[gclist] Precise GC's performance

[Darius Blasband]

Anthony Hoskins writes:

> 
> Following up on this topic of accurate versus conservative collection, I'll
> put in a blatant plug for some work a student of mine and I are currently
> doing.  We have resurrected (and extended) the original work of Diwan et al
> [PLDI'92] on accurate GC for the now-defunct UMass GNU Modula-3 effort.  We've
> taken that original design and much of the gcc-backend code, modified the SRC
> M3 front-end to emit the necessary type information, and extended the gcc
> backend to handle certain complications of modern RISC architectures, so that
> we can now accurately collect several significant Modula-3 programs (e.g.,
> m3browser).  We're still in debugging mode so I won't say we handle all the
> programs we've tried (moreover, unsafe programs can break the accurate
> collector by hiding pointers, etc., though I'm sure they could be rewritten to
> cooperate without too much trouble).  In any case, we should very shortly be
> in a position where we can run direct comparison of accurate copying versus
> Bartlett-style mostly-copying conservative roots collection, for gcc-optimized
> Modula-3 programs, with hard results expected in late spring.
> 
> On a side note, the recent bugs we've been encountering, mostly arising as a
> result of the generation of derived pointers through VAR parameters and
> compiler temporaries, may be of interest to others...  We should probably sit
> down and write up descriptions of them, sometime...  For now, we are still
> very much up to our necks in the code...
> 

I would be very interested in knowing more about this experiment, since 
we have similar plans with YAFL; which I think would be at least slighly
easier than M3 (No pointers arithmetics, no inside pointers).

The big issue for us is how manageable is the GNU intermediate format
interface. I would be very interested in any information you can provide.

Impatient regards,


Darius