[Mesa-dev] [PATCH 16/17] glsl: Add link time checks for GLSL precision qualifiers
Iago Toral
itoral at igalia.com
Wed Aug 5 01:43:37 PDT 2015
On Thu, 2015-07-30 at 12:33 +0200, Iago Toral wrote:
> 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?
Timothy pointed out to me recently that the GLSL ES spec has this
mention:
"Precision qualifiers for outputs in one shader matched to inputs in
another shader need not match when both shaders are linked into the same
program. When both shaders are in separate programs, mismatched
precision qualifiers will result in a program interface mismatch that
will result in program pipeline validation failures, as described in
section 7.4.1 (“Shader Interface Matching”) of the OpenGL ES 3.1
Specification."
This makes things a bit more complicated I guess, in any case it makes
clear that this is not exactly what the ES spec expects, so I need to
rethink how to approach this.
> > > 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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