2bit_local.hh revision 6226:f1076450ab2b 
1/*
2 * Copyright (c) 2004-2006 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 * Authors: Kevin Lim
29 */
30
31#ifndef __CPU_O3_2BIT_LOCAL_PRED_HH__
32#define __CPU_O3_2BIT_LOCAL_PRED_HH__
33
34#include <vector>
35
36#include "base/types.hh"
37#include "cpu/o3/sat_counter.hh"
38
39/**
40 * Implements a local predictor that uses the PC to index into a table of
41 * counters.  Note that any time a pointer to the bp_history is given, it
42 * should be NULL using this predictor because it does not have any branch
43 * predictor state that needs to be recorded or updated; the update can be
44 * determined solely by the branch being taken or not taken.
45 */
46class LocalBP
47{
48  public:
49    /**
50     * Default branch predictor constructor.
51     * @param localPredictorSize Size of the local predictor.
52     * @param localCtrBits Number of bits per counter.
53     * @param instShiftAmt Offset amount for instructions to ignore alignment.
54     */
55    LocalBP(unsigned localPredictorSize, unsigned localCtrBits,
56            unsigned instShiftAmt);
57
58    /**
59     * Looks up the given address in the branch predictor and returns
60     * a true/false value as to whether it is taken.
61     * @param branch_addr The address of the branch to look up.
62     * @param bp_history Pointer to any bp history state.
63     * @return Whether or not the branch is taken.
64     */
65    bool lookup(Addr &branch_addr, void * &bp_history);
66
67    /**
68     * Updates the branch predictor with the actual result of a branch.
69     * @param branch_addr The address of the branch to update.
70     * @param taken Whether or not the branch was taken.
71     */
72    void update(Addr &branch_addr, bool taken, void *bp_history);
73
74    void squash(void *bp_history)
75    { assert(bp_history == NULL); }
76
77    void reset();
78
79  private:
80    /**
81     *  Returns the taken/not taken prediction given the value of the
82     *  counter.
83     *  @param count The value of the counter.
84     *  @return The prediction based on the counter value.
85     */
86    inline bool getPrediction(uint8_t &count);
87
88    /** Calculates the local index based on the PC. */
89    inline unsigned getLocalIndex(Addr &PC);
90
91    /** Array of counters that make up the local predictor. */
92    std::vector<SatCounter> localCtrs;
93
94    /** Size of the local predictor. */
95    unsigned localPredictorSize;
96
97    /** Number of sets. */
98    unsigned localPredictorSets;
99
100    /** Number of bits of the local predictor's counters. */
101    unsigned localCtrBits;
102
103    /** Number of bits to shift the PC when calculating index. */
104    unsigned instShiftAmt;
105
106    /** Mask to get index bits. */
107    unsigned indexMask;
108};
109
110#endif // __CPU_O3_2BIT_LOCAL_PRED_HH__
111