1. Sung Kim and Michael D. Ernst {hunkim, mernst}@csail.mit.edu CSAIL • MIT

2. Sung Kim and Michael D. Ernst {hunkim, mernst}@csail.mit.edu CSAIL • MIT

3. Static analysis I can find bugs for you!

4. Bug-finding tool

5. Warnings

6. Warning examples

7. Bug candidate - Warning Category : Style - empty try/catch Priority : 3

8. Are warnings useful? Are all warnings important to be fixed? Does tools’ prioritization help to identify important ones?

11. Buggy lines Rev 100 …… Mark as a buggy line if a line is changed in future fixes.

12. Change logs indicate fixes …… [bugfix] Fixed bug #3576 fix File 1 Non-fix Non-fix Non-fix Non-fix

13. Buggy lines Rev 199 Rev 200 Fix If (x=y && Z=x) {

14. Buggy lines Rev 199 Rev 198 If (x=y && Z=x) { If (x=y && Z=x) { marks Fix

15. Buggy lines Rev 100 Rev 200 Rev 199 Rev 198 ……

16. Warning evaluation Rev 100 50% of warnings are fixed later

17. Evaluate warnings at revision n/2 Rev n/2 Rev n Mark buggy lines Rev n/2+1

18. Are warnings important? NO only 3~18% are fixed!

19. Does tools’ prioritization help? NO Tools’ priority 1 warnings are not better.

20. Does tools’ prioritization help?

21. Does tools’ prioritization help?

22. Does tools’ prioritization help? No, high priority warnings do not have high precision!

23. …… Our solution: using change history Warning A File Warning B Foo ……

25. Reprioritization algorithm …… Score(A) += non-fix-weight (0.1) Score(A) += fix-weight (0.9) Fixed bug #3576 Score(A) += Non-fix-weight(0.1) Score(A)=1.1 fix Score(A)=0 Score(A)=0.1 Score(A)=1 Warning A File 1 Warning B Foo …… Score(B)=0

26. Evaluation Rev n/2-1 Rev n/2 Rev 1 Train warnings Rev n Mark buggy lines Rev n/2+1

28. Columba

29. Columba

30. Lucene

31. Lucene

32. Scarab

33. Scarab

34. Summary

35. Sung Kim and Michael D. Ernst {hunkim, mernst}@csail.mit.edu CSAIL • MIT