Re: Fat references

Robert A Duff <bobduff@shell01.TheWorld.com>
Sat, 02 Jan 2010 15:39:48 -0500

          From comp.compilers

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[8 earlier articles]
Re: Fat references gah@ugcs.caltech.edu (glen herrmannsfeldt) (2009-12-31)
Re: Fat references jon@ffconsultancy.com (Jon Harrop) (2010-01-01)
Re: Fat references cr88192@hotmail.com (BGB / cr88192) (2010-01-01)
Re: Fat references cr88192@hotmail.com (BGB / cr88192) (2010-01-01)
Re: Fat references anton@mips.complang.tuwien.ac.at (2010-01-02)
Re: Fat references gah@ugcs.caltech.edu (glen herrmannsfeldt) (2010-01-02)
Re: Fat references bobduff@shell01.TheWorld.com (Robert A Duff) (2010-01-02)
Re: Fat references jon@ffconsultancy.com (Jon Harrop) (2010-01-03)
Re: Fat references DrDiettrich1@aol.com (Hans-Peter Diettrich) (2010-01-03)
Re: Fat references bear@sonic.net (Ray) (2010-01-03)
Re: Fat references anton@mips.complang.tuwien.ac.at (2010-01-03)
Re: Fat references gah@ugcs.caltech.edu (glen herrmannsfeldt) (2010-01-03)
Re: Fat references jon@ffconsultancy.com (Jon Harrop) (2010-01-04)
[14 later articles]
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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.compilers
Date: Sat, 02 Jan 2010 15:39:48 -0500
Organization: The World Public Access UNIX, Brookline, MA
References: 09-12-045 09-12-050 09-12-056
Keywords: storage, GC

Jon Harrop <jon@ffconsultancy.com> writes:


> Robert A Duff wrote:


>> Are you saying all pointers are fat (4
>> words per pointer!?)? Or just pointers to arrays?
>
> Yes, all pointers. Every single reference in the heap now occupies a
> quadword. I even blindly load and store entire quadwords when reading and
> writing references.


For pointer-heavy data structures, I'd be concerned about using
fat pointers all over -- damages cache behavior by making
everything bigger.


>> Under what circumstances are you worried about an extra copy?
>
> Extra copy of what?


In your original message, you said, "...because that would require C
arrays to be copied just to add this header." I was asking what
you mean. I guess you mean C code passes you an address,
and an array length, or something like that, and you want to avoid
putting your meta-data before the array data, because then you'd
have to copy that data.


>> By the way, if you're interested in GC, you should join the
>> GC list, which our esteemed moderator set up some years ago.
>
> I'd love to. Where is it?


I was hoping our esteemed moderator would point to it.
I don't have it handy, hmm.... let's see, google points
me here:


        http://www.iecc.com/gclist/


It's pretty low traffic these days.


> HLVM has another unusual characteristic in that it defines a high-level
> language (e.g. with tuples and tail call elimination) that is not only the
> target language but also the language the GC is written in.


Interesting.


- Bob



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