Machine model for scheduling, bundling, and heuristics. More...

#include "llvm/MC/MCSchedule.h"

Public Member Functions
bool	hasExtraProcessorInfo () const
unsigned	getProcessorID () const
bool	hasInstrSchedModel () const
	Does this machine model include instruction-level scheduling.
const MCExtraProcessorInfo &	getExtraProcessorInfo () const
bool	isComplete () const
	Return true if this machine model data for all instructions with a scheduling class (itinerary class or SchedRW list).
bool	isOutOfOrder () const
	Return true if machine supports out of order execution.
unsigned	getNumProcResourceKinds () const
const MCProcResourceDesc *	getProcResource (unsigned ProcResourceIdx) const
const MCSchedClassDesc *	getSchedClassDesc (unsigned SchedClassIdx) const
StringRef	getSchedClassName (unsigned SchedClassIdx) const
LLVM_ABI int	computeInstrLatency (const MCSubtargetInfo &STI, unsigned SClass) const
LLVM_ABI int	computeInstrLatency (const MCSubtargetInfo &STI, const MCInstrInfo &MCII, const MCInst &Inst) const
template<typename MCSubtargetInfo, typename MCInstrInfo, typename InstrItineraryData, typename MCInstOrMachineInstr>
int	computeInstrLatency (const MCSubtargetInfo &STI, const MCInstrInfo &MCII, const MCInstOrMachineInstr &Inst, llvm::function_ref< const MCSchedClassDesc (const MCSchedClassDesc )> ResolveVariantSchedClass=[](const MCSchedClassDesc *SCDesc) { return SCDesc;}) const
LLVM_ABI double	getReciprocalThroughput (const MCSubtargetInfo &STI, const MCInstrInfo &MCII, const MCInst &Inst) const

Static Public Member Functions
static LLVM_ABI int	computeInstrLatency (const MCSubtargetInfo &STI, const MCSchedClassDesc &SCDesc)
	Returns the latency value for the scheduling class.
static LLVM_ABI double	getReciprocalThroughput (const MCSubtargetInfo &STI, const MCSchedClassDesc &SCDesc)
static LLVM_ABI double	getReciprocalThroughput (unsigned SchedClass, const InstrItineraryData &IID)
static LLVM_ABI unsigned	getForwardingDelayCycles (ArrayRef< MCReadAdvanceEntry > Entries, unsigned WriteResourceIdx=0)
	Returns the maximum forwarding delay for register reads dependent on writes of scheduling class WriteResourceIdx.
static LLVM_ABI unsigned	getBypassDelayCycles (const MCSubtargetInfo &STI, const MCSchedClassDesc &SCDesc)
	Returns the bypass delay cycle for the maximum latency write cycle.

Static Public Attributes
static const unsigned	DefaultIssueWidth = 1
static const unsigned	DefaultMicroOpBufferSize = 0
static const unsigned	DefaultLoopMicroOpBufferSize = 0
static const unsigned	DefaultLoadLatency = 4
static const unsigned	DefaultHighLatency = 10
static const unsigned	DefaultMispredictPenalty = 10
static LLVM_ABI const MCSchedModel	Default
	Returns the default initialized model.

Friends
class	InstrItineraryData

Detailed Description

Machine model for scheduling, bundling, and heuristics.

The machine model directly provides basic information about the microarchitecture to the scheduler in the form of properties. It also optionally refers to scheduler resource tables and itinerary tables. Scheduler resource tables model the latency and cost for each instruction type. Itinerary tables are an independent mechanism that provides a detailed reservation table describing each cycle of instruction execution. Subtargets may define any or all of the above categories of data depending on the type of CPU and selected scheduler.

The machine independent properties defined here are used by the scheduler as an abstract machine model. A real micro-architecture has a number of buffers, queues, and stages. Declaring that a given machine-independent abstract property corresponds to a specific physical property across all subtargets can't be done. Nonetheless, the abstract model is useful. Futhermore, subtargets typically extend this model with processor specific resources to model any hardware features that can be exploited by scheduling heuristics and aren't sufficiently represented in the abstract.

