With my 30 years of both open and closed source software development I can safely say that in the vast majority of cases if you're developing performance-first you're doing it wrong. Develop for correctness first, maintainability second, and performance ... somewhere about nine thousandth. The only time I've felt the urge to develop performance-first was when I was writing code that ran under CP/M and was bit-banging directly at an industrial controller. It really needed to not miss any messages coming from the large potentially explodey thing, lest the potentially explodey thing notice and expensively shut itself down to prevent said explosion.
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