2bit_local.hh revision 10330:f54586c894e3
1/* 2 * Copyright (c) 2011, 2014 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 * Timothy M. Jones 42 */ 43 44#ifndef __CPU_PRED_2BIT_LOCAL_PRED_HH__ 45#define __CPU_PRED_2BIT_LOCAL_PRED_HH__ 46 47#include <vector> 48 49#include "base/types.hh" 50#include "cpu/pred/bpred_unit.hh" 51#include "cpu/pred/sat_counter.hh" 52 53/** 54 * Implements a local predictor that uses the PC to index into a table of 55 * counters. Note that any time a pointer to the bp_history is given, it 56 * should be NULL using this predictor because it does not have any branch 57 * predictor state that needs to be recorded or updated; the update can be 58 * determined solely by the branch being taken or not taken. 59 */ 60class LocalBP : public BPredUnit 61{ 62 public: 63 /** 64 * Default branch predictor constructor. 65 */ 66 LocalBP(const Params *params); 67 68 virtual void uncondBranch(void * &bp_history); 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, bool squashed); 94 95 void retireSquashed(void *bp_history) 96 { assert(bp_history == NULL); } 97 98 void squash(void *bp_history) 99 { assert(bp_history == NULL); } 100 101 void reset(); 102 103 private: 104 /** 105 * Returns the taken/not taken prediction given the value of the 106 * counter. 107 * @param count The value of the counter. 108 * @return The prediction based on the counter value. 109 */ 110 inline bool getPrediction(uint8_t &count); 111 112 /** Calculates the local index based on the PC. */ 113 inline unsigned getLocalIndex(Addr &PC); 114 115 /** Array of counters that make up the local predictor. */ 116 std::vector<SatCounter> localCtrs; 117 118 /** Size of the local predictor. */ 119 unsigned localPredictorSize; 120 121 /** Number of sets. */ 122 unsigned localPredictorSets; 123 124 /** Number of bits of the local predictor's counters. */ 125 unsigned localCtrBits; 126 127 /** Number of bits to shift the PC when calculating index. */ 128 unsigned instShiftAmt; 129 130 /** Mask to get index bits. */ 131 unsigned indexMask; 132}; 133 134#endif // __CPU_PRED_2BIT_LOCAL_PRED_HH__ 135