This doesn't seem right. The optimal direction for a call stack to grow is ISA dependent. I'd expect bump allocation to be likewise - either it doesn't matter at all, or the specific instructions available mean one is better.

I think what has happened here is the original post chose a specific representation for the start/current/end tuple and given that representation one direction was better, then the follow up post took that representation as foundational and noticed that some of the branches can be rolled together.

There's lots of representations available for start/current/end. It should always be possible to have arithmetic followed by a single branch, where you pick the state representation to make the test cheaper for a given direction on a given ISA.