nir: add shader_info::prev_stage_has_xfb
We will use it to skip lowering mediump IO to 16 bits if the previous
shader has XFB and mediump XFB doesn't work.
Drivers can decide not to lower mediump IO to 16 bits if nir->xfb_info
!= NULL for the pre-rast stage and if nir->info.prev_stage_has_xfb is
true for the FS stage. That way, drivers can lower mediump to 16 bits
for all cases except XFB.
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35315>
2 files changed
