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. TAGE is a global-history based
39 * branch predictor. It features a PC-indexed bimodal predictor and N
40 * partially tagged tables, indexed with a hash of the PC and the global
41 * branch history. The different lengths of global branch history used to
42 * index the partially tagged tables grow geometrically. A small path history
43 * is also used in the hash. L-TAGE also features a loop predictor that records
44 * iteration count of loops and predicts accordingly.
45 *
46 * All TAGE tables are accessed in parallel, and the one using the longest
47 * history that matches provides the prediction (some exceptions apply).
48 * Entries are allocated in components using a longer history than the
49 * one that predicted when the prediction is incorrect.
50 */
51
52#ifndef __CPU_PRED_LTAGE
53#define __CPU_PRED_LTAGE
54
55
56#include <vector>
57
58#include "base/types.hh"
59#include "cpu/pred/tage.hh"
60#include "params/LTAGE.hh"
61
62class LTAGE: public TAGE
63{
64 public:
65 LTAGE(const LTAGEParams *params);
66
67 // Base class methods.
68 void squash(ThreadID tid, void *bp_history) override;
| 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. TAGE is a global-history based
39 * branch predictor. It features a PC-indexed bimodal predictor and N
40 * partially tagged tables, indexed with a hash of the PC and the global
41 * branch history. The different lengths of global branch history used to
42 * index the partially tagged tables grow geometrically. A small path history
43 * is also used in the hash. L-TAGE also features a loop predictor that records
44 * iteration count of loops and predicts accordingly.
45 *
46 * All TAGE tables are accessed in parallel, and the one using the longest
47 * history that matches provides the prediction (some exceptions apply).
48 * Entries are allocated in components using a longer history than the
49 * one that predicted when the prediction is incorrect.
50 */
51
52#ifndef __CPU_PRED_LTAGE
53#define __CPU_PRED_LTAGE
54
55
56#include <vector>
57
58#include "base/types.hh"
59#include "cpu/pred/tage.hh"
60#include "params/LTAGE.hh"
61
62class LTAGE: public TAGE
63{
64 public:
65 LTAGE(const LTAGEParams *params);
66
67 // Base class methods.
68 void squash(ThreadID tid, void *bp_history) override;
|
| 69 void update(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
70 bool squashed, const StaticInstPtr & inst,
71 Addr corrTarget) override;
|
69
70 void regStats() override;
71
72 private:
73 // Prediction Structures
74 // Loop Predictor Entry
75 struct LoopEntry
76 {
77 uint16_t numIter;
78 uint16_t currentIter;
79 uint16_t currentIterSpec; // only for useSpeculation
80 uint8_t confidence;
81 uint16_t tag;
82 uint8_t age;
83 bool dir; // only for useDirectionBit
84
85 LoopEntry() : numIter(0), currentIter(0), currentIterSpec(0),
86 confidence(0), tag(0), age(0), dir(0) { }
87 };
88
89 // more provider types
90 enum {
| 72
73 void regStats() override;
74
75 private:
76 // Prediction Structures
77 // Loop Predictor Entry
78 struct LoopEntry
79 {
80 uint16_t numIter;
81 uint16_t currentIter;
82 uint16_t currentIterSpec; // only for useSpeculation
83 uint8_t confidence;
84 uint16_t tag;
85 uint8_t age;
86 bool dir; // only for useDirectionBit
87
88 LoopEntry() : numIter(0), currentIter(0), currentIterSpec(0),
89 confidence(0), tag(0), age(0), dir(0) { }
90 };
91
92 // more provider types
93 enum {
|
91 LOOP = LAST_TAGE_PROVIDER_TYPE + 1
| 94 LOOP = TAGEBase::LAST_TAGE_PROVIDER_TYPE + 1
|
92 };
93
94 // Primary branch history entry
95 struct LTageBranchInfo : public TageBranchInfo
96 {
97 uint16_t loopTag;
98 uint16_t currentIter;
99
100 bool loopPred;
101 bool loopPredValid;
102 int loopIndex;
103 int loopLowPcBits; // only for useHashing
104 int loopHit;
105
| 95 };
96
97 // Primary branch history entry
98 struct LTageBranchInfo : public TageBranchInfo
99 {
100 uint16_t loopTag;
101 uint16_t currentIter;
102
103 bool loopPred;
104 bool loopPredValid;
105 int loopIndex;
106 int loopLowPcBits; // only for useHashing
107 int loopHit;
108
|
106 LTageBranchInfo(int sz)
107 : TageBranchInfo(sz),
| 109 LTageBranchInfo(TAGEBase &tage)
110 : TageBranchInfo(tage),
|
108 loopTag(0), currentIter(0),
109 loopPred(false),
110 loopPredValid(false), loopIndex(0), loopLowPcBits(0), loopHit(0)
111 {}
| 111 loopTag(0), currentIter(0),
112 loopPred(false),
113 loopPredValid(false), loopIndex(0), loopLowPcBits(0), loopHit(0)
114 {}
|
| 115
116 virtual ~LTageBranchInfo()
117 {}
|
112 };
113
114 /**
115 * Computes the index used to access the
116 * loop predictor.
