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[88.192.28.243]) by smtp.gmail.com with ESMTPSA id d13-20020a2e330d000000b002b6cb40e9aasm3312538ljc.103.2023.08.02.00.02.08 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Aug 2023 00:02:08 -0700 (PDT) From: =?utf-8?q?Martin_Storsj=C3=B6?= To: ffmpeg-devel@ffmpeg.org Date: Wed, 2 Aug 2023 10:02:06 +0300 Message-Id: <20230802070206.28917-1-martin@martin.st> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH] intreadwrite: Indicate potential aliasing in AV_RN/AV_WN for Clang/MSVC mode X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" X-TUID: Gh9n+ACM5Nzy While MSVC proper doesn't have a way to signal potential aliasing corresponding to __attribute__((may_alias)) (which is what av_alias expands to, if supported), Clang does support it. When building with Clang in MSVC mode, __GNUC__ isn't defined but _MSC_VER is, so Clang uses the MSVC implementation of AV_RN/AV_WN which uses __unaligned. Add the av_alias macro there, to indicate that the reads/writes can alias other writes. Adding the attribute within the cast itself doesn't seem to have any effect, it only has an effect if added in a type definition. Alternatively the __GNUC__ specific codepath right above could also be used whenever __clang__ is defined; numerous __GNUC__ checks also separately check for __clang__ to use them when building with Clang in MSVC mode. This fixes a couple HEVC decoder tests when built with Clang 14 or newer in MSVC mode (with issues observed on all of x86_64, armv7 and aarch64). --- libavutil/intreadwrite.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/libavutil/intreadwrite.h b/libavutil/intreadwrite.h index c4679fdba4..126ac3c7f8 100644 --- a/libavutil/intreadwrite.h +++ b/libavutil/intreadwrite.h @@ -224,8 +224,12 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias; #elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_X64) || defined(_M_ARM64)) && AV_HAVE_FAST_UNALIGNED -# define AV_RN(s, p) (*((const __unaligned uint##s##_t*)(p))) -# define AV_WN(s, p, v) (*((__unaligned uint##s##_t*)(p)) = (v)) +typedef __unaligned uint64_t av_alias unaligned_64; +typedef __unaligned uint32_t av_alias unaligned_32; +typedef __unaligned uint16_t av_alias unaligned_16; + +# define AV_RN(s, p) (*((const unaligned_##s*)(p))) +# define AV_WN(s, p, v) (*((unaligned_##s*)(p)) = (v)) #elif AV_HAVE_FAST_UNALIGNED