Eliminate allocations in Trees.

2 files changed, 9 insertions, 4 deletions

diff --git a/src/reflect/scala/reflect/api/Trees.scala b/src/reflect/scala/reflect/api/Trees.scala
index 94226ae866..05458cb311 100644
--- a/src/reflect/scala/reflect/api/Trees.scala
+++ b/src/reflect/scala/reflect/api/Trees.scala
@@ -2951,8 +2951,10 @@ trait Trees { self: Universe =>
         if (exprOwner != currentOwner && stat.isTerm) atOwner(exprOwner)(transform(stat))
         else transform(stat)) filter (EmptyTree != _)
     /** Transforms `Modifiers`. */
-    def transformModifiers(mods: Modifiers): Modifiers =
-      mods.mapAnnotations(transformTrees)
+    def transformModifiers(mods: Modifiers): Modifiers = {
+      if (mods.annotations.isEmpty) mods
+      else mods mapAnnotations transformTrees
+    }
 
     /** Transforms a tree with a given owner symbol. */
     def atOwner[A](owner: Symbol)(trans: => A): A = {
diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index 9e737528d2..870c1ec5ed 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -926,8 +926,11 @@ trait Trees extends api.Trees { self: SymbolTable =>
     def withPosition(flag: Long, position: Position) =
       copy() setPositions positions + (flag -> position)
 
-    override def mapAnnotations(f: List[Tree] => List[Tree]): Modifiers =
-      Modifiers(flags, privateWithin, f(annotations)) setPositions positions
+    override def mapAnnotations(f: List[Tree] => List[Tree]): Modifiers = {
+      val newAnns = f(annotations)
+      if (annotations == newAnns) this
+      else Modifiers(flags, privateWithin, newAnns) setPositions positions
+    }
 
     override def toString = "Modifiers(%s, %s, %s)".format(flagString, annotations mkString ", ", positions)
   }