![]() Therefore, it is not considered crucial for performance to handle a failed check efficiently. Throw new ArrayIndexOutOfBoundsException() įailing range checks are usually caused by programmer errors, as is the case for null pointer exceptions. In practice, an array access looks like the following pseudocode: int array // an array of some type Range checks are tests that guard references to array elements in Java code to protect the program from out-of-bound accesses. Sometimes, as with null checks, a reasonable assumption is almost obvious: Null checks rarely cause an exception, so speculating that they don't cause one is expected to pay off.Ī similar pattern exists for range checks. Speculation means that the compiler starts by making an assumption that is likely true. I'll show examples of profile data collected at runtime, explain how the JIT compiler uses the data, and illustrate the benefits of runtime profiling. This article explains how profiling at runtime can improve speculation and contribute to optimization in other ways. ![]() If the assumption turns out to be wrong, the JIT compiler prevents incorrect execution by returning control to the bytecode interpreter. This optimization technique generates code under an assumption that is expected to be correct but can't be proven certain. In a previous article, I explained that OpenJDK's Just-in-Time (JIT) compiler relies heavily on speculation to achieve higher performance.
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