tage.hh

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/*
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 * Copyright (c) 2014 The University of Wisconsin
 *
 * Copyright (c) 2006 INRIA (Institut National de Recherche en
 * Informatique et en Automatique  / French National Research Institute
 * for Computer Science and Applied Mathematics)
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/* @file
 * Implementation of a TAGE branch predictor. TAGE is a global-history based
 * branch predictor. It features a PC-indexed bimodal predictor and N
 * partially tagged tables, indexed with a hash of the PC and the global
 * branch history. The different lengths of global branch history used to
 * index the partially tagged tables grow geometrically. A small path history
 * is also used in the hash.
 *
 * All TAGE tables are accessed in parallel, and the one using the longest
 * history that matches provides the prediction (some exceptions apply).
 * Entries are allocated in components using a longer history than the
 * one that predicted when the prediction is incorrect.
 */
 
#ifndef __CPU_PRED_TAGE_HH__
#define __CPU_PRED_TAGE_HH__
 
#include <vector>
 
#include "base/random.hh"
#include "base/types.hh"
#include "cpu/pred/bpred_unit.hh"
#include "cpu/pred/tage_base.hh"
#include "params/TAGE.hh"
 
namespace gem5
{
 
namespace branch_prediction
{
 
class TAGE: public BPredUnit
{
  protected:
    TAGEBase *tage;
 
    Random::RandomPtr rng = Random::genRandom();
 
    struct TageBranchInfo
    {
        TAGEBase::BranchInfo *tageBranchInfo;
 
        TageBranchInfo(TAGEBase &tage, Addr pc, bool conditional)
        : tageBranchInfo(tage.makeBranchInfo(pc, conditional))
        {}
 
        virtual ~TageBranchInfo()
        {
            delete tageBranchInfo;
        }
    };
 
    virtual bool predict(ThreadID tid, Addr branch_pc, bool cond_branch,
                         void* &b);
 
  public:
 
    TAGE(const TAGEParams &params);
 
    // Base class methods.
    bool lookup(ThreadID tid, Addr pc, void* &bp_history) override;
    void updateHistories(ThreadID tid, Addr pc, bool uncond,
                         bool taken, Addr target, const StaticInstPtr &inst,
                         void * &bp_history) override;
    void update(ThreadID tid, Addr pc, bool taken, void * &bp_history,
                bool squashed, const StaticInstPtr &inst,
                Addr target) override;
    void squash(ThreadID tid, void * &bp_history) override;
    void branchPlaceholder(ThreadID tid, Addr pc,
                           bool uncond, void * &bp_history) override;
};
 
} // namespace branch_prediction
} // namespace gem5
 
#endif // __CPU_PRED_TAGE_HH__