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47 #ifndef __CPU_PRED_BPRED_UNIT_HH__
48 #define __CPU_PRED_BPRED_UNIT_HH__
52 #include "base/statistics.hh"
53 #include "base/types.hh"
54 #include "cpu/pred/btb.hh"
55 #include "cpu/pred/ras.hh"
56 #include "cpu/inst_seq.hh"
57 #include "cpu/static_inst.hh"
58 #include "params/BranchPredictor.hh"
59 #include "sim/sim_object.hh"
62 * Basically a wrapper class to hold both the branch predictor
65 class BPredUnit : public SimObject
68 typedef BranchPredictorParams Params;
70 * @param params The params object, that has the size of the BP and BTB.
72 BPredUnit(const Params *p);
75 * Registers statistics.
79 /** Perform sanity checks after a drain. */
80 void drainSanityCheck() const;
83 * Predicts whether or not the instruction is a taken branch, and the
84 * target of the branch if it is taken.
85 * @param inst The branch instruction.
86 * @param PC The predicted PC is passed back through this parameter.
87 * @param tid The thread id.
88 * @return Returns if the branch is taken or not.
90 bool predict(StaticInstPtr &inst, const InstSeqNum &seqNum,
91 TheISA::PCState &pc, ThreadID tid);
92 bool predictInOrder(StaticInstPtr &inst, const InstSeqNum &seqNum,
93 int asid, TheISA::PCState &instPC,
94 TheISA::PCState &predPC, ThreadID tid);
96 // @todo: Rename this function.
97 virtual void uncondBranch(void * &bp_history) = 0;
100 * Tells the branch predictor to commit any updates until the given
102 * @param done_sn The sequence number to commit any older updates up until.
103 * @param tid The thread id.
105 void update(const InstSeqNum &done_sn, ThreadID tid);
108 * Squashes all outstanding updates until a given sequence number.
109 * @param squashed_sn The sequence number to squash any younger updates up
111 * @param tid The thread id.
113 void squash(const InstSeqNum &squashed_sn, ThreadID tid);
116 * Squashes all outstanding updates until a given sequence number, and
117 * corrects that sn's update with the proper address and taken/not taken.
118 * @param squashed_sn The sequence number to squash any younger updates up
120 * @param corr_target The correct branch target.
121 * @param actually_taken The correct branch direction.
122 * @param tid The thread id.
124 void squash(const InstSeqNum &squashed_sn,
125 const TheISA::PCState &corr_target,
126 bool actually_taken, ThreadID tid);
129 * @param bp_history Pointer to the history object. The predictor
130 * will need to update any state and delete the object.
132 virtual void squash(void *bp_history) = 0;
135 * Looks up a given PC in the BP to see if it is taken or not taken.
136 * @param inst_PC The PC to look up.
137 * @param bp_history Pointer that will be set to an object that
138 * has the branch predictor state associated with the lookup.
139 * @return Whether the branch is taken or not taken.
141 virtual bool lookup(Addr instPC, void * &bp_history) = 0;
144 * If a branch is not taken, because the BTB address is invalid or missing,
145 * this function sets the appropriate counter in the global and local
146 * predictors to not taken.
147 * @param inst_PC The PC to look up the local predictor.
148 * @param bp_history Pointer that will be set to an object that
149 * has the branch predictor state associated with the lookup.
151 virtual void btbUpdate(Addr instPC, void * &bp_history) = 0;
154 * Looks up a given PC in the BTB to see if a matching entry exists.
155 * @param inst_PC The PC to look up.
156 * @return Whether the BTB contains the given PC.
158 bool BTBValid(Addr instPC)
159 { return BTB.valid(instPC, 0); }
162 * Looks up a given PC in the BTB to get the predicted target.
163 * @param inst_PC The PC to look up.
164 * @return The address of the target of the branch.
166 TheISA::PCState BTBLookup(Addr instPC)
167 { return BTB.lookup(instPC, 0); }
170 * Updates the BP with taken/not taken information.
171 * @param inst_PC The branch's PC that will be updated.
172 * @param taken Whether the branch was taken or not taken.
173 * @param bp_history Pointer to the branch predictor state that is
174 * associated with the branch lookup that is being updated.
175 * @param squashed Set to true when this function is called during a
177 * @todo Make this update flexible enough to handle a global predictor.
179 virtual void update(Addr instPC, bool taken, void *bp_history,
182 * Deletes the associated history with a branch, performs no predictor
183 * updates. Used for branches that mispredict and update tables but
184 * are still speculative and later retire.
185 * @param bp_history History to delete associated with this predictor
187 virtual void retireSquashed(void *bp_history) = 0;
190 * Updates the BTB with the target of a branch.
191 * @param inst_PC The branch's PC that will be updated.
192 * @param target_PC The branch's target that will be added to the BTB.
194 void BTBUpdate(Addr instPC, const TheISA::PCState &target)
195 { BTB.update(instPC, target, 0); }
200 struct PredictorHistory {
202 * Makes a predictor history struct that contains any
203 * information needed to update the predictor, BTB, and RAS.
205 PredictorHistory(const InstSeqNum &seq_num, Addr instPC,
206 bool pred_taken, void *bp_history,
208 : seqNum(seq_num), pc(instPC), bpHistory(bp_history), RASTarget(0),
209 RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0), pushedRAS(0),
210 wasCall(0), wasReturn(0), wasSquashed(0)
213 bool operator==(const PredictorHistory &entry) const {
214 return this->seqNum == entry.seqNum;
217 /** The sequence number for the predictor history entry. */
220 /** The PC associated with the sequence number. */
223 /** Pointer to the history object passed back from the branch
224 * predictor. It is used to update or restore state of the
229 /** The RAS target (only valid if a return). */
230 TheISA::PCState RASTarget;
232 /** The RAS index of the instruction (only valid if a call). */
235 /** The thread id. */
238 /** Whether or not it was predicted taken. */
241 /** Whether or not the RAS was used. */
244 /* Whether or not the RAS was pushed */
247 /** Whether or not the instruction was a call. */
250 /** Whether or not the instruction was a return. */
253 /** Whether this instruction has already mispredicted/updated bp */
257 typedef std::deque<PredictorHistory> History;
259 /** Number of the threads for which the branch history is maintained. */
263 * The per-thread predictor history. This is used to update the predictor
264 * as instructions are committed, or restore it to the proper state after
267 std::vector<History> predHist;
272 /** The per-thread return address stack. */
273 std::vector<ReturnAddrStack> RAS;
275 /** Stat for number of BP lookups. */
276 Stats::Scalar lookups;
277 /** Stat for number of conditional branches predicted. */
278 Stats::Scalar condPredicted;
279 /** Stat for number of conditional branches predicted incorrectly. */
280 Stats::Scalar condIncorrect;
281 /** Stat for number of BTB lookups. */
282 Stats::Scalar BTBLookups;
283 /** Stat for number of BTB hits. */
284 Stats::Scalar BTBHits;
285 /** Stat for number of times the BTB is correct. */
286 Stats::Scalar BTBCorrect;
287 /** Stat for percent times an entry in BTB found. */
288 Stats::Formula BTBHitPct;
289 /** Stat for number of times the RAS is used to get a target. */
290 Stats::Scalar usedRAS;
291 /** Stat for number of times the RAS is incorrect. */
292 Stats::Scalar RASIncorrect;
295 #endif // __CPU_PRED_BPRED_UNIT_HH__