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

 /*
  * Copyright (c) 2011-2012, 2014 ARM Limited
  * Copyright (c) 2010 The University of Edinburgh
  * Copyright (c) 2012 Mark D. Hill and David A. Wood
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
  * not be construed as granting a license to any other intellectual
  * property including but not limited to intellectual property relating
  * to a hardware implementation of the functionality of the software
  * licensed hereunder.  You may use the software subject to the license
  * terms below provided that you ensure that this notice is replicated
  * unmodified and in its entirety in all distributions of the software,
  * modified or unmodified, in source code or in binary form.
  *
  * Copyright (c) 2004-2005 The Regents of The University of Michigan
  * 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/bpred_unit.hh"

 #include <algorithm>

 #include "arch/generic/pcstate.hh"
 #include "base/compiler.hh"
 #include "base/trace.hh"
 #include "config/the_isa.hh"
 #include "debug/Branch.hh"

 namespace gem5
 {

 namespace branch_prediction
 {

 BPredUnit::BPredUnit(const Params &params)
     : SimObject(params),
       numThreads(params.numThreads),
       predHist(numThreads),
       BTB(params.BTBEntries,
           params.BTBTagSize,
           params.instShiftAmt,
           params.numThreads),
       RAS(numThreads),
       iPred(params.indirectBranchPred),
       stats(this),
       instShiftAmt(params.instShiftAmt)
 {
     for (auto& r : RAS)
         r.init(params.RASSize);
 }

 BPredUnit::BPredUnitStats::BPredUnitStats(statistics::Group *parent)
     : statistics::Group(parent),
       ADD_STAT(lookups, statistics::units::Count::get(),
               "Number of BP lookups"),
       ADD_STAT(condPredicted, statistics::units::Count::get(),
                "Number of conditional branches predicted"),
       ADD_STAT(condIncorrect, statistics::units::Count::get(),
                "Number of conditional branches incorrect"),
       ADD_STAT(BTBLookups, statistics::units::Count::get(),
                "Number of BTB lookups"),
       ADD_STAT(BTBHits, statistics::units::Count::get(), "Number of BTB hits"),
       ADD_STAT(BTBHitRatio, statistics::units::Ratio::get(), "BTB Hit Ratio",
                BTBHits / BTBLookups),
       ADD_STAT(RASUsed, statistics::units::Count::get(),
                "Number of times the RAS was used to get a target."),
       ADD_STAT(RASIncorrect, statistics::units::Count::get(),
                "Number of incorrect RAS predictions."),
       ADD_STAT(indirectLookups, statistics::units::Count::get(),
                "Number of indirect predictor lookups."),
       ADD_STAT(indirectHits, statistics::units::Count::get(),
                "Number of indirect target hits."),
       ADD_STAT(indirectMisses, statistics::units::Count::get(),
                "Number of indirect misses."),
       ADD_STAT(indirectMispredicted, statistics::units::Count::get(),
                "Number of mispredicted indirect branches.")
 {
     BTBHitRatio.precision(6);
 }

 probing::PMUUPtr
 BPredUnit::pmuProbePoint(const char *name)
 {
     probing::PMUUPtr ptr;
     ptr.reset(new probing::PMU(getProbeManager(), name));

     return ptr;
 }

 void
 BPredUnit::regProbePoints()
 {
     ppBranches = pmuProbePoint("Branches");
     ppMisses = pmuProbePoint("Misses");
 }

 void
 BPredUnit::drainSanityCheck() const
 {
     // We shouldn't have any outstanding requests when we resume from
     // a drained system.
     for ([[maybe_unused]] const auto& ph : predHist)
         assert(ph.empty());
 }

 bool
 BPredUnit::predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
                    PCStateBase &pc, ThreadID tid)
 {
     // See if branch predictor predicts taken.
     // If so, get its target addr either from the BTB or the RAS.
     // Save off record of branch stuff so the RAS can be fixed
     // up once it's done.

     bool pred_taken = false;
     std::unique_ptr<PCStateBase> target(pc.clone());

     ++stats.lookups;
     ppBranches->notify(1);

     void *bp_history = NULL;
     void *indirect_history = NULL;

     if (inst->isUncondCtrl()) {
         DPRINTF(Branch, "[tid:%i] [sn:%llu] Unconditional control\n",
             tid,seqNum);
         pred_taken = true;
         // Tell the BP there was an unconditional branch.
         uncondBranch(tid, pc.instAddr(), bp_history);
     } else {
         ++stats.condPredicted;
         pred_taken = lookup(tid, pc.instAddr(), bp_history);

