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Diffstat (limited to 'src/cpu/o3/2bit_local_pred.cc')
| -rw-r--r-- | src/cpu/o3/2bit_local_pred.cc | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/src/cpu/o3/2bit_local_pred.cc b/src/cpu/o3/2bit_local_pred.cc new file mode 100644 index 000000000..d9744eec7 --- /dev/null +++ b/src/cpu/o3/2bit_local_pred.cc @@ -0,0 +1,129 @@ +/* + * 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; +} |