2bit_local.hh revision 1689 
1/*
2 * Copyright (c) 2004-2005 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_BETA_CPU_2BIT_LOCAL_PRED_HH__
30#define __CPU_BETA_CPU_2BIT_LOCAL_PRED_HH__
31
32// For Addr type.
33#include "arch/alpha/isa_traits.hh"
34#include "cpu/beta_cpu/sat_counter.hh"
35
36class DefaultBP
37{
38  public:
39    /**
40     * Default branch predictor constructor.
41     */
42    DefaultBP(unsigned localPredictorSize, unsigned localCtrBits,
43              unsigned instShiftAmt);
44
45    /**
46     * Looks up the given address in the branch predictor and returns
47     * a true/false value as to whether it is taken.
48     * @param branch_addr The address of the branch to look up.
49     * @return Whether or not the branch is taken.
50     */
51    bool lookup(Addr &branch_addr);
52
53    /**
54     * Updates the branch predictor with the actual result of a branch.
55     * @param branch_addr The address of the branch to update.
56     * @param taken Whether or not the branch was taken.
57     */
58    void update(Addr &branch_addr, bool taken);
59
60  private:
61
62    /** Returns the taken/not taken prediction given the value of the
63     *  counter.
64     */
65    inline bool getPrediction(uint8_t &count);
66
67    /** Calculates the local index based on the PC. */
68    inline unsigned getLocalIndex(Addr &PC);
69
70    /** Array of counters that make up the local predictor. */
71    SatCounter *localCtrs;
72
73    /** Size of the local predictor. */
74    unsigned localPredictorSize;
75
76    /** Number of bits of the local predictor's counters. */
77    unsigned localCtrBits;
78
79    /** Number of bits to shift the PC when calculating index. */
80    unsigned instShiftAmt;
81
82    /** Mask to get index bits. */
83    unsigned indexMask;
84};
85
86#endif // __CPU_BETA_CPU_2BIT_LOCAL_PRED_HH__
87