bpred_unit.hh (11427:fb512311295e) bpred_unit.hh (11429:cf5af0cc3be4)
1/*
2 * Copyright (c) 2011-2012, 2014 ARM Limited
3 * Copyright (c) 2010 The University of Edinburgh
4 * All rights reserved
5 *
6 * The license below extends only to copyright in the software and shall
7 * not be construed as granting a license to any other intellectual
8 * property including but not limited to intellectual property relating

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47#ifndef __CPU_PRED_BPRED_UNIT_HH__
48#define __CPU_PRED_BPRED_UNIT_HH__
49
50#include <deque>
51
52#include "base/statistics.hh"
53#include "base/types.hh"
54#include "cpu/pred/btb.hh"
1/*
2 * Copyright (c) 2011-2012, 2014 ARM Limited
3 * Copyright (c) 2010 The University of Edinburgh
4 * All rights reserved
5 *
6 * The license below extends only to copyright in the software and shall
7 * not be construed as granting a license to any other intellectual
8 * property including but not limited to intellectual property relating

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47#ifndef __CPU_PRED_BPRED_UNIT_HH__
48#define __CPU_PRED_BPRED_UNIT_HH__
49
50#include <deque>
51
52#include "base/statistics.hh"
53#include "base/types.hh"
54#include "cpu/pred/btb.hh"
55#include "cpu/pred/indirect.hh"
56#include "cpu/pred/ras.hh"
57#include "cpu/inst_seq.hh"
58#include "cpu/static_inst.hh"
59#include "params/BranchPredictor.hh"
60#include "sim/probe/pmu.hh"
61#include "sim/sim_object.hh"
62
63/**

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93 */
94 bool predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
95 TheISA::PCState &pc, ThreadID tid);
96 bool predictInOrder(const StaticInstPtr &inst, const InstSeqNum &seqNum,
97 int asid, TheISA::PCState &instPC,
98 TheISA::PCState &predPC, ThreadID tid);
99
100 // @todo: Rename this function.
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/probe/pmu.hh"
60#include "sim/sim_object.hh"
61
62/**

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92 */
93 bool predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
94 TheISA::PCState &pc, ThreadID tid);
95 bool predictInOrder(const StaticInstPtr &inst, const InstSeqNum &seqNum,
96 int asid, TheISA::PCState &instPC,
97 TheISA::PCState &predPC, ThreadID tid);
98
99 // @todo: Rename this function.
101 virtual void uncondBranch(ThreadID tid, Addr pc, void * &bp_history) = 0;
100 virtual void uncondBranch(Addr pc, void * &bp_history) = 0;
102
103 /**
104 * Tells the branch predictor to commit any updates until the given
105 * sequence number.
106 * @param done_sn The sequence number to commit any older updates up until.
107 * @param tid The thread id.
108 */
109 void update(const InstSeqNum &done_sn, ThreadID tid);

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128 void squash(const InstSeqNum &squashed_sn,
129 const TheISA::PCState &corr_target,
130 bool actually_taken, ThreadID tid);
131
132 /**
133 * @param bp_history Pointer to the history object. The predictor
134 * will need to update any state and delete the object.
135 */
101
102 /**
103 * Tells the branch predictor to commit any updates until the given
104 * sequence number.
105 * @param done_sn The sequence number to commit any older updates up until.
106 * @param tid The thread id.
107 */
108 void update(const InstSeqNum &done_sn, ThreadID tid);

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127 void squash(const InstSeqNum &squashed_sn,
128 const TheISA::PCState &corr_target,
129 bool actually_taken, ThreadID tid);
130
131 /**
132 * @param bp_history Pointer to the history object. The predictor
133 * will need to update any state and delete the object.
134 */
136 virtual void squash(ThreadID tid, void *bp_history) = 0;
135 virtual void squash(void *bp_history) = 0;
137
138 /**
139 * Looks up a given PC in the BP to see if it is taken or not taken.
140 * @param inst_PC The PC to look up.
141 * @param bp_history Pointer that will be set to an object that
142 * has the branch predictor state associated with the lookup.
143 * @return Whether the branch is taken or not taken.
144 */
136
137 /**
138 * Looks up a given PC in the BP to see if it is taken or not taken.
139 * @param inst_PC The PC to look up.
140 * @param bp_history Pointer that will be set to an object that
141 * has the branch predictor state associated with the lookup.
142 * @return Whether the branch is taken or not taken.
143 */
145 virtual bool lookup(ThreadID tid, Addr instPC, void * &bp_history) = 0;
144 virtual bool lookup(Addr instPC, void * &bp_history) = 0;
146
147 /**
148 * If a branch is not taken, because the BTB address is invalid or missing,
149 * this function sets the appropriate counter in the global and local
150 * predictors to not taken.
151 * @param inst_PC The PC to look up the local predictor.
152 * @param bp_history Pointer that will be set to an object that
153 * has the branch predictor state associated with the lookup.
154 */
145
146 /**
147 * If a branch is not taken, because the BTB address is invalid or missing,
148 * this function sets the appropriate counter in the global and local
149 * predictors to not taken.
150 * @param inst_PC The PC to look up the local predictor.
151 * @param bp_history Pointer that will be set to an object that
152 * has the branch predictor state associated with the lookup.
153 */
155 virtual void btbUpdate(ThreadID tid, Addr instPC, void * &bp_history) = 0;
154 virtual void btbUpdate(Addr instPC, void * &bp_history) = 0;
156
157 /**
158 * Looks up a given PC in the BTB to see if a matching entry exists.
159 * @param inst_PC The PC to look up.
160 * @return Whether the BTB contains the given PC.
161 */
162 bool BTBValid(Addr instPC)
163 { return BTB.valid(instPC, 0); }

