On Fri, Jan 13, 2017 at 3:37 AM, Ilia Mirkin <imir...@alum.mit.edu> wrote: > On Thu, Jan 12, 2017 at 9:13 PM, Jason Ekstrand <ja...@jlekstrand.net> wrote: >> Unless, of course, it's controlled by the same hardware bit... Clearly, we >> can can give you abs on rsq without denorm flushing (easy shader hacks) but >> not the other way around. > > OK, so somehow I missed that earlier. However there's an interesting > section in the PRM: > > https://01.org/sites/default/files/documentation/intel-gfx-prm-osrc-skl-vol07-3d_media_gpgpu.pdf > > on PDF page 854, "Dismissed Legacy Behaviors" which has a list of > suggested IEEE 754 deviations for DX9. One of them is indeed that 0 * > x = 0, but another is that input NaNs be propagated with certain > exceptions. Also they suggest that RCP(0)/RSQ(0) = fmax. Interesting. > > So at this point, the zero_wins thing is pretty much blown. i965 > appears to have an all-or-nothing approach, and additionally that > approach doesn't match up exactly to what NVIDIA does (or at least I'm > not aware of a clamp-everything mode). > > This will take some thought to figure out how something can be > specified so that a single spec works for both i965 and nv/amd. OTOH > we could have two different specs that just expose different things - > e.g. i965 could expose a MESA_shader_float_alt_mode or whatever which > is spec'd to do the things that the PRM says, and nv/amd have the > MESA_shader_float_zero_wins ext which does what we were talking about > earlier. > > I'm open to other suggestions too.
There is also the "small" problem that it would take a non-trivial effort for us on the LLVM side. You guys can flip a switch. We can't. Marek _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
