status of D optimizers benefiting from contracts ?

[Laeeth Isharc via Digitalmars-d-learn]

https://www.youtube.com/watch?v=e2F2pqeMLuw&list=PL4EvMyUrlAJmEfs8l6oW2BlnALiDu7kGy
31 minutes in, Walter Bright suggests that a supplementary 
benefit of using contrats is helping the compiler make 
optimisations.  He uses the example of being able to do faster 32 
bit arithmetic when the variables are longs but per contract 
within the bounds for 32 bits.

I wondered to what extent D compilers are doing this already 
(peeking at the contract), and what plans if any there are to 
incorporate these in generating fast code.


Thanks.


Laeeth