src/cpu/pred/loop_predictor.cc - public/gem5 - Git at Google

 /*
  * Copyright (c) 2014 The University of Wisconsin
  *
  * Copyright (c) 2006 INRIA (Institut National de Recherche en
  * Informatique et en Automatique  / French National Research Institute
  * for Computer Science and Applied Mathematics)
  *
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met: redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer;
  * redistributions in binary form must reproduce the above copyright
  * notice, this list of conditions and the following disclaimer in the
  * documentation and/or other materials provided with the distribution;
  * neither the name of the copyright holders nor the names of its
  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "cpu/pred/loop_predictor.hh"

 #include "base/random.hh"
 #include "base/trace.hh"
 #include "debug/LTage.hh"
 #include "params/LoopPredictor.hh"

 namespace gem5
 {

 namespace branch_prediction
 {

 LoopPredictor::LoopPredictor(const LoopPredictorParams &p)
   : SimObject(p), logSizeLoopPred(p.logSizeLoopPred),
     loopTableAgeBits(p.loopTableAgeBits),
     loopTableConfidenceBits(p.loopTableConfidenceBits),
     loopTableTagBits(p.loopTableTagBits),
     loopTableIterBits(p.loopTableIterBits),
     logLoopTableAssoc(p.logLoopTableAssoc),
     confidenceThreshold((1 << loopTableConfidenceBits) - 1),
     loopTagMask((1 << loopTableTagBits) - 1),
     loopNumIterMask((1 << loopTableIterBits) - 1),
     loopSetMask((1 << (logSizeLoopPred - logLoopTableAssoc)) - 1),
     loopUseCounter(-1),
     withLoopBits(p.withLoopBits),
     useDirectionBit(p.useDirectionBit),
     useSpeculation(p.useSpeculation),
     useHashing(p.useHashing),
     restrictAllocation(p.restrictAllocation),
     initialLoopIter(p.initialLoopIter),
     initialLoopAge(p.initialLoopAge),
     optionalAgeReset(p.optionalAgeReset),
     stats(this)
 {
     assert(initialLoopAge <= ((1 << loopTableAgeBits) - 1));
 }

 void
 LoopPredictor::init()
 {
     // we use uint16_t type for these vales, so they cannot be more than
     // 16 bits
     assert(loopTableTagBits <= 16);
     assert(loopTableIterBits <= 16);

     assert(logSizeLoopPred >= logLoopTableAssoc);

     ltable = new LoopEntry[1ULL << logSizeLoopPred];
 }

 LoopPredictor::BranchInfo*
 LoopPredictor::makeBranchInfo()
 {
     return new BranchInfo();
 }

 int
 LoopPredictor::lindex(Addr pc_in, unsigned instShiftAmt) const
 {
     // The loop table is implemented as a linear table
     // If associativity is N (N being 1 << logLoopTableAssoc),
     // the first N entries are for set 0, the next N entries are for set 1,
     // and so on.
     // Thus, this function calculates the set and then it gets left shifted
     // by logLoopTableAssoc in order to return the index of the first of the
     // N entries of the set
     Addr pc = pc_in >> instShiftAmt;
     if (useHashing) {
         pc ^= pc_in;
     }
     return ((pc & loopSetMask) << logLoopTableAssoc);
 }

 int
 LoopPredictor::finallindex(int index, int lowPcBits, int way) const
 {
     return (useHashing ? (index ^ ((lowPcBits >> way) << logLoopTableAssoc)) :
                          (index))
            + way;
 }

