The article does not mention optimization, but standard optimization levels (-O1, -O2, -O3) are not chosen optimally at all. See http://dl.acm.org/citation.cfm?id=1356080
Optimally is kind of a non-sensical term for this.
There is no optimality to be found here in any mathematical sense. Even COLE does not generate optimal, it finds something mildly reasonable.
However, the main problem with things like COLE, is that they mostly discover phase ordering issues or latent optimization bugs. Those are bugs and problems that should be fixed.
Most of phase ordering is decided by design and architecture, ie "we want it to work a certain way for certain reasons". To the degree it doesn't work best that way, it's usually a problem to be fixed, not a fundamental issue that COLE has discovered.
Optimally is kind of a non-sensical term for this. There is no optimality to be found here in any mathematical sense. Even COLE does not generate optimal, it finds something mildly reasonable.
However, the main problem with things like COLE, is that they mostly discover phase ordering issues or latent optimization bugs. Those are bugs and problems that should be fixed.
Most of phase ordering is decided by design and architecture, ie "we want it to work a certain way for certain reasons". To the degree it doesn't work best that way, it's usually a problem to be fixed, not a fundamental issue that COLE has discovered.