ltage.hh revision 13627:ec1395943cd2 
1/*
2 * Copyright (c) 2014 The University of Wisconsin
3 *
4 * Copyright (c) 2006 INRIA (Institut National de Recherche en
5 * Informatique et en Automatique  / French National Research Institute
6 * for Computer Science and Applied Mathematics)
7 *
8 * All rights reserved.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions are
12 * met: redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer;
14 * redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution;
17 * neither the name of the copyright holders nor the names of its
18 * contributors may be used to endorse or promote products derived from
19 * this software without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
24 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
25 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
26 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
27 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
28 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
29 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
30 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
31 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
32 *
33 * Authors: Vignyan Reddy, Dibakar Gope and Arthur Perais,
34 * from André Seznec's code.
35 */
36
37/* @file
38 * Implementation of a L-TAGE branch predictor. TAGE is a global-history based
39 * branch predictor. It features a PC-indexed bimodal predictor and N
40 * partially tagged tables, indexed with a hash of the PC and the global
41 * branch history. The different lengths of global branch history used to
42 * index the partially tagged tables grow geometrically. A small path history
43 * is also used in the hash. L-TAGE also features a loop predictor that records
44 * iteration count of loops and predicts accordingly.
45 *
46 * All TAGE tables are accessed in parallel, and the one using the longest
47 * history that matches provides the prediction (some exceptions apply).
48 * Entries are allocated in components using a longer history than the
49 * one that predicted when the prediction is incorrect.
50 */
51
52#ifndef __CPU_PRED_LTAGE
53#define __CPU_PRED_LTAGE
54
55
56#include <vector>
57
58#include "base/types.hh"
59#include "cpu/pred/loop_predictor.hh"
60#include "cpu/pred/tage.hh"
61#include "params/LTAGE.hh"
62
63class LTAGE : public TAGE
64{
65  public:
66    LTAGE(const LTAGEParams *params);
67
68    // Base class methods.
69    void squash(ThreadID tid, void *bp_history) override;
70    void update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
71                bool squashed, const StaticInstPtr & inst,
72                Addr corrTarget = MaxAddr) override;
73    virtual void regStats() override;
74
75  protected:
76    /** The loop predictor object */
77    LoopPredictor *loopPredictor;
78
79    // more provider types
80    enum {
81        LOOP = TAGEBase::LAST_TAGE_PROVIDER_TYPE + 1,
82        LAST_LTAGE_PROVIDER_TYPE = LOOP
83    };
84
85    // Primary branch history entry
86    struct LTageBranchInfo : public TageBranchInfo
87    {
88        LoopPredictor::BranchInfo *lpBranchInfo;
89        LTageBranchInfo(TAGEBase &tage, LoopPredictor &lp)
90          : TageBranchInfo(tage), lpBranchInfo(lp.makeBranchInfo())
91        {}
92
93        virtual ~LTageBranchInfo()
94        {
95            delete lpBranchInfo;
96        }
97    };
98
99    /**
100     * Get a branch prediction from LTAGE. *NOT* an override of
101     * BpredUnit::predict().
102     * @param tid The thread ID to select the global
103     * histories to use.
104     * @param branch_pc The unshifted branch PC.
105     * @param cond_branch True if the branch is conditional.
106     * @param b Reference to wrapping pointer to allow storing
107     * derived class prediction information in the base class.
108     */
109    bool predict(
110        ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) override;
111};
112
113#endif // __CPU_PRED_LTAGE
114