[Mesa-dev] [PATCH] i965: Use NIR by default for vertex shaders on GEN8+

[Jason Ekstrand]

On May 7, 2015 5:38 PM, "Ian Romanick" <idr at freedesktop.org> wrote:
>
> On 05/07/2015 04:50 PM, Jason Ekstrand wrote:
> > GLSL IR vs. NIR shader-db results for SIMD8 vertex shaders on Broadwell:
> >
> >    total instructions in shared programs: 2724483 -> 2711790 (-0.47%)
> >    instructions in affected programs:     1860859 -> 1848166 (-0.68%)
> >    helped:                                4387
> >    HURT:                                  4758
> >    GAINED:                                1499
> >
> > The gained programs are ARB vertext programs that were previously going
> > through the vec4 backend.  Now that we have prog_to_nir, ARB vertex
> > programs can go through the scalar backend so they show up as "gained"
in
> > the shader-db results.
>
> I thought we already did this... why didn't this happen when NIR became
> the default for the FS backend?  And has that reason (assuming there was
> one) been resolved?

We couldn't do copy propagation of values in the attribute register file.
That, it turn was blocked on reworking the LOAD_PAYLOAD instruction.  I
pushed a series this morning that fixed both of those and cut 7.5% off of
all SIMD8 VS instructions when using NIR.  It also helps GLSL IR but by
only 1% or so.
--Jason

> > ---
> >  src/mesa/drivers/dri/i965/brw_context.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_context.c
b/src/mesa/drivers/dri/i965/brw_context.c
> > index fd7420a..8615e5e 100644
> > --- a/src/mesa/drivers/dri/i965/brw_context.c
> > +++ b/src/mesa/drivers/dri/i965/brw_context.c
> > @@ -588,7 +588,7 @@ brw_initialize_context_constants(struct brw_context
*brw)
> >
ctx->Const.ShaderCompilerOptions[MESA_SHADER_VERTEX].EmitNoIndirectTemp =
true;
> >
ctx->Const.ShaderCompilerOptions[MESA_SHADER_VERTEX].OptimizeForAOS = false;
> >
> > -      if (brw_env_var_as_boolean("INTEL_USE_NIR", false))
> > +      if (brw_env_var_as_boolean("INTEL_USE_NIR", true))
> >
 ctx->Const.ShaderCompilerOptions[MESA_SHADER_VERTEX].NirOptions =
&nir_options;
> >     }
> >
>
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