tournament.cc revision 8842:a02932e2e73d 
1/*
2 * Copyright (c) 2011 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 "base/intmath.hh"
44#include "cpu/pred/tournament.hh"
45
46TournamentBP::TournamentBP(unsigned _localPredictorSize,
47                           unsigned _localCtrBits,
48                           unsigned _localHistoryTableSize,
49                           unsigned _localHistoryBits,
50                           unsigned _globalPredictorSize,
51                           unsigned _globalHistoryBits,
52                           unsigned _globalCtrBits,
53                           unsigned _choicePredictorSize,
54                           unsigned _choiceCtrBits,
55                           unsigned _instShiftAmt)
56    : localPredictorSize(_localPredictorSize),
57      localCtrBits(_localCtrBits),
58      localHistoryTableSize(_localHistoryTableSize),
59      localHistoryBits(_localHistoryBits),
60      globalPredictorSize(_globalPredictorSize),
61      globalCtrBits(_globalCtrBits),
62      globalHistoryBits(_globalHistoryBits),
63      choicePredictorSize(_globalPredictorSize),
64      choiceCtrBits(_choiceCtrBits),
65      instShiftAmt(_instShiftAmt)
66{
67    if (!isPowerOf2(localPredictorSize)) {
68        fatal("Invalid local predictor size!\n");
69    }
70
71    //Setup the array of counters for the local predictor
72    localCtrs.resize(localPredictorSize);
73
74    for (int i = 0; i < localPredictorSize; ++i)
75        localCtrs[i].setBits(localCtrBits);
76
77    localPredictorMask = floorPow2(localPredictorSize) - 1;
78
79    if (!isPowerOf2(localHistoryTableSize)) {
80        fatal("Invalid local history table size!\n");
81    }
82
83    //Setup the history table for the local table
84    localHistoryTable.resize(localHistoryTableSize);
85
86    for (int i = 0; i < localHistoryTableSize; ++i)
87        localHistoryTable[i] = 0;
88
89    // Setup the local history mask
90    localHistoryMask = (1 << localHistoryBits) - 1;
91
92    if (!isPowerOf2(globalPredictorSize)) {
93        fatal("Invalid global predictor size!\n");
94    }
95
96    //Setup the array of counters for the global predictor
97    globalCtrs.resize(globalPredictorSize);
98
99    for (int i = 0; i < globalPredictorSize; ++i)
100        globalCtrs[i].setBits(globalCtrBits);
101
102    //Clear the global history
103    globalHistory = 0;
104    // Setup the global history mask
105    globalHistoryMask = (1 << globalHistoryBits) - 1;
106
107    if (!isPowerOf2(choicePredictorSize)) {
108        fatal("Invalid choice predictor size!\n");
109    }
110
111    //Setup the array of counters for the choice predictor
112    choiceCtrs.resize(choicePredictorSize);
113
114    for (int i = 0; i < choicePredictorSize; ++i)
115        choiceCtrs[i].setBits(choiceCtrBits);
116
117    // @todo: Allow for different thresholds between the predictors.
118    threshold = (1 << (localCtrBits - 1)) - 1;
119}
120
121inline
122unsigned
123TournamentBP::calcLocHistIdx(Addr &branch_addr)
124{
125    // Get low order bits after removing instruction offset.
126    return (branch_addr >> instShiftAmt) & (localHistoryTableSize - 1);
127}
128
129inline
130void
131TournamentBP::updateGlobalHistTaken()
132{
133    globalHistory = (globalHistory << 1) | 1;
134    globalHistory = globalHistory & globalHistoryMask;
135}
136
137inline
138void
139TournamentBP::updateGlobalHistNotTaken()
140{
141    globalHistory = (globalHistory << 1);
142    globalHistory = globalHistory & globalHistoryMask;
143}
144
145inline
146void
147TournamentBP::updateLocalHistTaken(unsigned local_history_idx)
148{
149    localHistoryTable[local_history_idx] =
150        (localHistoryTable[local_history_idx] << 1) | 1;
151}
152
153inline
154void
155TournamentBP::updateLocalHistNotTaken(unsigned local_history_idx)
156{
157    localHistoryTable[local_history_idx] =
158        (localHistoryTable[local_history_idx] << 1);
159}
160
161
162void
163TournamentBP::BTBUpdate(Addr &branch_addr, void * &bp_history)
164{
165    unsigned local_history_idx = calcLocHistIdx(branch_addr);
166    //Update Global History to Not Taken
167    globalHistory = globalHistory & (globalHistoryMask - 1);
168    //Update Local History to Not Taken
169    localHistoryTable[local_history_idx] =
170       localHistoryTable[local_history_idx] & (localPredictorMask - 1);
171}
172
173bool
174TournamentBP::lookup(Addr &branch_addr, void * &bp_history)
175{
176    bool local_prediction;
177    unsigned local_history_idx;
178    unsigned local_predictor_idx;
179
180    bool global_prediction;
181    bool choice_prediction;
182
183    //Lookup in the local predictor to get its branch prediction
184    local_history_idx = calcLocHistIdx(branch_addr);
185    local_predictor_idx = localHistoryTable[local_history_idx]
186        & localPredictorMask;
187    local_prediction = localCtrs[local_predictor_idx].read() > threshold;
188
189    //Lookup in the global predictor to get its branch prediction
190    global_prediction = globalCtrs[globalHistory].read() > threshold;
191
192    //Lookup in the choice predictor to see which one to use
193    choice_prediction = choiceCtrs[globalHistory].read() > threshold;
194
195    // Create BPHistory and pass it back to be recorded.
