[Mesa-dev] [PATCH 10/10] glsl: fail when a shader's input var has not an equivalent out var in previous

[Ben Widawsky]

On Mon, Dec 01, 2014 at 02:04:50PM +0100, Eduardo Lima Mitev wrote:
> From: Samuel Iglesias Gonsalvez <siglesias at igalia.com>
> 
> GLSL ES 3.00 spec, 4.3.10 (Linking of Vertex Outputs and Fragment Inputs),
> page 45 says the following:
> 
> "The type of vertex outputs and fragment input with the same name must match,
> otherwise the link command will fail. The precision does not need to match.
> Only those fragment inputs statically used (i.e. read) in the fragment shader
> must be declared as outputs in the vertex shader; declaring superfluous vertex
> shader outputs is permissible."
> [...]
> "The term static use means that after preprocessing the shader includes at
> least one statement that accesses the input or output, even if that statement
> is never actually executed."
> 
> And it includes a table with all the possibilities.
> 
> Similar table or content is present in other GLSL specs: GLSL 4.40, GLSL 1.50,
> etc but for more stages (vertex and geometry shaders, etc).
> 
> This patch detects that case and returns a link error. It fixes the following
> dEQP test:
> 
>   dEQP-GLES3.functional.shaders.linkage.varying.rules.illegal_usage_1
> 
> However, it adds a new regression in piglit because the test hasn't a
> vertex shader and it checks the link status.
> 
> bin/glslparsertest \
> tests/spec/glsl-1.50/compiler/gs-also-uses-smooth-flat-noperspective.geom pass \
> 1.50 --check-link
> 
> This piglit test is wrong according to the spec wording above, so if this patch
> is merged it should be updated.
> 
> Signed-off-by: Samuel Iglesias Gonsalvez <siglesias at igalia.com>
> ---
>  src/glsl/link_varyings.cpp | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/src/glsl/link_varyings.cpp b/src/glsl/link_varyings.cpp
> index 1fe198a..036996f 100644
> --- a/src/glsl/link_varyings.cpp
> +++ b/src/glsl/link_varyings.cpp
> @@ -263,6 +263,22 @@ cross_validate_outputs_to_inputs(struct gl_shader_program *prog,
>           if (output != NULL) {
>              cross_validate_types_and_qualifiers(prog, input, output,
>                                                  consumer->Stage, producer->Stage);
> +         } else {
> +            /* Check for input vars with unmatched output vars in prev stage
> +             * taking into account that interface blocks could have a match
> +             * output but with different name, so we ignore them.
> +             */
> +            if (input->data.used && !input->data.assigned &&
> +                !(input->is_interface_instance() ||
> +                  input->get_interface_type() ||
> +                  input->is_in_uniform_block()) &&
> +                input->data.how_declared == ir_var_declared_normally &&
> +                input->data.location == -1)
> +               linker_error(prog,
> +                            "%s shader input `%s' "
> +                            "has no matching output in the previous stage\n",
> +                            _mesa_shader_stage_to_string(consumer->Stage),
> +                            input->name);

The current code isn't wrong, but it made things somewhat confusing for me when
reviewing. I don't think there is ever a case where input->data.assigned is
valid. Inputs are supposed to be read only, and so they would never be assigned.
How about instead: assert(!input->data.assigned);

I am also not certain if how_declared is correct. It seems like we shouldn't get
this far if that wasn't true, but I am not an expert (and I can't see it being
wrong).

With the data.assigned change, it's
Reviewed-by: Ben Widawsky <ben at bwidawsk.net>

>           }
>        }
>     }
> -- 
> 2.1.3
> 
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-- 
Ben Widawsky, Intel Open Source Technology Center