+ /* Some visitors may need to insert new variable declarations and
+ * assignments for portions of a subtree, which means they need a
+ * pointer to the current instruction in the stream, not just their
+ * node in the tree rooted at that instruction.
+ *
+ * This is implemented by visit_list_elements -- if the visitor is
+ * not called by it, nothing good will happen.
+ */
+ class ir_instruction *base_ir;
+