1/*
2 * Copyright (c) 2011, 2014 ARM Limited
3 * All rights reserved
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software
9 * licensed hereunder. You may use the software subject to the license
10 * terms below provided that you ensure that this notice is replicated
11 * unmodified and in its entirety in all distributions of the software,
12 * modified or unmodified, in source code or in binary form.
13 *
14 * Copyright (c) 2004-2006 The Regents of The University of Michigan
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions are
19 * met: redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer;
21 * redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution;
24 * neither the name of the copyright holders nor the names of its
25 * contributors may be used to endorse or promote products derived from
26 * this software without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
36 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Kevin Lim
41 */
42
43#include "cpu/pred/tournament.hh"
44
45#include "base/bitfield.hh"
46#include "base/intmath.hh"
47
48TournamentBP::TournamentBP(const TournamentBPParams *params)
49 : BPredUnit(params),
50 localPredictorSize(params->localPredictorSize),
51 localCtrBits(params->localCtrBits),
52 localHistoryTableSize(params->localHistoryTableSize),
53 localHistoryBits(ceilLog2(params->localPredictorSize)),
54 globalPredictorSize(params->globalPredictorSize),
55 globalCtrBits(params->globalCtrBits),
56 globalHistory(params->numThreads, 0),
57 globalHistoryBits(
58 ceilLog2(params->globalPredictorSize) >
59 ceilLog2(params->choicePredictorSize) ?
60 ceilLog2(params->globalPredictorSize) :
61 ceilLog2(params->choicePredictorSize)),
62 choicePredictorSize(params->choicePredictorSize),
63 choiceCtrBits(params->choiceCtrBits)
64{
65 if (!isPowerOf2(localPredictorSize)) {
66 fatal("Invalid local predictor size!\n");
67 }
68
69 if (!isPowerOf2(globalPredictorSize)) {
70 fatal("Invalid global predictor size!\n");
71 }
72
73 //Set up the array of counters for the local predictor
74 localCtrs.resize(localPredictorSize);
75
76 for (int i = 0; i < localPredictorSize; ++i)
77 localCtrs[i].setBits(localCtrBits);
78
79 localPredictorMask = mask(localHistoryBits);
80
81 if (!isPowerOf2(localHistoryTableSize)) {
82 fatal("Invalid local history table size!\n");
83 }
84
85 //Setup the history table for the local table
86 localHistoryTable.resize(localHistoryTableSize);
87
88 for (int i = 0; i < localHistoryTableSize; ++i)
89 localHistoryTable[i] = 0;
90
91 //Setup the array of counters for the global predictor
92 globalCtrs.resize(globalPredictorSize);
93
94 for (int i = 0; i < globalPredictorSize; ++i)
95 globalCtrs[i].setBits(globalCtrBits);
96
97 // Set up the global history mask
98 // this is equivalent to mask(log2(globalPredictorSize)
99 globalHistoryMask = globalPredictorSize - 1;
100
101 if (!isPowerOf2(choicePredictorSize)) {
102 fatal("Invalid choice predictor size!\n");
103 }
104
105 // Set up choiceHistoryMask
106 // this is equivalent to mask(log2(choicePredictorSize)
107 choiceHistoryMask = choicePredictorSize - 1;
108
109 //Setup the array of counters for the choice predictor
110 choiceCtrs.resize(choicePredictorSize);
111
112 for (int i = 0; i < choicePredictorSize; ++i)
113 choiceCtrs[i].setBits(choiceCtrBits);
114
115 //Set up historyRegisterMask
116 historyRegisterMask = mask(globalHistoryBits);
117
118 //Check that predictors don't use more bits than they have available
119 if (globalHistoryMask > historyRegisterMask) {
120 fatal("Global predictor too large for global history bits!\n");
121 }
122 if (choiceHistoryMask > historyRegisterMask) {
123 fatal("Choice predictor too large for global history bits!\n");
124 }
125
126 if (globalHistoryMask < historyRegisterMask &&
127 choiceHistoryMask < historyRegisterMask) {
128 inform("More global history bits than required by predictors\n");
129 }
130
131 // Set thresholds for the three predictors' counters
132 // This is equivalent to (2^(Ctr))/2 - 1
133 localThreshold = (ULL(1) << (localCtrBits - 1)) - 1;
134 globalThreshold = (ULL(1) << (globalCtrBits - 1)) - 1;
135 choiceThreshold = (ULL(1) << (choiceCtrBits - 1)) - 1;
136}
137
138inline
139unsigned
140TournamentBP::calcLocHistIdx(Addr &branch_addr)
141{
142 // Get low order bits after removing instruction offset.