The abstract pipeline is built around the notion of an "issue point". This is merely a reference point for counting machine cycles. The physical machine will have pipeline stages that delay execution. The scheduler does not model those delays because they are irrelevant as long as they are consistent. Inaccuracies arise when instructions have different execution delays relative to each other, in addition to their intrinsic latency. Those special cases can be handled by TableGen constructs such as, ReadAdvance, which reduces latency when reading data, and ReleaseAtCycles, which consumes a processor resource when writing data for a number of abstract cycles.

TODO: One tool currently missing is the ability to add a delay to ReleaseAtCycles. That would be easy to add and would likely cover all cases currently handled by the legacy itinerary tables.

A note on out-of-order execution and, more generally, instruction buffers. Part of the CPU pipeline is always in-order. The issue point, which is the point of reference for counting cycles, only makes sense as an in-order part of the pipeline. Other parts of the pipeline are sometimes falling behind and sometimes catching up. It's only interesting to model those other, decoupled parts of the pipeline if they may be predictably resource constrained in a way that the scheduler can exploit.

The LLVM machine model distinguishes between in-order constraints and out-of-order constraints so that the target's scheduling strategy can apply appropriate heuristics. For a well-balanced CPU pipeline, out-of-order resources would not typically be treated as a hard scheduling constraint. For example, in the GenericScheduler, a delay caused by limited out-of-order resources is not directly reflected in the number of cycles that the scheduler sees between issuing an instruction and its dependent instructions. In other words, out-of-order resources don't directly increase the latency between pairs of instructions. However, they can still be used to detect potential bottlenecks across a sequence of instructions and bias the scheduling heuristics appropriately.

Definition at line 258 of file MCSchedule.h.

Member Function Documentation

◆ computeInstrLatency() [1/4]

int MCSchedModel::computeInstrLatency	(	const MCSubtargetInfo &	STI,
		const MCInstrInfo &	MCII,
		const MCInst &	Inst ) const

Definition at line 70 of file MCSchedule.cpp.

References assert(), computeInstrLatency(), getProcessorID(), getSchedClassDesc(), InstrItineraryData, and llvm::MCSubtargetInfo::resolveVariantSchedClass().

◆ computeInstrLatency() [2/4]

template<typename MCSubtargetInfo, typename MCInstrInfo, typename InstrItineraryData, typename MCInstOrMachineInstr>

int llvm::MCSchedModel::computeInstrLatency	(	const MCSubtargetInfo &	STI,
		const MCInstrInfo &	MCII,
		const MCInstOrMachineInstr &	Inst,
		llvm::function_ref< const MCSchedClassDesc (const MCSchedClassDesc )>	ResolveVariantSchedClass = [](const MCSchedClassDesc *SCDesc) { return SCDesc; } ) const

Definition at line 433 of file MCSchedule.h.

References computeInstrLatency(), llvm::MCInstrInfo::get(), llvm::MCSubtargetInfo::getCPU(), llvm::MCSubtargetInfo::getInstrItineraryForCPU(), llvm::InstrItineraryData::getOperandCycle(), llvm::MCInstrDesc::getSchedClass(), getSchedClassDesc(), hasInstrSchedModel(), InstrItineraryData, llvm::MCSchedClassDesc::isValid(), and llvm::Latency.

◆ computeInstrLatency() [3/4]

int MCSchedModel::computeInstrLatency	(	const MCSubtargetInfo &	STI,
		const MCSchedClassDesc &	SCDesc )

static

Returns the latency value for the scheduling class.

Definition at line 43 of file MCSchedule.cpp.

References llvm::MCWriteLatencyEntry::Cycles, llvm::MCSubtargetInfo::getWriteLatencyEntry(), llvm::Latency, and llvm::MCSchedClassDesc::NumWriteLatencyEntries.

