Re: [eigen] about changeset 6eb14e380

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2010/8/20 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>

On Thu, Aug 19, 2010 at 6:51 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
> "The alignment requirement of SIMD memory operands is relaxed."
> ---> wowowowow, does anyone know what they mean here? Sounds important!

yes. Most of the instructions can deal with either two registers or
one memory operand and one register. With SSE the memory operand has
to be 16byte aligned. With AVX there is no particular alignment
requirement, but performance should be affected since there are still
two instructions to load data from memory: an unaligned and an aligned
version and the later require either 16 bytes or 32 bytes depending on
whether you load 16 or 32 bytes....

Oh OK, so it doesn't make a big difference for us.

Thanks
 Benoit

gael