Interprocedural Load Elimination for Dynamic Optimization of Parallel Programs

Load elimination is a classical compiler transformation that is increasing in importance for multi-core and many-core architectures. The effect of the transformation is to replace a memory access, such as a read of an object field or an array element, by a read of a compiler-generated temporary that can be allocated in faster and more energy-efficient storage structures such as registers and local memories (scratchpads). Unfortunately, current just-in-time and dynamic compilers perform load elimination only in limited situations. In particular, they usually make worst-case assumptions about potential side effects arising from parallel constructs and method calls. These two constraints interact with each other since parallel constructs are usually translated to low-level runtime library calls. In this paper, we introduce an interprocedural load elimination algorithm suitable for use in dynamic optimization of parallel programs. The main contributions of the paper include: a) an algorithm for load elimination in the presence of three core parallel constructs - async, finish, and isolated, b) efficient side-effect analysis for method calls, c) extended side-effect analysis for parallel constructs using an Isolation Consistency memory model, and d) performance results to study the impact of load elimination on a set of standard benchmarks using an implementation of the algorithm in Jikes RVM for optimizing programs written in a subset of the X10 v1.5 language. Our performance results show decreases in dynamic counts for getfield operations of up to 99.99%, and performance improvements of up to 1.76x on 1 core, and 1.39x on 16 cores, when comparing the algorithm in this paper with the load elimination algorithm available in Jikes RVM.