On 12.01.2012 23:10, Peter Alexander wrote:

On 12/01/12 8:13 PM, Norbert Nemec wrote:

Considering these hardware details of the SSE architecture alone, I fear
that portable low-level support for SIMD is very hard to achieve. If you
want to offer access to the raw power of each architecture, it might be
simpler to have machine-specific language extensions for SIMD and leave
the portability for a wrapper library with a common front-end and
various back-ends for the different architectures.

You are right, but don't forget that the same is true for instructions
already in the language. For example, (1 << x) is a very slow operation
on PPUs (it's micro-coded).

It's simply not possible to be portable and achieve maximum performance
for any language features, not just vectors. Algorithms must be tuned
for specific architectures in version statements. However, you can get a
decent baseline by providing the lowest common denominator in
functionality. This v128 type (or whatever it will be called) does that.

Actually, my essential message is: The single v128 is too simplistic for the SSE architecture. You actually need different types because the compiler needs to know what type is stored in any given register to be able to move it around.