[Development] QTBUG-30440: restricting the SIMD files

Karl Ruetz karl.ruetz at ruetzdogz.com
Mon Aug 19 15:34:15 CEST 2013


On 2013-08-19 05:56, Knoll Lars wrote: 

> On 19.08.13 09:56,
"Koehne Kai" <Kai.Koehne at digia.com> wrote:
>>> -----Original
Message----- From:
development-bounces+kai.koehne=digia.com at qt-project.org
[mailto:development-bounces+kai.koehne=digia.com at qt-project.org] On
Behalf Of Thiago Macieira Sent: Monday, August 19, 2013 9:42 AM To:
development at qt-project.orgSubject: Re: [Development] QTBUG-30440:
restricting the SIMD files On segunda-feira, 19 de agosto de 2013
07:37:58, Koehne Kai wrote: 
>>>> I don't know how big the
performance gains really are, but if it's noticeable, why not switch the
default for everyone using the default mkspec?
>>> Switching the default
means making it difficult to unset for those who want it unset.
>> Well,
it's just copying /editing the mkspec ... Arguably not the most obvious
way to do it, but maybe we should just document it a bit better, then :)

>>> We recommend people set the environment if they want different
flags, besides the stock from their compilers.
>> Where do we recommend
this? E.g. http://qt-project.org/doc/qt-5.0/qtdoc/install-x11.html
[1]just says to run configure ... Actually it doesn't look like CFLAGS,
LFLAGS is mentioned anywhere in the Qt documentation. If we recommend
that, why not use that ourselves? Well, I just think most people
compiling on their own will miss this optimization then. If we think
it's a useful optimization that helps >95% of our customers, it should
IMO be the default . If not, I'm not sure we should apply it t

> I tend to agree with Kai. Why should we penalize 99% of our users
> support a 15 year old CPU architecture? We don't do this with
> else. Ie. Qt won't compile on a 15 year old Linux
distribution, and we
> don't support Win98 anymore neither.
> Lars
> _______________________________________________
Development mailing list
> Development at qt-project.org
http://lists.qt-project.org/mailman/listinfo/development [2]

>From a
long time user's perspective: 

We still have customers using old test
equipment that runs Win NT 4.0. Like it or not, we have to support these
customers to stay in business no matter how unreasonable such a thing
seems. This support will not end for the foreseeable future. Our app
that runs on these systems was built using Qt 2, ported to Qt 3, and we
even managed to get it ported to Qt 4 by doing some mental gymnastics.
Qt 5 is likely out of the question. 

So as long as it is remembered
that somewhere there are a few of us old folks that still have to create
development environments for legacy systems, and those legacy
environments are still available to be built, new environments do not
need to support "ancient" equipment and it is okay for the "default"
settings to support 99. 5% of the users rather than the .5% of users
that need legacy support. 


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