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.

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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 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
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
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;
194};
195
196#endif // __CPU_PRED_LTAGE