Luciant

I'm sure this question has been asked, but I would like to make sure I'm doing it correctly. If you are able to re-roll attack dice, (i.e. Thanos UE re-roll attack dice ability) and you roll crits, do you first add the additional dice then re-roll all dice? So for example if you roll 6 dice and 2 are crits, do you roll the 2 additional dice first then if you have re-rolls, you can choose between all 8 dice? <-- of course only choosing those that failed to hit. :)