Class IsNullValueAnalysis

java.lang.Object

edu.umd.cs.findbugs.ba.BasicAbstractDataflowAnalysis<IsNullValueFrame>

edu.umd.cs.findbugs.ba.AbstractDataflowAnalysis<IsNullValueFrame>

edu.umd.cs.findbugs.ba.ForwardDataflowAnalysis<IsNullValueFrame>

edu.umd.cs.findbugs.ba.FrameDataflowAnalysis<IsNullValue, IsNullValueFrame>

edu.umd.cs.findbugs.ba.npe.IsNullValueAnalysis

All Implemented Interfaces:

DataflowAnalysis<IsNullValueFrame>, EdgeTypes, IsNullValueAnalysisFeatures

public class IsNullValueAnalysis
extends FrameDataflowAnalysis<IsNullValue, IsNullValueFrame>
implements EdgeTypes, IsNullValueAnalysisFeatures

A dataflow analysis to detect potential null pointer dereferences.

See Also:

• IsNullValue
• IsNullValueFrame
• IsNullValueFrameModelingVisitor

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	IsNullValueAnalysis.PointerEqualityCheck
(package private) static enum	IsNullValueAnalysis.PointerEqualityCheckState

Field Summary

Fields

Modifier and Type	Field	Description
private IsNullValueFrame	cachedEntryFact
private final CFG	cfg
private JavaClassAndMethod	classAndMethod
(package private) static final boolean	DEBUG
private IsNullValueFrame	instanceOfFrame
private IsNullValueFrame	lastFrame
private final Set<LocationWhereValueBecomesNull>	locationWhereValueBecomesNullSet
private final org.apache.bcel.generic.MethodGen	methodGen
private static final BitSet	nullComparisonInstructionSet
private final IsNullValueAnalysis.PointerEqualityCheck	pointerEqualityCheck
private final boolean	trackValueNumbers
private final IsNullValueFrameModelingVisitor	visitor
private final ValueNumberDataflow	vnaDataflow

Fields inherited from interface EdgeTypes

BACKEDGE_SOURCE_EDGE, BACKEDGE_TARGET_EDGE, CHECKED_EXCEPTIONS_FLAG, EXIT_EDGE, EXPLICIT_EXCEPTIONS_FLAG, FALL_THROUGH_EDGE, GOTO_EDGE, HANDLED_EXCEPTION_EDGE, IFCMP_EDGE, JSR_EDGE, RET_EDGE, RETURN_EDGE, START_EDGE, SWITCH_DEFAULT_EDGE, SWITCH_EDGE, UNHANDLED_EXCEPTION_EDGE, UNKNOWN_EDGE

Fields inherited from interface IsNullValueAnalysisFeatures

NCP_EXTRA_BRANCH, NO_SPLIT_DOWNGRADE_NSP, NO_SWITCH_DEFAULT_AS_EXCEPTION, UNKNOWN_VALUES_ARE_NSP, USE_TYPE_QUALIFIERS

Constructor Summary

Constructors

Constructor	Description
IsNullValueAnalysis(MethodDescriptor descriptor, org.apache.bcel.generic.MethodGen methodGen, CFG cfg, ValueNumberDataflow vnaDataflow, TypeDataflow typeDataflow, DepthFirstSearch dfs, AssertionMethods assertionMethods)

Method Summary

Modifier and Type	Method	Description
void	addLocationWhereValueBecomesNull(LocationWhereValueBecomesNull locationWhereValueBecomesNull)
IsNullValueFrame	createFact()	Create empty (uninitialized) dataflow facts for one program point.
void	endTransfer(BasicBlock basicBlock, org.apache.bcel.generic.InstructionHandle end, IsNullValueFrame result)
JavaClassAndMethod	getClassAndMethod()
private IsNullConditionDecision	getDecision(BasicBlock basicBlock, IsNullValueFrame lastFrame)	Determine if the given basic block ends in a redundant null comparison.
IsNullValueFrame	getFactAtMidEdge(Edge edge)
static IsNullValueAnalysis.PointerEqualityCheck	getForPointerEqualityCheck(CFG cfg, ValueNumberDataflow vna)
private ValueNumber	getKnownNonnullDueToPointerDisequality(ValueNumber knownNull, int pc)
Set<LocationWhereValueBecomesNull>	getLocationWhereValueBecomesNullSet()
private IsNullConditionDecision	handleIfNull(IsNullValue tos, ValueNumber prevTopValue, boolean ifnull)
void	initEntryFact(IsNullValueFrame result)	Initialize the "entry" fact for the graph.
void	meetInto(IsNullValueFrame fact, Edge edge, IsNullValueFrame result)	Meet a dataflow fact associated with an incoming edge into another fact.
void	meetInto(IsNullValueFrame fact, Edge edge, IsNullValueFrame result, boolean propagatePhiNodeInformation)
protected void	mergeInto(IsNullValueFrame other, IsNullValueFrame result)	Merge one frame into another.
protected void	mergeValues(IsNullValueFrame otherFrame, IsNullValueFrame resultFrame, int slot)	Merge the values contained in a given slot of two Frames.
private IsNullValueFrame	replaceValues(IsNullValueFrame origFrame, IsNullValueFrame frame, ValueNumber replaceMe, ValueNumberFrame prevVnaFrame, ValueNumberFrame targetVnaFrame, IsNullValue replacementValue)	Update is-null information at a branch target based on information gained at a null comparison branch.
void	setClassAndMethod(JavaClassAndMethod classAndMethod)
void	startIteration()	Called before beginning an iteration of analysis.
void	startTransfer()
void	transfer(BasicBlock basicBlock, org.apache.bcel.generic.InstructionHandle end, IsNullValueFrame start, IsNullValueFrame result)	Transfer function for the analysis.
void	transferInstruction(org.apache.bcel.generic.InstructionHandle handle, BasicBlock basicBlock, IsNullValueFrame fact)	Transfer function for a single instruction.

