This is needed because the information stored on the ATTR file for
multipolygon fragment shaders isn't stored as a contiguous sequence in
the GRF, instead the ATTR source may be lowered by assign_urb_setup()
to use a <16;8,0> region, which reads 4 SIMD16 GRFs for a SIMD32
instruction, even though the result of fs_inst::size_read() is
expected to be 2 GRFs. Special case ATTR sources for multipolygon PS
shaders to calculate the number of physical GRFs that will actually be
read by the instruction after lowering, based on the number of
polygons processed by the instruction.
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26606>
Francisco Jerez
50d084ec29