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, 0 insertions, 26 deletions

diff --git a/tests/untried/pos/t6891.scala b/tests/untried/pos/t6891.scala
deleted file mode 100644
index bed2d0d77..000000000
--- a/tests/untried/pos/t6891.scala
+++ /dev/null
@@ -1,26 +0,0 @@
-object O {
-  implicit class Foo[A](val value: String) extends AnyVal {
-    def bippy() = {
-      @annotation.tailrec def loop(x: A): Unit = loop(x)
-      ()
-    }
-
-    def boppy() = {
-      @annotation.tailrec def loop(x: value.type): Unit = loop(x)
-      ()
-    }
-
-    def beppy[C](c: => C) = {
-      () => c
-      @annotation.tailrec def loop(x: value.type): Unit = loop(x)
-        () => c
-      ()
-    }
-  }
-  // uncaught exception during compilation: Types$TypeError("type mismatch;
-  //  found   : A(in method bippy$extension)
-  //  required: A(in class Foo)") @ scala.tools.nsc.typechecker.Contexts$Context.issueCommon(Contexts.scala:396)
-  // error: scala.reflect.internal.Types$TypeError: type mismatch;
-  //  found   : A(in method bippy$extension)
-  //  required: A(in class Foo)
-}