143 return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
144}
145
146inline
147void
148TournamentBP::updateGlobalHistTaken(ThreadID tid)
149{
150 globalHistory[tid] = (globalHistory[tid] << 1) | 1;
151 globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
152}
153
154inline
155void
156TournamentBP::updateGlobalHistNotTaken(ThreadID tid)
157{
158 globalHistory[tid] = (globalHistory[tid] << 1);
159 globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
160}
161
162inline
163void
164TournamentBP::updateLocalHistTaken(unsigned local_history_idx)
165{
166 localHistoryTable[local_history_idx] =
167 (localHistoryTable[local_history_idx] << 1) | 1;
168}
169
170inline
171void
172TournamentBP::updateLocalHistNotTaken(unsigned local_history_idx)
173{
174 localHistoryTable[local_history_idx] =
175 (localHistoryTable[local_history_idx] << 1);
176}
177
178
179void
180TournamentBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history)
181{
182 unsigned local_history_idx = calcLocHistIdx(branch_addr);
183 //Update Global History to Not Taken (clear LSB)
184 globalHistory[tid] &= (historyRegisterMask & ~ULL(1));
185 //Update Local History to Not Taken
186 localHistoryTable[local_history_idx] =
187 localHistoryTable[local_history_idx] & (localPredictorMask & ~ULL(1));
188}
189
190bool
191TournamentBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history)
192{
193 bool local_prediction;
194 unsigned local_history_idx;
195 unsigned local_predictor_idx;
196
197 bool global_prediction;
198 bool choice_prediction;
199
200 //Lookup in the local predictor to get its branch prediction
201 local_history_idx = calcLocHistIdx(branch_addr);
202 local_predictor_idx = localHistoryTable[local_history_idx]
203 & localPredictorMask;
204 local_prediction = localCtrs[local_predictor_idx].read() > localThreshold;
205
206 //Lookup in the global predictor to get its branch prediction
207 global_prediction = globalThreshold <
208 globalCtrs[globalHistory[tid] & globalHistoryMask].read();
209
210 //Lookup in the choice predictor to see which one to use
211 choice_prediction = choiceThreshold <
212 choiceCtrs[globalHistory[tid] & choiceHistoryMask].read();
213
214 // Create BPHistory and pass it back to be recorded.
215 BPHistory *history = new BPHistory;
216 history->globalHistory = globalHistory[tid];
217 history->localPredTaken = local_prediction;
218 history->globalPredTaken = global_prediction;
219 history->globalUsed = choice_prediction;
220 history->localHistoryIdx = local_history_idx;
221 history->localHistory = local_predictor_idx;
222 bp_history = (void *)history;
223
224 assert(local_history_idx < localHistoryTableSize);
225
226 // Speculative update of the global history and the
227 // selected local history.
228 if (choice_prediction) {
229 if (global_prediction) {
230 updateGlobalHistTaken(tid);
231 updateLocalHistTaken(local_history_idx);
232 return true;
233 } else {
234 updateGlobalHistNotTaken(tid);
235 updateLocalHistNotTaken(local_history_idx);
236 return false;
237 }
238 } else {
239 if (local_prediction) {
240 updateGlobalHistTaken(tid);
241 updateLocalHistTaken(local_history_idx);
242 return true;
243 } else {
244 updateGlobalHistNotTaken(tid);
245 updateLocalHistNotTaken(local_history_idx);
246 return false;
247 }
248 }
249}
250
251void
252TournamentBP::uncondBranch(ThreadID tid, Addr pc, void * &bp_history)
253{
254 // Create BPHistory and pass it back to be recorded.