         DPRINTF(Branch, "[tid:%i] [sn:%llu] "
                 "Branch predictor predicted %i for PC %s\n",
                 tid, seqNum,  pred_taken, pc);
     }

     const bool orig_pred_taken = pred_taken;
     if (iPred) {
         iPred->genIndirectInfo(tid, indirect_history);
     }

     DPRINTF(Branch,
             "[tid:%i] [sn:%llu] Creating prediction history for PC %s\n",
             tid, seqNum, pc);

     PredictorHistory predict_record(seqNum, pc.instAddr(), pred_taken,
                                     bp_history, indirect_history, tid, inst);

     // Now lookup in the BTB or RAS.
     if (pred_taken) {
         if (inst->isReturn()) {
             ++stats.RASUsed;
             predict_record.wasReturn = true;
             // If it's a function return call, then look up the address
             // in the RAS.
             const PCStateBase *ras_top = RAS[tid].top();
             if (ras_top)
                 set(target, inst->buildRetPC(pc, *ras_top));

             // Record the top entry of the RAS, and its index.
             predict_record.usedRAS = true;
             predict_record.RASIndex = RAS[tid].topIdx();
             set(predict_record.RASTarget, ras_top);

             RAS[tid].pop();

             DPRINTF(Branch, "[tid:%i] [sn:%llu] Instruction %s is a return, "
                     "RAS predicted target: %s, RAS index: %i\n",
                     tid, seqNum, pc, *target, predict_record.RASIndex);
         } else {

             if (inst->isCall()) {
                 RAS[tid].push(pc);
                 predict_record.pushedRAS = true;

                 // Record that it was a call so that the top RAS entry can
                 // be popped off if the speculation is incorrect.
                 predict_record.wasCall = true;

                 DPRINTF(Branch,
                         "[tid:%i] [sn:%llu] Instruction %s was a call, adding "
                         "%s to the RAS index: %i\n",
                         tid, seqNum, pc, pc, RAS[tid].topIdx());
             }

             if (inst->isDirectCtrl() || !iPred) {
                 ++stats.BTBLookups;
                 // Check BTB on direct branches
                 if (BTB.valid(pc.instAddr(), tid)) {
                     ++stats.BTBHits;
                     // If it's not a return, use the BTB to get target addr.
                     set(target, BTB.lookup(pc.instAddr(), tid));
                     DPRINTF(Branch,
                             "[tid:%i] [sn:%llu] Instruction %s predicted "
                             "target is %s\n",
                             tid, seqNum, pc, *target);
                 } else {
                     DPRINTF(Branch, "[tid:%i] [sn:%llu] BTB doesn't have a "
                             "valid entry\n", tid, seqNum);
                     pred_taken = false;
                     predict_record.predTaken = pred_taken;
                     // The Direction of the branch predictor is altered
                     // because the BTB did not have an entry
                     // The predictor needs to be updated accordingly
                     if (!inst->isCall() && !inst->isReturn()) {
                         btbUpdate(tid, pc.instAddr(), bp_history);
                         DPRINTF(Branch,
                                 "[tid:%i] [sn:%llu] btbUpdate "
                                 "called for %s\n",
                                 tid, seqNum, pc);
                     } else if (inst->isCall() && !inst->isUncondCtrl()) {
                         RAS[tid].pop();
                         predict_record.pushedRAS = false;
                     }
                     inst->advancePC(*target);
                 }
             } else {
                 predict_record.wasIndirect = true;
                 ++stats.indirectLookups;
                 //Consult indirect predictor on indirect control
                 if (iPred->lookup(pc.instAddr(), *target, tid)) {
                     // Indirect predictor hit
                     ++stats.indirectHits;
                     DPRINTF(Branch,
                             "[tid:%i] [sn:%llu] Instruction %s predicted "
                             "indirect target is %s\n",
                             tid, seqNum, pc, *target);
                 } else {
                     ++stats.indirectMisses;
                     pred_taken = false;
                     predict_record.predTaken = pred_taken;
                     DPRINTF(Branch,
                             "[tid:%i] [sn:%llu] Instruction %s no indirect "
                             "target\n",
                             tid, seqNum, pc);
                     if (!inst->isCall() && !inst->isReturn()) {

