We describe a highly practical program specializer for Java programs. The specializer is powerful, because it specializes optimistically, using (potentially transient) constants in the heap; it is precise, because it specializes using data structures that are only partially invariant; it is deployable, because it is hidden in a JIT compiler and does not require any user annotations or offline preprocessing; it is simple, because it uses existing JIT compiler ingredients; and it is fast, because it specializes programs in under 1s.These properties are the result of (1) a new algorithm for selecting specializable code fragments, based on a notion of influence; (2) a precise store profile for identifying constant heap locations; and (3) an efficient invalidation mechanism for monitoring optimistic assumptions about heap constants. Our implementation of the specializer in the Jikes RVM has low overhead, selects specialization points that would be chosen manually, and produces speedups ranging from a factor of 1.2 to 6.4, comparable with annotation-guided specializers.

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It has been observed that component-based applications exhibit object churn , the excessive creation of short-lived objects, often caused by trading performance for modularity. Because churned objects are short-lived, they appear to be good candidates for stack allocation. Unfortunately, most churned objects escape their allocating function, making escape analysis ineffective. We reduce object churn with three contributions. First, we formalize two measures of churn, capture and control (15). Second, we develop lightweight dynamic analyses for measuring both capture and control . Third, we develop an algorithm that uses capture and control to inline portions of the call graph to make churned objects non-escaping, enabling churn optimization via escape analysis. JOLT is a lightweight dynamic churn optimizer that uses our algorithms. We embedded JOLT in the JIT compiler of the IBM J9 commercial JVM, and evaluated JOLT on large application frameworks, including Eclipse and JBoss. We found that JOLT eliminates over 4 times as many allocations as a state-of-the-art escape analysis alone.