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/*
* 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.
*/
#include "base/trace.hh"
#include "cpu/o3/2bit_local_pred.hh"
DefaultBP::DefaultBP(unsigned _localPredictorSize,
unsigned _localCtrBits,
unsigned _instShiftAmt)
: localPredictorSize(_localPredictorSize),
localCtrBits(_localCtrBits),
instShiftAmt(_instShiftAmt)
{
// Should do checks here to make sure sizes are correct (powers of 2).
// Setup the index mask.
indexMask = localPredictorSize - 1;
DPRINTF(Fetch, "Branch predictor: index mask: %#x\n", indexMask);
// Setup the array of counters for the local predictor.
localCtrs = new SatCounter[localPredictorSize];
for (int i = 0; i < localPredictorSize; ++i)
localCtrs[i].setBits(_localCtrBits);
DPRINTF(Fetch, "Branch predictor: local predictor size: %i\n",
localPredictorSize);
DPRINTF(Fetch, "Branch predictor: local counter bits: %i\n", localCtrBits);
DPRINTF(Fetch, "Branch predictor: instruction shift amount: %i\n",
instShiftAmt);
}
bool
DefaultBP::lookup(Addr &branch_addr)
{
bool taken;
uint8_t local_prediction;
unsigned local_predictor_idx = getLocalIndex(branch_addr);
DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n",
local_predictor_idx);
assert(local_predictor_idx < localPredictorSize);
local_prediction = localCtrs[local_predictor_idx].read();
DPRINTF(Fetch, "Branch predictor: prediction is %i.\n",
(int)local_prediction);
taken = getPrediction(local_prediction);
#if 0
// Speculative update.
if (taken) {
DPRINTF(Fetch, "Branch predictor: Branch updated as taken.\n");
localCtrs[local_predictor_idx].increment();
} else {
DPRINTF(Fetch, "Branch predictor: Branch updated as not taken.\n");
localCtrs[local_predictor_idx].decrement();
}
#endif
return taken;
}
void
DefaultBP::update(Addr &branch_addr, bool taken)
{
unsigned local_predictor_idx;
// Update the local predictor.
local_predictor_idx = getLocalIndex(branch_addr);
DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n",
local_predictor_idx);
assert(local_predictor_idx < localPredictorSize);
if (taken) {
DPRINTF(Fetch, "Branch predictor: Branch updated as taken.\n");
localCtrs[local_predictor_idx].increment();
} else {
DPRINTF(Fetch, "Branch predictor: Branch updated as not taken.\n");
localCtrs[local_predictor_idx].decrement();
}
}
inline
bool
DefaultBP::getPrediction(uint8_t &count)
{
// Get the MSB of the count
return (count >> (localCtrBits - 1));
}
inline
unsigned
DefaultBP::getLocalIndex(Addr &branch_addr)
{
return (branch_addr >> instShiftAmt) & indexMask;
}
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