This is especially true in the field of crypto, where timing attacks are a major issue. Knowing that your program will produce the correct result isn't enough, you need to know that the amount of time taken to compute that result doesn't leak information, and I don't think Haskell provides any way to ensure this.

Haskell in fact does the opposite. Changes in compiler version can drastically alter the performance of your code, even changing its O() class.

it's just probably correct ;)