Introduce op_this_operation

This adds class op_this_operation, which implements OP_THIS.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expop.h (class op_this_operation): New.
	* ax-gdb.c (op_this_operation::do_generate_ax): New method.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2021-03-08  Tom Tromey  <tom@tromey.com>
+
+	* expop.h (class op_this_operation): New.
+	* ax-gdb.c (op_this_operation::do_generate_ax): New method.
+
 2021-03-08  Tom Tromey  <tom@tromey.com>
 
 	* expop.h (class unop_memval_operation)

gdb/ax-gdb.c

@@ -2554,6 +2554,31 @@ unop_memval_type_operation::do_generate_ax (struct expression *exp,
   value->kind = axs_lvalue_memory;
 }
 
+void
+op_this_operation::do_generate_ax (struct expression *exp,
+				   struct agent_expr *ax,
+				   struct axs_value *value,
+				   struct type *cast_type)
+{
+  struct symbol *sym, *func;
+  const struct block *b;
+  const struct language_defn *lang;
+
+  b = block_for_pc (ax->scope);
+  func = block_linkage_function (b);
+  lang = language_def (func->language ());
+
+  sym = lookup_language_this (lang, b).symbol;
+  if (!sym)
+    error (_("no `%s' found"), lang->name_of_this ());
+
+  gen_var_ref (ax, value, sym);
+
+  if (value->optimized_out)
+    error (_("`%s' has been optimized out, cannot use"),
+	   sym->print_name ());
+}
+
 }
 
 /* This handles the middle-to-right-side of code generation for binary

gdb/expop.h

@@ -1713,6 +1713,33 @@ protected:
     override;
 };
 
+/* Implement the 'this' expression.  */
+class op_this_operation
+  : public tuple_holding_operation<>
+{
+public:
+
+  using tuple_holding_operation::tuple_holding_operation;
+
+  value *evaluate (struct type *expect_type,
+		   struct expression *exp,
+		   enum noside noside) override
+  {
+    return value_of_this (exp->language_defn);
+  }
+
+  enum exp_opcode opcode () const override
+  { return OP_THIS; }
+
+protected:
+
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override;
+};
+
 } /* namespace expr */
 
 #endif /* EXPOP_H */