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i965: Only emit interpolation setup if there are actual FS inputs.

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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 <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
This commit is contained in:
Kenneth Graunke 2013-10-19 21:27:37 -07:00
parent c4de86fd26
commit 43b05b8fac
1 changed files with 6 additions and 4 deletions
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10
src/mesa/drivers/dri/i965/brw_fs.cpp
View file

@ -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.