Boxing cleanup: erasure, post-erasure, value classes.

Introduces extractors for value class trees. Puts them to
work to make the value class tree manipulations believable.
Eliminated some boxing code in erasure which had been
marked "maybe subsumed by posterasure?" after deciding
that it had been subsumed by posterasure.

Added some same-bytecode tests involving value class boxing
(actually the lack thereof.)

1 files changed, 21 insertions, 39 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/PostErasure.scala b/src/compiler/scala/tools/nsc/transform/PostErasure.scala
index a8dc47046b..2a86d711f1 100644
--- a/src/compiler/scala/tools/nsc/transform/PostErasure.scala
+++ b/src/compiler/scala/tools/nsc/transform/PostErasure.scala
@@ -9,10 +9,10 @@ package transform
  *  performs peephole optimizations.
  */
 trait PostErasure extends InfoTransform with TypingTransformers {
-
   val global: Global
+
   import global._
-  import definitions._
+  import treeInfo._
 
   val phaseName: String = "posterasure"
 
@@ -21,51 +21,33 @@ trait PostErasure extends InfoTransform with TypingTransformers {
 
   object elimErasedValueType extends TypeMap {
     def apply(tp: Type) = tp match {
-      case ConstantType(Constant(tp: Type)) =>
-        ConstantType(Constant(apply(tp)))
-      case ErasedValueType(tref) =>
-        enteringPhase(currentRun.erasurePhase)(erasure.erasedValueClassArg(tref))
-      case _ => mapOver(tp)
+      case ConstantType(Constant(tp: Type)) => ConstantType(Constant(apply(tp)))
+      case ErasedValueType(tref)            => enteringErasure(erasure.erasedValueClassArg(tref))
+      case _                                => mapOver(tp)
     }
   }
 
   def transformInfo(sym: Symbol, tp: Type) = elimErasedValueType(tp)
 
   class PostErasureTransformer(unit: CompilationUnit) extends TypingTransformer(unit) {
+    override def transform(tree: Tree) = {
+      def finish(res: Tree) = logResult(s"Posterasure reduction\n  Old: $tree\n  New")(res)
+
+      /** We use the name of the operation being performed and not the symbol
+       *  itself because the symbol hails from the boxed class, and this transformation
+       *  exists to operate directly on the values. So we are for instance looking
+       *  up == on an lhs of type Int, whereas the symbol which has been passed in
+       *  is from java.lang.Integer.
+       */
+      def binop(lhs: Tree, op: Symbol, rhs: Tree) =
+        finish(localTyper typed (Apply(Select(lhs, op.name) setPos tree.pos, rhs :: Nil) setPos tree.pos))
 
-    override def transform(tree: Tree) =
       super.transform(tree) setType elimErasedValueType(tree.tpe) match {
-        case // new C(arg).underlying  ==>  arg
-          Apply(sel @ Select(
-            Apply(Select(New(tpt), nme.CONSTRUCTOR), List(arg)),
-            acc), List())
-        if enteringPhase(currentRun.erasurePhase) {
-          tpt.tpe.typeSymbol.isDerivedValueClass &&
-          sel.symbol == tpt.tpe.typeSymbol.derivedValueClassUnbox
-        } =>
-          if (settings.debug.value) log("Removing "+tree+" -> "+arg)
-          arg
-        case // new C(arg1) == new C(arg2)  ==>  arg1 == arg2
-          Apply(sel @ Select(
-            Apply(Select(New(tpt1), nme.CONSTRUCTOR), List(arg1)),
-            cmp),
-            List(Apply(Select(New(tpt2), nme.CONSTRUCTOR), List(arg2))))
-        if enteringPhase(currentRun.erasurePhase) {
-          tpt1.tpe.typeSymbol.isDerivedValueClass &&
-          (sel.symbol == Object_== || sel.symbol == Object_!=) &&
-          tpt2.tpe.typeSymbol == tpt1.tpe.typeSymbol
-        } =>
-          val result = Apply(Select(arg1, cmp) setPos sel.pos, List(arg2)) setPos tree.pos
-          log("shortcircuiting equality "+tree+" -> "+result)
-          localTyper.typed(result)
-
-        case // arg.asInstanceOf[T]  ==>  arg      if arg.tpe == T
-          Apply(TypeApply(cast @ Select(arg, asinstanceof), List(tpt)), List())
-        if cast.symbol == Object_asInstanceOf && arg.tpe =:= tpt.tpe => // !!! <:< ?
-          if (settings.debug.value) log("Shortening "+tree+" -> "+arg)
-          arg
-        case tree1 =>
-          tree1
+        case AsInstanceOf(v, tpe) if v.tpe <:< tpe => finish(v)          // x.asInstanceOf[X]       ==> x
+        case ValueClass.BoxAndUnbox(v)             => finish(v)          // (new B(v)).unbox        ==> v
+        case ValueClass.BoxAndCompare(v1, op, v2)  => binop(v1, op, v2)  // new B(v1) == new B(v2)  ==> v1 == v2
+        case tree                                  => tree
       }
+    }
   }
 }