How do we best make sure {Int,Word,Float,Double} to {Int,Word,Float,Double} conversions stay efficient

Hi, I've been tracking down a few (unrelated) performance bugs related to conversions between primitive types. What these issues had in common is that some rule failed to fire and the conversion went via Integer, killing performance. How do we best write a test that make sure that fromIntegral conversions between these types don't regress? Is it possible to test the output of the simplifier or do we have to do something less direct, like writing a loop that does such conversions and make sure that the allocation stay low? -- Johan