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

22 files changed, 21 insertions, 16 deletions

diff --git a/tests/untried/neg/t1672b.check b/tests/neg/tailcall/t1672b.check
index 60ccf7717..60ccf7717 100644
--- a/tests/untried/neg/t1672b.check
+++ b/tests/neg/tailcall/t1672b.check
diff --git a/tests/untried/neg/t1672b.scala b/tests/neg/tailcall/t1672b.scala
index 0ccdd0363..f05d05c34 100644
--- a/tests/untried/neg/t1672b.scala
+++ b/tests/neg/tailcall/t1672b.scala
@@ -1,4 +1,4 @@
-object Test {
+object Test1772B {
   @annotation.tailrec
   def bar : Nothing = {
     try {
diff --git a/tests/untried/neg/t3275.check b/tests/neg/tailcall/t3275.check
index 117c79232..117c79232 100644
--- a/tests/untried/neg/t3275.check
+++ b/tests/neg/tailcall/t3275.check
diff --git a/tests/untried/neg/t3275.scala b/tests/neg/tailcall/t3275.scala
index 18e38a1a9..18e38a1a9 100644
--- a/tests/untried/neg/t3275.scala
+++ b/tests/neg/tailcall/t3275.scala
diff --git a/tests/untried/neg/t6574.check b/tests/neg/tailcall/t6574.check
index c67b4ed80..c67b4ed80 100644
--- a/tests/untried/neg/t6574.check
+++ b/tests/neg/tailcall/t6574.check
diff --git a/tests/untried/neg/t6574.scala b/tests/neg/tailcall/t6574.scala
index 9e1d624e5..59f3108ad 100644
--- a/tests/untried/neg/t6574.scala
+++ b/tests/neg/tailcall/t6574.scala
@@ -4,7 +4,7 @@ class Bad[X, Y](val v: Int) extends AnyVal {
     println("tail")
   }
 
-  @annotation.tailrec final def differentTypeArgs {: Unit = 
+  @annotation.tailrec final def differentTypeArgs : Unit = { 
     {(); new Bad[String, Unit](0)}.differentTypeArgs
   }
 }
diff --git a/tests/untried/neg/tailrec-2.check b/tests/neg/tailcall/tailrec-2.check
index 1daad6922..1daad6922 100644
--- a/tests/untried/neg/tailrec-2.check
+++ b/tests/neg/tailcall/tailrec-2.check
diff --git a/tests/untried/neg/tailrec-2.scala b/tests/neg/tailcall/tailrec-2.scala
index d6b8b1355..d6b8b1355 100644
--- a/tests/untried/neg/tailrec-2.scala
+++ b/tests/neg/tailcall/tailrec-2.scala
diff --git a/tests/untried/neg/tailrec-3.check b/tests/neg/tailcall/tailrec-3.check
index a3542fb56..a3542fb56 100644
--- a/tests/untried/neg/tailrec-3.check
+++ b/tests/neg/tailcall/tailrec-3.check
diff --git a/tests/untried/neg/tailrec-3.scala b/tests/neg/tailcall/tailrec-3.scala
index 20361658e..20361658e 100644
--- a/tests/untried/neg/tailrec-3.scala
+++ b/tests/neg/tailcall/tailrec-3.scala
diff --git a/tests/untried/neg/tailrec.check b/tests/neg/tailcall/tailrec.check
index 946d3421e..946d3421e 100644
--- a/tests/untried/neg/tailrec.check
+++ b/tests/neg/tailcall/tailrec.check
diff --git a/tests/untried/neg/tailrec.scala b/tests/neg/tailcall/tailrec.scala
index 83a0c1a9e..83a0c1a9e 100644
--- a/tests/untried/neg/tailrec.scala
+++ b/tests/neg/tailcall/tailrec.scala
diff --git a/tests/pos/tailcall/t1672.scala b/tests/pos/tailcall/t1672.scala
new file mode 100644
index 000000000..9be5c6066
--- /dev/null
+++ b/tests/pos/tailcall/t1672.scala
@@ -0,0 +1,10 @@
+object Test1672 {
+  @annotation.tailrec
+  def bar(x: Int)(y: Int) : Nothing = {
+    try {
+      throw new RuntimeException
+    } catch {
+      case _: Throwable => bar(x)(y)
+    }
+  }
+}
diff --git a/tests/untried/pos/t4649.flags b/tests/pos/tailcall/t4649.flags
index e8fb65d50..e8fb65d50 100644
--- a/tests/untried/pos/t4649.flags
+++ b/tests/pos/tailcall/t4649.flags
diff --git a/tests/untried/pos/t4649.scala b/tests/pos/tailcall/t4649.scala
index 0d6caa8d7..5f009b7a4 100644
--- a/tests/untried/pos/t4649.scala
+++ b/tests/pos/tailcall/t4649.scala
@@ -1,4 +1,4 @@
-object Test {
+object Test4649 {
   // @annotation.tailrec
   def lazyFilter[E](s: Stream[E], p: E => Boolean): Stream[E] = s match {
     case h #:: t => if (p(h)) h #:: lazyFilter(t, p) else lazyFilter(t, p)
diff --git a/tests/untried/pos/t6479.scala b/tests/pos/tailcall/t6479.scala
index e4a4ff601..e4a4ff601 100644
--- a/tests/untried/pos/t6479.scala
+++ b/tests/pos/tailcall/t6479.scala
diff --git a/tests/untried/pos/t6574.scala b/tests/pos/tailcall/t6574.scala
index 6bb0042c6..cd0fdbb8d 100644
--- a/tests/untried/pos/t6574.scala
+++ b/tests/pos/tailcall/t6574.scala
@@ -4,7 +4,7 @@ class Bad[X, Y](val v: Int) extends AnyVal {
     this.foo[Z](a)(b)
   }
 
