Re: [Caml-list] Ocamlopt code generator question

[Jean-Marc Eber <jeanmarc.eber@lexifi.com>]

Hi Dimitry,

LexiFi for instance _is_ clearly interested by a sse2 32bit code generator.

One should probably have the following in mind and/or ask the following questions:

- it is probably not a good idea to support both backends (sse2 and old stack fp 
i386 architecture). It will be necessary to make a choice (especially taking in 
account the limited INRIA resources and the burden of already supporting 
different windows ports).

- would INRIA be ok to switch to a sse2 code generator (based on Dimitry's patch 
- supposing that he is ok to donate it to INRIA - or Xavier's work or whatever)?

- I also guess that a sse2 code generator would be simpler than the current one 
(that has to support this horrible fp stack architecture) and would therefore be 
a better candidate for further enhancements.

- what is the opinion on this list, as a switch to a sse2 backend would exclude 
"old" processors from being OCaml compatible (I don't have a precise list at 
hand for now) ?

My opinion is that this support of legacy hardware is not important, but I guess 
others are arguing in opposite directions... :-)

But again, having better floating point performance (and predictable behaviour, 
compared to the bytecode version) would be a big plus for some applications.

Best regards,

Jean-Marc




Dmitry Bely a écrit :
> 
> I see. Why I asked this: trying to improve floating-point performance
> on 32-bit x86 platform I have merged floating-point SSE2 code
> generator from amd64 ocamlopt back end to i386 one, making ia32sse2
> architecture. It also inlines sqrt() via -ffast-math flag and slightly
> optimizes emit_float_test (usually eliminates an extra jump) -
> features that are missed in the original amd64 code generator. All
> this seems to work OK: beyond my own code all tests found in Ocaml CVS
> test directory are passed. Of course this is idea is not new - you had
> working IA32+SSE2 back end several years ago [1] but unfortunately
> never released it to the public.
> 
> Is this of any interest to anybody?
> 
> - Dmitry Bely
> 
> [1] http://caml.inria.fr/pub/ml-archives/caml-list/2003/03/e0db2f3f54ce19e4bad589ffbb082484.fr.html
> 
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