#include <conditional.hh>

Inheritance diagram for gem5::branch_prediction::ConditionalPredictor:

Public Types
typedef ConditionalPredictorParams	Params
Public Types inherited from gem5::SimObject
typedef SimObjectParams	Params

Public Member Functions
	ConditionalPredictor (const Params &params)
virtual bool	lookup (ThreadID tid, Addr pc, void *&bp_history)=0
	Looks up a given conditional branch PC of in the BP to see if it is taken or not taken.
virtual void	updateHistories (ThreadID tid, Addr pc, bool uncond, bool taken, Addr target, const StaticInstPtr &inst, void *&bp_history)=0
	Ones done with the prediction this function updates the path and global history.
virtual void	squash (ThreadID tid, void *&bp_history)=0
virtual void	update (ThreadID tid, Addr pc, bool taken, void *&bp_history, bool squashed, const StaticInstPtr &inst, Addr target)=0
	Updates the BP with taken/not taken information.
virtual void	branchPlaceholder (ThreadID tid, Addr pc, bool uncond, void *&bp_history)
	Special function for the decoupled front-end.
Public Member Functions inherited from gem5::SimObject
const Params &	params () const
	SimObject (const Params &p)
virtual	~SimObject ()
virtual void	init ()
	init() is called after all C++ SimObjects have been created and all ports are connected.
virtual void	loadState (CheckpointIn &cp)
	loadState() is called on each SimObject when restoring from a checkpoint.
virtual void	initState ()
	initState() is called on each SimObject when not restoring from a checkpoint.
virtual void	regProbePoints ()
	Register probe points for this object.
virtual void	regProbeListeners ()
	Register probe listeners for this object.
ProbeManager *	getProbeManager ()
	Get the probe manager for this object.
virtual Port &	getPort (const std::string &if_name, PortID idx=InvalidPortID)
	Get a port with a given name and index.
virtual void	startup ()
	startup() is the final initialization call before simulation.
DrainState	drain () override
	Provide a default implementation of the drain interface for objects that don't need draining.
virtual void	memWriteback ()
	Write back dirty buffers to memory using functional writes.
virtual void	memInvalidate ()
	Invalidate the contents of memory buffers.
void	serialize (CheckpointOut &cp) const override
	Serialize an object.
void	unserialize (CheckpointIn &cp) override
	Unserialize an object.
Public Member Functions inherited from gem5::EventManager
EventQueue *	eventQueue () 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)
	This function is not needed by the usual gem5 event loop but may be necessary in derived EventQueues which host gem5 on other schedulers.
void	setCurTick (Tick newVal)
	EventManager (EventManager &em)
	Event manger manages events in the event queue.
	EventManager (EventManager *em)
	EventManager (EventQueue *eq)
Public Member Functions inherited from gem5::Serializable
	Serializable ()
virtual	~Serializable ()
void	serializeSection (CheckpointOut &cp, const char *name) const
	Serialize an object into a new section.
void	serializeSection (CheckpointOut &cp, const std::string &name) const
void	unserializeSection (CheckpointIn &cp, const char *name)
	Unserialize an a child object.
void	unserializeSection (CheckpointIn &cp, const std::string &name)
Public Member Functions inherited from gem5::Drainable
DrainState	drainState () const
	Return the current drain state of an object.
virtual void	notifyFork ()
	Notify a child process of a fork.
Public Member Functions inherited from gem5::statistics::Group
	Group (Group parent, const char name=nullptr)
	Construct a new statistics group.
virtual	~Group ()
virtual void	regStats ()
	Callback to set stat parameters.
virtual void	resetStats ()
	Callback to reset stats.
virtual void	preDumpStats ()
	Callback before stats are dumped.
void	addStat (statistics::Info *info)
	Register a stat with this group.
const std::map< std::string, Group * > &	getStatGroups () const
	Get all child groups associated with this object.
const std::vector< Info * > &	getStats () const
	Get all stats associated with this object.
void	addStatGroup (const char name, Group block)
	Add a stat block as a child of this block.
const Info *	resolveStat (std::string name) const
	Resolve a stat by its name within this group.
void	mergeStatGroup (Group *block)
	Merge the contents (stats & children) of a block to this block.
	Group ()=delete
	Group (const Group &)=delete
Group &	operator= (const Group &)=delete
Public Member Functions inherited from gem5::Named
	Named (std::string_view name_)
virtual	~Named ()=default
virtual std::string	name () const

