> "deoptimization"

pessimization?

But the code doesn't have to become more complicated for it to be premature optimization. It literally just means improving something (generally performance) before there's a clear need.

> Writing the same code in a fast compiled language is just the default thing that you should be doing when you are not doing premature optimization.

I assume you mean "rewriting" here, since we're talking about porting existing code. Sometimes it's the best use of time, sometimes it's premature.