gem5
 All Classes Namespaces Files Functions Variables Typedefs Enumerations Enumerator Friends Macros Groups Pages
Classes | Public Member Functions | Private Member Functions | Private Attributes | List of all members
BiModeBP Class Reference

Implements a bi-mode branch predictor. More...

#include <bi_mode.hh>

Inheritance diagram for BiModeBP:
BPredUnit SimObject EventManager Serializable Drainable

Classes

struct  BPHistory
 

Public Member Functions

 BiModeBP (const BiModeBPParams *params)
 
void uncondBranch (ThreadID tid, Addr pc, void *&bp_history)
 
void squash (ThreadID tid, void *bp_history)
 
bool lookup (ThreadID tid, Addr branch_addr, void *&bp_history)
 Looks up a given PC in the BP to see if it is taken or not taken. More...
 
void btbUpdate (ThreadID tid, Addr branch_addr, void *&bp_history)
 If a branch is not taken, because the BTB address is invalid or missing, this function sets the appropriate counter in the global and local predictors to not taken. More...
 
void update (ThreadID tid, Addr branch_addr, bool taken, void *bp_history, bool squashed)
 Updates the BP with taken/not taken information. More...
 
unsigned getGHR (ThreadID tid, void *bp_history) const
 
- Public Member Functions inherited from BPredUnit
 BPredUnit (const Params *p)
 
void regStats () override
 Registers statistics. More...
 
void regProbePoints () override
 Register probe points for this object. More...
 
void drainSanityCheck () const
 Perform sanity checks after a drain. More...
 
bool predict (const StaticInstPtr &inst, const InstSeqNum &seqNum, TheISA::PCState &pc, ThreadID tid)
 Predicts whether or not the instruction is a taken branch, and the target of the branch if it is taken. More...
 
void update (const InstSeqNum &done_sn, ThreadID tid)
 Tells the branch predictor to commit any updates until the given sequence number. More...
 
void squash (const InstSeqNum &squashed_sn, ThreadID tid)
 Squashes all outstanding updates until a given sequence number. More...
 
void squash (const InstSeqNum &squashed_sn, const TheISA::PCState &corr_target, bool actually_taken, ThreadID tid)
 Squashes all outstanding updates until a given sequence number, and corrects that sn's update with the proper address and taken/not taken. More...
 
bool BTBValid (Addr instPC)
 Looks up a given PC in the BTB to see if a matching entry exists. More...
 
TheISA::PCState BTBLookup (Addr instPC)
 Looks up a given PC in the BTB to get the predicted target. More...
 
void BTBUpdate (Addr instPC, const TheISA::PCState &target)
 Updates the BTB with the target of a branch. More...
 
void dump ()
 
- Public Member Functions inherited from SimObject
const Paramsparams () const
 
 SimObject (const Params *_params)
 
virtual ~SimObject ()
 
virtual const std::string name () const
 
virtual void init ()
 init() is called after all C++ SimObjects have been created and all ports are connected. More...
 
virtual void loadState (CheckpointIn &cp)
 loadState() is called on each SimObject when restoring from a checkpoint. More...
 
virtual void initState ()
 initState() is called on each SimObject when not restoring from a checkpoint. More...
 
virtual void resetStats ()
 Reset statistics associated with this object. More...
 
virtual void regProbeListeners ()
 Register probe listeners for this object. More...
 
ProbeManagergetProbeManager ()
 Get the probe manager for this object. More...
 
virtual void startup ()
 startup() is the final initialization call before simulation. More...
 
DrainState drain () override
 Provide a default implementation of the drain interface for objects that don't need draining. More...
 
virtual void memWriteback ()
 Write back dirty buffers to memory using functional writes. More...
 
virtual void memInvalidate ()
 Invalidate the contents of memory buffers. More...
 
void serialize (CheckpointOut &cp) const override
 Serialize an object. More...
 
void unserialize (CheckpointIn &cp) override
 Unserialize an object. More...
 
- Public Member Functions inherited from EventManager
 EventManager (EventManager &em)
 
 EventManager (EventManager *em)
 
 EventManager (EventQueue *eq)
 
EventQueueeventQueue () 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)
 
void setCurTick (Tick newVal)
 
- Public Member Functions inherited from Serializable
 Serializable ()
 
virtual ~Serializable ()
 
void serializeSection (CheckpointOut &cp, const char *name) const
 Serialize an object into a new section. More...
 
void serializeSection (CheckpointOut &cp, const std::string &name) const
 
void unserializeSection (CheckpointIn &cp, const char *name)
 Unserialize an a child object. More...
 
void unserializeSection (CheckpointIn &cp, const std::string &name)
 
- Public Member Functions inherited from Drainable
DrainState drainState () const
 Return the current drain state of an object. More...
 
virtual void notifyFork ()
 Notify a child process of a fork. More...
 

