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.

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45#include "base/random.hh"
46#include "base/trace.hh"
47#include "debug/Fetch.hh"
48#include "debug/LTage.hh"
49
50LTAGE::LTAGE(const LTAGEParams *params)
51 : BPredUnit(params),
52 logSizeBiMP(params->logSizeBiMP),
53 logRatioBiModalHystEntries(params->logRatioBiModalHystEntries),
54 logSizeTagTables(params->logSizeTagTables),
55 logSizeLoopPred(params->logSizeLoopPred),
56 nHistoryTables(params->nHistoryTables),
57 tagTableCounterBits(params->tagTableCounterBits),
58 histBufferSize(params->histBufferSize),
59 minHist(params->minHist),
60 maxHist(params->maxHist),
61 minTagWidth(params->minTagWidth),

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118 history.computeIndices[i].origLength, tagWidths[i]);
119 history.computeTags[1][i].init(
120 history.computeIndices[i].origLength, tagWidths[i] - 1);
121 DPRINTF(LTage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n",
122 histLengths[i], tagTableSizes[i], tagWidths[i]);
123 }
124 }
125
126 const uint64_t bimodalTableSize = ULL(1) << logSizeBiMP;
127 btablePrediction.resize(bimodalTableSize, false);
128 btableHysteresis.resize(bimodalTableSize >> logRatioBiModalHystEntries,
129 true);
130
131 ltable = new LoopEntry[ULL(1) << logSizeLoopPred];
132 gtable = new TageEntry*[nHistoryTables + 1];
133 for (int i = 1; i <= nHistoryTables; i++) {
134 gtable[i] = new TageEntry[1<<(tagTableSizes[i])];
135 }
136
137 tableIndices = new int [nHistoryTables+1];
138 tableTags = new int [nHistoryTables+1];

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211 ctr--;
212 }
213}
214
215// Bimodal prediction
216bool
217LTAGE::getBimodePred(Addr pc, BranchInfo* bi) const
218{
219 return btablePrediction[bi->bimodalIndex];
220}
221
222
223// Update the bimodal predictor: a hysteresis bit is shared among N prediction
224// bits (N = 2 ^ logRatioBiModalHystEntries)
225void
226LTAGE::baseUpdate(Addr pc, bool taken, BranchInfo* bi)
227{
228 int inter = (btablePrediction[bi->bimodalIndex] << 1)
229 + btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries];
230 if (taken) {
231 if (inter < 3)
232 inter++;
233 } else if (inter > 0) {
234 inter--;
235 }
236 const bool pred = inter >> 1;
237 const bool hyst = inter & 1;
238 btablePrediction[bi->bimodalIndex] = pred;
239 btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries] = hyst;
240 DPRINTF(LTage, "Updating branch %lx, pred:%d, hyst:%d\n", pc, pred, hyst);
241}
242
243
244//loop prediction: only used if high confidence
245bool
246LTAGE::getLoop(Addr pc, BranchInfo* bi) const
247{
248 bi->loopHit = -1;

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