117 * @param pc_in The unshifted branch PC.
118 */
119 int lindex(Addr pc_in) const;
120
121 /**
122 * Computes the index used to access the
123 * ltable structures.
124 * It may take hashing into account
125 * @param index Result of lindex function
126 * @param lowPcBits PC bits masked with set size
127 * @param way Way to be used
128 */
129 int finallindex(int lindex, int lowPcBits, int way) const;
130
131 /**
132 * Get a branch prediction from the loop
133 * predictor.
134 * @param pc The unshifted branch PC.
135 * @param bi Pointer to information on the
136 * prediction.
137 * @param speculative Use speculative number of iterations
138 */
139 bool getLoop(Addr pc, LTageBranchInfo* bi, bool speculative) const;
140
141 /**
142 * Updates the loop predictor.
143 * @param pc The unshifted branch PC.
144 * @param taken The actual branch outcome.
145 * @param bi Pointer to information on the
146 * prediction recorded at prediction time.
147 */
148 void loopUpdate(Addr pc, bool Taken, LTageBranchInfo* bi);
149
150 /**
151 * Speculatively updates the loop predictor
152 * iteration count (only for useSpeculation).
153 * @param taken The predicted branch outcome.
154 * @param bi Pointer to information on the prediction
155 * recorded at prediction time.
156 */
157 void specLoopUpdate(bool taken, LTageBranchInfo* bi);
158
159 /**
| 118 };
119
120 /**
121 * Computes the index used to access the
122 * loop predictor.
123 * @param pc_in The unshifted branch PC.
124 */
125 int lindex(Addr pc_in) const;
126
127 /**
128 * Computes the index used to access the
129 * ltable structures.
130 * It may take hashing into account
131 * @param index Result of lindex function
132 * @param lowPcBits PC bits masked with set size
133 * @param way Way to be used
134 */
135 int finallindex(int lindex, int lowPcBits, int way) const;
136
137 /**
138 * Get a branch prediction from the loop
139 * predictor.
140 * @param pc The unshifted branch PC.
141 * @param bi Pointer to information on the
142 * prediction.
143 * @param speculative Use speculative number of iterations
144 */
145 bool getLoop(Addr pc, LTageBranchInfo* bi, bool speculative) const;
146
147 /**
148 * Updates the loop predictor.
149 * @param pc The unshifted branch PC.
150 * @param taken The actual branch outcome.
151 * @param bi Pointer to information on the
152 * prediction recorded at prediction time.
153 */
154 void loopUpdate(Addr pc, bool Taken, LTageBranchInfo* bi);
155
156 /**
157 * Speculatively updates the loop predictor
158 * iteration count (only for useSpeculation).
159 * @param taken The predicted branch outcome.
160 * @param bi Pointer to information on the prediction
161 * recorded at prediction time.
162 */
163 void specLoopUpdate(bool taken, LTageBranchInfo* bi);
164
165 /**
|
160 * Update LTAGE for conditional branches.
