c9d933efb0
This patch implements an L-TAGE predictor, based on André Seznec's code available from CBP-2 (http://hpca23.cse.tamu.edu/taco/camino/cbp2/cbp-src/realistic-seznec.h). Signed-off-by Jason Lowe-Power <jason@lowepower.com>
747 lines
25 KiB
C++
747 lines
25 KiB
C++
/*
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* Copyright (c) 2014 The University of Wisconsin
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*
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* Copyright (c) 2006 INRIA (Institut National de Recherche en
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* Informatique et en Automatique / French National Research Institute
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* for Computer Science and Applied Mathematics)
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*
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Authors: Vignyan Reddy, Dibakar Gope and Arthur Perais,
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* from André Seznec's code.
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*/
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/* @file
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* Implementation of a L-TAGE branch predictor
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*/
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#include "cpu/pred/ltage.hh"
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#include "base/intmath.hh"
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#include "base/misc.hh"
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#include "base/random.hh"
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#include "base/trace.hh"
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#include "debug/Fetch.hh"
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#include "debug/LTage.hh"
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LTAGE::LTAGE(const LTAGEParams *params)
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: BPredUnit(params),
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logSizeBiMP(params->logSizeBiMP),
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logSizeTagTables(params->logSizeTagTables),
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logSizeLoopPred(params->logSizeLoopPred),
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nHistoryTables(params->nHistoryTables),
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tagTableCounterBits(params->tagTableCounterBits),
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histBufferSize(params->histBufferSize),
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minHist(params->minHist),
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maxHist(params->maxHist),
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minTagWidth(params->minTagWidth),
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threadHistory(params->numThreads)
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{
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assert(params->histBufferSize > params->maxHist * 2);
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useAltPredForNewlyAllocated = 0;
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logTick = 19;
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tCounter = ULL(1) << (logTick - 1);
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for (auto& history : threadHistory) {
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history.pathHist = 0;
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history.globalHistory = new uint8_t[histBufferSize];
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history.gHist = history.globalHistory;
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memset(history.gHist, 0, histBufferSize);
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history.ptGhist = 0;
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}
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histLengths = new int [nHistoryTables+1];
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histLengths[1] = minHist;
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histLengths[nHistoryTables] = maxHist;
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for (int i = 2; i <= nHistoryTables; i++) {
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histLengths[i] = (int) (((double) minHist *
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pow ((double) (maxHist) / (double) minHist,
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(double) (i - 1) / (double) ((nHistoryTables- 1))))
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+ 0.5);
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}
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tagWidths[1] = minTagWidth;
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tagWidths[2] = minTagWidth;
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tagWidths[3] = minTagWidth + 1;
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tagWidths[4] = minTagWidth + 1;
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tagWidths[5] = minTagWidth + 2;
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tagWidths[6] = minTagWidth + 3;
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tagWidths[7] = minTagWidth + 4;
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tagWidths[8] = minTagWidth + 5;
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tagWidths[9] = minTagWidth + 5;
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tagWidths[10] = minTagWidth + 6;
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tagWidths[11] = minTagWidth + 7;
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tagWidths[12] = minTagWidth + 8;
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for (int i = 1; i <= 2; i++)
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tagTableSizes[i] = logSizeTagTables - 1;
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for (int i = 3; i <= 6; i++)
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tagTableSizes[i] = logSizeTagTables;
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for (int i = 7; i <= 10; i++)
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tagTableSizes[i] = logSizeTagTables - 1;
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for (int i = 11; i <= 12; i++)
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tagTableSizes[i] = logSizeTagTables - 2;
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for (auto& history : threadHistory) {
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history.computeIndices = new FoldedHistory[nHistoryTables+1];
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history.computeTags[0] = new FoldedHistory[nHistoryTables+1];
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history.computeTags[1] = new FoldedHistory[nHistoryTables+1];
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for (int i = 1; i <= nHistoryTables; i++) {
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history.computeIndices[i].init(histLengths[i], (tagTableSizes[i]));
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history.computeTags[0][i].init(
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history.computeIndices[i].origLength, tagWidths[i]);
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history.computeTags[1][i].init(
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history.computeIndices[i].origLength, tagWidths[i] - 1);
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DPRINTF(LTage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n",
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histLengths[i], tagTableSizes[i], tagWidths[i]);
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}
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}
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btable = new BimodalEntry[ULL(1) << logSizeBiMP];
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ltable = new LoopEntry[ULL(1) << logSizeLoopPred];
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gtable = new TageEntry*[nHistoryTables + 1];
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for (int i = 1; i <= nHistoryTables; i++) {
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gtable[i] = new TageEntry[1<<(tagTableSizes[i])];
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}
