#include <ltage.hh>

Inheritance diagram for gem5::branch_prediction::LTAGE:

Classes
struct	LTageBranchInfo

Public Member Functions
	LTAGE (const LTAGEParams &params)

void	squash (ThreadID tid, void *&bp_history) override

void	update (ThreadID tid, Addr pc, bool taken, void *&bp_history, bool squashed, const StaticInstPtr &inst, Addr target) override
	Updates the BP with taken/not taken information.

void	branchPlaceholder (ThreadID tid, Addr pc, bool uncond, void *&bp_history) override
	Special function for the decoupled front-end.

void	init () override
	init() is called after all C++ SimObjects have been created and all ports are connected.

Public Member Functions inherited from gem5::branch_prediction::TAGE
	TAGE (const TAGEParams &params)

bool	lookup (ThreadID tid, Addr pc, void *&bp_history) override
	Looks up a given conditional branch PC of in the BP to see if it is taken or not taken.

void	updateHistories (ThreadID tid, Addr pc, bool uncond, bool taken, Addr target, const StaticInstPtr &inst, void *&bp_history) override
	Ones done with the prediction this function updates the path and global history.

void	update (ThreadID tid, Addr pc, bool taken, void *&bp_history, bool squashed, const StaticInstPtr &inst, Addr target) override
	Updates the BP with taken/not taken information.

void	squash (ThreadID tid, void *&bp_history) override

void	branchPlaceholder (ThreadID tid, Addr pc, bool uncond, void *&bp_history) override
	Special function for the decoupled front-end.

Public Member Functions inherited from gem5::branch_prediction::BPredUnit
	BPredUnit (const Params &p)
	Branch Predictor Unit (BPU) interface functions.

void	regProbePoints () override
	Register probe points for this object.

void	drainSanityCheck () const
	Perform sanity checks after a drain.

bool	predict (const StaticInstPtr &inst, const InstSeqNum &seqNum, PCStateBase &pc, ThreadID tid)
	Predicts whether or not the instruction is a taken branch, and the target of the branch if it is taken.

void	update (const InstSeqNum &done_sn, ThreadID tid)
	Tells the branch predictor to commit any updates until the given sequence number.

void	squash (const InstSeqNum &squashed_sn, ThreadID tid)
	Squashes all outstanding updates until a given sequence number.

void	squash (const InstSeqNum &squashed_sn, const PCStateBase &corr_target, bool actually_taken, ThreadID tid, bool from_commit=true)
	Squashes all outstanding updates until a given sequence number, and corrects that sn's update with the proper address and taken/not taken.

Public Member Functions inherited from gem5::SimObject
const Params &	params () const

	SimObject (const Params &p)

virtual	~SimObject ()

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	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 Types
enum	{ LOOP = TAGEBase::LAST_TAGE_PROVIDER_TYPE + 1 , LAST_LTAGE_PROVIDER_TYPE = LOOP }

Protected Member Functions
bool	predict (ThreadID tid, Addr branch_pc, bool cond_branch, void *&b) override
	Get a branch prediction from LTAGE.

Protected Member Functions inherited from gem5::branch_prediction::BPredUnit
bool	BTBValid (ThreadID tid, Addr pc)
	Looks up a given PC in the BTB to see if a matching entry exists.

const PCStateBase *	BTBLookup (ThreadID tid, PCStateBase &pc)
	Looks up a given PC in the BTB to get the predicted target.

const StaticInstPtr	BTBGetInst (ThreadID tid, Addr pc)
	Looks up a given PC in the BTB to get current static instruction information.

void	BTBUpdate (ThreadID tid, Addr pc, const PCStateBase &target)
	Updates the BTB with the target of a branch.

void	dump ()

probing::PMUUPtr	pmuProbePoint (const char *name)
	Helper method to instantiate probe points belonging to this object.

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.

Protected Attributes
LoopPredictor *	loopPredictor
	The loop predictor object.

Protected Attributes inherited from gem5::branch_prediction::TAGE
TAGEBase *	tage

Random::RandomPtr	rng = Random::genRandom()

Protected Attributes inherited from gem5::branch_prediction::BPredUnit
const unsigned	numThreads
	Number of the threads for which the branch history is maintained.

const bool	requiresBTBHit
	Requires the BTB to hit for returns and indirect branches.

const unsigned	instShiftAmt
	Number of bits to shift instructions by for predictor addresses.

std::vector< History >	predHist
	The per-thread predictor history.

BranchTargetBuffer *	btb
	The BTB.

ReturnAddrStack *	ras
	The return address stack.

