From 324899b7483529c336f399022c63721df14663ef Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?R=C3=A9mi=20Denis-Courmont?= Date: Thu, 30 May 2024 22:04:10 +0300 Subject: [PATCH] lavu/riscv: use Zbb REV8 at run-time This adds runtime support to use Zbb REV8 for 32- and 64-bit byte-wise swaps. The result is about five times slower than if targetting Zbb statically, but still a lot faster than the default bespoke C code or a call to GCC run-time functions. For 16-bit swap, this is however unsurprisingly a lot worse, and so this sticks to the baseline. In fact, even using REV8 statically does not seem to be beneficial in that case. Zbb static Zbb dynamic I baseline bswap16: 0.668184765 3.340764069 0.668029012 bswap32: 0.668174014 3.340763319 9.353855435 bswap64: 0.668221765 3.340496313 14.698672283 (seconds for 1 billion iterations on a SiFive-U74 core) --- libavutil/riscv/bswap.h | 44 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 42 insertions(+), 2 deletions(-) diff --git a/libavutil/riscv/bswap.h b/libavutil/riscv/bswap.h index ce75de974e..886893e241 100644 --- a/libavutil/riscv/bswap.h +++ b/libavutil/riscv/bswap.h @@ -22,11 +22,51 @@ #include #include "config.h" #include "libavutil/attributes.h" +#include "libavutil/riscv/cpu.h" #if defined (__GNUC__) || defined (__clang__) #define av_bswap16 __builtin_bswap16 -#define av_bswap32 __builtin_bswap32 -#define av_bswap64 __builtin_bswap64 + +static av_always_inline av_const uint32_t av_bswap32_rv(uint32_t x) +{ +#if HAVE_RV && !defined(__riscv_zbb) + if (!__builtin_constant_p(x) && + __builtin_expect(ff_rv_zbb_support(), 1)) { + uintptr_t y; + + __asm__ ( + ".option push\n" + ".option arch, +zbb\n" + "rev8 %0, %1\n" + ".option pop" : "=r" (y) : "r" (x)); + return y >> (__riscv_xlen - 32); + } +#endif + return __builtin_bswap32(x); +} +#define av_bswap32 av_bswap32_rv + +#if __riscv_xlen >= 64 +static av_always_inline av_const uint64_t av_bswap64_rv(uint64_t x) +{ +#if HAVE_RV && !defined(__riscv_zbb) + if (!__builtin_constant_p(x) && + __builtin_expect(ff_rv_zbb_support(), 1)) { + uintptr_t y; + + __asm__ ( + ".option push\n" + ".option arch, +zbb\n" + "rev8 %0, %1\n" + ".option pop" : "=r" (y) : "r" (x)); + return y >> (__riscv_xlen - 64); + } +#endif + return __builtin_bswap64(x); +} +#define av_bswap64 av_bswap64_rv +#endif + #endif #endif /* AVUTIL_RISCV_BSWAP_H */