Branch Predictor Unit (BPU) history object PredictorHistory This class holds all information needed to manage the speculative state of a in-flight branch prediction. More...

Public Member Functions
	PredictorHistory (ThreadID _tid, InstSeqNum sn, Addr _pc, const StaticInstPtr &inst)
	Makes a predictor history struct that contains any information needed to update the predictor, BTB, and RAS.
	~PredictorHistory ()
	PredictorHistory (const PredictorHistory &)=delete
PredictorHistory &	operator= (const PredictorHistory &)=delete
bool	operator== (const PredictorHistory &entry) const

Public Attributes
const InstSeqNum	seqNum
	The sequence number for the predictor history entry.
const ThreadID	tid
	The thread id.
const Addr	pc
	The PC associated with the sequence number.
const StaticInstPtr	inst
	The branch instrction.
const BranchType	type
	The type of the branch.
const bool	call
	Whether or not the instruction was a call.
const bool	uncond
	Was unconditional control.
bool	predTaken
	Whether or not it was predicted taken.
bool	actuallyTaken
	To record the actual outcome of the branch.
bool	condPred
	The prediction of the conditional predictor.
bool	btbHit
	Was BTB hit at prediction time.
TargetProvider	targetProvider
	Which component provided the target.
bool	resteered
	Resteered.
bool	mispredict
	The branch was corrected hence was mispredicted.
std::unique_ptr< PCStateBase >	target
	The predicted target.
void *	bpHistory = nullptr
	Pointer to the history objects passed back from the branch predictor subcomponents.
void *	indirectHistory = nullptr
void *	rasHistory = nullptr

Detailed Description

Branch Predictor Unit (BPU) history object PredictorHistory This class holds all information needed to manage the speculative state of a in-flight branch prediction.

In case of the default (coupled/synchronous) front-end, the branch predictor is queried whenever the a branch is decoded by the fetch unit. In case of the decoupled front-end, the branch predictor is queried whenever a branch is detected using the BTB.

Lifetime of a PredictorHistory (coupled front-end):

----------------------------------------— + | FETCH: | | - The fetch unit pre-decodes a branch. | | - The BPU is queried to make a prediction | | using the predict function | | - A PredictorHistory object is created. |
----------------------------------------— + | |
----------------------------------------— + | DECODE: | | - The branch is decoded and the target for | | direct branches is available. |
----------------------------------------— + | ( target correct ? ) -------------—+ | | +----------------------------------—+ | | Squash all predictions made AFTER | | | this branch using squashHistories.| | | Will revert all speculative history | | | updates and delete the history | | | history updates of those branches. | | | It also corrects the target of the | | | mispredicted branch using the | | | squash function. | | +----------------------------------—+ | | | | <----------------------—+ |

-----------------------------------------—+ | ( prediction correct ? ) -------------—+ | | +----------------------------------—+ | | Squash all predictions made AFTER | | | this branch using squashHistories.| | | Will revert all speculative history | | | updates and delete the history | | | history updates of those branches. | | | It also corrects the target and | | | the direction of the mispredicted | | | branch using the squash function. | | +----------------------------------—+ | | | | <----------------------—+ | +----------------------------------—+ | Update the internal state (counter) | | of the BPU using the update | | function. | +----------------------------------—+

Definition at line 341 of file bpred_unit.hh.

Constructor & Destructor Documentation

◆ PredictorHistory() [1/2]

gem5::branch_prediction::BPredUnit::PredictorHistory::PredictorHistory	(	ThreadID	_tid,
		InstSeqNum	sn,
		Addr	_pc,
		const StaticInstPtr &	inst )

inline

Makes a predictor history struct that contains any information needed to update the predictor, BTB, and RAS.

Definition at line 347 of file bpred_unit.hh.

References actuallyTaken, bpHistory, btbHit, call, condPred, gem5::branch_prediction::getBranchType(), indirectHistory, inst, mispredict, pc, predTaken, rasHistory, resteered, seqNum, target, targetProvider, tid, type, and uncond.

Referenced by operator=(), operator==(), and PredictorHistory().

◆ ~PredictorHistory()

gem5::branch_prediction::BPredUnit::PredictorHistory::~PredictorHistory ( )

inline

Definition at line 359 of file bpred_unit.hh.

References bpHistory, indirectHistory, and rasHistory.

◆ PredictorHistory() [2/2]

gem5::branch_prediction::BPredUnit::PredictorHistory::PredictorHistory ( const PredictorHistory & )

delete

References PredictorHistory().

Member Function Documentation

◆ operator=()

PredictorHistory & gem5::branch_prediction::BPredUnit::PredictorHistory::operator= ( const PredictorHistory & )

delete

References PredictorHistory().

◆ operator==()

bool gem5::branch_prediction::BPredUnit::PredictorHistory::operator== ( const PredictorHistory & entry ) const

inline

Definition at line 370 of file bpred_unit.hh.

References PredictorHistory(), and seqNum.

