Re: Ada 2012 Constraints (WRT an Ada IR)

["Randy Brukardt" <randy@rrsoftware.com>]

"Shark8" <onewingedshark@gmail.com> wrote in message 
news:10e8cb52-1cbd-40ed-ba11-f474c2263ced@googlegroups.com...
>On Tuesday, December 6, 2016 at 2:07:07 PM UTC-7, Dmitry A. Kazakov wrote:
>>
>> P1 = P3, sorry
>
>It's ok, I was just giving you a hard time.
>
>But something did occur to me in the interim:
>
>One reason that an IR could be handy is as an execution model -- like how
>Intel's iAPX 432 was designed for Ada's feature-set -- having a generalized
>form for constraints/violations would mean that the the chip would only 
>have
>to handle one kind of constraint-type instead of having to have specialized
>forms for P3 and P0.

You seem to be assuming that it is practical to represent all kinds of 
predicates as some sort of set. That's definitely not true; one of the major 
reasons that you can't use divide or mod in a static predicate is the 
difficulty of representing the set. For instance, consider:

     subtype Even is new Natural with Dynamic_Predicate => Even mod 2 = 0;

If Natural is a 64 bit type, Even is a set of 2**63 items, no two are 
contiguous. The representation of that is going to be a problem. One could 
imagine some special case to deal with this particular case, but then there 
are many other possible predicates with this property.

Thus, your hypothetical IR would have to represent ranges as predicates, 
rather than as some sort of set. But that would make it hard to do 
operations on the IR (such as merging and check elimination).

                                     Randy.