                     } else if (inst->isCall() && !inst->isUncondCtrl()) {
                         RAS[tid].pop();
                         predict_record.pushedRAS = false;
                     }
                     inst->advancePC(*target);
                 }
                 iPred->recordIndirect(pc.instAddr(), target->instAddr(),
                         seqNum, tid);
             }
         }
     } else {
         if (inst->isReturn()) {
            predict_record.wasReturn = true;
         }
         inst->advancePC(*target);
     }
     predict_record.target = target->instAddr();

     set(pc, *target);

     if (iPred) {
         // Update the indirect predictor with the direction prediction
         // Note that this happens after indirect lookup, so it does not use
         // the new information
         // Note also that we use orig_pred_taken instead of pred_taken in
         // as this is the actual outcome of the direction prediction
         iPred->updateDirectionInfo(tid, orig_pred_taken);
     }

     predHist[tid].push_front(predict_record);

     DPRINTF(Branch,
             "[tid:%i] [sn:%llu] History entry added. "
             "predHist.size(): %i\n",
             tid, seqNum, predHist[tid].size());

     return pred_taken;
 }

 void
 BPredUnit::update(const InstSeqNum &done_sn, ThreadID tid)
 {
     DPRINTF(Branch, "[tid:%i] Committing branches until "
             "sn:%llu]\n", tid, done_sn);

     while (!predHist[tid].empty() &&
            predHist[tid].back().seqNum <= done_sn) {
         // Update the branch predictor with the correct results.
         update(tid, predHist[tid].back().pc,
                     predHist[tid].back().predTaken,
                     predHist[tid].back().bpHistory, false,
                     predHist[tid].back().inst,
                     predHist[tid].back().target);

         if (iPred) {
             iPred->commit(done_sn, tid, predHist[tid].back().indirectHistory);
         }

         predHist[tid].pop_back();
     }
 }

 void
 BPredUnit::squash(const InstSeqNum &squashed_sn, ThreadID tid)
 {
     History &pred_hist = predHist[tid];

     if (iPred) {
         iPred->squash(squashed_sn, tid);
     }

     while (!pred_hist.empty() &&
            pred_hist.front().seqNum > squashed_sn) {
         if (pred_hist.front().usedRAS) {
             DPRINTF(Branch, "[tid:%i] [squash sn:%llu]"
                     " Restoring top of RAS to: %i,"
                     " target: %s\n", tid, squashed_sn,
                     pred_hist.front().RASIndex, *pred_hist.front().RASTarget);

             RAS[tid].restore(pred_hist.front().RASIndex,
                              pred_hist.front().RASTarget.get());
         } else if (pred_hist.front().wasCall && pred_hist.front().pushedRAS) {
              // Was a call but predicated false. Pop RAS here
              DPRINTF(Branch, "[tid:%i] [squash sn:%llu] Squashing"
                      "  Call [sn:%llu] PC: %s Popping RAS\n", tid, squashed_sn,
                      pred_hist.front().seqNum, pred_hist.front().pc);
              RAS[tid].pop();
         }

         // This call should delete the bpHistory.
         squash(tid, pred_hist.front().bpHistory);
         if (iPred) {
             iPred->deleteIndirectInfo(tid, pred_hist.front().indirectHistory);
         }

         DPRINTF(Branch, "[tid:%i] [squash sn:%llu] "
                 "Removing history for [sn:%llu] "
                 "PC %#x\n", tid, squashed_sn, pred_hist.front().seqNum,
                 pred_hist.front().pc);

         pred_hist.pop_front();

         DPRINTF(Branch, "[tid:%i] [squash sn:%llu] predHist.size(): %i\n",
                 tid, squashed_sn, predHist[tid].size());
     }
 }

 void
 BPredUnit::squash(const InstSeqNum &squashed_sn,
                   const PCStateBase &corr_target,
                   bool actually_taken, ThreadID tid)
 {
     // Now that we know that a branch was mispredicted, we need to undo
     // all the branches that have been seen up until this branch and
     // fix up everything.
     // NOTE: This should be call conceivably in 2 scenarios:
     // (1) After an branch is executed, it updates its status in the ROB
     //     The commit stage then checks the ROB update and sends a signal to
     //     the fetch stage to squash history after the mispredict
     // (2) In the decode stage, you can find out early if a unconditional
     //     PC-relative, branch was predicted incorrectly. If so, a signal
     //     to the fetch stage is sent to squash history after the mispredict

     History &pred_hist = predHist[tid];

     ++stats.condIncorrect;
     ppMisses->notify(1);

     DPRINTF(Branch, "[tid:%i] Squashing from sequence number %i, "
             "setting target to %s\n", tid, squashed_sn, corr_target);

     // Squash All Branches AFTER this mispredicted branch
     squash(squashed_sn, tid);

     // If there's a squash due to a syscall, there may not be an entry
     // corresponding to the squash.  In that case, don't bother trying to
     // fix up the entry.
     if (!pred_hist.empty()) {

         auto hist_it = pred_hist.begin();
         //HistoryIt hist_it = find(pred_hist.begin(), pred_hist.end(),
         //                       squashed_sn);

