Hi, On Mon, 13 Mar 2006, Jeffrey A Law wrote:
> > What do you mean by "abuse"? TYPE_MAX_VALUE means maximal value > > allowed by given type. > As long as you're *absolutely* clear that a variable with a > restricted range can never hold a value outside that the > restricted range in a conforming program, then I'll back off > the "abuse" label and merely call it pointless :-) I really really can't understand your strong opposition against the sensible semantics of TYPE_MAX_VALUE. If the type has only a certain range, than it obviously is a good thing to make this knowledge available to the optimizers, even if that range doesn't end at a power of two. That the value of variables of that type has to stay in that range is a tautology (i.e. whereever that's not the case it's a bug somewhere, either in the source, in the frontend or the optimizer). It doesn't make the notion of TYPE_MAX_VALUE pointless at all. > The scheme you're using "promoting" to a base type before all > arithmetic creates lots of useless type conversions and means > that the optimizers can't utilize TYPE_MIN_VALUE/TYPE_MAX_VALUE > anyway. ie, you don't gain anything over keeping that knowledge > in the front-end. Sure it can, namely in VRP, and connected optimizations. First: It's not clear that also the pascal frontend goes back to the base type for doing arithmetics. In fact you assume that arithmetics is done on such variables at all, which is not necessary. It can just be used as lookup value in switches for instance, or in comparisons. And second: even if it does promote to do arithmetics the final result probably is again in the restricted type, again providing the knowledge of the range to VRP (obviously the frontend has to somehow make sure that the result of this arithmetic indeed fits into the real type, but see above for why this is not a very special request). Ciao, Michael.
