On quinta-feira, 15 de agosto de 2013 20:20:04, Oswald Buddenhagen wrote: > On Thu, Aug 15, 2013 at 05:01:49PM +0000, Knoll Lars wrote: > > On 8/15/13 5:07 PM, "Sune Vuorela" <[email protected]> wrote: > > >On 2013-08-15, Thiago Macieira <[email protected]> wrote: > > >> Uh... no, I don't think we can assume that. I'm afraid of Sune and > > >> > > >>other > > >> > > >> distro packagers! :-) > > > > > >*whistles innocently* > > > > But honestly: What's the oldest CPU you still consider supported? It must > > be a bit newer then i386, which I think our default build flags currently > > are still compatible with... > > as a matter of fact, linux recently stopped supporting i386. it's > seriously about time to ignore it. :D
Right, we already do. QAtomicInt::fetchAndAdd* requires i486, so Qt hasn't run on i386 for many years now. > intel atoms are based on P5 (are they still?), so that might be a > reasonable minimum. Atoms are actually based on the Pentium-M, which is an offshot of the Pentium III. The Pentium IV line (Netburst) was abandoned and the Core line comes back to Pentium-M. In fact, all Atoms have support for SSSE3 (same level as Core2), which AMD CPUs didn't have until 2011. This was a major contention issue during MeeGo days, because MeeGo binaries were compiled with -march=core2 -mtune=atom and people running AMD CPUs couldn't run them. > otoh, it doesn't actually buy much over i386. P6 is the next really > interesting instruction set. > P6+sse2 (over a decade old) is *probably* a good default for desktop > builds. ^^ Agreed, but one of our most interesting optimisations in the draw helpers is to use the PALIGNR instruction, which came with SSSE3. We still need runtime detection then. > it would probably make most sense to have configure set some > target-specific optimization defaults (for the embedded devices it would > be possible to put them directly into the qmake specs). Just set the -march= that you want to set and it should be fine. -- Thiago Macieira - thiago.macieira (AT) intel.com Software Architect - Intel Open Source Technology Center
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