AsmParser: Don't allow null bytes in BB labels

Since Value objects can't have null bytes in their name, we shouldn't
allow them in the labels of basic blocks.

llvm-svn: 223907

llvm/lib/AsmParser/LLLexer.cpp

@@ -393,7 +393,12 @@ lltok::Kind LLLexer::LexQuote() {
 
   if (CurPtr[0] == ':') {
     ++CurPtr;
-    kind = lltok::LabelStr;
+    if (StringRef(StrVal).find_first_of(0) != StringRef::npos) {
+      Error("Null bytes are not allowed in names");
+      kind = lltok::Error;
+    } else {
+      kind = lltok::LabelStr;
+    }
   }
 
   return kind;