         //assert(hist_it != pred_hist.end());
         if (pred_hist.front().seqNum != squashed_sn) {
             DPRINTF(Branch, "Front sn %i != Squash sn %i\n",
                     pred_hist.front().seqNum, squashed_sn);

             assert(pred_hist.front().seqNum == squashed_sn);
         }


         if ((*hist_it).usedRAS) {
             ++stats.RASIncorrect;
             DPRINTF(Branch,
                     "[tid:%i] [squash sn:%llu] Incorrect RAS [sn:%llu]\n",
                     tid, squashed_sn, hist_it->seqNum);
         }

         // There are separate functions for in-order and out-of-order
         // branch prediction, but not for update. Therefore, this
         // call should take into account that the mispredicted branch may
         // be on the wrong path (i.e., OoO execution), and that the counter
         // counter table(s) should not be updated. Thus, this call should
         // restore the state of the underlying predictor, for instance the
         // local/global histories. The counter tables will be updated when
         // the branch actually commits.

         // Remember the correct direction for the update at commit.
         pred_hist.front().predTaken = actually_taken;
         pred_hist.front().target = corr_target.instAddr();

         update(tid, (*hist_it).pc, actually_taken,
                pred_hist.front().bpHistory, true, pred_hist.front().inst,
                corr_target.instAddr());

         if (iPred) {
             iPred->changeDirectionPrediction(tid,
                 pred_hist.front().indirectHistory, actually_taken);
         }

         if (actually_taken) {
             if (hist_it->wasReturn && !hist_it->usedRAS) {
                  DPRINTF(Branch, "[tid:%i] [squash sn:%llu] "
                         "Incorrectly predicted "
                         "return [sn:%llu] PC: %#x\n", tid, squashed_sn,
                         hist_it->seqNum,
                         hist_it->pc);
                  RAS[tid].pop();
                  hist_it->usedRAS = true;
             }
             if (hist_it->wasIndirect) {
                 ++stats.indirectMispredicted;
                 if (iPred) {
                     iPred->recordTarget(
                         hist_it->seqNum, pred_hist.front().indirectHistory,
                         corr_target, tid);
                 }
             } else {
                 DPRINTF(Branch,"[tid:%i] [squash sn:%llu] "
                         "BTB Update called for [sn:%llu] "
                         "PC %#x\n", tid, squashed_sn,
                         hist_it->seqNum, hist_it->pc);

                 BTB.update(hist_it->pc, corr_target, tid);
             }
         } else {
            //Actually not Taken
            if (hist_it->usedRAS) {
                 DPRINTF(Branch,
                         "[tid:%i] [squash sn:%llu] Incorrectly predicted "
                         "return [sn:%llu] PC: %#x Restoring RAS\n", tid,
                         squashed_sn,
                         hist_it->seqNum, hist_it->pc);
                 DPRINTF(Branch,
                         "[tid:%i] [squash sn:%llu] Restoring top of RAS "
                         "to: %i, target: %s\n", tid, squashed_sn,
                         hist_it->RASIndex, *hist_it->RASTarget);
                 RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget.get());
                 hist_it->usedRAS = false;
            } else if (hist_it->wasCall && hist_it->pushedRAS) {
                  //Was a Call but predicated false. Pop RAS here
                  DPRINTF(Branch,
                         "[tid:%i] [squash sn:%llu] "
                         "Incorrectly predicted "
                         "Call [sn:%llu] PC: %s Popping RAS\n",
                         tid, squashed_sn,
                         hist_it->seqNum, hist_it->pc);
                  RAS[tid].pop();
                  hist_it->pushedRAS = false;
            }
         }
     } else {
         DPRINTF(Branch, "[tid:%i] [sn:%llu] pred_hist empty, can't "
                 "update\n", tid, squashed_sn);
     }
 }

 void
 BPredUnit::dump()
 {
     int i = 0;
     for (const auto& ph : predHist) {
         if (!ph.empty()) {
             auto pred_hist_it = ph.begin();

             cprintf("predHist[%i].size(): %i\n", i++, ph.size());

             while (pred_hist_it != ph.end()) {
                 cprintf("sn:%llu], PC:%#x, tid:%i, predTaken:%i, "
                         "bpHistory:%#x\n",
                         pred_hist_it->seqNum, pred_hist_it->pc,
                         pred_hist_it->tid, pred_hist_it->predTaken,
                         pred_hist_it->bpHistory);
                 pred_hist_it++;
             }