IndirectPredictor *	iPred
	The indirect target predictor.

gem5::branch_prediction::BPredUnit::BPredUnitStats	stats

probing::PMUUPtr	ppBranches
	Branches seen by the branch predictor.

probing::PMUUPtr	ppMisses
	Miss-predicted branches.

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
Public Types inherited from gem5::SimObject
typedef SimObjectParams	Params

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.

Detailed Description

Definition at line 78 of file ltage.hh.

Member Enumeration Documentation

◆ anonymous enum

anonymous enum

protected

Enumerator
LOOP
LAST_LTAGE_PROVIDER_TYPE

Definition at line 97 of file ltage.hh.

Constructor & Destructor Documentation

◆ LTAGE()

gem5::branch_prediction::LTAGE::LTAGE ( const LTAGEParams & params )

Definition at line 64 of file ltage.cc.

References loopPredictor, gem5::SimObject::params(), and gem5::branch_prediction::TAGE::TAGE().

Referenced by gem5::branch_prediction::TAGE_SC_L::TAGE_SC_L().

Member Function Documentation

◆ branchPlaceholder()

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

overridevirtual

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 from gem5::branch_prediction::BPredUnit.

Reimplemented in gem5::branch_prediction::TAGE_SC_L.

Definition at line 76 of file ltage.cc.

References gem5::PowerISA::bi, loopPredictor, gem5::MipsISA::pc, and gem5::branch_prediction::TAGE::tage.

◆ init()

void gem5::branch_prediction::LTAGE::init ( )

overridevirtual

init() is called after all C++ SimObjects have been created and all ports are connected.

Initializations that are independent of unserialization but rely on a fully instantiated and connected SimObject graph should be done here.

Reimplemented from gem5::SimObject.

Definition at line 70 of file ltage.cc.

References gem5::SimObject::init().

◆ predict()

bool gem5::branch_prediction::LTAGE::predict	(	ThreadID	tid,
		Addr	branch_pc,
		bool	cond_branch,
		void *&	b )

overrideprotectedvirtual

Get a branch prediction from LTAGE.

NOT an override of BpredUnit::predict().

Parameters

tid	The thread ID to select the global histories to use.
branch_pc	The unshifted branch PC.
cond_branch	True if the branch is conditional.
b	Reference to wrapping pointer to allow storing derived class prediction information in the base class.

Reimplemented from gem5::branch_prediction::TAGE.

Reimplemented in gem5::branch_prediction::TAGE_SC_L.

Definition at line 86 of file ltage.cc.

References gem5::ArmISA::b, gem5::PowerISA::bi, DPRINTF, gem5::branch_prediction::BPredUnit::instShiftAmt, LOOP, loopPredictor, and gem5::branch_prediction::TAGE::tage.

◆ squash()

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

overridevirtual

Parameters

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

Implements gem5::branch_prediction::BPredUnit.

Reimplemented in gem5::branch_prediction::TAGE_SC_L.

Definition at line 161 of file ltage.cc.

References gem5::PowerISA::bi, loopPredictor, and gem5::branch_prediction::TAGE::squash().

Referenced by gem5::branch_prediction::TAGE_SC_L::squash().

◆ update()

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

overridevirtual

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.

Implements gem5::branch_prediction::BPredUnit.

Reimplemented in gem5::branch_prediction::TAGE_SC_L.

Definition at line 118 of file ltage.cc.

References gem5::PowerISA::bi, DPRINTF, gem5::branch_prediction::BPredUnit::instShiftAmt, loopPredictor, gem5::MipsISA::pc, gem5::branch_prediction::TAGE::rng, and gem5::branch_prediction::TAGE::tage.

Member Data Documentation

◆ loopPredictor

LoopPredictor* gem5::branch_prediction::LTAGE::loopPredictor

protected

The loop predictor object.

Definition at line 94 of file ltage.hh.

Referenced by branchPlaceholder(), LTAGE(), predict(), gem5::branch_prediction::TAGE_SC_L::predict(), squash(), update(), and gem5::branch_prediction::TAGE_SC_L::update().

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

cpu/pred/ltage.hh
cpu/pred/ltage.cc

Classes

Public Member Functions

Protected Types

Protected Member Functions

Protected Attributes

Additional Inherited Members

Detailed Description

Member Enumeration Documentation

◆ anonymous enum

Constructor & Destructor Documentation

◆ LTAGE()

Member Function Documentation

◆ branchPlaceholder()

◆ init()

◆ predict()

◆ squash()

◆ update()

Member Data Documentation

◆ loopPredictor