2bit_local.hh revision 11429:cf5af0cc3be4 
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#include "params/LocalBP.hh"
53
54/**
55 * Implements a local predictor that uses the PC to index into a table of
56 * counters.  Note that any time a pointer to the bp_history is given, it
57 * should be NULL using this predictor because it does not have any branch
58 * predictor state that needs to be recorded or updated; the update can be
59 * determined solely by the branch being taken or not taken.
60 */
61class LocalBP : public BPredUnit
62{
63  public:
64    /**
65     * Default branch predictor constructor.
66     */
67    LocalBP(const LocalBPParams *params);
68
69    virtual void uncondBranch(Addr pc, void * &bp_history);
70
71    /**
72     * Looks up the given address in the branch predictor and returns
73     * a true/false value as to whether it is taken.
74     * @param branch_addr The address of the branch to look up.
75     * @param bp_history Pointer to any bp history state.
76     * @return Whether or not the branch is taken.
77     */
78    bool lookup(Addr branch_addr, void * &bp_history);
79
80    /**
81     * Updates the branch predictor to Not Taken if a BTB entry is
82     * invalid or not found.
83     * @param branch_addr The address of the branch to look up.
84     * @param bp_history Pointer to any bp history state.
85     * @return Whether or not the branch is taken.
86     */
87    void btbUpdate(Addr branch_addr, void * &bp_history);
88
89    /**
90     * Updates the branch predictor with the actual result of a branch.
91     * @param branch_addr The address of the branch to update.
92     * @param taken Whether or not the branch was taken.
93     */
94    void update(Addr branch_addr, bool taken, void *bp_history, bool squashed);
95
96    void retireSquashed(void *bp_history)
97    { assert(bp_history == NULL); }
98
99    void squash(void *bp_history)
100    { assert(bp_history == NULL); }
101
102    void reset();
103
104  private:
105    /**
106     *  Returns the taken/not taken prediction given the value of the
107     *  counter.
108     *  @param count The value of the counter.
109     *  @return The prediction based on the counter value.
110     */
111    inline bool getPrediction(uint8_t &count);
112
113    /** Calculates the local index based on the PC. */
114    inline unsigned getLocalIndex(Addr &PC);
115
116    /** Array of counters that make up the local predictor. */
117    std::vector<SatCounter> localCtrs;
118
119    /** Size of the local predictor. */
120    unsigned localPredictorSize;
121
122    /** Number of sets. */
123    unsigned localPredictorSets;
124
125    /** Number of bits of the local predictor's counters. */
126    unsigned localCtrBits;
127
128    /** Mask to get index bits. */
129    unsigned indexMask;
130};
131
132#endif // __CPU_PRED_2BIT_LOCAL_PRED_HH__
133