196    BPHistory *history = new BPHistory;
197    history->globalHistory = globalHistory;
198    history->localPredTaken = local_prediction;
199    history->globalPredTaken = global_prediction;
200    history->globalUsed = choice_prediction;
201    history->localHistory = local_predictor_idx;
202    bp_history = (void *)history;
203
204    assert(globalHistory < globalPredictorSize &&
205           local_history_idx < localHistoryTableSize &&
206           local_predictor_idx < localPredictorSize);
207
208    // Commented code is for doing speculative update of counters and
209    // all histories.
210    if (choice_prediction) {
211        if (global_prediction) {
212            updateGlobalHistTaken();
213            updateLocalHistTaken(local_history_idx);
214            return true;
215        } else {
216            updateGlobalHistNotTaken();
217            updateLocalHistNotTaken(local_history_idx);
218            return false;
219        }
220    } else {
221        if (local_prediction) {
222            updateGlobalHistTaken();
223            updateLocalHistTaken(local_history_idx);
224            return true;
225        } else {
226            updateGlobalHistNotTaken();
227            updateLocalHistNotTaken(local_history_idx);
228            return false;
229        }
230    }
231}
232
233void
234TournamentBP::uncondBr(void * &bp_history)
235{
236    // Create BPHistory and pass it back to be recorded.
237    BPHistory *history = new BPHistory;
238    history->globalHistory = globalHistory;
239    history->localPredTaken = true;
240    history->globalPredTaken = true;
241    history->globalUsed = true;
242    history->localHistory = invalidPredictorIndex;
243    bp_history = static_cast<void *>(history);
244
245    updateGlobalHistTaken();
246}
247
248void
249TournamentBP::update(Addr &branch_addr, bool taken, void *bp_history,
250                     bool squashed)
251{
252    unsigned local_history_idx;
253    unsigned local_predictor_idx M5_VAR_USED;
254    unsigned local_predictor_hist;
255
256    // Get the local predictor's current prediction
257    local_history_idx = calcLocHistIdx(branch_addr);
258    local_predictor_hist = localHistoryTable[local_history_idx];
259    local_predictor_idx = local_predictor_hist & localPredictorMask;
260
261    // Update the choice predictor to tell it which one was correct if
262    // there was a prediction.
263    if (bp_history) {
264        BPHistory *history = static_cast<BPHistory *>(bp_history);
265        if (history->localPredTaken != history->globalPredTaken) {
266            // If the local prediction matches the actual outcome,
267            // decerement the counter.  Otherwise increment the
268            // counter.
269            if (history->localPredTaken == taken) {
270                choiceCtrs[history->globalHistory].decrement();
271            } else if (history->globalPredTaken == taken){
272                choiceCtrs[history->globalHistory].increment();
273            }
274
275        }
276
277        // Update the counters and local history with the proper
278        // resolution of the branch.  Global history is updated
279        // speculatively and restored upon squash() calls, so it does not
280        // need to be updated.
281        unsigned old_local_pred_index = history->localHistory
282                 & localPredictorMask;
283        if (taken) {
284               globalCtrs[history->globalHistory].increment();
285               if (old_local_pred_index != invalidPredictorIndex) {
286                      localCtrs[old_local_pred_index].increment();
287               }
288        } else {
289               globalCtrs[history->globalHistory].decrement();
290               if (old_local_pred_index != invalidPredictorIndex) {
291                      localCtrs[old_local_pred_index].decrement();
292               }
293       }
294
295       if (squashed) {
296           if (taken) {
297              globalHistory = (history->globalHistory << 1) | 1;
298              globalHistory = globalHistory & globalHistoryMask;
299              if (history->localHistory != invalidPredictorIndex)
300                  localHistoryTable[local_history_idx] =
301                     (history->localHistory << 1) | 1;
302           } else {
303              globalHistory = (history->globalHistory << 1);
304              globalHistory = globalHistory & globalHistoryMask;
305              if (history->localHistory != invalidPredictorIndex) {
306                  localHistoryTable[local_history_idx] =
307                     history->localHistory << 1;
308              }
309           }
310
311        }
312        // We're done with this history, now delete it.
313        delete history;
314    }
315
316    assert(globalHistory < globalPredictorSize &&
317           local_history_idx < localHistoryTableSize &&
318           local_predictor_idx < localPredictorSize);
319
320
321}
322
323void
324TournamentBP::squash(void *bp_history)
325{
326    BPHistory *history = static_cast<BPHistory *>(bp_history);
327
328    // Restore global history to state prior to this branch.
329    globalHistory = history->globalHistory;
330
331    // Delete this BPHistory now that we're done with it.
332    delete history;
333}
334
335#ifdef DEBUG
336int
337TournamentBP::BPHistory::newCount = 0;
338#endif
339