| /* |
| * 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 |
| */ |
| |
| #include "base/intmath.hh" |
| #include "base/misc.hh" |
| #include "base/trace.hh" |
| #include "cpu/pred/2bit_local.hh" |
| #include "debug/Fetch.hh" |
| |
| LocalBP::LocalBP(unsigned _localPredictorSize, |
| unsigned _localCtrBits, |
| unsigned _instShiftAmt) |
| : localPredictorSize(_localPredictorSize), |
| localCtrBits(_localCtrBits), |
| instShiftAmt(_instShiftAmt) |
| { |
| if (!isPowerOf2(localPredictorSize)) { |
| fatal("Invalid local predictor size!\n"); |
| } |
| |
| localPredictorSets = localPredictorSize / localCtrBits; |
| |
| if (!isPowerOf2(localPredictorSets)) { |
| fatal("Invalid number of local predictor sets! Check localCtrBits.\n"); |
| } |
| |
| // Setup the index mask. |
| indexMask = localPredictorSets - 1; |
| |
| DPRINTF(Fetch, "Branch predictor: index mask: %#x\n", indexMask); |
| |
| // Setup the array of counters for the local predictor. |
| localCtrs.resize(localPredictorSets); |
| |
| for (unsigned i = 0; i < localPredictorSets; ++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); |
| } |
| |
| void |
| LocalBP::reset() |
| { |
| for (unsigned i = 0; i < localPredictorSets; ++i) { |
| localCtrs[i].reset(); |
| } |
| } |
| |
| bool |
| LocalBP::lookup(Addr &branch_addr, void * &bp_history) |
| { |
| bool taken; |
| uint8_t counter_val; |
| unsigned local_predictor_idx = getLocalIndex(branch_addr); |
| |
| DPRINTF(Fetch, "Branch predictor: Looking up index %#x\n", |
| local_predictor_idx); |
| |
| counter_val = localCtrs[local_predictor_idx].read(); |
| |
| DPRINTF(Fetch, "Branch predictor: prediction is %i.\n", |
| (int)counter_val); |
| |
| taken = getPrediction(counter_val); |
| |
| #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 |
| LocalBP::update(Addr &branch_addr, bool taken, void *bp_history) |
| { |
| assert(bp_history == NULL); |
| 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); |
| |
| 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 |
| LocalBP::getPrediction(uint8_t &count) |
| { |
| // Get the MSB of the count |
| return (count >> (localCtrBits - 1)); |
| } |
| |
| inline |
| unsigned |
| LocalBP::getLocalIndex(Addr &branch_addr) |
| { |
| return (branch_addr >> instShiftAmt) & indexMask; |
| } |