LLVM  3.7.0
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llvm::DependenceAnalysis Class Reference

DependenceAnalysis - This class is the main dependence-analysis driver. More...

#include <DependenceAnalysis.h>

Inheritance diagram for llvm::DependenceAnalysis:
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Collaboration diagram for llvm::DependenceAnalysis:
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Public Member Functions

std::unique_ptr< Dependencedepends (Instruction *Src, Instruction *Dst, bool PossiblyLoopIndependent)
 depends - Tests for a dependence between the Src and Dst instructions. More...
 
const SCEVgetSplitIteration (const Dependence &Dep, unsigned Level)
 getSplitIteration - Give a dependence that's splittable at some particular level, return the iteration that should be used to split the loop. More...
 
 DependenceAnalysis ()
 
bool runOnFunction (Function &F) override
 runOnFunction - Virtual method overriden by subclasses to do the per-function processing of the pass. More...
 
void releaseMemory () override
 releaseMemory() - This member can be implemented by a pass if it wants to be able to release its memory when it is no longer needed. More...
 
void getAnalysisUsage (AnalysisUsage &) const override
 getAnalysisUsage - This function should be overriden by passes that need analysis information to do their job. More...
 
void print (raw_ostream &, const Module *=nullptr) const override
 print - Print out the internal state of the pass. More...
 
- Public Member Functions inherited from llvm::FunctionPass
 FunctionPass (char &pid)
 
PasscreatePrinterPass (raw_ostream &O, const std::string &Banner) const override
 createPrinterPass - Get a function printer pass. More...
 
void assignPassManager (PMStack &PMS, PassManagerType T) override
 Find appropriate Function Pass Manager or Call Graph Pass Manager in the PM Stack and add self into that manager. More...
 
PassManagerType getPotentialPassManagerType () const override
 Return what kind of Pass Manager can manage this pass. More...
 
- Public Member Functions inherited from llvm::Pass
 Pass (PassKind K, char &pid)
 
virtual ~Pass ()
 
PassKind getPassKind () const
 
virtual const char * getPassName () const
 getPassName - Return a nice clean name for a pass. More...
 
AnalysisID getPassID () const
 getPassID - Return the PassID number that corresponds to this pass. More...
 
virtual bool doInitialization (Module &)
 doInitialization - Virtual method overridden by subclasses to do any necessary initialization before any pass is run. More...
 
virtual bool doFinalization (Module &)
 doFinalization - Virtual method overriden by subclasses to do any necessary clean up after all passes have run. More...
 
void dump () const
 
virtual void preparePassManager (PMStack &)
 Check if available pass managers are suitable for this pass or not. More...
 
void setResolver (AnalysisResolver *AR)
 
AnalysisResolvergetResolver () const
 
virtual void * getAdjustedAnalysisPointer (AnalysisID ID)
 getAdjustedAnalysisPointer - This method is used when a pass implements an analysis interface through multiple inheritance. More...
 
virtual ImmutablePassgetAsImmutablePass ()
 
virtual PMDataManagergetAsPMDataManager ()
 
virtual void verifyAnalysis () const
 verifyAnalysis() - This member can be implemented by a analysis pass to check state of analysis information. More...
 
virtual void dumpPassStructure (unsigned Offset=0)
 
template<typename AnalysisType >
AnalysisType * getAnalysisIfAvailable () const
 getAnalysisIfAvailable<AnalysisType>() - Subclasses use this function to get analysis information that might be around, for example to update it. More...
 
bool mustPreserveAnalysisID (char &AID) const
 mustPreserveAnalysisID - This method serves the same function as getAnalysisIfAvailable, but works if you just have an AnalysisID. More...
 
template<typename AnalysisType >
AnalysisType & getAnalysis () const
 getAnalysis<AnalysisType>() - This function is used by subclasses to get to the analysis information that they claim to use by overriding the getAnalysisUsage function. More...
 
template<typename AnalysisType >
AnalysisType & getAnalysis (Function &F)
 getAnalysis<AnalysisType>() - This function is used by subclasses to get to the analysis information that they claim to use by overriding the getAnalysisUsage function. More...
 
