CPP: Add test case.

Author: geoffw0

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/BadAdditionOverflowCheck/PointlessSelfComparison.expected

@@ -3,3 +3,4 @@
 | test.cpp:83:10:83:15 | ... == ... | Self comparison. |
 | test.cpp:90:10:90:15 | ... == ... | Self comparison. |
 | test.cpp:118:7:118:32 | ... != ... | Self comparison. |
+| test.cpp:145:2:145:30 | ... == ... | Self comparison. |

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/BadAdditionOverflowCheck/test.cpp

@@ -123,3 +123,24 @@ int isSmallEnough(unsigned long long x) {
   // get compiled away on others.
   return x == (size_t)x && x == (u64)x; // GOOD
 }
+
+#define markRange(str, x, y) \
+	if ((x) == (y)) { \
+		str[x] = '^'; \
+	} else { \
+		int i; \
+		str[x] = '<'; \
+		for (i = x + 1; i < y; i++) { \
+			str[i] = '-'; \
+		} \
+		str[y] = '>'; \
+	}
+
+void useMarkRange(int offs) {
+	char buffer[100];
+
+	markRange(buffer, 10, 20);
+	markRange(buffer, 30, 30);
+	markRange(buffer, offs, offs + 10);
+	markRange(buffer, offs, offs); // GOOD (comparison is in the macro) [FALSE POSITIVE]
+}