btb.hh revision 2669
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 29#ifndef __CPU_O3_BTB_HH__ 30#define __CPU_O3_BTB_HH__ 31 32// For Addr type. 33#include "arch/isa_traits.hh" 34#include "base/misc.hh" 35 36class DefaultBTB 37{ 38 private: 39 struct BTBEntry 40 { 41 BTBEntry() 42 : tag(0), target(0), valid(false) 43 { 44 } 45 46 /** The entry's tag. */ 47 Addr tag; 48 49 /** The entry's target. */ 50 Addr target; 51 52 /** The entry's thread id. */ 53 unsigned tid; 54 55 /** Whether or not the entry is valid. */ 56 bool valid; 57 }; 58 59 public: 60 /** Creates a BTB with the given number of entries, number of bits per 61 * tag, and instruction offset amount. 62 * @param numEntries Number of entries for the BTB. 63 * @param tagBits Number of bits for each tag in the BTB. 64 * @param instShiftAmt Offset amount for instructions to ignore alignment. 65 */ 66 DefaultBTB(unsigned numEntries, unsigned tagBits, 67 unsigned instShiftAmt); 68 69 void reset(); 70 71 /** Looks up an address in the BTB. Must call valid() first on the address. 72 * @param inst_PC The address of the branch to look up. 73 * @param tid The thread id. 74 * @return Returns the target of the branch. 75 */ 76 Addr lookup(const Addr &inst_PC, unsigned tid); 77 78 /** Checks if a branch is in the BTB. 79 * @param inst_PC The address of the branch to look up. 80 * @param tid The thread id. 81 * @return Whether or not the branch exists in the BTB. 82 */ 83 bool valid(const Addr &inst_PC, unsigned tid); 84 85 /** Updates the BTB with the target of a branch. 86 * @param inst_PC The address of the branch being updated. 87 * @param target_PC The target address of the branch. 88 * @param tid The thread id. 89 */ 90 void update(const Addr &inst_PC, const Addr &target_PC, 91 unsigned tid); 92 93 private: 94 /** Returns the index into the BTB, based on the branch's PC. 95 * @param inst_PC The branch to look up. 96 * @return Returns the index into the BTB. 97 */ 98 inline unsigned getIndex(const Addr &inst_PC); 99 100 /** Returns the tag bits of a given address. 101 * @param inst_PC The branch's address. 102 * @return Returns the tag bits. 103 */ 104 inline Addr getTag(const Addr &inst_PC); 105 106 /** The actual BTB. */ 107 std::vector<BTBEntry> btb; 108 109 /** The number of entries in the BTB. */ 110 unsigned numEntries; 111 112 /** The index mask. */ 113 unsigned idxMask; 114 115 /** The number of tag bits per entry. */ 116 unsigned tagBits; 117 118 /** The tag mask. */ 119 unsigned tagMask; 120 121 /** Number of bits to shift PC when calculating index. */ 122 unsigned instShiftAmt; 123 124 /** Number of bits to shift PC when calculating tag. */ 125 unsigned tagShiftAmt; 126}; 127 128#endif // __CPU_O3_BTB_HH__ 129