[Development] Using SSE/NEON in Qt 6

[Bogdan Vatra]

Hi,

For *Android*:
 - NEON is turned on by default for armv7a starting with NDKr21[0] (for armv8 
NEON is mandatory).
 - for x86 all up to SSE3 [1]
 - for x86_64 all up to SSE4.2 [1]

Cheers,
BogDan.
[0] https://github.com/android/ndk/wiki/Changelog-r21#changes
[1] https://developer.android.com/ndk/guides/abis#sa

În ziua de joi, 6 februarie 2020, la 13:45:51 EET, Lars Knoll a scris:
> Hi,
> 
> We’ve seen that in a couple of places things like matrix operations are a
> CPU bottleneck. Being able to provide SSE/NEON optimised versions of some
> of those operations could help significantly. 
 
> On x86/x64, we require SSE2 already anyway, so we should be able to use
> those unconditionally. On ARM, we can make this a compile time option with
> a C implementation as the fallback.
 
> One problem is, that we can only get full benefit out of those if we can
> offer them inline. That would basically imply making our qsimd_p.h header
> public and including that one from qvectornd.h and qmatrixnxn.h (so that we
> can implement the operations using the SSE/NEON intrinsics). If we do that,
> we could e.g. implement QVector4D holding a __m128 value (and the neon
> equivalent on ARM).
 
> I personally don’t think including qsimd.h (and implicitly immintrin.h) from
> our public headers would be a problem, but I’d be happy to hear arguments
> for/against it.
 
> As a side note: SSE 4.1 offers some nice additional instructions that would
> simplify some of the operations. Should we keep the minimum requirement for
> SSE at version 2, or can we raise it to 4.1?
 
> Cheers,
> Lars
> 
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