src/cpu/pred/tage.cc

   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 TAGE branch predictor
  36  */
  37
  38 #include "cpu/pred/tage.hh"
  39
  40 #include "base/intmath.hh"
  41 #include "base/logging.hh"
  42 #include "base/random.hh"
  43 #include "base/trace.hh"
  44 #include "debug/Fetch.hh"
  45 #include "debug/Tage.hh"
  46
  47 TAGE::TAGE(const TAGEParams *params) : BPredUnit(params), tage(params->tage)
  48 {
  49 }
  50
  51 // PREDICTOR UPDATE
  52 void
  53 TAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
  54               bool squashed, const StaticInstPtr & inst, Addr corrTarget)
  55 {
  56     assert(bp_history);
  57
  58     TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
  59     TAGEBase::BranchInfo *tage_bi = bi->tageBranchInfo;
  60
  61     if (squashed) {
  62         // This restores the global history, then update it
  63         // and recomputes the folded histories.
  64         tage->squash(tid, taken, tage_bi, corrTarget);
  65         return;
  66     }
  67
  68     int nrand = random_mt.random<int>() & 3;
  69     if (bi->tageBranchInfo->condBranch) {
  70         DPRINTF(Tage, "Updating tables for branch:%lx; taken?:%d\n",
  71                 branch_pc, taken);
  72         tage->updateStats(taken, bi->tageBranchInfo);
  73         tage->condBranchUpdate(tid, branch_pc, taken, tage_bi, nrand,
  74                                corrTarget, bi->tageBranchInfo->tagePred);
  75     }
  76
  77     // optional non speculative update of the histories
  78     tage->updateHistories(tid, branch_pc, taken, tage_bi, false, inst,
  79                           corrTarget);
  80     delete bi;
  81 }
  82
  83 void
  84 TAGE::squash(ThreadID tid, void *bp_history)
  85 {
  86     TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
  87     DPRINTF(Tage, "Deleting branch info: %lx\n", bi->tageBranchInfo->branchPC);
  88     delete bi;
  89 }
  90
  91 bool
  92 TAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
  93 {
  94     TageBranchInfo *bi = new TageBranchInfo(*tage);//nHistoryTables+1);
  95     b = (void*)(bi);
  96     return tage->tagePredict(tid, branch_pc, cond_branch, bi->tageBranchInfo);
  97 }
  98
  99 bool
 100 TAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history)
 101 {
 102     bool retval = predict(tid, branch_pc, true, bp_history);
 103
 104     TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
 105
 106     DPRINTF(Tage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval);
 107
 108     tage->updateHistories(tid, branch_pc, retval, bi->tageBranchInfo, true);
 109
 110     return retval;
 111 }
 112
 113 void
 114 TAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history)
 115 {
 116     TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
 117     tage->btbUpdate(tid, branch_pc, bi->tageBranchInfo);
 118 }
 119
 120 void
 121 TAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
 122 {
 123     DPRINTF(Tage, "UnConditionalBranch: %lx\n", br_pc);
 124     predict(tid, br_pc, false, bp_history);
 125     TageBranchInfo *bi = static_cast<TageBranchInfo*>(bp_history);
 126     tage->updateHistories(tid, br_pc, true, bi->tageBranchInfo, true);
 127 }
 128
 129 TAGE*
 130 TAGEParams::create()
 131 {
 132     return new TAGE(this);
 133 }