Performance tweak: check presence of apply

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/SpecializeFunctions.scala

@@ -25,11 +25,11 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
   /** Transforms the type to include decls for specialized applys  */
   override def transformInfo(tp: Type, sym: Symbol)(using Context) = tp match {
     case tp: ClassInfo =>
-      val newApplys = new mutable.ListBuffer[Symbol]
       val apply = tp.decls.lookup(nme.apply)
-
       if (!apply.exists) return tp
 
+      val newApplys = new mutable.ListBuffer[Symbol]
+
       var arity = 0
       while (arity < 3) {
         val func = defn.FunctionClass(arity)
@@ -72,7 +72,8 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
   override def transformTemplate(tree: Template)(using Context) = {
     val cls = tree.symbol.owner.asClass
 
-    if (!derivesFromFn012(cls)) return tree
+    val apply = cls.info.decls.lookup(nme.apply)
+    if (!apply.exists || !derivesFromFn012(cls)) return tree
 
     val applyBuf = new mutable.ListBuffer[Tree]
     val newBody = tree.body.mapConserve {