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tableIndices = new int [nHistoryTables+1];
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tableTags = new int [nHistoryTables+1];
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loopUseCounter = 0;
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}
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int
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LTAGE::bindex(Addr pc_in) const
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{
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return ((pc_in) & ((ULL(1) << (logSizeBiMP)) - 1));
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}
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int
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LTAGE::lindex(Addr pc_in) const
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{
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return (((pc_in) & ((ULL(1) << (logSizeLoopPred - 2)) - 1)) << 2);
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}
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int
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LTAGE::F(int A, int size, int bank) const
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{
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int A1, A2;
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A = A & ((ULL(1) << size) - 1);
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A1 = (A & ((ULL(1) << tagTableSizes[bank]) - 1));
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A2 = (A >> tagTableSizes[bank]);
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A2 = ((A2 << bank) & ((ULL(1) << tagTableSizes[bank]) - 1))
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+ (A2 >> (tagTableSizes[bank] - bank));
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A = A1 ^ A2;
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A = ((A << bank) & ((ULL(1) << tagTableSizes[bank]) - 1))
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+ (A >> (tagTableSizes[bank] - bank));
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return (A);
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}
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// gindex computes a full hash of pc, ghist and pathHist
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int
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LTAGE::gindex(ThreadID tid, Addr pc, int bank) const
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{
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int index;
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int hlen = (histLengths[bank] > 16) ? 16 : histLengths[bank];
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index =
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(pc) ^ ((pc) >> ((int) abs(tagTableSizes[bank] - bank) + 1)) ^
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threadHistory[tid].computeIndices[bank].comp ^
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F(threadHistory[tid].pathHist, hlen, bank);
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return (index & ((ULL(1) << (tagTableSizes[bank])) - 1));
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}
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// Tag computation
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uint16_t
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LTAGE::gtag(ThreadID tid, Addr pc, int bank) const
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{
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int tag = (pc) ^ threadHistory[tid].computeTags[0][bank].comp
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^ (threadHistory[tid].computeTags[1][bank].comp << 1);
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return (tag & ((ULL(1) << tagWidths[bank]) - 1));
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}
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// Up-down saturating counter
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void
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LTAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits)
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{
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assert(nbits <= sizeof(int8_t) << 3);
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if (taken) {
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if (ctr < ((1 << (nbits - 1)) - 1))
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ctr++;
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} else {
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if (ctr > -(1 << (nbits - 1)))
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ctr--;
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}
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}
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// Bimodal prediction
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bool
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LTAGE::getBimodePred(Addr pc, BranchInfo* bi) const
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{
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return (btable[bi->bimodalIndex].pred > 0);
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}
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// Update the bimodal predictor: a hysteresis bit is shared among 4 prediction
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// bits
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void
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LTAGE::baseUpdate(Addr pc, bool taken, BranchInfo* bi)
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{
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int inter = (btable[bi->bimodalIndex].pred << 1)
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+ btable[bi->bimodalIndex ].hyst;
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if (taken) {
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if (inter < 3)
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inter++;
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} else if (inter > 0) {
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inter--;
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}
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btable[bi->bimodalIndex].pred = inter >> 1;
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btable[bi->bimodalIndex].hyst = (inter & 1);
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DPRINTF(LTage, "Updating branch %lx, pred:%d, hyst:%d\n",
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pc, btable[bi->bimodalIndex].pred,btable[bi->bimodalIndex].hyst);
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}
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//loop prediction: only used if high confidence
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bool
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LTAGE::getLoop(Addr pc, BranchInfo* bi) const
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{
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bi->loopHit = -1;
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bi->loopPredValid = false;
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bi->loopIndex = lindex(pc);
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bi->loopTag = ((pc) >> (logSizeLoopPred - 2));
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for (int i = 0; i < 4; i++) {
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if (ltable[bi->loopIndex + i].tag == bi->loopTag) {
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bi->loopHit = i;
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bi->loopPredValid = (ltable[bi->loopIndex + i].confidence >= 3);
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bi->currentIter = ltable[bi->loopIndex + i].currentIterSpec;
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if (ltable[bi->loopIndex + i].currentIterSpec + 1 ==
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ltable[bi->loopIndex + i].numIter) {
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return !(ltable[bi->loopIndex + i].dir);
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}else {
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return (ltable[bi->loopIndex + i].dir);
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}
