[Mesa-dev] [PATCH] glsl: Optimize certain if-statements to just casts from the condition

[Kenneth Graunke]

On Friday, January 16, 2015 05:53:09 PM Ian Romanick wrote:
> On 01/16/2015 08:15 AM, Matt Turner wrote:
> > From: Ian Romanick <ian.d.romanick at intel.com>
> > 
> > Some shaders end up with code that looks something like:
> > 
> >     if (some_condition)
> >         result = 1.0;
> >     else
> >         result = 0.0;
> > 
> > This pass converts those if-statements to
> > 
> >      result = float(some_condition);
> > 
> > total instructions in shared programs: 5934568 -> 5921818 (-0.21%)
> > instructions in affected programs:     723433 -> 710683 (-1.76%)
> > GAINED:                                26
> > LOST:                                  7
> 
> Arg.  I'm going to have to investigate why the old patch and the new
> patch are so different. :(  On the current patch I get
> 
> LOST:   shaders/closed/steam/brutal-legend/326.shader_test SIMD16
> LOST:   shaders/closed/steam/costume-quest/1339.shader_test SIMD16
> LOST:   shaders/closed/steam/portal-2/high/5143.shader_test SIMD16
> LOST:   shaders/closed/steam/portal-2/very-high/2700.shader_test SIMD16
> LOST:   shaders/closed/steam/the-cave/2429.shader_test SIMD16
> LOST:   shaders/closed/steam/the-cave/2492.shader_test SIMD16
> LOST:   shaders/closed/steam/the-cave/2661.shader_test SIMD16
> LOST:   shaders/closed/steam/the-cave/3089.shader_test SIMD16
> LOST:   shaders/closed/steam/the-cave/3362.shader_test SIMD16
> 
> GAINED: shaders/closed/steam/portal-2/high/2677.shader_test SIMD16
> GAINED: shaders/closed/steam/portal-2/high/902.shader_test SIMD16
> GAINED: shaders/closed/steam/portal-2/low/2337.shader_test SIMD16
> GAINED: shaders/closed/steam/portal-2/low/902.shader_test SIMD16
> 
> total instructions in shared programs: 4663189 -> 4652744 (-0.22%)
> instructions in affected programs:     749395 -> 738950 (-1.39%)
> GAINED:                                4
> LOST:                                  9
> total helped:                          3159
> total HURT:                            8
> 
> You don't think IVB vs HSW makes a difference here?
> 
> I also notice that the 12 vertex shaders no longer appear in the hurt
> list or the helped list.  Ugh.
> 
> And OMG... I need to update to a distro that has render nodes so that I
> can use the updated runner. :(

You just need to boot with "drm.rnodes=1", they've been around forever.

--Ken
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