ir_variable: Track the location of uniforms, varings, attributes, etc.

ir.cpp

@@ -731,6 +731,7 @@ ir_variable::ir_variable(const struct glsl_type *type, const char *name)
 {
    this->type = type;
    this->name = name;
+   this->location = -1;
    this->constant_value = NULL;
 
    if (type && type->base_type == GLSL_TYPE_SAMPLER)

ir.h

@@ -217,6 +217,23 @@ public:
     */
    unsigned array_lvalue:1;
 
+   /**
+    * Storage location of the base of this variable
+    *
+    * The precise meaning of this field depends on the nature of the variable.
+    *
+    *   - Vertex shader input: one of the values from \c gl_vert_attrib.
+    *   - Vertex shader output: one of the values from \c gl_vert_result.
+    *   - Fragment shader input: one of the values from \c gl_frag_attrib.
+    *   - Fragment shader output: one of the values from \c gl_frag_result.
+    *   - Uniforms: Per-stage uniform slot number.
+    *   - Other: This field is not currently used.
+    *
+    * If the variable is a uniform, shader input, or shader output, and the
+    * slot has not been assigned, the value will be -1.
+    */
+   int location;
+
    /**
     * Emit a warning if this variable is accessed.
     */