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}
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}
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return false;
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}
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void
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LTAGE::specLoopUpdate(Addr pc, bool taken, BranchInfo* bi)
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{
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if (bi->loopHit>=0) {
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int index = lindex(pc);
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if (taken != ltable[index].dir) {
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ltable[index].currentIterSpec = 0;
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} else {
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ltable[index].currentIterSpec++;
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}
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}
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}
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void
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LTAGE::loopUpdate(Addr pc, bool taken, BranchInfo* bi)
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{
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int idx = bi->loopIndex + bi->loopHit;
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if (bi->loopHit >= 0) {
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//already a hit
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if (bi->loopPredValid) {
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if (taken != bi->loopPred) {
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// free the entry
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ltable[idx].numIter = 0;
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ltable[idx].age = 0;
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ltable[idx].confidence = 0;
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ltable[idx].currentIter = 0;
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return;
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} else if (bi->loopPred != bi->tagePred) {
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DPRINTF(LTage, "Loop Prediction success:%lx\n",pc);
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if (ltable[idx].age < 7)
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ltable[idx].age++;
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}
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}
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ltable[idx].currentIter++;
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if (ltable[idx].currentIter > ltable[idx].numIter) {
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ltable[idx].confidence = 0;
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if (ltable[idx].numIter != 0) {
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// free the entry
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ltable[idx].numIter = 0;
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ltable[idx].age = 0;
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ltable[idx].confidence = 0;
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}
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}
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if (taken != ltable[idx].dir) {
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if (ltable[idx].currentIter == ltable[idx].numIter) {
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DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc);
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if (ltable[idx].confidence < 7) {
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ltable[idx].confidence++;
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}
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//just do not predict when the loop count is 1 or 2
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if (ltable[idx].numIter < 3) {
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// free the entry
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ltable[idx].dir = taken;
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ltable[idx].numIter = 0;
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ltable[idx].age = 0;
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ltable[idx].confidence = 0;
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}
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} else {
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DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc);
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if (ltable[idx].numIter == 0) {
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// first complete nest;
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ltable[idx].confidence = 0;
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ltable[idx].numIter = ltable[idx].currentIter;
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} else {
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//not the same number of iterations as last time: free the
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//entry
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ltable[idx].numIter = 0;
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ltable[idx].age = 0;
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ltable[idx].confidence = 0;
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}
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}
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ltable[idx].currentIter = 0;
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}
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} else if (taken) {
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//try to allocate an entry on taken branch
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int nrand = random_mt.random<int>();
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for (int i = 0; i < 4; i++) {
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int loop_hit = (nrand + i) & 3;
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idx = bi->loopIndex + loop_hit;
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if (ltable[idx].age == 0) {
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DPRINTF(LTage, "Allocating loop pred entry for branch %lx\n",
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pc);
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ltable[idx].dir = !taken;
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ltable[idx].tag = bi->loopTag;
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ltable[idx].numIter = 0;
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ltable[idx].age = 7;
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ltable[idx].confidence = 0;
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ltable[idx].currentIter = 1;
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break;
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}
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else
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ltable[idx].age--;
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}
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}
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}
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// shifting the global history: we manage the history in a big table in order
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// to reduce simulation time
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void
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LTAGE::updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &pt)
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{
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if (pt == 0) {
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DPRINTF(LTage, "Rolling over the histories\n");
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// Copy beginning of globalHistoryBuffer to end, such that
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// the last maxHist outcomes are still reachable
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// through pt[0 .. maxHist - 1].
