C++: Add a test.

Author: MathiasVP

cpp/ql/test/library-tests/controlflow/guards/Guards.expected

@@ -42,3 +42,6 @@
 | test.cpp:99:6:99:6 | f |
 | test.cpp:105:6:105:14 | ... != ... |
 | test.cpp:111:6:111:14 | ... != ... |
+| test.cpp:122:9:122:9 | b |
+| test.cpp:125:13:125:20 | ! ... |
+| test.cpp:125:14:125:17 | call to safe |

cpp/ql/test/library-tests/controlflow/guards/GuardsControl.expected

@@ -100,3 +100,7 @@
 | test.cpp:99:6:99:6 | f | true | 99 | 100 |
 | test.cpp:105:6:105:14 | ... != ... | true | 105 | 106 |
 | test.cpp:111:6:111:14 | ... != ... | true | 111 | 112 |
+| test.cpp:122:9:122:9 | b | true | 123 | 125 |
+| test.cpp:122:9:122:9 | b | true | 125 | 125 |
+| test.cpp:125:13:125:20 | ! ... | true | 125 | 125 |
+| test.cpp:125:14:125:17 | call to safe | false | 125 | 125 |

cpp/ql/test/library-tests/controlflow/guards/test.cpp

@@ -112,3 +112,17 @@ void int_float_comparison(int i) {
     use(i);
   }
 }
+
+int source();
+bool safe(int);
+
+void test(bool b)
+{
+    int x;
+    if (b)
+    {
+        x = source();
+        if (!safe(x)) return;
+    }
+    use(x);
+}