 //loop prediction: only used if high confidence
 bool
 LoopPredictor::getLoop(Addr pc, BranchInfo* bi, bool speculative,
                        unsigned instShiftAmt) const
 {
     bi->loopHit = -1;
     bi->loopPredValid = false;
     bi->loopIndex = lindex(pc, instShiftAmt);

     if (useHashing) {
         unsigned pcShift = logSizeLoopPred - logLoopTableAssoc;
         bi->loopIndexB = (pc >> pcShift) & loopSetMask;
         bi->loopTag = (pc >> pcShift) ^ (pc >> (pcShift + loopTableTagBits));
         bi->loopTag &= loopTagMask;
     } else {
         unsigned pcShift = instShiftAmt + logSizeLoopPred - logLoopTableAssoc;
         bi->loopTag = (pc >> pcShift) & loopTagMask;
         // bi->loopIndexB is not used without hash
     }

     for (int i = 0; i < (1 << logLoopTableAssoc); i++) {
         int idx = finallindex(bi->loopIndex, bi->loopIndexB, i);
         if (ltable[idx].tag == bi->loopTag) {
             bi->loopHit = i;
             bi->loopPredValid = calcConf(idx);

             uint16_t iter = speculative ? ltable[idx].currentIterSpec
                                         : ltable[idx].currentIter;

             if ((iter + 1) == ltable[idx].numIter) {
                 return useDirectionBit ? !(ltable[idx].dir) : false;
             } else {
                 return useDirectionBit ? (ltable[idx].dir) : true;
             }
         }
     }
     return false;
 }

 bool
 LoopPredictor::calcConf(int index) const
 {
     return ltable[index].confidence == confidenceThreshold;
 }

 void
 LoopPredictor::specLoopUpdate(bool taken, BranchInfo* bi)
 {
     if (bi->loopHit>=0) {
         int index = finallindex(bi->loopIndex, bi->loopIndexB, bi->loopHit);
         if (taken != ltable[index].dir) {
             ltable[index].currentIterSpec = 0;
         } else {
             ltable[index].currentIterSpec =
                 (ltable[index].currentIterSpec + 1) & loopNumIterMask;
         }
     }
 }

 bool
 LoopPredictor::optionalAgeInc() const
 {
     return false;
 }

 void
 LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred)
 {
     int idx = finallindex(bi->loopIndex, bi->loopIndexB, bi->loopHit);
     if (bi->loopHit >= 0) {
         //already a hit
         if (bi->loopPredValid) {
             if (taken != bi->loopPred) {
                 // free the entry
                 ltable[idx].numIter = 0;
                 ltable[idx].age = 0;
                 ltable[idx].confidence = 0;
                 ltable[idx].currentIter = 0;
                 return;
             } else if (bi->loopPred != tage_pred || optionalAgeInc()) {
                 DPRINTF(LTage, "Loop Prediction success:%lx\n",pc);
                 unsignedCtrUpdate(ltable[idx].age, true, loopTableAgeBits);
             }
         }

         ltable[idx].currentIter =
             (ltable[idx].currentIter + 1) & loopNumIterMask;
         if (ltable[idx].currentIter > ltable[idx].numIter) {
             ltable[idx].confidence = 0;
             if (ltable[idx].numIter != 0) {
                 // free the entry
                 ltable[idx].numIter = 0;
                 if (optionalAgeReset) {
                     ltable[idx].age = 0;
                 }
             }
         }

         if (taken != (useDirectionBit ? ltable[idx].dir : true)) {
             if (ltable[idx].currentIter == ltable[idx].numIter) {
                 DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc);
                 unsignedCtrUpdate(ltable[idx].confidence, true,
                                   loopTableConfidenceBits);
                 //just do not predict when the loop count is 1 or 2
                 if (ltable[idx].numIter < 3) {
                     // free the entry
                     ltable[idx].dir = taken; // ignored if no useDirectionBit
                     ltable[idx].numIter = 0;
                     ltable[idx].age = 0;
                     ltable[idx].confidence = 0;
                 }
             } else {
                 DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc);
                 if (ltable[idx].numIter == 0) {
                     // first complete nest;
                     ltable[idx].confidence = 0;
                     ltable[idx].numIter = ltable[idx].currentIter;
                 } else {
                     //not the same number of iterations as last time: free the
                     //entry
                     ltable[idx].numIter = 0;
                     if (optionalAgeReset) {
                         ltable[idx].age = 0;
                     }
                     ltable[idx].confidence = 0;
                 }
             }
             ltable[idx].currentIter = 0;
         }

