Messages in this thread | | | Subject | Re: [PATCH] lib/raid6: use vdupq_n_u8 to avoid endianness warnings | From | Robin Murphy <> | Date | Thu, 28 Feb 2019 18:00:15 +0000 |
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On 26/02/2019 20:44, Nick Desaulniers wrote: > On Mon, Feb 25, 2019 at 11:19 PM Ard Biesheuvel > <ard.biesheuvel@linaro.org> wrote: >> >> On Tue, 26 Feb 2019 at 05:03, <ndesaulniers@google.com> 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@gmail.com> >>> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> >> >> 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?).
FWIW the most recent 'proper' spec document I know of is this one:
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0073b/index.html
Apparently we have a more interactive playground on the new site, too:
https://developer.arm.com/technologies/neon/intrinsics
Robin.
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