Class NullDerefAndRedundantComparisonFinder

java.lang.Object

edu.umd.cs.findbugs.ba.npe.NullDerefAndRedundantComparisonFinder

public class NullDerefAndRedundantComparisonFinder
extends Object

A user-friendly front end for finding null pointer dereferences and redundant null comparisons.

See Also:

• IsNullValueAnalysis

Field Summary

Fields

Modifier and Type	Field	Description
private final AssertionMethods	assertionMethods
private final ClassContext	classContext
private final NullDerefAndRedundantComparisonCollector	collector
private static final boolean	DEBUG
private static final boolean	DEBUG_DEREFS
private final BitSet	definitelyDifferentBranchSet
private final BitSet	definitelySameBranchSet
private final boolean	findGuaranteedDerefs
private IsNullValueDataflow	invDataflow
private final BitSet	lineMentionedMultipleTimes
private final org.apache.bcel.classfile.Method	method
private static final boolean	MY_DEBUG
private static final boolean	PRUNE_GUARANTEED_DEREFERENCES
private final List<RedundantBranch>	redundantBranchList
private final BitSet	undeterminedBranchSet
private UnconditionalValueDerefDataflow	uvdDataflow
private ValueNumberDataflow	vnaDataflow

Constructor Summary

Constructors

Constructor	Description
NullDerefAndRedundantComparisonFinder(ClassContext classContext, org.apache.bcel.classfile.Method method, NullDerefAndRedundantComparisonCollector collector)	Constructor.

Method Summary

Modifier and Type	Method	Description
private void	analyzeIfNullBranch(BasicBlock basicBlock, org.apache.bcel.generic.InstructionHandle lastHandle)	This is called for both IFNULL and IFNONNULL instructions.
private void	analyzeNullCheck(IsNullValueDataflow invDataflow, BasicBlock basicBlock)
private void	analyzeRefComparisonBranch(BasicBlock basicBlock, org.apache.bcel.generic.InstructionHandle lastHandle)
void	checkEdges(CFG cfg, Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap, Map<ValueNumber, SortedSet<Location>> bugEdgeLocationMap)
private void	checkForUnconditionallyDereferencedNullValues(Location thisLocation, Map<ValueNumber, SortedSet<Location>> knownNullAndDoomedAt, Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap, ValueNumberFrame vnaFrame, IsNullValueFrame invFrame, UnconditionalValueDerefSet derefSet, boolean isEdge)	Check for unconditionally dereferenced null values at a particular location in the CFG.
private void	examineBasicBlocks()	Examine basic blocks for null checks and potentially-redundant null comparisons.
private void	examineNullValues()	Examine null values.
private void	examineRedundantBranches()	Examine redundant branches.
void	execute()
static BugAnnotation	findAnnotationFromValueNumber(org.apache.bcel.classfile.Method method, Location location, ValueNumber valueNumber, ValueNumberFrame vnaFrame)	Deprecated. Use ValueNumberSourceInfo.findRequiredAnnotationFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame, String) instead
static FieldAnnotation	findFieldAnnotationFromValueNumber(org.apache.bcel.classfile.Method method, Location location, ValueNumber valueNumber, ValueNumberFrame vnaFrame)	Deprecated. Use ValueNumberSourceInfo.findFieldAnnotationFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame) instead
static LocalVariableAnnotation	findLocalAnnotationFromValueNumber(org.apache.bcel.classfile.Method method, Location location, ValueNumber valueNumber, ValueNumberFrame vnaFrame)	Deprecated. Use ValueNumberSourceInfo.findLocalAnnotationFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame) instead
Map<ValueNumber, Set<Location>>	findNullAssignments(Set<LocationWhereValueBecomesNull> locationWhereValueBecomesNullSet)
static XField	findXFieldFromValueNumber(org.apache.bcel.classfile.Method method, Location location, ValueNumber valueNumber, ValueNumberFrame vnaFrame)	Deprecated. Use ValueNumberSourceInfo.findXFieldFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame) instead
private static int	getLineNumber(org.apache.bcel.classfile.Method method, org.apache.bcel.generic.InstructionHandle handle)
private void	noteUnconditionallyDereferencedNullValue(Location thisLocation, Map<ValueNumber, SortedSet<Location>> bugLocations, Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap, UnconditionalValueDerefSet derefSet, IsNullValue isNullValue, ValueNumber valueNumber)	Note the locations where a known-null value is unconditionally dereferenced.
private void	removeStrictlyDominatedLocations(Set<Location> locations, DominatorsAnalysis domAnalysis)
private void	removeStrictlyPostDominatedLocations(Set<Location> locations, PostDominatorsAnalysis postDomAnalysis)
void	reportBugs(Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap, HashSet<ValueNumber> npeIfStatementCovered, Map<ValueNumber, SortedSet<Location>> bugLocationMap, Map<ValueNumber, Set<Location>> nullValueAssignmentMap)

