C++: accept loops with arbitrary labels or cases

Author: Robert Marsh

cpp/ql/src/Critical/DeadCodeGoto.ql

@@ -27,6 +27,7 @@ where b.getStmt(i) = js
   and not s instanceof SwitchCase
   // the next statement isn't breaking out of a switch
   and not s.(BreakStmt).getBreakable() instanceof SwitchStmt
-  // the jump isn't a goto into the body of the next statement
-  and not exists (LabelStmt ls | s.(Loop).getStmt().getAChild*() = ls | ls.getName() = js.(GotoStmt).getName())
+  // the next statement isn't a loop that can be jumped into
+  and not exists (LabelStmt ls | s.(Loop).getStmt().getAChild*() = ls)
+  and not exists (SwitchCase sc | s.(Loop).getStmt().getAChild*() = sc)
 select js, "This statement makes $@ unreachable.", s, s.toString()

cpp/ql/test/query-tests/Critical/DeadCodeGoto/test.cpp

@@ -50,3 +50,34 @@ int test5(int x, int y) {
 	return x;
 }
 
+void test6(int x, int cond) {
+	if (cond) {
+		x++;
+	} else goto end; // GOOD
+	x++;
+	end:
+}
+
+void test7(int x, int cond) {
+	if (cond)
+	{
+		goto target;
+	}
+	goto somewhere_else; // GOOD
+	while (x < 10) // not dead code
+	{
+	target:
+		x++;
+	}
+	somewhere_else:
+	switch (1)
+	{
+	  goto end;
+	  while (x < 10) // not dead code
+	  {
+	case 1:
+	    x++;
+	  } break;
+	}
+	end:
+}