[FFmpeg-devel] [FFmpeg-devel, v2] gcc: Relaxing auto-vectorization limitation.

[Jiawei <jiawei@iscas.ac.cn>]

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-jiawei@iscas.ac.cn/

---
 configure | 1 -
 1 file changed, 1 deletion(-)

Signed-off-by: Jiawei <jiawei@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

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