Imported foreign functions should be strict

[Favonia]

Hi all,

Recently I am tuning one of our incomplete libraries that uses FFI.
After dumping the interface file I realized strictness/demand analysis
failed for imported foreign functions---that is, they are not inferred
to be strict in their arguments. In my naive understanding all
imported foreign functions are strict! Here's a minimum example (with
GHC 7.4.2):

{-# LANGUAGE ForeignFunctionInterface #-}
module Main where
import Foreign.C
foreign import ccall unsafe "sin" sin' :: CDouble -> CDouble

where in the interface file the function sin' will have strictness
U(L) (meaning Unpackable(Lazy)).

Regards,
Favonia