Comparison checking

We present a novel approach to avoid the debugging of optimized code through comparison checking. In the technique presented, both the unoptimized and optimized versions of an application program are executed, and computed values are compared to ensure the behaviors of the two versions are the same under the given input. If the values are different, the comparison checker displays where in the application program the differences occurred and what optimizations were involved. The user can utilize this information and a conventional debugger to determine if an error is in the unoptimized code. If the error is in the optimized code, the user can turn off those offending optimizations and leave the other optimizations in place. We implemented our comparison checking scheme, which executes the unoptimized and optimized versions of C programs, and ran experiments that demonstrate the approach is effective and practical.