Codechange: add unit test against enum over optimisation

src/tests/CMakeLists.txt

@@ -1,5 +1,6 @@
 add_test_files(
     bitmath_func.cpp
+    enum_over_optimisation.cpp
     landscape_partial_pixel_z.cpp
     math_func.cpp
     mock_environment.h

src/tests/enum_over_optimisation.cpp

@@ -0,0 +1,31 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @file enum_over_optimisation.cpp Test whether we do not trigger an over optimisation of enums.
+ *
+ * For more details, see http://gcc.gnu.org/PR43680 and PR#5246.
+ */
+
+#include "../stdafx.h"
+
+#include "../3rdparty/catch2/catch.hpp"
+
+enum TestEnum : int8_t {
+	ZERO,
+	ONE,
+	TWO
+};
+
+TEST_CASE("EnumOverOptimisation_BoundsCheck")
+{
+	TestEnum negative_one = static_cast<TestEnum>(-1);
+	CHECK(negative_one < ZERO);
+
+	TestEnum three = static_cast<TestEnum>(3);
+	CHECK(TWO < three);
+}