[Mesa-dev] [PATCH 16/17] glsl: Add link time checks for GLSL precision qualifiers

[Iago Toral]

On Wed, 2015-07-29 at 15:21 -0700, Ian Romanick wrote:
> On 07/29/2015 07:01 AM, Samuel Iglesias Gonsalvez wrote:
> > From: Iago Toral Quiroga <itoral at igalia.com>
> > 
> > Currently, we only consider precision qualifiers at compile-time. This patch
> > adds precision information to ir_variable so we can also do link time checks.
> > Specifically, from the GLSL ES3 spec, 4.5.3 Precision Qualifiers:
> > 
> > "The same uniform declared in different shaders that are linked together
> >  must have the same precision qualification."
> > 
> > Notice that this patch will check the above also for GLSL ES globals that are
> > not uniforms. This is not explicitly stated in the spec, but seems to be
> > the only consistent choice since we can only have one definition of a global
> > all its declarations should be identical, including precision qualifiers.
> 
> That's not right.  Global variables from different stages that are not
> inputs/outputs or uniforms are distinct... they don't even have to be
> the same type.  ES shaders only allow a single compliation unit per
> stage, so we don't have to worry about inter-stage globals.

Ugh, sorry, the commit log does not make a good job at explaining the
situation. This patch does not produce a linker error for globals that
are not uniforms, I only meant to say that for globals *in interface
blocks*, for which we are producing a linker error in the case of type
mismatches, precision will also be considered to decide if the types
mismatch.

Sorry for being so imprecise in the description, I'll fix the commit
log. I guess with this clarification there are no issues with this,
right?

Iago

> > These checks don't affect desktop GLSL shaders because we ignore precision
> > information in this case (all variables have precision GLSL_PRECISION_NONE).
> > 
> > Fixes the following 5 dEQP tests:
> > dEQP-GLES3.functional.shaders.linkage.uniform.struct.precision_conflict_1
> > dEQP-GLES3.functional.shaders.linkage.uniform.struct.precision_conflict_2
> > dEQP-GLES3.functional.shaders.linkage.uniform.struct.precision_conflict_3
> > dEQP-GLES3.functional.shaders.linkage.uniform.struct.precision_conflict_4
> > dEQP-GLES3.functional.shaders.linkage.uniform.block.precision_mismatch
> > ---
> >  src/glsl/linker.cpp | 34 +++++++++++++++++++++++++++++++++-
> >  1 file changed, 33 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
> > index 12b7780..fd68f43 100644
> > --- a/src/glsl/linker.cpp
> > +++ b/src/glsl/linker.cpp
> > @@ -958,13 +958,22 @@ cross_validate_globals(struct gl_shader_program *prog,
> >                    if (var->type->is_record() && existing->type->is_record()
> >                        && existing->type->record_compare(var->type)) {
> >                       existing->type = var->type;
> > -                  } else {
> > +                  } else if (strcmp(var->type->name, existing->type->name)) {
> >                       linker_error(prog, "%s `%s' declared as type "
> >                                    "`%s' and type `%s'\n",
> >                                    mode_string(var),
> >                                    var->name, var->type->name,
> >                                    existing->type->name);
> >                       return;
> > +                  } else {
> > +                     /* The global is declared with the same type name but the type
> > +                      * declarations mismatch (e.g. the same struct type name, but
> > +                      * the actual struct declarations mismatch).
> > +                      */
> > +                     linker_error(prog, "%s `%s' declared with mismatching definitions "
> > +                                  "of type `%s'\n",
> > +                                  mode_string(var), var->name, var->type->name);
> > +                     return;
> >                    }
> >  	       }
> >  	    }
> > @@ -1121,6 +1130,29 @@ cross_validate_globals(struct gl_shader_program *prog,
> >                              mode_string(var), var->name);
> >                 return;
> >              }
> > +            /* From the GLSL ES3 spec, 4.5.3 Precision qualifiers:
> > +             *
> > +             * "The same uniform declared in different shaders that are linked
> > +             *  together must have the same precision qualification."
> > +             *
> > +             * In the GLSL ES2 spec this was resolved in the issue amendments
> > +             * (10.3 Precision Qualifiers). The GLSL ES1 spec overlooked this,
> > +             * but seems like an obvious error since we can only have one
> > +             * consistent definition of a global.
> > +             *
> > +             * The desktop GLSL spec does not include this reference
> > +             * because precision qualifiers are ignored. We will never
> > +             * hit this scenario in desktop GLSL though because we always set
> > +             * the precision of variables to GLSL_PRECISION_NONE.
> > +             */
> > +            if (var->data.mode == ir_var_uniform) {
> > +               if (existing->data.precision != var->data.precision) {
> > +                  linker_error(prog, "declarations for %s `%s` have "
> > +                               "mismatching precision qualifiers\n",
> > +                               mode_string(var), var->name);
> > +                  return;
> > +               }
> > +            }
> >  	 } else
> >  	    variables.add_variable(var);
> >        }
> > 
> 
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