Partial Escape Analysis and Scalar Replacement for Java

Escape Analysis allows a compiler to determine whether an object is accessible outside the allocating method or thread. This information is used to perform optimizations such as Scalar Replacement, Stack Allocation and Lock Elision, allowing modern dynamic compilers to remove some of the abstractions introduced by advanced programming models. The all-or-nothing approach taken by most Escape Analysis algorithms prevents all these optimizations as soon as there is one branch where the object escapes, no matter how unlikely this branch is at runtime. This paper presents a new, practical algorithm that performs control flow sensitive Partial Escape Analysis in a dynamic Java compiler. It allows Escape Analysis, Scalar Replacement and Lock Elision to be performed on individual branches. We implemented the algorithm on top of Graal, an open-source Java just-in-time compiler, and it performs well on a diverse set of benchmarks. In this paper, we evaluate the effect of Partial Escape Analysis on the DaCapo, ScalaDaCapo and SpecJBB2005 benchmarks, in terms of run-time, number and size of allocations and number of monitor operations. It performs particularly well in situations with additional levels of abstraction, such as code generated by the Scala compiler. It reduces the amount of allocated memory by up to 58.5%, and improves performance by up to 33%.