Methods inherited from class Object

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

Field Details

DEBUG

private static final boolean DEBUG

PRUNE_GUARANTEED_DEREFERENCES

private static final boolean PRUNE_GUARANTEED_DEREFERENCES

DEBUG_DEREFS

private static final boolean DEBUG_DEREFS

classContext

private final ClassContext classContext

method

private final org.apache.bcel.classfile.Method method

collector

private final NullDerefAndRedundantComparisonCollector collector

findGuaranteedDerefs

private final boolean findGuaranteedDerefs

redundantBranchList

private final List<RedundantBranch> redundantBranchList

definitelySameBranchSet

private final BitSet definitelySameBranchSet

definitelyDifferentBranchSet

private final BitSet definitelyDifferentBranchSet

undeterminedBranchSet

private final BitSet undeterminedBranchSet

lineMentionedMultipleTimes

private final BitSet lineMentionedMultipleTimes

invDataflow

private IsNullValueDataflow invDataflow

vnaDataflow

private ValueNumberDataflow vnaDataflow

uvdDataflow

private UnconditionalValueDerefDataflow uvdDataflow

assertionMethods

private final AssertionMethods assertionMethods

MY_DEBUG

private static final boolean MY_DEBUG

See Also:

• Constant Field Values

Constructor Details

NullDerefAndRedundantComparisonFinder

public NullDerefAndRedundantComparisonFinder(ClassContext classContext,
 org.apache.bcel.classfile.Method method,
 NullDerefAndRedundantComparisonCollector collector)

Constructor.

Parameters:

classContext - the ClassContext

method - the method to analyze

collector - the NullDerefAndRedundantComparisonCollector used to report null derefs and redundant null comparisons

Method Details

execute

public void execute()

examineBasicBlocks

private void examineBasicBlocks()
                         throws DataflowAnalysisException,
CFGBuilderException

Examine basic blocks for null checks and potentially-redundant null comparisons.

Throws:

DataflowAnalysisException

CFGBuilderException

examineNullValues

private void examineNullValues()
                        throws CFGBuilderException,
DataflowAnalysisException

Examine null values. Report any that are guaranteed to be dereferenced on non-implicit-exception paths.

Throws:

CFGBuilderException

DataflowAnalysisException

findNullAssignments

public Map<ValueNumber, Set<Location>> findNullAssignments(Set<LocationWhereValueBecomesNull> locationWhereValueBecomesNullSet)

reportBugs

public void reportBugs(Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap,
 HashSet<ValueNumber> npeIfStatementCovered,
 Map<ValueNumber, SortedSet<Location>> bugLocationMap,
 Map<ValueNumber, Set<Location>> nullValueAssignmentMap)
                throws CFGBuilderException,
DataflowAnalysisException

Throws:

CFGBuilderException

DataflowAnalysisException

checkEdges

public void checkEdges(CFG cfg,
 Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap,
 Map<ValueNumber, SortedSet<Location>> bugEdgeLocationMap)
                throws DataflowAnalysisException

Throws:

DataflowAnalysisException

removeStrictlyPostDominatedLocations

private void removeStrictlyPostDominatedLocations(Set<Location> locations,
 PostDominatorsAnalysis postDomAnalysis)

removeStrictlyDominatedLocations

private void removeStrictlyDominatedLocations(Set<Location> locations,
 DominatorsAnalysis domAnalysis)

checkForUnconditionallyDereferencedNullValues

private void checkForUnconditionallyDereferencedNullValues(Location thisLocation,
 Map<ValueNumber, SortedSet<Location>> knownNullAndDoomedAt,
 Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap,
 ValueNumberFrame vnaFrame,
 IsNullValueFrame invFrame,
 UnconditionalValueDerefSet derefSet,
 boolean isEdge)

Check for unconditionally dereferenced null values at a particular location in the CFG.