Methods inherited from class FrameDataflowAnalysis

copy, getFactAtPC, getFactBeforeExceptionCheck, getLastUpdateTimestamp, isFactValid, isTop, makeFactTop, modifyFrame, same, setLastUpdateTimestamp

Methods inherited from class ForwardDataflowAnalysis

getBlockOrder, getDepthFirstSearch, isForwards

Methods inherited from class AbstractDataflowAnalysis

getFactAfterLocation, getFactAtLocation

Methods inherited from class BasicAbstractDataflowAnalysis

edgeTransfer, factToString, finishIteration, getFactOnEdge, getResultFact, getStartFact, resultFactIterator

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

DEBUG

static final boolean DEBUG

methodGen

private final org.apache.bcel.generic.MethodGen methodGen

visitor

private final IsNullValueFrameModelingVisitor visitor

vnaDataflow

private final ValueNumberDataflow vnaDataflow

cfg

private final CFG cfg

locationWhereValueBecomesNullSet

private final Set<LocationWhereValueBecomesNull> locationWhereValueBecomesNullSet

trackValueNumbers

private final boolean trackValueNumbers

lastFrame

private IsNullValueFrame lastFrame

instanceOfFrame

private IsNullValueFrame instanceOfFrame

cachedEntryFact

private IsNullValueFrame cachedEntryFact

classAndMethod

private JavaClassAndMethod classAndMethod

pointerEqualityCheck

@CheckForNull
private final IsNullValueAnalysis.PointerEqualityCheck pointerEqualityCheck

nullComparisonInstructionSet

private static final BitSet nullComparisonInstructionSet

Constructor Details

IsNullValueAnalysis

public IsNullValueAnalysis(MethodDescriptor descriptor,
 org.apache.bcel.generic.MethodGen methodGen,
 CFG cfg,
 ValueNumberDataflow vnaDataflow,
 TypeDataflow typeDataflow,
 DepthFirstSearch dfs,
 AssertionMethods assertionMethods)

Method Details

getForPointerEqualityCheck

@CheckForNull
public static IsNullValueAnalysis.PointerEqualityCheck getForPointerEqualityCheck(CFG cfg,
 ValueNumberDataflow vna)

getKnownNonnullDueToPointerDisequality

@CheckForNull
private ValueNumber getKnownNonnullDueToPointerDisequality(ValueNumber knownNull,
 int pc)

setClassAndMethod

public void setClassAndMethod(JavaClassAndMethod classAndMethod)

getClassAndMethod

public JavaClassAndMethod getClassAndMethod()

createFact

public IsNullValueFrame createFact()

Description copied from interface: DataflowAnalysis

Create empty (uninitialized) dataflow facts for one program point. A valid value will be copied into it before it is used.

Specified by:

createFact in interface DataflowAnalysis<IsNullValueFrame>

initEntryFact

public void initEntryFact(IsNullValueFrame result)

Description copied from interface: DataflowAnalysis

Initialize the "entry" fact for the graph.

Specified by:

initEntryFact in interface DataflowAnalysis<IsNullValueFrame>

transfer

public void transfer(BasicBlock basicBlock,
 @CheckForNull
 org.apache.bcel.generic.InstructionHandle end,
 IsNullValueFrame start,
 IsNullValueFrame result)
              throws DataflowAnalysisException

Description copied from interface: DataflowAnalysis

Transfer function for the analysis. Taking dataflow facts at start (which might be either the entry or exit of the block, depending on whether the analysis is forwards or backwards), modify result to be the facts at the other end of the block.

