Re: using vector extension in gcc slows down my code

[Da Zheng <zhengda1936 at gmail dot com>]

Hi,

On 10-2-10 äå10:57, Brian Budge wrote:
> Hi -
> 
> To me it is not at all surprising.  These hairy strides and mods
> certainly aren't going to help.  You're doing very little math vs
> load/store which means that you're not going to get much out of the
This is what my code needs to do. I cannot change it. I see GCC can
auto-vectorize the code like:
  for (i=0; i<256; i++){
    a[i] = b[i] + c[i];
  }
It has even less math, but vectorization should achieve better performance in
the code since GCC does it.
> vector units.  Really you need more of a struct-of-arrays type layout
> (pack your doubles together so you can load them in a less strided
> fashion, and pack your ints together.  This may have the extra benefit
> of unobfuscating the code :)
I don't understand. What do you mean by less strided fashion? Do you mean all
elements in the array should be of the v2df type and then I access each element
in the loop by i++? Why will this make difference?

Best regards,
Zheng Da