Method and apparatus for optimizing away a null-check

摘要

A garbage collection system that needs to meet real-time requirements combines a null-check required for an application with a null check required by its read barrier. The null-check for the application may be the null-check required for a Java object dereference and may be performed via explicit comparisons or implicit traps. To facilitate the combining of the null-checks, the read barrier is broken into portions and sunk to its point of use. Thus, any exception due to a null-pointer in the read barrier will occur at the same location as the exception occurs in the application. Combining the null-checks reduces the overhead costs associated with the read barrier and improves the performance of the real-time application.