[FFmpeg-devel] [PATCH 4/4] lavu/riscv: use Zbb CLZ/CTZ/CLZW/CTZW at run-time

[Rémi Denis-Courmont]

Le lauantaina 8. kesäkuuta 2024, 21.01.08 EEST Lynne via ffmpeg-devel a écrit :
> >   #if HAVE_RV && !defined(__riscv_zbb)
> 
> Could you add a ./configure flag or a check for enabling non-dynamic Zbb?

That's defined by the compiler target architecture and/or CPU. Adding a 
configure flag wouldn't work since the compiler wouldn't know that it can use 
emit Zbb instructions for the corresponding built-ins.

And before you ask, to my knowledge, GCC exposes no ad-hoc `-m` flags. This has 
to be included in -march or -mcpu instead, e.g.:
CFLAGS="-march=rv64gc_zba_zbb"

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