When we are creating a new pull request, this page instantly loads the difference between two branches, which most of the time are not the ones you really want to create the PR.
Sometimes the difference between one branch and the other is very large and once done you will have to change the branchs again, wasting time.
So I believe that it would be ideal to have a button to calculate the difference, or start with the two selects in the same branch, so that there is no difference and load quickly. For example when you open the page the selects are on the same branch (dev-> dev).
Another nice thing would be to be able to pass the comparison branches through Query Parameters. So when you load the page it will already load with the correct branches and even make it easier if you want to share it with someone else. Just pass the link with the query parameters.