[LAD] GCC Vector extensions

Dan Kegel dank at kegel.com
Wed Jul 20 15:03:48 UTC 2011


On Wed, Jul 20, 2011 at 1:27 AM, Maurizio De Cecco <jmax at dececco.name> wrote:
> On clang/MacOSX i get an impressive improvement in performance,
> around 4x on the operations, even just using the vector types for copying
> data; my impression is that the compiler use some kind of vector
> load/store instruction that properly use the available memory bandwidth, but
> unfortunately i do not know more about the x86 architecture.
>
> On gcc/Linux, (gcc 4.5.2) the same code produce a *slow down* of around
> 2.5x.

It's possible gcc generates code for lowest-common-denominator hardware
by default, and you might need to give some compiler option to get it to use
vector operations.  See
http://gcc.gnu.org/onlinedocs/gcc/i386-and-x86_002d64-Options.html



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