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
|
#ifndef __CPU_BETA_CPU_TOURNAMENT_PRED_HH__
#define __CPU_BETA_CPU_TOURNAMENT_PRED_HH__
// For Addr type.
#include "arch/alpha/isa_traits.hh"
#include "cpu/beta_cpu/sat_counter.hh"
class TournamentBP
{
public:
/**
* Default branch predictor constructor.
*/
TournamentBP(unsigned local_predictor_size,
unsigned local_ctr_bits,
unsigned local_history_table_size,
unsigned local_history_bits,
unsigned global_predictor_size,
unsigned global_history_bits,
unsigned global_ctr_bits,
unsigned choice_predictor_size,
unsigned choice_ctr_bits,
unsigned instShiftAmt);
/**
* Looks up the given address in the branch predictor and returns
* a true/false value as to whether it is taken.
* @param branch_addr The address of the branch to look up.
* @return Whether or not the branch is taken.
*/
bool lookup(Addr &branch_addr);
/**
* Updates the branch predictor with the actual result of a branch.
* @param branch_addr The address of the branch to update.
* @param taken Whether or not the branch was taken.
*/
void update(Addr &branch_addr, unsigned global_history, bool taken);
inline unsigned readGlobalHist() { return globalHistory; }
private:
inline bool getPrediction(uint8_t &count);
inline unsigned calcLocHistIdx(Addr &branch_addr);
inline void updateHistoriesTaken(unsigned local_history_idx);
inline void updateHistoriesNotTaken(unsigned local_history_idx);
/** Local counters. */
SatCounter *localCtrs;
/** Size of the local predictor. */
unsigned localPredictorSize;
/** Number of bits of the local predictor's counters. */
unsigned localCtrBits;
/** Array of local history table entries. */
unsigned *localHistoryTable;
/** Size of the local history table. */
unsigned localHistoryTableSize;
/** Number of bits for each entry of the local history table.
* @todo Doesn't this come from the size of the local predictor?
*/
unsigned localHistoryBits;
/** Mask to get the proper local history. */
unsigned localHistoryMask;
/** Array of counters that make up the global predictor. */
SatCounter *globalCtrs;
/** Size of the global predictor. */
unsigned globalPredictorSize;
/** Number of bits of the global predictor's counters. */
unsigned globalCtrBits;
/** Global history register. */
unsigned globalHistory;
/** Number of bits for the global history. */
unsigned globalHistoryBits;
/** Mask to get the proper global history. */
unsigned globalHistoryMask;
/** Array of counters that make up the choice predictor. */
SatCounter *choiceCtrs;
/** Size of the choice predictor (identical to the global predictor). */
unsigned choicePredictorSize;
/** Number of bits of the choice predictor's counters. */
unsigned choiceCtrBits;
/** Number of bits to shift the instruction over to get rid of the word
* offset.
*/
unsigned instShiftAmt;
/** Threshold for the counter value; above the threshold is taken,
* equal to or below the threshold is not taken.
*/
unsigned threshold;
};
#endif // __CPU_BETA_CPU_TOURNAMENT_PRED_HH__
|
