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
| 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
|
| 70 void regStats() override;
71
|
70 private:
71 // Prediction Structures
72 // Loop Predictor Entry
73 struct LoopEntry
74 {
75 uint16_t numIter;
76 uint16_t currentIter;
77 uint16_t currentIterSpec;
78 uint8_t confidence;
79 uint16_t tag;
80 uint8_t age;
81 bool dir;
82
83 LoopEntry() : numIter(0), currentIter(0), currentIterSpec(0),
84 confidence(0), tag(0), age(0), dir(0) { }
85 };
86
| 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;
80 uint8_t confidence;
81 uint16_t tag;
82 uint8_t age;
83 bool dir;
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 {
91 LOOP = LAST_TAGE_PROVIDER_TYPE + 1
92 };
93
|
87 // Primary branch history entry
88 struct LTageBranchInfo : public TageBranchInfo
89 {
90 uint16_t loopTag;
91 uint16_t currentIter;
92
93 bool loopPred;
94 bool loopPredValid;
95 int loopIndex;
96 int loopHit;
97
98 LTageBranchInfo(int sz)
99 : TageBranchInfo(sz),
100 loopTag(0), currentIter(0),
101 loopPred(false),
102 loopPredValid(false), loopIndex(0), loopHit(0)
103 {}
104 };
105
106 /**
107 * Computes the index used to access the
108 * loop predictor.
109 * @param pc_in The unshifted branch PC.
110 */
111 int lindex(Addr pc_in) const;
112
113 /**
114 * Get a branch prediction from the loop
115 * predictor.
116 * @param pc The unshifted branch PC.
117 * @param bi Pointer to information on the
118 * prediction.
119 */
120 bool getLoop(Addr pc, LTageBranchInfo* bi) const;
121
122 /**
123 * Updates the loop predictor.
124 * @param pc The unshifted branch PC.
125 * @param taken The actual branch outcome.
126 * @param bi Pointer to information on the
127 * prediction recorded at prediction time.
128 */
129 void loopUpdate(Addr pc, bool Taken, LTageBranchInfo* bi);
130
131 /**
132 * Speculatively updates the loop predictor
133 * iteration count.
134 * @param pc The unshifted branch PC.
135 * @param taken The predicted branch outcome.
136 * @param bi Pointer to information on the prediction
137 * recorded at prediction time.
138 */
139 void specLoopUpdate(Addr pc, bool taken, LTageBranchInfo* bi);
140
141 /**
142 * Update LTAGE for conditional branches.
143 * @param branch_pc The unshifted branch PC.
144 * @param taken Actual branch outcome.
145 * @param bi Pointer to information on the prediction
146 * recorded at prediction time.
147 * @nrand Random int number from 0 to 3
148 */
149 void condBranchUpdate(
150 Addr branch_pc, bool taken, TageBranchInfo* bi, int nrand) override;
151
152 /**
153 * Get a branch prediction from LTAGE. *NOT* an override of
154 * BpredUnit::predict().
155 * @param tid The thread ID to select the global
156 * histories to use.
157 * @param branch_pc The unshifted branch PC.
158 * @param cond_branch True if the branch is conditional.
159 * @param b Reference to wrapping pointer to allow storing
160 * derived class prediction information in the base class.
161 */
162 bool predict(
163 ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) override;
164
165 /**
166 * Restores speculatively updated path and direction histories.
167 * Also recomputes compressed (folded) histories based on the
168 * correct branch outcome.
169 * This version of squash() is called once on a branch misprediction.
170 * @param tid The Thread ID to select the histories to rollback.
171 * @param taken The correct branch outcome.
172 * @param bp_history Wrapping pointer to TageBranchInfo (to allow
173 * storing derived class prediction information in the
174 * base class).
175 * @post bp_history points to valid memory.
176 */
177 void squash(
178 ThreadID tid, bool taken, void *bp_history) override;
179
| 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 loopHit;
104
105 LTageBranchInfo(int sz)
106 : TageBranchInfo(sz),
107 loopTag(0), currentIter(0),
108 loopPred(false),
109 loopPredValid(false), loopIndex(0), loopHit(0)
110 {}
111 };
112
113 /**
114 * Computes the index used to access the
115 * loop predictor.
