[opus] [RFC PATCHv1] cover: celt_pitch_xcorr: Introduce ARM neon intrinsics

[Viswanath Puttagunta]

On 25 November 2014 at 10:18, Jonathan Lennox <jonathan at vidyo.com> wrote:
>
> On Nov 25, 2014, at 11:13 AM, Viswanath Puttagunta
> <viswanath.puttagunta at linaro.org> wrote:
>
> On 25 November 2014 at 10:11, Viswanath Puttagunta
> <viswanath.puttagunta at linaro.org> wrote:
>
>
> On 25 November 2014 at 09:39, Jonathan Lennox <jonathan at vidyo.com> wrote:
>
>
> On Nov 25, 2014, at 10:07 AM, Viswanath Puttagunta
> <viswanath.puttagunta at linaro.org> wrote:
>
>
> Also is there plans to make the NEON optimisations on ARMv7 run time
> detectable like they have in cairo/pixman? For generic distributions
> it would nice to be able to be able to enable them as they offer
> decent performance improvements but have the code fall back on devices
> that don't support NEON.
>
> Yep, adding support for ARMv8 is the final objective. I did not want to
> introduce too many changes in the first shot... and hence only introduced
> for ARMv7. In theory, most of the code (neon intrinsic code) in this patch
> should remain unchanged for ARMv8. Only the mechanism by which neon/asimd
> presence is detected during runtime and the flags used during compile are
> the only ones that should change. I will work on this once this patch gets
> reviewed and accepted. I made sure these changes are fairly localized.
>
> And yes, this patch also supports runtime detection of neon. Actually, most
> of code to do run time detection of neon was already there in the project
> before this patch. I just re-used the infrastructure.
>
>
> ARMv8 shouldn’t need Neon detection at all — Neon is a mandatory part of the
> ARMv8 architecture, unlike ARMv7, where it’s optional.
>
> As I understand, your statement for ARMv8 is true for AAarch64 mode. But for
> ARMv8 in AAarch32 mode, neon is still optional (although I haven't heard of
> an implementation that does not support NEON even in AAarch32 mode). So, for
> AArch64 mode, I think rtcd can be disabled. Also, even the neon detection
> procedure currently in opus will not work on ARMv8 AArch32 mode. Please
> refer
> http://community.arm.com/groups/android-community/blog/2014/10/10/runtime-detection-of-cpu-features-on-an-armv8-a-cpu
> This is one of my todo lists after this patchset gets reviewed and accepted.
>
> It looks like this is what the configure script is already doing — arm64
> sets rtcd_support to no.
>
> I can't find any evidence of this in configure.ac. Can you please
> point me to where rtcd_support is set to no for armv8 (AAarch64)?
>
>
> Tip of git, starting line 202:
>
>     202     case $host_cpu in
>     203           arm64*|aarch64*)
>     204         dnl Currently we only have asm for fixed-point
>     205         AS_IF([test "$enable_float" != "yes"],[
>     206             cpu_arm64=yes
>     207             AC_DEFINE([OPUS_ARM64_ASM], [],  [Make use of ARM64 asm
> optimization])
>     208             AS_GCC_INLINE_ASSEMBLY(
>     209                 [inline_optimization="ARM64"],
>     210                 [inline_optimization="disabled"]
>     211             )
>     212             AS_IF([test x"$inline_optimization" = x"ARM64"],[
>     213                 AM_CONDITIONAL([OPUS_ARM64_INLINE_ASM],[true])
>     214                 AC_DEFINE([OPUS_ARM64_INLINE_ASM], 1,
>     215                     [Use ARM64 inline asm optimizations])
>     216             ])
>     217                         dnl Don't yet have external asm for arm64
>     218                         asm_optimization="disabled"
>     219                         dnl Don't need RTCD for arm64
>     220                         rtcd_support=no
>     221         ])
>     222           ;;
>
> This actually should probably be modified to support compilers that have ARM
> intrinsics but not GCC assembly (e.g. Visual Studio), however.
Hmm... I don't see this on tip of (git://git.xiph.org/opus.git,
"master" branch, commit:
d10755e95c49f5ec925e70598877c82ad865a189). Am I looking at the wrong place?