btb.hh revision 6221
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#ifndef __CPU_O3_BTB_HH__ 32#define __CPU_O3_BTB_HH__ 33 34#include "base/misc.hh" 35#include "base/types.hh" 36 37class DefaultBTB 38{ 39 private: 40 struct BTBEntry 41 { 42 BTBEntry() 43 : tag(0), target(0), valid(false) 44 { 45 } 46 47 /** The entry's tag. */ 48 Addr tag; 49 50 /** The entry's target. */ 51 Addr target; 52 53 /** The entry's thread id. */ 54 ThreadID tid; 55 56 /** Whether or not the entry is valid. */ 57 bool valid; 58 }; 59 60 public: 61 /** Creates a BTB with the given number of entries, number of bits per 62 * tag, and instruction offset amount. 63 * @param numEntries Number of entries for the BTB. 64 * @param tagBits Number of bits for each tag in the BTB. 65 * @param instShiftAmt Offset amount for instructions to ignore alignment. 66 */ 67 DefaultBTB(unsigned numEntries, unsigned tagBits, 68 unsigned instShiftAmt); 69 70 void reset(); 71 72 /** Looks up an address in the BTB. Must call valid() first on the address. 73 * @param inst_PC The address of the branch to look up. 74 * @param tid The thread id. 75 * @return Returns the target of the branch. 76 */ 77 Addr lookup(const Addr &inst_PC, ThreadID tid); 78 79 /** Checks if a branch is in the BTB. 80 * @param inst_PC The address of the branch to look up. 81 * @param tid The thread id. 82 * @return Whether or not the branch exists in the BTB. 83 */ 84 bool valid(const Addr &inst_PC, ThreadID tid); 85 86 /** Updates the BTB with the target of a branch. 87 * @param inst_PC The address of the branch being updated. 88 * @param target_PC The target address of the branch. 89 * @param tid The thread id. 90 */ 91 void update(const Addr &inst_PC, const Addr &target_PC, 92 ThreadID tid); 93 94 private: 95 /** Returns the index into the BTB, based on the branch's PC. 96 * @param inst_PC The branch to look up. 97 * @return Returns the index into the BTB. 98 */ 99 inline unsigned getIndex(const Addr &inst_PC); 100 101 /** Returns the tag bits of a given address. 102 * @param inst_PC The branch's address. 103 * @return Returns the tag bits. 104 */ 105 inline Addr getTag(const Addr &inst_PC); 106 107 /** The actual BTB. */ 108 std::vector<BTBEntry> btb; 109 110 /** The number of entries in the BTB. */ 111 unsigned numEntries; 112 113 /** The index mask. */ 114 unsigned idxMask; 115 116 /** The number of tag bits per entry. */ 117 unsigned tagBits; 118 119 /** The tag mask. */ 120 unsigned tagMask; 121 122 /** Number of bits to shift PC when calculating index. */ 123 unsigned instShiftAmt; 124 125 /** Number of bits to shift PC when calculating tag. */ 126 unsigned tagShiftAmt; 127}; 128 129#endif // __CPU_O3_BTB_HH__ 130