[Mesa-dev] llvmpipe broken on Skylake Pentium (LP_NATIVE_VECTOR_WIDTH=128)

[Roland Scheidegger]

Am 13.10.2015 um 19:59 schrieb Adam Jackson:
> On Mon, 2015-10-12 at 22:55 +0200, Roland Scheidegger wrote:
> 
>> I don't know that looks like a generic string you're getting back.
>> x86-64 IIRC implies sse2 in llvm, but not the other sseX flags (and if
>> we detected sse41 we're going to use intrinsics for these, which then
>> may not be available in llvm _potentially_ (I'm really not sure here as
>> this code changed, and mesa generally is only adapted to such changes
>> once it breaks..., but the string here will be something less generic
>> like "ivybridge" usually on real hw).
> 
> This was the clue I needed, SSE4.1 intrinsics die because llvm doesn't
> think they're legal for the target, because llvm 3.6 doesn't know about
> broadwell or skylake so they just appear as generic.  Adding their
> model numbers to the Haswell path seems to do the trick (since
> apparently Haswell Pentium has the same property re AVX).
> 
> - ajax
> 

I think though it's still possible to tell llvm that these are legal by
setting mattr's, so they'd work regardless the cpu detected. So we
could/should probably fix this in mesa too. Albeit as mentioned the
mechanism there changed somewhat over time in llvm.

Roland