The lightweight macro layer in ffmpeg takes care of v prefixes.
In FFmpeg, x264 and dav1d there are many different examples of code that couldn't be written in intrinsics or other abstraction layer.
https://twitter.com/FFmpeg/status/1705543447245988245?t=Ul9e...
hm, I vaguely remember there was a vzeroupper problem, perhaps one fell through the cracks.
Interesting, can you share more details on the magic? Looks mainly like function call overhead. If functions aren't called often, we can inline (by moving into headers or enabling LTCG/LTO).
If they are called often, are visible to the compiler, have internal linkage, but shouldn't be inlined, I'd be curious to learn why, and also why the compiler is then generating the full prolog/epilog.