     } else if (useDirectionBit ? (bi->predTaken != taken) : taken) {
         if ((random_mt.random<int>() & 3) == 0 || !restrictAllocation) {
             //try to allocate an entry on taken branch
             int nrand = random_mt.random<int>();
             for (int i = 0; i < (1 << logLoopTableAssoc); i++) {
                 int loop_hit = (nrand + i) & ((1 << logLoopTableAssoc) - 1);
                 idx = finallindex(bi->loopIndex, bi->loopIndexB, loop_hit);
                 if (ltable[idx].age == 0) {
                     DPRINTF(LTage,
                             "Allocating loop pred entry for branch %lx\n",
                             pc);
                     ltable[idx].dir = !taken; // ignored if no useDirectionBit
                     ltable[idx].tag = bi->loopTag;
                     ltable[idx].numIter = 0;
                     ltable[idx].age = initialLoopAge;
                     ltable[idx].confidence = 0;
                     ltable[idx].currentIter = initialLoopIter;
                     break;

                 } else {
                     ltable[idx].age--;
                 }
                 if (restrictAllocation) {
                     break;
                 }
             }
         }
     }
 }

 bool
 LoopPredictor::loopPredict(ThreadID tid, Addr branch_pc, bool cond_branch,
                    BranchInfo* bi, bool prev_pred_taken, unsigned instShiftAmt)
 {
     bool pred_taken = prev_pred_taken;
     if (cond_branch) {
         // loop prediction
         bi->loopPred = getLoop(branch_pc, bi, useSpeculation, instShiftAmt);

         if ((loopUseCounter >= 0) && bi->loopPredValid) {
             pred_taken = bi->loopPred;
             bi->loopPredUsed = true;
         }

         if (useSpeculation) {
             specLoopUpdate(pred_taken, bi);
         }
     }

     return pred_taken;
 }

 void
 LoopPredictor::squash(ThreadID tid, BranchInfo *bi)
 {
     if (bi->loopHit >= 0) {
         int idx = finallindex(bi->loopIndex,
                 bi->loopIndexB,
                 bi->loopHit);
         ltable[idx].currentIterSpec = bi->currentIter;
     }
 }

 void
 LoopPredictor::squashLoop(BranchInfo* bi)
 {
     if (bi->loopHit >= 0) {
         int idx = finallindex(bi->loopIndex,
                 bi->loopIndexB,
                 bi->loopHit);
         ltable[idx].currentIterSpec = bi->currentIter;
     }
 }

 void
 LoopPredictor::updateStats(bool taken, BranchInfo* bi)
 {
     if (taken == bi->loopPred) {
         stats.correct++;
     } else {
         stats.wrong++;
     }
 }

 void
 LoopPredictor::condBranchUpdate(ThreadID tid, Addr branch_pc, bool taken,
                                 bool tage_pred, BranchInfo* bi,
                                 unsigned instShiftAmt)
 {
     if (useSpeculation) {
         // recalculate loop prediction without speculation
         // It is ok to overwrite the loop prediction fields in bi
         // as the stats have already been updated with the previous
         // values
         bi->loopPred = getLoop(branch_pc, bi, false, instShiftAmt);
     }

     if (bi->loopPredValid) {
         if (bi->predTaken != bi->loopPred) {
             signedCtrUpdate(loopUseCounter,
                       (bi->loopPred == taken),
                       withLoopBits);
         }
     }

     loopUpdate(branch_pc, taken, bi, tage_pred);
 }

 LoopPredictor::LoopPredictorStats::LoopPredictorStats(
     statistics::Group *parent)
     : statistics::Group(parent),
       ADD_STAT(correct, statistics::units::Count::get(),
                "Number of times the loop predictor is the provider and the "
                "prediction is correct"),
       ADD_STAT(wrong, statistics::units::Count::get(),
                "Number of times the loop predictor is the provider and the "
                "prediction is wrong")
 {
 }

 size_t
 LoopPredictor::getSizeInBits() const
 {
     return (1ULL << logSizeLoopPred) *
         ((useSpeculation ? 3 : 2) * loopTableIterBits +
         loopTableConfidenceBits + loopTableTagBits +
         loopTableAgeBits + useDirectionBit);
 }

