From 620e6e14878de7392f9b5fd109cc8f5ed90dd835 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?R=C3=A9mi=20Denis-Courmont?= Date: Sat, 3 Sep 2022 18:05:18 +0300 Subject: [PATCH] arm: relax byte-swap assembler constraints MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit There are no particular reasons to force the compiler to use the same register as output and input operand. This forces an extra MOV instruction if the input value needs to be reused after the swap. In most cases, this makes no differences, as the compiler will seleect the same register for both operands either way. Signed-off-by: Martin Storsjö --- libavutil/arm/bswap.h | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) diff --git a/libavutil/arm/bswap.h b/libavutil/arm/bswap.h index 611ff0ad5b..c3460e035d 100644 --- a/libavutil/arm/bswap.h +++ b/libavutil/arm/bswap.h @@ -39,8 +39,10 @@ static av_always_inline av_const uint32_t av_bswap32(uint32_t x) #define av_bswap16 av_bswap16 static av_always_inline av_const unsigned av_bswap16(unsigned x) { - __asm__("rev16 %0, %0" : "+r"(x)); - return x; + unsigned y; + + __asm__("rev16 %0, %1" : "=r"(y) : "r"(x)); + return y; } #endif @@ -48,17 +50,18 @@ static av_always_inline av_const unsigned av_bswap16(unsigned x) #define av_bswap32 av_bswap32 static av_always_inline av_const uint32_t av_bswap32(uint32_t x) { + uint32_t y; #if HAVE_ARMV6_INLINE - __asm__("rev %0, %0" : "+r"(x)); + __asm__("rev %0, %1" : "=r"(y) : "r"(x)); #else uint32_t t; - __asm__ ("eor %1, %0, %0, ror #16 \n\t" + __asm__ ("eor %1, %2, %2, ror #16 \n\t" "bic %1, %1, #0xFF0000 \n\t" - "mov %0, %0, ror #8 \n\t" + "mov %0, %2, ror #8 \n\t" "eor %0, %0, %1, lsr #8 \n\t" - : "+r"(x), "=&r"(t)); + : "=r"(y), "=&r"(t) : "r"(x)); #endif /* HAVE_ARMV6_INLINE */ - return x; + return y; } #endif /* AV_GCC_VERSION_AT_MOST(4,4) */