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 * Authors: Vignyan Reddy, Dibakar Gope and Arthur Perais,
34 * from André Seznec's code.
35 */
36
37/* @file
38 * Implementation of a L-TAGE branch predictor
39 */
40
41#include "cpu/pred/ltage.hh"
42
43#include "base/intmath.hh"
44#include "base/logging.hh"
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),
| 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 * Authors: Vignyan Reddy, Dibakar Gope and Arthur Perais,
34 * from André Seznec's code.
35 */
36
37/* @file
38 * Implementation of a L-TAGE branch predictor
39 */
40
41#include "cpu/pred/ltage.hh"
42
43#include "base/intmath.hh"
44#include "base/logging.hh"
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),
| 52 logRatioBiModalHystEntries(params->logRatioBiModalHystEntries),
|
54 logSizeTagTables(params->logSizeTagTables),
| |
55 logSizeLoopPred(params->logSizeLoopPred),
56 nHistoryTables(params->nHistoryTables),
57 tagTableCounterBits(params->tagTableCounterBits),
58 tagTableUBits(params->tagTableUBits),
59 histBufferSize(params->histBufferSize),
60 minHist(params->minHist),
61 maxHist(params->maxHist),
| 53 logSizeLoopPred(params->logSizeLoopPred),
54 nHistoryTables(params->nHistoryTables),
55 tagTableCounterBits(params->tagTableCounterBits),
56 tagTableUBits(params->tagTableUBits),
57 histBufferSize(params->histBufferSize),
58 minHist(params->minHist),
59 maxHist(params->maxHist),
|
62 minTagWidth(params->minTagWidth),
| 60 pathHistBits(params->pathHistBits),
|
63 loopTableAgeBits(params->loopTableAgeBits),
64 loopTableConfidenceBits(params->loopTableConfidenceBits),
65 loopTableTagBits(params->loopTableTagBits),
66 loopTableIterBits(params->loopTableIterBits),
| 61 loopTableAgeBits(params->loopTableAgeBits),
62 loopTableConfidenceBits(params->loopTableConfidenceBits),
63 loopTableTagBits(params->loopTableTagBits),
64 loopTableIterBits(params->loopTableIterBits),
|
| 65 logLoopTableAssoc(params->logLoopTableAssoc),
|
67 confidenceThreshold((1 << loopTableConfidenceBits) - 1),
68 loopTagMask((1 << loopTableTagBits) - 1),
69 loopNumIterMask((1 << loopTableIterBits) - 1),
| 66 confidenceThreshold((1 << loopTableConfidenceBits) - 1),
67 loopTagMask((1 << loopTableTagBits) - 1),
68 loopNumIterMask((1 << loopTableIterBits) - 1),
|
70 threadHistory(params->numThreads)
| 69 tagTableTagWidths(params->tagTableTagWidths),
70 logTagTableSizes(params->logTagTableSizes),
71 threadHistory(params->numThreads),
72 logUResetPeriod(params->logUResetPeriod),
73 useAltOnNaBits(params->useAltOnNaBits),
74 withLoopBits(params->withLoopBits)
|
71{
72 // Current method for periodically resetting the u counter bits only
73 // works for 1 or 2 bits
74 // Also make sure that it is not 0
75 assert(tagTableUBits <= 2 && (tagTableUBits > 0));
76
77 // we use uint16_t type for these vales, so they cannot be more than
78 // 16 bits
79 assert(loopTableTagBits <= 16);
80 assert(loopTableIterBits <= 16);
81
| 75{
76 // Current method for periodically resetting the u counter bits only
77 // works for 1 or 2 bits
78 // Also make sure that it is not 0
79 assert(tagTableUBits <= 2 && (tagTableUBits > 0));
80
81 // we use uint16_t type for these vales, so they cannot be more than
82 // 16 bits
83 assert(loopTableTagBits <= 16);
84 assert(loopTableIterBits <= 16);
85
|
| 86 assert(logSizeLoopPred >= logLoopTableAssoc);
87
88 // we use int type for the path history, so it cannot be more than
89 // its size
90 assert(pathHistBits <= (sizeof(int)*8));
91
92 // initialize the counter to half of the period
93 assert(logUResetPeriod != 0);
94 tCounter = ULL(1) << (logUResetPeriod - 1);
95
|
82 assert(params->histBufferSize > params->maxHist * 2);
83 useAltPredForNewlyAllocated = 0;
| 96 assert(params->histBufferSize > params->maxHist * 2);
97 useAltPredForNewlyAllocated = 0;
|
84 logTick = 19;
85 tCounter = ULL(1) << (logTick - 1);
| |
86
87 for (auto& history : threadHistory) {
88 history.pathHist = 0;
89 history.globalHistory = new uint8_t[histBufferSize];
90 history.gHist = history.globalHistory;
91 memset(history.gHist, 0, histBufferSize);
92 history.ptGhist = 0;
93 }
94
95 histLengths = new int [nHistoryTables+1];
96 histLengths[1] = minHist;
97 histLengths[nHistoryTables] = maxHist;
98
99 for (int i = 2; i <= nHistoryTables; i++) {
100 histLengths[i] = (int) (((double) minHist *
101 pow ((double) (maxHist) / (double) minHist,
102 (double) (i - 1) / (double) ((nHistoryTables- 1))))
103 + 0.5);
104 }
105
| 98
99 for (auto& history : threadHistory) {
100 history.pathHist = 0;
101 history.globalHistory = new uint8_t[histBufferSize];
102 history.gHist = history.globalHistory;
103 memset(history.gHist, 0, histBufferSize);
104 history.ptGhist = 0;
105 }
106
107 histLengths = new int [nHistoryTables+1];
108 histLengths[1] = minHist;
109 histLengths[nHistoryTables] = maxHist;
110
111 for (int i = 2; i <= nHistoryTables; i++) {
112 histLengths[i] = (int) (((double) minHist *
113 pow ((double) (maxHist) / (double) minHist,
114 (double) (i - 1) / (double) ((nHistoryTables- 1))))
115 + 0.5);
116 }
117
|
106 tagWidths[1] = minTagWidth;
107 tagWidths[2] = minTagWidth;
108 tagWidths[3] = minTagWidth + 1;
109 tagWidths[4] = minTagWidth + 1;
110 tagWidths[5] = minTagWidth + 2;
111 tagWidths[6] = minTagWidth + 3;
112 tagWidths[7] = minTagWidth + 4;
113 tagWidths[8] = minTagWidth + 5;
114 tagWidths[9] = minTagWidth + 5;
115 tagWidths[10] = minTagWidth + 6;
116 tagWidths[11] = minTagWidth + 7;
117 tagWidths[12] = minTagWidth + 8;
| 118 assert(tagTableTagWidths.size() == (nHistoryTables+1));
119 assert(logTagTableSizes.size() == (nHistoryTables+1));
|
118
| 120
|
119 for (int i = 1; i <= 2; i++)
120 tagTableSizes[i] = logSizeTagTables - 1;
