a slicing method for object-oriented programs using lightweight dynamic information

Software Engineering Research Group, Graduate School of Engineering Science, Osaka University

A Slicing Method forObject-Oriented Programs

UsingLightweight Dynamic

Information

Fumiaki OHATA, Kouya HIROSE, Masato FUJII and Katsuro INOUE

Osaka University, JAPAN


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ContentsProgram SliceDependence-Cache (DC) SliceObject-Oriented Dependence-Cache (OODC) SliceImplementationEvaluationSummary and Future Work


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Contents (1/6)Program SliceDependence-Cache (DC) SliceObject-Oriented Dependence-Cache (OODC) SliceImplementationEvaluationSummary and Future Work


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Program Slice (Slice)Subprogram which affects the value of slicing criterion <s, v> in ps : Statementv : Variablep : Program

ApplicationsProgram understandingProgram debugging…


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Application Example [Program Debugging]

Slice is effective on fault localization process.

The slice for <9, max> indicates the statements that might cause the unexpected value of max at line 9, so that we have only to focus on them.

1: scanf("%d", &a);2: scanf("%d", &b); 3: max = a;4: min = b;5: if (a > b) {6: max = b;7: min = a;8: }9: printf("%d", max);


Slice for <9, max>



- Incorrect program -

1: scanf("%d", &a);2: scanf("%d", &b); 3: max = a;4: min = b;5: if (a < b) {6: max = b;7: min = a;8: }9: printf("%d", max);

1: scanf("%d", &a);2: scanf("%d", &b); 3: max = a;4: min = b;5: if (a < b) {6: max = b;7: min = a;8: }9: printf("%d", max);

- Correct program -


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Computation ProcessPhase 1 : Defined and referred variables

extractionPhase 2 : Dependence analysis

Data dependence (DD) analysisControl dependence (CD) analysis

Phase 3 : Program dependence graph (PDG) construction

Phase 4 : Slice extraction using PDG traversal


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Data Dependence (DD) Analysis

Extract DD relations between two statements

DD relation represents data-flowthrough variable.

1: a = 3; 2: b = 2; 3: scanf("%d", &c); 4: if ( c == 0 ) 5: d = a; 6: else 7: d = a + 1; 8: e = a + b; 9: printf("%d", d);10: printf("%d", e);


dd


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Control Dependence (CD) Analysis

Extract CD relations between two statements

CD relation represents control-flowfrom conditional expression to conditional predicateorfrom method invocationto method definition.




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Static SliceScope : all possible execution paths

Target : source codeExecution : not required

Dependence analysisDD : staticCD : static

AdvantageSmall analysis cost

DisadvantageImprecise analysis results



dd

Slice for <9, d>


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Dynamic SliceScope : single execution path

Target : execution traceExecution : required

Dependence analysisDD : dynamicCD : dynamic

AdvantagePrecise analysis results

DisadvantageLarge analysis cost



- input ‘0’ for c -

dd


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ProblemsStatic slice has two problems,

array indexes problem : it is difficult for us to determine the values of array indices, andpointer alias problem : it is difficult for us to determine the destination of pointer variables,

so that extracted DD relations are imprecise.Dynamic slice can resolve these problems; however, it requires large analysis cost.


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Dependence-Cache (DC) SliceScope : single execution path

Target : source codeExecution : required

Dependence analysisDD : dynamicCD : static

AdvantageMore precise analysis results than static sliceSmaller analysis cost than dynamic slice



- input ‘0’ for c -


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Dynamic DD AnalysisDD relation DD(s, t, v) exists when the following conditions are all satisfied:

statement s defines variable v, andstatement t refers v, andat least one execution path from s to t without re-defining v exists.

Dynamic analysisOn program execution, we have only to trace the most-recently defined statement for each variable using cache.


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CacheCache(v) : statement that defined variable v most-recently.Operations for cachesBefore program execution,

For each variable v, Cache(v) .On program execution,

For each statement s,- when v is defined, Cache(v) s.- when v is referred, we extract DD relation “DD(Cache(v), s, v)”.