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for (int i = 0; i < maxHist; i++)
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tab[histBufferSize - maxHist + i] = tab[i];
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pt = histBufferSize - maxHist;
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h = &tab[pt];
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}
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pt--;
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h--;
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h[0] = (dir) ? 1 : 0;
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}
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// Get GHR for hashing indirect predictor
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// Build history backwards from pointer in
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// bp_history.
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unsigned
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LTAGE::getGHR(ThreadID tid, void *bp_history) const
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{
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BranchInfo* bi = static_cast<BranchInfo*>(bp_history);
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unsigned val = 0;
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for (unsigned i = 0; i < 32; i++) {
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// Make sure we don't go out of bounds
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int gh_offset = bi->ptGhist + i;
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assert(&(threadHistory[tid].globalHistory[gh_offset]) <
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threadHistory[tid].globalHistory + histBufferSize);
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val |= ((threadHistory[tid].globalHistory[gh_offset] & 0x1) << i);
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}
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return val;
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}
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//prediction
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bool
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LTAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
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{
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BranchInfo *bi = new BranchInfo(nHistoryTables+1);
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b = (void*)(bi);
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Addr pc = branch_pc;
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bool pred_taken = true;
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bi->loopHit = -1;
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if (cond_branch) {
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// TAGE prediction
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// computes the table addresses and the partial tags
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for (int i = 1; i <= nHistoryTables; i++) {
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tableIndices[i] = gindex(tid, pc, i);
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bi->tableIndices[i] = tableIndices[i];
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tableTags[i] = gtag(tid, pc, i);
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bi->tableTags[i] = tableTags[i];
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}
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bi->bimodalIndex = bindex(pc);
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bi->hitBank = 0;
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bi->altBank = 0;
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//Look for the bank with longest matching history
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for (int i = nHistoryTables; i > 0; i--) {
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if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
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bi->hitBank = i;
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bi->hitBankIndex = tableIndices[bi->hitBank];
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break;
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}
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}
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//Look for the alternate bank
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for (int i = bi->hitBank - 1; i > 0; i--) {
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if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
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bi->altBank = i;
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bi->altBankIndex = tableIndices[bi->altBank];
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break;
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}
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}
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//computes the prediction and the alternate prediction
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if (bi->hitBank > 0) {
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if (bi->altBank > 0) {
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bi->altTaken =
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gtable[bi->altBank][tableIndices[bi->altBank]].ctr >= 0;
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}else {
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bi->altTaken = getBimodePred(pc, bi);
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}
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bi->longestMatchPred =
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gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr >= 0;
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bi->pseudoNewAlloc =
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abs(2 * gtable[bi->hitBank][bi->hitBankIndex].ctr + 1) <= 1;
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//if the entry is recognized as a newly allocated entry and
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//useAltPredForNewlyAllocated is positive use the alternate
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//prediction
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if ((useAltPredForNewlyAllocated < 0)
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|| abs(2 *
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gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1)
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bi->tagePred = bi->longestMatchPred;
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else
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bi->tagePred = bi->altTaken;
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} else {
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bi->altTaken = getBimodePred(pc, bi);
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bi->tagePred = bi->altTaken;
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bi->longestMatchPred = bi->altTaken;
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}
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//end TAGE prediction
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bi->loopPred = getLoop(pc, bi); // loop prediction
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pred_taken = (((loopUseCounter >= 0) && bi->loopPredValid)) ?
