Verifying Compilers and ASMs or ASMs for uniform description of multistep transformations

A verifying compiler ensures that the compiled code is always correct but the compiler may also terminate with an error mesage and then fails to generate code. We argue that with respect to compiler correctness this is the best possible result which can be achieved in practice. Such a compiler may even include unverified code provided the results of such code can be proven correct independently from how they are generated. We then show how abstract state machines (ASMs) can be used to uniformly describe the dynamic semantics of the programs being compiled across the various intermediate transformation steps occurring within a compiler. Besides being a convenient tool for describing dynamic semantics the fact that we do not have to switch between different descriptional methods is found to be extremely useful.