Referenced by computeInstrLatency(), computeInstrLatency(), computeInstrLatency(), llvm::mca::computeMaxLatency(), emitComments(), and emitLatency().

◆ computeInstrLatency() [4/4]

int MCSchedModel::computeInstrLatency	(	const MCSubtargetInfo &	STI,
		unsigned	SClass ) const

Definition at line 59 of file MCSchedule.cpp.

References computeInstrLatency(), getSchedClassDesc(), llvm::MCSchedClassDesc::isValid(), llvm::MCSchedClassDesc::isVariant(), and llvm_unreachable.

◆ getBypassDelayCycles()

unsigned MCSchedModel::getBypassDelayCycles	(	const MCSubtargetInfo &	STI,
		const MCSchedClassDesc &	SCDesc )

static

Returns the bypass delay cycle for the maximum latency write cycle.

Definition at line 182 of file MCSchedule.cpp.

References llvm::MCWriteLatencyEntry::Cycles, llvm::ArrayRef< T >::empty(), llvm::MCSubtargetInfo::getReadAdvanceEntries(), llvm::MCSubtargetInfo::getWriteLatencyEntry(), llvm::MCSchedClassDesc::NumWriteLatencyEntries, and llvm::MCWriteLatencyEntry::WriteResourceID.

◆ getExtraProcessorInfo()

const MCExtraProcessorInfo & llvm::MCSchedModel::getExtraProcessorInfo ( ) const

inline

Definition at line 342 of file MCSchedule.h.

References assert(), ExtraProcessorInfo, and hasExtraProcessorInfo().

Referenced by llvm::mca::RetireControlUnit::RetireControlUnit().

◆ getForwardingDelayCycles()

unsigned MCSchedModel::getForwardingDelayCycles	(	ArrayRef< MCReadAdvanceEntry >	Entries,
		unsigned	WriteResourceIdx = 0 )

static

Returns the maximum forwarding delay for register reads dependent on writes of scheduling class WriteResourceIdx.

Definition at line 167 of file MCSchedule.cpp.

References llvm::ArrayRef< T >::empty().

◆ getNumProcResourceKinds()

unsigned llvm::MCSchedModel::getNumProcResourceKinds ( ) const

inline

Definition at line 355 of file MCSchedule.h.

References NumProcResourceKinds.

Referenced by llvm::mca::computeBlockRThroughput(), llvm::mca::computeProcResourceMasks(), llvm::mca::initializeUsedResources(), and llvm::mca::InstrBuilder::InstrBuilder().

◆ getProcessorID()

unsigned llvm::MCSchedModel::getProcessorID ( ) const

inline

Definition at line 337 of file MCSchedule.h.

References ProcID.

Referenced by computeInstrLatency(), and getReciprocalThroughput().

◆ getProcResource()

const MCProcResourceDesc * llvm::MCSchedModel::getProcResource ( unsigned ProcResourceIdx ) const

inline

Definition at line 359 of file MCSchedule.h.

References assert(), hasInstrSchedModel(), NumProcResourceKinds, and ProcResourceTable.

Referenced by llvm::mca::computeBlockRThroughput(), llvm::mca::computeProcResourceMasks(), getReciprocalThroughput(), and llvm::mca::initializeUsedResources().

◆ getReciprocalThroughput() [1/3]

double MCSchedModel::getReciprocalThroughput	(	const MCSubtargetInfo &	STI,
		const MCInstrInfo &	MCII,
		const MCInst &	Inst ) const

Definition at line 123 of file MCSchedule.cpp.

References llvm::MCInstrInfo::get(), llvm::MCInst::getOpcode(), getProcessorID(), getReciprocalThroughput(), llvm::MCInstrDesc::getSchedClass(), getSchedClassDesc(), IssueWidth, llvm::MCSchedClassDesc::isValid(), llvm::MCSchedClassDesc::isVariant(), llvm_unreachable, and llvm::MCSubtargetInfo::resolveVariantSchedClass().