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(bi->loopPred): (bi->tagePred);
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DPRINTF(LTage, "Predict for %lx: taken?:%d, loopTaken?:%d, "
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"loopValid?:%d, loopUseCounter:%d, tagePred:%d, altPred:%d\n",
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branch_pc, pred_taken, bi->loopPred, bi->loopPredValid,
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loopUseCounter, bi->tagePred, bi->altTaken);
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}
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bi->branchPC = branch_pc;
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bi->condBranch = cond_branch;
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specLoopUpdate(branch_pc, pred_taken, bi);
|
|
return pred_taken;
|
|
}
|
|
|
|
// PREDICTOR UPDATE
|
|
void
|
|
LTAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
|
|
bool squashed)
|
|
{
|
|
assert(bp_history);
|
|
|
|
BranchInfo *bi = static_cast<BranchInfo*>(bp_history);
|
|
|
|
if (squashed) {
|
|
// This restores the global history, then update it
|
|
// and recomputes the folded histories.
|
|
squash(tid, taken, bp_history);
|
|
return;
|
|
}
|
|
|
|
int nrand = random_mt.random<int>(0,3);
|
|
Addr pc = branch_pc;
|
|
if (bi->condBranch) {
|
|
DPRINTF(LTage, "Updating tables for branch:%lx; taken?:%d\n",
|
|
branch_pc, taken);
|
|
// first update the loop predictor
|
|
loopUpdate(pc, taken, bi);
|
|
|
|
if (bi->loopPredValid) {
|
|
if (bi->tagePred != bi->loopPred) {
|
|
ctrUpdate(loopUseCounter, (bi->loopPred== taken), 7);
|
|
}
|
|
}
|
|
|
|
// TAGE UPDATE
|
|
// try to allocate a new entries only if prediction was wrong
|
|
bool longest_match_pred = false;
|
|
bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables);
|
|
if (bi->hitBank > 0) {
|
|
// Manage the selection between longest matching and alternate
|
|
// matching for "pseudo"-newly allocated longest matching entry
|
|
longest_match_pred = bi->longestMatchPred;
|
|
bool PseudoNewAlloc = bi->pseudoNewAlloc;
|
|
// an entry is considered as newly allocated if its prediction
|
|
// counter is weak
|
|
if (PseudoNewAlloc) {
|
|
if (longest_match_pred == taken) {
|
|
alloc = false;
|
|
}
|
|
// if it was delivering the correct prediction, no need to
|
|
// allocate new entry even if the overall prediction was false
|
|
if (longest_match_pred != bi->altTaken) {
|
|
ctrUpdate(useAltPredForNewlyAllocated,
|
|
bi->altTaken == taken, 4);
|
|
}
|
|
}
|
|
}
|
|
|
|
if (alloc) {
|
|
// is there some "unuseful" entry to allocate
|
|
int8_t min = 1;
|
|
for (int i = nHistoryTables; i > bi->hitBank; i--) {
|
|
if (gtable[i][bi->tableIndices[i]].u < min) {
|
|
min = gtable[i][bi->tableIndices[i]].u;
|
|
}
|
|
}
|
|
|
|
// we allocate an entry with a longer history
|
|
// to avoid ping-pong, we do not choose systematically the next
|
|
// entry, but among the 3 next entries
|
|
int Y = nrand &
|
|
((ULL(1) << (nHistoryTables - bi->hitBank - 1)) - 1);
|
|
int X = bi->hitBank + 1;
|
|
if (Y & 1) {
|
|
X++;
|
|
if (Y & 2)
|
|
X++;
|
|
}
|
|
// No entry available, forces one to be available
|
|
if (min > 0) {
|
|
gtable[X][bi->tableIndices[X]].u = 0;
|
|
}
|
|
|
|
|
|
//Allocate only one entry
|
|
for (int i = X; i <= nHistoryTables; i++) {
|
|
if ((gtable[i][bi->tableIndices[i]].u == 0)) {
|
|
gtable[i][bi->tableIndices[i]].tag = bi->tableTags[i];
|
|
gtable[i][bi->tableIndices[i]].ctr = (taken) ? 0 : -1;
|
|
gtable[i][bi->tableIndices[i]].u = 0; //?
