DefaultBTB Class Reference

#include <btb.hh>

Classes
struct	BTBEntry

Public Member Functions
	DefaultBTB (unsigned numEntries, unsigned tagBits, unsigned instShiftAmt, unsigned numThreads)
	Creates a BTB with the given number of entries, number of bits per tag, and instruction offset amount. More...
void	reset ()
TheISA::PCState	lookup (Addr instPC, ThreadID tid)
	Looks up an address in the BTB. More...
bool	valid (Addr instPC, ThreadID tid)
	Checks if a branch is in the BTB. More...
void	update (Addr instPC, const TheISA::PCState &targetPC, ThreadID tid)
	Updates the BTB with the target of a branch. More...

Private Member Functions
unsigned	getIndex (Addr instPC, ThreadID tid)
	Returns the index into the BTB, based on the branch's PC. More...
Addr	getTag (Addr instPC)
	Returns the tag bits of a given address. More...

Private Attributes
std::vector< BTBEntry >	btb
	The actual BTB. More...
unsigned	numEntries
	The number of entries in the BTB. More...
unsigned	idxMask
	The index mask. More...
unsigned	tagBits
	The number of tag bits per entry. More...
unsigned	tagMask
	The tag mask. More...
unsigned	instShiftAmt
	Number of bits to shift PC when calculating index. More...
unsigned	tagShiftAmt
	Number of bits to shift PC when calculating tag. More...
unsigned	log2NumThreads
	Log2 NumThreads used for hashing threadid. More...

Detailed Description

Definition at line 39 of file btb.hh.

Constructor & Destructor Documentation

DefaultBTB()

DefaultBTB::DefaultBTB	(	unsigned	numEntries,
		unsigned	tagBits,
		unsigned	instShiftAmt,
		unsigned	numThreads
	)

Creates a BTB with the given number of entries, number of bits per tag, and instruction offset amount.

Parameters

numEntries	Number of entries for the BTB.
tagBits	Number of bits for each tag in the BTB.
instShiftAmt	Offset amount for instructions to ignore alignment.

Definition at line 37 of file btb.cc.

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

Member Function Documentation

getIndex()

unsigned DefaultBTB::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 75 of file btb.cc.

References idxMask, instShiftAmt, log2NumThreads, and tagShiftAmt.

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

getTag()

Addr DefaultBTB::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 85 of file btb.cc.

References tagMask, and tagShiftAmt.

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

lookup()

TheISA::PCState DefaultBTB::lookup	(	Addr	instPC,
		ThreadID	tid
	)

Looks up an address in the BTB.

Must call valid() first on the address.

Parameters

inst_PC	The address of the branch to look up.
tid	The thread id.

Returns

Returns the target of the branch.

Definition at line 112 of file btb.cc.

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

Referenced by BPredUnit::BTBLookup(), and BPredUnit::predict().

reset()

void DefaultBTB::reset

(

)

Definition at line 66 of file btb.cc.

References btb, ArmISA::i, and numEntries.

update()

void DefaultBTB::update	(	Addr	instPC,
		const TheISA::PCState &	targetPC,
		ThreadID	tid
	)

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.
tid	The thread id.

Definition at line 130 of file btb.cc.

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

Referenced by BPredUnit::BTBUpdate(), and BPredUnit::squash().

valid()

bool DefaultBTB::valid	(	Addr	instPC,
		ThreadID	tid
	)

Checks if a branch is in the BTB.

Parameters

inst_PC	The address of the branch to look up.
tid	The thread id.

Returns

Whether or not the branch exists in the BTB.

Definition at line 91 of file btb.cc.

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

Referenced by BPredUnit::BTBValid(), lookup(), and BPredUnit::predict().

Member Data Documentation

btb

std::vector<BTBEntry> DefaultBTB::btb

private

The actual BTB.

Definition at line 109 of file btb.hh.

Referenced by DefaultBTB(), lookup(), reset(), update(), and valid().

idxMask

unsigned DefaultBTB::idxMask

private

The index mask.

Definition at line 115 of file btb.hh.

Referenced by DefaultBTB(), and getIndex().

instShiftAmt

unsigned DefaultBTB::instShiftAmt

private

Number of bits to shift PC when calculating index.

Definition at line 124 of file btb.hh.

Referenced by DefaultBTB(), and getIndex().

log2NumThreads

unsigned DefaultBTB::log2NumThreads

private

Log2 NumThreads used for hashing threadid.

Definition at line 130 of file btb.hh.

Referenced by getIndex().

numEntries

unsigned DefaultBTB::numEntries

private

The number of entries in the BTB.

Definition at line 112 of file btb.hh.

Referenced by DefaultBTB(), lookup(), reset(), update(), and valid().

tagBits

unsigned DefaultBTB::tagBits

private

The number of tag bits per entry.

Definition at line 118 of file btb.hh.

Referenced by DefaultBTB().

tagMask

unsigned DefaultBTB::tagMask

private

The tag mask.

Definition at line 121 of file btb.hh.

Referenced by DefaultBTB(), and getTag().

tagShiftAmt

unsigned DefaultBTB::tagShiftAmt

private

Number of bits to shift PC when calculating tag.

Definition at line 127 of file btb.hh.

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

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

• cpu/pred/btb.hh
• cpu/pred/btb.cc