On Wed, Jun 5, 2013 at 9:00 AM, John Cowan <[email protected]> wrote:
> Alex Shinn scripsit:
>
> > As I see it, once a procedure escapes, the existence of any semantics
> > in the language which can discriminate the procedure location requires
> > it to be boxed. This is true whether the discriminator is eq? or eqv?.
>
> Well, it depends what you mean by "boxed".
>
> It means that the location tag no longer has to be identified with the
> unique address of the procedure. The procedure can be copied any number
> of times (each of which is distinguishable by `eq?`), but the location
> tag (which is what `eqv?` looks at) has to be copied with it; it can be
> any arbitrary value at least as wide as an address.
>
Sorry, I think I finally see what is being suggested.
Is the idea basically to transform:
(let ((f (lambda ...)))
(... f ...)
...
(... f ...))
into:
(let ((f (lambda ...))
(location (generate-unique-value)))
(... (box f location) ...)
...
(... (box f location) ...))
?
Thus the escaped f's would not be eq? but could the
location tag could be compared by eqv?.
Using addresses wouldn't work, generate-unique-value
would have to increment a global counter (which need
not be unique to this location). Though if the counter
ever overflows into a bignum all optimization is lost.
--
Alex
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