116 * @param pc_in The unshifted branch PC.
117 */
118 int lindex(Addr pc_in) const;
119
120 /**
121 * Get a branch prediction from the loop
122 * predictor.
123 * @param pc The unshifted branch PC.
124 * @param bi Pointer to information on the
125 * prediction.
126 */
127 bool getLoop(Addr pc, LTageBranchInfo* bi) const;
128
129 /**
130 * Updates the loop predictor.
131 * @param pc The unshifted branch PC.
132 * @param taken The actual branch outcome.
133 * @param bi Pointer to information on the
134 * prediction recorded at prediction time.
135 */
136 void loopUpdate(Addr pc, bool Taken, LTageBranchInfo* bi);
137
138 /**
139 * Speculatively updates the loop predictor
140 * iteration count.
141 * @param pc The unshifted branch PC.
142 * @param taken The predicted branch outcome.
143 * @param bi Pointer to information on the prediction
144 * recorded at prediction time.
145 */
146 void specLoopUpdate(Addr pc, bool taken, LTageBranchInfo* bi);
147
148 /**
149 * Update LTAGE for conditional branches.
150 * @param branch_pc The unshifted branch PC.
151 * @param taken Actual branch outcome.
152 * @param bi Pointer to information on the prediction
153 * recorded at prediction time.
154 * @nrand Random int number from 0 to 3
155 */
156 void condBranchUpdate(
157 Addr branch_pc, bool taken, TageBranchInfo* bi, int nrand) override;
158
159 /**
160 * Get a branch prediction from LTAGE. *NOT* an override of
161 * BpredUnit::predict().
162 * @param tid The thread ID to select the global
163 * histories to use.
164 * @param branch_pc The unshifted branch PC.
165 * @param cond_branch True if the branch is conditional.
166 * @param b Reference to wrapping pointer to allow storing
167 * derived class prediction information in the base class.
168 */
169 bool predict(
170 ThreadID tid, Addr branch_pc, bool cond_branch, void* &b) override;
171
172 /**
173 * Restores speculatively updated path and direction histories.
174 * Also recomputes compressed (folded) histories based on the
175 * correct branch outcome.
176 * This version of squash() is called once on a branch misprediction.
177 * @param tid The Thread ID to select the histories to rollback.
178 * @param taken The correct branch outcome.
179 * @param bp_history Wrapping pointer to TageBranchInfo (to allow
180 * storing derived class prediction information in the
181 * base class).
182 * @post bp_history points to valid memory.
183 */
184 void squash(
185 ThreadID tid, bool taken, void *bp_history) override;
186
|
| 187 /**
188 * Update the stats
189 * @param taken Actual branch outcome
190 * @param bi Pointer to information on the prediction
191 * recorded at prediction time.
192 */
193 void updateStats(bool taken, TageBranchInfo* bi) override;
194
|
180 const unsigned logSizeLoopPred;
181 const unsigned loopTableAgeBits;
182 const unsigned loopTableConfidenceBits;
183 const unsigned loopTableTagBits;
184 const unsigned loopTableIterBits;
185 const unsigned logLoopTableAssoc;
186 const uint8_t confidenceThreshold;
187 const uint16_t loopTagMask;
188 const uint16_t loopNumIterMask;
189
190 LoopEntry *ltable;
191
192 int8_t loopUseCounter;
193 unsigned withLoopBits;
| 195 const unsigned logSizeLoopPred;
196 const unsigned loopTableAgeBits;
197 const unsigned loopTableConfidenceBits;
198 const unsigned loopTableTagBits;
199 const unsigned loopTableIterBits;
200 const unsigned logLoopTableAssoc;
201 const uint8_t confidenceThreshold;
202 const uint16_t loopTagMask;
203 const uint16_t loopNumIterMask;
204
205 LoopEntry *ltable;
206
207 int8_t loopUseCounter;
208 unsigned withLoopBits;
|
| 209
210 // stats
211 Stats::Scalar loopPredictorCorrect;
212 Stats::Scalar loopPredictorWrong;
|
194};
195
196#endif // __CPU_PRED_LTAGE
| 213};
214
215#endif // __CPU_PRED_LTAGE
|