GCC optimizations: What does -O4 do?
 

I compiled mplayer svn recently and noticed that it used the -O4 flag. I was under the impression that -O3 was the highest gcc would go. I read through the gcc manual and there is no mention -O4. Well I was just wondering if anyone knew what it does, specifically what it does that -O3 does not do?

Hmmm. There's definitely no -O4 listed in the docs.
http://gcc.gnu.org/onlinedocs/gcc/Op...timize-Options

I've just tried it with a small app of my own, and the executable created is exactly the same size as with -O3. I'd imagine it does the same thing.

Odd though.

Dave

You can use -Os to get smaller binaries....I have checked it and haven't found any improvements though

I hear from the gentoo folks that this is very effective for firefox, haven't tried it myself, I quite like konqueror.

Well I found the answer if anyone is interested. -O4 at the moment is the same as -O3, -O4 is for further optimisations that may be introduced in future versions of gcc. Mplayer uses them just in case they are actually introduced (you know what their release cycle is like).

I was hoping the answer would be more interesting than that. Oh well.

As far as I know, -Os is what Fedora uses as the standard optimization flag for its Firefox RPM.