1. Region Inference for an Object-Oriented Language Wei Ngan Chin 1,2 Joint work with Florin Craciun 1 , Shengchao Qin 1,2 , Martin Rinard 3 1 National University of Singapore 2 Singapore-MIT Alliance 3 MIT

6. Region-Annotated Core-Java region parameters for polymorphism constraint abstractions class invariant method precondition region constraint s

7. Inferring for Class Step 4 : Inherit constraint of superclass. Step 1 : Reserve first region for the receiver object ( this ). Step 2 : Keep regions of fields distinct for precision. Step 3 : No dangling property as class invariant.

8. Inferring for Class Step 1 : Reserve first region for the receiver object ( this ). Step 2 : Keep regions of fields distinct for precision. Step 3 : No dangling requirement as class invariant.

9. Inferring for Methods Step 3 : Localise regions that do not escape. Step 4 : Fix-point analysis for recursion. method precondition Step 2 : Gather constraints from method body. Step 1 : Region parameters from method signature.

11. (Object) Region Subtyping concept pioneered in Cyclone [PLDI02] an object w of type c <r,..> can be passed to a location v of type c <s,..> provided r º s (e.g. in assignment and parameter/result passing)

12. Example Without region subtyping, regions of a and b are forced to be equal . With region subtyping, these regions may be distinct .

13. Problem – Recursive Fields Recursive nodes being forced into the same region Some programs work better with recursive nodes in different regions …

14. (Field) Region Subtyping SOLUTION : Covariance for Read-Only Fields. Example: read-only mutable

17. Inference Rule : Sequence Inference is flow-insensitive but can be improved by SSA form

18. Inference Rule : Expression Block rs : the set of regions that do not escape the block Regions of rs coalesced into a single localised region r

19. Example – Localised Region

20. Example – Localised Region localised region r

21. Example : Recursive Function

30. Correctness

31. Core-Java

33. No Region Subtyping [Boyapati et al PLDI03] supports class subtyping but not region subtyping

34. No Region Subtyping [Boyapati et al PLDI03] supports class subtyping but not region subtyping

36. Example - Reynolds3 With field region subtyping, the List(x,p) object can be allocated in a local region of the recursive call.

39. Region Subtyping concept from [Cyclone PLDI02] allows v=w where location v::c <s,..> can be passed an object w of type c <r,..> provided r  s

41. Experiments

42. Inference of Methods class invariant method precondition

43. Inferring for Class class invariant to prevent dangling references

46. Example – Cyclic Structure p1 p2

47. Inference of Methods method precondition