Capturing the effects of code improving transformations

Symbolic debugging of transformed code requires information about the impact of applying transformations on statement instances so that the appropriate values can be displayed to a user. We present a technique to automatically identify statement instance correspondences between untransformed and transformed code and generate mappings reflecting these correspondences as code improving transformations are applied. The mappings support classical optimizations as well as loop transformations. Establishing mappings requires analyzing how the position, number, and order of instances of a statement can change in a particular context when transformations are applied. In addition to enabling symbolic debugging of transformed code, these mappings can be used to understand transformed code and to compare values computed in both program versions either manually or automatically.