A fresh look at optimizing array bound checking

This paper describes techniques for optimizing range checks performed to detect array bound violations. In addition to the elimination of range checks, the optimizations discussed in this paper also reduce the overhead due to range checks that cannot be eliminated by compile-time analysis. The optimizations reduce the program execution time and the object code size through elimination of redundant checks, propagation of checks out of loops, and combination of multiple checks into a single check. A minimal control flow graph (MCFG) is constructed using which the minimal amount of data flow information required for range check optimizations is computed. The range check optimizations are performed using the MCFG rather the CFG for the entire program. This allows the global range check optimizations to be performed efficiently since the MCFG is significantly smaller than the CFG. Any array bound violation that is detected by a program with all range checks included, will also be detected by the program after range check optimization and vice versa. Even though the above optimizations may appear to be similar to traditional code optimizations, similar reduction in the number of range checks executed can not be achieved by a traditional code optimizer. Experimental results indicate that the number of range checks performed in executing a program is greatly reduced using the above techniques.