> As an example, it doesn't matter that it does in 5ms what it takes to do in 15ms without the optimization, if in the end anything less than 20ms doesn't have visibile outcome.
That hasn't been true ever since power consumption started mattering.
If it really mattered at that level, people would have already stopped trying to do Web based OS or applications for mobile phones.
Also Apple, Google and Microsoft would expose the complete set of mobile and watch OS APIs to C and C++ developers, which they don't. They are kept down to the bare minimum for the upper OS layers.
If you mean takes 15ms vs 5ms to compile yes. However if you're talking executions speed those low hanging fruit optimizations were picked in the 1980's. What we're talking about here are optimizations that speed up some obscure benchmark on a disused architecture by 5%. Bonus no telling if performance is worse on next years silicon.
That hasn't been true ever since power consumption started mattering.