121 for (int i = 3; i <= 6; i++)
122 tagTableSizes[i] = logSizeTagTables;
123 for (int i = 7; i <= 10; i++)
124 tagTableSizes[i] = logSizeTagTables - 1;
125 for (int i = 11; i <= 12; i++)
126 tagTableSizes[i] = logSizeTagTables - 2;
| 121 // First entry is for the Bimodal table and it is untagged in this
122 // implementation
123 assert(tagTableTagWidths[0] == 0);
|
127
128 for (auto& history : threadHistory) {
129 history.computeIndices = new FoldedHistory[nHistoryTables+1];
130 history.computeTags[0] = new FoldedHistory[nHistoryTables+1];
131 history.computeTags[1] = new FoldedHistory[nHistoryTables+1];
132
133 for (int i = 1; i <= nHistoryTables; i++) {
| 124
125 for (auto& history : threadHistory) {
126 history.computeIndices = new FoldedHistory[nHistoryTables+1];
127 history.computeTags[0] = new FoldedHistory[nHistoryTables+1];
128 history.computeTags[1] = new FoldedHistory[nHistoryTables+1];
129
130 for (int i = 1; i <= nHistoryTables; i++) {
|
134 history.computeIndices[i].init(histLengths[i], (tagTableSizes[i]));
| 131 history.computeIndices[i].init(
132 histLengths[i], (logTagTableSizes[i]));
|
135 history.computeTags[0][i].init(
| 133 history.computeTags[0][i].init(
|
136 history.computeIndices[i].origLength, tagWidths[i]);
| 134 history.computeIndices[i].origLength, tagTableTagWidths[i]);
|
137 history.computeTags[1][i].init(
| 135 history.computeTags[1][i].init(
|
138 history.computeIndices[i].origLength, tagWidths[i] - 1);
| 136 history.computeIndices[i].origLength, tagTableTagWidths[i]-1);
|
139 DPRINTF(LTage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n",
| 137 DPRINTF(LTage, "HistLength:%d, TTSize:%d, TTTWidth:%d\n",
|
140 histLengths[i], tagTableSizes[i], tagWidths[i]);
| 138 histLengths[i], logTagTableSizes[i], tagTableTagWidths[i]);
|
141 }
142 }
143
| 139 }
140 }
141
|
144 const uint64_t bimodalTableSize = ULL(1) << logSizeBiMP;
| 142 const uint64_t bimodalTableSize = ULL(1) << logTagTableSizes[0];
|
145 btablePrediction.resize(bimodalTableSize, false);
146 btableHysteresis.resize(bimodalTableSize >> logRatioBiModalHystEntries,
147 true);
148
149 ltable = new LoopEntry[ULL(1) << logSizeLoopPred];
150 gtable = new TageEntry*[nHistoryTables + 1];
151 for (int i = 1; i <= nHistoryTables; i++) {
| 143 btablePrediction.resize(bimodalTableSize, false);
144 btableHysteresis.resize(bimodalTableSize >> logRatioBiModalHystEntries,
145 true);
146
147 ltable = new LoopEntry[ULL(1) << logSizeLoopPred];
148 gtable = new TageEntry*[nHistoryTables + 1];
149 for (int i = 1; i <= nHistoryTables; i++) {
|
152 gtable[i] = new TageEntry[1<<(tagTableSizes[i])];
| 150 gtable[i] = new TageEntry[1<<(logTagTableSizes[i])];
|
153 }
154
155 tableIndices = new int [nHistoryTables+1];
156 tableTags = new int [nHistoryTables+1];
157
158 loopUseCounter = 0;
159}
160
161int
162LTAGE::bindex(Addr pc_in) const
163{
| 151 }
152
153 tableIndices = new int [nHistoryTables+1];
154 tableTags = new int [nHistoryTables+1];
155
156 loopUseCounter = 0;
157}
158
159int
160LTAGE::bindex(Addr pc_in) const
161{
|
164 return ((pc_in >> instShiftAmt) & ((ULL(1) << (logSizeBiMP)) - 1));
| 162 return ((pc_in >> instShiftAmt) & ((ULL(1) << (logTagTableSizes[0])) - 1));
|
165}
166
167int
168LTAGE::lindex(Addr pc_in) const
169{
| 163}
164
165int
166LTAGE::lindex(Addr pc_in) const
167{
|
170 return (((pc_in >> instShiftAmt) &
171 ((ULL(1) << (logSizeLoopPred - 2)) - 1)) << 2);
| 168 // The loop table is implemented as a linear table
169 // If associativity is N (N being 1 << logLoopTableAssoc),
170 // the first N entries are for set 0, the next N entries are for set 1,
171 // and so on.
172 // Thus, this function calculates the set and then it gets left shifted
173 // by logLoopTableAssoc in order to return the index of the first of the
174 // N entries of the set
175 Addr mask = (ULL(1) << (logSizeLoopPred - logLoopTableAssoc)) - 1;
176 return (((pc_in >> instShiftAmt) & mask) << logLoopTableAssoc);
|
172}
173
174int
175LTAGE::F(int A, int size, int bank) const
176{
177 int A1, A2;
178
179 A = A & ((ULL(1) << size) - 1);
| 177}
178
179int
180LTAGE::F(int A, int size, int bank) const
181{
182 int A1, A2;
183
184 A = A & ((ULL(1) << size) - 1);
|
180 A1 = (A & ((ULL(1) << tagTableSizes[bank]) - 1));
181 A2 = (A >> tagTableSizes[bank]);
182 A2 = ((A2 << bank) & ((ULL(1) << tagTableSizes[bank]) - 1))
183 + (A2 >> (tagTableSizes[bank] - bank));
| 185 A1 = (A & ((ULL(1) << logTagTableSizes[bank]) - 1));
186 A2 = (A >> logTagTableSizes[bank]);
187 A2 = ((A2 << bank) & ((ULL(1) << logTagTableSizes[bank]) - 1))
188 + (A2 >> (logTagTableSizes[bank] - bank));
|
184 A = A1 ^ A2;
| 189 A = A1 ^ A2;
|
185 A = ((A << bank) & ((ULL(1) << tagTableSizes[bank]) - 1))
186 + (A >> (tagTableSizes[bank] - bank));
| 190 A = ((A << bank) & ((ULL(1) << logTagTableSizes[bank]) - 1))
191 + (A >> (logTagTableSizes[bank] - bank));
|
187 return (A);
188}
189
190
191// gindex computes a full hash of pc, ghist and pathHist
192int
193LTAGE::gindex(ThreadID tid, Addr pc, int bank) const
194{
195 int index;
| 192 return (A);
193}
194
195
196// gindex computes a full hash of pc, ghist and pathHist
197int
198LTAGE::gindex(ThreadID tid, Addr pc, int bank) const
199{
200 int index;
|
196 int hlen = (histLengths[bank] > 16) ? 16 : histLengths[bank];
| 201 int hlen = (histLengths[bank] > pathHistBits) ? pathHistBits :
202 histLengths[bank];
203 const Addr shiftedPc = pc >> instShiftAmt;
|
197 index =
| 204 index =
|
198 (pc >> instShiftAmt) ^
199 ((pc >> instShiftAmt) >> ((int) abs(tagTableSizes[bank] - bank) + 1)) ^
| 205 shiftedPc ^
206 (shiftedPc >> ((int) abs(logTagTableSizes[bank] - bank) + 1)) ^
|
200 threadHistory[tid].computeIndices[bank].comp ^