255 BPHistory *history = new BPHistory;
256 history->globalHistory = globalHistory[tid];
257 history->localPredTaken = true;
258 history->globalPredTaken = true;
259 history->globalUsed = true;
260 history->localHistoryIdx = invalidPredictorIndex;
261 history->localHistory = invalidPredictorIndex;
262 bp_history = static_cast<void *>(history);
263
264 updateGlobalHistTaken(tid);
265}
266
267void
268TournamentBP::update(ThreadID tid, Addr branch_addr, bool taken,
| 1/*
2 * Copyright (c) 2011, 2014 ARM Limited
3 * All rights reserved
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software
9 * licensed hereunder. You may use the software subject to the license
10 * terms below provided that you ensure that this notice is replicated
11 * unmodified and in its entirety in all distributions of the software,
12 * modified or unmodified, in source code or in binary form.
13 *
14 * Copyright (c) 2004-2006 The Regents of The University of Michigan
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions are
19 * met: redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer;
21 * redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution;
24 * neither the name of the copyright holders nor the names of its
25 * contributors may be used to endorse or promote products derived from
26 * this software without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
36 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Kevin Lim
41 */
42
43#include "cpu/pred/tournament.hh"
44
45#include "base/bitfield.hh"
46#include "base/intmath.hh"
47
48TournamentBP::TournamentBP(const TournamentBPParams *params)
49 : BPredUnit(params),
50 localPredictorSize(params->localPredictorSize),
51 localCtrBits(params->localCtrBits),
52 localHistoryTableSize(params->localHistoryTableSize),
53 localHistoryBits(ceilLog2(params->localPredictorSize)),
54 globalPredictorSize(params->globalPredictorSize),
55 globalCtrBits(params->globalCtrBits),
56 globalHistory(params->numThreads, 0),
57 globalHistoryBits(
58 ceilLog2(params->globalPredictorSize) >
59 ceilLog2(params->choicePredictorSize) ?
60 ceilLog2(params->globalPredictorSize) :
61 ceilLog2(params->choicePredictorSize)),
62 choicePredictorSize(params->choicePredictorSize),
63 choiceCtrBits(params->choiceCtrBits)
64{
65 if (!isPowerOf2(localPredictorSize)) {
66 fatal("Invalid local predictor size!\n");
67 }
68
69 if (!isPowerOf2(globalPredictorSize)) {
70 fatal("Invalid global predictor size!\n");
71 }
72
73 //Set up the array of counters for the local predictor
74 localCtrs.resize(localPredictorSize);
75
76 for (int i = 0; i < localPredictorSize; ++i)
77 localCtrs[i].setBits(localCtrBits);
78
79 localPredictorMask = mask(localHistoryBits);
80
81 if (!isPowerOf2(localHistoryTableSize)) {
82 fatal("Invalid local history table size!\n");
83 }
84
85 //Setup the history table for the local table
86 localHistoryTable.resize(localHistoryTableSize);
87
88 for (int i = 0; i < localHistoryTableSize; ++i)
89 localHistoryTable[i] = 0;
90
91 //Setup the array of counters for the global predictor
92 globalCtrs.resize(globalPredictorSize);
93
94 for (int i = 0; i < globalPredictorSize; ++i)
95 globalCtrs[i].setBits(globalCtrBits);
96
97 // Set up the global history mask
98 // this is equivalent to mask(log2(globalPredictorSize)
99 globalHistoryMask = globalPredictorSize - 1;
100
101 if (!isPowerOf2(choicePredictorSize)) {
102 fatal("Invalid choice predictor size!\n");
103 }
104
105 // Set up choiceHistoryMask
106 // this is equivalent to mask(log2(choicePredictorSize)
107 choiceHistoryMask = choicePredictorSize - 1;
108
109 //Setup the array of counters for the choice predictor
110 choiceCtrs.resize(choicePredictorSize);
111
112 for (int i = 0; i < choicePredictorSize; ++i)
113 choiceCtrs[i].setBits(choiceCtrBits);
114
115 //Set up historyRegisterMask
116 historyRegisterMask = mask(globalHistoryBits);
117
118 //Check that predictors don't use more bits than they have available
119 if (globalHistoryMask > historyRegisterMask) {
120 fatal("Global predictor too large for global history bits!\n");
121 }
122 if (choiceHistoryMask > historyRegisterMask) {
123 fatal("Choice predictor too large for global history bits!\n");
124 }
125
126 if (globalHistoryMask < historyRegisterMask &&
127 choiceHistoryMask < historyRegisterMask) {
128 inform("More global history bits than required by predictors\n");
129 }
130
131 // Set thresholds for the three predictors' counters
132 // This is equivalent to (2^(Ctr))/2 - 1
133 localThreshold = (ULL(1) << (localCtrBits - 1)) - 1;
134 globalThreshold = (ULL(1) << (globalCtrBits - 1)) - 1;
135 choiceThreshold = (ULL(1) << (choiceCtrBits - 1)) - 1;
136}
137
138inline
139unsigned
140TournamentBP::calcLocHistIdx(Addr &branch_addr)
141{
142 // Get low order bits after removing instruction offset.
