#include <simple_btb.hh>

Inheritance diagram for gem5::branch_prediction::SimpleBTB:

Classes
struct	BTBEntry

Public Member Functions
	SimpleBTB (const SimpleBTBParams &params)

void	memInvalidate () override
	Invalidate the contents of memory buffers.

bool	valid (ThreadID tid, Addr instPC) override
	Checks if a branch address is in the BTB.

const PCStateBase *	lookup (ThreadID tid, Addr instPC, BranchType type=BranchType::NoBranch) override
	Looks up an address in the BTB to get the target of the branch.

void	update (ThreadID tid, Addr instPC, const PCStateBase &target_pc, BranchType type=BranchType::NoBranch, StaticInstPtr inst=nullptr) override
	Updates the BTB with the target of a branch.

const StaticInstPtr	getInst (ThreadID tid, Addr instPC) override
	Looks up an address in the BTB and return the instruction information if existant.

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

virtual void	incorrectTarget (Addr inst_pc, BranchType type=BranchType::NoBranch)
	Update BTB statistics.

Public Member Functions inherited from gem5::ClockedObject
	ClockedObject (const ClockedObjectParams &p)

void	serialize (CheckpointOut &cp) const override
	Serialize an object.

void	unserialize (CheckpointIn &cp) override
	Unserialize an object.

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.

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 (const std::string &name_)

virtual	~Named ()=default

virtual std::string	name () const

Public Member Functions inherited from gem5::Clocked
void	updateClockPeriod ()
	Update the tick to the current tick.

Tick	clockEdge (Cycles cycles=Cycles(0)) const
	Determine the tick when a cycle begins, by default the current one, but the argument also enables the caller to determine a future cycle.

Cycles	curCycle () const
	Determine the current cycle, corresponding to a tick aligned to a clock edge.

Tick	nextCycle () const
	Based on the clock of the object, determine the start tick of the first cycle that is at least one cycle in the future.

uint64_t	frequency () const

Tick	clockPeriod () const

double	voltage () const

Cycles	ticksToCycles (Tick t) const

Tick	cyclesToTicks (Cycles c) const

Private Member Functions
unsigned	getIndex (Addr instPC, ThreadID tid)
	Returns the index into the BTB, based on the branch's PC.

Addr	getTag (Addr instPC)
	Returns the tag bits of a given address.

BTBEntry *	findEntry (Addr instPC, ThreadID tid)
	Internal call to find an address in the BTB.

Private Attributes
std::vector< BTBEntry >	btb
	The actual BTB.

unsigned	numEntries
	The number of entries in the BTB.

unsigned	idxMask
	The index mask.

unsigned	tagBits
	The number of tag bits per entry.

unsigned	tagMask
	The tag mask.

unsigned	instShiftAmt
	Number of bits to shift PC when calculating index.

unsigned	tagShiftAmt
	Number of bits to shift PC when calculating tag.

unsigned	log2NumThreads
	Log2 NumThreads used for hashing threadid.

Additional Inherited Members
Public Types inherited from gem5::branch_prediction::BranchTargetBuffer
typedef BranchTargetBufferParams	Params

typedef enums::BranchType	BranchType

Public Types inherited from gem5::ClockedObject
using	Params = ClockedObjectParams
	Parameters of ClockedObject.

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.

Public Attributes inherited from gem5::ClockedObject
PowerState *	powerState

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 Member Functions inherited from gem5::Clocked
	Clocked (ClockDomain &clk_domain)
	Create a clocked object and set the clock domain based on the parameters.

	Clocked (Clocked &)=delete

Clocked &	operator= (Clocked &)=delete

virtual	~Clocked ()
	Virtual destructor due to inheritance.

void	resetClock () const
	Reset the object's clock using the current global tick value.

virtual void	clockPeriodUpdated ()
	A hook subclasses can implement so they can do any extra work that's needed when the clock rate is changed.

