Recap from last time

1. Recap from last time • We saw various different issues related to program analysis and program transformations • You were not expected to know all of these things • We will learn more about each one of the topics we touched upon last time

2. Program Analyzer Issues (discuss) Input Output Program Analyzer

3. Instructor’s discussion notes Input Output Program Analyzer Input issues • Input is a program, but… • What language is the program written in? • imperative vs. functional vs. object-oriented? maybe even declarative? • what pointer model does the language use? • reflection, exceptions, continuations? • type system trusted or not? • one often analyzes an intermediate language... how does one design such a language?

4. Instructor’s discussion notes Input Output Program Analyzer Input issues • How much of the program do we see? • all? • one file at a time? • one library at a time? • reflection… • Any additional inputs? • any human help? • profile info?

5. Instructor’s discussion notes Input Output Program Analyzer Analysis issues • Analysis/compilation model • Separate compilation/analysis • quick, but no opportunities for interprocedural analysis • Link-time • allows interprocedural and whole program analysis • but what about shared precompiled libraries? • and what about compile-time? • Run-time • best optimization/analysis potential (can even use run-time state as additional information) • can handle run-time extensions to the program • but severe pressure to limit compilation time • Selective run-time compilation • choose what part of compilation to delay until run-time • can balance compile-time/benefit tradeoffs

6. Instructor’s discussion notes Input Output Program Analyzer Analysis issues • Does running-time matter? • for use in IDE? • or in overnight compile?

7. Instructor’s discussion notes Input Output Program Analyzer Output issues • Form of output varies widely, depending on analysis • alias information • constantness information • loop terminates/does not terminate • Correctness of analysis results • depends on what the results are used for • are we attempting to design algorithsm for solving undecidable problems? • notion of approximation • statistical output

8. Program Transformation Issues (discuss) Input Output Program Transformer

9. Instructor’s discussion notes Input Output Program Transformer Input issues • A program, and … • Program analysis results • Profile info? • Environment: # of CPUs, # of cores/CPU, cache size, etc. • Anything else?

10. Instructor’s discussion notes Input Output Program Transformer Transformation issues • What is profitable? • What order to perform transformations? • What happens to the program representation? • What happens to the computed information? For example alias information? Need to recompute?

11. Instructor’s discussion notes Input Output Program Transformer Output issues • Output in same IL as input? • Should the output program behave the same way as the input program?

12. Project schedule • Find groups a week from today • groups of 2-3 • groups of 1 possible if you ask me • Project proposal due the following Tuesday • but... how are we supposed to come up with ideas!!!!

13. Ideas for generating project ideas • If you are currently doing research • that is related to programming languages/compilers • carve out some part of your current research, and do it for the project • Think about what annoys youthe most • in programming • and fix it using program analysis techniques

14. Ideas for generating project ideas • Think about technology trends • iphone, mobile devices • multicore, parallelism • web browsers, java scripts, etc. • bluetooth, ad-hoc networks • how do these change the way we program/compile? • Try to find bugs in real programs using PL techniques • search for “Dawson Engler” and look at some of his papers. Try to use similar techniques to find real bugs.

15. Ideas for generating project ideas • How can I use information that is out there? • ask yourself: what information is out there? And how can I record it/analyze it/use it to improve programmer productivity? • For example: cvs logs, bugzilla, keystrokes, mouse movements, etc. • Talk to your neighbor • in the 231 class, that is • have a discussion

16. Tour of common optimizations

17. Simple example foo(z) { x := 3 + 6; y := x – 5 return z * y }

18. Simple example foo(z) { x := 3 + 6; y := x – 5 return z * y }

19. Another example x := a + b; ... y := a + b;

20. Another example x := a + b; ... y := a + b;

21. Another example if (...) { x := a + b; } ... y := a + b;

22. Another example if (...) { x := a + b; } ... y := a + b;

23. Another example x := y ... z := z + x

24. Another example x := y ... z := z + x

25. Another example x := y ... z := z + y What if we run CSE now?

26. Another example x := y ... z := z + y What if we run CSE now?

27. Another example x := y**z ... x := ...

28. Another example • Often used as a clean-up pass x := y**z ... x := ... Copy prop DAE x := y z := z + x x := y z := z + y x := y z := z + y

29. Another example if (false) { ... }

30. Another example if (false) { ... }

31. Another example • In Java: a = new int [10]; for (index = 0; index < 10; index ++) { a[index] = 100; }

32. Another example • In “lowered” Java: a = new int [10]; for (index = 0; index < 10; index ++) { if (index < 0 || index >= a.length()) { throw OutOfBoundsException; } a[index] = 0; }

33. Another example • In “lowered” Java: a = new int [10]; for (index = 0; index < 10; index ++) { if (index < 0 || index >= a.length()) { throw OutOfBoundsException; } a[index] = 0; }