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 *
 * Copyright (c) 2004-2006 The Regents of The University of Michigan
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 * met: redistributions of source code must retain the above copyright
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#ifndef __CPU_PRED_TOURNAMENT_PRED_HH__
#define __CPU_PRED_TOURNAMENT_PRED_HH__

#include <vector>

#include "base/sat_counter.hh"
#include "base/types.hh"
#include "cpu/pred/bpred_unit.hh"
#include "params/TournamentBP.hh"

namespace gem5
{

namespace branch_prediction
{

/**
 * 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.
     * @param inst Static instruction information
     * @param corrTarget Resolved target of the branch (only needed if
     * squashed)
     */
    void update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
                bool squashed, const StaticInstPtr & inst, Addr corrTarget);

    /**
     * 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);

  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;
    /** 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;

    /** Local counters. */
    std::vector<SatCounter8> localCtrs;

    /** 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;

    /** Number of entries in the global predictor. */
    unsigned globalPredictorSize;

    /** Number of bits of the global predictor's counters. */
    unsigned globalCtrBits;

    /** Array of counters that make up the global predictor. */
    std::vector<SatCounter8> globalCtrs;

    /** Global history register. Contains as much history as specified by
     *  globalHistoryBits. Actual number of bits used is determined by
     *  globalHistoryMask and choiceHistoryMask. */
    std::vector<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;

    /** Number of entries in the choice predictor. */
    unsigned choicePredictorSize;

    /** Number of bits in the choice predictor's counters. */
    unsigned choiceCtrBits;

    /** Array of counters that make up the choice predictor. */
    std::vector<SatCounter8> choiceCtrs;

    /** 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;
};

} // namespace branch_prediction
} // namespace gem5

#endif // __CPU_PRED_TOURNAMENT_PRED_HH__