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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: GNAT & GCC performace (bad news)
Date: 1999/12/10
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Date: 1999-12-10T00:00:00+00:00
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In article <384FEBF9.5F4F6BD2@ftw.rsc.raytheon.com>,
  Wes Groleau <wwgrol@ftw.rsc.raytheon.com> wrote:
> But how much (if any) of this information is also lost by
> going from Ada to the common intermediate format used by the
> GCC suite?

The answer to this is, less and less as time goes on. We teach
the gcc backend more details about Ada, and also the backend
improves its capabilities. For example, when we move GNAT to
the new merged GCC, the backend has much more capabilties
for dealing with aliasing, and we will be able to pass aliasing
information along from the GNAT front end to take advantage
of the more precise aliasing information possible in a strongly
typed language.

With C, you are stuck with the definition of the language
permanently, you can't go teaching C more Ada, or adding
features to C to help the Ada-to-C translation process.

Still, I do want to emphasize that I think it is very valuable
to have this capability (Ada to C translation) because it allows
Ada 95 to be used on a wider variety of targets. Note that of
course the preferred implementation of the Intermetrics front
end is to wed it to an Ada specific code generator as is done in
the Aonix and Green Hills products, but it is certainly
attractive to have an alternative path on processors for which
no such specialized Ada code generator is available! Yes, there
are some losses from this approach, but the Intermetrics
implementation shows that these can be minimized in practice to
the point where the resulting compiler is quite practical for
production use.

Robert Dewar


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