template<typename AnalysisType >
AnalysisType & getAnalysisID (AnalysisID PI) const
 
template<typename AnalysisType >
AnalysisType & getAnalysisID (AnalysisID PI, Function &F)
 

Static Public Attributes

static char ID = 0
 

Additional Inherited Members

- Static Public Member Functions inherited from llvm::Pass
static const PassInfolookupPassInfo (const void *TI)
 
static const PassInfolookupPassInfo (StringRef Arg)
 
static PasscreatePass (AnalysisID ID)
 
- Protected Member Functions inherited from llvm::FunctionPass
bool skipOptnoneFunction (const Function &F) const
 skipOptnoneFunction - This function has Attribute::OptimizeNone and most transformation passes should skip it. More...
 

Detailed Description

DependenceAnalysis - This class is the main dependence-analysis driver.

Definition at line 278 of file DependenceAnalysis.h.

Constructor & Destructor Documentation

llvm::DependenceAnalysis::DependenceAnalysis ( )
inline

Member Function Documentation

std::unique_ptr< Dependence > DependenceAnalysis::depends ( Instruction Src,
Instruction Dst,
bool  PossiblyLoopIndependent 
)

depends - Tests for a dependence between the Src and Dst instructions.

Returns NULL if no dependence; otherwise, returns a Dependence (or a FullDependence) with as much information as can be gleaned. The flag PossiblyLoopIndependent should be set by the caller if it appears that control flow can reach from Src to Dst without traversing a loop back edge.

Definition at line 3346 of file DependenceAnalysis.cpp.

References llvm::SmallBitVector::any(), llvm::SmallBitVector::count(), llvm::dbgs(), DEBUG, Delinearize, llvm::Dependence::DVEntry::Direction, dumpSmallBitVector(), llvm::dyn_cast(), llvm::Dependence::DVEntry::EQ, F(), llvm::SmallBitVector::find_first(), llvm::SmallBitVector::find_next(), llvm::FullDependence::getDirection(), llvm::ScalarEvolution::getElementSize(), llvm::LoopInfoBase< N, M >::getLoopFor(), llvm::User::getNumOperands(), llvm::Instruction::getParent(), llvm::GEPOperator::getPointerOperand(), getPointerOperand(), llvm::GEPOperator::getPointerOperandType(), llvm::ScalarEvolution::getSCEV(), llvm::GEPOperator::idx_begin(), llvm::GEPOperator::idx_end(), isLoadOrStore(), isLoopInvariant(), llvm_unreachable, llvm::MayAlias, llvm::Instruction::mayReadFromMemory(), llvm::Instruction::mayWriteToMemory(), llvm::MustAlias, llvm::NoAlias, llvm::Dependence::DVEntry::NONE, P, llvm::PartialAlias, llvm::SmallVectorTemplateBase< T, isPodLike< T >::value >::push_back(), llvm::SmallBitVector::reset(), llvm::SmallVectorImpl< T >::resize(), llvm::Dependence::DVEntry::Scalar, llvm::SmallBitVector::set(), llvm::SI, llvm::SmallVectorTemplateCommon< T >::size(), and underlyingObjectsAlias().

Referenced by dumpExampleDependence().

void DependenceAnalysis::getAnalysisUsage ( AnalysisUsage ) const
overridevirtual

getAnalysisUsage - This function should be overriden by passes that need analysis information to do their job.

If a pass specifies that it uses a particular analysis result to this function, it can then use the getAnalysis<AnalysisType>() function, below.

Reimplemented from llvm::Pass.

Definition at line 146 of file DependenceAnalysis.cpp.

References llvm::AnalysisUsage::addRequiredTransitive(), and llvm::AnalysisUsage::setPreservesAll().

const SCEV * DependenceAnalysis::getSplitIteration ( const Dependence Dep,
unsigned  Level 
)

getSplitIteration - Give a dependence that's splittable at some particular level, return the iteration that should be used to split the loop.

