Merge pull request #4036 from retronym/topic/opt-tail-calls

SI-8893 Restore linear perf in TailCalls with nested matches

3 files changed, 184 insertions, 0 deletions

diff --git a/test/files/pos/t8893.scala b/test/files/pos/t8893.scala
new file mode 100644
index 0000000000..b87c8bdd3c
--- /dev/null
+++ b/test/files/pos/t8893.scala
@@ -0,0 +1,129 @@
+// Took > 10 minutes to run the tail call phase.
+object Test {
+    def a(): Option[String] = Some("a")
+
+    def main(args: Array[String]) {
+        a() match {
+            case Some(b1) =>
+        a() match {
+            case Some(b2) =>
+        a() match {
+            case Some(b3) =>
+        a() match {
+            case Some(b4) =>
+        a() match {
+            case Some(b5) =>
+        a() match {
+            case Some(b6) =>
+        a() match {
+            case Some(b7) =>
+        a() match {
+            case Some(b8) =>
+        a() match {
+            case Some(b9) =>
+        a() match {
+            case Some(b10) =>
+        a() match {
+            case Some(b11) =>
+        a() match {
+            case Some(b12) =>
+        a() match {
+            case Some(b13) =>
+        a() match {
+            case Some(b14) =>
+        a() match {
+            case Some(b15) =>
+        a() match {
+            case Some(b16) =>
+        a() match {
+            case Some(b17) =>
+        a() match {
+            case Some(b18) =>
+        a() match {
+            case Some(b19) =>
+        a() match {
+            case Some(b20) =>
+        a() match {
+            case Some(b21) =>
+        a() match {
+            case Some(b22) =>
+        a() match {
+            case Some(b23) =>
+        a() match {
+            case Some(b24) =>
+        a() match {
+            case Some(b25) =>
+        a() match {
+            case Some(b26) =>
+        a() match {
+            case Some(b27) =>
+        a() match {
+            case Some(b28) =>
+        a() match {
+            case Some(b29) =>
+        a() match {
+            case Some(b30) =>
+                println("yay")
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+            case None => None
+        }
+    }
+}
+
diff --git a/test/files/run/t8893.scala b/test/files/run/t8893.scala
new file mode 100644
index 0000000000..6fef8ae912
--- /dev/null
+++ b/test/files/run/t8893.scala
@@ -0,0 +1,40 @@
+import annotation.tailrec
+
+object Test {
+  def a(): Option[String] = Some("a")
+
+  def test1: Any = {
+    a() match {
+      case Some(b1) =>
+        a() match {
+          case Some(b2) =>
+            @tailrec
+            def tick(i: Int): Unit = if (i < 0) () else tick(i - 1)
+            tick(10000000) // testing that this doesn't SOE
+          case None => None
+        }
+      case None => None
+    }
+  }
+
+  def test2: Any = {
+    a() match {
+      case Some(b1) =>
+        a() match {
+          case Some(b2) =>
+            @tailrec
+            def tick(i: Int): Unit = if (i < 0) () else tick(i - 1)
+            tick(10000000) // testing that this doesn't SOE
+          case None => test1
+        }
+      case None =>
+        test1 // not a tail call
+        test1
+    }
+  }
+
+  def main(args: Array[String]) {
+    test1
+    test2
+  }
+}
diff --git a/test/files/run/t8893b.scala b/test/files/run/t8893b.scala
new file mode 100644
index 0000000000..19120871aa
--- /dev/null
+++ b/test/files/run/t8893b.scala
@@ -0,0 +1,15 @@
+// Testing that recursive calls in tail positions are replaced with
+// jumps, even though the method contains recursive calls outside
+// of the tail position.
+object Test {
+  def tick(i : Int): Unit =
+    if (i == 0) ()
+    else if (i == 42) {
+      tick(0) /*not in tail posiiton*/
+      tick(i - 1)
+    } else tick(i - 1)
+
+  def main(args: Array[String]): Unit = {
+    tick(1000000)
+  }
+}