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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Everything You Know Is Wrong
Date: Tue, 29 Dec 2015 18:36:40 +0100
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Xref: news.eternal-september.org comp.lang.ada:28926
Date: 2015-12-29T18:36:40+01:00
List-Id: <comp.lang.ada>

On 2015-12-29 17:57, G.B. wrote:

> The point is that, since order does not matter among these parallel
> computations, and since parallel loops are not just fantasy,
> the possibility of postponement follows from parallel loops.

Ada does not have parallel loops. The job is done!

> Consider F1 and F2 from a Pure package, X a variable of type T
> and T without progenitors:
>
>     declare
>        A : T := F1 (1,2,3);
>        B : T := F2 (X);
>     begin
>        G (A, B);
>     end;
>
> Is it impossible for a compiler to see that the initializing parts of
> the declarations of A and B are independent?

No, because initialization of T may have side effects. Ada mandates B 
initialized after A. Again, the "optimization" you wanted is done.

BTW, why do you believe that the same amount of computation performed 
consecutively should require less energy or (not quite same) less 
battery drain? It is no obvious. In any case it might depend on the 
specifics of the battery, the board, the memory controller, the number 
of cores etc. You cannot optimize for these, it would lead a 
combinatoric explosion of targets. All that mess to save 0.1% drain?

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de