Generally, the dependence analyzer will be used to build a dependence graph for a function (basically a map from instructions to dependences). Looking for cycles in the graph shows us loops that cannot be trivially vectorized/parallelized.

We can try to improve the situation by examining all the dependences that make up the cycle, looking for ones we can break. Sometimes, peeling the first or last iteration of a loop will break dependences, and there are flags for those possibilities. Sometimes, splitting a loop at some other iteration will do the trick, and we've got a flag for that case. Rather than waste the space to record the exact iteration (since we rarely know), we provide a method that calculates the iteration. It's a drag that it must work from scratch, but wonderful in that it's possible.

Here's an example:

for (i = 0; i < 10; i++) A[i] = ... ... = A[11 - i]

There's a loop-carried flow dependence from the store to the load, found by the weak-crossing SIV test. The dependence will have a flag, indicating that the dependence can be broken by splitting the loop. Calling getSplitIteration will return 5. Splitting the loop breaks the dependence, like so:

for (i = 0; i <= 5; i++) A[i] = ... ... = A[11 - i] for (i = 6; i < 10; i++) A[i] = ... ... = A[11 - i]

breaks the dependence and allows us to vectorize/parallelize both loops.

Definition at line 3803 of file DependenceAnalysis.cpp.

References llvm::SmallBitVector::any(), llvm::SmallBitVector::count(), llvm::dbgs(), DEBUG, Delinearize, llvm::dyn_cast(), F(), llvm::SmallBitVector::find_first(), llvm::SmallBitVector::find_next(), llvm::Dependence::getDst(), llvm::ScalarEvolution::getElementSize(), llvm::LoopInfoBase< N, M >::getLoopFor(), llvm::User::getNumOperands(), llvm::Instruction::getParent(), llvm::GEPOperator::getPointerOperand(), getPointerOperand(), llvm::GEPOperator::getPointerOperandType(), llvm::ScalarEvolution::getSCEV(), llvm::Dependence::getSrc(), llvm::GEPOperator::idx_begin(), llvm::GEPOperator::idx_end(), isLoadOrStore(), isLoopInvariant(), llvm::Dependence::isSplitable(), llvm_unreachable, llvm::Instruction::mayReadFromMemory(), llvm::Instruction::mayWriteToMemory(), llvm::MustAlias, P, llvm::SmallBitVector::reset(), llvm::SmallVectorImpl< T >::resize(), llvm::SmallBitVector::set(), llvm::SI, llvm::SmallVectorTemplateCommon< T >::size(), and underlyingObjectsAlias().

Referenced by dumpExampleDependence().

void DependenceAnalysis::print ( raw_ostream O,
const Module M = nullptr 
) const
overridevirtual

print - Print out the internal state of the pass.

This is called by Analyze to print out the contents of an analysis. Otherwise it is not necessary to implement this method. Beware that the module pointer MAY be null. This automatically forwards to a virtual function that does not provide the Module* in case the analysis doesn't need it it can just be ignored.

Reimplemented from llvm::Pass.

Definition at line 187 of file DependenceAnalysis.cpp.

References dumpExampleDependence(), and F().

void DependenceAnalysis::releaseMemory ( )
overridevirtual

releaseMemory() - This member can be implemented by a pass if it wants to be able to release its memory when it is no longer needed.

The default behavior of passes is to hold onto memory for the entire duration of their lifetime (which is the entire compile time). For pipelined passes, this is not a big deal because that memory gets recycled every time the pass is invoked on another program unit. For IP passes, it is more important to free memory when it is unused.

Optionally implement this function to release pass memory when it is no longer used.

Reimplemented from llvm::Pass.

Definition at line 142 of file DependenceAnalysis.cpp.

bool DependenceAnalysis::runOnFunction ( Function F)
overridevirtual

runOnFunction - Virtual method overriden by subclasses to do the per-function processing of the pass.

Implements llvm::FunctionPass.

Definition at line 133 of file DependenceAnalysis.cpp.

References F().

Member Data Documentation

Dependence true char DependenceAnalysis::ID = 0
static

Definition at line 921 of file DependenceAnalysis.h.


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