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Comparison withStatic Slice & Dynamic Slice¶

Analysis precision (slice size) : Static slice DC slice Dynamic slice

Analysis cost (memory space & computation time) : Static slice < DC slice « Dynamic slice

Static slice

DC sliceDynamic

slice

DD analysis

Static Dynamic Dynamic

CD analysis

Static Static Dynamic

TargetSource code

Source code

Execution trace

¶ Ashida, Y., Ohata, F. and Inoue, K. : “Slicing Methods Using Static and Dynamic Information”, Proceedings of the 6th Asia Pacific Software Engineering Conference, 344-350, 1999.


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Object-Oriented DC (OODC) Slice

Extended DC slice for Object-Oriented (OO) programs

OO languages have concepts which procedural languages do not have.

Class, Object (Instance)Inheritance, Class hierarchy, Method overridingDynamic binding : based on the reference-type of the object, an appropriate overriding method is selected and invoked.


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Analysis PolicyCharacter 1 : object is a collection of

attributes and methods that operate them.Character 2 : dynamic binding feature

exists; however, static analysis can not handle it sufficiently.

Policy 1 : when a variable is created, the corresponding cache is also created.

Policy 2 : we use dynamic CD analysis for method invocation.


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Dynamic CD analysis for Method Invocation

CD relation CD(s, t) about method invocation exists when the following conditions are all satisfied:

statement t is a method definition, andstatement s calls t.

Dynamic analysisOn program execution, we have only to watch the execution trace from a method invocation to a method definition.


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ImplementationDC Slicing System for Java

Analysis librariesGUI

Developing environmentJDK1.3.0_01JavaCC2.0

Program

JavaCompiler

JavaVirtual

Machine

Slice

PDG

GUI (Graphical User Interface)

Program +Analysis Code

[Source]

Program +Analysis Code

[Bytecode]

Preprocessor

Slicing Criterion

Slicer

Analysis Libraries


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Analysis Libraries10,000 lines

Analysis method : preprocessor stylePreprocessor loads target program p, and generate program p’ that contains p and the code to analyze p dynamically.

Easily developmentEasily optimization using JIT or JavaVM


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Example [Preprocessed Code]

0 : initPDG();1’: def(a, 1); 1 : int a = 10;2’: def(b, 2); 2 : int b = 20;3’: def(c, 3);3 : int c;4’: ref(a, 4); 4’: ref(b, 4); 4’: def(c, 4); 4 : c = a + b;5’: ref(c, 5);5 : printf(“%d\n”, c);

0 : initPDG();1’: def(a, 1); 1 : int a = 10;2’: def(b, 2); 2 : int b = 20;3’: def(c, 3);3 : int c;4’: ref(a, 4); 4’: ref(b, 4); 4’: def(c, 4); 4 : c = a + b;5’: ref(c, 5);5 : printf(“%d\n”, c);

1 : int a = 10;2 : int b = 20;3 : int c;4 : c = a + b;5 : printf(“%d\n”, c);

1 : int a = 10;2 : int b = 20;3 : int c;4 : c = a + b;5 : printf(“%d\n”, c);

- Preprocessed code -- Original code -

DevelopedPreprocessor

For each statement s,when variable v is referred, we insert ref(v, s) before s.when v is defined,we insert def(v, s) before s.


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GUI3,000 lines

FeaturesProgram editingSlice computation


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Metrics Values (1/2)Sample programs

Analysis precision (slice size) [lines]

Program

Classes

Override methods

Lines

Description

P1 2 0 223 CGI program

P2 3 7 226 Paint programSlicing

criterionStatic

DC

Dynamic

P1(1) 26 15 15

P1(2) 83 27 27

P2(1) 48 14 14

P2(2) 45 12 12


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Metrics Values (2/2)Analysis cost

Computation cost (execution time) [ms]

T1 : original code, T2 : preprocessed code (original code + analysis code)

Space cost (memory use on execution) [KByte]

Program

T1 T2 T2/T1

P1 138

582

4.22

P2 N/A

N/A

N/A

Program

T1 T2 T2/T1

P1 478

645

1.35

P2 836

920

1.10


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EvaluationAnalysis precision

Slice size : 30-60% of Static sliceStatic slice DC slice Dynamic slice¶

Analysis costAdditional cost for dynamic DD analysis and dynamic CD analysis for method invocation is not so large.

