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From: "Samuel T. Harris" <samuel_t_harris@Raytheon.com>
Subject: Re: question about functions
Date: 2000/01/21
Message-ID: <38889682.ACA87787@Raytheon.com>#1/1
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Organization: Raytheon Aerospace Engineering Services
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Newsgroups: comp.lang.ada
Date: 2000-01-21T00:00:00+00:00
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tmoran@bix.com wrote:
> 
> function ADD (A, B : in T) return T is
>    tmp : T;
> begin
>    -- call a procedure which use directly the hardware :
>    proc (a'address, b'address, tmp'address);
>    return tmp;
> end ADD;

The compiler may pass A and B in registers instead of
on the stack. In this case a'address and b'address
will cause runtime errors. VADS on SGI IRIX causes
a either a bus error or segmentation fault (I can't
remember now) for a similar subprogram we needed.

To get around this, you need temps for A and B, ala ...

function ADD (A, B : in T) return T is
  temp_a : t := a;
  temp_b : t := b;
  result : t;
begin
  proc (temp_a'address, temp_b'address, result'address);
  return result;
end;

In our case VADS was not smart enough to recognize that
the usage of the parameters includes a 'address attribution
which should preclude passing A and B in registers. Given
the other complex data flow analysis employed by the
compiler for other optimizations, this seems a reasonable
check.

Of course VADS is Ada 83. Perhaps the language laywers
in the news group can expound on any new Ada 95 rules
which eliminates this situation?

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"