201 F(threadHistory[tid].pathHist, hlen, bank);
202
| 207 threadHistory[tid].computeIndices[bank].comp ^
208 F(threadHistory[tid].pathHist, hlen, bank);
209
|
203 return (index & ((ULL(1) << (tagTableSizes[bank])) - 1));
| 210 return (index & ((ULL(1) << (logTagTableSizes[bank])) - 1));
|
204}
205
206
207// Tag computation
208uint16_t
209LTAGE::gtag(ThreadID tid, Addr pc, int bank) const
210{
211 int tag = (pc >> instShiftAmt) ^
212 threadHistory[tid].computeTags[0][bank].comp ^
213 (threadHistory[tid].computeTags[1][bank].comp << 1);
214
| 211}
212
213
214// Tag computation
215uint16_t
216LTAGE::gtag(ThreadID tid, Addr pc, int bank) const
217{
218 int tag = (pc >> instShiftAmt) ^
219 threadHistory[tid].computeTags[0][bank].comp ^
220 (threadHistory[tid].computeTags[1][bank].comp << 1);
221
|
215 return (tag & ((ULL(1) << tagWidths[bank]) - 1));
| 222 return (tag & ((ULL(1) << tagTableTagWidths[bank]) - 1));
|
216}
217
218
219// Up-down saturating counter
220void
221LTAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits)
222{
223 assert(nbits <= sizeof(int8_t) << 3);
224 if (taken) {
225 if (ctr < ((1 << (nbits - 1)) - 1))
226 ctr++;
227 } else {
228 if (ctr > -(1 << (nbits - 1)))
229 ctr--;
230 }
231}
232
233// Up-down unsigned saturating counter
234void
235LTAGE::unsignedCtrUpdate(uint8_t & ctr, bool up, unsigned nbits)
236{
237 assert(nbits <= sizeof(uint8_t) << 3);
238 if (up) {
239 if (ctr < ((1 << nbits) - 1))
240 ctr++;
241 } else {
242 if (ctr)
243 ctr--;
244 }
245}
246
247// Bimodal prediction
248bool
249LTAGE::getBimodePred(Addr pc, BranchInfo* bi) const
250{
251 return btablePrediction[bi->bimodalIndex];
252}
253
254
255// Update the bimodal predictor: a hysteresis bit is shared among N prediction
256// bits (N = 2 ^ logRatioBiModalHystEntries)
257void
258LTAGE::baseUpdate(Addr pc, bool taken, BranchInfo* bi)
259{
260 int inter = (btablePrediction[bi->bimodalIndex] << 1)
261 + btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries];
262 if (taken) {
263 if (inter < 3)
264 inter++;
265 } else if (inter > 0) {
266 inter--;
267 }
268 const bool pred = inter >> 1;
269 const bool hyst = inter & 1;
270 btablePrediction[bi->bimodalIndex] = pred;
271 btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries] = hyst;
272 DPRINTF(LTage, "Updating branch %lx, pred:%d, hyst:%d\n", pc, pred, hyst);
273}
274
275
276//loop prediction: only used if high confidence
277bool
278LTAGE::getLoop(Addr pc, BranchInfo* bi) const
279{
280 bi->loopHit = -1;
281 bi->loopPredValid = false;
282 bi->loopIndex = lindex(pc);
| 223}
224
225
226// Up-down saturating counter
227void
228LTAGE::ctrUpdate(int8_t & ctr, bool taken, int nbits)
229{
230 assert(nbits <= sizeof(int8_t) << 3);
231 if (taken) {
232 if (ctr < ((1 << (nbits - 1)) - 1))
233 ctr++;
234 } else {
235 if (ctr > -(1 << (nbits - 1)))
236 ctr--;
237 }
238}
239
240// Up-down unsigned saturating counter
241void
242LTAGE::unsignedCtrUpdate(uint8_t & ctr, bool up, unsigned nbits)
243{
244 assert(nbits <= sizeof(uint8_t) << 3);
245 if (up) {
246 if (ctr < ((1 << nbits) - 1))
247 ctr++;
248 } else {
249 if (ctr)
250 ctr--;
251 }
252}
253
254// Bimodal prediction
255bool
256LTAGE::getBimodePred(Addr pc, BranchInfo* bi) const
257{
258 return btablePrediction[bi->bimodalIndex];
259}
260
261
262// Update the bimodal predictor: a hysteresis bit is shared among N prediction
263// bits (N = 2 ^ logRatioBiModalHystEntries)
264void
265LTAGE::baseUpdate(Addr pc, bool taken, BranchInfo* bi)
266{
267 int inter = (btablePrediction[bi->bimodalIndex] << 1)
268 + btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries];
269 if (taken) {
270 if (inter < 3)
271 inter++;
272 } else if (inter > 0) {
273 inter--;
274 }
275 const bool pred = inter >> 1;
276 const bool hyst = inter & 1;
277 btablePrediction[bi->bimodalIndex] = pred;
278 btableHysteresis[bi->bimodalIndex >> logRatioBiModalHystEntries] = hyst;
279 DPRINTF(LTage, "Updating branch %lx, pred:%d, hyst:%d\n", pc, pred, hyst);
280}
281
282
283//loop prediction: only used if high confidence
284bool
285LTAGE::getLoop(Addr pc, BranchInfo* bi) const
286{
287 bi->loopHit = -1;
288 bi->loopPredValid = false;
289 bi->loopIndex = lindex(pc);
|
283 bi->loopTag = ((pc) >> (instShiftAmt + logSizeLoopPred - 2)) & loopTagMask;
| 290 unsigned pcShift = instShiftAmt + logSizeLoopPred - logLoopTableAssoc;
291 bi->loopTag = ((pc) >> pcShift) & loopTagMask;
|
284
| 292
|
285 for (int i = 0; i < 4; i++) {
| 293 for (int i = 0; i < (1 << logLoopTableAssoc); i++) {
|
286 if (ltable[bi->loopIndex + i].tag == bi->loopTag) {
287 bi->loopHit = i;
288 bi->loopPredValid =
289 ltable[bi->loopIndex + i].confidence == confidenceThreshold;
290 bi->currentIter = ltable[bi->loopIndex + i].currentIterSpec;
291 if (ltable[bi->loopIndex + i].currentIterSpec + 1 ==
292 ltable[bi->loopIndex + i].numIter) {
293 return !(ltable[bi->loopIndex + i].dir);
294 }else {
295 return (ltable[bi->loopIndex + i].dir);
296 }
297 }
298 }
299 return false;
300}
301
302void
303LTAGE::specLoopUpdate(Addr pc, bool taken, BranchInfo* bi)
304{
305 if (bi->loopHit>=0) {
306 int index = lindex(pc);
307 if (taken != ltable[index].dir) {
308 ltable[index].currentIterSpec = 0;
309 } else {
310 ltable[index].currentIterSpec =
311 (ltable[index].currentIterSpec + 1) & loopNumIterMask;
312 }
313 }
314}
315
316void
317LTAGE::loopUpdate(Addr pc, bool taken, BranchInfo* bi)
318{
319 int idx = bi->loopIndex + bi->loopHit;
320 if (bi->loopHit >= 0) {
321 //already a hit
322 if (bi->loopPredValid) {
323 if (taken != bi->loopPred) {
324 // free the entry
325 ltable[idx].numIter = 0;
326 ltable[idx].age = 0;
327 ltable[idx].confidence = 0;
