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/*
* 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_2BIT_LOCAL_PRED_HH__
#define __CPU_O3_2BIT_LOCAL_PRED_HH__
// For Addr type.
#include "arch/isa_traits.hh"
#include "cpu/o3/sat_counter.hh"
#include <vector>
/**
* Implements a local predictor that uses the PC to index into a table of
* counters. Note that any time a pointer to the bp_history is given, it
* should be NULL using this predictor because it does not have any branch
* predictor state that needs to be recorded or updated; the update can be
* determined solely by the branch being taken or not taken.
*/
class LocalBP
{
public:
/**
* Default branch predictor constructor.
* @param localPredictorSize Size of the local predictor.
* @param localCtrBits Number of bits per counter.
* @param instShiftAmt Offset amount for instructions to ignore alignment.
*/
LocalBP(unsigned localPredictorSize, unsigned localCtrBits,
unsigned instShiftAmt);
/**
* Looks up the given address in the branch predictor and returns
* a true/false value as to whether it is taken.
* @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.
*/
bool lookup(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.
*/
void update(Addr &branch_addr, bool taken, void *bp_history);
void squash(void *bp_history)
{ assert(bp_history == NULL); }
void reset();
private:
/**
* Returns the taken/not taken prediction given the value of the
* counter.
* @param count The value of the counter.
* @return The prediction based on the counter value.
*/
inline bool getPrediction(uint8_t &count);
/** Calculates the local index based on the PC. */
inline unsigned getLocalIndex(Addr &PC);
/** Array of counters that make up the local predictor. */
std::vector<SatCounter> localCtrs;
/** Size of the local predictor. */
unsigned localPredictorSize;
/** Number of sets. */
unsigned localPredictorSets;
/** Number of bits of the local predictor's counters. */
unsigned localCtrBits;
/** Number of bits to shift the PC when calculating index. */
unsigned instShiftAmt;
/** Mask to get index bits. */
unsigned indexMask;
};
#endif // __CPU_O3_2BIT_LOCAL_PRED_HH__
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