Re: [FFmpeg-devel] [PATCH v5] gcc: Don't disable '-ftree-vectorize' if gcc version higher than 13.

[Michael Niedermayer <michael@niedermayer.cc>]

[-- Attachment #1.1: Type: text/plain, Size: 2471 bytes --]

Hi Martin

On Fri, Jun 13, 2025 at 11:42:11AM +0300, Martin Storsjö wrote:
> On Fri, 13 Jun 2025, Jiawei wrote:
> 
> > This patch modifies the FFmpeg build system to allow GCC to use the
> > `-ftree-vectorize` flag when the compiler version is 13 or newer.
> > Enabling this flag can improve performance through better loop analysis
> > and auto-vectorization (SIMD) opportunities in modern GCC versions.
> > 
> > The explicit `-fno-tree-vectorize` flag was originally added in commit
> > 973859f5230e (2009). A previous attempt to enable `-ftree-vectorize`
> > was made in commit cb8646af24bd (2016), but it was reverted in
> > fd6dbc53855f. The reason for the revert was that the inline x86 CABAC
> > assembly code caused compiler errors ??? the compiler would run out of
> > available registers during vectorization, making it unable to compile
> > some functions.
> > 
> > In commit 182663a58a7a (2023), the problematic CABAC function was made
> > non-inline. This significantly reduces the risk of register exhaustion
> > caused by inlining large assembly blocks, making the vectorizer safer
> > to enable for other functions.
> > 
> > Given improvements in GCC's vectorizer and the mitigation of the
> > original issue, we now re-enable `-ftree-vectorize` for GCC version 13
> > and above.
> > 
> > Version log:
> >  Only allow GCC versions >= 13 to use -ftree-vectorize.
> >  Modify the commit description.
> >  Add historical context and rationale for the change.
> > 
> > Disscussion see:
> > https://patchwork.ffmpeg.org/project/ffmpeg/patch/20250521061750.54882-1-jiawei@iscas.ac.cn/
> > 
> > 
> > Signed-off-by: Jiawei <jiawei@iscas.ac.cn>
> > ---
> > configure | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> 
> Thanks; I'm ok with this version. Whoever applies it can touch up the commit
> message to remove the ???? word (maybe just replace it with an "as"), it
> sounds reasonably right like that.

the patch seems not to be on the mailing list
I have v4 in my inbox but not v5, so if the patch is ok, maybe you are
the only one who can apply it

Maybe Jiawei is not subscribed to the ML so his mails would go to the
moderation que (i didnt check)

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 195 bytes --]

[-- Attachment #2: Type: text/plain, Size: 251 bytes --]

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".