- Computation cost : 4.2- Space cost : 1.2

¶ Ashida, Y., Ohata, F. and Inoue, K. : “Slicing Methods Using Static and Dynamic Information”, Proceedings of the 6th Asia Pacific Software Engineering Conference, 344-350, 1999.


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SummaryClassification of slicing methodsOODC slice

An intermediate slice between static slice and dynamic slice for OO programs

Dynamic DD analysisDynamic CD analysis for method invocationStatic CD analysis (except method invocation)

Implementation (DC Slicing System for Java)Evaluation (Experimentation using sample Java programs)


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Future WorkApplication of dynamic CD analysis to other dynamically determined elements in Java

ExceptionThread

Experimental comparison with other slicing methods on analysis costApplication of OODC slice to large programsJavaVM-based (interpreter style) DC Slicing System for Java (now developing)


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End.


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Example [Phase 2] (DD Analysis)

1: #include <stdio.h> 2: 3: float absolute(float x) 4: { 5: if(x < 0) { 6: x = -1 * x; 7: } 8: return x; 9: }10: 11: float ave(int a, int b, int c)12: {13: int sum;14: float x;15: 16: sum = a + b + c;17: x = (float) sum / 3.0;18: x = absolute(x);19: return x;20: }21: 22: int main(void)23: {24: int a, b, c;25: float x;26: 27: printf("Input a b c ?");28: scanf("%d %d %d", &a, &b, &c);29: 30: x = ave(a, b, c);31: printf("Ave = %9.3f\n", x);32: return 0;33: }


16: sum = a + b + c;17: x = (float) sum / 3.0;

Data dependence (DD) relation

sum


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Example [Phase 2] (CD Analysis) 1: #include <stdio.h> 2: 3: float absolute(float x) 4: { 5: if(x < 0) { 6: x = -1 * x; 7: } 8: return x; 9: }10: 11: float ave(int a, int b, int c)12: {13: int sum;14: float x;15: 16: sum = a + b + c;17: x = (float) sum / 3.0;18: x = absolute(x);19: return x;20: }21: 22: int main(void)23: {24: int a, b, c;25: float x;26: 27: printf("Input a b c ?");28: scanf("%d %d %d", &a, &b, &c);29: 30: x = ave(a, b, c);31: printf("Ave = %9.3f\n", x);32: return 0;33: }


5: if (x < 0) {6: x = -1 * x;7: }

Control dependence (CD) relation[intra-method]

11: float ave(int a, int b, int c)12: {18: x = absolute(x);20: }

3: float absolute(float x)4: {5: if(x < 0) {6: x = -1 * x;7: }8: return x;9: }

Control dependence (CD) relation[inter-method]

return

call


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Example [Phase 3]28

30

31

11

16

17

18

19

3

5

6

827

a b

x

c

sum

x

x

x

xx

cb a

DDCD


1: #include <stdio.h> 2: 3: float absolute(float x) 4: { 5: if(x < 0) { 6: x = -1 * x; 7: } 8: return x; 9: }10: 11: float ave(int a, int b, int c)12: {13: int sum;14: float x;15: 16: sum = a + b + c;17: x = (float) sum / 3.0;18: x = absolute(x);19: return x;20: }21: 22: int main(void)23: {24: int a, b, c;25: float x;26: 27: printf("Input a b c ?");28: scanf("%d %d %d", &a, &b, &c);29: 30: x = ave(a, b, c);31: printf("Ave = %9.3f\n", x);32: return 0;33: } Node : statement or conditional expression

Edge : dependence relation between two nodes

Node : statement or conditional expressionEdge : dependence relation between two

nodes


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Example [Phase 4] (Slice for <30, x>)



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30

31

11

16

17

18

19

3

5

6

827

a b

x

c

sum

x

x

x

x xx

cb a

We start PDG traversal from the slicing criterion node in reverse order.

The corresponding statements to the reachable nodes form the slice.

We start PDG traversal from the slicing criterion node in reverse order.

The corresponding statements to the reachable nodes form the slice.

a slicing method for object-oriented programs using lightweight dynamic information

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