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/*
* Copyright (c) 2014 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: Anthony Gutierrez
*/
/* @file
* Implementation of a bi-mode branch predictor
*/
#ifndef __CPU_PRED_BI_MODE_PRED_HH__
#define __CPU_PRED_BI_MODE_PRED_HH__
#include "cpu/pred/bpred_unit.hh"
#include "cpu/pred/sat_counter.hh"
/**
* Implements a bi-mode branch predictor. The bi-mode predictor is a two-level
* branch predictor that has three seprate history arrays: a taken array, a
* not-taken array, and a choice array. The taken/not-taken arrays are indexed
* by a hash of the PC and the global history. The choice array is indexed by
* the PC only. Because the taken/not-taken arrays use the same index, they must
* be the same size.
*
* The bi-mode branch predictor aims to eliminate the destructive aliasing that
* occurs when two branches of opposite biases share the same global history
* pattern. By separating the predictors into taken/not-taken arrays, and using
* the branch's PC to choose between the two, destructive aliasing is reduced.
*/
class BiModeBP : public BPredUnit
{
public:
BiModeBP(const Params *params);
void uncondBranch(void * &bp_history);
void squash(void *bp_history);
bool lookup(Addr branch_addr, void * &bp_history);
void btbUpdate(Addr branch_addr, void * &bp_history);
void update(Addr branch_addr, bool taken, void *bp_history, bool squashed);
void retireSquashed(void *bp_history);
private:
void updateGlobalHistReg(bool taken);
struct BPHistory {
unsigned globalHistoryReg;
// was the taken array's prediction used?
// true: takenPred used
// false: notPred used
bool takenUsed;
// prediction of the taken array
// true: predict taken
// false: predict not-taken
bool takenPred;
// prediction of the not-taken array
// true: predict taken
// false: predict not-taken
bool notTakenPred;
// the final taken/not-taken prediction
// true: predict taken
// false: predict not-taken
bool finalPred;
};
// choice predictors
std::vector<SatCounter> choiceCounters;
// taken direction predictors
std::vector<SatCounter> takenCounters;
// not-taken direction predictors
std::vector<SatCounter> notTakenCounters;
unsigned instShiftAmt;
unsigned globalHistoryReg;
unsigned globalHistoryBits;
unsigned historyRegisterMask;
unsigned choicePredictorSize;
unsigned choiceCtrBits;
unsigned choiceHistoryMask;
unsigned globalPredictorSize;
unsigned globalCtrBits;
unsigned globalHistoryMask;
unsigned choiceThreshold;
unsigned takenThreshold;
unsigned notTakenThreshold;
};
#endif // __CPU_PRED_BI_MODE_PRED_HH__
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