Protected Attributes
const unsigned	instShiftAmt
	Number of bits to shift instructions by for predictor addresses.
Protected Attributes inherited from gem5::SimObject
const SimObjectParams &	_params
	Cached copy of the object parameters.
Protected Attributes inherited from gem5::EventManager
EventQueue *	eventq
	A pointer to this object's event queue.

Additional Inherited Members
Static Public Member Functions inherited from gem5::SimObject
static void	serializeAll (const std::string &cpt_dir)
	Create a checkpoint by serializing all SimObjects in the system.
static SimObject *	find (const char *name)
	Find the SimObject with the given name and return a pointer to it.
static void	setSimObjectResolver (SimObjectResolver *resolver)
	There is a single object name resolver, and it is only set when simulation is restoring from checkpoints.
static SimObjectResolver *	getSimObjectResolver ()
	There is a single object name resolver, and it is only set when simulation is restoring from checkpoints.
Static Public Member Functions inherited from gem5::Serializable
static const std::string &	currentSection ()
	Gets the fully-qualified name of the active section.
static void	generateCheckpointOut (const std::string &cpt_dir, std::ofstream &outstream)
	Generate a checkpoint file so that the serialization can be routed to it.
Protected Member Functions inherited from gem5::Drainable
	Drainable ()
virtual	~Drainable ()
virtual void	drainResume ()
	Resume execution after a successful drain.
void	signalDrainDone () const
	Signal that an object is drained.

Detailed Description

Definition at line 57 of file conditional.hh.

Member Typedef Documentation

◆ Params

typedef ConditionalPredictorParams gem5::branch_prediction::ConditionalPredictor::Params

Definition at line 61 of file conditional.hh.

Constructor & Destructor Documentation

◆ ConditionalPredictor()

gem5::branch_prediction::ConditionalPredictor::ConditionalPredictor ( const Params & params )

Definition at line 50 of file conditional.cc.

References instShiftAmt, gem5::SimObject::params(), and gem5::SimObject::SimObject().

Referenced by gem5::branch_prediction::BiModeBP::BiModeBP(), gem5::branch_prediction::LocalBP::LocalBP(), gem5::branch_prediction::MultiperspectivePerceptron::MultiperspectivePerceptron(), gem5::branch_prediction::TAGE::TAGE(), and gem5::branch_prediction::TournamentBP::TournamentBP().

Member Function Documentation

◆ branchPlaceholder()

void gem5::branch_prediction::ConditionalPredictor::branchPlaceholder	(	ThreadID	tid,
		Addr	pc,
		bool	uncond,
		void *&	bp_history )

virtual

Special function for the decoupled front-end.

In it there can be branches which are not detected by the BPU in the first place as it requires a BTB hit. This function will generate a placeholder for such a branch once it is pre-decoded in the fetch stage. It will only create the branch history object but not update any internal state of the BPU. If the branch turns to be wrong then decode or commit will be able to use the normal squash functionality to correct the branch. Note that not all branch predictors implement this functionality.

Parameters

tid	The thread id.
pc	The branch's PC.
uncond	Whether or not this branch is an unconditional branch.
bp_history	Pointer that will be set to an branch history object.

Reimplemented in gem5::branch_prediction::LocalBP, gem5::branch_prediction::LTAGE, gem5::branch_prediction::MultiperspectivePerceptronTAGE, gem5::branch_prediction::TAGE, and gem5::branch_prediction::TAGE_SC_L.

Definition at line 58 of file conditional.cc.

References panic, and gem5::MipsISA::pc.