Specified by:

transfer in interface DataflowAnalysis<IsNullValueFrame>

Overrides:

transfer in class AbstractDataflowAnalysis<IsNullValueFrame>

Parameters:

basicBlock - the basic block

end - if nonnull, stop before considering this instruction; otherwise, consider all of the instructions in the basic block

start - dataflow facts at beginning of block (if forward analysis) or end of block (if backwards analysis)

result - resulting dataflow facts at other end of block

Throws:

DataflowAnalysisException

startTransfer

public void startTransfer()

endTransfer

public void endTransfer(BasicBlock basicBlock,
 @CheckForNull
 org.apache.bcel.generic.InstructionHandle end,
 IsNullValueFrame result)
                 throws DataflowAnalysisException

Throws:

DataflowAnalysisException

transferInstruction

public void transferInstruction(org.apache.bcel.generic.InstructionHandle handle,
 BasicBlock basicBlock,
 IsNullValueFrame fact)
                         throws DataflowAnalysisException

Description copied from class: AbstractDataflowAnalysis

Transfer function for a single instruction.

Specified by:

transferInstruction in class AbstractDataflowAnalysis<IsNullValueFrame>

Parameters:

handle - the instruction

basicBlock - the BasicBlock containing the instruction; needed to disambiguate instructions in inlined JSR subroutines

fact - which should be modified based on the instruction

Throws:

DataflowAnalysisException

meetInto

public void meetInto(IsNullValueFrame fact,
 Edge edge,
 IsNullValueFrame result)
              throws DataflowAnalysisException

Description copied from interface: DataflowAnalysis

Meet a dataflow fact associated with an incoming edge into another fact. This is used to determine the start fact for a basic block.

Specified by:

meetInto in interface DataflowAnalysis<IsNullValueFrame>

Parameters:

fact - the predecessor fact (incoming edge)

edge - the edge from the predecessor

result - the result fact

Throws:

DataflowAnalysisException

meetInto

public void meetInto(IsNullValueFrame fact,
 Edge edge,
 IsNullValueFrame result,
 boolean propagatePhiNodeInformation)
              throws DataflowAnalysisException

Throws:

DataflowAnalysisException

mergeInto

protected void mergeInto(IsNullValueFrame other,
 IsNullValueFrame result)
                  throws DataflowAnalysisException

Description copied from class: FrameDataflowAnalysis

Merge one frame into another.

Overrides:

mergeInto in class FrameDataflowAnalysis<IsNullValue, IsNullValueFrame>

Parameters:

other - the frame to merge with the result

result - the result frame, which is modified to be the merge of the two frames

Throws:

DataflowAnalysisException

startIteration

public void startIteration()

Description copied from interface: DataflowAnalysis

Called before beginning an iteration of analysis. Each iteration visits every basic block in the CFG.

Specified by:

startIteration in interface DataflowAnalysis<IsNullValueFrame>

Overrides:

startIteration in class BasicAbstractDataflowAnalysis<IsNullValueFrame>

addLocationWhereValueBecomesNull

public void addLocationWhereValueBecomesNull(LocationWhereValueBecomesNull locationWhereValueBecomesNull)

getLocationWhereValueBecomesNullSet

public Set<LocationWhereValueBecomesNull> getLocationWhereValueBecomesNullSet()

mergeValues

protected void mergeValues(IsNullValueFrame otherFrame,
 IsNullValueFrame resultFrame,
 int slot)
                    throws DataflowAnalysisException

Description copied from class: FrameDataflowAnalysis

Merge the values contained in a given slot of two Frames.

Specified by:

mergeValues in class FrameDataflowAnalysis<IsNullValue, IsNullValueFrame>

Parameters:

otherFrame - a Frame

resultFrame - a Frame which will contain the resulting merged value

slot - a slot in both frames

Throws:

DataflowAnalysisException

getDecision

private IsNullConditionDecision getDecision(BasicBlock basicBlock,
 IsNullValueFrame lastFrame)
                                     throws DataflowAnalysisException

Determine if the given basic block ends in a redundant null comparison.

Parameters:

basicBlock - the basic block

lastFrame - the IsNullValueFrame representing values at the final instruction of the block

Returns:

an IsNullConditionDecision object representing the is-null information gained about the compared value, or null if no information is gained

Throws:

DataflowAnalysisException

handleIfNull

private IsNullConditionDecision handleIfNull(IsNullValue tos,
 ValueNumber prevTopValue,
 boolean ifnull)

replaceValues

private IsNullValueFrame replaceValues(IsNullValueFrame origFrame,
 IsNullValueFrame frame,
 ValueNumber replaceMe,
 ValueNumberFrame prevVnaFrame,
 ValueNumberFrame targetVnaFrame,
 IsNullValue replacementValue)

Update is-null information at a branch target based on information gained at a null comparison branch.

Parameters:

origFrame - the original is-null frame at entry to basic block

frame - the modified version of the is-null entry frame; null if the entry frame has not been modified yet

replaceMe - the ValueNumber in the value number frame at the if comparison whose is-null information will be updated

prevVnaFrame - the ValueNumberFrame at the if comparison

targetVnaFrame - the ValueNumberFrame at entry to the basic block

replacementValue - the IsNullValue representing the updated is-null information

Returns:

a modified IsNullValueFrame with updated is-null information

getFactAtMidEdge

public IsNullValueFrame getFactAtMidEdge(Edge edge)
                                  throws DataflowAnalysisException

Throws:

DataflowAnalysisException