[Bug tree-optimization/21712] missed optimization due with const function and pulling out of loops

[Daniel Berlin]

> .
> 
> Nevertheless, even if we are very strict with the definition, moving
> get_type2 out of the loop is not a good idea, since get_type2 might
> potentially be very expensive (and we have no way how to determine
> that this is not the case), thus we would lose in case get_type2
> should be never executed.
> 
> 

Don't we attempt to detect zero trip loops?
(If not, we should :P)