 } // namespace branch_prediction
 } // namespace gem5
	/*
	* Copyright (c) 2014 The University of Wisconsin
	*
	* Copyright (c) 2006 INRIA (Institut National de Recherche en
	* Informatique et en Automatique / French National Research Institute
	* for Computer Science and Applied Mathematics)
	*
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions are
	* met: redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer;
	* redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution;
	* neither the name of the copyright holders nor the names of its
	* contributors may be used to endorse or promote products derived from
	* this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "cpu/pred/loop_predictor.hh"

	#include "base/random.hh"
	#include "base/trace.hh"
	#include "debug/LTage.hh"
	#include "params/LoopPredictor.hh"

	namespace gem5
	{

	namespace branch_prediction
	{

	LoopPredictor::LoopPredictor(const LoopPredictorParams &p)
	: SimObject(p), logSizeLoopPred(p.logSizeLoopPred),
	loopTableAgeBits(p.loopTableAgeBits),
	loopTableConfidenceBits(p.loopTableConfidenceBits),
	loopTableTagBits(p.loopTableTagBits),
	loopTableIterBits(p.loopTableIterBits),
	logLoopTableAssoc(p.logLoopTableAssoc),
	confidenceThreshold((1 << loopTableConfidenceBits) - 1),
	loopTagMask((1 << loopTableTagBits) - 1),
	loopNumIterMask((1 << loopTableIterBits) - 1),
	loopSetMask((1 << (logSizeLoopPred - logLoopTableAssoc)) - 1),
	loopUseCounter(-1),
	withLoopBits(p.withLoopBits),
	useDirectionBit(p.useDirectionBit),
	useSpeculation(p.useSpeculation),
	useHashing(p.useHashing),
	restrictAllocation(p.restrictAllocation),
	initialLoopIter(p.initialLoopIter),
	initialLoopAge(p.initialLoopAge),
	optionalAgeReset(p.optionalAgeReset),
	stats(this)
	{
	assert(initialLoopAge <= ((1 << loopTableAgeBits) - 1));
	}

	void
	LoopPredictor::init()
	{
	// we use uint16_t type for these vales, so they cannot be more than
	// 16 bits
	assert(loopTableTagBits <= 16);
	assert(loopTableIterBits <= 16);

	assert(logSizeLoopPred >= logLoopTableAssoc);

	ltable = new LoopEntry[1ULL << logSizeLoopPred];
	}

	LoopPredictor::BranchInfo*
	LoopPredictor::makeBranchInfo()
	{
	return new BranchInfo();
	}

	int
	LoopPredictor::lindex(Addr pc_in, unsigned instShiftAmt) const
	{
	// The loop table is implemented as a linear table
	// If associativity is N (N being 1 << logLoopTableAssoc),
	// the first N entries are for set 0, the next N entries are for set 1,
	// and so on.
	// Thus, this function calculates the set and then it gets left shifted
	// by logLoopTableAssoc in order to return the index of the first of the
	// N entries of the set
	Addr pc = pc_in >> instShiftAmt;
	if (useHashing) {
	pc ^= pc_in;
	}
	return ((pc & loopSetMask) << logLoopTableAssoc);
	}

	int
	LoopPredictor::finallindex(int index, int lowPcBits, int way) const
	{
	return (useHashing ? (index ^ ((lowPcBits >> way) << logLoopTableAssoc)) :
	(index))
	+ way;
	}

	//loop prediction: only used if high confidence
	bool
	LoopPredictor::getLoop(Addr pc, BranchInfo* bi, bool speculative,
	unsigned instShiftAmt) const
	{
	bi->loopHit = -1;
	bi->loopPredValid = false;
	bi->loopIndex = lindex(pc, instShiftAmt);

	if (useHashing) {
	unsigned pcShift = logSizeLoopPred - logLoopTableAssoc;
	bi->loopIndexB = (pc >> pcShift) & loopSetMask;
	bi->loopTag = (pc >> pcShift) ^ (pc >> (pcShift + loopTableTagBits));
	bi->loopTag &= loopTagMask;
	} else {
	unsigned pcShift = instShiftAmt + logSizeLoopPred - logLoopTableAssoc;
	bi->loopTag = (pc >> pcShift) & loopTagMask;
	// bi->loopIndexB is not used without hash
	}

