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BPredUnit Class Referenceabstract

Basically a wrapper class to hold both the branch predictor and the BTB. More...

#include <bpred_unit.hh>

Inheritance diagram for BPredUnit:
SimObject EventManager Serializable Drainable BiModeBP LocalBP LTAGE TournamentBP

Classes

struct  PredictorHistory
 

Public Types

typedef BranchPredictorParams Params
 
- Public Types inherited from SimObject
typedef SimObjectParams Params
 

Public Member Functions

 BPredUnit (const Params *p)
 
void regStats () override
 Registers statistics. More...
 
void regProbePoints () override
 Register probe points for this object. More...
 
void drainSanityCheck () const
 Perform sanity checks after a drain. More...
 
bool predict (const StaticInstPtr &inst, const InstSeqNum &seqNum, TheISA::PCState &pc, ThreadID tid)
 Predicts whether or not the instruction is a taken branch, and the target of the branch if it is taken. More...
 
virtual void uncondBranch (ThreadID tid, Addr pc, void *&bp_history)=0
 
void update (const InstSeqNum &done_sn, ThreadID tid)
 Tells the branch predictor to commit any updates until the given sequence number. More...
 
void squash (const InstSeqNum &squashed_sn, ThreadID tid)
 Squashes all outstanding updates until a given sequence number. More...
 
void squash (const InstSeqNum &squashed_sn, const TheISA::PCState &corr_target, bool actually_taken, ThreadID tid)
 Squashes all outstanding updates until a given sequence number, and corrects that sn's update with the proper address and taken/not taken. More...
 
virtual void squash (ThreadID tid, void *bp_history)=0
 
virtual bool lookup (ThreadID tid, Addr instPC, void *&bp_history)=0
 Looks up a given PC in the BP to see if it is taken or not taken. More...
 
virtual void btbUpdate (ThreadID tid, Addr instPC, void *&bp_history)=0
 If a branch is not taken, because the BTB address is invalid or missing, this function sets the appropriate counter in the global and local predictors to not taken. More...
 
bool BTBValid (Addr instPC)
 Looks up a given PC in the BTB to see if a matching entry exists. More...
 
TheISA::PCState BTBLookup (Addr instPC)
 Looks up a given PC in the BTB to get the predicted target. More...
 
virtual void update (ThreadID tid, Addr instPC, bool taken, void *bp_history, bool squashed)=0
 Updates the BP with taken/not taken information. More...
 
void BTBUpdate (Addr instPC, const TheISA::PCState &target)
 Updates the BTB with the target of a branch. More...
 
virtual unsigned getGHR (ThreadID tid, void *bp_history) const
 
void dump ()
 
- Public Member Functions inherited from SimObject
const Paramsparams () const
 
 SimObject (const Params *_params)
 
virtual ~SimObject ()
 
virtual const std::string name () const
 
virtual void init ()
 init() is called after all C++ SimObjects have been created and all ports are connected. More...
 
virtual void loadState (CheckpointIn &cp)
 loadState() is called on each SimObject when restoring from a checkpoint. More...
 
virtual void initState ()
 initState() is called on each SimObject when not restoring from a checkpoint. More...
 
virtual void resetStats ()
 Reset statistics associated with this object. More...
 
virtual void regProbeListeners ()
 Register probe listeners for this object. More...
 
ProbeManagergetProbeManager ()
 Get the probe manager for this object. More...
 
virtual void startup ()
 startup() is the final initialization call before simulation. More...
 
DrainState drain () override
 Provide a default implementation of the drain interface for objects that don't need draining. More...
 
virtual void memWriteback ()
 Write back dirty buffers to memory using functional writes. More...
 
virtual void memInvalidate ()
 Invalidate the contents of memory buffers. More...
 
void serialize (CheckpointOut &cp) const override
 Serialize an object. More...
 
void unserialize (CheckpointIn &cp) override
 Unserialize an object. More...
 
