[osg-users] Using SSE within OSG

James Killian James_Killian at hotmail.com
Tue Jul 29 08:37:31 PDT 2008


I interpreted Gordon's response as follows:
MS does a poor job (insert here with compiling SSE intrinsics), as a result
most of his SSE is asm'ed.
The asm'ed approach is where you don't trust the compiler to do the right
thing with intrinsics, where it has the flexibility of scheduling and
assigning registers etc.

I disagree with "MS does a poor job compiling intrinsic code", and that you
should not *ever need to resort to __asm anymore.
*this is not absolute, there was once a rare case where we found a strange
anomaly, but later solved by doing an un-intuitive c code change

>Do you find that MS compilers will produce SSE vectorised code _without_
use of intrinsics or raw __asm?
Ah this is a tricky question.  There is in fact an option in VS 8 and VS 9
project settings to generate SSE or SSE2 code.  What this does is that it
will evaluate c code and try to use SSE for it.  I was surprised to find
that this actually lowered the performance of c code, especially c code for
matrixf.  I'm so glad that the project settings for osg do not turn this on,
and I'd recommend not using that, but instead write intrisics ourselves for
places that need it.

I hope this clears things up.

----- Original Message ----- 
From: "David Spilling" <david.spilling at gmail.com>
To: "OpenSceneGraph Users" <osg-users at lists.openscenegraph.org>
Sent: Tuesday, July 29, 2008 10:17 AM
Subject: Re: [osg-users] Using SSE within OSG

> James,
> > I have to disagree, using VS 7 and up to VS 9.
> Just to clarify - what are you disagreeing with? Do you find that MS
> compilers will produce SSE vectorised code _without_ use of intrinsics or
> raw __asm?
> David


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