nir: add how_declared to nir_variable.data

Equivalent to the already existing how_declared at GLSL IR. The only
difference is that we are not adding all the declaration_type
available on GLSL, only the one that we will use on the short term. We
would add more mode if needed on the future.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/nir/nir.h

@@ -162,6 +162,22 @@ typedef enum {
     nir_depth_layout_unchanged
 } nir_depth_layout;
 
+/**
+ * Enum keeping track of how a variable was declared.
+ */
+typedef enum {
+   /**
+    * Normal declaration.
+    */
+   nir_var_declared_normally = 0,
+
+   /**
+    * Variable is implicitly generated by the compiler and should not be
+    * visible via the API.
+    */
+   nir_var_hidden,
+} nir_var_declaration_type;
+
 /**
  * Either a uniform, global variable, shader input, or shader output. Based on
  * ir_variable - it should be easy to translate between the two.
@@ -349,6 +365,14 @@ typedef struct nir_variable {
        */
       unsigned xfb_stride;
 
+      /**
+       * How the variable was declared.  See nir_var_declaration_type.
+       *
+       * This is used to detect variables generated by the compiler, so should
+       * not be visible via the API.
+       */
+      unsigned how_declared:2;
+
       /**
        * ARB_shader_image_load_store qualifiers.
        */