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

Timothy Gu timothygu99 at gmail.com
Sat May 7 01:48:11 CEST 2016

On Fri, May 06, 2016 at 12:08:14PM +0200, Hendrik Leppkes wrote:
> 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.

I don't have a problem with reverting this commit, but as James mentioned I do
prefer the bug to be reported to GCC if possible.

Have you also considered the possibility to enable this feature only if inline
assembly is not enabled?


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