143 return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
144}
145
146inline
147void
148TournamentBP::updateGlobalHistTaken(ThreadID tid)
149{
150 globalHistory[tid] = (globalHistory[tid] << 1) | 1;
151 globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
152}
153
154inline
155void
156TournamentBP::updateGlobalHistNotTaken(ThreadID tid)
157{
158 globalHistory[tid] = (globalHistory[tid] << 1);
159 globalHistory[tid] = globalHistory[tid] & historyRegisterMask;
160}
161
162inline
163void
164TournamentBP::updateLocalHistTaken(unsigned local_history_idx)
165{
166 localHistoryTable[local_history_idx] =
167 (localHistoryTable[local_history_idx] << 1) | 1;
168}
169
170inline
171void
172TournamentBP::updateLocalHistNotTaken(unsigned local_history_idx)
173{
174 localHistoryTable[local_history_idx] =
175 (localHistoryTable[local_history_idx] << 1);
176}
177
178
179void
180TournamentBP::btbUpdate(ThreadID tid, Addr branch_addr, void * &bp_history)
181{
182 unsigned local_history_idx = calcLocHistIdx(branch_addr);
183 //Update Global History to Not Taken (clear LSB)
184 globalHistory[tid] &= (historyRegisterMask & ~ULL(1));
185 //Update Local History to Not Taken
186 localHistoryTable[local_history_idx] =
187 localHistoryTable[local_history_idx] & (localPredictorMask & ~ULL(1));
188}
189
190bool
191TournamentBP::lookup(ThreadID tid, Addr branch_addr, void * &bp_history)
192{
193 bool local_prediction;
194 unsigned local_history_idx;
195 unsigned local_predictor_idx;
196
197 bool global_prediction;
198 bool choice_prediction;
199
200 //Lookup in the local predictor to get its branch prediction
201 local_history_idx = calcLocHistIdx(branch_addr);
202 local_predictor_idx = localHistoryTable[local_history_idx]
203 & localPredictorMask;
204 local_prediction = localCtrs[local_predictor_idx].read() > localThreshold;
205
206 //Lookup in the global predictor to get its branch prediction
207 global_prediction = globalThreshold <
208 globalCtrs[globalHistory[tid] & globalHistoryMask].read();
209
210 //Lookup in the choice predictor to see which one to use
211 choice_prediction = choiceThreshold <
212 choiceCtrs[globalHistory[tid] & choiceHistoryMask].read();
213
214 // Create BPHistory and pass it back to be recorded.
215 BPHistory *history = new BPHistory;
216 history->globalHistory = globalHistory[tid];
217 history->localPredTaken = local_prediction;
218 history->globalPredTaken = global_prediction;
219 history->globalUsed = choice_prediction;
220 history->localHistoryIdx = local_history_idx;
221 history->localHistory = local_predictor_idx;
222 bp_history = (void *)history;
223
224 assert(local_history_idx < localHistoryTableSize);
225
226 // Speculative update of the global history and the
227 // selected local history.