328 ltable[idx].currentIter = 0;
329 return;
330 } else if (bi->loopPred != bi->tagePred) {
331 DPRINTF(LTage, "Loop Prediction success:%lx\n",pc);
332 unsignedCtrUpdate(ltable[idx].age, true, loopTableAgeBits);
333 }
334 }
335
336 ltable[idx].currentIter =
337 (ltable[idx].currentIter + 1) & loopNumIterMask;
338 if (ltable[idx].currentIter > ltable[idx].numIter) {
339 ltable[idx].confidence = 0;
340 if (ltable[idx].numIter != 0) {
341 // free the entry
342 ltable[idx].numIter = 0;
343 ltable[idx].age = 0;
344 ltable[idx].confidence = 0;
345 }
346 }
347
348 if (taken != ltable[idx].dir) {
349 if (ltable[idx].currentIter == ltable[idx].numIter) {
350 DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc);
351
352 unsignedCtrUpdate(ltable[idx].confidence, true,
353 loopTableConfidenceBits);
354 //just do not predict when the loop count is 1 or 2
355 if (ltable[idx].numIter < 3) {
356 // free the entry
357 ltable[idx].dir = taken;
358 ltable[idx].numIter = 0;
359 ltable[idx].age = 0;
360 ltable[idx].confidence = 0;
361 }
362 } else {
363 DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc);
364 if (ltable[idx].numIter == 0) {
365 // first complete nest;
366 ltable[idx].confidence = 0;
367 ltable[idx].numIter = ltable[idx].currentIter;
368 } else {
369 //not the same number of iterations as last time: free the
370 //entry
371 ltable[idx].numIter = 0;
372 ltable[idx].age = 0;
373 ltable[idx].confidence = 0;
374 }
375 }
376 ltable[idx].currentIter = 0;
377 }
378
379 } else if (taken) {
380 //try to allocate an entry on taken branch
381 int nrand = random_mt.random<int>();
| 294 if (ltable[bi->loopIndex + i].tag == bi->loopTag) {
295 bi->loopHit = i;
296 bi->loopPredValid =
297 ltable[bi->loopIndex + i].confidence == confidenceThreshold;
298 bi->currentIter = ltable[bi->loopIndex + i].currentIterSpec;
299 if (ltable[bi->loopIndex + i].currentIterSpec + 1 ==
300 ltable[bi->loopIndex + i].numIter) {
301 return !(ltable[bi->loopIndex + i].dir);
302 }else {
303 return (ltable[bi->loopIndex + i].dir);
304 }
305 }
306 }
307 return false;
308}
309
310void
311LTAGE::specLoopUpdate(Addr pc, bool taken, BranchInfo* bi)
312{
313 if (bi->loopHit>=0) {
314 int index = lindex(pc);
315 if (taken != ltable[index].dir) {
316 ltable[index].currentIterSpec = 0;
317 } else {
318 ltable[index].currentIterSpec =
319 (ltable[index].currentIterSpec + 1) & loopNumIterMask;
320 }
321 }
322}
323
324void
325LTAGE::loopUpdate(Addr pc, bool taken, BranchInfo* bi)
326{
327 int idx = bi->loopIndex + bi->loopHit;
328 if (bi->loopHit >= 0) {
329 //already a hit
330 if (bi->loopPredValid) {
331 if (taken != bi->loopPred) {
332 // free the entry
333 ltable[idx].numIter = 0;
334 ltable[idx].age = 0;
335 ltable[idx].confidence = 0;
336 ltable[idx].currentIter = 0;
337 return;
338 } else if (bi->loopPred != bi->tagePred) {
339 DPRINTF(LTage, "Loop Prediction success:%lx\n",pc);
340 unsignedCtrUpdate(ltable[idx].age, true, loopTableAgeBits);
341 }
342 }
343
344 ltable[idx].currentIter =
345 (ltable[idx].currentIter + 1) & loopNumIterMask;
346 if (ltable[idx].currentIter > ltable[idx].numIter) {
347 ltable[idx].confidence = 0;
348 if (ltable[idx].numIter != 0) {
349 // free the entry
350 ltable[idx].numIter = 0;
351 ltable[idx].age = 0;
352 ltable[idx].confidence = 0;
353 }
354 }
355
356 if (taken != ltable[idx].dir) {
357 if (ltable[idx].currentIter == ltable[idx].numIter) {
358 DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc);
359
360 unsignedCtrUpdate(ltable[idx].confidence, true,
361 loopTableConfidenceBits);
362 //just do not predict when the loop count is 1 or 2
363 if (ltable[idx].numIter < 3) {
364 // free the entry
365 ltable[idx].dir = taken;
366 ltable[idx].numIter = 0;
367 ltable[idx].age = 0;
368 ltable[idx].confidence = 0;
369 }
370 } else {
371 DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc);
372 if (ltable[idx].numIter == 0) {
373 // first complete nest;
374 ltable[idx].confidence = 0;
375 ltable[idx].numIter = ltable[idx].currentIter;
376 } else {
377 //not the same number of iterations as last time: free the
378 //entry
379 ltable[idx].numIter = 0;
380 ltable[idx].age = 0;
381 ltable[idx].confidence = 0;
382 }
383 }
384 ltable[idx].currentIter = 0;
385 }
386
387 } else if (taken) {
388 //try to allocate an entry on taken branch
389 int nrand = random_mt.random<int>();
|
382 for (int i = 0; i < 4; i++) {
383 int loop_hit = (nrand + i) & 3;
| 390 for (int i = 0; i < (1 << logLoopTableAssoc); i++) {
391 int loop_hit = (nrand + i) & ((1 << logLoopTableAssoc) - 1);
|
384 idx = bi->loopIndex + loop_hit;
385 if (ltable[idx].age == 0) {
386 DPRINTF(LTage, "Allocating loop pred entry for branch %lx\n",
387 pc);
388 ltable[idx].dir = !taken;
389 ltable[idx].tag = bi->loopTag;
390 ltable[idx].numIter = 0;
391 ltable[idx].age = (1 << loopTableAgeBits) - 1;
392 ltable[idx].confidence = 0;
393 ltable[idx].currentIter = 1;
394 break;
395
396 }
397 else
398 ltable[idx].age--;
399 }
400 }
401
402}
403
404// shifting the global history: we manage the history in a big table in order
405// to reduce simulation time
406void
407LTAGE::updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &pt)
408{
409 if (pt == 0) {
410 DPRINTF(LTage, "Rolling over the histories\n");
411 // Copy beginning of globalHistoryBuffer to end, such that
412 // the last maxHist outcomes are still reachable
413 // through pt[0 .. maxHist - 1].
414 for (int i = 0; i < maxHist; i++)
415 tab[histBufferSize - maxHist + i] = tab[i];
416 pt = histBufferSize - maxHist;
417 h = &tab[pt];
418 }
419 pt--;
420 h--;
421 h[0] = (dir) ? 1 : 0;
422}
423
424// Get GHR for hashing indirect predictor
425// Build history backwards from pointer in
426// bp_history.