Parameters:

thisLocation -

knownNullAndDoomedAt -

nullValueGuaranteedDerefMap - map to be populated with null values and where they are derefed

vnaFrame - value number frame to check

invFrame - null-value frame to check

derefSet - set of unconditionally derefed values at this location

isEdge -

noteUnconditionallyDereferencedNullValue

private void noteUnconditionallyDereferencedNullValue(Location thisLocation,
 Map<ValueNumber, SortedSet<Location>> bugLocations,
 Map<ValueNumber, NullValueUnconditionalDeref> nullValueGuaranteedDerefMap,
 UnconditionalValueDerefSet derefSet,
 IsNullValue isNullValue,
 ValueNumber valueNumber)

Note the locations where a known-null value is unconditionally dereferenced.

Parameters:

thisLocation -

bugLocations -

nullValueGuaranteedDerefMap - map of null values to sets of Locations where they are derefed

derefSet - set of values known to be unconditionally dereferenced

isNullValue - the null value

valueNumber - the value number of the null value

examineRedundantBranches

private void examineRedundantBranches()

Examine redundant branches.

analyzeRefComparisonBranch

private void analyzeRefComparisonBranch(BasicBlock basicBlock,
 org.apache.bcel.generic.InstructionHandle lastHandle)
                                 throws DataflowAnalysisException

Throws:

DataflowAnalysisException

analyzeIfNullBranch

private void analyzeIfNullBranch(BasicBlock basicBlock,
 org.apache.bcel.generic.InstructionHandle lastHandle)
                          throws DataflowAnalysisException

This is called for both IFNULL and IFNONNULL instructions.

Throws:

DataflowAnalysisException

analyzeNullCheck

private void analyzeNullCheck(IsNullValueDataflow invDataflow,
 BasicBlock basicBlock)
                       throws DataflowAnalysisException,
CFGBuilderException

Throws:

DataflowAnalysisException

CFGBuilderException

findXFieldFromValueNumber

@Deprecated
public static XField findXFieldFromValueNumber(org.apache.bcel.classfile.Method method,
 Location location,
 ValueNumber valueNumber,
 ValueNumberFrame vnaFrame)

Deprecated.

Use ValueNumberSourceInfo.findXFieldFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame) instead

findFieldAnnotationFromValueNumber

@Deprecated
public static FieldAnnotation findFieldAnnotationFromValueNumber(org.apache.bcel.classfile.Method method,
 Location location,
 ValueNumber valueNumber,
 ValueNumberFrame vnaFrame)

Deprecated.

Use ValueNumberSourceInfo.findFieldAnnotationFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame) instead

findLocalAnnotationFromValueNumber

@Deprecated
public static LocalVariableAnnotation findLocalAnnotationFromValueNumber(org.apache.bcel.classfile.Method method,
 Location location,
 ValueNumber valueNumber,
 ValueNumberFrame vnaFrame)

Deprecated.

Use ValueNumberSourceInfo.findLocalAnnotationFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame) instead

findAnnotationFromValueNumber

@Deprecated
public static BugAnnotation findAnnotationFromValueNumber(org.apache.bcel.classfile.Method method,
 Location location,
 ValueNumber valueNumber,
 ValueNumberFrame vnaFrame)

Deprecated.

Use ValueNumberSourceInfo.findRequiredAnnotationFromValueNumber(Method,Location,ValueNumber,ValueNumberFrame, String) instead

getLineNumber

private static int getLineNumber(org.apache.bcel.classfile.Method method,
 org.apache.bcel.generic.InstructionHandle handle)