-  @annotation.tailrec final def differentReceiver {: Unit = 
+  @annotation.tailrec final def differentReceiver : Unit = {
     {(); new Bad[X, Y](0)}.differentReceiver
   }
 
diff --git a/tests/untried/pos/t6891.flags b/tests/pos/tailcall/t6891.flags
index fe048006a..fe048006a 100644
--- a/tests/untried/pos/t6891.flags
+++ b/tests/pos/tailcall/t6891.flags
diff --git a/tests/untried/pos/t6891.scala b/tests/pos/tailcall/t6891.scala
index bed2d0d77..edbe6f097 100644
--- a/tests/untried/pos/t6891.scala
+++ b/tests/pos/tailcall/t6891.scala
@@ -1,4 +1,4 @@
-object O {
+object O6891 {
   implicit class Foo[A](val value: String) extends AnyVal {
     def bippy() = {
       @annotation.tailrec def loop(x: A): Unit = loop(x)
diff --git a/tests/pos/tailcall/tailcall.scala b/tests/pos/tailcall/tailcall.scala
new file mode 100644
index 000000000..9cf373cf0
--- /dev/null
+++ b/tests/pos/tailcall/tailcall.scala
@@ -0,0 +1,5 @@
+class tailcall {
+  val shift = 1
+  final def fact(x: Int, acc: Int = 1): Int = if (x == 0) acc else fact(x - shift, acc * x)
+  def id[T <: AnyRef](x: T): T = if (x eq null) x else id(x)
+}
diff --git a/tests/pos/typers.scala b/tests/pos/typers.scala
index 4f012e7bf..a95af558e 100644
--- a/tests/pos/typers.scala
+++ b/tests/pos/typers.scala
@@ -77,7 +77,7 @@ object typers {
 
   class C {
 
-    @tailrec def factorial(acc: Int, n: Int): Int = (n: @switch) match {
+    @tailrec final def factorial(acc: Int, n: Int): Int = (n: @switch) match {
       case 0 => acc
       case _ => factorial(acc * n, n - 1)
     }
diff --git a/tests/untried/pos/t1672.scala b/tests/untried/pos/t1672.scala
deleted file mode 100644
index 5ee6bb175..000000000
--- a/tests/untried/pos/t1672.scala
+++ /dev/null
@@ -1,10 +0,0 @@
-object Test {
-  @annotation.tailrec
-  def bar : Nothing = {
-    try {
-      throw new RuntimeException
-    } catch {
-      case _: Throwable => bar
-    }
-  }
-}