/* * 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 #include "base/types.hh" #include "cpu/pred/bpred_unit.hh" #include "cpu/pred/sat_counter.hh" #include "params/TournamentBP.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. Both the global history register * and the selected local history are speculatively updated. */ class TournamentBP : public BPredUnit { public: /** * Default branch predictor constructor. */ TournamentBP(const TournamentBPParams *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(ThreadID tid, 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(ThreadID tid, Addr pc, 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(ThreadID tid, 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(ThreadID tid, Addr branch_addr, bool taken, void *bp_history, bool squashed); /** * 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(ThreadID tid, void *bp_history); unsigned getGHR(ThreadID tid, void *bp_history) const; 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(ThreadID tid); /** Updates global history as not taken. */ inline void updateGlobalHistNotTaken(ThreadID tid); /** * 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 localHistoryIdx; unsigned localHistory; bool localPredTaken; bool globalPredTaken; bool globalUsed; }; /** Flag for invalid predictor index */ static const int invalidPredictorIndex = -1; /** Local counters. */ std::vector 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 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 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. */ std::vector 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 choiceCtrs; /** Number of entries in the choice predictor. */ unsigned choicePredictorSize; /** Number of bits in the choice predictor's counters. */ unsigned choiceCtrBits; /** 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__