btb.cc revision 11432:4209ec56e923
1/* 2 * Copyright (c) 2004-2005 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/trace.hh" 33#include "cpu/pred/btb.hh" 34#include "debug/Fetch.hh" 35 36DefaultBTB::DefaultBTB(unsigned _numEntries, 37 unsigned _tagBits, 38 unsigned _instShiftAmt, 39 unsigned _num_threads) 40 : numEntries(_numEntries), 41 tagBits(_tagBits), 42 instShiftAmt(_instShiftAmt), 43 log2NumThreads(floorLog2(_num_threads)) 44{ 45 DPRINTF(Fetch, "BTB: Creating BTB object.\n"); 46 47 if (!isPowerOf2(numEntries)) { 48 fatal("BTB entries is not a power of 2!"); 49 } 50 51 btb.resize(numEntries); 52 53 for (unsigned i = 0; i < numEntries; ++i) { 54 btb[i].valid = false; 55 } 56 57 idxMask = numEntries - 1; 58 59 tagMask = (1 << tagBits) - 1; 60 61 tagShiftAmt = instShiftAmt + floorLog2(numEntries); 62} 63 64void 65DefaultBTB::reset() 66{ 67 for (unsigned i = 0; i < numEntries; ++i) { 68 btb[i].valid = false; 69 } 70} 71 72inline 73unsigned 74DefaultBTB::getIndex(Addr instPC, ThreadID tid) 75{ 76 // Need to shift PC over by the word offset. 77 return ((instPC >> instShiftAmt) 78 ^ (tid << (tagShiftAmt - instShiftAmt - log2NumThreads))) 79 & idxMask; 80} 81 82inline 83Addr 84DefaultBTB::getTag(Addr instPC) 85{ 86 return (instPC >> tagShiftAmt) & tagMask; 87} 88 89bool 90DefaultBTB::valid(Addr instPC, ThreadID tid) 91{ 92 unsigned btb_idx = getIndex(instPC, tid); 93 94 Addr inst_tag = getTag(instPC); 95 96 assert(btb_idx < numEntries); 97 98 if (btb[btb_idx].valid 99 && inst_tag == btb[btb_idx].tag 100 && btb[btb_idx].tid == tid) { 101 return true; 102 } else { 103 return false; 104 } 105} 106 107// @todo Create some sort of return struct that has both whether or not the 108// address is valid, and also the address. For now will just use addr = 0 to 109// represent invalid entry. 110TheISA::PCState 111DefaultBTB::lookup(Addr instPC, ThreadID tid) 112{ 113 unsigned btb_idx = getIndex(instPC, tid); 114 115 Addr inst_tag = getTag(instPC); 116 117 assert(btb_idx < numEntries); 118 119 if (btb[btb_idx].valid 120 && inst_tag == btb[btb_idx].tag 121 && btb[btb_idx].tid == tid) { 122 return btb[btb_idx].target; 123 } else { 124 return 0; 125 } 126} 127 128void 129DefaultBTB::update(Addr instPC, const TheISA::PCState &target, ThreadID tid) 130{ 131 unsigned btb_idx = getIndex(instPC, tid); 132 133 assert(btb_idx < numEntries); 134 135 btb[btb_idx].tid = tid; 136 btb[btb_idx].valid = true; 137 btb[btb_idx].target = target; 138 btb[btb_idx].tag = getTag(instPC); 139} 140