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

gem5::branch_prediction::BranchTargetBuffer::BranchTargetBufferStats	stats

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.

Detailed Description

Definition at line 55 of file simple_btb.hh.

Constructor & Destructor Documentation

◆ SimpleBTB()

gem5::branch_prediction::SimpleBTB::SimpleBTB ( const SimpleBTBParams & params )

Definition at line 53 of file simple_btb.cc.

References btb, DPRINTF, fatal, gem5::floorLog2(), gem5::ArmISA::i, idxMask, instShiftAmt, gem5::isPowerOf2(), numEntries, tagBits, tagMask, and tagShiftAmt.

Member Function Documentation

◆ findEntry()

SimpleBTB::BTBEntry * gem5::branch_prediction::SimpleBTB::findEntry	(	Addr	instPC,
		ThreadID	tid )

private

Internal call to find an address in the BTB.

Parameters

instPC The branch's address.

Returns: Returns a pointer to the BTB entry if found, nullptr otherwise.

Definition at line 105 of file simple_btb.cc.

References btb, getIndex(), getTag(), numEntries, and valid().

Referenced by getInst(), lookup(), and valid().

◆ getIndex()

unsigned gem5::branch_prediction::SimpleBTB::getIndex	(	Addr	instPC,
		ThreadID	tid )

inlineprivate

Returns the index into the BTB, based on the branch's PC.

Parameters

inst_PC The branch to look up.

Returns: Returns the index into the BTB.

Definition at line 89 of file simple_btb.cc.

References idxMask, instShiftAmt, log2NumThreads, and tagShiftAmt.

Referenced by findEntry(), and update().

◆ getInst()

const StaticInstPtr gem5::branch_prediction::SimpleBTB::getInst	(	ThreadID	tid,
		Addr	instPC )

overridevirtual

Looks up an address in the BTB and return the instruction information if existant.

Does not update statistics.

Parameters

inst_PC The address of the branch to look up.

Returns: Returns the target of the branch.

Implements gem5::branch_prediction::BranchTargetBuffer.

Definition at line 147 of file simple_btb.cc.

References findEntry(), and gem5::branch_prediction::SimpleBTB::BTBEntry::inst.

◆ getTag()

Addr gem5::branch_prediction::SimpleBTB::getTag ( Addr instPC )

inlineprivate

Returns the tag bits of a given address.

Parameters

inst_PC The branch's address.

Returns: Returns the tag bits.

Definition at line 99 of file simple_btb.cc.

References tagMask, and tagShiftAmt.

Referenced by findEntry(), and update().

◆ lookup()

const PCStateBase * gem5::branch_prediction::SimpleBTB::lookup	(	ThreadID	tid,
		Addr	instPC,
		BranchType	type = BranchType::NoBranch )

overridevirtual

Looks up an address in the BTB to get the target of the branch.

Parameters

inst_PC	The address of the branch to look up.
type	Optional type of the branch to look up.

Returns: The target of the branch or nullptr if the branch is not in the BTB.

Implements gem5::branch_prediction::BranchTargetBuffer.

Definition at line 133 of file simple_btb.cc.

References findEntry(), gem5::branch_prediction::BranchTargetBuffer::BranchTargetBufferStats::lookups, gem5::branch_prediction::BranchTargetBuffer::BranchTargetBufferStats::misses, gem5::branch_prediction::BranchTargetBuffer::stats, gem5::branch_prediction::SimpleBTB::BTBEntry::target, and gem5::X86ISA::type.

◆ memInvalidate()

void gem5::branch_prediction::SimpleBTB::memInvalidate ( )

overridevirtual

Invalidate the contents of memory buffers.

When the switching to hardware virtualized CPU models, we need to make sure that we don't have any cached state in the system that might become stale when we return. This method is used to flush all such state back to main memory.

@warn This does not cause any dirty state to be written back to memory.

Implements gem5::branch_prediction::BranchTargetBuffer.

