[Development] Enabling SSE2 by default on x86 builds (32-bit)

[Knoll Lars]

On 11/12/13 10:03, "Simon Hausmann" <simon.hausmann at digia.com> wrote:

>On Wednesday 11. December 2013 09.36.46 Simon Hausmann wrote:
>[...]
>> > If we apply the change I mentioned in the other email, we change
>>cases 2
>> > and 3:
>> > 
>> > 2bis) distro builds Qt once with -no-sse2 flags
>> > 
>> > 	=> all libs compiled without SSE2
>> > 	=> QtQml generates interpreted code only
>> > 
>> > 3bis) distro builds Qt once with -no-sse2 and then some libs with
>>-config
>> > sse2 => most libs compiled without SSE2, a few with SSE2 code
>> > 
>> > 	=> the non-SSE2 QtQml will generate interpreted code, the SSE2 one
>>will
>> > 	generate SSE2 code and will be used only in machines less than 14
>>years
>> > 	old
>> 
>> Yep, let's do that. It's relatively painless to support this kind of
>>build
>> configuration in QtQml at least.
>
>To puts words where my mouth is, here's a proposed fix for QtQml:
>
>	https://codereview.qt-project.org/#change,73710

Is this the right fix for 5.2? I'm a bit afraid that this would cause
Linux distributions to install the sse disabled QtQml by default, leading
to pretty bad performance.

The other option for 5.2 would be to do runtime detection of SSE2 and
enable/disable the JIT according to that.

Cheers,
Lars

PS: Actually I think QtQml in 5.0 and 5.1 was also requiring SSE (because
of V8).