2bit_local.cc revision 9480:d059f8a95a42
1/* 2 * Copyright (c) 2004-2006 The Regents of The University of Michigan 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are 7 * met: redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer; 9 * redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution; 12 * neither the name of the copyright holders nor the names of its 13 * contributors may be used to endorse or promote products derived from 14 * this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 * 28 * Authors: Kevin Lim 29 */ 30 31#include "base/intmath.hh" 32#include "base/misc.hh" 33#include "base/trace.hh" 34#include "cpu/pred/2bit_local.hh" 35#include "debug/Fetch.hh" 36 37LocalBP::LocalBP(const Params *params) 38 : BPredUnit(params), 39 localPredictorSize(params->localPredictorSize), 40 localCtrBits(params->localCtrBits), 41 instShiftAmt(params->instShiftAmt) 42{ 43 if (!isPowerOf2(localPredictorSize)) { 44 fatal("Invalid local predictor size!\n"); 45 } 46 47 localPredictorSets = localPredictorSize / localCtrBits; 48 49 if (!isPowerOf2(localPredictorSets)) { 50 fatal("Invalid number of local predictor sets! Check localCtrBits.\n"); 51 } 52 53 // Setup the index mask. 54 indexMask = localPredictorSets - 1; 55 56 DPRINTF(Fetch, "index mask: %#x\n", indexMask); 57 58 // Setup the array of counters for the local predictor. 59 localCtrs.resize(localPredictorSets); 60 61 for (unsigned i = 0; i < localPredictorSets; ++i) 62 localCtrs[i].setBits(localCtrBits); 63 64 DPRINTF(Fetch, "local predictor size: %i\n", 65 localPredictorSize); 66 67 DPRINTF(Fetch, "local counter bits: %i\n", localCtrBits); 68 69 DPRINTF(Fetch, "instruction shift amount: %i\n", 70 instShiftAmt); 71} 72 73void 74LocalBP::reset() 75{ 76 for (unsigned i = 0; i < localPredictorSets; ++i) { 77 localCtrs[i].reset(); 78 } 79} 80 81void 82LocalBP::btbUpdate(Addr branch_addr, void * &bp_history) 83{ 84// Place holder for a function that is called to update predictor history when 85// a BTB entry is invalid or not found. 86} 87 88 89bool 90LocalBP::lookup(Addr branch_addr, void * &bp_history) 91{ 92 bool taken; 93 uint8_t counter_val; 94 unsigned local_predictor_idx = getLocalIndex(branch_addr); 95 96 DPRINTF(Fetch, "Looking up index %#x\n", 97 local_predictor_idx); 98 99 counter_val = localCtrs[local_predictor_idx].read(); 100 101 DPRINTF(Fetch, "prediction is %i.\n", 102 (int)counter_val); 103 104 taken = getPrediction(counter_val); 105 106#if 0 107 // Speculative update. 108 if (taken) { 109 DPRINTF(Fetch, "Branch updated as taken.\n"); 110 localCtrs[local_predictor_idx].increment(); 111 } else { 112 DPRINTF(Fetch, "Branch updated as not taken.\n"); 113 localCtrs[local_predictor_idx].decrement(); 114 } 115#endif 116 117 return taken; 118} 119 120void 121LocalBP::update(Addr branch_addr, bool taken, void *bp_history, bool squashed) 122{ 123 assert(bp_history == NULL); 124 unsigned local_predictor_idx; 125 126 // Update the local predictor. 127 local_predictor_idx = getLocalIndex(branch_addr); 128 129 DPRINTF(Fetch, "Looking up index %#x\n", local_predictor_idx); 130 131 if (taken) { 132 DPRINTF(Fetch, "Branch updated as taken.\n"); 133 localCtrs[local_predictor_idx].increment(); 134 } else { 135 DPRINTF(Fetch, "Branch updated as not taken.\n"); 136 localCtrs[local_predictor_idx].decrement(); 137 } 138} 139 140inline 141bool 142LocalBP::getPrediction(uint8_t &count) 143{ 144 // Get the MSB of the count 145 return (count >> (localCtrBits - 1)); 146} 147 148inline 149unsigned 150LocalBP::getLocalIndex(Addr &branch_addr) 151{ 152 return (branch_addr >> instShiftAmt) & indexMask; 153} 154 155void 156LocalBP::uncondBranch(void *&bp_history) 157{ 158} 159