Definition at line 80 of file simple_btb.cc.

References btb, gem5::ArmISA::i, and numEntries.

◆ update()

void gem5::branch_prediction::SimpleBTB::update	(	ThreadID	tid,
		Addr	inst_pc,
		const PCStateBase &	target_pc,
		BranchType	type = BranchType::NoBranch,
		StaticInstPtr	inst = nullptr )

overridevirtual

Updates the BTB with the target of a branch.

Parameters

inst_pc	The address of the branch being updated.
target_pc	The target address of the branch.

Implements gem5::branch_prediction::BranchTargetBuffer.

Definition at line 158 of file simple_btb.cc.

References btb, getIndex(), getTag(), numEntries, gem5::ArmISA::set, gem5::branch_prediction::BranchTargetBuffer::stats, gem5::X86ISA::type, and gem5::branch_prediction::BranchTargetBuffer::BranchTargetBufferStats::updates.

◆ valid()

bool gem5::branch_prediction::SimpleBTB::valid	(	ThreadID	tid,
		Addr	instPC )

overridevirtual

Checks if a branch address is in the BTB.

Intended as a quick check before calling lookup. Does not update statistics.

Parameters

inst_PC The address of the branch to look up.

Returns: Whether or not the branch exists in the BTB.

Implements gem5::branch_prediction::BranchTargetBuffer.

Definition at line 122 of file simple_btb.cc.

References findEntry().

Referenced by findEntry().

Member Data Documentation

◆ btb

std::vector<BTBEntry> gem5::branch_prediction::SimpleBTB::btb

private

The actual BTB.

Definition at line 109 of file simple_btb.hh.

Referenced by findEntry(), memInvalidate(), SimpleBTB(), and update().

◆ idxMask

unsigned gem5::branch_prediction::SimpleBTB::idxMask

private

The index mask.

Definition at line 115 of file simple_btb.hh.

Referenced by getIndex(), and SimpleBTB().

◆ instShiftAmt

unsigned gem5::branch_prediction::SimpleBTB::instShiftAmt

private

Number of bits to shift PC when calculating index.

Definition at line 124 of file simple_btb.hh.

Referenced by getIndex(), and SimpleBTB().

◆ log2NumThreads

unsigned gem5::branch_prediction::SimpleBTB::log2NumThreads

private

Log2 NumThreads used for hashing threadid.

Definition at line 130 of file simple_btb.hh.

Referenced by getIndex().

◆ numEntries

unsigned gem5::branch_prediction::SimpleBTB::numEntries

private

The number of entries in the BTB.

Definition at line 112 of file simple_btb.hh.

Referenced by findEntry(), memInvalidate(), SimpleBTB(), and update().

◆ tagBits

unsigned gem5::branch_prediction::SimpleBTB::tagBits

private

The number of tag bits per entry.

Definition at line 118 of file simple_btb.hh.

Referenced by SimpleBTB().

◆ tagMask

unsigned gem5::branch_prediction::SimpleBTB::tagMask

private

The tag mask.

Definition at line 121 of file simple_btb.hh.

Referenced by getTag(), and SimpleBTB().

◆ tagShiftAmt

unsigned gem5::branch_prediction::SimpleBTB::tagShiftAmt

private

Number of bits to shift PC when calculating tag.

Definition at line 127 of file simple_btb.hh.

Referenced by getIndex(), getTag(), and SimpleBTB().

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

cpu/pred/simple_btb.hh
cpu/pred/simple_btb.cc

Classes

Public Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ SimpleBTB()

Member Function Documentation

◆ findEntry()

◆ getIndex()

◆ getInst()

◆ getTag()

◆ lookup()

◆ memInvalidate()

◆ update()

◆ valid()

Member Data Documentation

◆ btb

◆ idxMask

◆ instShiftAmt

◆ log2NumThreads

◆ numEntries

◆ tagBits

◆ tagMask

◆ tagShiftAmt