[squeak-dev] FullBlockClosures and ignoreOuterContext?

Eliot Miranda eliot.miranda at gmail.com
Tue Dec 15 02:06:12 UTC 2020

Hi Fabio,

On Mon, Dec 14, 2020 at 1:33 PM Fabio Niephaus <lists at fniephaus.com> wrote:

> Hi all,
> While digging through the implementation of FullBlockClosure with
> Hernan, we were wondering about full closures that ignore their
> outerContext. We noticed that the following method has two senders:
> EncoderForSistaV1>>#genPushFullClosure:numCopied:receiverOnStack:ignoreOuterContext:
> One of them seems to be the only one in use, and it's passing in false
> as defaults for both receiverOnstack and ignoreOuterContext. The other
> sender
> (BytecodeEncoder>>#sizePushFullClosure:numCopied:receiverOnStack:ignoreOuterContext:),
> in turn, doesn't seem to have any further senders.
> Unless we missed something, it looks like the outerContext will never
> be ignored at the moment. Similarly, the receiver is never on the
> stack. Is this something only Scorch can do or is this just "not yet
> implemented"?
> When can the outerContext be ignored?

When the Sista optimizer determines that it isn't needed. i.e. this option
is nover used in vanilla code but exists for an optimizing compiler to
avoid the overhead in cases where it wants to avoid inlining but knows
there is no real suspension point during some evaluation.  Now, whether
we'll ever use this facility I can't say, but it was certainly in Clément's
mind to do so at some point.

> When does it make sense to pop the receiver from the stack?

The point isn't really to pop the receiver from the stack.  The point is to
be able to take the closures receiver form the stack rather than it being
implicitly the receiver of the current method.  If closure creation gets
inlined by the optimizer then there will be potentially a mismatch between
the current method's receiver and an inlined closure's receiver, which
necessitates having the facility to specify a distinct receiver.

> And where can we find the latest version
> of Scorch. Is it still the one at [1]?


If you're interested in looking at Scorch I'm very interested in
collaborating.  And there ius one significant modification to perform first
which will make development much easier, and that is to restructure the
interface between the optimizer and the image via mirrors, allowing the
optimizer to be mated with an image being simulated, rather than having to
be a full peer of the image it is optimizing.

> Cheers,
> Fabio
> [1] https://github.com/clementbera/Scorch

best, Eliot
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