	for (int i = 0; i < (1 << logLoopTableAssoc); i++) {
	int idx = finallindex(bi->loopIndex, bi->loopIndexB, i);
	if (ltable[idx].tag == bi->loopTag) {
	bi->loopHit = i;
	bi->loopPredValid = calcConf(idx);

	uint16_t iter = speculative ? ltable[idx].currentIterSpec
	: ltable[idx].currentIter;

	if ((iter + 1) == ltable[idx].numIter) {
	return useDirectionBit ? !(ltable[idx].dir) : false;
	} else {
	return useDirectionBit ? (ltable[idx].dir) : true;
	}
	}
	}
	return false;
	}

	bool
	LoopPredictor::calcConf(int index) const
	{
	return ltable[index].confidence == confidenceThreshold;
	}

	void
	LoopPredictor::specLoopUpdate(bool taken, BranchInfo* bi)
	{
	if (bi->loopHit>=0) {
	int index = finallindex(bi->loopIndex, bi->loopIndexB, bi->loopHit);
	if (taken != ltable[index].dir) {
	ltable[index].currentIterSpec = 0;
	} else {
	ltable[index].currentIterSpec =
	(ltable[index].currentIterSpec + 1) & loopNumIterMask;
	}
	}
	}

	bool
	LoopPredictor::optionalAgeInc() const
	{
	return false;
	}

	void
	LoopPredictor::loopUpdate(Addr pc, bool taken, BranchInfo* bi, bool tage_pred)
	{
	int idx = finallindex(bi->loopIndex, bi->loopIndexB, bi->loopHit);
	if (bi->loopHit >= 0) {
	//already a hit
	if (bi->loopPredValid) {
	if (taken != bi->loopPred) {
	// free the entry
	ltable[idx].numIter = 0;
	ltable[idx].age = 0;
	ltable[idx].confidence = 0;
	ltable[idx].currentIter = 0;
	return;
	} else if (bi->loopPred != tage_pred \|\| optionalAgeInc()) {
	DPRINTF(LTage, "Loop Prediction success:%lx\n",pc);
	unsignedCtrUpdate(ltable[idx].age, true, loopTableAgeBits);
	}
	}

	ltable[idx].currentIter =
	(ltable[idx].currentIter + 1) & loopNumIterMask;
	if (ltable[idx].currentIter > ltable[idx].numIter) {
	ltable[idx].confidence = 0;
	if (ltable[idx].numIter != 0) {
	// free the entry
	ltable[idx].numIter = 0;
	if (optionalAgeReset) {
	ltable[idx].age = 0;
	}
	}
	}

	if (taken != (useDirectionBit ? ltable[idx].dir : true)) {
	if (ltable[idx].currentIter == ltable[idx].numIter) {
	DPRINTF(LTage, "Loop End predicted successfully:%lx\n", pc);
	unsignedCtrUpdate(ltable[idx].confidence, true,
	loopTableConfidenceBits);
	//just do not predict when the loop count is 1 or 2
	if (ltable[idx].numIter < 3) {
	// free the entry
	ltable[idx].dir = taken; // ignored if no useDirectionBit
	ltable[idx].numIter = 0;
	ltable[idx].age = 0;
	ltable[idx].confidence = 0;
	}
	} else {
	DPRINTF(LTage, "Loop End predicted incorrectly:%lx\n", pc);
	if (ltable[idx].numIter == 0) {
	// first complete nest;
	ltable[idx].confidence = 0;
	ltable[idx].numIter = ltable[idx].currentIter;
	} else {
	//not the same number of iterations as last time: free the
	//entry
	ltable[idx].numIter = 0;
	if (optionalAgeReset) {
	ltable[idx].age = 0;
	}
	ltable[idx].confidence = 0;
	}
	}
	ltable[idx].currentIter = 0;
	}