|
|
}
|
|
}
|
|
}
|
|
//periodic reset of u: reset is not complete but bit by bit
|
|
tCounter++;
|
|
if ((tCounter & ((ULL(1) << logTick) - 1)) == 0) {
|
|
// reset least significant bit
|
|
// most significant bit becomes least significant bit
|
|
for (int i = 1; i <= nHistoryTables; i++) {
|
|
for (int j = 0; j < (ULL(1) << tagTableSizes[i]); j++) {
|
|
gtable[i][j].u = gtable[i][j].u >> 1;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (bi->hitBank > 0) {
|
|
DPRINTF(LTage, "Updating tag table entry (%d,%d) for branch %lx\n",
|
|
bi->hitBank, bi->hitBankIndex, branch_pc);
|
|
ctrUpdate(gtable[bi->hitBank][bi->hitBankIndex].ctr, taken,
|
|
tagTableCounterBits);
|
|
// if the provider entry is not certified to be useful also update
|
|
// the alternate prediction
|
|
if (gtable[bi->hitBank][bi->hitBankIndex].u == 0) {
|
|
if (bi->altBank > 0) {
|
|
ctrUpdate(gtable[bi->altBank][bi->altBankIndex].ctr, taken,
|
|
tagTableCounterBits);
|
|
DPRINTF(LTage, "Updating tag table entry (%d,%d) for"
|
|
" branch %lx\n", bi->hitBank, bi->hitBankIndex,
|
|
branch_pc);
|
|
}
|
|
if (bi->altBank == 0) {
|
|
baseUpdate(pc, taken, bi);
|
|
}
|
|
}
|
|
|
|
// update the u counter
|
|
if (longest_match_pred != bi->altTaken) {
|
|
if (longest_match_pred == taken) {
|
|
if (gtable[bi->hitBank][bi->hitBankIndex].u < 1) {
|
|
gtable[bi->hitBank][bi->hitBankIndex].u++;
|
|
}
|
|
}
|
|
}
|
|
} else {
|
|
baseUpdate(pc, taken, bi);
|
|
}
|
|
|
|
//END PREDICTOR UPDATE
|
|
}
|
|
if (!squashed) {
|
|
delete bi;
|
|
}
|
|
}
|
|
|
|
void
|
|
LTAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b)
|
|
{
|
|
BranchInfo* bi = (BranchInfo*)(b);
|
|
ThreadHistory& tHist = threadHistory[tid];
|
|
// UPDATE HISTORIES
|
|
bool pathbit = ((branch_pc) & 1);
|
|
//on a squash, return pointers to this and recompute indices.
|
|
//update user history
|
|
updateGHist(tHist.gHist, taken, tHist.globalHistory, tHist.ptGhist);
|
|
tHist.pathHist = (tHist.pathHist << 1) + pathbit;
|
|
tHist.pathHist = (tHist.pathHist & ((ULL(1) << 16) - 1));
|
|
|
|
bi->ptGhist = tHist.ptGhist;
|
|
bi->pathHist = tHist.pathHist;
|
|
//prepare next index and tag computations for user branchs
|
|
for (int i = 1; i <= nHistoryTables; i++)
|
|
{
|
|
bi->ci[i] = tHist.computeIndices[i].comp;
|
|
bi->ct0[i] = tHist.computeTags[0][i].comp;
|
|
bi->ct1[i] = tHist.computeTags[1][i].comp;
|
|
tHist.computeIndices[i].update(tHist.gHist);
|
|
tHist.computeTags[0][i].update(tHist.gHist);
|
|
tHist.computeTags[1][i].update(tHist.gHist);
|
|
}
|
|
DPRINTF(LTage, "Updating global histories with branch:%lx; taken?:%d, "
|
|
"path Hist: %x; pointer:%d\n", branch_pc, taken, tHist.pathHist,
|
|
tHist.ptGhist);
|
|
}
|
|
|
|
void
|
|
LTAGE::squash(ThreadID tid, bool taken, void *bp_history)
|
|
{
|
|
BranchInfo* bi = (BranchInfo*)(bp_history);
