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

[Michael Niedermayer]

On Fri, May 06, 2016 at 12:08:14PM +0200, Hendrik Leppkes wrote:
> On Tue, Feb 9, 2016 at 1:28 AM, Timothy Gu <timothygu99 at gmail.com> wrote:
> > On Sun, Jan 31, 2016 at 3:38 PM Timothy Gu <timothygu99 at gmail.com> wrote:
> >>
> >> On Sat, Jan 30, 2016 at 07:27:22PM +0000, Derek Buitenhuis wrote:
> >> > On 1/30/2016 7:15 PM, Timothy Gu wrote:
> >> > > FATE passes here on a x86-64 machine with both GCC 4.9.2 and 5.3.1.
> >> >
> >> > Perhaps this should be restricted to x86?
> >>
> >> Fair enough.
> >
> >
> > Pushed.
> >
> 
> Just to document it, this has caused build breakage in various
> scenarios, even in GCC 5.3 (6.1 not tested).
> 
> The latest reported on IRC just today here:
> libavcodec/sbrdsp.c: In function 'sbr_neg_odd_64_c':
> libavcodec/sbrdsp.c:47:13: internal compiler error: in
> vect_analyze_data_ref_accesses, at tree-vect-data-refs.c:2596
>  static void sbr_neg_odd_64_c(float *x)
> 
> There are various other cases which usually involve inline asm when
> building with SIMD (ie. --cpu=host) and the optimizer running out of
> registers, for example:
> libavcodec/x86/cabac.h:192:5: error: 'asm' operand has impossible constraints
> 
> IMHO this feature is not quite ready to be enabled unconditionally in
> our code base, and we should re-evaluate this change.

+1

i had a bad feeling since i saw the patch but failed to find a
case that actually broke with a easy installable compiler at that time
when i tested this back then ...

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

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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