[FFmpeg-devel] [PATCH v2 00/10] avcodec/vc1: Arm optimisations

[Ben Avison]

The VC1 decoder was missing lots of important fast paths for Arm, especially
for 64-bit Arm. This submission fills in implementations for all functions
where a fast path already existed and the fallback C implementation was
taking 1% or more of the runtime, and adds a new fast path to permit
vc1_unescape_buffer() to be overridden.

I've measured the playback speed on a 1.5 GHz Cortex-A72 (Raspberry Pi 4)
using `ffmpeg -i <bitstream> -f null -` for a couple of example streams:

Architecture:  AArch32    AArch32    AArch64    AArch64
Stream:        1          2          1          2
Before speed:  1.22x      0.82x      1.00x      0.67x
After speed:   1.31x      0.98x      1.39x      1.06x
Improvement:   7.4%       20%        39%        58%

`make fate` passes on both AArch32 and AArch64.

Changes in v2:

* Use AV_RL32 when performing unaligned loads from C.
* Work around bug in some assemblers which require a size specifier on VMOV
  scalar-to-general-purpose-register for AArch32.
* Increase operand indentation in AArch64 assembly.
* Add checkasm tests for each fast path for which they did not yet exist.
* Add benchmarks (generated via checkasm) to individual commits.
* Remove AArch64 blockdsp fast paths since it was impossible to demonstrate
  that they had any appreciable effect on timings.

Ben Avison (10):
  checkasm: Add vc1dsp in-loop deblocking filter tests
  checkasm: Add vc1dsp inverse transform tests
  checkasm: Add idctdsp add/put-pixels-clamped tests
  avcodec/vc1: Introduce fast path for unescaping bitstream buffer
  avcodec/vc1: Arm 64-bit NEON deblocking filter fast paths
  avcodec/vc1: Arm 32-bit NEON deblocking filter fast paths
  avcodec/vc1: Arm 64-bit NEON inverse transform fast paths
  avcodec/idctdsp: Arm 64-bit NEON block add and clamp fast paths
  avcodec/vc1: Arm 64-bit NEON unescape fast path
  avcodec/vc1: Arm 32-bit NEON unescape fast path

 libavcodec/aarch64/Makefile               |    4 +-
 libavcodec/aarch64/idctdsp_init_aarch64.c |   26 +-
 libavcodec/aarch64/idctdsp_neon.S         |  130 ++
 libavcodec/aarch64/vc1dsp_init_aarch64.c  |   94 ++
 libavcodec/aarch64/vc1dsp_neon.S          | 1552 +++++++++++++++++++++
 libavcodec/arm/idctdsp_init_arm.c         |    2 +
 libavcodec/arm/vc1dsp_init_neon.c         |   75 +
 libavcodec/arm/vc1dsp_neon.S              |  761 ++++++++++
 libavcodec/vc1dec.c                       |   20 +-
 libavcodec/vc1dsp.c                       |    2 +
 libavcodec/vc1dsp.h                       |    3 +
 tests/checkasm/Makefile                   |    2 +
 tests/checkasm/checkasm.c                 |    6 +
 tests/checkasm/checkasm.h                 |    2 +
 tests/checkasm/idctdsp.c                  |   85 ++
 tests/checkasm/vc1dsp.c                   |  411 ++++++
 tests/fate/checkasm.mak                   |    2 +
 17 files changed, 3158 insertions(+), 19 deletions(-)
 create mode 100644 libavcodec/aarch64/idctdsp_neon.S
 create mode 100644 libavcodec/aarch64/vc1dsp_neon.S
 create mode 100644 tests/checkasm/idctdsp.c
 create mode 100644 tests/checkasm/vc1dsp.c

-- 
2.25.1