TailRec phase and tests for it.

Ported tailcall phase from scalac with such changes:
  - all transformation is done in the phase itself
     (previously half of the work was done in backend)
  - it is now able to run before uncurry
  - it is now a treeTransform
  - renamed to tailrec to make it more obvious that
     this phase transforms only recursive calls.

For now this is a single phase which speculatively
transforms DefDefs.
Speculation can be potentially removed by
splitting into 2 phases:
  one detecting which methods should be transformed
  second performing transformation.

But, as transformation requires as same amount of work
as detection, I believe it will be simpler to maintain
it as a single phase.

Conflicts:
	tests/pos/typers.scala

1 files changed, 29 insertions, 0 deletions

diff --git a/tests/neg/tailcall/tailrec-2.scala b/tests/neg/tailcall/tailrec-2.scala
new file mode 100644
index 000000000..d6b8b1355
--- /dev/null
+++ b/tests/neg/tailcall/tailrec-2.scala
@@ -0,0 +1,29 @@
+sealed abstract class Super[+A] {
+  def f[B >: A](mem: List[B]) : List[B]
+  def g(mem: List[_]) = ???
+}
+// This one should fail, target is a supertype
+class Bop1[+A](val element: A) extends Super[A] {
+
+  @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Super[A]).f(mem)
+  @annotation.tailrec final def f1[B >: A](mem: List[B]): List[B] = this.g(mem)
+}
+// These succeed
+class Bop2[+A](val element: A) extends Super[A] {
+  @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Bop2[A]).f(mem)
+}
+object Bop3 extends Super[Nothing] {
+  @annotation.tailrec final def f[B](mem: List[B]): List[B] = (null: Bop3.type).f(mem)
+}
+class Bop4[+A](val element: A) extends Super[A] {
+  @annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = Other.f[A].f(mem)
+}
+
+object Other {
+  def f[T] : Bop4[T] = sys.error("")
+}
+
+object Bop {
+  def m1[A] : Super[A] = sys.error("")
+  def m2[A] : Bop2[A] = sys.error("")
+}