Private Member Functions

void updateGlobalHistReg (ThreadID tid, bool taken)
 

Private Attributes

std::vector< SatCounterchoiceCounters
 
std::vector< SatCountertakenCounters
 
std::vector< SatCounternotTakenCounters
 
std::vector< unsigned > globalHistoryReg
 
unsigned globalHistoryBits
 
unsigned historyRegisterMask
 
unsigned choicePredictorSize
 
unsigned choiceCtrBits
 
unsigned choiceHistoryMask
 
unsigned globalPredictorSize
 
unsigned globalCtrBits
 
unsigned globalHistoryMask
 
unsigned choiceThreshold
 
unsigned takenThreshold
 
unsigned notTakenThreshold
 

Additional Inherited Members

- Public Types inherited from BPredUnit
typedef BranchPredictorParams Params
 
- Public Types inherited from SimObject
typedef SimObjectParams Params
 
- Static Public Member Functions inherited from SimObject
static void serializeAll (CheckpointOut &cp)
 Serialize all SimObjects in the system. More...
 
static SimObjectfind (const char *name)
 Find the SimObject with the given name and return a pointer to it. More...
 
- Static Public Member Functions inherited from Serializable
static const std::string & currentSection ()
 Get the fully-qualified name of the active section. More...
 
static void serializeAll (const std::string &cpt_dir)
 
static void unserializeGlobals (CheckpointIn &cp)
 
- Static Public Attributes inherited from Serializable
static int ckptCount = 0
 
static int ckptMaxCount = 0
 
static int ckptPrevCount = -1
 
- Protected Member Functions inherited from BPredUnit
ProbePoints::PMUUPtr pmuProbePoint (const char *name)
 Helper method to instantiate probe points belonging to this object. More...
 
- Protected Member Functions inherited from Drainable
 Drainable ()
 
virtual ~Drainable ()
 
virtual void drainResume ()
 Resume execution after a successful drain. More...
 
void signalDrainDone () const
 Signal that an object is drained. More...
 
- Protected Attributes inherited from BPredUnit
const unsigned instShiftAmt
 Number of bits to shift instructions by for predictor addresses. More...
 
ProbePoints::PMUUPtr ppBranches
 Branches seen by the branch predictor. More...
 
ProbePoints::PMUUPtr ppMisses
 Miss-predicted branches. More...
 
- Protected Attributes inherited from SimObject
const SimObjectParams * _params
 Cached copy of the object parameters. More...
 
- Protected Attributes inherited from EventManager
EventQueueeventq
 A pointer to this object's event queue. More...
 

Detailed Description

Implements a bi-mode branch predictor.

The bi-mode predictor is a two-level branch predictor that has three seprate history arrays: a taken array, a not-taken array, and a choice array. The taken/not-taken arrays are indexed by a hash of the PC and the global history. The choice array is indexed by the PC only. Because the taken/not-taken arrays use the same index, they must be the same size.

The bi-mode branch predictor aims to eliminate the destructive aliasing that occurs when two branches of opposite biases share the same global history pattern. By separating the predictors into taken/not-taken arrays, and using the branch's PC to choose between the two, destructive aliasing is reduced.

Definition at line 56 of file bi_mode.hh.

Constructor & Destructor Documentation

BiModeBP::BiModeBP ( const BiModeBPParams *  params)

Member Function Documentation

void BiModeBP::btbUpdate ( ThreadID  tid,
Addr  instPC,
void *&  bp_history 
)
virtual

If a branch is not taken, because the BTB address is invalid or missing, this function sets the appropriate counter in the global and local predictors to not taken.

Parameters
inst_PCThe PC to look up the local predictor.
bp_historyPointer that will be set to an object that has the branch predictor state associated with the lookup.

Implements BPredUnit.

Definition at line 151 of file bi_mode.cc.

References globalHistoryReg, historyRegisterMask, and ULL.

unsigned BiModeBP::getGHR ( ThreadID  tid,
void *  bp_history 
) const
virtual

Reimplemented from BPredUnit.

Definition at line 233 of file bi_mode.cc.

References globalHistoryReg.

bool BiModeBP::lookup ( ThreadID  tid,
Addr  instPC,
void *&  bp_history 
)
virtual

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

Parameters
inst_PCThe PC to look up.
bp_historyPointer 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.