228 if (choice_prediction) {
229 if (global_prediction) {
230 updateGlobalHistTaken(tid);
231 updateLocalHistTaken(local_history_idx);
232 return true;
233 } else {
234 updateGlobalHistNotTaken(tid);
235 updateLocalHistNotTaken(local_history_idx);
236 return false;
237 }
238 } else {
239 if (local_prediction) {
240 updateGlobalHistTaken(tid);
241 updateLocalHistTaken(local_history_idx);
242 return true;
243 } else {
244 updateGlobalHistNotTaken(tid);
245 updateLocalHistNotTaken(local_history_idx);
246 return false;
247 }
248 }
249}
250
251void
252TournamentBP::uncondBranch(ThreadID tid, Addr pc, void * &bp_history)
253{
254 // Create BPHistory and pass it back to be recorded.
255 BPHistory *history = new BPHistory;
256 history->globalHistory = globalHistory[tid];
257 history->localPredTaken = true;
258 history->globalPredTaken = true;
259 history->globalUsed = true;
260 history->localHistoryIdx = invalidPredictorIndex;
261 history->localHistory = invalidPredictorIndex;
262 bp_history = static_cast<void *>(history);
263
264 updateGlobalHistTaken(tid);
265}
266
267void
268TournamentBP::update(ThreadID tid, Addr branch_addr, bool taken,
|
270{
271 assert(bp_history);
272
273 BPHistory *history = static_cast<BPHistory *>(bp_history);
274
275 unsigned local_history_idx = calcLocHistIdx(branch_addr);
276
277 assert(local_history_idx < localHistoryTableSize);
278
279 // Unconditional branches do not use local history.
280 bool old_local_pred_valid = history->localHistory !=
281 invalidPredictorIndex;
282
283 // If this is a misprediction, restore the speculatively
284 // updated state (global history register and local history)
285 // and update again.
286 if (squashed) {
287 // Global history restore and update
288 globalHistory[tid] = (history->globalHistory << 1) | taken;
289 globalHistory[tid] &= historyRegisterMask;
290
291 // Local history restore and update.
292 if (old_local_pred_valid) {
293 localHistoryTable[local_history_idx] =
294 (history->localHistory << 1) | taken;
295 }
296
297 return;
298 }
299
300 unsigned old_local_pred_index = history->localHistory &
301 localPredictorMask;
302
303 assert(old_local_pred_index < localPredictorSize);
304
305 // Update the choice predictor to tell it which one was correct if
306 // there was a prediction.
307 if (history->localPredTaken != history->globalPredTaken &&
308 old_local_pred_valid)
309 {
310 // If the local prediction matches the actual outcome,
311 // decrement the counter. Otherwise increment the
312 // counter.
313 unsigned choice_predictor_idx =
314 history->globalHistory & choiceHistoryMask;
315 if (history->localPredTaken == taken) {
316 choiceCtrs[choice_predictor_idx].decrement();
317 } else if (history->globalPredTaken == taken) {
318 choiceCtrs[choice_predictor_idx].increment();
319 }
320 }
321
322 // Update the counters with the proper
323 // resolution of the branch. Histories are updated
324 // speculatively, restored upon squash() calls, and
325 // recomputed upon update(squash = true) calls,
326 // so they do not need to be updated.
327 unsigned global_predictor_idx =
328 history->globalHistory & globalHistoryMask;
329 if (taken) {
330 globalCtrs[global_predictor_idx].increment();
331 if (old_local_pred_valid) {
332 localCtrs[old_local_pred_index].increment();
333 }
334 } else {
335 globalCtrs[global_predictor_idx].decrement();
336 if (old_local_pred_valid) {
337 localCtrs[old_local_pred_index].decrement();
338 }
339 }
340
341 // We're done with this history, now delete it.
342 delete history;
343}
344
345void
346TournamentBP::squash(ThreadID tid, void *bp_history)
347{
348 BPHistory *history = static_cast<BPHistory *>(bp_history);
349
350 // Restore global history to state prior to this branch.