- Public Member Functions inherited from EventManager
 EventManager (EventManager &em)
 
 EventManager (EventManager *em)
 
 EventManager (EventQueue *eq)
 
EventQueueeventQueue () const
 
void schedule (Event &event, Tick when)
 
void deschedule (Event &event)
 
void reschedule (Event &event, Tick when, bool always=false)
 
void schedule (Event *event, Tick when)
 
void deschedule (Event *event)
 
void reschedule (Event *event, Tick when, bool always=false)
 
void wakeupEventQueue (Tick when=(Tick)-1)
 
void setCurTick (Tick newVal)
 
- Public Member Functions inherited from Serializable
 Serializable ()
 
virtual ~Serializable ()
 
void serializeSection (CheckpointOut &cp, const char *name) const
 Serialize an object into a new section. More...
 
void serializeSection (CheckpointOut &cp, const std::string &name) const
 
void unserializeSection (CheckpointIn &cp, const char *name)
 Unserialize an a child object. More...
 
void unserializeSection (CheckpointIn &cp, const std::string &name)
 
- Public Member Functions inherited from Drainable
DrainState drainState () const
 Return the current drain state of an object. More...
 
virtual void notifyFork ()
 Notify a child process of a fork. More...
 

Protected Attributes

const unsigned instShiftAmt
 Number of bits to shift instructions by for predictor addresses. More...
 
- Protected Attributes inherited from SimObject
const SimObjectParams * _params
 Cached copy of the object parameters. More...
 
- Protected Attributes inherited from EventManager
EventQueueeventq
 A pointer to this object's event queue. More...
 

Private Types

typedef std::deque
< PredictorHistory
History
 

Private Attributes

const unsigned numThreads
 Number of the threads for which the branch history is maintained. More...
 
std::vector< HistorypredHist
 The per-thread predictor history. More...
 
DefaultBTB BTB
 The BTB. More...
 
std::vector< ReturnAddrStackRAS
 The per-thread return address stack. More...
 
const bool useIndirect
 Option to disable indirect predictor. More...
 
IndirectPredictor iPred
 The indirect target predictor. More...
 
Stats::Scalar lookups
 Stat for number of BP lookups. More...
 
Stats::Scalar condPredicted
 Stat for number of conditional branches predicted. More...
 
Stats::Scalar condIncorrect
 Stat for number of conditional branches predicted incorrectly. More...
 
Stats::Scalar BTBLookups
 Stat for number of BTB lookups. More...
 
Stats::Scalar BTBHits
 Stat for number of BTB hits. More...
 
Stats::Scalar BTBCorrect
 Stat for number of times the BTB is correct. More...
 
Stats::Formula BTBHitPct
 Stat for percent times an entry in BTB found. More...
 
Stats::Scalar usedRAS
 Stat for number of times the RAS is used to get a target. More...
 
Stats::Scalar RASIncorrect
 Stat for number of times the RAS is incorrect. More...
 
Stats::Scalar indirectLookups
 Stat for the number of indirect target lookups. More...
 
Stats::Scalar indirectHits
 Stat for the number of indirect target hits. More...
 
Stats::Scalar indirectMisses
 Stat for the number of indirect target misses. More...
 
Stats::Scalar indirectMispredicted
 Stat for the number of indirect target mispredictions. More...
 

PMU Probe points.

ProbePoints::PMUUPtr ppBranches
 Branches seen by the branch predictor. More...
 
ProbePoints::PMUUPtr ppMisses
 Miss-predicted branches. More...
 
ProbePoints::PMUUPtr pmuProbePoint (const char *name)
 Helper method to instantiate probe points belonging to this object. More...
 

Additional Inherited Members

- Static Public Member Functions inherited from SimObject
static void serializeAll (CheckpointOut &cp)
 Serialize all SimObjects in the system. More...
 
static SimObjectfind (const char *name)
 Find the SimObject with the given name and return a pointer to it. More...
 
- Static Public Member Functions inherited from Serializable
static const std::string & currentSection ()
 Get the fully-qualified name of the active section. More...
 
static void serializeAll (const std::string &cpt_dir)
 
static void unserializeGlobals (CheckpointIn &cp)
 
- Static Public Attributes inherited from Serializable
static int ckptCount = 0
 
static int ckptMaxCount = 0
 
static int ckptPrevCount = -1
 
- Protected Member Functions inherited from Drainable
 Drainable ()
 
virtual ~Drainable ()
 
virtual void drainResume ()
 Resume execution after a successful drain. More...
 
void signalDrainDone () const
 Signal that an object is drained. More...
 

