1 files changed, 16 insertions, 2 deletions
diff --git a/include/llvm/ADT/StringRef.h b/include/llvm/ADT/StringRef.h
index 4661b1e68b2f..52baab17bede 100644
--- a/include/llvm/ADT/StringRef.h
+++ b/include/llvm/ADT/StringRef.h
@@ -67,6 +67,20 @@ namespace llvm {
       return ::memcmp(Lhs,Rhs,Length);
     }
 
+    // Constexpr version of std::strlen.
+    static constexpr size_t strLen(const char *Str) {
+#if __cplusplus > 201402L
+      return std::char_traits<char>::length(Str);
+#elif __has_builtin(__builtin_strlen) || defined(__GNUC__)
+      return __builtin_strlen(Str);
+#else
+      const char *Begin = Str;
+      while (*Str != '\0')
+        ++Str;
+      return Str - Begin;
+#endif
+    }
+
   public:
     /// @name Constructors
     /// @{
@@ -79,8 +93,8 @@ namespace llvm {
     StringRef(std::nullptr_t) = delete;
 
     /// Construct a string ref from a cstring.
-    /*implicit*/ StringRef(const char *Str)
-        : Data(Str), Length(Str ? ::strlen(Str) : 0) {}
+    /*implicit*/ constexpr StringRef(const char *Str)
+        : Data(Str), Length(Str ? strLen(Str) : 0) {}
 
     /// Construct a string ref from a pointer and length.
     /*implicit*/ constexpr StringRef(const char *data, size_t length)