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

[Johan Tibell]

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