427unsigned
428LTAGE::getGHR(ThreadID tid, void *bp_history) const
429{
430 BranchInfo* bi = static_cast<BranchInfo*>(bp_history);
431 unsigned val = 0;
432 for (unsigned i = 0; i < 32; i++) {
433 // Make sure we don't go out of bounds
434 int gh_offset = bi->ptGhist + i;
435 assert(&(threadHistory[tid].globalHistory[gh_offset]) <
436 threadHistory[tid].globalHistory + histBufferSize);
437 val |= ((threadHistory[tid].globalHistory[gh_offset] & 0x1) << i);
438 }
439
440 return val;
441}
442
443//prediction
444bool
445LTAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
446{
447 BranchInfo *bi = new BranchInfo(nHistoryTables+1);
448 b = (void*)(bi);
449 Addr pc = branch_pc;
450 bool pred_taken = true;
451 bi->loopHit = -1;
452
453 if (cond_branch) {
454 // TAGE prediction
455
456 // computes the table addresses and the partial tags
457 for (int i = 1; i <= nHistoryTables; i++) {
458 tableIndices[i] = gindex(tid, pc, i);
459 bi->tableIndices[i] = tableIndices[i];
460 tableTags[i] = gtag(tid, pc, i);
461 bi->tableTags[i] = tableTags[i];
462 }
463
464 bi->bimodalIndex = bindex(pc);
465
466 bi->hitBank = 0;
467 bi->altBank = 0;
468 //Look for the bank with longest matching history
469 for (int i = nHistoryTables; i > 0; i--) {
470 if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
471 bi->hitBank = i;
472 bi->hitBankIndex = tableIndices[bi->hitBank];
473 break;
474 }
475 }
476 //Look for the alternate bank
477 for (int i = bi->hitBank - 1; i > 0; i--) {
478 if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
479 bi->altBank = i;
480 bi->altBankIndex = tableIndices[bi->altBank];
481 break;
482 }
483 }
484 //computes the prediction and the alternate prediction
485 if (bi->hitBank > 0) {
486 if (bi->altBank > 0) {
487 bi->altTaken =
488 gtable[bi->altBank][tableIndices[bi->altBank]].ctr >= 0;
489 }else {
490 bi->altTaken = getBimodePred(pc, bi);
491 }
492
493 bi->longestMatchPred =
494 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr >= 0;
495 bi->pseudoNewAlloc =
496 abs(2 * gtable[bi->hitBank][bi->hitBankIndex].ctr + 1) <= 1;
497
498 //if the entry is recognized as a newly allocated entry and
499 //useAltPredForNewlyAllocated is positive use the alternate
500 //prediction
501 if ((useAltPredForNewlyAllocated < 0)
502 || abs(2 *
503 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1)
504 bi->tagePred = bi->longestMatchPred;
505 else
506 bi->tagePred = bi->altTaken;
507 } else {
508 bi->altTaken = getBimodePred(pc, bi);
509 bi->tagePred = bi->altTaken;
510 bi->longestMatchPred = bi->altTaken;
511 }
512 //end TAGE prediction
513
514 bi->loopPred = getLoop(pc, bi); // loop prediction
515
516 pred_taken = (((loopUseCounter >= 0) && bi->loopPredValid)) ?
517 (bi->loopPred): (bi->tagePred);
518 DPRINTF(LTage, "Predict for %lx: taken?:%d, loopTaken?:%d, "
519 "loopValid?:%d, loopUseCounter:%d, tagePred:%d, altPred:%d\n",
520 branch_pc, pred_taken, bi->loopPred, bi->loopPredValid,
521 loopUseCounter, bi->tagePred, bi->altTaken);
522 }
523 bi->branchPC = branch_pc;
524 bi->condBranch = cond_branch;
525 specLoopUpdate(branch_pc, pred_taken, bi);
526 return pred_taken;
527}
528
529// PREDICTOR UPDATE
530void
531LTAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
532 bool squashed)
533{
534 assert(bp_history);
535
536 BranchInfo *bi = static_cast<BranchInfo*>(bp_history);
537
538 if (squashed) {
539 // This restores the global history, then update it
540 // and recomputes the folded histories.
541 squash(tid, taken, bp_history);
542 return;
543 }
544
545 int nrand = random_mt.random<int>(0,3);
546 Addr pc = branch_pc;
547 if (bi->condBranch) {
548 DPRINTF(LTage, "Updating tables for branch:%lx; taken?:%d\n",
549 branch_pc, taken);
550 // first update the loop predictor
551 loopUpdate(pc, taken, bi);
552
553 if (bi->loopPredValid) {
554 if (bi->tagePred != bi->loopPred) {
| 392 idx = bi->loopIndex + loop_hit;
393 if (ltable[idx].age == 0) {
394 DPRINTF(LTage, "Allocating loop pred entry for branch %lx\n",
395 pc);
396 ltable[idx].dir = !taken;
397 ltable[idx].tag = bi->loopTag;
398 ltable[idx].numIter = 0;
399 ltable[idx].age = (1 << loopTableAgeBits) - 1;
400 ltable[idx].confidence = 0;
401 ltable[idx].currentIter = 1;
402 break;
403
404 }
405 else
406 ltable[idx].age--;
407 }
408 }
409
410}
411
412// shifting the global history: we manage the history in a big table in order
413// to reduce simulation time
414void
415LTAGE::updateGHist(uint8_t * &h, bool dir, uint8_t * tab, int &pt)
416{
417 if (pt == 0) {
418 DPRINTF(LTage, "Rolling over the histories\n");
419 // Copy beginning of globalHistoryBuffer to end, such that
420 // the last maxHist outcomes are still reachable
421 // through pt[0 .. maxHist - 1].
422 for (int i = 0; i < maxHist; i++)
423 tab[histBufferSize - maxHist + i] = tab[i];
424 pt = histBufferSize - maxHist;
425 h = &tab[pt];
426 }
427 pt--;
428 h--;
429 h[0] = (dir) ? 1 : 0;
430}
431
432// Get GHR for hashing indirect predictor
433// Build history backwards from pointer in
434// bp_history.
435unsigned
436LTAGE::getGHR(ThreadID tid, void *bp_history) const
437{
438 BranchInfo* bi = static_cast<BranchInfo*>(bp_history);
439 unsigned val = 0;
440 for (unsigned i = 0; i < 32; i++) {
441 // Make sure we don't go out of bounds
442 int gh_offset = bi->ptGhist + i;
443 assert(&(threadHistory[tid].globalHistory[gh_offset]) <
444 threadHistory[tid].globalHistory + histBufferSize);
445 val |= ((threadHistory[tid].globalHistory[gh_offset] & 0x1) << i);
446 }
447
448 return val;
449}
450
451//prediction
452bool
453LTAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
454{
455 BranchInfo *bi = new BranchInfo(nHistoryTables+1);
456 b = (void*)(bi);
457 Addr pc = branch_pc;
458 bool pred_taken = true;
459 bi->loopHit = -1;
460
461 if (cond_branch) {
462 // TAGE prediction
463
464 // computes the table addresses and the partial tags
465 for (int i = 1; i <= nHistoryTables; i++) {
466 tableIndices[i] = gindex(tid, pc, i);
467 bi->tableIndices[i] = tableIndices[i];
468 tableTags[i] = gtag(tid, pc, i);
469 bi->tableTags[i] = tableTags[i];
470 }
471
472 bi->bimodalIndex = bindex(pc);
473
474 bi->hitBank = 0;
475 bi->altBank = 0;
476 //Look for the bank with longest matching history
477 for (int i = nHistoryTables; i > 0; i--) {
478 if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
479 bi->hitBank = i;
480 bi->hitBankIndex = tableIndices[bi->hitBank];
481 break;
482 }
483 }
484 //Look for the alternate bank
485 for (int i = bi->hitBank - 1; i > 0; i--) {
486 if (gtable[i][tableIndices[i]].tag == tableTags[i]) {
487 bi->altBank = i;
488 bi->altBankIndex = tableIndices[bi->altBank];
489 break;
490 }
491 }
492 //computes the prediction and the alternate prediction
493 if (bi->hitBank > 0) {
494 if (bi->altBank > 0) {
495 bi->altTaken =
496 gtable[bi->altBank][tableIndices[bi->altBank]].ctr >= 0;
497 }else {
498 bi->altTaken = getBimodePred(pc, bi);
499 }
500
501 bi->longestMatchPred =
502 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr >= 0;
503 bi->pseudoNewAlloc =
504 abs(2 * gtable[bi->hitBank][bi->hitBankIndex].ctr + 1) <= 1;
505
506 //if the entry is recognized as a newly allocated entry and
507 //useAltPredForNewlyAllocated is positive use the alternate
508 //prediction
509 if ((useAltPredForNewlyAllocated < 0)
510 || abs(2 *
511 gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1)
512 bi->tagePred = bi->longestMatchPred;
513 else
514 bi->tagePred = bi->altTaken;
515 } else {
516 bi->altTaken = getBimodePred(pc, bi);
517 bi->tagePred = bi->altTaken;
518 bi->longestMatchPred = bi->altTaken;
519 }
520 //end TAGE prediction
521
522 bi->loopPred = getLoop(pc, bi); // loop prediction
523
524 pred_taken = (((loopUseCounter >= 0) && bi->loopPredValid)) ?