Detailed Description

Basically a wrapper class to hold both the branch predictor and the BTB.

Definition at line 67 of file bpred_unit.hh.

Member Typedef Documentation

Definition at line 253 of file bpred_unit.hh.

typedef BranchPredictorParams BPredUnit::Params

Definition at line 70 of file bpred_unit.hh.

Constructor & Destructor Documentation

BPredUnit::BPredUnit ( const Params p)
Parameters
paramsThe params object, that has the size of the BP and BTB.

Definition at line 56 of file bpred_unit.cc.

References MipsISA::r, and RAS.

Member Function Documentation

TheISA::PCState BPredUnit::BTBLookup ( Addr  instPC)
inline

Looks up a given PC in the BTB to get the predicted target.

Parameters
inst_PCThe PC to look up.
Returns
The address of the target of the branch.

Definition at line 167 of file bpred_unit.hh.

References BTB, and DefaultBTB::lookup().

virtual void BPredUnit::btbUpdate ( ThreadID  tid,
Addr  instPC,
void *&  bp_history 
)
pure virtual

If a branch is not taken, because the BTB address is invalid or missing, this function sets the appropriate counter in the global and local predictors to not taken.

Parameters
inst_PCThe PC to look up the local predictor.
bp_historyPointer that will be set to an object that has the branch predictor state associated with the lookup.

Implemented in TournamentBP, LocalBP, LTAGE, and BiModeBP.

Referenced by predict().

void BPredUnit::BTBUpdate ( Addr  instPC,
const TheISA::PCState &  target 
)
inline

Updates the BTB with the target of a branch.

Parameters
inst_PCThe branch's PC that will be updated.
target_PCThe branch's target that will be added to the BTB.

Definition at line 187 of file bpred_unit.hh.

References BTB, and DefaultBTB::update().

bool BPredUnit::BTBValid ( Addr  instPC)
inline

Looks up a given PC in the BTB to see if a matching entry exists.

Parameters
inst_PCThe PC to look up.
Returns
Whether the BTB contains the given PC.

Definition at line 159 of file bpred_unit.hh.

References BTB, and DefaultBTB::valid().

void BPredUnit::drainSanityCheck ( ) const

Perform sanity checks after a drain.

Definition at line 171 of file bpred_unit.cc.

References M5_VAR_USED, and predHist.

void BPredUnit::dump ( )

Definition at line 491 of file bpred_unit.cc.

References cprintf(), ArmISA::i, and predHist.

virtual unsigned BPredUnit::getGHR ( ThreadID  tid,
void *  bp_history 
) const
inlinevirtual

Reimplemented in TournamentBP, LTAGE, and BiModeBP.

Definition at line 191 of file bpred_unit.hh.

Referenced by predict(), and squash().

virtual bool BPredUnit::lookup ( ThreadID  tid,
Addr  instPC,
void *&  bp_history 
)
pure virtual

Looks up a given PC in the BP to see if it is taken or not taken.

Parameters
inst_PCThe PC to look up.
bp_historyPointer that will be set to an object that has the branch predictor state associated with the lookup.
Returns
Whether the branch is taken or not taken.

Implemented in TournamentBP, LocalBP, LTAGE, and BiModeBP.

Referenced by predict().

ProbePoints::PMUUPtr BPredUnit::pmuProbePoint ( const char *  name)
protected

Helper method to instantiate probe points belonging to this object.

Parameters
nameName of the probe point.
Returns
A unique_ptr to the new probe point.

Definition at line 155 of file bpred_unit.cc.

References SimObject::getProbeManager().

Referenced by regProbePoints().

bool BPredUnit::predict ( const StaticInstPtr inst,
const InstSeqNum seqNum,
TheISA::PCState &  pc,
ThreadID  tid 
)

Predicts whether or not the instruction is a taken branch, and the target of the branch if it is taken.

Parameters
instThe branch instruction.
PCThe predicted PC is passed back through this parameter.
tidThe thread id.
Returns
Returns if the branch is taken or not.

Definition at line 180 of file bpred_unit.cc.

