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From: Robert Dewar <dewar@gnat.com>
Subject: Re: Apex vs GNAT on solaris
Date: 1999/12/07
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In article <82hiuj$74o$1@nnrp1.deja.com>,
  reason67@my-deja.com wrote:


You need to say what options you are using for both compilers.
We have sometimes found people making the *amazing* mistake
of compiling GNAT with -O0. Generally the appropriate options
for benchmarking are -O2 -gnatn.

The options are critical, because otherwise you may simply
be measuring differences in choices of default options. For
example if one compiler inlines by default, the other one
does not, then the comparison may be meaningless.

You also need to specify all other parameters. For instance,
if you are running tasking, make sure you are comparing
comparable underlying threads implementations, otherwise you
again have apples and oranges (e.g. which of the two threads
libraries did you use for GNAT).

We often work with customers running benchmarks, and we often
find that the comparisons are meaningless for various reasons,
sometimes to the disadvantage of GNAT, sometimes to its bogus
advantage.

It is very hard to do meaningful comparison testing.

Robert Dewar
Ada Core Technologies


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