Member Data Documentation

◆ actuallyTaken

bool gem5::branch_prediction::BPredUnit::PredictorHistory::actuallyTaken

To record the actual outcome of the branch.

Definition at line 400 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ bpHistory

void* gem5::branch_prediction::BPredUnit::PredictorHistory::bpHistory = nullptr

Pointer to the history objects passed back from the branch predictor subcomponents.

It is used to update or restore state. Respectively for conditional, indirect and RAS.

Definition at line 426 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), gem5::branch_prediction::BPredUnit::squash(), gem5::branch_prediction::BPredUnit::squashHistory(), and ~PredictorHistory().

◆ btbHit

bool gem5::branch_prediction::BPredUnit::PredictorHistory::btbHit

Was BTB hit at prediction time.

Definition at line 406 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ call

const bool gem5::branch_prediction::BPredUnit::PredictorHistory::call

Whether or not the instruction was a call.

Definition at line 391 of file bpred_unit.hh.

Referenced by PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ condPred

bool gem5::branch_prediction::BPredUnit::PredictorHistory::condPred

The prediction of the conditional predictor.

Definition at line 403 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ indirectHistory

void* gem5::branch_prediction::BPredUnit::PredictorHistory::indirectHistory = nullptr

Definition at line 428 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), gem5::branch_prediction::BPredUnit::squash(), gem5::branch_prediction::BPredUnit::squashHistory(), and ~PredictorHistory().

◆ inst

const StaticInstPtr gem5::branch_prediction::BPredUnit::PredictorHistory::inst

The branch instrction.

Definition at line 385 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ mispredict

bool gem5::branch_prediction::BPredUnit::PredictorHistory::mispredict

The branch was corrected hence was mispredicted.

Definition at line 415 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ pc

const Addr gem5::branch_prediction::BPredUnit::PredictorHistory::pc

The PC associated with the sequence number.

Definition at line 382 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), gem5::branch_prediction::BPredUnit::squash(), and gem5::branch_prediction::BPredUnit::squashHistory().

◆ predTaken

bool gem5::branch_prediction::BPredUnit::PredictorHistory::predTaken

Whether or not it was predicted taken.

Definition at line 397 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), and PredictorHistory().

◆ rasHistory

void* gem5::branch_prediction::BPredUnit::PredictorHistory::rasHistory = nullptr

Definition at line 430 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), gem5::branch_prediction::BPredUnit::squash(), gem5::branch_prediction::BPredUnit::squashHistory(), and ~PredictorHistory().

◆ resteered

bool gem5::branch_prediction::BPredUnit::PredictorHistory::resteered

Resteered.

Definition at line 412 of file bpred_unit.hh.

Referenced by PredictorHistory().

◆ seqNum

const InstSeqNum gem5::branch_prediction::BPredUnit::PredictorHistory::seqNum

The sequence number for the predictor history entry.

Definition at line 376 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), operator==(), PredictorHistory(), gem5::branch_prediction::BPredUnit::squash(), and gem5::branch_prediction::BPredUnit::squashHistory().

◆ target

std::unique_ptr<PCStateBase> gem5::branch_prediction::BPredUnit::PredictorHistory::target

The predicted target.

Definition at line 418 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ targetProvider

TargetProvider gem5::branch_prediction::BPredUnit::PredictorHistory::targetProvider

Which component provided the target.

Definition at line 409 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::predict(), PredictorHistory(), and gem5::branch_prediction::BPredUnit::squash().

◆ tid

const ThreadID gem5::branch_prediction::BPredUnit::PredictorHistory::tid

The thread id.

Definition at line 379 of file bpred_unit.hh.

Referenced by PredictorHistory().

◆ type

const BranchType gem5::branch_prediction::BPredUnit::PredictorHistory::type

The type of the branch.

Definition at line 388 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::commitBranch(), PredictorHistory(), gem5::branch_prediction::BPredUnit::squash(), and gem5::branch_prediction::BPredUnit::squashHistory().

◆ uncond

const bool gem5::branch_prediction::BPredUnit::PredictorHistory::uncond

Was unconditional control.

Definition at line 394 of file bpred_unit.hh.

Referenced by gem5::branch_prediction::BPredUnit::predict(), and PredictorHistory().

The documentation for this struct was generated from the following file:

cpu/pred/bpred_unit.hh

Public Member Functions

Public Attributes

Detailed Description

Constructor & Destructor Documentation

◆ PredictorHistory() [1/2]

◆ ~PredictorHistory()

◆ PredictorHistory() [2/2]

Member Function Documentation

◆ operator=()

◆ operator==()

Member Data Documentation

◆ actuallyTaken

◆ bpHistory

◆ btbHit

◆ call

◆ condPred

◆ indirectHistory

◆ inst

◆ mispredict

◆ pc

◆ predTaken

◆ rasHistory

◆ resteered

◆ seqNum

◆ target

◆ targetProvider

◆ tid

◆ type

◆ uncond