[jean_lannes]

These seem like two different things. Testing many different optimizations is not the same experiment; it's many different experiments. The SE equivalent of the practice being described would be repeatedly benchmarking code without making any changes and reporting results only from the favorable runs.

[pizlonator]

Doesn’t matter if it’s the same experiment or not.

Say I’m after p<0.05. That means that if I try 40 different purported optimizations that are all actually neutral duds, one of them will seem like a speedup and one of them will seem like a slowdown, on average.

[daveFNbuck]

That's not p hacking. That's just the nature of p values. P hacking is when you do things to make a particular experiment more likely to show as a success.