forgot Vec8d []

dune/perftool/common/vectorclass.hh

@@ -689,6 +689,10 @@ struct Vec8d
     return _d[index];
   }
 
+  F operator [] (uint32_t index) const {
+    return extract(index);
+  }
+
   constexpr static int size()
   {
     return 8;