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As a type-safe program language, Java requires bounds checks of array accesses. Whenever an array element is accessed, a cmp (compare) instruction is executed to check whether the index value is within the valid bounds. Array bounds checks may prevent many useful optimizations because of precise exception. We present a new ABCE (array bounds check elimination) algorithm to eliminate redundant checks based on sparse representation for a Java static compiler. In contrast to other approaches performing in JVMs, we adhere to the design principle of the static compiler to optimize scientific Java applications. The algorithm is a light-weight algorithm working on an intermediate representation in static single assignment form. It fully removes bounds checks if it can be proven that they never fail. Whenever possible, it moves bounds checks out of loops to reduce the total number of executed checks. If such a check fails, the executing program branches into the unmodified loop to preserve the exception semantics of Java. For the scientific SciMark 2.0 benchmark suite, this algorithm removes on average 76% of bounds check instructions. The evaluation shows a speedup near to the theoretical maximum for LU test case.
Date of Conference: 2-4 Dec. 2009