Flow Propagation Algorithm

Transcription

1 SOMA Flow Propagation Algorithm Univ.Prof. Dr. Franz Wotawa, Birgit Hofer Institut für Softwaretechnologie {wotawa, Institute for Software Technology

2 Agenda Flow Propagation Algorithm Forward Slicing Outlook: Object Flow Graphs Assignment 4 Programming Assignment Birgit Hofer Roxane Koitz Institute for Software Technology VU Software Maintenance 2

3 Up to now: Backward slicing Motivation Computation of statements influencing the value of a variable Identification of faulty statements Now: Correction of the fault Identification of side-effectseffects Compute the statements/variables which are influenced by a statement Institute for Software Technology VU Software Maintenance 3

4 Slicing Backward Computation of statements influencing the value of a variable upwards Forward Computation of statements influenced by a statement downwards Institute for Software Technology VU Software Maintenance 4

5 How to compute forward slices? Reuse backward algorithm? Compute slice for each successor Too time consuming New approach well-known Construct CFG Flow propagation algorithm new Institute for Software Technology VU Software Maintenance 5

6 Flow Propagation Algorithm Graph g Each node n in g consists of 4 sets: in(n) out(n) gen(n) kill(n) determined by the algorithm application specific Institute for Software Technology VU Software Maintenance 6

7 Flow Propagation Algorithm Institute for Software Technology VU Software Maintenance 7

8 Example Institute for Software Technology VU Software Maintenance 8

9 FPA for forward slicing Definitions of application specific sets inslice Initial: false for all nodes slicing criterion Set inslice(n) to true for all nodes n where Set inslice(m) to true for all nodes m where Institute for Software Technology VU Software Maintenance 9

10 Example Forward slice for statement in line 3 Institute for Software Technology VU Software Maintenance 10

11 Application areas of the flow propagation algorithm Forward slicing Backward slicing Compiler optimization Improvement of class diagrams Institute for Software Technology VU Software Maintenance 11

12 Class diagram recovery Institute for Software Technology VU Software Maintenance 12

13 Problems with class diagram recovery Containers Member of type Object Association/dependency in diagram is inaccurate Mismatch between declared type and actual type of objects super classes interfaces Institute for Software Technology VU Software Maintenance 13

14 public class ToyCollection{ static BinaryTreeNode toys = new BinaryTreeNode(); public static addtoy(toy t) { BinaryTreeNode n = new BinaryTreeNode(t); toys.insert(n); } public static void main (String args[]) { Toy t = new Toy("PS2"); addtoy(t); } } class Toy implements Comparable { Object id; public Toy () { id = null; } public void name (Object name) { id = name; } } public class BinaryTreeNode{ BinaryTreeNode left,right; Comparable obj; public BinaryTreeNode(Comparable x) { obj = x; } Example Missing connection! BinaryTreeNode ToyCollection String Comparable Toy Object } Institute for Software Technology VU Software Maintenance 14

15 How can we improve the class diagram? next week Institute for Software Technology VU Software Maintenance 15

16 SOMA Assignment 4 Roxane Koitz Institute for Software Technology

17 1. begin 2. s =5; 3. r = 2 * x; 4. if((s + 1 ) >= 6 ) then 5. begin Calculate the relevant slice for 6. while( r > 10) do 7. begin the slicing criterion: 8. s = r * 2; 5 9. r = r 2; 10. end; 11. od; 12. end; 13. else 14. begin 15. s = s+1; 16. r = 2 + s; 17. end; 18. fi; end; Institute for Software Technology Relevant Slicing ( x = 5,19,{ s})

18 1. begin 2. b= a * 3; 3. k = 2/k; 4. if( k > b ) then 5. begin 6. k = 2 * b; 7. b = 3; 8. end; 9. else 10. begin 11. while( k < 5 ) do 12. begin 13. k = k + b; 14. end; 15. od; 16. end; 17. fi; 18. write(b); 19. end; Relevant Slicing Calculate the relevant slice for the slicing criterion: 7 ( a = 2, k = 2,18,{ b }) Institute for Software Technology

19 Delta Debugging Input: c = 1234abcd Function test: test(x) = iff a2 x c test(x) =, otherwise Institute for Software Technology

20 Questions? Institute for Software Technology VU Software Maintenance 20