[r6rs-discuss] [Formal] bytevector aliasing severely impedes optimizations

From: Felix Klock <pfr6rs>
Date: Mon Mar 5 13:13:35 2007

On Mar 5, 2007, at 12:47 PM, Bradley Lucier wrote:

>
> On Mar 5, 2007, at 10:36 AM, William D Clinger wrote:
>
>> Brad Lucier wrote:
>>> I presume that many people might want to use bytevectors as
>>> described
>>> in this report to increase computational speed and decrease memory
>>> requirements by avoiding boxing/unboxing of objects that might
>>> otherwise be boxed when held in generic vectors.
>>
>> Me too. I have been assuming that someone would write
>> a SRFI for type-specific numeric vectors together with
>> a portable R6RS reference implementation using bytevectors
>> encapsulated within records.
>>
>> If you or I were to write that SRFI, it would solve the
>> aliasing problem without even having to mention it.
>
> Will it? The components of two records, one holding ints, one
> holding floats (or, here we go, one holding *both* floats and ints,
> which is what is really envisaged by this proposal) could not be
> the same bytevector?
>
> I haven't looked at the record proposal, so I don't know.

I interpreted the proposal as saying that this hypothetical SRFI
would be specified in a manner that *allows* an implementation to
choose a implementation-specific representation that enforces the
aliasing guarantees you desire. The hypothetical SRFI would also
provide a reference implementation that has observationally
equivalent behavior, but would probably not be able to be similarly
optimized by standard compilation technology.

(I am assuming that the record system proposed in R^{5.92}RS allows
for this sort of encapsulation, but I have not verified this.)

-Felix
Received on Mon Mar 05 2007 - 13:13:19 UTC