             cprintf("\n");
         }
     }
 }

 } // namespace branch_prediction
 } // namespace gem5
	/*
	* Copyright (c) 2011-2012, 2014 ARM Limited
	* Copyright (c) 2010 The University of Edinburgh
	* Copyright (c) 2012 Mark D. Hill and David A. Wood
	* All rights reserved
	*
	* The license below extends only to copyright in the software and shall
	* not be construed as granting a license to any other intellectual
	* property including but not limited to intellectual property relating
	* to a hardware implementation of the functionality of the software
	* licensed hereunder. You may use the software subject to the license
	* terms below provided that you ensure that this notice is replicated
	* unmodified and in its entirety in all distributions of the software,
	* modified or unmodified, in source code or in binary form.
	*
	* Copyright (c) 2004-2005 The Regents of The University of Michigan
	* 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/bpred_unit.hh"

	#include <algorithm>

	#include "arch/generic/pcstate.hh"
	#include "base/compiler.hh"
	#include "base/trace.hh"
	#include "config/the_isa.hh"
	#include "debug/Branch.hh"

	namespace gem5
	{

	namespace branch_prediction
	{

	BPredUnit::BPredUnit(const Params &params)
	: SimObject(params),
	numThreads(params.numThreads),
	predHist(numThreads),
	BTB(params.BTBEntries,
	params.BTBTagSize,
	params.instShiftAmt,
	params.numThreads),
	RAS(numThreads),
	iPred(params.indirectBranchPred),
	stats(this),
	instShiftAmt(params.instShiftAmt)
	{
	for (auto& r : RAS)
	r.init(params.RASSize);
	}

	BPredUnit::BPredUnitStats::BPredUnitStats(statistics::Group *parent)
	: statistics::Group(parent),
	ADD_STAT(lookups, statistics::units::Count::get(),
	"Number of BP lookups"),
	ADD_STAT(condPredicted, statistics::units::Count::get(),
	"Number of conditional branches predicted"),
	ADD_STAT(condIncorrect, statistics::units::Count::get(),
	"Number of conditional branches incorrect"),
	ADD_STAT(BTBLookups, statistics::units::Count::get(),
	"Number of BTB lookups"),
	ADD_STAT(BTBHits, statistics::units::Count::get(), "Number of BTB hits"),
	ADD_STAT(BTBHitRatio, statistics::units::Ratio::get(), "BTB Hit Ratio",
	BTBHits / BTBLookups),
	ADD_STAT(RASUsed, statistics::units::Count::get(),
	"Number of times the RAS was used to get a target."),
	ADD_STAT(RASIncorrect, statistics::units::Count::get(),
	"Number of incorrect RAS predictions."),
	ADD_STAT(indirectLookups, statistics::units::Count::get(),
	"Number of indirect predictor lookups."),
	ADD_STAT(indirectHits, statistics::units::Count::get(),
	"Number of indirect target hits."),
	ADD_STAT(indirectMisses, statistics::units::Count::get(),
	"Number of indirect misses."),
	ADD_STAT(indirectMispredicted, statistics::units::Count::get(),
	"Number of mispredicted indirect branches.")
	{
	BTBHitRatio.precision(6);
	}

	probing::PMUUPtr
	BPredUnit::pmuProbePoint(const char *name)
	{
	probing::PMUUPtr ptr;
	ptr.reset(new probing::PMU(getProbeManager(), name));

	return ptr;
	}

	void
	BPredUnit::regProbePoints()
	{
	ppBranches = pmuProbePoint("Branches");
	ppMisses = pmuProbePoint("Misses");
	}

	void
	BPredUnit::drainSanityCheck() const
	{
	// We shouldn't have any outstanding requests when we resume from
	// a drained system.
	for ([[maybe_unused]] const auto& ph : predHist)
	assert(ph.empty());
	}

	bool
	BPredUnit::predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
	PCStateBase &pc, ThreadID tid)
	{
	// See if branch predictor predicts taken.
	// If so, get its target addr either from the BTB or the RAS.
	// Save off record of branch stuff so the RAS can be fixed
	// up once it's done.

	bool pred_taken = false;
	std::unique_ptr<PCStateBase> target(pc.clone());

	++stats.lookups;
	ppBranches->notify(1);

	void *bp_history = NULL;
	void *indirect_history = NULL;

	if (inst->isUncondCtrl()) {
	DPRINTF(Branch, "[tid:%i] [sn:%llu] Unconditional control\n",
	tid,seqNum);
	pred_taken = true;
	// Tell the BP there was an unconditional branch.
	uncondBranch(tid, pc.instAddr(), bp_history);
	} else {
	++stats.condPredicted;
	pred_taken = lookup(tid, pc.instAddr(), bp_history);

