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Diffstat (limited to 'src/cpu/pred/bi_mode.hh')
| -rw-r--r-- | src/cpu/pred/bi_mode.hh | 114 |
1 files changed, 114 insertions, 0 deletions
diff --git a/src/cpu/pred/bi_mode.hh b/src/cpu/pred/bi_mode.hh new file mode 100644 index 000000000..a412d63cf --- /dev/null +++ b/src/cpu/pred/bi_mode.hh @@ -0,0 +1,114 @@ +/* + * 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__ |