Speed up LazyVals isCompanion needed

Brings time to compile stdlib down from 185s to 44s.

Author: odersky

src/dotty/tools/dotc/core/Types.scala

@@ -609,7 +609,7 @@ object Types {
         (name, buf) => buf ++= member(name).altsWith(x => !x.is(Method)))
     }
 
-    /** The set of members  of this type  having at least one of `requiredFlags` but none of  `excludedFlags` set */
+    /** The set of members of this type having at least one of `requiredFlags` but none of `excludedFlags` set */
     final def membersBasedOnFlags(requiredFlags: FlagSet, excludedFlags: FlagSet)(implicit ctx: Context): Seq[SingleDenotation] = track("implicitMembers") {
       memberDenots(takeAllFilter,
         (name, buf) => buf ++= member(name).altsWith(x => x.is(requiredFlags, butNot = excludedFlags)))

src/dotty/tools/dotc/transform/LazyVals.scala

@@ -48,7 +48,7 @@ class LazyVals extends MiniPhaseTransform with IdentityDenotTransformer with Nee
   override def runsAfter = Set(classOf[Mixin])
 
   def isCompanionNeeded(cls: ClassSymbol)(implicit ctx: Context): Boolean = {
-    def hasLazyVal(x: ClassSymbol) = x.classInfo.membersBasedOnFlags(Flags.Lazy, excludedFlags = Flags.EmptyFlags).nonEmpty
+    def hasLazyVal(cls: ClassSymbol) = cls.info.decls.exists(_.is(Flags.Lazy))
     hasLazyVal(cls) || cls.mixins.exists(hasLazyVal)
   }