	DPRINTF(Branch, "[tid:%i] [sn:%llu] "
	"Branch predictor predicted %i for PC %s\n",
	tid, seqNum, pred_taken, pc);
	}

	const bool orig_pred_taken = pred_taken;
	if (iPred) {
	iPred->genIndirectInfo(tid, indirect_history);
	}

	DPRINTF(Branch,
	"[tid:%i] [sn:%llu] Creating prediction history for PC %s\n",
	tid, seqNum, pc);

	PredictorHistory predict_record(seqNum, pc.instAddr(), pred_taken,
	bp_history, indirect_history, tid, inst);

	// Now lookup in the BTB or RAS.
	if (pred_taken) {
	if (inst->isReturn()) {
	++stats.RASUsed;
	predict_record.wasReturn = true;
	// If it's a function return call, then look up the address
	// in the RAS.
	const PCStateBase *ras_top = RAS[tid].top();
	if (ras_top)
	set(target, inst->buildRetPC(pc, *ras_top));

	// Record the top entry of the RAS, and its index.
	predict_record.usedRAS = true;
	predict_record.RASIndex = RAS[tid].topIdx();
	set(predict_record.RASTarget, ras_top);

	RAS[tid].pop();

	DPRINTF(Branch, "[tid:%i] [sn:%llu] Instruction %s is a return, "
	"RAS predicted target: %s, RAS index: %i\n",
	tid, seqNum, pc, *target, predict_record.RASIndex);
	} else {

	if (inst->isCall()) {
	RAS[tid].push(pc);
	predict_record.pushedRAS = true;

	// Record that it was a call so that the top RAS entry can
	// be popped off if the speculation is incorrect.
	predict_record.wasCall = true;

	DPRINTF(Branch,
	"[tid:%i] [sn:%llu] Instruction %s was a call, adding "
	"%s to the RAS index: %i\n",
	tid, seqNum, pc, pc, RAS[tid].topIdx());
	}

	if (inst->isDirectCtrl() \|\| !iPred) {
	++stats.BTBLookups;
	// Check BTB on direct branches
	if (BTB.valid(pc.instAddr(), tid)) {
	++stats.BTBHits;
	// If it's not a return, use the BTB to get target addr.
	set(target, BTB.lookup(pc.instAddr(), tid));
	DPRINTF(Branch,
	"[tid:%i] [sn:%llu] Instruction %s predicted "
	"target is %s\n",
	tid, seqNum, pc, *target);
	} else {
	DPRINTF(Branch, "[tid:%i] [sn:%llu] BTB doesn't have a "
	"valid entry\n", tid, seqNum);
	pred_taken = false;
	predict_record.predTaken = pred_taken;
	// The Direction of the branch predictor is altered
	// because the BTB did not have an entry
	// The predictor needs to be updated accordingly
	if (!inst->isCall() && !inst->isReturn()) {
	btbUpdate(tid, pc.instAddr(), bp_history);
	DPRINTF(Branch,
	"[tid:%i] [sn:%llu] btbUpdate "
	"called for %s\n",
	tid, seqNum, pc);
	} else if (inst->isCall() && !inst->isUncondCtrl()) {
	RAS[tid].pop();
	predict_record.pushedRAS = false;
	}
	inst->advancePC(*target);
	}
	} else {
	predict_record.wasIndirect = true;
	++stats.indirectLookups;
	//Consult indirect predictor on indirect control
	if (iPred->lookup(pc.instAddr(), *target, tid)) {
	// Indirect predictor hit
	++stats.indirectHits;
	DPRINTF(Branch,
	"[tid:%i] [sn:%llu] Instruction %s predicted "
	"indirect target is %s\n",
	tid, seqNum, pc, *target);
	} else {
	++stats.indirectMisses;
	pred_taken = false;
	predict_record.predTaken = pred_taken;
	DPRINTF(Branch,
	"[tid:%i] [sn:%llu] Instruction %s no indirect "
	"target\n",
	tid, seqNum, pc);
	if (!inst->isCall() && !inst->isReturn()) {

