Although I can't claim a long tenure in the software development field. One of my favorite tricks/rediscovered performance enhancer can be found in a similarity between very old-school self-modifying code, and modern day profile guided JIT optimizer.

I think I read somewhere that, at some point, it was all the rage to have self-modifying code that could patch conditional branch instructions into unconditional ones (I think it was used on game consoles to save space). These days profile guided JIT compilers (or even AOT compiler) will de-virtualize calls to increase performance, which to me looks like a really similar technique.