Fixed logic error in UnreachableCodeChecker's marking algorithm that would sometimes allow for multiple sequential statements to be flagged.

llvm-svn: 110353

clang/lib/Checker/UnreachableCodeChecker.cpp

@@ -149,10 +149,13 @@ void UnreachableCodeChecker::FindUnreachableEntryPoints(const CFGBlock *CB) {
   for (CFGBlock::const_pred_iterator I = CB->pred_begin(); I != CB->pred_end();
       ++I) {
     // Recurse over all unreachable blocks
-    if (!reachable.count((*I)->getBlockID())
-        && !visited.count((*I)->getBlockID())) {
-      FindUnreachableEntryPoints(*I);
+    if (!reachable.count((*I)->getBlockID())) {
+      // At least one predeccessor was unreachable
       allPredecessorsReachable = false;
+
+      // Only visit the block once
+      if (!visited.count((*I)->getBlockID()))
+        FindUnreachableEntryPoints(*I);
     }
   }
 

clang/test/Analysis/unreachable-code-path.c

@@ -88,3 +88,17 @@ void test8() {
   a = 5;
 }
 
+// Check for bugs where multiple statements are reported
+void test9(unsigned a) {
+  switch (a) {
+    if (a) // expected-warning{{never executed}}
+      foo(a + 5); // no-warning
+    else // no-warning
+      foo(a); // no-warning
+    case 1:
+    case 2:
+      break;
+    default:
+      break;
+  }
+}