| /* |
| * 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; |
| } |