525 (bi->loopPred): (bi->tagePred);
526 DPRINTF(LTage, "Predict for %lx: taken?:%d, loopTaken?:%d, "
527 "loopValid?:%d, loopUseCounter:%d, tagePred:%d, altPred:%d\n",
528 branch_pc, pred_taken, bi->loopPred, bi->loopPredValid,
529 loopUseCounter, bi->tagePred, bi->altTaken);
530 }
531 bi->branchPC = branch_pc;
532 bi->condBranch = cond_branch;
533 specLoopUpdate(branch_pc, pred_taken, bi);
534 return pred_taken;
535}
536
537// PREDICTOR UPDATE
538void
539LTAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
540 bool squashed)
541{
542 assert(bp_history);
543
544 BranchInfo *bi = static_cast<BranchInfo*>(bp_history);
545
546 if (squashed) {
547 // This restores the global history, then update it
548 // and recomputes the folded histories.
549 squash(tid, taken, bp_history);
550 return;
551 }
552
553 int nrand = random_mt.random<int>(0,3);
554 Addr pc = branch_pc;
555 if (bi->condBranch) {
556 DPRINTF(LTage, "Updating tables for branch:%lx; taken?:%d\n",
557 branch_pc, taken);
558 // first update the loop predictor
559 loopUpdate(pc, taken, bi);
560
561 if (bi->loopPredValid) {
562 if (bi->tagePred != bi->loopPred) {
|
555 ctrUpdate(loopUseCounter, (bi->loopPred== taken), 7);
| 563 ctrUpdate(loopUseCounter,
564 (bi->loopPred == taken),
565 withLoopBits);
|
556 }
557 }
558
559 // TAGE UPDATE
560 // try to allocate a new entries only if prediction was wrong
561 bool longest_match_pred = false;
562 bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables);
563 if (bi->hitBank > 0) {
564 // Manage the selection between longest matching and alternate
565 // matching for "pseudo"-newly allocated longest matching entry
566 longest_match_pred = bi->longestMatchPred;
567 bool PseudoNewAlloc = bi->pseudoNewAlloc;
568 // an entry is considered as newly allocated if its prediction
569 // counter is weak
570 if (PseudoNewAlloc) {
571 if (longest_match_pred == taken) {
572 alloc = false;
573 }
574 // if it was delivering the correct prediction, no need to
575 // allocate new entry even if the overall prediction was false
576 if (longest_match_pred != bi->altTaken) {
577 ctrUpdate(useAltPredForNewlyAllocated,
| 566 }
567 }
568
569 // TAGE UPDATE
570 // try to allocate a new entries only if prediction was wrong
571 bool longest_match_pred = false;
572 bool alloc = (bi->tagePred != taken) && (bi->hitBank < nHistoryTables);
573 if (bi->hitBank > 0) {
574 // Manage the selection between longest matching and alternate
575 // matching for "pseudo"-newly allocated longest matching entry
576 longest_match_pred = bi->longestMatchPred;
577 bool PseudoNewAlloc = bi->pseudoNewAlloc;
578 // an entry is considered as newly allocated if its prediction
579 // counter is weak
580 if (PseudoNewAlloc) {
581 if (longest_match_pred == taken) {
582 alloc = false;
583 }
584 // if it was delivering the correct prediction, no need to
585 // allocate new entry even if the overall prediction was false
586 if (longest_match_pred != bi->altTaken) {
587 ctrUpdate(useAltPredForNewlyAllocated,
|
578 bi->altTaken == taken, 4);
| 588 bi->altTaken == taken, useAltOnNaBits);
|
579 }
580 }
581 }
582
583 if (alloc) {
584 // is there some "unuseful" entry to allocate
585 uint8_t min = 1;
586 for (int i = nHistoryTables; i > bi->hitBank; i--) {
587 if (gtable[i][bi->tableIndices[i]].u < min) {
588 min = gtable[i][bi->tableIndices[i]].u;
589 }
590 }
591
592 // we allocate an entry with a longer history
593 // to avoid ping-pong, we do not choose systematically the next
594 // entry, but among the 3 next entries
595 int Y = nrand &
596 ((ULL(1) << (nHistoryTables - bi->hitBank - 1)) - 1);
597 int X = bi->hitBank + 1;
598 if (Y & 1) {
599 X++;
600 if (Y & 2)
601 X++;
602 }
603 // No entry available, forces one to be available
604 if (min > 0) {
605 gtable[X][bi->tableIndices[X]].u = 0;
606 }
607
608
609 //Allocate only one entry
610 for (int i = X; i <= nHistoryTables; i++) {
611 if ((gtable[i][bi->tableIndices[i]].u == 0)) {
612 gtable[i][bi->tableIndices[i]].tag = bi->tableTags[i];
613 gtable[i][bi->tableIndices[i]].ctr = (taken) ? 0 : -1;
614 break;
615 }
616 }
617 }
618 //periodic reset of u: reset is not complete but bit by bit
619 tCounter++;
| 589 }
590 }
591 }
592
593 if (alloc) {
594 // is there some "unuseful" entry to allocate
595 uint8_t min = 1;
596 for (int i = nHistoryTables; i > bi->hitBank; i--) {
597 if (gtable[i][bi->tableIndices[i]].u < min) {
