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 ? I cannot be the first person thinking of that thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Awnsering whenever a program halts or runs forever is On a turing machine, in general impossible (turings halting problem). On any real computer, always possible as a real computer has a finite number of states N, and will either halt in less than N cycles or never halt.
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