Re: PCL/CLOS performance

[Gregor.pa@Xerox.COM]

    Date: Fri, 14 Oct 88 15:27:30 BST
    From: Jeff Dalton <jeff%aiai.edinburgh.ac.uk@NSS.Cs.Ucl.AC.UK>

    Well, (1) is it not the case that TICLOS is not PCL?  If so, it may
    not say all that much about PCL performance.  (2) If a Common Lisp
    is reasonably fast otherwise but slow for PCL, it is at least
    reasonable to suspect PCL rather than the Common Lisp's code
    generation.

I assume that since you have sent your message (6 days) enough other
messages have gone by to clarify this.  But this is important enough
that it is worth addressing directly.

    Well, (1) is it not the case that TICLOS is not PCL?  If so, it may
    not say all that much about PCL performance.  

Yes, TICLOS is not PCL.  But it has an architecture quite similar to the
one PCL has.  There are some differences which stem from having the kind
of hardware tag checking they have, and some other differences which are
a matter of differing philosophy.  

It is also important to note that the TICLOS implementation could be
converted to run on stock hardware.  Some changes would have to be made
to account for the absence of tags, but much of the code could be
retained.

                                               (2) If a Common Lisp
    is reasonably fast otherwise but slow for PCL, it is at least
    reasonable to suspect PCL rather than the Common Lisp's code
    generation.

No No No.  If an unoptimized port of PCL is slow in a Common Lisp which
otherwise has good performance it says absolutely nothing about real PCL
performance.  PCL is fundamentally designed to require implementation
specific tuning.  There are certain critical code sequences which must
be "hand coded" because no sane Common Lisp compiler will emit the
proper code sequence.

The feature of PCL is that these code sequences are quite isolated,
quite small, and it should be possible to write them for any Common
Lisp (any one I have seen anyways).

    Besides, not everyone can afford a super-CL.  The object system should
    be such that it is not too hard to get performance from it comparable
    to that of the rest of CL.

I think the fact that PCL can be gotten to competitive performance in
any Common Lisp satisifies this concern.
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