bpred_unit.hh revision 1062 
1
2#ifndef __BPRED_UNIT_HH__
3#define __BPRED_UNIT_HH__
4
5// For Addr type.
6#include "arch/alpha/isa_traits.hh"
7#include "base/statistics.hh"
8#include "cpu/inst_seq.hh"
9
10#include "cpu/beta_cpu/2bit_local_pred.hh"
11#include "cpu/beta_cpu/tournament_pred.hh"
12#include "cpu/beta_cpu/btb.hh"
13#include "cpu/beta_cpu/ras.hh"
14
15#include <list>
16
17/**
18 * Basically a wrapper class to hold both the branch predictor
19 * and the BTB.  Right now I'm unsure of the implementation; it would
20 * be nicer to have something closer to the CPUPolicy or the Impl where
21 * this is just typedefs, but it forces the upper level stages to be
22 * aware of the constructors of the BP and the BTB.  The nicer thing
23 * to do is have this templated on the Impl, accept the usual Params
24 * object, and be able to call the constructors on the BP and BTB.
25 */
26template<class Impl>
27class TwobitBPredUnit
28{
29  public:
30    typedef typename Impl::Params Params;
31    typedef typename Impl::DynInstPtr DynInstPtr;
32
33    TwobitBPredUnit(Params &params);
34
35    void regStats();
36
37    bool predict(DynInstPtr &inst, Addr &PC);
38
39    void squash(const InstSeqNum &squashed_sn, const Addr &corr_target,
40                bool actually_taken);
41
42    void squash(const InstSeqNum &squashed_sn);
43
44    void update(const InstSeqNum &done_sn);
45
46    bool BPLookup(Addr &inst_PC)
47    { return BP.lookup(inst_PC); }
48
49    unsigned BPReadGlobalHist()
50    { return 0; }
51
52    bool BTBValid(Addr &inst_PC)
53    { return BTB.valid(inst_PC); }
54
55    Addr BTBLookup(Addr &inst_PC)
56    { return BTB.lookup(inst_PC); }
57
58    // Will want to include global history.
59    void BPUpdate(Addr &inst_PC, unsigned global_history, bool taken)
60    { BP.update(inst_PC, taken); }
61
62    void BTBUpdate(Addr &inst_PC, Addr &target_PC)
63    { BTB.update(inst_PC, target_PC); }
64
65  private:
66    struct PredictorHistory {
67        PredictorHistory(const InstSeqNum &seq_num, const Addr &inst_PC,
68                         const bool pred_taken)
69            : seqNum(seq_num), PC(inst_PC), predTaken(pred_taken),
70              globalHistory(0), usedRAS(0), wasCall(0), RASIndex(0),
71              RASTarget(0)
72        { }
73
74        InstSeqNum seqNum;
75
76        Addr PC;
77
78        bool predTaken;
79
80        unsigned globalHistory;
81
82        bool usedRAS;
83
84        bool wasCall;
85
86        unsigned RASIndex;
87
88        Addr RASTarget;
89    };
90
91    std::list<PredictorHistory> predHist;
92
93    DefaultBP BP;
94
95    DefaultBTB BTB;
96
97    ReturnAddrStack RAS;
98
99    Stats::Scalar<> lookups;
100    Stats::Scalar<> condPredicted;
101    Stats::Scalar<> condIncorrect;
102    Stats::Scalar<> BTBLookups;
103    Stats::Scalar<> BTBHits;
104    Stats::Scalar<> BTBCorrect;
105    Stats::Scalar<> usedRAS;
106    Stats::Scalar<> RASIncorrect;
107};
108
109#endif // __BPRED_UNIT_HH__
110