	} else if (useDirectionBit ? (bi->predTaken != taken) : taken) {
	if ((random_mt.random<int>() & 3) == 0 \|\| !restrictAllocation) {
	//try to allocate an entry on taken branch
	int nrand = random_mt.random<int>();
	for (int i = 0; i < (1 << logLoopTableAssoc); i++) {
	int loop_hit = (nrand + i) & ((1 << logLoopTableAssoc) - 1);
	idx = finallindex(bi->loopIndex, bi->loopIndexB, loop_hit);
	if (ltable[idx].age == 0) {
	DPRINTF(LTage,
	"Allocating loop pred entry for branch %lx\n",
	pc);
	ltable[idx].dir = !taken; // ignored if no useDirectionBit
	ltable[idx].tag = bi->loopTag;
	ltable[idx].numIter = 0;
	ltable[idx].age = initialLoopAge;
	ltable[idx].confidence = 0;
	ltable[idx].currentIter = initialLoopIter;
	break;

	} else {
	ltable[idx].age--;
	}
	if (restrictAllocation) {
	break;
	}
	}
	}
	}
	}

	bool
	LoopPredictor::loopPredict(ThreadID tid, Addr branch_pc, bool cond_branch,
	BranchInfo* bi, bool prev_pred_taken, unsigned instShiftAmt)
	{
	bool pred_taken = prev_pred_taken;
	if (cond_branch) {
	// loop prediction
	bi->loopPred = getLoop(branch_pc, bi, useSpeculation, instShiftAmt);

	if ((loopUseCounter >= 0) && bi->loopPredValid) {
	pred_taken = bi->loopPred;
	bi->loopPredUsed = true;
	}

	if (useSpeculation) {
	specLoopUpdate(pred_taken, bi);
	}
	}

	return pred_taken;
	}

	void
	LoopPredictor::squash(ThreadID tid, BranchInfo *bi)
	{
	if (bi->loopHit >= 0) {
	int idx = finallindex(bi->loopIndex,
	bi->loopIndexB,
	bi->loopHit);
	ltable[idx].currentIterSpec = bi->currentIter;
	}
	}

	void
	LoopPredictor::squashLoop(BranchInfo* bi)
	{
	if (bi->loopHit >= 0) {
	int idx = finallindex(bi->loopIndex,
	bi->loopIndexB,
	bi->loopHit);
	ltable[idx].currentIterSpec = bi->currentIter;
	}
	}

	void
	LoopPredictor::updateStats(bool taken, BranchInfo* bi)
	{
	if (taken == bi->loopPred) {
	stats.correct++;
	} else {
	stats.wrong++;
	}
	}

	void
	LoopPredictor::condBranchUpdate(ThreadID tid, Addr branch_pc, bool taken,
	bool tage_pred, BranchInfo* bi,
	unsigned instShiftAmt)
	{
	if (useSpeculation) {
	// recalculate loop prediction without speculation
	// It is ok to overwrite the loop prediction fields in bi
	// as the stats have already been updated with the previous
	// values
	bi->loopPred = getLoop(branch_pc, bi, false, instShiftAmt);
	}

	if (bi->loopPredValid) {
	if (bi->predTaken != bi->loopPred) {
	signedCtrUpdate(loopUseCounter,
	(bi->loopPred == taken),
	withLoopBits);
	}
	}

	loopUpdate(branch_pc, taken, bi, tage_pred);
	}

	LoopPredictor::LoopPredictorStats::LoopPredictorStats(
	statistics::Group *parent)
	: statistics::Group(parent),
	ADD_STAT(correct, statistics::units::Count::get(),
	"Number of times the loop predictor is the provider and the "
	"prediction is correct"),
	ADD_STAT(wrong, statistics::units::Count::get(),
	"Number of times the loop predictor is the provider and the "
	"prediction is wrong")
	{
	}

	size_t
	LoopPredictor::getSizeInBits() const
	{
	return (1ULL << logSizeLoopPred) *
	((useSpeculation ? 3 : 2) * loopTableIterBits +
	loopTableConfidenceBits + loopTableTagBits +
	loopTableAgeBits + useDirectionBit);
	}

	} // namespace branch_prediction
	} // namespace gem5