diff --git a/llvm/include/llvm/Support/Regex.h b/llvm/include/llvm/Support/Regex.h
--- a/llvm/include/llvm/Support/Regex.h
+++ b/llvm/include/llvm/Support/Regex.h
@@ -44,6 +44,9 @@
 
     Regex();
     /// Compiles the given regular expression \p Regex.
+    ///
+    /// \param Regex - referenced string lifetime is no longer needed after this
+    /// constructor does finish.  Only its compiled form is kept stored.
     Regex(StringRef Regex, unsigned Flags = NoFlags);
     Regex(const Regex &) = delete;
     Regex &operator=(Regex regex) {