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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"
53 #include "params/TournamentBP.hh"
56 * Implements a tournament branch predictor, hopefully identical to the one
57 * used in the 21264. It has a local predictor, which uses a local history
58 * table to index into a table of counters, and a global predictor, which
59 * uses a global history to index into a table of counters. A choice
60 * predictor chooses between the two. Both the global history register
61 * and the selected local history are speculatively updated.
63 class TournamentBP : public BPredUnit
67 * Default branch predictor constructor.
69 TournamentBP(const TournamentBPParams *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(ThreadID tid, 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(ThreadID tid, Addr pc, 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(ThreadID tid, 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(ThreadID tid, Addr branch_addr, bool taken, void *bp_history,
109 * Restores the global branch history on a squash.
110 * @param bp_history Pointer to the BPHistory object that has the
111 * previous global branch history in it.
113 void squash(ThreadID tid, void *bp_history);
115 unsigned getGHR(ThreadID tid, void *bp_history) const;
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(ThreadID tid);
134 /** Updates global history as not taken. */
135 inline void updateGlobalHistNotTaken(ThreadID tid);
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 localHistoryIdx;
168 unsigned localHistory;
170 bool globalPredTaken;
174 /** Flag for invalid predictor index */
175 static const int invalidPredictorIndex = -1;
176 /** Local counters. */
177 std::vector<SatCounter> localCtrs;
179 /** Number of counters in the local predictor. */
180 unsigned localPredictorSize;
182 /** Mask to truncate values stored in the local history table. */
183 unsigned localPredictorMask;
185 /** Number of bits of the local predictor's counters. */
186 unsigned localCtrBits;
188 /** Array of local history table entries. */
189 std::vector<unsigned> localHistoryTable;
191 /** Number of entries in the local history table. */
192 unsigned localHistoryTableSize;
194 /** Number of bits for each entry of the local history table. */
195 unsigned localHistoryBits;
197 /** Array of counters that make up the global predictor. */
198 std::vector<SatCounter> globalCtrs;
200 /** Number of entries in the global predictor. */
201 unsigned globalPredictorSize;
203 /** Number of bits of the global predictor's counters. */
204 unsigned globalCtrBits;
206 /** Global history register. Contains as much history as specified by
207 * globalHistoryBits. Actual number of bits used is determined by
208 * globalHistoryMask and choiceHistoryMask. */
209 std::vector<unsigned> globalHistory;
211 /** Number of bits for the global history. Determines maximum number of
212 entries in global and choice predictor tables. */
213 unsigned globalHistoryBits;
215 /** Mask to apply to globalHistory to access global history table.
216 * Based on globalPredictorSize.*/
217 unsigned globalHistoryMask;
219 /** Mask to apply to globalHistory to access choice history table.
220 * Based on choicePredictorSize.*/
221 unsigned choiceHistoryMask;
223 /** Mask to control how much history is stored. All of it might not be
225 unsigned historyRegisterMask;
227 /** Array of counters that make up the choice predictor. */
228 std::vector<SatCounter> choiceCtrs;
230 /** Number of entries in the choice predictor. */
231 unsigned choicePredictorSize;
233 /** Number of bits in the choice predictor's counters. */
234 unsigned choiceCtrBits;
236 /** Thresholds for the counter value; above the threshold is taken,
237 * equal to or below the threshold is not taken.
239 unsigned localThreshold;
240 unsigned globalThreshold;
241 unsigned choiceThreshold;
244 #endif // __CPU_PRED_TOURNAMENT_PRED_HH__