I've added a special case for branch instructions that set the link register to reduce visual noise, which turns this: https://user-images.githubusercontent.com/4522237/75113261-82c9fc00-564c-11ea-804d-61dca888cf76.png
into something much more readable-at-a-glance: https://user-images.githubusercontent.com/4522237/75202872-eb0fff00-576c-11ea-869c-0a9ca0b208ef.png

Since instructions that set the link register usually jump to another function, and thus very rarely actually have the target visible, this seems like a good idea to me.

I'll see if I can do something about using the horizontal space better, too.

Alright, I tried to use the horizontal space better, looks pretty good now if you ask me: https://user-images.githubusercontent.com/4522237/75385411-ff283d80-58df-11ea-9155-3db9a41efe2f.png

I'm not entirely sure I like how the indentation calculation code is written (in particular the lambda-in-lambda there...), but I suppose it does the job.

One thing I'm not sure here is if I have to make sure BranchDisplayDelegate::paint() and CodeViewWidget::Update() don't run at the same time in different threads, or if those two are both only already allowed on the GUI thread anyway. Does anyone know?

Looks like CodeViewWidget::Update is only called from the UI thread, so there shouldn't be any issues