On Date: Mon, 20 Nov 2023 16:05:43PM +0700, John Naylor wrote:
>On Wed, Nov 8, 2023 at 2:44=E2=80=AFPM Xiang Gao <Xiang.Gao@arm.com> wrote:
>> * function. We could instead adopt the behavior of Arm's vmaxvq_u32(), i=
>.e.
>> * check each 32-bit element, but that would require an additional mask
>> * operation on x86.
>> */
>
>> But I still don't understand why the vmaxvq_u32 intrinsic is not used on=
the arm platform.
>The current use case expects all 1's or all 0's in a 32-bit lane. If
>anyone tried using it for arbitrary values, vmaxvq_u32 could give a
>different answer than on x86 using _mm_movemask_epi8, so I think
>that's the origin of that comment. But it's still a maintenance hazard
>as is, since x86 wouldn't work for arbitrary values. It seems the path
>forward is to rename this function to vector32_is_any_lane_set(), as
>in the attached (untested on Arm). That would allow each
>implementation to use the most efficient path, whether it's by 8- or
>32-bit lanes. If we someday needed to look at only the high bits, we
>would need a new function that performed the necessary masking on x86.
>
>It's possible this method could shave cycles on Arm in some 8-bit lane
>cases where we don't actually care about the high bit specifically,
>since the movemask equivalent is slow on that platform, but I haven't
>looked yet.
Thank you for your detailed explanation.
Can I do some testing and submit this patch?
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you
arenot the intended recipient, please notify the sender immediately and do not disclose the contents to any other
person,use it for any purpose, or store or copy the information in any medium. Thank you.