[Vm-dev] [SqueakJS] Faster JIT ideas

[Florin Mateoc]

Hi Vanessa,

Sorry for the delay in responding - as somebody who has been inspired by
your SqueakJS project, I think I should mention that I am working on a
related project, for now tentatively called JsSqueak.
In addition to the inspiration provided by SqueakJS, it also scratches my
longstanding itch about compiling (transpiling) Squeak.

I hesitated to talk about it, as it is still a work in progress - after
small bits and pieces that I worked on over a long period, I had the
opportunity to spend a significant and uninterrupted chunk of time on it
last summer, when I was unemployed for 3 months, and I was able to make
good progress. I was optimistically thinking of releasing a first version
before the end of last year, but after I started working on my new job,
progress on JsSqueak has slowed down significantly. I must confess that I
(and especially my wife) hesitate in recreating that productive unemployed
situation :)

I started with Squeak 4.5 - I already had code transforming Smalltalk code
to a form more suitable for translation - and I also started with
VMMakerJS-dtl.18 for the plugin generation part. Of course, I had to
heavily modify it, since I have to get rid of the stack usage for
arguments/receiver and returns.
Both of these big parts are working. I also implemented most numbered
primitives by hand - they are inlined at generation time in the methods
calling them.
I am also taking advantage of the latest and greatest additions to
JavaScript. I am, of course, using classes, and the parallel class-side
hierarchy is implemented using statics. To implement green threads/process
switching, all translated methods are implemented as generator functions,
and all calls are through yield* expressions. The preemption/interrupt
check points are inlined. With this, a process switch is achieved by simply
yield-ing (in the process/semaphore primitives).
With this, the Integer>>#benchFib method is translated (as a method in
Number.prototype, there is one more, simpler, implementation in BigInt) as:

*_benchFib() {
   if (Number.isSafeInteger(this.valueOf())) { // Effective (inherited
or local) source for #benchFib in SmallInteger
      /*Handy send-heavy benchmark*/
   /*(result // seconds to run) = approx calls per second*/
   /* | r t |
     t := Time millisecondsToRun: [r := 26 benchFib].
     (r // 1000) // t*/
   /*138000 on a Mac 8100//100*/
   if (GlobalActivationCounter-- < 0) yield* GlobalCheckForInterrupts();

   return (yield* this._lt( 2)).booleanValueOf("questionMark:colon:")
? (1) : (yield* (yield* (yield* (yield* this._sub(
1))._benchFib())._add( yield* (yield* this._sub(
2))._benchFib()))._add( 1));
} else // No implementation for #benchFib in Float hierarchy, trigger a DNU
      return yield* super._benchFib()
}

The top-level check for smallIntegers is because both SmallInteger and
Float are mapped to Number.

The booleanValueOf call is for implementing the mustBeBoolean
machinery (it actually translates directly to DNU, like it is done
nowadays in Squeak).

Of course, in Boolean, booleanValueOf is just an alias for valueOf

As you can see, though, this is not terribly efficient, but there is
room for improvement/optimizations. With more work, in this case, the
_lt call could be replaced by the < operator, and even the _sub and
_add calls could be optimized,
although not completely, since their result can morph into
LargeInteger (mapped to BigInt).

As hinted above, SmallInteger is mapped to Number (in the safeInteger
range), Float is mapped to Number as well, and LargeInteger is mapped
to BigInt.

BlockClosure is mapped to Function, Boolean is mapped to Boolean,
Character is mapped to String, weak references are implemented via
WeakRef.
I have briefly considered also doing slightly higher-level mappings,
for IdentitySet to Set and IdentityDictionary to Map, but this is not
a priority.

The image is serialized sort of like a JavaScript storeString. No
processes or contexts though, or rather they are not brought back in
on the JavaScript side. Blocks are both stored and loaded.

Non-local returns, unwind blocks, resumable and restartable exceptions
are implemented via JavaScript exception handling plus explicit
handler block chains associated with the processes.

The "image" starts with the global state loaded, but all processes are
started from scratch instead of resumed. A non-UI image is thus
trivially started.

One major todo left is hooking up the UI/browser. I did take
vm.display.browser.js from SqueakJS and adapted the code in order to
implement its numbered primitives, but I still have to work through
squeak.js from the same to initialize
and hook up the display.

Florin




On Sun, Mar 7, 2021 at 11:17 PM Vanessa Freudenberg <vanessa at codefrau.net>
wrote:

>
> Hi all,
>
> ideas for a faster SqueakJS JIT have been swirling around in my head for
> many years. This weekend I took the time to write some of them down:
>
> https://squeak.js.org/docs/jit.md.html
>
> Feedback welcome!
>
> Vanessa
>
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