How to find out GHC's memory representations of data types?

Recently, blog entries such as Computing the Size of a Hashmap explained how to reason about space complexities of commonly used container types. Now I'm facing the question of how to actually "see" which memory layout my GHC version chooses (depending on compile flags and target architecture) for weird data types (constructors) such as

data BitVec257 = BitVec257 {-# UNPACK #-} !Word64
                           {-# UNPACK #-} !Word64
                           {-# UNPACK #-} !Bool
                           {-# UNPACK #-} !Word64
                           {-# UNPACK #-} !Word64

data BitVec514 = BitVec514 {-# UNPACK #-} !BitVec257
                           {-# UNPACK #-} !BitVec257

In C there's the sizeof and offsetof operator, which allows me to "see" what size and alignment was chosen for the fields of C struct.

I've tried to look at GHC Core in the hope to find some hint there, but I didn't know what to look for. Can somebody point me in the right direction?