Re: CPS thoughts

[Noah Lavine <noah.b.lavine@gmail.com>]

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An update: I just rebased wip-rtl-cps on top of wip-rtl-may-2013 and
pushed. The most interesting thing was how trivial it was: all I had to do
was make a one-line change in how I called `begin-program'.

Best,
Noah


On Wed, May 22, 2013 at 12:33 AM, Noah Lavine <noah.b.lavine@gmail.com>wrote:

> Hello,
>
> On Tue, May 21, 2013 at 3:46 PM, Andy Wingo <wingo@pobox.com> wrote:
>
>> You should have two names: the original ones and the gensyms that come
>> from tree-il.  Creating new gensyms should happen when copying or
>> fabricating new nodes, as peval does, but in most cases you don't need
>> to do it, and in any case it can be tricky.
>>
>> I would take tree-il as the guide here.
>>
>
> I'll look at it, thanks.
>
>
>> I haven't handled source information yet, but to the CPS->RTL compiler
>> it will look like emitting special instructions, like the tree-il->glil
>> compiler emits <glil-source> nodes.
>>
>
> That sounds fairly simple to implement.
>
>
>> This is lambda-properties.  You just pass them through, and add them to
>> the begin-program in the RTL.
>>
>
> Again, this seems relatively simple to do.
>
>
>> Note that wip-rtl-may-2013 and the RTL branches that are under review
>> for master are slightly different from the ones you have.  Their
>> begin-program has a second argument, the procedure properties, and the
>> first argument is a label and not a name.  They have begin-*-arity and
>> end-arity for marking arity information and performing arity prologues.
>> There are some slight changes to instructions but not much.  OTOH they
>> do have some better type checking and a disassembler that works, so many
>> things should be easier ;) Compare the rtl.test there and your rtl.test
>> for details.
>>
>> >       * Why is there no "let" that can bind functions?  You don't always
>> >     want
>> >        to set up a recursive binding environment.
>>
>
> I think right now the Tree-IL->CPS compiler will turn (let ((f (lambda
> ...))) ...) into something like this:
>
>  ((lambda (f-12345)
>   .... let body here ....)
>  (letrec ((f-func (lambda ... f's body here ...))) f-func))
>
> (I'm not showing the continuation's name because it would make it even
> more complicated than it already is.)
>
> I agree that this is a crazy way to do it. It should detect this case and
> skip the extra steps.
>
>
>> Understood.  However the question of language is fundamental for
>> enabling collaboration on this code.  I would be very happy to see a CPS
>> language definition that could express all of Tree-IL.  I don't think
>> this would take a lot of work -- it is perfectly acceptable to throw
>> "unimplemented" for those parts of the compiler that aren't there yet,
>> but the language itself should be adequately expressive.  IMHO anyway.
>>
>> Do you think you will have time to do that over the next few days or so?
>> Apologies for the pressure, just that I would like to do some things in
>> this area and am not sure how best to do them :)
>>
>
> This is interesting - I had been adding to the language as I needed
> features, and not really thinking of it as an interface. But you might be
> right. I just started rebasing tonight, and I hope to work more on it in
> the next two days. But I don't want to be a blocker for your work - what
> are you trying to do?
>
> Thanks a lot,
> Noah
>
>

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