[analyzer] Tweak the UnreachableCode checker to not warning about unreachable default blocks. Patch by Cyril Roelandt!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151709 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 25 insertions, 0 deletions

diff --git a/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp b/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
index 2b550df2b9..8ac785ce7d 100644
--- a/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/UnreachableCodeChecker.cpp
@@ -116,6 +116,14 @@ void UnreachableCodeChecker::checkEndAnalysis(ExplodedGraph &G,
     if (CB->size() > 0 && isInvalidPath(CB, *PM))
       continue;
 
+    // It is good practice to always have a "default" label in a "switch", even
+    // if we should never get there. It can be used to detect errors, for
+    // instance. Unreachable code directly under a "default" label is therefore
+    // likely to be a false positive.
+    if (const Stmt *label = CB->getLabel())
+      if (label->getStmtClass() == Stmt::DefaultStmtClass)
+        continue;
+
     // Special case for __builtin_unreachable.
     // FIXME: This should be extended to include other unreachable markers,
     // such as llvm_unreachable.
diff --git a/test/Analysis/unreachable-code-path.c b/test/Analysis/unreachable-code-path.c
index da14f4c010..48a3462ca1 100644
--- a/test/Analysis/unreachable-code-path.c
+++ b/test/Analysis/unreachable-code-path.c
@@ -122,3 +122,20 @@ void test10() {
   goto d;
   f: ;
 }
+
+// test11: we can actually end up in the default case, even if it is not
+// obvious: there might be something wrong with the given argument.
+enum foobar { FOO, BAR };
+extern void error();
+void test11(enum foobar fb) {
+  switch (fb) {
+    case FOO:
+      break;
+    case BAR:
+      break;
+    default:
+      error(); // no-warning
+      return;
+      error(); // expected-warning {{never executed}}
+  }
+}