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45 #ifndef __CPU_PRED_TOURNAMENT_PRED_HH__
46 #define __CPU_PRED_TOURNAMENT_PRED_HH__
50 #include "base/types.hh"
51 #include "cpu/pred/bpred_unit.hh"
52 #include "cpu/pred/sat_counter.hh"
55 * Implements a tournament branch predictor, hopefully identical to the one
56 * used in the 21264. It has a local predictor, which uses a local history
57 * table to index into a table of counters, and a global predictor, which
58 * uses a global history to index into a table of counters. A choice
59 * predictor chooses between the two. Only the global history register
60 * is speculatively updated, the rest are updated upon branches committing
63 class TournamentBP : public BPredUnit
67 * Default branch predictor constructor.
69 TournamentBP(const Params *params);
72 * Looks up the given address in the branch predictor and returns
73 * a true/false value as to whether it is taken. Also creates a
74 * BPHistory object to store any state it will need on squash/update.
75 * @param branch_addr The address of the branch to look up.
76 * @param bp_history Pointer that will be set to the BPHistory object.
77 * @return Whether or not the branch is taken.
79 bool lookup(Addr branch_addr, void * &bp_history);
82 * Records that there was an unconditional branch, and modifies
83 * the bp history to point to an object that has the previous
84 * global history stored in it.
85 * @param bp_history Pointer that will be set to the BPHistory object.
87 void uncondBranch(void * &bp_history);
89 * Updates the branch predictor to Not Taken if a BTB entry is
90 * invalid or not found.
91 * @param branch_addr The address of the branch to look up.
92 * @param bp_history Pointer to any bp history state.
93 * @return Whether or not the branch is taken.
95 void btbUpdate(Addr branch_addr, void * &bp_history);
97 * Updates the branch predictor with the actual result of a branch.
98 * @param branch_addr The address of the branch to update.
99 * @param taken Whether or not the branch was taken.
100 * @param bp_history Pointer to the BPHistory object that was created
101 * when the branch was predicted.
102 * @param squashed is set when this function is called during a squash
105 void update(Addr branch_addr, bool taken, void *bp_history, bool squashed);
108 * Restores the global branch history on a squash.
109 * @param bp_history Pointer to the BPHistory object that has the
110 * previous global branch history in it.
112 void squash(void *bp_history);
114 /** Returns the global history. */
115 inline unsigned readGlobalHist() { return globalHistory; }
119 * Returns if the branch should be taken or not, given a counter
121 * @param count The counter value.
123 inline bool getPrediction(uint8_t &count);
126 * Returns the local history index, given a branch address.
127 * @param branch_addr The branch's PC address.
129 inline unsigned calcLocHistIdx(Addr &branch_addr);
131 /** Updates global history as taken. */
132 inline void updateGlobalHistTaken();
134 /** Updates global history as not taken. */
135 inline void updateGlobalHistNotTaken();
138 * Updates local histories as taken.
139 * @param local_history_idx The local history table entry that
142 inline void updateLocalHistTaken(unsigned local_history_idx);
145 * Updates local histories as not taken.
146 * @param local_history_idx The local history table entry that
149 inline void updateLocalHistNotTaken(unsigned local_history_idx);
152 * The branch history information that is created upon predicting
153 * a branch. It will be passed back upon updating and squashing,
154 * when the BP can use this information to update/restore its
166 unsigned globalHistory;
167 unsigned localHistory;
169 bool globalPredTaken;
173 /** Flag for invalid predictor index */
174 static const int invalidPredictorIndex = -1;
175 /** Local counters. */
176 std::vector<SatCounter> localCtrs;
178 /** Number of counters in the local predictor. */
179 unsigned localPredictorSize;
181 /** Mask to truncate values stored in the local history table. */
182 unsigned localPredictorMask;
184 /** Number of bits of the local predictor's counters. */
185 unsigned localCtrBits;
187 /** Array of local history table entries. */
188 std::vector<unsigned> localHistoryTable;
190 /** Number of entries in the local history table. */
191 unsigned localHistoryTableSize;
193 /** Number of bits for each entry of the local history table. */
194 unsigned localHistoryBits;
196 /** Array of counters that make up the global predictor. */
197 std::vector<SatCounter> globalCtrs;
199 /** Number of entries in the global predictor. */
200 unsigned globalPredictorSize;
202 /** Number of bits of the global predictor's counters. */
203 unsigned globalCtrBits;
205 /** Global history register. Contains as much history as specified by
206 * globalHistoryBits. Actual number of bits used is determined by
207 * globalHistoryMask and choiceHistoryMask. */
208 unsigned globalHistory;
210 /** Number of bits for the global history. Determines maximum number of
211 entries in global and choice predictor tables. */
212 unsigned globalHistoryBits;
214 /** Mask to apply to globalHistory to access global history table.
215 * Based on globalPredictorSize.*/
216 unsigned globalHistoryMask;
218 /** Mask to apply to globalHistory to access choice history table.
219 * Based on choicePredictorSize.*/
220 unsigned choiceHistoryMask;
222 /** Mask to control how much history is stored. All of it might not be
224 unsigned historyRegisterMask;
226 /** Array of counters that make up the choice predictor. */
227 std::vector<SatCounter> choiceCtrs;
229 /** Number of entries in the choice predictor. */
230 unsigned choicePredictorSize;
232 /** Number of bits in the choice predictor's counters. */
233 unsigned choiceCtrBits;
235 /** Number of bits to shift the instruction over to get rid of the word
238 unsigned instShiftAmt;
240 /** Thresholds for the counter value; above the threshold is taken,
241 * equal to or below the threshold is not taken.
243 unsigned localThreshold;
244 unsigned globalThreshold;
245 unsigned choiceThreshold;
248 #endif // __CPU_PRED_TOURNAMENT_PRED_HH__