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

[Timothy Arceri]

On Thu, 2015-03-26 at 23:10 -0700, Ben Widawsky wrote:
> 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);

Currently the compile check for read only inputs is missing. I wrote a
patch for it in December [1], it needs to be rebased. I will do that and
also track down and create a second patch for interface support if your
interested in reviewing them.

[1]
http://lists.freedesktop.org/archives/mesa-dev/2014-December/073358.html