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From: kilgallen@eisner.decus.org (Larry Kilgallen)
Subject: Re: Apex vs GNAT on solaris
Date: 1999/12/08
Message-ID: <1999Dec8.151848.1@eisner>#1/1
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Date: 1999-12-08T00:00:00+00:00
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In article <384ea194.799371745@newsnew.draper.com>, rracine@myremarq.com (Roger Racine) writes:

> For example, the GNAT documentation simply states that you get no
> optimization with -O0, "normal optimization" with -O1, "extensive
> optimization" with -O2, and automatic inlining with -O3.  It does not
> say anything about the speed of compilation difference, any debugger
> deficiency with the various options, or any other reason one might
> want to use one vs the other.  Is everyone supposed to have to check
> the compile time for each option?

No, just those who care about the compile time.  Certainly ACT cannot
document the compile time, because differences in compile time will
depend on how heavily the program being compiled uses the features
that get more optimization.  A very good heuristic is that more
optimization takes longer during compilation.

Another heuristic is that more optimization makes debugging at the
machine code level harder, because the machine code layout bears
less resemblence to the source code layout.  ACT cannot document
how much harder, because that is in the eye of the beholder.
I have debugged a lot of Alpha machine code, but using GNAT
I would be less well equipped than someone else because I am
accustomed to looking at the output of a different code generator.

Both of these heuristics can be combined into one easy-to-remember saying:

	"There ain't no such thing as a free lunch."

Where the word "free" means anything I want it to mean :-).

Larry Kilgallen