CPP: Exclude functions containing preprocessor logic.

Author: geoffw0

cpp/ql/src/Critical/DeadCodeGoto.ql

@@ -10,6 +10,7 @@
  */
 
 import cpp
+import semmle.code.cpp.commons.Exclusions
 
 Stmt getNextRealStmt(Block b, int i) {
   result = b.getStmt(i + 1) and
@@ -30,4 +31,6 @@ where b.getStmt(i) = js
   // 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)
+  // no preprocessor logic applies
+  and not functionContainsPreprocCode(js.getEnclosingFunction())
 select js, "This statement makes $@ unreachable.", s, s.toString()

cpp/ql/src/semmle/code/cpp/commons/Exclusions.qll

@@ -58,3 +58,16 @@ predicate functionContainsDisabledCode(Function f) {
     )
   )
 }
+
+/**
+ * Holds if the function `f` contains code that could be excluded by the preprocessor.
+ */
+predicate functionContainsPreprocCode(Function f) {
+  // `f` contains a preprocessor branch
+  exists(PreprocessorBranchDirective pbd, string file, int pbdStartLine, int fBlockStartLine, int fBlockEndLine |
+    functionLocation(f, file, fBlockStartLine, fBlockEndLine) and
+    pbdLocation(pbd, file, pbdStartLine) and
+    pbdStartLine <= fBlockEndLine and
+    pbdStartLine >= fBlockStartLine
+  )
+}

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

@@ -1,4 +1,3 @@
 | test.cpp:2:2:2:12 | goto ... | This statement makes $@ unreachable. | test.cpp:3:2:3:5 | ExprStmt | ExprStmt |
 | test.cpp:9:3:9:8 | break; | This statement makes $@ unreachable. | test.cpp:10:3:10:6 | ExprStmt | ExprStmt |
 | test.cpp:37:3:37:8 | break; | This statement makes $@ unreachable. | test.cpp:38:3:38:11 | return ... | return ... |
-| test.cpp:91:2:91:11 | goto ... | This statement makes $@ unreachable. | test.cpp:93:2:93:5 | ExprStmt | ExprStmt |

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

@@ -88,7 +88,7 @@ void test8() {
 	int x = 0;
 
 #ifdef CONFIG_DEFINE
-	goto skip; // GOOD (the `x++` is still reachable in some configurations) [FALSE POSITIVE]
+	goto skip; // GOOD (the `x++` is still reachable in some configurations)
 #endif
 	x++;