2bit_local.cc revision 13959:ea907b02c800
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 "cpu/pred/2bit_local.hh" 32 33#include "base/intmath.hh" 34#include "base/logging.hh" 35#include "base/trace.hh" 36#include "debug/Fetch.hh" 37 38LocalBP::LocalBP(const LocalBPParams *params) 39 : BPredUnit(params), 40 localPredictorSize(params->localPredictorSize), 41 localCtrBits(params->localCtrBits), 42 localPredictorSets(localPredictorSize / localCtrBits), 43 localCtrs(localPredictorSets, SatCounter(localCtrBits)), 44 indexMask(localPredictorSets - 1) 45{ 46 if (!isPowerOf2(localPredictorSize)) { 47 fatal("Invalid local predictor size!\n"); 48 } 49 50 if (!isPowerOf2(localPredictorSets)) { 51 fatal("Invalid number of local predictor sets! Check localCtrBits.\n"); 52 } 53 54 DPRINTF(Fetch, "index mask: %#x\n", indexMask); 55 56 DPRINTF(Fetch, "local predictor size: %i\n", 57 localPredictorSize); 58 59 DPRINTF(Fetch, "local counter bits: %i\n", localCtrBits); 60 61 DPRINTF(Fetch, "instruction shift amount: %i\n", 62 instShiftAmt); 63} 64 65void 66LocalBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history) 67{ 68// Place holder for a function that is called to update predictor history when 69// a BTB entry is invalid or not found. 70} 71 72 73bool 74LocalBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history) 75{ 76 bool taken; 77 unsigned local_predictor_idx = getLocalIndex(branch_addr); 78 79 DPRINTF(Fetch, "Looking up index %#x\n", 80 local_predictor_idx); 81 82 uint8_t counter_val = localCtrs[local_predictor_idx]; 83 84 DPRINTF(Fetch, "prediction is %i.\n", 85 (int)counter_val); 86 87 taken = getPrediction(counter_val); 88 89#if 0 90 // Speculative update. 91 if (taken) { 92 DPRINTF(Fetch, "Branch updated as taken.\n"); 93 localCtrs[local_predictor_idx]++; 94 } else { 95 DPRINTF(Fetch, "Branch updated as not taken.\n"); 96 localCtrs[local_predictor_idx]--; 97 } 98#endif 99 100 return taken; 101} 102 103void 104LocalBP::update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history, 105 bool squashed, const StaticInstPtr & inst, Addr corrTarget) 106{ 107 assert(bp_history == NULL); 108 unsigned local_predictor_idx; 109 110 // No state to restore, and we do not update on the wrong 111 // path. 112 if (squashed) { 113 return; 114 } 115 116 // Update the local predictor. 117 local_predictor_idx = getLocalIndex(branch_addr); 118 119 DPRINTF(Fetch, "Looking up index %#x\n", local_predictor_idx); 120 121 if (taken) { 122 DPRINTF(Fetch, "Branch updated as taken.\n"); 123 localCtrs[local_predictor_idx]++; 124 } else { 125 DPRINTF(Fetch, "Branch updated as not taken.\n"); 126 localCtrs[local_predictor_idx]--; 127 } 128} 129 130inline 131bool 132LocalBP::getPrediction(uint8_t &count) 133{ 134 // Get the MSB of the count 135 return (count >> (localCtrBits - 1)); 136} 137 138inline 139unsigned 140LocalBP::getLocalIndex(Addr &branch_addr) 141{ 142 return (branch_addr >> instShiftAmt) & indexMask; 143} 144 145void 146LocalBP::uncondBranch(ThreadID tid, Addr pc, void *&bp_history) 147{ 148} 149 150LocalBP* 151LocalBPParams::create() 152{ 153 return new LocalBP(this); 154} 155