Automatic isolation of compiler errors

Abstract

This paper describes a tool called vpoiso that was developed to isolate errors automatically in the vpo compiler system. The two general types of compiler errors isolated by this tool are optimization and nonoptimization errors. When isolating optimization errors, vpoiso relies on the vpo optimizer to identify sequences of changes, referred to as transformations, that result in semantically equivalent code and to provide the ability to stop performing improving (or unnecessary) transformations after a specified number have been performed. A compilation of a typical program by vpo often results in thousands of improving transformations being performed. The vpoiso tool can automatically isolate the first improving transformation that causes incorrect output of the execution of the compiled programs by using a binary search that varies the number of improving transformation performed. Not only is the illegal transformation automatically isolated, but vpoiso also identifies the location and instant the transformation is performed in vpo . Nonoptimization errors occur from problems in the front end, code generator, and necessary transformations in the optimizer. If another compiler is available that can produce correct (but perhaps more inefficient) code, then vpoiso can isolate nonoptimization errors to a single function. Automatic isolation of compiler errors facilitates retargeting a compiler to a new machine, maintenance of the compiler, and supporting experimentation with new optimizations.