As of r202325, CFGBlock predecessors may be NULL. Ignore such preds. Fixes a crasher, PR18983.

llvm-svn: 202340

clang/lib/Sema/AnalysisBasedWarnings.cpp

@@ -887,6 +887,7 @@ namespace {
       while (!BlockQueue.empty()) {
         const CFGBlock *P = BlockQueue.front();
         BlockQueue.pop_front();
+        if (!P) continue;
 
         const Stmt *Term = P->getTerminator();
         if (Term && isa<SwitchStmt>(Term))

clang/test/SemaCXX/switch-implicit-fallthrough.cpp

@@ -265,3 +265,16 @@ void fallthrough_in_local_class() {
   };
 }
 
+namespace PR18983 {
+  void fatal() __attribute__((noreturn));
+  int num();
+  void test() {
+    switch (num()) {
+    case 1:
+      fatal();
+      // Don't issue a warning.
+    case 2:
+      break;
+    }
+  }
+}