edu.umd.cs.findbugs.ba
Class IsNullValueAnalysis

java.lang.Object
  edu.umd.cs.findbugs.ba.AbstractDataflowAnalysis<Fact>
      edu.umd.cs.findbugs.ba.ForwardDataflowAnalysis<FrameType>
          edu.umd.cs.findbugs.ba.FrameDataflowAnalysis<IsNullValue,IsNullValueFrame>
              edu.umd.cs.findbugs.ba.IsNullValueAnalysis

All Implemented Interfaces:

DataflowAnalysis<IsNullValueFrame>, EdgeTypes

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

A dataflow analysis to detect potential null pointer dereferences.

Author:

David Hovemeyer

See Also:

IsNullValue, IsNullValueFrame, IsNullValueFrameModelingVisitor

Field Summary

private static boolean	DEBUG
private IsNullValueFrame	lastFrame
private org.apache.bcel.generic.MethodGen	methodGen
private static boolean	NO_SPLIT_DOWNGRADE_NSP
private static boolean	NO_SWITCH_DEFAULT_AS_EXCEPTION
private static java.util.BitSet	nullComparisonInstructionSet
private int[]	numNonExceptionSuccessorMap
(package private) static boolean	UNKNOWN_VALUES_ARE_NSP If this property is true, then we assume parameters and return values can be null (but aren't definitely null).
private IsNullValueFrameModelingVisitor	visitor
private ValueNumberDataflow	vnaDataflow

Fields inherited from interface edu.umd.cs.findbugs.ba.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

Constructor Summary

IsNullValueAnalysis(org.apache.bcel.generic.MethodGen methodGen, CFG cfg, ValueNumberDataflow vnaDataflow, DepthFirstSearch dfs, AssertionMethods assertionMethods)

Method Summary

IsNullValueFrame	createFact() Create empty (uninitialized) dataflow facts for one program point.
void	endTransfer(BasicBlock basicBlock, org.apache.bcel.generic.InstructionHandle end, java.lang.Object result_) Subclasses may override this.
private IsNullConditionDecision	getDecision(BasicBlock basicBlock, IsNullValueFrame lastFrame) Determine if the given basic block ends in a redundant null comparison.
void	initEntryFact(IsNullValueFrame result) Initialize the "entry" fact for the graph.
static void	main(java.lang.String[] argv) Test driver.
void	meetInto(IsNullValueFrame fact, Edge edge, IsNullValueFrame result) Meet a dataflow fact associated with an incoming edge into another fact.
protected IsNullValue	mergeValues(IsNullValueFrame frame, int slot, IsNullValue a, IsNullValue b) Merge two values in a particular slot of a Frame.
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	startTransfer(BasicBlock basicBlock, java.lang.Object start_) Subclasses may override this.
void	transferInstruction(org.apache.bcel.generic.InstructionHandle handle, BasicBlock basicBlock, IsNullValueFrame fact) Transfer function for a single instruction.

Methods inherited from class edu.umd.cs.findbugs.ba.FrameDataflowAnalysis

copy, initResultFact, isFactValid, makeFactTop, mergeInto, modifyFrame, same

Methods inherited from class edu.umd.cs.findbugs.ba.ForwardDataflowAnalysis

getBlockOrder, getDepthFirstSearch, isForwards

Methods inherited from class edu.umd.cs.findbugs.ba.AbstractDataflowAnalysis

factToString, getFactAfterLocation, getFactAtLocation, getResultFact, getStartFact, resultFactIterator, transfer

Methods inherited from class java.lang.Object

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

Field Detail

DEBUG

private static final boolean DEBUG

NO_SPLIT_DOWNGRADE_NSP

private static final boolean NO_SPLIT_DOWNGRADE_NSP

NO_SWITCH_DEFAULT_AS_EXCEPTION

private static final boolean NO_SWITCH_DEFAULT_AS_EXCEPTION

UNKNOWN_VALUES_ARE_NSP

static final boolean UNKNOWN_VALUES_ARE_NSP

If this property is true, then we assume parameters and return values can be null (but aren't definitely null).

methodGen

private org.apache.bcel.generic.MethodGen methodGen

visitor

private IsNullValueFrameModelingVisitor visitor

vnaDataflow

private ValueNumberDataflow vnaDataflow

numNonExceptionSuccessorMap

private int[] numNonExceptionSuccessorMap

lastFrame

private IsNullValueFrame lastFrame

nullComparisonInstructionSet

private static final java.util.BitSet nullComparisonInstructionSet

Constructor Detail

IsNullValueAnalysis

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

Method Detail

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>

startTransfer

public void startTransfer(BasicBlock basicBlock,
                          java.lang.Object start_)
                   throws DataflowAnalysisException

Description copied from class: AbstractDataflowAnalysis

Subclasses may override this. Due to a bug in the 2.2 version of the generics-enabled javac, it is not possible to directly override the transfer() method. This method will be called immediately upon entry to transfer().

Overrides:

startTransfer in class AbstractDataflowAnalysis<IsNullValueFrame>

Parameters:

basicBlock - the basic block

start_ - the start fact for the block

Throws:

DataflowAnalysisException

endTransfer

public void endTransfer(BasicBlock basicBlock,
                        org.apache.bcel.generic.InstructionHandle end,
                        java.lang.Object result_)
                 throws DataflowAnalysisException

Description copied from class: AbstractDataflowAnalysis

Subclasses may override this. Due to a bug in the 2.2 version of the generics-enabled javac, it is not possible to directly override the transfer() method. This method will be called just before exiting transfer().

Overrides:

endTransfer in class AbstractDataflowAnalysis<IsNullValueFrame>

Parameters:

basicBlock - the basic block

end - last instruction analyzed (null if entire block was analyzed)

result_ - the result fact for the block

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

mergeValues

protected IsNullValue mergeValues(IsNullValueFrame frame,
                                  int slot,
                                  IsNullValue a,
                                  IsNullValue b)
                           throws DataflowAnalysisException

Description copied from class: FrameDataflowAnalysis

Merge two values in a particular slot of a Frame.

Specified by:

mergeValues in class FrameDataflowAnalysis<IsNullValue,IsNullValueFrame>

Parameters:

frame - the Frame

slot - the slot of the Frame

a - a value

b - another value

Returns:

the merged value

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

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

main

public static void main(java.lang.String[] argv)
                 throws java.lang.Exception

Test driver.

Throws:

java.lang.Exception