161 * @param branch_pc The unshifted branch PC.
162 * @param taken Actual branch outcome.
163 * @param bi Pointer to information on the prediction
164 * recorded at prediction time.
165 * @nrand Random int number from 0 to 3
166 */
167 void condBranchUpdate(
168 Addr branch_pc, bool taken, TageBranchInfo* bi, int nrand) override;
169
170 /**
| |
171 * Get a branch prediction from LTAGE. *NOT* an override of
172 * BpredUnit::predict().
173 * @param tid The thread ID to select the global
174 * histories to use.
175 * @param branch_pc The unshifted branch PC.
176 * @param cond_branch True if the branch is conditional.
177 * @param b Reference to wrapping pointer to allow storing
178 * derived class prediction information in the base class.
179 */
180 bool predict(
181 ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) override;
182
183 /**
184 * Restores speculatively updated path and direction histories.
185 * Also recomputes compressed (folded) histories based on the
186 * correct branch outcome.
| 166 * Get a branch prediction from LTAGE. *NOT* an override of
167 * BpredUnit::predict().
168 * @param tid The thread ID to select the global
169 * histories to use.
170 * @param branch_pc The unshifted branch PC.
171 * @param cond_branch True if the branch is conditional.
172 * @param b Reference to wrapping pointer to allow storing
173 * derived class prediction information in the base class.
174 */
175 bool predict(
176 ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) override;
177
178 /**
179 * Restores speculatively updated path and direction histories.
180 * Also recomputes compressed (folded) histories based on the
181 * correct branch outcome.
|
187 * This version of squash() is called once on a branch misprediction.
188 * @param tid The Thread ID to select the histories to rollback.
189 * @param taken The correct branch outcome.
190 * @param bp_history Wrapping pointer to TageBranchInfo (to allow
191 * storing derived class prediction information in the
192 * base class).
193 * @post bp_history points to valid memory.
| 182 * @param bi Branch information.
|
194 */
| 183 */
|
195 void squash(
196 ThreadID tid, bool taken, void *bp_history) override;
| 184 void squashLoop(LTageBranchInfo * bi);
|
197
| 185
|
198 /**
199 * Update the stats
200 * @param taken Actual branch outcome
201 * @param bi Pointer to information on the prediction
202 * recorded at prediction time.
203 */
204 void updateStats(bool taken, TageBranchInfo* bi) override;
205
| |
206 const unsigned logSizeLoopPred;
207 const unsigned loopTableAgeBits;
208 const unsigned loopTableConfidenceBits;
209 const unsigned loopTableTagBits;
210 const unsigned loopTableIterBits;
211 const unsigned logLoopTableAssoc;
212 const uint8_t confidenceThreshold;
213 const uint16_t loopTagMask;
214 const uint16_t loopNumIterMask;
215 const int loopSetMask;
216
217 LoopEntry *ltable;
218
219 int8_t loopUseCounter;
220 unsigned withLoopBits;
221
222 const bool useDirectionBit;
223 const bool useSpeculation;
224 const bool useHashing;
225
226 // stats
227 Stats::Scalar loopPredictorCorrect;
228 Stats::Scalar loopPredictorWrong;
229};
230
231#endif // __CPU_PRED_LTAGE
| 186 const unsigned logSizeLoopPred;
187 const unsigned loopTableAgeBits;
188 const unsigned loopTableConfidenceBits;
189 const unsigned loopTableTagBits;
190 const unsigned loopTableIterBits;
191 const unsigned logLoopTableAssoc;
192 const uint8_t confidenceThreshold;
193 const uint16_t loopTagMask;
194 const uint16_t loopNumIterMask;
195 const int loopSetMask;
196
197 LoopEntry *ltable;
198
199 int8_t loopUseCounter;
200 unsigned withLoopBits;
201
202 const bool useDirectionBit;
203 const bool useSpeculation;
204 const bool useHashing;
205
206 // stats
207 Stats::Scalar loopPredictorCorrect;
208 Stats::Scalar loopPredictorWrong;
209};
210
211#endif // __CPU_PRED_LTAGE
|