From 5c36442c4781fac97edfd196c9aa15dd35084a65 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Mon, 24 Mar 2014 22:14:12 +0100
Subject: Transform for normalizing type tests and type casts

To be executed before erasure.
---
 .../tools/dotc/transform/TypeTestsCasts.scala      | 101 +++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 src/dotty/tools/dotc/transform/TypeTestsCasts.scala

diff --git a/src/dotty/tools/dotc/transform/TypeTestsCasts.scala b/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
new file mode 100644
index 000000000..1c453750e
--- /dev/null
+++ b/src/dotty/tools/dotc/transform/TypeTestsCasts.scala
@@ -0,0 +1,101 @@
+package dotty.tools.dotc
+package transform
+
+import TreeTransforms._
+import core.DenotTransformers._
+import core.Denotations._
+import core.SymDenotations._
+import core.Contexts._
+import core.Symbols._
+import core.Types._
+import core.Constants._
+import core.StdNames._
+import core.transform.Erasure.isUnboundedGeneric
+import typer.ErrorReporting._
+import ast.Trees._
+
+/** This transform normalizes type tests and type casts.
+ *  Any remaining type tests
+ *   - use the object methods $isInstanceOf and $asInstanceOf
+ *   - have a reference type as receiver
+ *   - can be translated directly to machine instructions
+ */
+class TypeTestsCasts extends TreeTransform {
+  import ast.tpd._
+
+  def box(tree: Tree): Tree = ???
+
+  override def name: String = "typeTestsCasts"
+
+  override def transformTypeApply(tree: TypeApply)(implicit ctx: Context, info: TransformerInfo): Tree = ctx.traceIndented(s"transforming ${tree.show}", show = true) {
+    tree.fun match {
+      case fun @ Select(qual, selector) =>
+        val sym = tree.symbol
+
+        def isPrimitive(tp: Type) = tp.classSymbol.isPrimitiveValueClass
+
+        def derivedTree(qual1: Tree, sym: Symbol) =
+          cpy.TypeApply(tree, Select(qual1, sym) withPos qual.pos, tree.args)
+
+        def qualCls = qual.tpe.classSymbol
+
+        def transformIsInstanceOf(argType: Type): Tree = {
+          if (qual.tpe <:< argType)
+            Literal(Constant(true)) withPos tree.pos
+          else if (qualCls.isPrimitiveValueClass) {
+            val argCls = argType.classSymbol
+            if (argCls.isPrimitiveValueClass) Literal(Constant(qualCls == argCls))
+            else errorTree(tree, "isInstanceOf cannot test if value types are references")
+          }
+          else argType.dealias match {
+            case _: SingletonType =>
+              val cmpOp = if (argType derivesFrom defn.AnyValClass) defn.Any_equals else defn.Object_eq
+              Apply(Select(qual, cmpOp), singleton(argType) :: Nil)
+            case AndType(tp1, tp2) =>
+              evalOnce(fun) { fun =>
+                val erased1 = transformIsInstanceOf(tp1)
+                val erased2 = transformIsInstanceOf(tp2)
+                erased1 match {
+                  case Literal(Constant(true)) => erased2
+                  case _ =>
+                    erased2 match {
+                      case Literal(Constant(true)) => erased1
+                      case _ => mkAnd(erased1, erased2)
+                    }
+                }
+              }
+            case defn.MultiArrayType(elem, ndims) if isUnboundedGeneric(elem) =>
+              def isArrayTest(arg: Tree) =
+                runtimeCall(nme.isArray, arg :: Literal(Constant(ndims)) :: Nil)
+              if (ndims == 1) isArrayTest(qual)
+              else evalOnce(qual) { qual1 =>
+                mkAnd(derivedTree(qual1, defn.Object_isInstanceOf), isArrayTest(qual1))
+              }
+            case _ =>
+              derivedTree(qual, defn.Object_isInstanceOf)
+          }
+        }
+
+        def transformAsInstanceOf(argType: Type): Tree = {
+          if (qual.tpe <:< argType)
+            Typed(qual, tree.args.head)
+          else if (qualCls.isPrimitiveValueClass) {
+            val argCls = argType.classSymbol
+            if (argCls.isPrimitiveValueClass) numericConversion(qual, argCls)
+            else derivedTree(box(qual), defn.Object_asInstanceOf)
+          }
+          else
+            derivedTree(qual, defn.Object_asInstanceOf)
+        }
+
+        if (sym eq defn.Any_isInstanceOf)
+          transformIsInstanceOf(tree.args.head.tpe)
+        else if (defn.asInstanceOfMethods contains sym)
+          transformAsInstanceOf(tree.args.head.tpe)
+        else tree
+
+      case _ =>
+        tree
+    }
+  }
+}
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