1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
|
/*
* Copyright (c) 2014 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Anthony Gutierrez
*/
/* @file
* Implementation of a bi-mode branch predictor
*/
#ifndef __CPU_PRED_BI_MODE_PRED_HH__
#define __CPU_PRED_BI_MODE_PRED_HH__
#include "cpu/pred/bpred_unit.hh"
#include "cpu/pred/sat_counter.hh"
#include "params/BiModeBP.hh"
/**
* Implements a bi-mode branch predictor. The bi-mode predictor is a two-level
* branch predictor that has three seprate history arrays: a taken array, a
* not-taken array, and a choice array. The taken/not-taken arrays are indexed
* by a hash of the PC and the global history. The choice array is indexed by
* the PC only. Because the taken/not-taken arrays use the same index, they must
* be the same size.
*
* The bi-mode branch predictor aims to eliminate the destructive aliasing that
* occurs when two branches of opposite biases share the same global history
* pattern. By separating the predictors into taken/not-taken arrays, and using
* the branch's PC to choose between the two, destructive aliasing is reduced.
*/
class BiModeBP : public BPredUnit
{
public:
BiModeBP(const BiModeBPParams *params);
void uncondBranch(ThreadID tid, Addr pc, void * &bp_history);
void squash(ThreadID tid, void *bp_history);
bool lookup(ThreadID tid, Addr branch_addr, void * &bp_history);
void btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history);
void update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
bool squashed);
void retireSquashed(ThreadID tid, void *bp_history);
unsigned getGHR(ThreadID tid, void *bp_history) const;
private:
void updateGlobalHistReg(ThreadID tid, bool taken);
struct BPHistory {
unsigned globalHistoryReg;
// was the taken array's prediction used?
// true: takenPred used
// false: notPred used
bool takenUsed;
// prediction of the taken array
// true: predict taken
// false: predict not-taken
bool takenPred;
// prediction of the not-taken array
// true: predict taken
// false: predict not-taken
bool notTakenPred;
// the final taken/not-taken prediction
// true: predict taken
// false: predict not-taken
bool finalPred;
};
// choice predictors
std::vector<SatCounter> choiceCounters;
// taken direction predictors
std::vector<SatCounter> takenCounters;
// not-taken direction predictors
std::vector<SatCounter> notTakenCounters;
std::vector<unsigned> globalHistoryReg;
unsigned globalHistoryBits;
unsigned historyRegisterMask;
unsigned choicePredictorSize;
unsigned choiceCtrBits;
unsigned choiceHistoryMask;
unsigned globalPredictorSize;
unsigned globalCtrBits;
unsigned globalHistoryMask;
unsigned choiceThreshold;
unsigned takenThreshold;
unsigned notTakenThreshold;
};
#endif // __CPU_PRED_BI_MODE_PRED_HH__
|
