On Sun, Jul 19, 2020 at 2:06 AM Tanu Kaskinen <[email protected]> wrote: > > Hi! > > If a recipe provides NEON optimizations, should those be explicitly > disabled when "neon" is not in TUNE_FEATUERS, even if the software is > able to detect NEON availability at runtime? > > I'm currently converting the pulseaudio recipe from Autotools to Meson, > and the old Autotools build system supports disabling NEON > optimizations but the Meson build system doesn't. So I'm wondering if I > should add the missing feature to the Meson build system, or just let > the runtime detection do its work. > > Is there ever need for disabling NEON optimizations if the CPU > indicates NEON support? I guess it could be useful for testing the "no > NEON" case (I today found out that dropping "neon" from TUNE_FEATURES > doesn't remove NEON support from the qemuarm machine), but otherwise it > seems unnecessary, unless there are CPUs that advertise NEON support > but don't actually support it. >
I think the issue will result in a compiler error perhaps when neon is disabled via compiler command line which would be the case when neon is not in TUNE_FEATURES the compiler might warn or error out when it finds neon instructions being compiled via inline assembly. you just can try passing something like -mfpu=vfpv3d16 or some such and see if compiler/assembler complains during build, if not then perhaps its fine. > PulseAudio doesn't have a similar configure switch for the x86 > optimizations, so in the name of consistency I would like to rely only > on the runtime CPU detection also for the NEON optimizations. > > -- > Tanu > > https://www.patreon.com/tanuk > https://liberapay.com/tanuk > >
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