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From: Stephen Leake <Stephen.Leake@gsfc.nasa.gov>
Subject: Re: question about functions
Date: 2000/01/21
Message-ID: <uln5jjhz8.fsf@gsfc.nasa.gov>#1/1
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 <VmUh4.255$bT1.11162@nnrp2-w.snfc21.pbi.net> <38889682.ACA87787@Raytheon.com>
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 20:22:43 GMT)
Organization: NASA Goddard Space Flight Center
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Newsgroups: comp.lang.ada
Date: 2000-01-21T20:22:43+00:00
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"Samuel T. Harris" <samuel_t_harris@Raytheon.com> writes:

> tmoran@bix.com wrote:
> <snip> 
> 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?

At a guess, adding 'aliased' should help. Or pragma Volatile.

-- Stephe