[FFmpeg-devel] Patch to fix Chromium issues with ARMv8

Hendrik Leppkes h.leppkes at gmail.com
Thu Jun 15 23:51:36 EEST 2017

On Sat, Jun 3, 2017 at 12:57 AM, Amaury LeLeyzour
<Amaury.LeLeyzour at arm.com> wrote:
> Hi there,
> Here's a patch requested by Google in the context of the Chromium project. See:
> https://bugs.chromium.org/p/chromium/issues/detail?id=686903
> The ARMv8 deprecates some IT block usage that this patch tries to address. I've ran some regression tests (the part that works on a native ARM build), and it looks fine, but some tests are failing for a vanilla top of the tree ffmpeg, so it's hard for me to confirm unless you trust me because I have tested the only relevant part of this patch thoroughly with my own unit tests. This patch does not add any new regressions.

Your implementation of FASTDIV looks almost like the original macro we
have in the generic code, if there is no need for an optimized
assembly, then it should be removed entirely, and fallback to the
generic macro.
On that note, wouldn't older systems still benefit from having the
assembly over the C code, and it should just be disabled conditionally
if needed?

A similar thing goes for av_clipl_int32_arm, we generally don't like
"platform optimized" C code, either we can tune the original C code to
be fast, or we write CPU specific assembly.
Same remark about older systems applies.

- Hendrik

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