[loeg]

-O3 doesn't cause undefined behavior.

[MyOutfitIsVague]

No, but it can often expose undefined behavior that doesn't stop a program from "working" on lower optimization levels.

Which is why I'm in support of always building your own software with -O3.

[vlovich123]

Are you sure about that? I’m not aware of any additional UB exploitation enabled by O3 vs O2 or Os.

[MyOutfitIsVague]

Nope, I'm not sure about it. I remember when I was using Gentoo about 10 years ago, this was the common reason given for using -O2 instead of -O3 in your build flags, and I'm just speaking from that memory.

[vlovich123]

Yeah there’s lots of cargo culting FUD like that that happens (see other posters in this thread that claim that glibc is a more stable allocator )