WordX/IntX wrap Word#/Int#?

Simon Marlow marlowsd at gmail.com
Thu Jun 15 09:25:23 UTC 2017

On 11 June 2017 at 22:44, Joachim Breitner <mail at joachim-breitner.de> wrote:

> Hi,
> Am Sonntag, den 11.06.2017, 10:44 -0400 schrieb Ben Gamari:
> > This is certainly one consideration. Another is that you would also
> > need to teach the garbage collector to understand closures with sub-
> > word-size fields. Currently we can encode whether each field of a
> > closure is a pointer or not with a simple bitmap. If we naively
> > allowed smaller fields we would need to increase the granularity of
> > this representation to encode bytes.
> >
> > Of course, one way to work around this would be to impose an
> > invariant that guarantees that pointers are always word-aligned. Then
> > we would probably want to shuffle sub-word sized fields, allowing two
> > Word16s to inhabit a single word.
> that is not an issue; we already sort field into pointers first, and
> non-pointers later. So all pointers are at the beginning and nicely
> aligned, and all the non-pointer data can follow in whatever weird
> format. The GC only needs to know how many words in total are used by
> the non-pointer data.

But the compiler has no support for sub-word-sized fields yet.  I made a
partial patch to support it a while ago: https://phabricator.haskell.org/D38


> Joachim
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> Joachim “nomeata” Breitner
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