[shmerl]

> he was very disappointed because Rust version was twice as fast than the C version which was hand-optimised by pulling off all the tricks he knew to make it perform well.

Why disappointed? It just highlights the quality of Rust's approach.

[ncmncm]

Evidently the tricks were what made it slow.

This happens all too often: once the code changes enough that the optimizer doesn't recognize the pattern anymore, it throws up its hands, and you're on your own. Some people call this optimizer roulette.

It's not just compilers, either. CPUs have their own peephole optimizers, and patterns they recognize, or don't, and it can easily make a 2x difference in your run time depending on if it cottons to what you're trying, or doesn't.

[pjmlp]

With CPUs it gets even worse, because that clever optimized Assembly code can stop being so in another CPU or after a firmware update.

The days of Z80, 6502 and similar are long gone.