Re: [PATCH] lib/raid6: use vdupq_n_u8 to avoid endianness warnings

[Nick Desaulniers]

On Mon, Feb 25, 2019 at 11:19 PM Ard Biesheuvel
<ard.biesheuvel@xxxxxxxxxx> wrote:
>
> On Tue, 26 Feb 2019 at 05:03, <ndesaulniers@xxxxxxxxxx> wrote:
> >
> > Clang warns: vector initializers are not compatible with NEON intrinsics
> > in big endian mode [-Wnonportable-vector-initialization]
> >
> > While this is usually the case, it's not an issue for this case since
> > we're initializing the uint8x16_t (16x uint8_t's) with the same value.
> >
> > Instead, use vdupq_n_u8 which both compilers lower into a single movi
> > instruction: https://godbolt.org/z/vBrgzt
> >
> > This avoids the static storage for a constant value.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/214
> > Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
>
> Much better, thanks,
>
> Did you double check that the intrinsic exists on 32-bit ARM as well?
> I assume it does, but please make sure if you haven't yet.

Thanks for the review!
Looking through Clang's generated arm_neon.h, vdupq_n_u8 seems to have
2 definitions predicated on __LITTLE_ENDIAN__ (not __arch64__ or
__ARM_ARCH >= 8 like some of the other types and functions).

So NEON got some additions in v8?  Is there a doc that lists them?
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0491g/BABDBBJB.html
is where I found vdupq_n_u8, but it doesn't seem to mention
compatibility (so I assume it's been around since the introduction of
NEON?).
-- 
Thanks,
~Nick Desaulniers