[racket] Calling TR modules from Racket modules is slow?

At Fri, 6 Jan 2012 13:15:54 -0800,
John Clements wrote:
> Welcome to DrRacket, version 5.2.0.7--2012-01-05(fd5e40f/g) [3m].
> Language: racket/load; memory limit: 256 MB.
> a million in-module typed adds
> cpu time: 404 real time: 425 gc time: 273
> a million untyped adds
> cpu time: 372 real time: 394 gc time: 212
> a million untyped->typed adds
> cpu time: 3763 real time: 3979 gc time: 2077
> 
> 
> ... so in fact, TR is about the same speed as plain-old racket in
> adding these (even though the plain-old-racket call is across
> modules);

Ignoring GC time, TR is faster, but these measurements are very small
(and GC-dominated) so I don't know how significant they are. That, and
the bulk of the work is happening in the looping code (which is the
same in both cases), not in the loop body.

> I conjecture that racket's optimizer is discovering the same
> optimizations as TR, here.

I don't see how it could. There's nothing about the `ut' module that
could help Racket specialize its addition to floats.

> However, making a cross-module call to a TR module is *much* slower.
> Is this because this module-crossing requires a contract check?

Yes. Both arguments to `float-add' need to be checked for float-ness
every time the function is called.

Vincent