Implements BPredUnit.

Definition at line 112 of file bi_mode.cc.

References choiceCounters, choiceHistoryMask, choicePredictorSize, choiceThreshold, BiModeBP::BPHistory::finalPred, globalHistoryMask, BiModeBP::BPHistory::globalHistoryReg, globalHistoryReg, globalPredictorSize, BPredUnit::instShiftAmt, notTakenCounters, BiModeBP::BPHistory::notTakenPred, notTakenThreshold, takenCounters, BiModeBP::BPHistory::takenPred, takenThreshold, BiModeBP::BPHistory::takenUsed, and updateGlobalHistReg().

void BiModeBP::squash ( ThreadID  tid,
void *  bp_history 
)
virtual
Parameters
bp_historyPointer to the history object. The predictor will need to update any state and delete the object.

Implements BPredUnit.

Definition at line 94 of file bi_mode.cc.

References BiModeBP::BPHistory::globalHistoryReg, and globalHistoryReg.

void BiModeBP::uncondBranch ( ThreadID  tid,
Addr  pc,
void *&  bp_history 
)
virtual
void BiModeBP::update ( ThreadID  tid,
Addr  instPC,
bool  taken,
void *  bp_history,
bool  squashed 
)
virtual

Updates the BP with taken/not taken information.

Parameters
inst_PCThe branch's PC that will be updated.
takenWhether the branch was taken or not taken.
bp_historyPointer to the branch predictor state that is associated with the branch lookup that is being updated.
squashedSet to true when this function is called during a squash operation.
Todo:
Make this update flexible enough to handle a global predictor.

Implements BPredUnit.

Definition at line 163 of file bi_mode.cc.

References choiceCounters, choiceHistoryMask, choicePredictorSize, BiModeBP::BPHistory::finalPred, globalHistoryMask, BiModeBP::BPHistory::globalHistoryReg, globalHistoryReg, globalPredictorSize, BPredUnit::instShiftAmt, notTakenCounters, takenCounters, and BiModeBP::BPHistory::takenUsed.

void BiModeBP::updateGlobalHistReg ( ThreadID  tid,
bool  taken 
)
private

Definition at line 239 of file bi_mode.cc.

References globalHistoryReg, and historyRegisterMask.

Referenced by lookup(), and uncondBranch().

Member Data Documentation

std::vector<SatCounter> BiModeBP::choiceCounters
private

Definition at line 92 of file bi_mode.hh.

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

unsigned BiModeBP::choiceCtrBits
private

Definition at line 103 of file bi_mode.hh.

Referenced by BiModeBP().

unsigned BiModeBP::choiceHistoryMask
private

Definition at line 104 of file bi_mode.hh.

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

unsigned BiModeBP::choicePredictorSize
private

Definition at line 102 of file bi_mode.hh.

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

unsigned BiModeBP::choiceThreshold
private

Definition at line 109 of file bi_mode.hh.

Referenced by BiModeBP(), and lookup().

unsigned BiModeBP::globalCtrBits
private

Definition at line 106 of file bi_mode.hh.

Referenced by BiModeBP().

unsigned BiModeBP::globalHistoryBits
private

Definition at line 99 of file bi_mode.hh.

Referenced by BiModeBP().

unsigned BiModeBP::globalHistoryMask
private

Definition at line 107 of file bi_mode.hh.

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

std::vector<unsigned> BiModeBP::globalHistoryReg
private

Definition at line 98 of file bi_mode.hh.

Referenced by btbUpdate(), getGHR(), lookup(), squash(), uncondBranch(), update(), and updateGlobalHistReg().

unsigned BiModeBP::globalPredictorSize
private

Definition at line 105 of file bi_mode.hh.

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

unsigned BiModeBP::historyRegisterMask
private

Definition at line 100 of file bi_mode.hh.

Referenced by BiModeBP(), btbUpdate(), and updateGlobalHistReg().

std::vector<SatCounter> BiModeBP::notTakenCounters
private

Definition at line 96 of file bi_mode.hh.

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

unsigned BiModeBP::notTakenThreshold
private

Definition at line 111 of file bi_mode.hh.

Referenced by BiModeBP(), and lookup().

std::vector<SatCounter> BiModeBP::takenCounters
private

Definition at line 94 of file bi_mode.hh.

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

unsigned BiModeBP::takenThreshold
private

Definition at line 110 of file bi_mode.hh.

Referenced by BiModeBP(), and lookup().


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

Generated on Fri Jun 9 2017 13:04:03 for gem5 by doxygen 1.8.6