	} else if (inst->isCall() && !inst->isUncondCtrl()) {
	RAS[tid].pop();
	predict_record.pushedRAS = false;
	}
	inst->advancePC(*target);
	}
	iPred->recordIndirect(pc.instAddr(), target->instAddr(),
	seqNum, tid);
	}
	}
	} else {
	if (inst->isReturn()) {
	predict_record.wasReturn = true;
	}
	inst->advancePC(*target);
	}
	predict_record.target = target->instAddr();

	set(pc, *target);

	if (iPred) {
	// Update the indirect predictor with the direction prediction
	// Note that this happens after indirect lookup, so it does not use
	// the new information
	// Note also that we use orig_pred_taken instead of pred_taken in
	// as this is the actual outcome of the direction prediction
	iPred->updateDirectionInfo(tid, orig_pred_taken);
	}

	predHist[tid].push_front(predict_record);

	DPRINTF(Branch,
	"[tid:%i] [sn:%llu] History entry added. "
	"predHist.size(): %i\n",
	tid, seqNum, predHist[tid].size());

	return pred_taken;
	}

	void
	BPredUnit::update(const InstSeqNum &done_sn, ThreadID tid)
	{
	DPRINTF(Branch, "[tid:%i] Committing branches until "
	"sn:%llu]\n", tid, done_sn);

	while (!predHist[tid].empty() &&
	predHist[tid].back().seqNum <= done_sn) {
	// Update the branch predictor with the correct results.
	update(tid, predHist[tid].back().pc,
	predHist[tid].back().predTaken,
	predHist[tid].back().bpHistory, false,
	predHist[tid].back().inst,
	predHist[tid].back().target);

	if (iPred) {
	iPred->commit(done_sn, tid, predHist[tid].back().indirectHistory);
	}

	predHist[tid].pop_back();
	}
	}

	void
	BPredUnit::squash(const InstSeqNum &squashed_sn, ThreadID tid)
	{
	History &pred_hist = predHist[tid];

	if (iPred) {
	iPred->squash(squashed_sn, tid);
	}

	while (!pred_hist.empty() &&
	pred_hist.front().seqNum > squashed_sn) {
	if (pred_hist.front().usedRAS) {
	DPRINTF(Branch, "[tid:%i] [squash sn:%llu]"
	" Restoring top of RAS to: %i,"
	" target: %s\n", tid, squashed_sn,
	pred_hist.front().RASIndex, *pred_hist.front().RASTarget);

	RAS[tid].restore(pred_hist.front().RASIndex,
	pred_hist.front().RASTarget.get());
	} else if (pred_hist.front().wasCall && pred_hist.front().pushedRAS) {
	// Was a call but predicated false. Pop RAS here
	DPRINTF(Branch, "[tid:%i] [squash sn:%llu] Squashing"
	" Call [sn:%llu] PC: %s Popping RAS\n", tid, squashed_sn,
	pred_hist.front().seqNum, pred_hist.front().pc);
	RAS[tid].pop();
	}

	// This call should delete the bpHistory.
	squash(tid, pred_hist.front().bpHistory);
	if (iPred) {
	iPred->deleteIndirectInfo(tid, pred_hist.front().indirectHistory);
	}

	DPRINTF(Branch, "[tid:%i] [squash sn:%llu] "
	"Removing history for [sn:%llu] "
	"PC %#x\n", tid, squashed_sn, pred_hist.front().seqNum,
	pred_hist.front().pc);

	pred_hist.pop_front();

	DPRINTF(Branch, "[tid:%i] [squash sn:%llu] predHist.size(): %i\n",
	tid, squashed_sn, predHist[tid].size());
	}
	}

	void
	BPredUnit::squash(const InstSeqNum &squashed_sn,
	const PCStateBase &corr_target,
	bool actually_taken, ThreadID tid)
	{
	// Now that we know that a branch was mispredicted, we need to undo
	// all the branches that have been seen up until this branch and
	// fix up everything.
	// NOTE: This should be call conceivably in 2 scenarios:
	// (1) After an branch is executed, it updates its status in the ROB
	// The commit stage then checks the ROB update and sends a signal to
	// the fetch stage to squash history after the mispredict
	// (2) In the decode stage, you can find out early if a unconditional
	// PC-relative, branch was predicted incorrectly. If so, a signal
	// to the fetch stage is sent to squash history after the mispredict

	History &pred_hist = predHist[tid];

	++stats.condIncorrect;
	ppMisses->notify(1);

	DPRINTF(Branch, "[tid:%i] Squashing from sequence number %i, "
	"setting target to %s\n", tid, squashed_sn, corr_target);

	// Squash All Branches AFTER this mispredicted branch
	squash(squashed_sn, tid);

	// If there's a squash due to a syscall, there may not be an entry
	// corresponding to the squash. In that case, don't bother trying to
	// fix up the entry.
	if (!pred_hist.empty()) {

	auto hist_it = pred_hist.begin();
	//HistoryIt hist_it = find(pred_hist.begin(), pred_hist.end(),
	// squashed_sn);

