glsl/linker: Allow unused in blocks which are not declated on previous stage

>From Section 4.3.4 (Inputs) of the GLSL 1.50 spec:

    "Only the input variables that are actually read need to be written
     by the previous stage; it is allowed to have superfluous
     declarations of input variables."

Fixes:
    * interstage-multiple-shader-objects.shader_test

v2:
  Update comment in ir.h since the usage of "used" field
  has been extended.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101247
Signed-off-by: Vadym Shovkoplias <[email protected]>
Reviewed-by: Alejandro Piñeiro <[email protected]>
Reviewed-by: Timothy Arceri <[email protected]>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/compiler/glsl/link_interface_blocks.cpp b/src/compiler/glsl/link_interface_blocks.cpp
index e5eca9460e3..801fbcd5d9f 100644
--- a/src/compiler/glsl/link_interface_blocks.cpp
+++ b/src/compiler/glsl/link_interface_blocks.cpp
@@ -417,9 +417,15 @@ validate_interstage_inout_blocks(struct gl_shader_program *prog,
        * write to any of the pre-defined outputs (e.g. if the vertex shader
        * does not write to gl_Position, etc), which is allowed and results in
        * undefined behavior.
+       *
+       * From Section 4.3.4 (Inputs) of the GLSL 1.50 spec:
+       *
+       *    "Only the input variables that are actually read need to be written
+       *     by the previous stage; it is allowed to have superfluous
+       *     declarations of input variables."
        */
       if (producer_def == NULL &&
-          !is_builtin_gl_in_block(var, consumer->Stage)) {
+          !is_builtin_gl_in_block(var, consumer->Stage) && var->data.used) {
          linker_error(prog, "Input block `%s' is not an output of "
                       "the previous stage\n", var->get_interface_type()->name);
          return;