◆ getReciprocalThroughput() [2/3]

double MCSchedModel::getReciprocalThroughput	(	const MCSubtargetInfo &	STI,
		const MCSchedClassDesc &	SCDesc )

static

Definition at line 98 of file MCSchedule.cpp.

References assert(), getProcResource(), llvm::MCSubtargetInfo::getSchedModel(), llvm::MCSubtargetInfo::getWriteProcResBegin(), llvm::MCSubtargetInfo::getWriteProcResEnd(), I, IssueWidth, llvm::MCSchedClassDesc::NumMicroOps, and llvm::MCProcResourceDesc::NumUnits.

Referenced by llvm::TargetSchedModel::computeReciprocalThroughput(), llvm::TargetSchedModel::computeReciprocalThroughput(), getReciprocalThroughput(), and llvm::AArch64TTIImpl::hasKnownLowerThroughputFromSchedulingModel().

◆ getReciprocalThroughput() [3/3]

double MCSchedModel::getReciprocalThroughput	(	unsigned	SchedClass,
		const InstrItineraryData &	IID )

static

Definition at line 147 of file MCSchedule.cpp.

References llvm::InstrItineraryData::beginStage(), DefaultIssueWidth, llvm::InstrItineraryData::endStage(), I, InstrItineraryData, and llvm::popcount().

◆ getSchedClassDesc()

const MCSchedClassDesc * llvm::MCSchedModel::getSchedClassDesc ( unsigned SchedClassIdx ) const

inline

Definition at line 366 of file MCSchedule.h.

References assert(), hasInstrSchedModel(), NumSchedClasses, and SchedClassTable.

Referenced by llvm::mca::RegisterFile::addRegisterRead(), llvm::mca::RegisterFile::checkRAWHazards(), llvm::mca::RegisterFile::collectWrites(), computeInstrLatency(), computeInstrLatency(), computeInstrLatency(), and getReciprocalThroughput().

◆ getSchedClassName()

StringRef llvm::MCSchedModel::getSchedClassName ( unsigned SchedClassIdx ) const

inline

Definition at line 373 of file MCSchedule.h.

References SchedClassNames, and SchedClassTable.

Referenced by llvm::mca::initializeUsedResources().

◆ hasExtraProcessorInfo()

bool llvm::MCSchedModel::hasExtraProcessorInfo ( ) const

inline

Definition at line 335 of file MCSchedule.h.

References ExtraProcessorInfo.

Referenced by getExtraProcessorInfo(), llvm::mca::LSUnitBase::LSUnitBase(), and llvm::mca::RetireControlUnit::RetireControlUnit().

◆ hasInstrSchedModel()

bool llvm::MCSchedModel::hasInstrSchedModel ( ) const

inline

Does this machine model include instruction-level scheduling.

Definition at line 340 of file MCSchedule.h.

References SchedClassTable.

Referenced by computeInstrLatency(), getProcResource(), and getSchedClassDesc().

◆ isComplete()

bool llvm::MCSchedModel::isComplete ( ) const

inline

Return true if this machine model data for all instructions with a scheduling class (itinerary class or SchedRW list).

Definition at line 350 of file MCSchedule.h.

References CompleteModel.

◆ isOutOfOrder()

bool llvm::MCSchedModel::isOutOfOrder ( ) const

inline

Return true if machine supports out of order execution.

Definition at line 353 of file MCSchedule.h.

References MicroOpBufferSize.

Referenced by llvm::mca::Context::createDefaultPipeline(), and llvm::mca::RetireControlUnit::RetireControlUnit().

◆ InstrItineraryData

friend class InstrItineraryData

friend

Definition at line 330 of file MCSchedule.h.

References InstrItineraryData.

Referenced by computeInstrLatency(), computeInstrLatency(), getReciprocalThroughput(), and InstrItineraryData.