References AlphaISA::advancePC(), BTB, BTBHits, BTBLookups, btbUpdate(), AlphaISA::buildRetPC(), condPredicted, DPRINTF, getGHR(), indirectHits, indirectLookups, indirectMisses, iPred, StaticInst::isCall(), StaticInst::isDirectCtrl(), StaticInst::isReturn(), StaticInst::isUncondCtrl(), IndirectPredictor::lookup(), DefaultBTB::lookup(), lookup(), lookups, pc, ppBranches, predHist, RAS, IndirectPredictor::recordIndirect(), X86ISA::size(), uncondBranch(), usedRAS, useIndirect, and DefaultBTB::valid().

Referenced by Minor::Fetch2::predictBranch(), and BaseSimpleCPU::preExecute().

void BPredUnit::regProbePoints ( )
overridevirtual

Register probe points for this object.

No probe points by default, so do nothing in base.

Reimplemented from SimObject.

Definition at line 164 of file bpred_unit.cc.

References pmuProbePoint(), ppBranches, and ppMisses.

void BPredUnit::regStats ( )
overridevirtual
void BPredUnit::squash ( const InstSeqNum squashed_sn,
ThreadID  tid 
)

Squashes all outstanding updates until a given sequence number.

Parameters
squashed_snThe sequence number to squash any younger updates up until.
tidThe thread id.

Definition at line 342 of file bpred_unit.cc.

References DPRINTF, iPred, predHist, RAS, X86ISA::size(), and IndirectPredictor::squash().

Referenced by BaseSimpleCPU::advancePC(), squash(), and Minor::Fetch2::updateBranchPrediction().

void BPredUnit::squash ( const InstSeqNum squashed_sn,
const TheISA::PCState &  corr_target,
bool  actually_taken,
ThreadID  tid 
)

Squashes all outstanding updates until a given sequence number, and corrects that sn's update with the proper address and taken/not taken.

Parameters
squashed_snThe sequence number to squash any younger updates up until.
corr_targetThe correct branch target.
actually_takenThe correct branch direction.
tidThe thread id.

Definition at line 379 of file bpred_unit.cc.

References BTB, condIncorrect, DPRINTF, getGHR(), indirectMispredicted, iPred, ppMisses, predHist, RAS, RASIncorrect, IndirectPredictor::recordTarget(), squash(), DefaultBTB::update(), and update().

virtual void BPredUnit::squash ( ThreadID  tid,
void *  bp_history 
)
pure virtual
Parameters
bp_historyPointer to the history object. The predictor will need to update any state and delete the object.

Implemented in TournamentBP, LocalBP, LTAGE, and BiModeBP.

virtual void BPredUnit::uncondBranch ( ThreadID  tid,
Addr  pc,
void *&  bp_history 
)
pure virtual

Implemented in TournamentBP, LocalBP, LTAGE, and BiModeBP.

Referenced by predict().

void BPredUnit::update ( const InstSeqNum done_sn,
ThreadID  tid 
)

Tells the branch predictor to commit any updates until the given sequence number.

Parameters
done_snThe sequence number to commit any older updates up until.
tidThe thread id.

Definition at line 324 of file bpred_unit.cc.

References IndirectPredictor::commit(), DPRINTF, iPred, pc, and predHist.

Referenced by BaseSimpleCPU::advancePC(), squash(), and Minor::Fetch2::updateBranchPrediction().

virtual void BPredUnit::update ( ThreadID  tid,
Addr  instPC,
bool  taken,
void *  bp_history,
bool  squashed 
)
pure virtual

Updates the BP with taken/not taken information.

Parameters
inst_PCThe branch's PC that will be updated.
takenWhether the branch was taken or not taken.
bp_historyPointer to the branch predictor state that is associated with the branch lookup that is being updated.
squashedSet to true when this function is called during a squash operation.
Todo:
Make this update flexible enough to handle a global predictor.

Implemented in TournamentBP, LocalBP, LTAGE, and BiModeBP.

Member Data Documentation

DefaultBTB BPredUnit::BTB
private

The BTB.

Definition at line 267 of file bpred_unit.hh.

Referenced by BTBLookup(), BTBUpdate(), BTBValid(), predict(), and squash().

Stats::Scalar BPredUnit::BTBCorrect
private

Stat for number of times the BTB is correct.

