Small optimization

Author: odersky

compiler/src/dotty/tools/dotc/typer/Inferencing.scala

@@ -45,7 +45,8 @@ object Inferencing {
 
   /** Instantiate selected type variables `tvars` in type `tp` */
   def instantiateSelected(tp: Type, tvars: List[Type])(implicit ctx: Context): Unit =
-    new IsFullyDefinedAccumulator(new ForceDegree.Value(tvars.contains, minimizeAll = true)).process(tp)
+    if (tvars.nonEmpty)
+      new IsFullyDefinedAccumulator(new ForceDegree.Value(tvars.contains, minimizeAll = true)).process(tp)
 
   /** Instantiate any type variables in `tp` whose bounds contain a reference to
    *  one of the parameters in `tparams` or `vparamss`.