RE: ocaml, simd, & fftwgel RE: [Caml-list] Caml productivity.

["Gurr, David (MED, self)" <David.Gurr@med.ge.com>]

Noel Welsh:

> There are a least two parallelising C compilers for
> the PC: Intel's and CodePlay's.  CodePlay say they do
> a better job than Intel.  I imagine Intel hold a
> differing opinion.

But do they do a better job than fftwgel or Spiral
or Atlas?

> I'm interested in knowing the deficiencies of these
> compilers.  I imagine they run into problems with
> dependency analysis on complicated array expressions. 
> Similarly, I'm interested in knowing in what areas HPF
> and SAC are performant.  It appears to me that a
> functional language (where dependency analysis is
> simple) with array shape inference should be capable
> of creating very array fast code is almost all
> situations (and the SAC benchmarks show them beating
> HPF).

Is SAC available for public inspection?

> 
> Cheers,
> Noel
 
I have not used either compiler.  From the FFTW, Atlas, etc experience
the only way to get consistently high performance from a C compiler is
to do most of the work for the compiler and carefully feed it code that
it correctly optimizes.  This is a compiler and application specific
trial and error process.  FFTW does the optimization and scheduling for
the C compiler.  Once you do this, it is much less clear what
the value added of the C compiler is.  In particular, the amount of 
refinement that would be needed to get ocamlopt to match C compilers
at this task might be relatively small.  I have not read to code to
fftwgel but if fftwgel could be married to ocamlopt, they might well
produce code superior to intel or codeplay since C is notoriously
difficult to optimize even without SIMD.

-D
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