From: Kenneth Graunke Date: Sun, 20 Oct 2013 04:27:37 +0000 (-0700) Subject: i965: Only emit interpolation setup if there are actual FS inputs. X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=43b05b8fac68784bc8d61851125bd49783e5ebd0;p=mesa.git i965: Only emit interpolation setup if there are actual FS inputs. Dead code elimination would get rid of the extra instructions, but skipping this saves iterations through the optimization loop. From shader-db: N Min Max Median Avg Stddev x 14672 3 16 3 3.1334515 0.59904168 + 14672 1 16 3 2.8955153 0.77732963 Difference at 95.0% confidence -0.237936 +/- 0.0158798 -7.59342% +/- 0.506783% (Student's t, pooled s = 0.693935) Embarassingly, the classic shadow mapping shader: void main() { } used to require three iterations through the optimization loop. With this patch, it only requires one (which makes no progress). Signed-off-by: Kenneth Graunke Reviewed-by: Matt Turner Reviewed-by: Eric Anholt --- diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp index 65a4b66c6b9..a3268fb73bf 100644 --- a/src/mesa/drivers/dri/i965/brw_fs.cpp +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp @@ -3025,10 +3025,12 @@ fs_visitor::run() emit_shader_time_begin(); calculate_urb_setup(); - if (brw->gen < 6) - emit_interpolation_setup_gen4(); - else - emit_interpolation_setup_gen6(); + if (fp->Base.InputsRead > 0) { + if (brw->gen < 6) + emit_interpolation_setup_gen4(); + else + emit_interpolation_setup_gen6(); + } /* We handle discards by keeping track of the still-live pixels in f0.1. * Initialize it with the dispatched pixels.