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Diffstat (limited to 'src/cpu/o3/bpred_unit.hh')
| -rw-r--r-- | src/cpu/o3/bpred_unit.hh | 226 |
1 files changed, 226 insertions, 0 deletions
diff --git a/src/cpu/o3/bpred_unit.hh b/src/cpu/o3/bpred_unit.hh new file mode 100644 index 000000000..b7814b2e9 --- /dev/null +++ b/src/cpu/o3/bpred_unit.hh @@ -0,0 +1,226 @@ +/* + * Copyright (c) 2004-2005 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. + */ + +#ifndef __CPU_O3_BPRED_UNIT_HH__ +#define __CPU_O3_BPRED_UNIT_HH__ + +// For Addr type. +#include "arch/isa_traits.hh" +#include "base/statistics.hh" +#include "cpu/inst_seq.hh" + +#include "cpu/o3/2bit_local_pred.hh" +#include "cpu/o3/btb.hh" +#include "cpu/o3/ras.hh" +#include "cpu/o3/tournament_pred.hh" + +#include <list> + +/** + * Basically a wrapper class to hold both the branch predictor + * and the BTB. + */ +template<class Impl> +class TwobitBPredUnit +{ + public: + typedef typename Impl::Params Params; + typedef typename Impl::DynInstPtr DynInstPtr; + + /** + * @param params The params object, that has the size of the BP and BTB. + */ + TwobitBPredUnit(Params *params); + + /** + * Registers statistics. + */ + void regStats(); + + void switchOut(); + + void takeOverFrom(); + + /** + * Predicts whether or not the instruction is a taken branch, and the + * target of the branch if it is taken. + * @param inst The branch instruction. + * @param PC The predicted PC is passed back through this parameter. + * @param tid The thread id. + * @return Returns if the branch is taken or not. + */ + bool predict(DynInstPtr &inst, Addr &PC, unsigned tid); + + /** + * Tells the branch predictor to commit any updates until the given + * sequence number. + * @param done_sn The sequence number to commit any older updates up until. + * @param tid The thread id. + */ + void update(const InstSeqNum &done_sn, unsigned tid); + + /** + * Squashes all outstanding updates until a given sequence number. + * @param squashed_sn The sequence number to squash any younger updates up + * until. + * @param tid The thread id. + */ + void squash(const InstSeqNum &squashed_sn, unsigned tid); + + /** + * Squashes all outstanding updates until a given sequence number, and + * corrects that sn's update with the proper address and taken/not taken. + * @param squashed_sn The sequence number to squash any younger updates up + * until. + * @param corr_target The correct branch target. + * @param actually_taken The correct branch direction. + * @param tid The thread id. + */ + void squash(const InstSeqNum &squashed_sn, const Addr &corr_target, + bool actually_taken, unsigned tid); + + /** + * Looks up a given PC in the BP to see if it is taken or not taken. + * @param inst_PC The PC to look up. + * @return Whether the branch is taken or not taken. + */ + bool BPLookup(Addr &inst_PC) + { return BP.lookup(inst_PC); } + + /** + * Looks up a given PC in the BTB to see if a matching entry exists. + * @param inst_PC The PC to look up. + * @return Whether the BTB contains the given PC. + */ + bool BTBValid(Addr &inst_PC) + { return BTB.valid(inst_PC, 0); } + + /** + * Looks up a given PC in the BTB to get the predicted target. + * @param inst_PC The PC to look up. + * @return The address of the target of the branch. + */ + Addr BTBLookup(Addr &inst_PC) + { return BTB.lookup(inst_PC, 0); } + + /** + * Updates the BP with taken/not taken information. + * @param inst_PC The branch's PC that will be updated. + * @param taken Whether the branch was taken or not taken. + * @todo Make this update flexible enough to handle a global predictor. + */ + void BPUpdate(Addr &inst_PC, bool taken) + { BP.update(inst_PC, taken); } + + /** + * Updates the BTB with the target of a branch. + * @param inst_PC The branch's PC that will be updated. + * @param target_PC The branch's target that will be added to the BTB. + */ + void BTBUpdate(Addr &inst_PC, Addr &target_PC) + { BTB.update(inst_PC, target_PC,0); } + + private: + struct PredictorHistory { + /** + * Makes a predictor history struct that contains a sequence number, + * the PC of its instruction, and whether or not it was predicted + * taken. + */ + PredictorHistory(const InstSeqNum &seq_num, const Addr &inst_PC, + const bool pred_taken, const unsigned _tid) + : seqNum(seq_num), PC(inst_PC), RASTarget(0), globalHistory(0), + RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0), + wasCall(0) + { } + + /** The sequence number for the predictor history entry. */ + InstSeqNum seqNum; + + /** The PC associated with the sequence number. */ + Addr PC; + + /** The RAS target (only valid if a return). */ + Addr RASTarget; + + /** The global history at the time this entry was created. */ + unsigned globalHistory; + + /** The RAS index of the instruction (only valid if a call). */ + unsigned RASIndex; + + /** The thread id. */ + unsigned tid; + + /** Whether or not it was predicted taken. */ + bool predTaken; + + /** Whether or not the RAS was used. */ + bool usedRAS; + + /** Whether or not the instruction was a call. */ + bool wasCall; + }; + + typedef std::list<PredictorHistory> History; + + /** + * The per-thread predictor history. This is used to update the predictor + * as instructions are committed, or restore it to the proper state after + * a squash. + */ + History predHist[Impl::MaxThreads]; + + /** The branch predictor. */ + DefaultBP BP; + + /** The BTB. */ + DefaultBTB BTB; + + /** The per-thread return address stack. */ + ReturnAddrStack RAS[Impl::MaxThreads]; + + /** Stat for number of BP lookups. */ + Stats::Scalar<> lookups; + /** Stat for number of conditional branches predicted. */ + Stats::Scalar<> condPredicted; + /** Stat for number of conditional branches predicted incorrectly. */ + Stats::Scalar<> condIncorrect; + /** Stat for number of BTB lookups. */ + Stats::Scalar<> BTBLookups; + /** Stat for number of BTB hits. */ + Stats::Scalar<> BTBHits; + /** Stat for number of times the BTB is correct. */ + Stats::Scalar<> BTBCorrect; + /** Stat for number of times the RAS is used to get a target. */ + Stats::Scalar<> usedRAS; + /** Stat for number of times the RAS is incorrect. */ + Stats::Scalar<> RASIncorrect; +}; + +#endif // __CPU_O3_BPRED_UNIT_HH__ |