|
|
ThreadHistory& tHist = threadHistory[tid];
|
|
DPRINTF(LTage, "Restoring branch info: %lx; taken? %d; PathHistory:%x, "
|
|
"pointer:%d\n", bi->branchPC,taken, bi->pathHist, bi->ptGhist);
|
|
tHist.pathHist = bi->pathHist;
|
|
tHist.ptGhist = bi->ptGhist;
|
|
tHist.gHist = &(tHist.globalHistory[tHist.ptGhist]);
|
|
tHist.gHist[0] = (taken ? 1 : 0);
|
|
for (int i = 1; i <= nHistoryTables; i++) {
|
|
tHist.computeIndices[i].comp = bi->ci[i];
|
|
tHist.computeTags[0][i].comp = bi->ct0[i];
|
|
tHist.computeTags[1][i].comp = bi->ct1[i];
|
|
tHist.computeIndices[i].update(tHist.gHist);
|
|
tHist.computeTags[0][i].update(tHist.gHist);
|
|
tHist.computeTags[1][i].update(tHist.gHist);
|
|
}
|
|
|
|
if (bi->condBranch) {
|
|
if (bi->loopHit >= 0) {
|
|
int idx = bi->loopIndex + bi->loopHit;
|
|
ltable[idx].currentIterSpec = bi->currentIter;
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
void
|
|
LTAGE::squash(ThreadID tid, void *bp_history)
|
|
{
|
|
BranchInfo* bi = (BranchInfo*)(bp_history);
|
|
DPRINTF(LTage, "Deleting branch info: %lx\n", bi->branchPC);
|
|
if (bi->condBranch) {
|
|
if (bi->loopHit >= 0) {
|
|
int idx = bi->loopIndex + bi->loopHit;
|
|
ltable[idx].currentIterSpec = bi->currentIter;
|
|
}
|
|
}
|
|
|
|
delete bi;
|
|
}
|
|
|
|
bool
|
|
LTAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history)
|
|
{
|
|
bool retval = predict(tid, branch_pc, true, bp_history);
|
|
|
|
DPRINTF(LTage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval);
|
|
updateHistories(tid, branch_pc, retval, bp_history);
|
|
assert(threadHistory[tid].gHist ==
|
|
&threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
|
|
|
|
return retval;
|
|
}
|
|
|
|
void
|
|
LTAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history)
|
|
{
|
|
BranchInfo* bi = (BranchInfo*) bp_history;
|
|
ThreadHistory& tHist = threadHistory[tid];
|
|
DPRINTF(LTage, "BTB miss resets prediction: %lx\n", branch_pc);
|
|
assert(tHist.gHist == &tHist.globalHistory[tHist.ptGhist]);
|
|
tHist.gHist[0] = 0;
|
|
for (int i = 1; i <= nHistoryTables; i++) {
|
|
tHist.computeIndices[i].comp = bi->ci[i];
|
|
tHist.computeTags[0][i].comp = bi->ct0[i];
|
|
tHist.computeTags[1][i].comp = bi->ct1[i];
|
|
tHist.computeIndices[i].update(tHist.gHist);
|
|
tHist.computeTags[0][i].update(tHist.gHist);
|
|
tHist.computeTags[1][i].update(tHist.gHist);
|
|
}
|
|
}
|
|
|
|
void
|
|
LTAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
|
|
{
|
|
DPRINTF(LTage, "UnConditionalBranch: %lx\n", br_pc);
|
|
predict(tid, br_pc, false, bp_history);
|
|
updateHistories(tid, br_pc, true, bp_history);
|
|
assert(threadHistory[tid].gHist ==
|
|
&threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
|
|
}
|
|
|
|
LTAGE*
|
|
LTAGEParams::create()
|
|
{
|
|
return new LTAGE(this);
|
|
}
|