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175 * @param inst_PC The branch's PC that will be updated.
176 * @param taken Whether the branch was taken or not taken.
177 * @param bp_history Pointer to the branch predictor state that is
178 * associated with the branch lookup that is being updated.
179 * @param squashed Set to true when this function is called during a
180 * squash operation.
181 * @todo Make this update flexible enough to handle a global predictor.
182 */
155
156 /**
157 * Looks up a given PC in the BTB to see if a matching entry exists.
158 * @param inst_PC The PC to look up.
159 * @return Whether the BTB contains the given PC.
160 */
161 bool BTBValid(Addr instPC)
162 { return BTB.valid(instPC, 0); }

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174 * @param inst_PC The branch's PC that will be updated.
175 * @param taken Whether the branch was taken or not taken.
176 * @param bp_history Pointer to the branch predictor state that is
177 * associated with the branch lookup that is being updated.
178 * @param squashed Set to true when this function is called during a
179 * squash operation.
180 * @todo Make this update flexible enough to handle a global predictor.
181 */
183 virtual void update(ThreadID tid, Addr instPC, bool taken,
184 void *bp_history, bool squashed) = 0;
182 virtual void update(Addr instPC, bool taken, void *bp_history,
183 bool squashed) = 0;
185 /**
186 * Deletes the associated history with a branch, performs no predictor
187 * updates. Used for branches that mispredict and update tables but
188 * are still speculative and later retire.
189 * @param bp_history History to delete associated with this predictor
190 */
184 /**
185 * Deletes the associated history with a branch, performs no predictor
186 * updates. Used for branches that mispredict and update tables but
187 * are still speculative and later retire.
188 * @param bp_history History to delete associated with this predictor
189 */
191 virtual void retireSquashed(ThreadID tid, void *bp_history) = 0;
190 virtual void retireSquashed(void *bp_history) = 0;
192
193 /**
194 * Updates the BTB with the target of a branch.
195 * @param inst_PC The branch's PC that will be updated.
196 * @param target_PC The branch's target that will be added to the BTB.
197 */
198 void BTBUpdate(Addr instPC, const TheISA::PCState &target)
199 { BTB.update(instPC, target, 0); }
200
191
192 /**
193 * Updates the BTB with the target of a branch.
194 * @param inst_PC The branch's PC that will be updated.
195 * @param target_PC The branch's target that will be added to the BTB.
196 */
197 void BTBUpdate(Addr instPC, const TheISA::PCState &target)
198 { BTB.update(instPC, target, 0); }
199
201
202 virtual unsigned getGHR(ThreadID tid, void* bp_history) const { return 0; }
203
204 void dump();
205
206 private:
207 struct PredictorHistory {
208 /**
209 * Makes a predictor history struct that contains any
210 * information needed to update the predictor, BTB, and RAS.
211 */
212 PredictorHistory(const InstSeqNum &seq_num, Addr instPC,
213 bool pred_taken, void *bp_history,
214 ThreadID _tid)
215 : seqNum(seq_num), pc(instPC), bpHistory(bp_history), RASTarget(0),
216 RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0), pushedRAS(0),
200 void dump();
201
202 private:
203 struct PredictorHistory {
204 /**
205 * Makes a predictor history struct that contains any
206 * information needed to update the predictor, BTB, and RAS.
207 */
208 PredictorHistory(const InstSeqNum &seq_num, Addr instPC,
209 bool pred_taken, void *bp_history,
210 ThreadID _tid)
211 : seqNum(seq_num), pc(instPC), bpHistory(bp_history), RASTarget(0),
212 RASIndex(0), tid(_tid), predTaken(pred_taken), usedRAS(0), pushedRAS(0),
217 wasCall(0), wasReturn(0), wasSquashed(0), wasIndirect(0)
213 wasCall(0), wasReturn(0), wasSquashed(0)
218 {}
219
220 bool operator==(const PredictorHistory &entry) const {
221 return this->seqNum == entry.seqNum;
222 }
223
224 /** The sequence number for the predictor history entry. */
225 InstSeqNum seqNum;

