Bug#842143: severity

[Sylvestre Ledru]

Le 06/11/2016 à 11:59, Emilio Pozuelo Monfort a écrit :
> Hi Sylvestre,
>
> On Fri, 4 Nov 2016 09:50:27 +0100 Sylvestre Ledru <s at mozilla.com> wrote:
>> severity 842143 normal
>> thanks
>>
>> See the bug report.
> If I understood things correctly, the problem is that by default, LLVM assumes
> NEON extensions are available when compiling for armhf. That causes rdeps to
> fail with illegal instruction when running on armhf hardware without NEON
> support, however rare that may be, which is officially supported on armhf.
>
> According to the upstream bug, this can be changed by passing a flag to the
> compiler. That's not good enough as that means we have to change all rdeps.
> Instead, the default should be changed, and users can tune the flags if they
> want performance at the cost of supporting less hardware (e.g. to run code in
> their own machine). This is not different to other architectures or to GCC,
> where we default to the baseline that is officially supported by Debian.
Well, this is the same issue as SSE2 for i386. I would like to avoid 
penalizing performances the whole population using
this arch just for a small percentage...
As example, two projects focusing on performance (Firefox and Chrome) 
made that call.

Do we have a clue how many armhf systems don't have NEON?

> So I think this should go back to RC and be fixed for stretch. BTW I think
> Gianfranco had a patch for this, maybe he can attach it here.
The patch has not been tested. We are not sure we can force NEON with 
the patch.

> BTW on an unrelated note, llvm-toolchain-3.6 is out of testing!
>
Good! Thanks.

Sylvestre