Re: Announce: The Ultimate SI Units Cracker

[Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>]

Mark Biggar wrote:

> Dmitry A.Kazakov wrote:
>> Wes Groleau wrote:
>> 
>>>I prefer to look at it as
>>>"There's no rule to prevent a compiler vendor from ....
>>> and no way to prevent a user from selecting that compiler."
>> 
>> Is it absolutely true? I mean, ARM precisely defines what is "static" and
>> what is not. So an expression involving static discriminants could be
>> *formally* non-static, even if its outcome were known at compile-time.
>> Thus such an outcome would be not allowed to appear where a static value
>> is expected.
> 
> Yes, the ARM precisely defines which expressions must be static, but
> it also goes on the define a "duck test"* for all expressions that
> says that even though the expression is not in a static context
> if it only contains static values then it should be statically
> evaulated at compile time.  In addition, the optimization "as if" rule
> allows a compiler to do all sorts of things like Wes wants.

Right (*), but it is only a part of the problem. Even if an outcome is 
known, it may not appear in a static context. One cannot heal that without 
redefining the term "static" in ARM 4.9.

* However I saw no compiler capable to do it even in such a straightforward 
case as dimensioned units. Neither GNAT nor Aonix does it.

-- 
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de