Member Data Documentation

◆ CompleteModel

bool llvm::MCSchedModel::CompleteModel

Definition at line 316 of file MCSchedule.h.

Referenced by isComplete().

◆ Default

const MCSchedModel MCSchedModel::Default

static

Initial value:

= {DefaultIssueWidth,
                                            DefaultMicroOpBufferSize,
                                            DefaultLoopMicroOpBufferSize,
                                            DefaultLoadLatency,
                                            DefaultHighLatency,
                                            DefaultMispredictPenalty,
                                            false,
                                            true,
                                            false,
                                            0,
                                            nullptr,
                                            nullptr,
                                            0,
                                            0,
                                            nullptr,
                                            nullptr,
                                            nullptr}

Returns the default initialized model.

Definition at line 424 of file MCSchedule.h.

Referenced by llvm::MCSubtargetInfo::getSchedModelForCPU(), and llvm::MCSubtargetInfo::InitMCProcessorInfo().

◆ DefaultHighLatency

const unsigned llvm::MCSchedModel::DefaultHighLatency = 10

static

Definition at line 307 of file MCSchedule.h.

◆ DefaultIssueWidth

const unsigned llvm::MCSchedModel::DefaultIssueWidth = 1

static

Definition at line 271 of file MCSchedule.h.

Referenced by getReciprocalThroughput().

◆ DefaultLoadLatency

const unsigned llvm::MCSchedModel::DefaultLoadLatency = 4

static

Definition at line 300 of file MCSchedule.h.

◆ DefaultLoopMicroOpBufferSize

const unsigned llvm::MCSchedModel::DefaultLoopMicroOpBufferSize = 0

static

Definition at line 296 of file MCSchedule.h.

◆ DefaultMicroOpBufferSize

const unsigned llvm::MCSchedModel::DefaultMicroOpBufferSize = 0

static

Definition at line 288 of file MCSchedule.h.

◆ DefaultMispredictPenalty

const unsigned llvm::MCSchedModel::DefaultMispredictPenalty = 10

static

Definition at line 312 of file MCSchedule.h.

◆ EnableIntervals

bool llvm::MCSchedModel::EnableIntervals

Definition at line 321 of file MCSchedule.h.

◆ ExtraProcessorInfo

const MCExtraProcessorInfo* llvm::MCSchedModel::ExtraProcessorInfo

Definition at line 333 of file MCSchedule.h.

Referenced by getExtraProcessorInfo(), and hasExtraProcessorInfo().

◆ HighLatency

unsigned llvm::MCSchedModel::HighLatency

Definition at line 306 of file MCSchedule.h.

Referenced by llvm::TargetInstrInfo::defaultDefLatency().

◆ InstrItineraries

const InstrItinerary* llvm::MCSchedModel::InstrItineraries

Definition at line 331 of file MCSchedule.h.

Referenced by llvm::HexagonMCInstrInfo::getCVIResources(), llvm::HexagonMCInstrInfo::getOtherReservedSlots(), and llvm::HexagonMCInstrInfo::getUnits().

◆ IssueWidth

unsigned llvm::MCSchedModel::IssueWidth

Definition at line 270 of file MCSchedule.h.

Referenced by llvm::mca::DispatchStage::DispatchStage(), getReciprocalThroughput(), and getReciprocalThroughput().

◆ LoadLatency

unsigned llvm::MCSchedModel::LoadLatency

Definition at line 299 of file MCSchedule.h.

Referenced by llvm::TargetInstrInfo::defaultDefLatency().

◆ LoopMicroOpBufferSize

unsigned llvm::MCSchedModel::LoopMicroOpBufferSize

Definition at line 295 of file MCSchedule.h.

◆ MicroOpBufferSize

unsigned llvm::MCSchedModel::MicroOpBufferSize

Definition at line 287 of file MCSchedule.h.

Referenced by isOutOfOrder().

◆ MispredictPenalty

unsigned llvm::MCSchedModel::MispredictPenalty

Definition at line 311 of file MCSchedule.h.

