The now stabilized opt-levels s and z could use some better documentation. rustc -C help still only outputs:
opt-level=val -- optimize with possible levels 0-3, s, or z
I already asked this question some time ago, still without satisfactory answer. I just tried to research this again, but couldn’t find anything useful. I just keep reading s is to optimize for size, z is optimizing for size even moar! Now the release notes say something about z disabling loop vectorization. That’s the kind of information I’d like to easily find about this!