351 globalHistory[tid] = history->globalHistory;
352
353 // Restore local history
354 if (history->localHistoryIdx != invalidPredictorIndex) {
355 localHistoryTable[history->localHistoryIdx] = history->localHistory;
356 }
357
358 // Delete this BPHistory now that we're done with it.
359 delete history;
360}
361
362TournamentBP*
363TournamentBPParams::create()
364{
365 return new TournamentBP(this);
366}
367
368unsigned
369TournamentBP::getGHR(ThreadID tid, void *bp_history) const
370{
371 return static_cast<BPHistory *>(bp_history)->globalHistory;
372}
373
374#ifdef DEBUG
375int
376TournamentBP::BPHistory::newCount = 0;
377#endif
| 271{
272 assert(bp_history);
273
274 BPHistory *history = static_cast<BPHistory *>(bp_history);
275
276 unsigned local_history_idx = calcLocHistIdx(branch_addr);
277
278 assert(local_history_idx < localHistoryTableSize);
279
280 // Unconditional branches do not use local history.
281 bool old_local_pred_valid = history->localHistory !=
282 invalidPredictorIndex;
283
284 // If this is a misprediction, restore the speculatively
285 // updated state (global history register and local history)
286 // and update again.
287 if (squashed) {
288 // Global history restore and update
289 globalHistory[tid] = (history->globalHistory << 1) | taken;
290 globalHistory[tid] &= historyRegisterMask;
291
292 // Local history restore and update.
293 if (old_local_pred_valid) {
294 localHistoryTable[local_history_idx] =
295 (history->localHistory << 1) | taken;
296 }
297
298 return;
299 }
300
301 unsigned old_local_pred_index = history->localHistory &
302 localPredictorMask;
303
304 assert(old_local_pred_index < localPredictorSize);
305
306 // Update the choice predictor to tell it which one was correct if
307 // there was a prediction.
308 if (history->localPredTaken != history->globalPredTaken &&
309 old_local_pred_valid)
310 {
311 // If the local prediction matches the actual outcome,
312 // decrement the counter. Otherwise increment the
313 // counter.
314 unsigned choice_predictor_idx =
315 history->globalHistory & choiceHistoryMask;
316 if (history->localPredTaken == taken) {
317 choiceCtrs[choice_predictor_idx].decrement();
318 } else if (history->globalPredTaken == taken) {
319 choiceCtrs[choice_predictor_idx].increment();
320 }
321 }
322
323 // Update the counters with the proper
324 // resolution of the branch. Histories are updated
325 // speculatively, restored upon squash() calls, and
326 // recomputed upon update(squash = true) calls,
327 // so they do not need to be updated.
328 unsigned global_predictor_idx =
329 history->globalHistory & globalHistoryMask;
330 if (taken) {
331 globalCtrs[global_predictor_idx].increment();
332 if (old_local_pred_valid) {
333 localCtrs[old_local_pred_index].increment();
334 }
335 } else {
336 globalCtrs[global_predictor_idx].decrement();
337 if (old_local_pred_valid) {
338 localCtrs[old_local_pred_index].decrement();
339 }
340 }
341
342 // We're done with this history, now delete it.
343 delete history;
344}
345
346void
347TournamentBP::squash(ThreadID tid, void *bp_history)
348{
349 BPHistory *history = static_cast<BPHistory *>(bp_history);
350
351 // Restore global history to state prior to this branch.
352 globalHistory[tid] = history->globalHistory;
353
354 // Restore local history
355 if (history->localHistoryIdx != invalidPredictorIndex) {
356 localHistoryTable[history->localHistoryIdx] = history->localHistory;
357 }
358
359 // Delete this BPHistory now that we're done with it.
360 delete history;
361}
362
363TournamentBP*
364TournamentBPParams::create()
365{
366 return new TournamentBP(this);
367}
368
369unsigned
370TournamentBP::getGHR(ThreadID tid, void *bp_history) const
371{
372 return static_cast<BPHistory *>(bp_history)->globalHistory;
373}
374
375#ifdef DEBUG
376int
377TournamentBP::BPHistory::newCount = 0;
378#endif
|