[Numpy-discussion] NEP 38 - Universal SIMD intrinsics

[Charles R Harris]

On Wed, Feb 12, 2020 at 12:19 AM Matti Picus <matti.picus at gmail.com> wrote:

> On 11/2/20 8:02 pm, Devulapalli, Raghuveer wrote:
> >
> > On top of that the performance implications aren’t clear. Software
> > implementations of hardware instructions might perform worse and might
> > not even produce the same result.
> >
>
> The proposal for universal intrinsics does not enable replacing an
> intrinsic on one platform with a software emulation on another: the
> intrinsics are meant to be compile-time defines that overlay the
> universal intrinsic with a platform specific one. In order to use a new
> intrinsic, it must have parallel intrinsics on the other platforms, or
> cannot be used there: "NPY_CPU_HAVE(FEATURE_NAME)" will always return
> false so the compiler will not even build a loop for that platform. I
> will try to clarify that intention in the NEP.
>
>
> I hope there will not be a demand to use many non-universal intrinsics
> in ufuncs, we will need to work this out on a case-by-case basis in each
> ufunc. Does that sound reasonable? Are there intrinsics you have already
> used that have no parallel on other platforms?
>
>
Intrinsics are not an irreversible change, they are, after all, private.
The question is whether they are sufficiently useful to justify the time
spent on them. I don't think we will know that until we attempt actual
implementations. There will probably be some changes as a result of
experience, but that is normal.

Chuck
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