sizeExpr:size_up_alloc is wrong for unlifted data types.

    ------------
    -- Cost to allocate binding with given binder
    size_up_alloc bndr
      |  isTyVar bndr                 -- Doesn't exist at runtime
      || isJoinId bndr                -- Not allocated at all
      || isUnliftedType (idType bndr) -- Doesn't live in heap
           -- OK to call isUnliftedType: binders have a fixed RuntimeRep (search for FRRBinder)
      = 0
      | otherwise
      = 10

This is from GHC.Core.Unfold:581

Unlifted data types very much live in the heap. And so does ByteArray# for what it's worth. It might also be wrong for unboxed tuples but not entirely sure if they get their own handling somewhere else.