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From: "Samuel T. Harris" <sam_harris@hso.link.com>
Subject: Re: Apex vs GNAT on solaris
Date: 1999/12/07
Message-ID: <384D4AB1.57D79E2A@hso.link.com>#1/1
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References: <82hiuj$74o$1@nnrp1.deja.com> <82hnll$ahu$1@nnrp1.deja.com>
 <384cfdb3.691883075@newsnew.draper.com>
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Organization: Raytheon Scientific & Technical Services
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Date: 1999-12-07T00:00:00+00:00
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Roger Racine wrote:
> 
> On Tue, 07 Dec 1999 01:25:13 GMT, Robert Dewar <dewar@gnat.com> wrote:
> 
> >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).
> >
> 
> Is it a mistake to use the default options for a compiler?  Many
> people will assume that the default options are the most reliable
> options.  Others will assume that the default options are the best
> options.  The default options generally turn out to be the most
> reliable because most people use them, and bugs will be discovered and
> corrected sooner than those to be found using the non-default options.

As a general rule, I try to avoid relying upon "default" values.
Given any tool you wish to discuss, by not explicitly configuring
the tool I am exposed to the maintenance question of "Am I relying
upon the defaults or did I just not know how to configure the tool."
So I try to configure whatever seems reasonable, even if my explicit
values are the default values.

As far as settings for compilers for benchmarks, I really am not
particularly interested in the faster speed possible. I am primarily
concerned with execution performance of the actual deliverable loads.
Therefore, when I run benchmarks I run them with the compiler
settings I'll be using for the final builds.

> 
> The same can be said for tasking.
> 
> I have been hit many times by optimizer bugs, and generally assume
> that the compiler vendors knows what they are doing when the defaults
> are created.  They are giving what they think should be the most
> common values for the options.
> 
> Roger Racine

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Scientific and Technical Systems
"If you can make it, We can fake it!"