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Re: [patch] Move loop structures to gc memory

From: Ian Lance Taylor <iant at google dot com>
To: Mike Stump <mrs at apple dot com>
Cc: Paolo Bonzini <bonzini at gnu dot org>, Steven Bosscher <stevenb dot gcc at gmail dot com>, gcc-patches at gcc dot gnu dot org, Daniel Jacobowitz <drow at false dot org>, Zdenek Dvorak <rakdver at kam dot mff dot cuni dot cz>
Date: 15 May 2007 07:59:02 -0700
Subject: Re: [patch] Move loop structures to gc memory
References: <20070513180823.GA25352@kam.mff.cuni.cz> <m3ps53vxor.fsf@localhost.localdomain> <3D8EA365-0D65-4964-97F4-B5CFD700ACBC@apple.com> <200705150607.57354.steven.bosscher@gmail.com> <00FDBECC-A587-4B2B-8378-508940104772@apple.com> <46495AFE.8020502@gnu.org> <17F09B7E-CD2E-4970-9929-C1835B320EE0@apple.com>

Mike Stump <mrs@apple.com> writes:

> First, I don't really understand to what bug Ian refers to, so, I
> couldn't fix it, even if I wanted to.  Second, I'd predict at this
> point, that even if the bug were fixed, it would not be as fast as
> ggc_free.  If it isn't faster, I don't see what relevance it has to
> the two quoted above.  And lastly, I don't think this issue was
> contained in either of those two messages, just for the record.

The bug, if it is indeed a bug, is that the set of GC roots is static.
If you want to have a dynamically allocated pointer into GC memory,
you must put that pointer into GC memory itself.

Fixing that, and using it for the loop structures, would not be slower
than using ggc_free.  It would be a trade between recording the
dynamic root in some fashion on the one hand, and manipulating the
more complex data structures required by GC allocation on the other.

Ian

Follow-Ups:
- Re: [patch] Move loop structures to gc memory
  - From: Michael Matz
- Re: [patch] Move loop structures to gc memory
  - From: Mike Stump

References:
- [patch] Move loop structures to gc memory
  - From: Zdenek Dvorak
- Re: [patch] Move loop structures to gc memory
  - From: Ian Lance Taylor
- Re: [patch] Move loop structures to gc memory
  - From: Mike Stump
- Re: [patch] Move loop structures to gc memory
  - From: Steven Bosscher
- Re: [patch] Move loop structures to gc memory
  - From: Mike Stump
- Re: [patch] Move loop structures to gc memory
  - From: Paolo Bonzini
- Re: [patch] Move loop structures to gc memory
  - From: Mike Stump

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