btb.hh revision 7720:65d338a8dba4 
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 * Authors: Kevin Lim
29 */
30
31#ifndef __CPU_O3_BTB_HH__
32#define __CPU_O3_BTB_HH__
33
34#include "arch/types.hh"
35#include "base/misc.hh"
36#include "base/types.hh"
37#include "config/the_isa.hh"
38
39class DefaultBTB
40{
41  private:
42    struct BTBEntry
43    {
44        BTBEntry()
45            : tag(0), target(0), valid(false)
46        {}
47
48        /** The entry's tag. */
49        Addr tag;
50
51        /** The entry's target. */
52        TheISA::PCState target;
53
54        /** The entry's thread id. */
55        ThreadID tid;
56
57        /** Whether or not the entry is valid. */
58        bool valid;
59    };
60
61  public:
62    /** Creates a BTB with the given number of entries, number of bits per
63     *  tag, and instruction offset amount.
64     *  @param numEntries Number of entries for the BTB.
65     *  @param tagBits Number of bits for each tag in the BTB.
66     *  @param instShiftAmt Offset amount for instructions to ignore alignment.
67     */
68    DefaultBTB(unsigned numEntries, unsigned tagBits,
69               unsigned instShiftAmt);
70
71    void reset();
72
73    /** Looks up an address in the BTB. Must call valid() first on the address.
74     *  @param inst_PC The address of the branch to look up.
75     *  @param tid The thread id.
76     *  @return Returns the target of the branch.
77     */
78    TheISA::PCState lookup(Addr instPC, ThreadID tid);
79
80    /** Checks if a branch is in the BTB.
81     *  @param inst_PC The address of the branch to look up.
82     *  @param tid The thread id.
83     *  @return Whether or not the branch exists in the BTB.
84     */
85    bool valid(Addr instPC, ThreadID tid);
86
87    /** Updates the BTB with the target of a branch.
88     *  @param inst_PC The address of the branch being updated.
89     *  @param target_PC The target address of the branch.
90     *  @param tid The thread id.
91     */
92    void update(Addr instPC, const TheISA::PCState &targetPC,
93                ThreadID tid);
94
95  private:
96    /** Returns the index into the BTB, based on the branch's PC.
97     *  @param inst_PC The branch to look up.
98     *  @return Returns the index into the BTB.
99     */
100    inline unsigned getIndex(Addr instPC);
101
102    /** Returns the tag bits of a given address.
103     *  @param inst_PC The branch's address.
104     *  @return Returns the tag bits.
105     */
106    inline Addr getTag(Addr instPC);
107
108    /** The actual BTB. */
109    std::vector<BTBEntry> btb;
110
111    /** The number of entries in the BTB. */
112    unsigned numEntries;
113
114    /** The index mask. */
115    unsigned idxMask;
116
117    /** The number of tag bits per entry. */
118    unsigned tagBits;
119
120    /** The tag mask. */
121    unsigned tagMask;
122
123    /** Number of bits to shift PC when calculating index. */
124    unsigned instShiftAmt;
125
126    /** Number of bits to shift PC when calculating tag. */
127    unsigned tagShiftAmt;
128};
129
130#endif // __CPU_O3_BTB_HH__
131