[Mesa-dev] [PATCH 4/6] glsl/linker: don't fail non static used inputs without matching outputs

[Andres Gomez]

On Fri, 2019-02-01 at 18:37 -0500, Ilia Mirkin wrote:
> On Fri, Feb 1, 2019 at 1:08 PM Andres Gomez <agomez at igalia.com> wrote:
> > If there is no Static Use of an input variable, the linker shouldn't
> > fail whenever there is no defined matching output variable in the
> > previous stage.
> > 
> > From page 47 (page 51 of the PDF) of the GLSL 4.60 v.5 spec:
> > 
> >   " Only the input variables that are statically read need to be
> >     written by the previous stage; it is allowed to have superfluous
> >     declarations of input variables."
> > 
> > Now, we complete this exception whenever the input variable has an
> > explicit location. Previously, 18004c338f6 ("glsl: fail when a
> > shader's input var has not an equivalent out var in previous") took
> > care of the cases in which the input variable didn't have an explicit
> > location.
> > 
> > Additionally, likewise 1aa5738e666 ("glsl: relax input->output
> > validation for SSO programs"), avoid failing also for programs that
> > utilize GL_ARB_separate_shader_objects.
> > 
> > Cc: Timothy Arceri <tarceri at itsqueeze.com>
> > Cc: Iago Toral Quiroga <itoral at igalia.com>
> > Cc: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
> > Cc: Tapani Pälli <tapani.palli at intel.com>
> > Cc: Ian Romanick <ian.d.romanick at intel.com>
> > Signed-off-by: Andres Gomez <agomez at igalia.com>
> > ---
> >  src/compiler/glsl/link_varyings.cpp | 16 ++++++++++++++--
> >  1 file changed, 14 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
> > index e5f7d3e322a..6cebc5b3c5a 100644
> > --- a/src/compiler/glsl/link_varyings.cpp
> > +++ b/src/compiler/glsl/link_varyings.cpp
> > @@ -808,8 +808,20 @@ cross_validate_outputs_to_inputs(struct gl_context *ctx,
> > 
> >                 output = output_explicit_locations[idx][input->data.location_frac].var;
> > 
> > -               if (output == NULL ||
> > -                   input->data.location != output->data.location) {
> > +               if (output == NULL) {
> > +                  /* A linker failure should only happen when, for programs
> > +                   * not using sso, there is no output declaration and there
> > +                   * is Static Use of the declared input.
> > +                   */
> > +                  if (input->data.used && !prog->SeparateShader) {
> 
> Should this differentiate whether this is the first stage of a
> separable program vs a later one? Presumably the exception only
> applies at the separate program boundary, not to each shader within
> the program?

Cc-ing Tapani and Anuj.

As I understand the spec, it applies to every shader within the
separable program.

>From the ARB_separate_shader_objects spec:

  " With separable program objects, interfaces between shader stages
    may involve the outputs from one program object and the inputs
    from a second program object.  For such interfaces, it is not
    possible to detect mismatches at link time, because the programs
    are linked separately.  When each such program is linked, all
    inputs or outputs interfacing with another program stage are
    treated as active.  The linker will generate an executable that
    assumes the presence of a compatible program on the other side of
    the interface.  If a mismatch between programs occurs, no GL error
    will be generated, but some or all of the inputs on the interface
    will be undefined."

Notice that this has also been the interpretation from:

1aa5738e666 ("glsl: relax input->output validation for SSO programs")

> 
> > +                     linker_error(prog,
> > +                                  "%s shader input `%s' with explicit location "
> > +                                  "has no matching output\n",
> > +                                  _mesa_shader_stage_to_string(consumer->Stage),
> > +                                  input->name);
> > +                     break;
> > +                  }
> > +               } else if (input->data.location != output->data.location) {
> >                    linker_error(prog,
> >                                 "%s shader input `%s' with explicit location "
> >                                 "has no matching output\n",
> > --
> > 2.20.1
> > 
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
-- 
Br,

Andres