There are no such thing...

> Nobody uses -O3.

Wrong.

I use -O3 on Linux, and -O4 on AIX (xlc) for my product builds.

To be fair, there a few modules that don't fair well at -O4, but only because I've not had time to find out what is wrong with them (usually uninitialized variables).

My next step on AIX is IPA at link time, it will do inlining and other code movement that couldn't be done at compile time, due to the plethora of little pieces, all compiled separately.