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, 14 insertions, 0 deletions

diff --git a/tests/neg/tailcall/tailrec-3.scala b/tests/neg/tailcall/tailrec-3.scala
new file mode 100644
index 000000000..20361658e
--- /dev/null
+++ b/tests/neg/tailcall/tailrec-3.scala
@@ -0,0 +1,14 @@
+import annotation.tailrec
+
+object Test {
+  @tailrec private def quux(xs: List[String]): List[String] = quux(quux(xs))
+  @tailrec private def quux2(xs: List[String]): List[String] = xs match {
+    case x1 :: x2 :: rest => quux2(x1 :: quux2(rest))
+    case _                => Nil
+  }
+  @tailrec private def quux3(xs: List[String]): Boolean = xs match {
+    case x :: xs if quux3(List("abc"))  => quux3(xs)
+    case _                              => false
+  }
+}
+