On Thu, May 29, 2025 at 07:26:09PM +0200, Andreas Rheinhardt wrote: > Michael Niedermayer: > > Hi > > > > On Thu, May 29, 2025 at 04:37:16PM +0800, Zhao Zhili wrote: > >> > >> > >>> 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. > >> > >> 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. > > > > can gcc or clang not build code like our runtime cpudetect ? > > i mean build functions for each major type and detect cpu once > > and switch accordingly ? > > How would this "once" work in practice? If the cpu is supposed to be > detected only once, the result needs to be stored somewhere (in static > storage). Even if this is initialized in the libraries .init function > (so that we can be sure that it is initialized when the actual code is > run), this would still need a check every time one of these code > snippets is run.
Iam not a compiler developer, nor an expert in ELF but the cpu detect could edit the PLT or use an approuch similar to how our code works, that is function pointers thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB When you are offended at any man's fault, turn to yourself and study your own failings. Then you will forget your anger. -- Epictetus
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