[Mesa-dev] [PATCH v2 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.

v2: do the location based interface matching check regardless on
    whehter it is a separable program or not (Ilia).

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>
Cc: Ilia Mirkin <imirkin at alum.mit.edu>
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..36908d95263 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 there is no
+                   * output declaration and there is Static Use of the
+                   * declared input.
+                   */
+                  if (input->data.used) {
+                     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