FreeGameDev

I've been wondering: how many opensource games distribute optimized builds? I.e. the production (not debugging) builds shall, for example, be compiled with gcc's " -O3" flag? And if so, how widespread is the practice?

Are you looking for exact numbers or just talk about this? If you're just worried, then don't, I am pretty sure all sane projects optimize the release versions they distribute. Most games I've been building have a CMake or other option with which you either set release or debug.

Pretty much everywhere, it's the default when making release builds.

Although, please note that -O3 may not actually be faster than -O2, it's just a more aggressive optimisation technique.