[FFmpeg-devel] [PATCH 2/2] configure: Enable GCC vectorization on ≥4.9

[Timothy Gu]

4.9 was released precisely nine years after the first GCC version with
autovectorizer (4.0) and six years after the first GCC version with
`-ftree-vectorize` default to enabled on `-O3` (4.3). We've given GCC
enough time to fix those bugs.

FATE passes here on a x86-64 machine with both GCC 4.9.2 and 5.3.1.

Some optimization hotspots benefit greatly from this change, especially
those without handwritten assembly. For instance, the main function in
vf_phase is now 1.6x faster (1.2x overall).
---
 configure | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index dba8180..074c4e5 100755
--- a/configure
+++ b/configure
@@ -5933,7 +5933,10 @@ elif enabled ccc; then
     add_cflags -msg_disable nonstandcast
     add_cflags -msg_disable unsupieee
 elif enabled gcc; then
-    check_optflags -fno-tree-vectorize
+    case $gcc_basever in
+        4.9*) ;;
+        4.*) check_optflags -fno-tree-vectorize ;;
+    esac
     check_cflags -Werror=format-security
     check_cflags -Werror=implicit-function-declaration
     check_cflags -Werror=missing-prototypes
-- 
2.1.4