I assume that the author means, when it is easy to change something in the code (i.e. without fear because you have a very good test automation), then it is easy to apply changes like performance optimizations.
Things like loop unrolling is probably something I wouldnt do by hand on the source code, I would probably write a script that transforms the code automatically, so the original source code stays readable.
Things like loop unrolling is probably something I wouldnt do by hand on the source code, I would probably write a script that transforms the code automatically, so the original source code stays readable.