2bit_local.hh revision 9480:d059f8a95a42 
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 *          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 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_PRED_2BIT_LOCAL_PRED_HH__
132