◆ lookup()

virtual bool gem5::branch_prediction::ConditionalPredictor::lookup	(	ThreadID	tid,
		Addr	pc,
		void *&	bp_history )

pure virtual

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

Parameters

tid	The thread id.
pc	The PC to look up.
bp_history	Pointer 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 gem5::branch_prediction::BiModeBP, gem5::branch_prediction::LocalBP, gem5::branch_prediction::MultiperspectivePerceptron, gem5::branch_prediction::MultiperspectivePerceptronTAGE, gem5::branch_prediction::TAGE, and gem5::branch_prediction::TournamentBP.

References gem5::MipsISA::pc.

◆ squash()

virtual void gem5::branch_prediction::ConditionalPredictor::squash	(	ThreadID	tid,
		void *&	bp_history )

pure virtual

Parameters

tid	The thread id.
bp_history	Pointer to the history object. The predictor will need to update any state and delete the object.

Implemented in gem5::branch_prediction::BiModeBP, gem5::branch_prediction::LocalBP, gem5::branch_prediction::LTAGE, gem5::branch_prediction::MultiperspectivePerceptron, gem5::branch_prediction::MultiperspectivePerceptronTAGE, gem5::branch_prediction::TAGE, gem5::branch_prediction::TAGE_SC_L, and gem5::branch_prediction::TournamentBP.

◆ update()

virtual void gem5::branch_prediction::ConditionalPredictor::update	(	ThreadID	tid,
		Addr	pc,
		bool	taken,
		void *&	bp_history,
		bool	squashed,
		const StaticInstPtr &	inst,
		Addr	target )

pure virtual

Updates the BP with taken/not taken information.

Parameters

tid	The thread id.
pc	The branch's PC that will be updated.
taken	Whether the branch was taken or not taken.
bp_history	Pointer to the branch predictor state that is associated with the branch lookup that is being updated.
squashed	Set to true when this function is called during a squash operation.
inst	Static instruction information
target	The resolved target of the branch (only needed for squashed branches)

Todo: Make this update flexible enough to handle a global predictor.

Implemented in gem5::branch_prediction::BiModeBP, gem5::branch_prediction::LocalBP, gem5::branch_prediction::LTAGE, gem5::branch_prediction::MultiperspectivePerceptron, gem5::branch_prediction::MultiperspectivePerceptronTAGE, gem5::branch_prediction::TAGE, gem5::branch_prediction::TAGE_SC_L, and gem5::branch_prediction::TournamentBP.

References gem5::MipsISA::pc.

◆ updateHistories()

virtual void gem5::branch_prediction::ConditionalPredictor::updateHistories	(	ThreadID	tid,
		Addr	pc,
		bool	uncond,
		bool	taken,
		Addr	target,
		const StaticInstPtr &	inst,
		void *&	bp_history )

pure virtual

Ones done with the prediction this function updates the path and global history.

All branches call this function including unconditional once.

Parameters

tid	The thread id.
pc	The branch's pc that will be updated.
uncond	Wheather or not this branch is an unconditional branch.
taken	Whether or not the branch was taken
target	The final target of branch. Some modern predictors use the target in their history.
inst	Static instruction information
bp_history	Pointer that will be set to an object that has the branch predictor state associated with the lookup.

Implemented in gem5::branch_prediction::BiModeBP, gem5::branch_prediction::LocalBP, gem5::branch_prediction::MultiperspectivePerceptron, gem5::branch_prediction::MultiperspectivePerceptronTAGE, gem5::branch_prediction::TAGE, gem5::branch_prediction::TAGE_SC_L, and gem5::branch_prediction::TournamentBP.

References gem5::MipsISA::pc.

Member Data Documentation

◆ instShiftAmt

const unsigned gem5::branch_prediction::ConditionalPredictor::instShiftAmt

protected

Number of bits to shift instructions by for predictor addresses.

Definition at line 143 of file conditional.hh.

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

cpu/pred/conditional.hh
cpu/pred/conditional.cc

Public Types

Public Member Functions

Protected Attributes

Additional Inherited Members

Detailed Description

Member Typedef Documentation

◆ Params

Constructor & Destructor Documentation

◆ ConditionalPredictor()

Member Function Documentation

◆ branchPlaceholder()

◆ lookup()

◆ squash()

◆ update()

◆ updateHistories()

Member Data Documentation

◆ instShiftAmt