blob: 32a7972d0cf3ca514cf9daff338b4fc719512c61 (
plain)
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
|
#ifndef __2BIT_LOCAL_PRED_HH__
#define __2BIT_LOCAL_PRED_HH__
// For Addr type.
#include "arch/alpha/isa_traits.hh"
class DefaultBP
{
public:
/**
* Default branch predictor constructor.
*/
DefaultBP(unsigned localPredictorSize, unsigned localCtrBits,
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, bool taken);
private:
inline bool getPrediction(uint8_t &count);
inline unsigned getLocalIndex(Addr &PC);
/**
* Private counter class for the internal saturating counters.
* Implements an n bit saturating counter and provides methods to
* increment, decrement, and read it.
* @todo Consider making this something that more closely mimics a
* built in class so you can use ++ or --.
*/
class SatCounter
{
public:
/**
* Constructor for the counter.
* @param bits How many bits the counter will have.
*/
SatCounter(unsigned bits);
/**
* Constructor for the counter.
* @param bits How many bits the counter will have.
* @param initial_val Starting value for each counter.
*/
SatCounter(unsigned bits, unsigned initial_val);
/**
* Increments the counter's current value.
*/
void increment();
/**
* Decrements the counter's current value.
*/
void decrement();
/**
* Read the counter's value.
*/
uint8_t read()
{
return counter;
}
private:
uint8_t maxVal;
uint8_t counter;
};
/** Array of counters that make up the local predictor. */
SatCounter *localCtrs;
/** Size of the local predictor. */
unsigned localPredictorSize;
/** Number of bits of the local predictor's counters. */
unsigned localCtrBits;
/** Number of bits to shift the PC when calculating index. */
unsigned instShiftAmt;
/** Mask to get index bits. */
unsigned indexMask;
};
#endif // __2BIT_LOCAL_PRED_HH__
|
