2bit_local.hh revision 8842:a02932e2e73d
1/* 2 * Copyright (c) 2011 ARM Limited 3 * All rights reserved 4 * 5 * The license below extends only to copyright in the software and shall 6 * not be construed as granting a license to any other intellectual 7 * property including but not limited to intellectual property relating 8 * to a hardware implementation of the functionality of the software 9 * licensed hereunder. You may use the software subject to the license 10 * terms below provided that you ensure that this notice is replicated 11 * unmodified and in its entirety in all distributions of the software, 12 * modified or unmodified, in source code or in binary form. 13 * 14 * Copyright (c) 2004-2006 The Regents of The University of Michigan 15 * All rights reserved. 16 * 17 * Redistribution and use in source and binary forms, with or without 18 * modification, are permitted provided that the following conditions are 19 * met: redistributions of source code must retain the above copyright 20 * notice, this list of conditions and the following disclaimer; 21 * redistributions in binary form must reproduce the above copyright 22 * notice, this list of conditions and the following disclaimer in the 23 * documentation and/or other materials provided with the distribution; 24 * neither the name of the copyright holders nor the names of its 25 * contributors may be used to endorse or promote products derived from 26 * this software without specific prior written permission. 27 * 28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 36 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 39 * 40 * Authors: Kevin Lim 41 */ 42 43#ifndef __CPU_O3_2BIT_LOCAL_PRED_HH__ 44#define __CPU_O3_2BIT_LOCAL_PRED_HH__ 45 46#include <vector> 47 48#include "base/types.hh" 49#include "cpu/o3/sat_counter.hh" 50 51/** 52 * Implements a local predictor that uses the PC to index into a table of 53 * counters. Note that any time a pointer to the bp_history is given, it 54 * should be NULL using this predictor because it does not have any branch 55 * predictor state that needs to be recorded or updated; the update can be 56 * determined solely by the branch being taken or not taken. 57 */ 58class LocalBP 59{ 60 public: 61 /** 62 * Default branch predictor constructor. 63 * @param localPredictorSize Size of the local predictor. 64 * @param localCtrBits Number of bits per counter. 65 * @param instShiftAmt Offset amount for instructions to ignore alignment. 66 */ 67 LocalBP(unsigned localPredictorSize, unsigned localCtrBits, 68 unsigned instShiftAmt); 69 70 /** 71 * Looks up the given address in the branch predictor and returns 72 * a true/false value as to whether it is taken. 73 * @param branch_addr The address of the branch to look up. 74 * @param bp_history Pointer to any bp history state. 75 * @return Whether or not the branch is taken. 76 */ 77 bool lookup(Addr &branch_addr, void * &bp_history); 78 79 /** 80 * Updates the branch predictor to Not Taken if a BTB entry is 81 * invalid or not found. 82 * @param branch_addr The address of the branch to look up. 83 * @param bp_history Pointer to any bp history state. 84 * @return Whether or not the branch is taken. 85 */ 86 void BTBUpdate(Addr &branch_addr, void * &bp_history); 87 88 /** 89 * Updates the branch predictor with the actual result of a branch. 90 * @param branch_addr The address of the branch to update. 91 * @param taken Whether or not the branch was taken. 92 */ 93 void update(Addr &branch_addr, bool taken, void *bp_history); 94 95 void squash(void *bp_history) 96 { assert(bp_history == NULL); } 97 98 void reset(); 99 100 private: 101 /** 102 * Returns the taken/not taken prediction given the value of the 103 * counter. 104 * @param count The value of the counter. 105 * @return The prediction based on the counter value. 106 */ 107 inline bool getPrediction(uint8_t &count); 108 109 /** Calculates the local index based on the PC. */ 110 inline unsigned getLocalIndex(Addr &PC); 111 112 /** Array of counters that make up the local predictor. */ 113 std::vector<SatCounter> localCtrs; 114 115 /** Size of the local predictor. */ 116 unsigned localPredictorSize; 117 118 /** Number of sets. */ 119 unsigned localPredictorSets; 120 121 /** Number of bits of the local predictor's counters. */ 122 unsigned localCtrBits; 123 124 /** Number of bits to shift the PC when calculating index. */ 125 unsigned instShiftAmt; 126 127 /** Mask to get index bits. */ 128 unsigned indexMask; 129}; 130 131#endif // __CPU_O3_2BIT_LOCAL_PRED_HH__ 132