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254 /** Whether or not the instruction was a call. */
255 bool wasCall;
256
257 /** Whether or not the instruction was a return. */
258 bool wasReturn;
259
260 /** Whether this instruction has already mispredicted/updated bp */
261 bool wasSquashed;
214 {}
215
216 bool operator==(const PredictorHistory &entry) const {
217 return this->seqNum == entry.seqNum;
218 }
219
220 /** The sequence number for the predictor history entry. */
221 InstSeqNum seqNum;

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250 /** Whether or not the instruction was a call. */
251 bool wasCall;
252
253 /** Whether or not the instruction was a return. */
254 bool wasReturn;
255
256 /** Whether this instruction has already mispredicted/updated bp */
257 bool wasSquashed;
262
263 /** Wether this instruction was an indirect branch */
264 bool wasIndirect;
265 };
266
267 typedef std::deque<PredictorHistory> History;
268
269 /** Number of the threads for which the branch history is maintained. */
270 const unsigned numThreads;
271
272

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278 std::vector<History> predHist;
279
280 /** The BTB. */
281 DefaultBTB BTB;
282
283 /** The per-thread return address stack. */
284 std::vector<ReturnAddrStack> RAS;
285
258 };
259
260 typedef std::deque<PredictorHistory> History;
261
262 /** Number of the threads for which the branch history is maintained. */
263 const unsigned numThreads;
264
265

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271 std::vector<History> predHist;
272
273 /** The BTB. */
274 DefaultBTB BTB;
275
276 /** The per-thread return address stack. */
277 std::vector<ReturnAddrStack> RAS;
278
286 /** Option to disable indirect predictor. */
287 const bool useIndirect;
288
289 /** The indirect target predictor. */
290 IndirectPredictor iPred;
291
292 /** Stat for number of BP lookups. */
293 Stats::Scalar lookups;
294 /** Stat for number of conditional branches predicted. */
295 Stats::Scalar condPredicted;
296 /** Stat for number of conditional branches predicted incorrectly. */
297 Stats::Scalar condIncorrect;
298 /** Stat for number of BTB lookups. */
299 Stats::Scalar BTBLookups;
300 /** Stat for number of BTB hits. */
301 Stats::Scalar BTBHits;
302 /** Stat for number of times the BTB is correct. */
303 Stats::Scalar BTBCorrect;
304 /** Stat for percent times an entry in BTB found. */
305 Stats::Formula BTBHitPct;
306 /** Stat for number of times the RAS is used to get a target. */
307 Stats::Scalar usedRAS;
308 /** Stat for number of times the RAS is incorrect. */
309 Stats::Scalar RASIncorrect;
310
279 /** Stat for number of BP lookups. */
280 Stats::Scalar lookups;
281 /** Stat for number of conditional branches predicted. */
282 Stats::Scalar condPredicted;
283 /** Stat for number of conditional branches predicted incorrectly. */
284 Stats::Scalar condIncorrect;
285 /** Stat for number of BTB lookups. */
286 Stats::Scalar BTBLookups;
287 /** Stat for number of BTB hits. */
288 Stats::Scalar BTBHits;
289 /** Stat for number of times the BTB is correct. */
290 Stats::Scalar BTBCorrect;
291 /** Stat for percent times an entry in BTB found. */
292 Stats::Formula BTBHitPct;
293 /** Stat for number of times the RAS is used to get a target. */
294 Stats::Scalar usedRAS;
295 /** Stat for number of times the RAS is incorrect. */
296 Stats::Scalar RASIncorrect;
297
311 /** Stat for the number of indirect target lookups.*/
312 Stats::Scalar indirectLookups;
313 /** Stat for the number of indirect target hits.*/
314 Stats::Scalar indirectHits;
315 /** Stat for the number of indirect target misses.*/
316 Stats::Scalar indirectMisses;
317 /** Stat for the number of indirect target mispredictions.*/
318 Stats::Scalar indirectMispredicted;
319
320 protected:
321 /** Number of bits to shift instructions by for predictor addresses. */
322 const unsigned instShiftAmt;
323
324 /**
325 * @{
326 * @name PMU Probe points.
327 */

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299 /** Number of bits to shift instructions by for predictor addresses. */
300 const unsigned instShiftAmt;
301
302 /**
303 * @{
304 * @name PMU Probe points.
305 */

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