On 29/05/2025 11:20, Jiawei wrote: > > 在 2025/5/29 16:37, Zhao Zhili 写道: >> >>> On May 29, 2025, at 15:03, Jiawei <jia...@iscas.ac.cn> wrote: >>> >>> This patch modifies the FFmpeg build system to remove the explicit disabling >>> of GCC's auto-vectorization feature. >>> >>> Modern GCC versions have demonstrated stable auto-vectorization capabilities >>> through extensive optimizations in loop analysis and SIMD code generation. >>> The explicit -fno-tree-vectorize flag originally added in commit 973859f >>> (2009) to workaround early GCC vectorization instability is no longer >>> necessary for recent gcc versions. >>> >>> Key improvements justifying this change: >>> 1. Enhanced heuristics for loop vectorization cost models >>> 2. Mature handling of alignment and memory access patterns >>> 3. Robust fallback mechanisms for unsupported architectures >>> >>> This change allows FFmpeg to benefit from automated SIMD optimizations >>> when built with -O3 optimization level, particularly improving >>> performance on x86_64 (AVX), ARM64 (SVE) and RISC-V(RVV) architectures. >>> >>> [1] >>> https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/973859f5230e77beea7bb59dc081870689d6d191 >>> >>> Version log: >>> Only allow GCC versions >= 13 to use auto-vectorization. >>> Disscussion see: >>> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20250521061750.54882-1-jia...@iscas.ac.cn/ >>> >>> --- >>> configure | 1 - >>> 1 file changed, 1 deletion(-) >>> >>> Signed-off-by: Jiawei <jia...@iscas.ac.cn> >>> --- >>> configure | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/configure b/configure >>> index 3730b0524c..91e3e107c2 100755 >>> --- a/configure >>> +++ b/configure >>> @@ -7656,7 +7656,11 @@ if enabled icc; then >>> disable aligned_stack >>> fi >>> elif enabled gcc; then >>> - check_optflags -fno-tree-vectorize >>> + gcc_version=$($cc -dumpversion) >>> + major_version=${gcc_version%%.*} >>> + if [ $major_version -lt 13 ]; then >>> + check_optflags -fno-tree-vectorize >>> + fi >>> check_cflags -Werror=format-security >>> check_cflags -Werror=implicit-function-declaration >>> check_cflags -Werror=missing-prototypes >>> -- >>> 2.43.0 >>> >>> This patch modifies the FFmpeg build system to remove the explicit disabling >>> of GCC's auto-vectorization feature. >>> >>> Modern GCC versions have demonstrated stable auto-vectorization capabilities >>> through extensive optimizations in loop analysis and SIMD code generation. >>> The explicit -fno-tree-vectorize flag originally added in commit 973859f >>> (2009) to workaround early GCC vectorization instability is no longer >>> necessary for recent gcc versions. >>> >>> Key improvements justifying this change: >>> 1. Enhanced heuristics for loop vectorization cost models >>> 2. Mature handling of alignment and memory access patterns >>> 3. Robust fallback mechanisms for unsupported architectures >>> >>> This change allows FFmpeg to benefit from automated SIMD optimizations >>> when built with -O3 optimization level, particularly improving >>> performance on x86_64 (AVX), ARM64 (SVE) and RISC-V(RVV) architectures. >>> >>> [1] >>> https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/973859f5230e77beea7bb59dc081870689d6d191 >>> >>> Version log: >>> Only allow GCC versions >= 13 to use auto-vectorization. >>> Disscussion see: >>> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20250521061750.54882-1-jia...@iscas.ac.cn/ >>> >>> --- >>> configure | 1 - >>> 1 file changed, 1 deletion(-) >>> >>> Signed-off-by: Jiawei <jia...@iscas.ac.cn> >>> --- >>> configure | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/configure b/configure >>> index 3730b0524c..91e3e107c2 100755 >>> --- a/configure >>> +++ b/configure >>> @@ -7656,7 +7656,11 @@ if enabled icc; then >>> disable aligned_stack >>> fi >>> elif enabled gcc; then >>> - check_optflags -fno-tree-vectorize >>> + gcc_version=$($cc -dumpversion) >>> + major_version=${gcc_version%%.*} >>> + if [ $major_version -lt 13 ]; then >>> + check_optflags -fno-tree-vectorize >>> + fi >>> check_cflags -Werror=format-security >>> check_cflags -Werror=implicit-function-declaration >>> check_cflags -Werror=missing-prototypes >>> -- >>> 2.43.0 >>> >>> This patch modifies the FFmpeg build system to remove the explicit disabling >>> of GCC's auto-vectorization feature. >>> >>> Modern GCC versions have demonstrated stable auto-vectorization capabilities >>> through extensive optimizations in loop analysis and SIMD code generation. >>> The explicit -fno-tree-vectorize flag originally added in commit 973859f >>> (2009) to workaround early GCC vectorization instability is no longer >>> necessary for recent gcc versions. >>> >>> Key improvements justifying this change: >>> 1. Enhanced heuristics for loop vectorization cost models >>> 2. Mature handling of alignment and memory access patterns >>> 3. Robust fallback mechanisms for unsupported architectures >>> >>> This change allows FFmpeg to benefit from automated SIMD optimizations >>> when built with -O3 optimization level, particularly improving >>> performance on x86_64 (AVX), ARM64 (SVE) and RISC-V(RVV) architectures. >>> >>> [1] >>> https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/973859f5230e77beea7bb59dc081870689d6d191 >>> >>> Version log: >>> Only allow GCC versions >= 13 to use auto-vectorization. >>> Disscussion see: >>> https://patchwork.ffmpeg.org/project/ffmpeg/patch/20250521061750.54882-1-jia...@iscas.ac.cn/ >>> >>> --- >>> configure | 1 - >>> 1 file changed, 1 deletion(-) >>> >>> Signed-off-by: Jiawei <jia...@iscas.ac.cn> >>> --- >>> configure | 6 +++++- >>> 1 file changed, 5 insertions(+), 1 deletion(-) >>> >>> diff --git a/configure b/configure >>> index 3730b0524c..91e3e107c2 100755 >>> --- a/configure >>> +++ b/configure >>> @@ -7656,7 +7656,11 @@ if enabled icc; then >>> disable aligned_stack >>> fi >>> elif enabled gcc; then >>> - check_optflags -fno-tree-vectorize >>> + gcc_version=$($cc -dumpversion) >>> + major_version=${gcc_version%%.*} >>> + if [ $major_version -lt 13 ]; then >>> + check_optflags -fno-tree-vectorize >>> + fi >>> check_cflags -Werror=format-security >>> check_cflags -Werror=implicit-function-declaration >>> check_cflags -Werror=missing-prototypes >>> -- >>> 2.43.0 >>> >> It looks like the patch format is corrupted. > Sorry, I don't know how this happened. >> >> I’m OK with the code change. However, the commit message is misleading. As >> already pointed out >> by multiple developers, this option doesn’t help with AVX, SVE and RVV >> because we can’t assume >> they are available at runtime, unless build and run on a particular hardware. > > Do you think change it into 'gcc: Allow `-fno-tree-vectorize` when gcc > version greater than 13.' will be better? >
I don't think it's the header line (gcc: Relaxing auto-vectorization limitation.) that's being called problematic, though maybe the full stop could be removed. Moreso it's the body text beneath it: "particularly improving performance on x86_64 (AVX)..." Note that when using git send-email, lines below the subject line will also become part of the commit message. Specifically, all text before the first line that begins --- will form the commit message, so if you wish to add extra text to your email but not to your commit message, you can insert it after the first ---. -- Frank _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
