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, 3 insertions, 0 deletions

diff --git a/tests/neg/tailcall/t3275.scala b/tests/neg/tailcall/t3275.scala
new file mode 100644
index 000000000..18e38a1a9
--- /dev/null
+++ b/tests/neg/tailcall/t3275.scala
@@ -0,0 +1,3 @@
+object Test {
+  @annotation.tailrec def foo() = 5
+}