2bit_local.hh revision 2345 
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
29#ifndef __CPU_O3_2BIT_LOCAL_PRED_HH__
30#define __CPU_O3_2BIT_LOCAL_PRED_HH__
31
32// For Addr type.
33#include "arch/isa_traits.hh"
34#include "cpu/o3/sat_counter.hh"
35
36#include <vector>
37
38/**
39 * Implements a local predictor that uses the PC to index into a table of
40 * counters.  Note that any time a pointer to the bp_history is given, it
41 * should be NULL using this predictor because it does not have any branch
42 * predictor state that needs to be recorded or updated; the update can be
43 * determined solely by the branch being taken or not taken.
44 */
45class LocalBP
46{
47  public:
48    /**
49     * Default branch predictor constructor.
50     * @param localPredictorSize Size of the local predictor.
51     * @param localCtrBits Number of bits per counter.
52     * @param instShiftAmt Offset amount for instructions to ignore alignment.
53     */
54    LocalBP(unsigned localPredictorSize, unsigned localCtrBits,
55            unsigned instShiftAmt);
56
57    /**
58     * Looks up the given address in the branch predictor and returns
59     * a true/false value as to whether it is taken.
60     * @param branch_addr The address of the branch to look up.
61     * @param bp_history Pointer to any bp history state.
62     * @return Whether or not the branch is taken.
63     */
64    bool lookup(Addr &branch_addr, void * &bp_history);
65
66    /**
67     * Updates the branch predictor with the actual result of a branch.
68     * @param branch_addr The address of the branch to update.
69     * @param taken Whether or not the branch was taken.
70     */
71    void update(Addr &branch_addr, bool taken, void *bp_history);
72
73    void squash(void *bp_history)
74    { assert(bp_history == NULL); }
75
76    void reset();
77
78  private:
79    /**
80     *  Returns the taken/not taken prediction given the value of the
81     *  counter.
82     *  @param count The value of the counter.
83     *  @return The prediction based on the counter value.
84     */
85    inline bool getPrediction(uint8_t &count);
86
87    /** Calculates the local index based on the PC. */
88    inline unsigned getLocalIndex(Addr &PC);
89
90    /** Array of counters that make up the local predictor. */
91    std::vector<SatCounter> localCtrs;
92
93    /** Size of the local predictor. */
94    unsigned localPredictorSize;
95
96    /** Number of sets. */
97    unsigned localPredictorSets;
98
99    /** Number of bits of the local predictor's counters. */
100    unsigned localCtrBits;
101
102    /** Number of bits to shift the PC when calculating index. */
103    unsigned instShiftAmt;
104
105    /** Mask to get index bits. */
106    unsigned indexMask;
107};
108
109#endif // __CPU_O3_2BIT_LOCAL_PRED_HH__
110