Relative speedup vs (autovectorized) C code:
Cortex A53 A72 A73
selfguided_3x3_8bpc_neon: 2.91 2.12 2.68
selfguided_5x5_8bpc_neon: 3.18 2.65 3.39
selfguided_mix_8bpc_neon: 3.04 2.29 2.98
The relative speedup vs non-vectorized C code is around 2.6-4.6x.
The relative speedup compared to C code is around 4.2 for a Cortex A53
and 5.1 for a Snapdragon 835 (compared to GCC's autovectorized code),
6-7x compared to GCC's output without autovectorization, and ~8x
compared to clang's output (which doesn't seem to try to vectorize
this function).