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, 16 insertions, 0 deletions

diff --git a/tests/neg/tailcall/t1672b.check b/tests/neg/tailcall/t1672b.check
new file mode 100644
index 000000000..60ccf7717
--- /dev/null
+++ b/tests/neg/tailcall/t1672b.check
@@ -0,0 +1,16 @@
+t1672b.scala:3: error: could not optimize @tailrec annotated method bar: it contains a recursive call not in tail position
+  def bar : Nothing = {
+      ^
+t1672b.scala:14: error: could not optimize @tailrec annotated method baz: it contains a recursive call not in tail position
+  def baz : Nothing = {
+      ^
+t1672b.scala:29: error: could not optimize @tailrec annotated method boz: it contains a recursive call not in tail position
+      case _: Throwable => boz; ???
+                                ^
+t1672b.scala:34: error: could not optimize @tailrec annotated method bez: it contains a recursive call not in tail position
+  def bez : Nothing = {
+      ^
+t1672b.scala:46: error: could not optimize @tailrec annotated method bar: it contains a recursive call not in tail position
+    else 1 + (try {
+           ^
+5 errors found