src/cpu/o3/tournament_pred.hh - arm/gem5 - Git at Google

 /*
  * 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
  */

 #ifndef __CPU_O3_TOURNAMENT_PRED_HH__
 #define __CPU_O3_TOURNAMENT_PRED_HH__

 #include "cpu/o3/sat_counter.hh"
 #include "sim/host.hh"
 #include <vector>

 /**
  * 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.  Only the global history register
  * is speculatively updated, the rest are updated upon branches committing
  * or misspeculating.
  */
 class TournamentBP
 {
   public:
     /**
      * Default branch predictor constructor.
      */
     TournamentBP(unsigned localPredictorSize,
                  unsigned localCtrBits,
                  unsigned localHistoryTableSize,
                  unsigned localHistoryBits,
                  unsigned globalPredictorSize,
                  unsigned globalHistoryBits,
                  unsigned globalCtrBits,
                  unsigned choicePredictorSize,
                  unsigned choiceCtrBits,
                  unsigned instShiftAmt);

     /**
      * 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(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 uncondBr(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.
      */
     void update(Addr &branch_addr, bool taken, void *bp_history);

     /**
      * 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(void *bp_history);

     /** Returns the global history. */
     inline unsigned readGlobalHist() { return globalHistory; }

   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();

     /** Updates global history as not taken. */
     inline void updateGlobalHistNotTaken();

     /**
      * 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;
         bool localPredTaken;
         bool globalPredTaken;
         bool globalUsed;
     };

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

     /** Size of the local predictor. */
     unsigned localPredictorSize;

     /** Mask to get the proper index bits into the predictor. */
     unsigned localPredictorMask;

     /** Number of bits of the local predictor's counters. */
     unsigned localCtrBits;

     /** Array of local history table entries. */
     std::vector<unsigned> localHistoryTable;

     /** Size of the local history table. */
     unsigned localHistoryTableSize;

     /** Number of bits for each entry of the local history table.
      *  @todo Doesn't this come from the size of the local predictor?
      */
     unsigned localHistoryBits;

     /** Mask to get the proper local history. */
     unsigned localHistoryMask;

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

     /** Size of the global predictor. */
     unsigned globalPredictorSize;

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

     /** Global history register. */
     unsigned globalHistory;

     /** Number of bits for the global history. */
     unsigned globalHistoryBits;

     /** Mask to get the proper global history. */
     unsigned globalHistoryMask;

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

     /** Size of the choice predictor (identical to the global predictor). */
     unsigned choicePredictorSize;

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

     /** Number of bits to shift the instruction over to get rid of the word
      *  offset.
      */
     unsigned instShiftAmt;

     /** Threshold for the counter value; above the threshold is taken,
      *  equal to or below the threshold is not taken.
      */
     unsigned threshold;
 };

 #endif // __CPU_O3_TOURNAMENT_PRED_HH__
	/*
	* 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
	*/

	#ifndef __CPU_O3_TOURNAMENT_PRED_HH__
	#define __CPU_O3_TOURNAMENT_PRED_HH__

	#include "cpu/o3/sat_counter.hh"
	#include "sim/host.hh"
	#include <vector>

	/**
	* 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. Only the global history register
	* is speculatively updated, the rest are updated upon branches committing
	* or misspeculating.
	*/
	class TournamentBP
	{
	public:
	/**
	* Default branch predictor constructor.
	*/
	TournamentBP(unsigned localPredictorSize,
	unsigned localCtrBits,
	unsigned localHistoryTableSize,
	unsigned localHistoryBits,
	unsigned globalPredictorSize,
	unsigned globalHistoryBits,
	unsigned globalCtrBits,
	unsigned choicePredictorSize,
	unsigned choiceCtrBits,
	unsigned instShiftAmt);

	/**
	* 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(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 uncondBr(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.
	*/
	void update(Addr &branch_addr, bool taken, void *bp_history);

	/**
	* 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(void *bp_history);

	/** Returns the global history. */
	inline unsigned readGlobalHist() { return globalHistory; }

	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();

	/** Updates global history as not taken. */
	inline void updateGlobalHistNotTaken();

	/**
	* 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;
	bool localPredTaken;
	bool globalPredTaken;
	bool globalUsed;
	};

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

	/** Size of the local predictor. */
	unsigned localPredictorSize;

	/** Mask to get the proper index bits into the predictor. */
	unsigned localPredictorMask;

	/** Number of bits of the local predictor's counters. */
	unsigned localCtrBits;

	/** Array of local history table entries. */
	std::vector<unsigned> localHistoryTable;

	/** Size of the local history table. */
	unsigned localHistoryTableSize;

	/** Number of bits for each entry of the local history table.
	* @todo Doesn't this come from the size of the local predictor?
	*/
	unsigned localHistoryBits;

	/** Mask to get the proper local history. */
	unsigned localHistoryMask;

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

	/** Size of the global predictor. */
	unsigned globalPredictorSize;

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

	/** Global history register. */
	unsigned globalHistory;

	/** Number of bits for the global history. */
	unsigned globalHistoryBits;

	/** Mask to get the proper global history. */
	unsigned globalHistoryMask;

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

	/** Size of the choice predictor (identical to the global predictor). */
	unsigned choicePredictorSize;

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

	/** Number of bits to shift the instruction over to get rid of the word
	* offset.
	*/
	unsigned instShiftAmt;

	/** Threshold for the counter value; above the threshold is taken,
	* equal to or below the threshold is not taken.
	*/
	unsigned threshold;
	};

	#endif // __CPU_O3_TOURNAMENT_PRED_HH__