Re: Implementing an Ada compiler and libraries.

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message
news:wccfy65n2pq.fsf@shell01.TheWorld.com...
...
> If you do this, you need to design a permanent (on disk) representation
> that is small.  I think it's possible, but it's not easy -- the
> "obvious" representation of symbol tables will be 10 times larger than
> the source code.  If it's 10 times larger, then it defeats the purpose
> -- reading it in from disk will be slower than re-analyzing the original
> source code.

I don't quite buy this. "10 times larger" seems to be a gross overestimate
(for Janus/Ada, it tends to be more like 2-3 times, and we did little to
make the disk files smaller -- they're not the limited factor for
compilation speed). It's necessary to keep the symbol table memory use
reasonable (else paging costs will eat you up), and directly translating
that to disk files is straightforward.

Also, the cost of reading files vs. reparsing depends very much on how much
effort is encoded in the files. Reading text is slower than known size
binary files to begin with (although on modern machines, the difference
isn't that significant), and there is a lot of other work that needs to go
on to analyze a source file. My experience is that Janus/Ada is faster than
Gnat on most compilations (although the difference isn't really significant,
except on very large files where Gnat is faster because the Janus/Ada
optimizer is worse than quadratic in program size).

                     Randy.