Advice about using SIMD extensions

Brian Budge
Mon Feb 28 19:03:00 GMT 2005

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.


On Fri, 25 Feb 2005 14:24:27 -0500, Daniel Berlin <> 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)

More information about the Gcc-help mailing list