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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Papers saying Ada as an overly complex language and hard to
 implement
Date: 1998/02/17
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Date: 1998-02-17T00:00:00+00:00
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Joe said

<<As for the relative complexity of Ada83 as of ten years ago, the
comparison of the day was C, and there was no doubt then that Ada83
compilers were a great deal more complex than C compilers.  I became
curious on the issue, and compared the DEC Ada compiler with the DEC "C"
compiler on the VAXen here.  The DEC Ada compiler executable image was
about ten times larger than the DEC C compiler image.  While size is not a
direct measure of complexity, ten to one is still a significant
difference.
>>

The factor of ten, if real, means that the C compiler was very poor indeed.
Why do I say this? Because in a good C compiler, the code generator will
be by FAR the largest component of the compiler, and the same is true
of an Ada compiler. For example, in GNAT, the gcc backend is larger
than the gnat front end.

The complexity required for high levels of optimization is staggering,
and this is by far the hardest part of a compiler. One of the things
that made GNAT possible was that we did NOT have to reinvent this.

The differences between C and C++ compilers are basically in the front
end (C-front provides a good hint that this is indeed true).

In fact I suspect the factor of ten was, for whatever reasons, an apple
and oranges comparison (all sorts of things can distort such comparisons,
e.g. static vs dynamic linked libraries, debugging information, inclusion
of tools etc.

Actually I rather suspect the C compiler for the Vax was pretty simple
minded. The Vax was one of these machines where you can write a fairly
simple minded compiler and it is not too terrible :-)