Merge pull request #2173 from ianpartridge/string-data-conversion-perf

Author: swift-ci

Foundation/NSStringAPI.swift

@@ -800,9 +800,14 @@ extension StringProtocol where Index == String.Index {
         using encoding: String.Encoding,
         allowLossyConversion: Bool = false
         ) -> Data? {
-        return _ns.data(
-            using: encoding.rawValue,
-            allowLossyConversion: allowLossyConversion)
+        switch encoding {
+        case .utf8:
+            return Data(self.utf8)
+        default:
+            return _ns.data(
+                using: encoding.rawValue,
+                allowLossyConversion: allowLossyConversion)
+        }
     }
 
     // @property NSString* decomposedStringWithCanonicalMapping;