Re: use ARM intrinsics in pg_lfind32() where available

On Sat, Aug 20, 2022 at 5:28 AM Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> On Fri, Aug 19, 2022 at 02:26:02PM -0700, Andres Freund wrote:
> > Are you sure there's not an appropriate define for us to use here instead of a
> > configure test? E.g.
> >
> > echo|cc -dM -P -E -|grep -iE 'arm|aarch'
> > ...
> > #define __AARCH64_SIMD__ 1
> > ...
> > #define __ARM_NEON 1
> > #define __ARM_NEON_FP 0xE
> > #define __ARM_NEON__ 1
> > ..
> >
> > I strikes me as non-scalable to explicitly test all the simd instructions we'd
> > use.
>
> Thanks for the pointer.  GCC, Clang, and the Arm compiler all seem to
> define __ARM_NEON, so here is a patch that uses that instead.

Is this also ever defined on 32-bit? If so, is it safe, meaning the
compiler will not emit these instructions without additional flags?
I'm wondering if  __aarch64__ would be clearer on that, and if we get
windows-on-arm support as has been proposed, could also add _M_ARM64.

I also see #if defined(__aarch64__) || defined(__aarch64) in our
codebase already, but I'm not sure what recognizes the latter.

-- 
John Naylor
EDB: http://www.enterprisedb.com