Re: [boost] [gsoc] boost.simd news from the front.

Subject: Re: [boost] [gsoc] boost.simd news from the front.
From: Joel falcou (joel.falcou_at_[hidden])
Date: 2011-06-10 19:34:40

On 10/06/11 18:05, David A. Greene wrote:
> For writing new code, I contend that a good compiler, with a few
> directives here and there, can accomplish the same result as this
> library and with less programmer effort.

I dont really think so, especially if you take your "portable" stuff in 
the equation.

> A simple example:
>
> void foo(float *a, float *b, int n)
> {
>     for (int i = 0; i<  n; ++i)
>        a[i] = b[i];
> }
>
> This is not obviously parallel but with some simple help the user can
> get the compiler to vectorize it.

Seriously, are you kidding me ? This is a friggin for_all ...
You can not get more embarrasingly parallel.

> Another less simple case:

And this accumulate, they are like the most basic EP example you can get.

> This is much less obviously parallel, but good compilers can make it so
> if the user allows slightly different answers, which they often do.

Yeah and any brain dead developper can write the proper

boost::accumulate( simd::range(v), 0. )

to get it right.

So, who's the compiler's daddy here ?

> Can you explain why not?  Assembly code in and of itself is not bad but
> it raises some maintainability questions.  How many different
> implementations of a particular ISA will the library support?

Because it is C functions maybe :E

Currently we support all SSEx familly, all AMD specific stuff and 
Altivec for PPC and Cell adn we have a protocol to extend that.

> 4 floats are available.  That does not mean one always wants to use all
> of them.  Heck, it's often the case one wants to use none of them.

Not usign all element in a SIMD vector is Doing It Wrong.

> I'm demonstrating what I mean by "performance portable."  Substitute
> "GPU" with any CPU sufficiently different from the baseline.

I wish you read about what a "library scope" and "rationale" mean.
Are you complaining that Boost.MPI dont cover GPU too ?

> Intel and PGI.

Ok, what guys on non intel nor PGI supproted machine does ?
Cry blood ?

Someone is trolling someone hard here I suppose ...