btb.hh revision 2292
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 35class DefaultBTB 36{ 37 private: 38 struct BTBEntry 39 { 40 BTBEntry() 41 : tag(0), target(0), valid(false) 42 { 43 } 44 45 /** The entry's tag. */ 46 Addr tag; 47 48 /** The entry's target. */ 49 Addr target; 50 51 /** The entry's thread id. */ 52 unsigned tid; 53 54 /** Whether or not the entry is valid. */ 55 bool valid; 56 }; 57 58 public: 59 /** Creates a BTB with the given number of entries, number of bits per 60 * tag, and instruction offset amount. 61 * @param numEntries Number of entries for the BTB. 62 * @param tagBits Number of bits for each tag in the BTB. 63 * @param instShiftAmt Offset amount for instructions to ignore alignment. 64 */ 65 DefaultBTB(unsigned numEntries, unsigned tagBits, 66 unsigned instShiftAmt); 67 68 /** Looks up an address in the BTB. Must call valid() first on the address. 69 * @param inst_PC The address of the branch to look up. 70 * @param tid The thread id. 71 * @return Returns the target of the branch. 72 */ 73 Addr lookup(const Addr &inst_PC, unsigned tid); 74 75 /** Checks if a branch is in the BTB. 76 * @param inst_PC The address of the branch to look up. 77 * @param tid The thread id. 78 * @return Whether or not the branch exists in the BTB. 79 */ 80 bool valid(const Addr &inst_PC, unsigned tid); 81 82 /** Updates the BTB with the target of a branch. 83 * @param inst_PC The address of the branch being updated. 84 * @param target_PC The target address of the branch. 85 * @param tid The thread id. 86 */ 87 void update(const Addr &inst_PC, const Addr &target_PC, 88 unsigned tid); 89 90 private: 91 /** Returns the index into the BTB, based on the branch's PC. 92 * @param inst_PC The branch to look up. 93 * @return Returns the index into the BTB. 94 */ 95 inline unsigned getIndex(const Addr &inst_PC); 96 97 /** Returns the tag bits of a given address. 98 * @param inst_PC The branch's address. 99 * @return Returns the tag bits. 100 */ 101 inline Addr getTag(const Addr &inst_PC); 102 103 /** The actual BTB. */ 104 std::vector<BTBEntry> btb; 105 106 /** The number of entries in the BTB. */ 107 unsigned numEntries; 108 109 /** The index mask. */ 110 unsigned idxMask; 111 112 /** The number of tag bits per entry. */ 113 unsigned tagBits; 114 115 /** The tag mask. */ 116 unsigned tagMask; 117 118 /** Number of bits to shift PC when calculating index. */ 119 unsigned instShiftAmt; 120 121 /** Number of bits to shift PC when calculating tag. */ 122 unsigned tagShiftAmt; 123}; 124 125#endif // __CPU_O3_BTB_HH__ 126