tage.cc

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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)
 *
 * All rights reserved.
 *
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 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
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 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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/* @file
 * Implementation of a TAGE branch predictor
 */
 
#include "cpu/pred/tage.hh"
 
#include "base/intmath.hh"
#include "base/logging.hh"
#include "base/random.hh"
#include "base/trace.hh"
#include "debug/Fetch.hh"
#include "debug/Tage.hh"
 
namespace gem5
{
 
namespace branch_prediction
{
 
TAGE::TAGE(const TAGEParams &params) : BPredUnit(params), tage(params.tage)
{
}
 
// PREDICTOR UPDATE
void
TAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
              bool squashed, const StaticInstPtr & inst, Addr corrTarget)
{
    assert(bp_history);
 
    TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
    TAGEBase::BranchInfo *tage_bi = bi->tageBranchInfo;
 
    if (squashed) {
        // This restores the global history, then update it
        // and recomputes the folded histories.
        tage->squash(tid, taken, tage_bi, corrTarget);
        return;
    }
 
    int nrand = random_mt.random<int>() & 3;
    if (bi->tageBranchInfo->condBranch) {
        DPRINTF(Tage, "Updating tables for branch:%lx; taken?:%d\n",
                branch_pc, taken);
        tage->updateStats(taken, bi->tageBranchInfo);
        tage->condBranchUpdate(tid, branch_pc, taken, tage_bi, nrand,
                               corrTarget, bi->tageBranchInfo->tagePred);
    }
 
    // optional non speculative update of the histories
    tage->updateHistories(tid, branch_pc, taken, tage_bi, false, inst,
                          corrTarget);
    delete bi;
}
 
void
TAGE::squash(ThreadID tid, void *bp_history)
{
    TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
    DPRINTF(Tage, "Deleting branch info: %lx\n", bi->tageBranchInfo->branchPC);
    delete bi;
}
 
bool
TAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
{
    TageBranchInfo *bi = new TageBranchInfo(*tage);//nHistoryTables+1);
    b = (void*)(bi);
    return tage->tagePredict(tid, branch_pc, cond_branch, bi->tageBranchInfo);
}
 
bool
TAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history)
{
    bool retval = predict(tid, branch_pc, true, bp_history);
 
    TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
 
    DPRINTF(Tage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval);
 
    tage->updateHistories(tid, branch_pc, retval, bi->tageBranchInfo, true);
 
    return retval;
}
 
void
TAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history)
{
    TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
    tage->btbUpdate(tid, branch_pc, bi->tageBranchInfo);
}
 
void
TAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
{
    DPRINTF(Tage, "UnConditionalBranch: %lx\n", br_pc);
    predict(tid, br_pc, false, bp_history);
    TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
    tage->updateHistories(tid, br_pc, true, bi->tageBranchInfo, true);
}
 
} // namespace branch_prediction
} // namespace gem5