	//assert(hist_it != pred_hist.end());
	if (pred_hist.front().seqNum != squashed_sn) {
	DPRINTF(Branch, "Front sn %i != Squash sn %i\n",
	pred_hist.front().seqNum, squashed_sn);

	assert(pred_hist.front().seqNum == squashed_sn);
	}


	if ((*hist_it).usedRAS) {
	++stats.RASIncorrect;
	DPRINTF(Branch,
	"[tid:%i] [squash sn:%llu] Incorrect RAS [sn:%llu]\n",
	tid, squashed_sn, hist_it->seqNum);
	}

	// There are separate functions for in-order and out-of-order
	// branch prediction, but not for update. Therefore, this
	// call should take into account that the mispredicted branch may
	// be on the wrong path (i.e., OoO execution), and that the counter
	// counter table(s) should not be updated. Thus, this call should
	// restore the state of the underlying predictor, for instance the
	// local/global histories. The counter tables will be updated when
	// the branch actually commits.

	// Remember the correct direction for the update at commit.
	pred_hist.front().predTaken = actually_taken;
	pred_hist.front().target = corr_target.instAddr();

	update(tid, (*hist_it).pc, actually_taken,
	pred_hist.front().bpHistory, true, pred_hist.front().inst,
	corr_target.instAddr());

	if (iPred) {
	iPred->changeDirectionPrediction(tid,
	pred_hist.front().indirectHistory, actually_taken);
	}

	if (actually_taken) {
	if (hist_it->wasReturn && !hist_it->usedRAS) {
	DPRINTF(Branch, "[tid:%i] [squash sn:%llu] "
	"Incorrectly predicted "
	"return [sn:%llu] PC: %#x\n", tid, squashed_sn,
	hist_it->seqNum,
	hist_it->pc);
	RAS[tid].pop();
	hist_it->usedRAS = true;
	}
	if (hist_it->wasIndirect) {
	++stats.indirectMispredicted;
	if (iPred) {
	iPred->recordTarget(
	hist_it->seqNum, pred_hist.front().indirectHistory,
	corr_target, tid);
	}
	} else {
	DPRINTF(Branch,"[tid:%i] [squash sn:%llu] "
	"BTB Update called for [sn:%llu] "
	"PC %#x\n", tid, squashed_sn,
	hist_it->seqNum, hist_it->pc);

	BTB.update(hist_it->pc, corr_target, tid);
	}
	} else {
	//Actually not Taken
	if (hist_it->usedRAS) {
	DPRINTF(Branch,
	"[tid:%i] [squash sn:%llu] Incorrectly predicted "
	"return [sn:%llu] PC: %#x Restoring RAS\n", tid,
	squashed_sn,
	hist_it->seqNum, hist_it->pc);
	DPRINTF(Branch,
	"[tid:%i] [squash sn:%llu] Restoring top of RAS "
	"to: %i, target: %s\n", tid, squashed_sn,
	hist_it->RASIndex, *hist_it->RASTarget);
	RAS[tid].restore(hist_it->RASIndex, hist_it->RASTarget.get());
	hist_it->usedRAS = false;
	} else if (hist_it->wasCall && hist_it->pushedRAS) {
	//Was a Call but predicated false. Pop RAS here
	DPRINTF(Branch,
	"[tid:%i] [squash sn:%llu] "
	"Incorrectly predicted "
	"Call [sn:%llu] PC: %s Popping RAS\n",
	tid, squashed_sn,
	hist_it->seqNum, hist_it->pc);
	RAS[tid].pop();
	hist_it->pushedRAS = false;
	}
	}
	} else {
	DPRINTF(Branch, "[tid:%i] [sn:%llu] pred_hist empty, can't "
	"update\n", tid, squashed_sn);
	}
	}

	void
	BPredUnit::dump()
	{
	int i = 0;
	for (const auto& ph : predHist) {
	if (!ph.empty()) {
	auto pred_hist_it = ph.begin();

	cprintf("predHist[%i].size(): %i\n", i++, ph.size());

	while (pred_hist_it != ph.end()) {
	cprintf("sn:%llu], PC:%#x, tid:%i, predTaken:%i, "
	"bpHistory:%#x\n",
	pred_hist_it->seqNum, pred_hist_it->pc,
	pred_hist_it->tid, pred_hist_it->predTaken,
	pred_hist_it->bpHistory);
	pred_hist_it++;
	}

	cprintf("\n");
	}
	}
	}

	} // namespace branch_prediction
	} // namespace gem5