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

[Andres Gomez]

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) {
+                     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