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From: munck@STARS.RESTON.UNISYS.COM (Bob Munck)
Newsgroups: comp.lang.ada
Subject: Re: Ada vs C implementation efficiency
Message-ID: <1336.677341010@osprey>
Date: 19 Jun 91 14:16:50 GMT
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In INFO-ADA Digest V91 #165, eachus@mitre-bedford.arpa  (Robert I. Eachus)
said:

> ...  In general, for good compilers
>and good benchmarks a program will run fastest in the language it was
>originally written in.

You CAN'T mean that exactly as written.  Surely the history of a benchmark
has little to do with its results.  Maybe you mean something like "line-at-
a-time, uncritical translation of a program from one language to another
almost always result in poor performance of the translated program compared
to the original."?

>     My personal approach, based on this experiment and others, is to
>go for correctness first, and if you need better performance, look at
>the algorithms, THEN at the code.  I have gotten to the point of
>looking at generated code once or twice, but in every case I have
>found a way to coerce the compiler to generate what I wanted.

An important point, and something that a lot of programmers learn late in
their careers or not at all.  Note too that this approach to performance
tends to preserve maintainability.  My way of stating this approach:

                RULES FOR PROGRAM OPTIMIZATION:
                
                1. Don't do it.
                
                2. (Experts only) Don't do it yet.
                
I do have my doubts about "coerce the compiler to generate what I wanted."
What happens when a new compiler release doesn't coerce the same way?  Besides,
playing with object code makes hair grow on your palms.

Bob Munck