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Re: Advice about using SIMD extensions
In the example above, it's not only register allocation, but also
scheduling. The data needs to be loaded from memory, and how that
happens can affect performance quite a bit.
And yeah, I can't understand how 8.1 could get decent performance
without instruction scheduling... but maybe I'm stuck in my own little
RISC processing world (the (toy) compilers I have written have been
for SPARC and MIPS), and I just don't understand enough about how the
pentium works.
Brian
On Fri, 25 Feb 2005 14:24:27 -0500, Daniel Berlin <dberlin@dberlin.org> wrote:
> On Fri, 2005-02-25 at 12:18 +0100, Brian Budge wrote:
> > Hmmm, I doubt that. It seems very important that your data be in
> > registers when you want to do arithmetic on it.
>
> That's register allocation, not scheduling :)
>
> >
> > I can see that if your data was already in registers, maybe a
> > "randomized" instruction ordering would perform okay, but loading the
> > data properly is time consuming. At least these are the things I've
> > observed.
> >
>
> stevenb was the source of this information for me, so maybe he can
> confirm it (Steven, i mentioned to brian that icc 8.1 doesn't do
> scheduling for the pentium4 anymore, and he doubts it :P)
>
>