src/cpu/pred/ltage.hh

   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
  34 /* @file
  35  * Implementation of a L-TAGE branch predictor. TAGE is a global-history based
  36  * branch predictor. It features a PC-indexed bimodal predictor and N
  37  * partially tagged tables, indexed with a hash of the PC and the global
  38  * branch history. The different lengths of global branch history used to
  39  * index the partially tagged tables grow geometrically. A small path history
  40  * is also used in the hash. L-TAGE also features a loop predictor that records
  41  * iteration count of loops and predicts accordingly.
  42  *
  43  * All TAGE tables are accessed in parallel, and the one using the longest
  44  * history that matches provides the prediction (some exceptions apply).
  45  * Entries are allocated in components using a longer history than the
  46  * one that predicted when the prediction is incorrect.
  47  */
  48
  49 #ifndef __CPU_PRED_LTAGE
  50 #define __CPU_PRED_LTAGE
  51
  52
  53 #include <vector>
  54
  55 #include "base/types.hh"
  56 #include "cpu/pred/loop_predictor.hh"
  57 #include "cpu/pred/tage.hh"
  58 #include "params/LTAGE.hh"
  59
  60 class LTAGE : public TAGE
  61 {
  62   public:
  63     LTAGE(const LTAGEParams *params);
  64
  65     // Base class methods.
  66     void squash(ThreadID tid, void *bp_history) override;
  67     void update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
  68                 bool squashed, const StaticInstPtr & inst,
  69                 Addr corrTarget) override;
  70
  71     void init() override;
  72     virtual void regStats() override;
  73
  74   protected:
  75     /** The loop predictor object */
  76     LoopPredictor *loopPredictor;
  77
  78     // more provider types
  79     enum {
  80         LOOP = TAGEBase::LAST_TAGE_PROVIDER_TYPE + 1,
  81         LAST_LTAGE_PROVIDER_TYPE = LOOP
  82     };
  83
  84     // Primary branch history entry
  85     struct LTageBranchInfo : public TageBranchInfo
  86     {
  87         LoopPredictor::BranchInfo *lpBranchInfo;
  88         LTageBranchInfo(TAGEBase &tage, LoopPredictor &lp)
  89           : TageBranchInfo(tage), lpBranchInfo(lp.makeBranchInfo())
  90         {}
  91
  92         virtual ~LTageBranchInfo()
  93         {
  94             delete lpBranchInfo;
  95         }
  96     };
  97
  98     /**
  99      * Get a branch prediction from LTAGE. *NOT* an override of
 100      * BpredUnit::predict().
 101      * @param tid The thread ID to select the global
 102      * histories to use.
 103      * @param branch_pc The unshifted branch PC.
 104      * @param cond_branch True if the branch is conditional.
 105      * @param b Reference to wrapping pointer to allow storing
 106      * derived class prediction information in the base class.
 107      */
 108     bool predict(
 109         ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) override;
 110 };
 111
 112 #endif // __CPU_PRED_LTAGE