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From: "Jean-Pierre Rosen" <rosen.adalog@wanadoo.fr>
Subject: Re: Right of Optimize Eager Evaluation Away
Date: 1999/11/29
Message-ID: <81uhd2$nl4$1@wanadoo.fr>#1/1
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Date: 1999-11-29T18:41:38+00:00
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Laurent Guerby <guerby@acm.org> a �crit dans le message :
863dtqfo26.fsf@ppp-173-146.villette.club-internet.fr...
> [I originally posted this in the 11.6 thread, but got no answer]
>
> If we have the following function:
>
>    function Cond_T (C : in Boolean; If_True, If_False : in T) return T;
>    pragma Inline (Cond_T);
>
>    function Cond_T (C : in Boolean; If_True, If_False : in T) return T is
>    begin
>       if C then
>          return If_True;
>       else
>          return If_False;
>       end if;
>    end Cond_T;
>
> And the following expression:
>
>    C : constant Boolean :=
Some_Run_Time_Value_That_The_Compiler_Cannot_Guess;
>
>    X : constant T := Cont_T (C, If_True =>
Super_Expensive_Function_Call_1,
>                                 If_False =>
Super_Expensive_Function_Call_2);
>
> The question is: is a smart Ada 95 compiler allowed to generate code
> that looks like this:
>
>    if C then
>       X := Super_Expensive_Function_Call_1;
>    else
>       X := Super_Expensive_Function_Call_2;
>    end if;
>
> that is to say, be lazy about its argument, and so might
> save execution time.
>
The simplest solution in this case would be to pass pointers to the
Super_Expensive_Function_Calls;
This way, only the *pointers* are evaluated at the call, the functions are
actually called only as necessary...

--
---------------------------------------------------------
           J-P. Rosen (Rosen.Adalog@wanadoo.fr)
Visit Adalog's web site at http://pro.wanadoo.fr/adalog