598 min = gtable[i][bi->tableIndices[i]].u;
599 }
600 }
601
602 // we allocate an entry with a longer history
603 // to avoid ping-pong, we do not choose systematically the next
604 // entry, but among the 3 next entries
605 int Y = nrand &
606 ((ULL(1) << (nHistoryTables - bi->hitBank - 1)) - 1);
607 int X = bi->hitBank + 1;
608 if (Y & 1) {
609 X++;
610 if (Y & 2)
611 X++;
612 }
613 // No entry available, forces one to be available
614 if (min > 0) {
615 gtable[X][bi->tableIndices[X]].u = 0;
616 }
617
618
619 //Allocate only one entry
620 for (int i = X; i <= nHistoryTables; i++) {
621 if ((gtable[i][bi->tableIndices[i]].u == 0)) {
622 gtable[i][bi->tableIndices[i]].tag = bi->tableTags[i];
623 gtable[i][bi->tableIndices[i]].ctr = (taken) ? 0 : -1;
624 break;
625 }
626 }
627 }
628 //periodic reset of u: reset is not complete but bit by bit
629 tCounter++;
|
620 if ((tCounter & ((ULL(1) << logTick) - 1)) == 0) {
| 630 if ((tCounter & ((ULL(1) << logUResetPeriod) - 1)) == 0) {
|
621 // reset least significant bit
622 // most significant bit becomes least significant bit
623 for (int i = 1; i <= nHistoryTables; i++) {
| 631 // reset least significant bit
632 // most significant bit becomes least significant bit
633 for (int i = 1; i <= nHistoryTables; i++) {
|
624 for (int j = 0; j < (ULL(1) << tagTableSizes[i]); j++) {
| 634 for (int j = 0; j < (ULL(1) << logTagTableSizes[i]); j++) {
|
625 gtable[i][j].u = gtable[i][j].u >> 1;
626 }
627 }
628 }
629
630 if (bi->hitBank > 0) {
631 DPRINTF(LTage, "Updating tag table entry (%d,%d) for branch %lx\n",
632 bi->hitBank, bi->hitBankIndex, branch_pc);
633 ctrUpdate(gtable[bi->hitBank][bi->hitBankIndex].ctr, taken,
634 tagTableCounterBits);
635 // if the provider entry is not certified to be useful also update
636 // the alternate prediction
637 if (gtable[bi->hitBank][bi->hitBankIndex].u == 0) {
638 if (bi->altBank > 0) {
639 ctrUpdate(gtable[bi->altBank][bi->altBankIndex].ctr, taken,
640 tagTableCounterBits);
641 DPRINTF(LTage, "Updating tag table entry (%d,%d) for"
642 " branch %lx\n", bi->hitBank, bi->hitBankIndex,
643 branch_pc);
644 }
645 if (bi->altBank == 0) {
646 baseUpdate(pc, taken, bi);
647 }
648 }
649
650 // update the u counter
651 if (bi->tagePred != bi->altTaken) {
652 unsignedCtrUpdate(gtable[bi->hitBank][bi->hitBankIndex].u,
653 bi->tagePred == taken, tagTableUBits);
654 }
655 } else {
656 baseUpdate(pc, taken, bi);
657 }
658
659 //END PREDICTOR UPDATE
660 }
661 if (!squashed) {
662 delete bi;
663 }
664}
665
666void
667LTAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b)
668{
669 BranchInfo* bi = (BranchInfo*)(b);
670 ThreadHistory& tHist = threadHistory[tid];
671 // UPDATE HISTORIES
672 bool pathbit = ((branch_pc >> instShiftAmt) & 1);
673 //on a squash, return pointers to this and recompute indices.
674 //update user history
675 updateGHist(tHist.gHist, taken, tHist.globalHistory, tHist.ptGhist);
676 tHist.pathHist = (tHist.pathHist << 1) + pathbit;
| 635 gtable[i][j].u = gtable[i][j].u >> 1;
636 }
637 }
638 }
639
640 if (bi->hitBank > 0) {
641 DPRINTF(LTage, "Updating tag table entry (%d,%d) for branch %lx\n",
642 bi->hitBank, bi->hitBankIndex, branch_pc);
643 ctrUpdate(gtable[bi->hitBank][bi->hitBankIndex].ctr, taken,
644 tagTableCounterBits);
645 // if the provider entry is not certified to be useful also update
646 // the alternate prediction
647 if (gtable[bi->hitBank][bi->hitBankIndex].u == 0) {
648 if (bi->altBank > 0) {
649 ctrUpdate(gtable[bi->altBank][bi->altBankIndex].ctr, taken,
650 tagTableCounterBits);
651 DPRINTF(LTage, "Updating tag table entry (%d,%d) for"
652 " branch %lx\n", bi->hitBank, bi->hitBankIndex,
653 branch_pc);
654 }
655 if (bi->altBank == 0) {
656 baseUpdate(pc, taken, bi);
657 }
658 }
659
660 // update the u counter
661 if (bi->tagePred != bi->altTaken) {
662 unsignedCtrUpdate(gtable[bi->hitBank][bi->hitBankIndex].u,
663 bi->tagePred == taken, tagTableUBits);
664 }
665 } else {
666 baseUpdate(pc, taken, bi);
667 }
668
669 //END PREDICTOR UPDATE
670 }
671 if (!squashed) {
672 delete bi;
673 }
674}
675
676void
677LTAGE::updateHistories(ThreadID tid, Addr branch_pc, bool taken, void* b)
678{
679 BranchInfo* bi = (BranchInfo*)(b);
680 ThreadHistory& tHist = threadHistory[tid];
681 // UPDATE HISTORIES
682 bool pathbit = ((branch_pc >> instShiftAmt) & 1);
683 //on a squash, return pointers to this and recompute indices.
