[racket] translate from Racket to Common Lisp

From: Marc Feeley (feeley at iro.umontreal.ca)
Date: Tue Nov 6 07:29:13 EST 2012

Le 2012-11-06 à 3:50 AM, Hugh Aguilar <hughaguilar96 at yahoo.com> a écrit :

> I am very impressed that Racket is as fast as it is. I had expected the compilers such as Gambit to be much faster than the VM-JIT system. If Racket had a 64-bit x86 assembler available, I might even consider using it instead of Gambit.
> Message: 1
> Date: Mon, 5 Nov 2012 08:09:19 -0500
> From: Sam Tobin-Hochstadt <samth at ccs.neu.edu>
> To: Matthew Flatt <mflatt at cs.utah.edu>
> Cc: "users at racket-lang.org" <users at racket-lang.org>
> Subject: Re: [racket] translate from Racket to Common Lisp
> Message-ID:
>     <CAK=HD+Yyr1R4K6emrgSXqie2c_AmT1BzhLpP1X=1NDXRgzsjGg at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
> It's impressive to note the change in relative performance for Racket
> over past 3 years since you published the benchmarks on the blog --
> Racket has gone from slower than Gambit on the majority of benchmarks,
> sometimes by a significant margin, to faster on most of them, and
> never more than 2x slower (except ctak).

For your information, it seems that the change in relative performance has more to do with the change in C compiler over the past 3 years than anything else.  The benchmarks were run on Mac OS X with the C compiler available with Xcode.  Recently Apple dropped distributing the GNU gcc compiler with Xcode, and the "gcc" program that is installed is actually a version which uses the gcc compiler parser but LLVM as a back-end (i.e. llvm-gcc).  That C compiler has bugs which prevent using gcc's computed gotos which are critical for the best performance.  This is what Gambit's "configure" script has to say when using llvm-gcc:

***                                                                    ***
*** The LLVM GCC compiler that is being used may have a bug in the     ***
*** compilation of label values (i.e. &&label).  This bug was          ***
*** discovered when compiling Gambit with Xcode on Mac OS X (see bug   ***
*** ID# 9956714).  For this reason the use of computed gotos in the    ***
*** generated code has been disabled.  This greatly reduces the run    ***
*** time performance.  The system runs 5 times slower than when it is  ***
*** compiled with GNU GCC.  It is highly recommended that you use      ***
*** another C compiler if possible.                                    ***
***                                                                    ***

I have suggested to Matthew that he rerun the benchmarks on a linux machine where GNU gcc is the default C compiler.  It will be interesting to see how that affects performance.


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