Re: Short Vectors Versus Long Vectors

On Tue, 23 Apr 2024 06:22:38 GMT, Anton Ertl wrote:

So what's the benefit of using vector/SIMD instructions at all rather
than doing it with scalar code?

On the original Cray machines, I read somewhere the benefit of using the
vector versions over the scalar ones was a net positive for a vector
length as low as 2.

If your OoO capabilities are limited (and I think
they are on the Cray machines), you cannot start the second iteration of
the doall loop before the processing step of the first iteration has
finished with the register.

How would out-of-order execution help, anyway, given all the operations on
the vector elements are supposed to be identical? Unless it’s just greater
parallelism.