684 //update user history
685 updateGHist(tHist.gHist, taken, tHist.globalHistory, tHist.ptGhist);
686 tHist.pathHist = (tHist.pathHist << 1) + pathbit;
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677 tHist.pathHist = (tHist.pathHist & ((ULL(1) << 16) - 1));
| 687 tHist.pathHist = (tHist.pathHist & ((ULL(1) << pathHistBits) - 1));
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678
679 bi->ptGhist = tHist.ptGhist;
680 bi->pathHist = tHist.pathHist;
681 //prepare next index and tag computations for user branchs
682 for (int i = 1; i <= nHistoryTables; i++)
683 {
684 bi->ci[i] = tHist.computeIndices[i].comp;
685 bi->ct0[i] = tHist.computeTags[0][i].comp;
686 bi->ct1[i] = tHist.computeTags[1][i].comp;
687 tHist.computeIndices[i].update(tHist.gHist);
688 tHist.computeTags[0][i].update(tHist.gHist);
689 tHist.computeTags[1][i].update(tHist.gHist);
690 }
691 DPRINTF(LTage, "Updating global histories with branch:%lx; taken?:%d, "
692 "path Hist: %x; pointer:%d\n", branch_pc, taken, tHist.pathHist,
693 tHist.ptGhist);
694}
695
696void
697LTAGE::squash(ThreadID tid, bool taken, void *bp_history)
698{
699 BranchInfo* bi = (BranchInfo*)(bp_history);
700 ThreadHistory& tHist = threadHistory[tid];
701 DPRINTF(LTage, "Restoring branch info: %lx; taken? %d; PathHistory:%x, "
702 "pointer:%d\n", bi->branchPC,taken, bi->pathHist, bi->ptGhist);
703 tHist.pathHist = bi->pathHist;
704 tHist.ptGhist = bi->ptGhist;
705 tHist.gHist = &(tHist.globalHistory[tHist.ptGhist]);
706 tHist.gHist[0] = (taken ? 1 : 0);
707 for (int i = 1; i <= nHistoryTables; i++) {
708 tHist.computeIndices[i].comp = bi->ci[i];
709 tHist.computeTags[0][i].comp = bi->ct0[i];
710 tHist.computeTags[1][i].comp = bi->ct1[i];
711 tHist.computeIndices[i].update(tHist.gHist);
712 tHist.computeTags[0][i].update(tHist.gHist);
713 tHist.computeTags[1][i].update(tHist.gHist);
714 }
715
716 if (bi->condBranch) {
717 if (bi->loopHit >= 0) {
718 int idx = bi->loopIndex + bi->loopHit;
719 ltable[idx].currentIterSpec = bi->currentIter;
720 }
721 }
722
723}
724
725void
726LTAGE::squash(ThreadID tid, void *bp_history)
727{
728 BranchInfo* bi = (BranchInfo*)(bp_history);
729 DPRINTF(LTage, "Deleting branch info: %lx\n", bi->branchPC);
730 if (bi->condBranch) {
731 if (bi->loopHit >= 0) {
732 int idx = bi->loopIndex + bi->loopHit;
733 ltable[idx].currentIterSpec = bi->currentIter;
734 }
735 }
736
737 delete bi;
738}
739
740bool
741LTAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history)
742{
743 bool retval = predict(tid, branch_pc, true, bp_history);
744
745 DPRINTF(LTage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval);
746 updateHistories(tid, branch_pc, retval, bp_history);
747 assert(threadHistory[tid].gHist ==
748 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
749
750 return retval;
751}
752
753void
754LTAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history)
755{
756 BranchInfo* bi = (BranchInfo*) bp_history;
757 ThreadHistory& tHist = threadHistory[tid];
758 DPRINTF(LTage, "BTB miss resets prediction: %lx\n", branch_pc);
759 assert(tHist.gHist == &tHist.globalHistory[tHist.ptGhist]);
760 tHist.gHist[0] = 0;
761 for (int i = 1; i <= nHistoryTables; i++) {
762 tHist.computeIndices[i].comp = bi->ci[i];
763 tHist.computeTags[0][i].comp = bi->ct0[i];
764 tHist.computeTags[1][i].comp = bi->ct1[i];
765 tHist.computeIndices[i].update(tHist.gHist);
766 tHist.computeTags[0][i].update(tHist.gHist);
767 tHist.computeTags[1][i].update(tHist.gHist);
768 }
769}
770
771void
772LTAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
773{
774 DPRINTF(LTage, "UnConditionalBranch: %lx\n", br_pc);
775 predict(tid, br_pc, false, bp_history);
776 updateHistories(tid, br_pc, true, bp_history);
777 assert(threadHistory[tid].gHist ==
778 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
779}
780
781LTAGE*
782LTAGEParams::create()
783{
784 return new LTAGE(this);
785}
| 688
689 bi->ptGhist = tHist.ptGhist;
690 bi->pathHist = tHist.pathHist;
691 //prepare next index and tag computations for user branchs
692 for (int i = 1; i <= nHistoryTables; i++)
693 {
694 bi->ci[i] = tHist.computeIndices[i].comp;
695 bi->ct0[i] = tHist.computeTags[0][i].comp;
696 bi->ct1[i] = tHist.computeTags[1][i].comp;
697 tHist.computeIndices[i].update(tHist.gHist);
698 tHist.computeTags[0][i].update(tHist.gHist);
699 tHist.computeTags[1][i].update(tHist.gHist);
700 }
701 DPRINTF(LTage, "Updating global histories with branch:%lx; taken?:%d, "
702 "path Hist: %x; pointer:%d\n", branch_pc, taken, tHist.pathHist,
703 tHist.ptGhist);
704}
705
706void
707LTAGE::squash(ThreadID tid, bool taken, void *bp_history)
708{
709 BranchInfo* bi = (BranchInfo*)(bp_history);
710 ThreadHistory& tHist = threadHistory[tid];
711 DPRINTF(LTage, "Restoring branch info: %lx; taken? %d; PathHistory:%x, "
712 "pointer:%d\n", bi->branchPC,taken, bi->pathHist, bi->ptGhist);
713 tHist.pathHist = bi->pathHist;
714 tHist.ptGhist = bi->ptGhist;
715 tHist.gHist = &(tHist.globalHistory[tHist.ptGhist]);
716 tHist.gHist[0] = (taken ? 1 : 0);
717 for (int i = 1; i <= nHistoryTables; i++) {
718 tHist.computeIndices[i].comp = bi->ci[i];
719 tHist.computeTags[0][i].comp = bi->ct0[i];
720 tHist.computeTags[1][i].comp = bi->ct1[i];
721 tHist.computeIndices[i].update(tHist.gHist);
722 tHist.computeTags[0][i].update(tHist.gHist);
723 tHist.computeTags[1][i].update(tHist.gHist);
724 }
725
726 if (bi->condBranch) {
727 if (bi->loopHit >= 0) {
728 int idx = bi->loopIndex + bi->loopHit;
729 ltable[idx].currentIterSpec = bi->currentIter;
730 }
731 }
732
733}
734
735void
736LTAGE::squash(ThreadID tid, void *bp_history)
737{
738 BranchInfo* bi = (BranchInfo*)(bp_history);
739 DPRINTF(LTage, "Deleting branch info: %lx\n", bi->branchPC);
740 if (bi->condBranch) {
741 if (bi->loopHit >= 0) {
742 int idx = bi->loopIndex + bi->loopHit;
743 ltable[idx].currentIterSpec = bi->currentIter;
744 }
745 }
746
747 delete bi;
748}
749
750bool
751LTAGE::lookup(ThreadID tid, Addr branch_pc, void* &bp_history)
752{
753 bool retval = predict(tid, branch_pc, true, bp_history);
754
755 DPRINTF(LTage, "Lookup branch: %lx; predict:%d\n", branch_pc, retval);
756 updateHistories(tid, branch_pc, retval, bp_history);
757 assert(threadHistory[tid].gHist ==
758 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
759
760 return retval;
761}
762
763void
764LTAGE::btbUpdate(ThreadID tid, Addr branch_pc, void* &bp_history)
765{
766 BranchInfo* bi = (BranchInfo*) bp_history;
767 ThreadHistory& tHist = threadHistory[tid];
768 DPRINTF(LTage, "BTB miss resets prediction: %lx\n", branch_pc);
769 assert(tHist.gHist == &tHist.globalHistory[tHist.ptGhist]);
770 tHist.gHist[0] = 0;
771 for (int i = 1; i <= nHistoryTables; i++) {
772 tHist.computeIndices[i].comp = bi->ci[i];
773 tHist.computeTags[0][i].comp = bi->ct0[i];
774 tHist.computeTags[1][i].comp = bi->ct1[i];
775 tHist.computeIndices[i].update(tHist.gHist);
776 tHist.computeTags[0][i].update(tHist.gHist);
777 tHist.computeTags[1][i].update(tHist.gHist);
778 }
779}
780
781void
782LTAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
783{
784 DPRINTF(LTage, "UnConditionalBranch: %lx\n", br_pc);
785 predict(tid, br_pc, false, bp_history);
786 updateHistories(tid, br_pc, true, bp_history);
787 assert(threadHistory[tid].gHist ==
788 &threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
789}
790
791LTAGE*
792LTAGEParams::create()
793{
794 return new LTAGE(this);
795}
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