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Re: Faster compilation speed


Mike Stump wrote:-

> I'd like to introduce lots of various changes to improve compiler 
> speed.

Just my opinion, Mike, but I think a lot of current slowness is due to
redo-ing too many things, and not taking advantage of ordering or whatever
technique so that conclusions deduced from internal representations are
made in a logical, efficent way.  (e.g. I think we try to constant fold
things that we've already tried to constant fold and failed, repeatedly,
and we don't do the constant folding we do do in an optimal way.  I could
be wrong, though; I've not looked in detail).  I cannot explain this
clearly, or with any specific example, but IMO we work far too hard to
do what we do.  I'd like to see this cleaned up instead.

For example, see some of Mark's recent patches.  I think we could continue
doing that for ages.  I also believe that using Bison (and our
ill-considered extensions like attributes pretty much anywhere) don't
help efficiency.  We could probably do better in the C front end with
a tree representation that is closer to C than the current
multi-language form of trees.

What worries me about PCH and similar schemes is it's too easy to fix
the symptoms, rather than the real reasons for the slowness.  As a
result, such things might never be fixed.

Neil.


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