Okay, you have my attention... let's see that isomorphism in practice. I have seen my own measurements, and invariably they produce code that is 30% slower for CPS form than direct form. Perhaps the compilers producing the actual native code have been tuned to look for common human idioms and not CPS traits?

Dr. David McClain
Sr. VP, Embedded Systems
Asyrmatos Inc.
Boston & Tucson
phone:  520-529-2437
cell:  520-390-3995
web:  www.asyrmatos.com




On May 22, 2009, at 12:38, Taylor R Campbell wrote:

   Date: Fri, 22 May 2009 12:18:49 -0700
   From: "D.McClain" <dbm@asyrmatos.com>

   Very interesting... I would like to see your claims backed up by  
   actual measurements.

How about an isomorphism between the set of direct-style Scheme
programs and (a subset of) the set of CPS Scheme programs?  Then if
you give me a compiler C, I can construct a compiler C' that uses a
CPS intermediate representation and such that C(P) = C'(P) for any
program P.  No measurement is necessary to observe that the code
generated by C and C' is identical.

Put another way, turning a program into CPS doesn't add to or remove
from the information in a program.  So it doesn't make a compiler any
more or less able to make assumptions about a program that enable it
to generate better or worse code.  All it changes is how convenient it
is to write the compiler.  It's just a way to lay out some data
structures in the compiler.  If someone told you that a compiler
turned programs into an XML-based intermediate representation, would
you believe that person if he claimed that the use of XML caused the
compiler to generate bad code?  (It might be indicative of incompetent
software engineering on the part of the compiler's writers, but that's
a different issue.)