On Feb 15, 2015 11:55 PM, "Ben Widawsky" <<a href="mailto:benjamin.widawsky@intel.com">benjamin.widawsky@intel.com</a>> wrote: > > The short version: we need to set bits in R0.7 which provide a mask to be used > for PS kill samples/pixels. Since the VS has no such concept, we just need to > set all 1. > > The longer version... > Execution for SIMD8 atomics is defined as follows: > SIMD8: The low 8 bits of the execution mask are ANDed with 8 bits of the > Pixel/Sample Mask from the message header. For the typed messages, the Slot > Group in the message descriptor selects either the low or high 8 bits. For the > untyped messages, the low 8 bits are always selected. The resulting mask is used > to determine which slots are read into the destination GRF register (for read), > or which slots are written to the surface (for write). If the header is not > present, only the low 8 bits of the execution mask are used. > > The message header for untyped messages is defined in R0.7 "This field contains > the 16-bit pixel/sample mask to be used for SIMD16 and SIMD8 messages. All 16 > bits are used for SIMD16 messages. For typed SIMD8 messages, Slot Group selects > which 8 bits of this field are used. For untyped SIMD8 messages, the low 8 bits > of this field are used." Furthermore, "The message header for the untyped > messages only needs to be delivered for pixel shader threads, where the > execution mask may indicate pixels/samples that are enabled only due to > derivative (LOD) calculations, but the corresponding slot on the surface must > not be accessed." We're not using a pixel shader here, but AFAICT, this mask is > used for all stages. > > This leaves two options, Remove the header, or make the VS code emit the correct > thing for the header. I believe one of the goals of using SIMD8 VS was to get as > much code reuse as possible, and so I chose the latter. Since the VS has no such > thing as kill instructions, the mask is derived simple as all 1's. Hm. This seems a little fishy. Don't we still have an execution mask for vertex shaders? The second half of the if copies that into the bit field. > Bugzilla: <a href="https://bugs.freedesktop.org/show_bug.cgi?id=87258">https://bugs.freedesktop.org/show_bug.cgi?id=87258</a> > Cc: Kristian Høgsberg <<a href="mailto:krh@bitplanet.net">krh@bitplanet.net</a>> > Signed-off-by: Ben Widawsky <<a href="mailto:ben@bwidawsk.net">ben@bwidawsk.net</a>> > --- > src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp > index 2a36d94..c20289f 100644 > --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp > +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp > @@ -2994,6 +2994,9 @@ fs_visitor::emit_untyped_atomic(unsigned atomic_op, unsigned surf_index, > if (uses_kill) { > emit(MOV(component(sources[0], 7), brw_flag_reg(0, 1))) > ->force_writemask_all = true; > + } else if (stage == MESA_SHADER_VERTEX) { > + emit(MOV(component(sources[0], 7), > + brw_imm_ud(0xff)))->force_writemask_all = true; > } else { > emit(MOV(component(sources[0], 7), > retype(brw_vec1_grf(1, 7), BRW_REGISTER_TYPE_UD)); Also would you mind rearranging the logic a bit here. Something like this would make it more clear that the header stuff is only for vertex shaders: If (fragment) { If (uses_kill) { } else { } } else { // vertex stuff } > -- > 2.3.0 > > _______________________________________________ > mesa-dev mailing list > <a href="mailto:mesa-dev@lists.freedesktop.org">mesa-dev@lists.freedesktop.org</a> > <a href="http://lists.freedesktop.org/mailman/listinfo/mesa-dev">http://lists.freedesktop.org/mailman/listinfo/mesa-dev</a>