Definition at line 289 of file bpred_unit.hh.

Referenced by regStats().

Stats::Formula BPredUnit::BTBHitPct
private

Stat for percent times an entry in BTB found.

Definition at line 291 of file bpred_unit.hh.

Referenced by regStats().

Stats::Scalar BPredUnit::BTBHits
private

Stat for number of BTB hits.

Definition at line 287 of file bpred_unit.hh.

Referenced by predict(), and regStats().

Stats::Scalar BPredUnit::BTBLookups
private

Stat for number of BTB lookups.

Definition at line 285 of file bpred_unit.hh.

Referenced by predict(), and regStats().

Stats::Scalar BPredUnit::condIncorrect
private

Stat for number of conditional branches predicted incorrectly.

Definition at line 283 of file bpred_unit.hh.

Referenced by regStats(), and squash().

Stats::Scalar BPredUnit::condPredicted
private

Stat for number of conditional branches predicted.

Definition at line 281 of file bpred_unit.hh.

Referenced by predict(), and regStats().

Stats::Scalar BPredUnit::indirectHits
private

Stat for the number of indirect target hits.

Definition at line 300 of file bpred_unit.hh.

Referenced by predict(), and regStats().

Stats::Scalar BPredUnit::indirectLookups
private

Stat for the number of indirect target lookups.

Definition at line 298 of file bpred_unit.hh.

Referenced by predict(), and regStats().

Stats::Scalar BPredUnit::indirectMispredicted
private

Stat for the number of indirect target mispredictions.

Definition at line 304 of file bpred_unit.hh.

Referenced by regStats(), and squash().

Stats::Scalar BPredUnit::indirectMisses
private

Stat for the number of indirect target misses.

Definition at line 302 of file bpred_unit.hh.

Referenced by predict(), and regStats().

const unsigned BPredUnit::instShiftAmt
protected

Number of bits to shift instructions by for predictor addresses.

Definition at line 308 of file bpred_unit.hh.

Referenced by TournamentBP::calcLocHistIdx(), LocalBP::getLocalIndex(), LocalBP::LocalBP(), BiModeBP::lookup(), and BiModeBP::update().

IndirectPredictor BPredUnit::iPred
private

The indirect target predictor.

Definition at line 276 of file bpred_unit.hh.

Referenced by predict(), squash(), and update().

Stats::Scalar BPredUnit::lookups
private

Stat for number of BP lookups.

Definition at line 279 of file bpred_unit.hh.

Referenced by predict(), and regStats().

const unsigned BPredUnit::numThreads
private

Number of the threads for which the branch history is maintained.

Definition at line 256 of file bpred_unit.hh.

ProbePoints::PMUUPtr BPredUnit::ppBranches
protected

Branches seen by the branch predictor.

Note
This counter includes speculative branches.

Definition at line 330 of file bpred_unit.hh.

Referenced by predict(), and regProbePoints().

ProbePoints::PMUUPtr BPredUnit::ppMisses
protected

Miss-predicted branches.

Definition at line 333 of file bpred_unit.hh.

Referenced by regProbePoints(), and squash().

std::vector<History> BPredUnit::predHist
private

The per-thread predictor history.

This is used to update the predictor as instructions are committed, or restore it to the proper state after a squash.

Definition at line 264 of file bpred_unit.hh.

Referenced by drainSanityCheck(), dump(), predict(), squash(), and update().

std::vector<ReturnAddrStack> BPredUnit::RAS
private

The per-thread return address stack.

Definition at line 270 of file bpred_unit.hh.

Referenced by BPredUnit(), predict(), and squash().

Stats::Scalar BPredUnit::RASIncorrect
private

Stat for number of times the RAS is incorrect.

Definition at line 295 of file bpred_unit.hh.

Referenced by regStats(), and squash().

Stats::Scalar BPredUnit::usedRAS
private

Stat for number of times the RAS is used to get a target.

Definition at line 293 of file bpred_unit.hh.

Referenced by predict(), and regStats().

const bool BPredUnit::useIndirect
private

Option to disable indirect predictor.

Definition at line 273 of file bpred_unit.hh.

Referenced by predict().


The documentation for this class was generated from the following files:

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