Re: When to do a constraint check and not ??

[Jeffrey Carter <jrcarter@acm.org>]

Per Sandberg wrote:
> 
> Assume the folowing code:
> 
> procedue bla is
>         b : boolean; --< B may contain any bit pattern at this point.
> 
>         procedure test( p : in out boolean ) is
>         begin
>                 b := false;
>         end test;
> 
> begin
>         test(b); --<< Is the compiler allowed to insert a constraint check on b
> here ??
> end;
> 
> Is the answer that it is up to the wendor.
> I did not get any clues from the LRM.

The answer is that you have incorrectly specified the parameter mode of
P in Test. Since you do not reference the in value of P, the mode should
be out.

The compiler is required to insert a constraint check on B if it has a
subtype different from P, see 6.4.1(11). The subtype conversion and
assignment mentioned require a range check, just as if you did them
manually.

In this case B and P have the same subtype, so the compiler may assume
the value of B is valid for the subtype and eliminate the range check.
However, it is not required to eliminate the check, so the above appears
to be a bounded error.

-- 
Jeff Carter
"I wave my private parts at your aunties."
Monty Python & the Holy Grail