I'll make closer benchmarking of auto forcing later, but, it incurs a quite steep overhead. Meanwhile, I have a question:

With --enable-auto-forcing, at procedure calls, that is (procedure 'arg1 'arg2 'etc.), |procedure| is forced, as we can see by the example that in both interpreted and compiled mode, ((delay (begin (println "Forced.") (lambda (v) v))) #t) evaluates (and it prints out "Forced.").

I'd wildly guess that quite a lot of the overhead in auto-forcing is here. If you're sure the operator will never be a promise in any procedure call, then this particular aspect of auto forcing could be disabled.

(Without checking, I would guess that while Gambit may optimize so that local procedure calls may avoid being brought through the |force| logics, then, this optimization would do so that calls to procedures defined in *other* modules such as the runtime, would *not* be taken through |force| also. That should be positive for speed.)

Would it be possible for me to disable this particular aspect of the auto-forcing, to get higher performance?

2017-06-16 13:52 GMT+08:00 Marc Feeley <feeley@iro.umontreal.ca>:

Here is the definition of + from lib/_num.scm:

(define-prim-nary (+ x y)
0
(if (##number? x) x '(1))
(##+ x y)
macro-force-vars
macro-no-check
(##pair? ##fail-check-number))

The define-prim-nary macro will expand this to an n-ary procedure definition where the 0 argument case returns 0, the 1 argument case returns the argument if it is a number otherwise it raises a type error (by calling ##fail-check-number), and the general >= 2 argument case calls ##+ to fold the argument list. All arguments are passed to macro-force-vars to force the argument if it is a promise (and --enable-auto-forcing is used).

Using set! to “short-circuit” promises is not a good idea because it introduces a cell for the variable (if local and not previously assigned) and this slows things down. In early versions of Gambit (on Motorola 68K), the garbage collector did this short-circuiting (i.e. a reference to a promise was replaced with the value of the promise if it was previously forced). This isn’t done currently but probably easy to add.

Marc

> On Jun 15, 2017, at 11:04 PM, Adam <adam.mlmb@gmail.com> wrote:
>
> 2017-06-13 5:30 GMT+07:00 Bradley Lucier <lucier@math.purdue.edu>:
>
> > On Jun 11, 2017, at 5:08 AM, Adam <adam.mlmb@gmail.com> wrote:
> >
> > Possibly the "macro-force-vars", which is used all over the runtime and compiler, would have something to do with this, but I don't find its definition anywhere.
> >
>
> In _gambit#.scm:
>
> (macro-define-syntax macro-force-vars
> (lambda (stx)
> (syntax-case stx ()
> ((_ vars expr)
> (if (let* ((co
> (##global-var-ref
> (##make-global-var '##compilation-options)))
> (comp-opts
> (if (##unbound? co) '() co)))
> (assq 'force comp-opts))
>
> (syntax-case (datum->syntax
> #'vars
> (map (lambda (x) `(,x (##force ,x)))
> (syntax->list #'vars)))
> ()
> (bindings #'(let bindings expr)))
>
> #'expr)))))
>
>
> Ah right, https://github.com/gambit/gambit/blob/9c3dcbdc322a10673370c0880696ba131144251d/lib/_gambit%23.scm#L316 , and used to be a define-macro, https://github.com/gambit/gambit/blob/29103e6a29b8fbbf7d6fc772a344b814be3f1c1a/lib/_gambit%23.scm#L492 , and all the rest of the code is meticulously padded with its use.
>
>
> This also sheds a bit of light on why the slot containing the promise is not replaced with the forced value. Maybe that would be possible in some situations though.. When |x| is a symbol, it could be |set!| with the forced value?
>
> That would cover standard variable slots and not typedef, vector, pair etc. slots though, I guess I'd need to dig in a bit more to understand how this one actually works out. If you have any spontaneous ideas, feel free to share.
>
>
> Any idea where in the sources fundamental primitives like |+| , |if| , |or| autoforce?