glsl/linker: eliminate unused and set-but-unused built-in varyings

This eliminates built-in varyings such as gl_Color, gl_SecondaryColor,
gl_TexCoord, and gl_FogFragCoord if they are unused by the next stage or
not written at all (e.g. gl_TexCoord elements). The gl_TexCoord array is
broken down into separate vec4s if needed.

v2: - use a switch statement in varying_info_visitor::visit(ir_variable*)
    - use snprintf
    - disable the optimization for GLES2

Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/glsl/link_varyings.h b/src/glsl/link_varyings.h
index daa9d79c94f..7f7be353b6d 100644
--- a/src/glsl/link_varyings.h
+++ b/src/glsl/link_varyings.h
@@ -125,6 +125,10 @@ public:
          return this->vector_elements * this->matrix_columns * this->size;
    }
 
+   unsigned get_location() const {
+      return this->location;
+   }
+
 private:
    /**
     * The name that was supplied to glTransformFeedbackVaryings.  Used for