2bit_local.cc revision 11434:b5aed9d2d54e
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 LocalBPParams *params) 38 : BPredUnit(params), 39 localPredictorSize(params->localPredictorSize), 40 localCtrBits(params->localCtrBits) 41{ 42 if (!isPowerOf2(localPredictorSize)) { 43 fatal("Invalid local predictor size!\n"); 44 } 45 46 localPredictorSets = localPredictorSize / localCtrBits; 47 48 if (!isPowerOf2(localPredictorSets)) { 49 fatal("Invalid number of local predictor sets! Check localCtrBits.\n"); 50 } 51 52 // Setup the index mask. 53 indexMask = localPredictorSets - 1; 54 55 DPRINTF(Fetch, "index mask: %#x\n", indexMask); 56 57 // Setup the array of counters for the local predictor. 58 localCtrs.resize(localPredictorSets); 59 60 for (unsigned i = 0; i < localPredictorSets; ++i) 61 localCtrs[i].setBits(localCtrBits); 62 63 DPRINTF(Fetch, "local predictor size: %i\n", 64 localPredictorSize); 65 66 DPRINTF(Fetch, "local counter bits: %i\n", localCtrBits); 67 68 DPRINTF(Fetch, "instruction shift amount: %i\n", 69 instShiftAmt); 70} 71 72void 73LocalBP::reset() 74{ 75 for (unsigned i = 0; i < localPredictorSets; ++i) { 76 localCtrs[i].reset(); 77 } 78} 79 80void 81LocalBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history) 82{ 83// Place holder for a function that is called to update predictor history when 84// a BTB entry is invalid or not found. 85} 86 87 88bool 89LocalBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history) 90{ 91 bool taken; 92 uint8_t counter_val; 93 unsigned local_predictor_idx = getLocalIndex(branch_addr); 94 95 DPRINTF(Fetch, "Looking up index %#x\n", 96 local_predictor_idx); 97 98 counter_val = localCtrs[local_predictor_idx].read(); 99 100 DPRINTF(Fetch, "prediction is %i.\n", 101 (int)counter_val); 102 103 taken = getPrediction(counter_val); 104 105#if 0 106 // Speculative update. 107 if (taken) { 108 DPRINTF(Fetch, "Branch updated as taken.\n"); 109 localCtrs[local_predictor_idx].increment(); 110 } else { 111 DPRINTF(Fetch, "Branch updated as not taken.\n"); 112 localCtrs[local_predictor_idx].decrement(); 113 } 114#endif 115 116 return taken; 117} 118 119void 120LocalBP::update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history, 121 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(ThreadID tid, Addr pc, void *&bp_history) 157{ 158} 159 160LocalBP* 161LocalBPParams::create() 162{ 163 return new LocalBP(this); 164} 165