◆ NumProcResourceKinds

unsigned llvm::MCSchedModel::NumProcResourceKinds

Definition at line 326 of file MCSchedule.h.

Referenced by getNumProcResourceKinds(), and getProcResource().

◆ NumSchedClasses

unsigned llvm::MCSchedModel::NumSchedClasses

Definition at line 327 of file MCSchedule.h.

Referenced by getSchedClassDesc().

◆ PostRAScheduler

bool llvm::MCSchedModel::PostRAScheduler

Definition at line 314 of file MCSchedule.h.

Referenced by llvm::TargetSubtargetInfo::enablePostRAScheduler().

◆ ProcID

unsigned llvm::MCSchedModel::ProcID

Definition at line 323 of file MCSchedule.h.

Referenced by getProcessorID().

◆ ProcResourceTable

const MCProcResourceDesc* llvm::MCSchedModel::ProcResourceTable

Definition at line 324 of file MCSchedule.h.

Referenced by getProcResource().

◆ SchedClassNames

const StringTable* llvm::MCSchedModel::SchedClassNames

Definition at line 328 of file MCSchedule.h.

Referenced by getSchedClassName().

◆ SchedClassTable

const MCSchedClassDesc* llvm::MCSchedModel::SchedClassTable

Definition at line 325 of file MCSchedule.h.

Referenced by getSchedClassDesc(), getSchedClassName(), and hasInstrSchedModel().

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

include/llvm/MC/MCSchedule.h
lib/MC/MCSchedule.cpp

Public Attributes
unsigned	IssueWidth
unsigned	MicroOpBufferSize
unsigned	LoopMicroOpBufferSize
unsigned	LoadLatency
unsigned	HighLatency
unsigned	MispredictPenalty
bool	PostRAScheduler
bool	CompleteModel
bool	EnableIntervals
unsigned	ProcID
const MCProcResourceDesc *	ProcResourceTable
const MCSchedClassDesc *	SchedClassTable
unsigned	NumProcResourceKinds
unsigned	NumSchedClasses
const StringTable *	SchedClassNames
const InstrItinerary *	InstrItineraries
const MCExtraProcessorInfo *	ExtraProcessorInfo

Public Member Functions

Static Public Member Functions

Public Attributes

Static Public Attributes

Friends

Detailed Description

Member Function Documentation

◆ computeInstrLatency() [1/4]

◆ computeInstrLatency() [2/4]

◆ computeInstrLatency() [3/4]

◆ computeInstrLatency() [4/4]

◆ getBypassDelayCycles()

◆ getExtraProcessorInfo()

◆ getForwardingDelayCycles()

◆ getNumProcResourceKinds()

◆ getProcessorID()

◆ getProcResource()

◆ getReciprocalThroughput() [1/3]

◆ getReciprocalThroughput() [2/3]

◆ getReciprocalThroughput() [3/3]

◆ getSchedClassDesc()

◆ getSchedClassName()

◆ hasExtraProcessorInfo()

◆ hasInstrSchedModel()

◆ isComplete()

◆ isOutOfOrder()

Friends And Related Symbol Documentation

◆ InstrItineraryData

Member Data Documentation

◆ CompleteModel

◆ Default

◆ DefaultHighLatency

◆ DefaultIssueWidth

◆ DefaultLoadLatency

◆ DefaultLoopMicroOpBufferSize

◆ DefaultMicroOpBufferSize

◆ DefaultMispredictPenalty

◆ EnableIntervals

◆ ExtraProcessorInfo

◆ HighLatency

◆ InstrItineraries

◆ IssueWidth

◆ LoadLatency

◆ LoopMicroOpBufferSize

◆ MicroOpBufferSize

◆ MispredictPenalty

◆ NumProcResourceKinds

◆ NumSchedClasses

◆ PostRAScheduler

◆ ProcID

◆ ProcResourceTable

◆ SchedClassNames

◆ SchedClassTable