Sliding genioplasty before or after facelift?

Sliding genioplasty can be performed before or after. It can also be combined at the time of the other surgery. There isn't a clear consensus on whether before or after is better so you should discuss your expectations with your surgeon in order to decide what would be best.

Chin increas procedures (either sliding genioplasty or multidimensional augmentation genioplasty) does entail a facelift for free; see one example among many other in the link.

You could do it before during or after, but I prefer to do it before or at the same time of the facelift.

There is no reason why a sliding genioplasty can not be done at the time of a facelift. It is no different than doing a chin implant with a facelift. If one can not do the two together the order (before or after the facelift) does not matter.

This is a very common question among patients. If possible, I prefer to do both procedures together in order for them to compliment each other and provide one surgery and healing time for the patient. If it is not possible to do at the same time, the genioplasty before the facelift will provide necessary bony structure to help support the lower face and neck. 

It is more logical to do genioplasty before the facelift (ie do the bone foundation structure first rather than the overlying soft tissue); but both will yield a good result in any order.