[Mesa-dev] [PATCH V5] mesa: add SSE optimisation for glDrawElements

Steven Newbury steve at snewbury.org.uk
Fri Nov 7 03:44:41 PST 2014

On Thu, 2014-11-06 at 21:00 -0800, Matt Turner wrote:
> On Thu, Nov 6, 2014 at 8:56 PM, Siavash Eliasi <
> siavashserver at gmail.com> wrote:
> > Then I do recommend removing the "if (cpu_has_sse4_1)" from this 
> > patch and similar places, because there is no runtime CPU 
> > dispatching happening for SSE optimized code paths in action and 
> > just adds extra overhead (unnecessary branches) to the generated 
> > code.
> No. Sorry, I realize I misread your previous question:
> > > I guess checking for "cpu_has_sse4_1" is unnecessary if it isn't 
> > > controllable by user at runtime; because "USE_SSE41" is a 
> > > compile time check and requires the target machine to be SSE 4.1 
> > > capable already.
> USE_SSE41 is set if the *compiler* supports SSE 4.1. This allows you 
> to build the code and then use it only on systems that actually 
> support it.
> All of this could have been pretty easily answered by a few greps 
> though...

I wonder what difference it would make to have an option to compile 
out the run-time check code to avoid the additional overhead in cases 
where the builder *knows* at compile time what the run-time system is? 
(ie Gentoo)
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