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From: lutz@iks-jena.de (Lutz Donnerhacke)
Newsgroups: comp.lang.ada
Subject: Re: efficient vector/matrix operations in Ada
Date: Tue, 14 Aug 2001 08:56:51 +0000 (UTC)
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* Russ wrote:
>Larry Hazel <lhazel@mindspring.com> wrote in message news:<3B783732.A3A1EB82@mindspring.com>...
>> Seems to me if a compiler can't generate the most efficient code for
>> A = B + C + D
>>   or
>> A := B + C + D
>> in any language, you need a different compiler.
>
>I'm no compiler expert, but I seriously doubt that you are correct here.
>Come to think of it, I'll just say that you are flat out wrong--and I'll
>eat crow if you are right. The difference (in C++) between
>
>    A = B + C + D;
>and
>    A = B; A += C; A += D;
>
>is more fundamental than a compiler can account for. Don't forget that
>"+" and "+=" are user-defined operators to start with. The former says
>to add B, C, and D, place the result in a temporary matrix, and copy
>that matrix by value back into A.

Even the dragon book contains a chapter about data flow analysis, which is
invented to remove unnecessary temporary copies and does a wonderful job on
this subject.