Eliminate allocations in Trees and Symbols.

2 files changed, 13 insertions, 2 deletions

diff --git a/src/reflect/scala/reflect/api/Trees.scala b/src/reflect/scala/reflect/api/Trees.scala
index 05458cb311..0b44d6a237 100644
--- a/src/reflect/scala/reflect/api/Trees.scala
+++ b/src/reflect/scala/reflect/api/Trees.scala
@@ -2921,7 +2921,8 @@ trait Trees { self: Universe =>
     def transform(tree: Tree): Tree = itransform(this, tree)
 
     /** Transforms a list of trees. */
-    def transformTrees(trees: List[Tree]): List[Tree] = trees mapConserve transform
+    def transformTrees(trees: List[Tree]): List[Tree] =
+      if (trees.isEmpty) Nil else trees mapConserve transform
 
     /** Transforms a `Template`. */
     def transformTemplate(tree: Template): Template =
diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index fd5c3909b8..3d43500ef1 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -2048,7 +2048,17 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     /** Returns all symbols overriden by this symbol. */
     final def allOverriddenSymbols: List[Symbol] = (
       if ((this eq NoSymbol) || !owner.isClass) Nil
-      else owner.ancestors map overriddenSymbol filter (_ != NoSymbol)
+      else {
+        def loop(xs: List[Symbol]): List[Symbol] = xs match {
+          case Nil     => Nil
+          case x :: xs =>
+            overriddenSymbol(x) match {
+              case NoSymbol => loop(xs)
+              case sym      => sym :: loop(xs)
+            }
+        }
+        loop(owner.ancestors)
+      }
     )
 
     /** Equivalent to allOverriddenSymbols.nonEmpty, but more efficient. */