of entries in the global predictor. */
unsigned globalPredictorSize;
/** Number of bits of the global predictor's counters. */
unsigned globalCtrBits;
/** Global history register. Contains as much history as specified by
* globalHistoryBits. Actual number of bits used is determined by
* globalHistoryMask and choiceHistoryMask. */
unsigned globalHistory;
/** Number of bits for the global history. Determines maximum number of
entries in global and choice predictor tables. */
unsigned globalHistoryBits;
/** Mask to apply to globalHistory to access global history table.
* Based on globalPredictorSize.*/
unsigned globalHistoryMask;
/** Mask to apply to globalHistory to access choice history table.
* Based on choicePredictorSize.*/
unsigned choiceHistoryMask;
/** Mask to control how much history is stored. All of it might not be
* used. */
unsigned historyRegisterMask;
/** Array of counters that make up the choice predictor. */
std::vector<SatCounter> choiceCtrs;
/** Number of entries in the choice predictor. */
unsigned choicePredictorSize;
/** Number of bits in the choice predictor's counters. */
unsigned choiceCtrBits;
/** Number of bits to shift the instruction over to get rid of the word
* offset.
*/
unsigned instShiftAmt;
/** Thresholds for the counter value; above the threshold is taken,
* equal to or below the threshold is not taken.
*/
unsigned localThreshold;
unsigned globalThreshold;
unsigned choiceThreshold;
};
#endif // __CPU_PRED_TOURNAMENT_PRED_HH__
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