Fix/workaround for inliner bug uncovered by fin...

Fix/workaround for inliner bug uncovered by finalizing Option methods.
Something in the backend is leaving open but empty blocks in the
worklist. Rather than freaking out at the merest mention of an empty
block, I quietly remove the empty ones. A proper fix will involve not
leaving empty blocks lying around but we're on a schedule here people.
Review by dragos.

1 files changed, 30 insertions, 0 deletions

diff --git a/test/files/run/run-bug4840.scala b/test/files/run/run-bug4840.scala
new file mode 100644
index 0000000000..dda280fd17
--- /dev/null
+++ b/test/files/run/run-bug4840.scala
@@ -0,0 +1,30 @@
+object Test {
+  def g(x: Boolean): Option[String] = if (x) Some("booya") else None
+
+  def f1() = {
+    for (x <- g(true)) yield {
+      g(false) match {
+        case Some(_) => sys.error("")
+        case None    => 5
+      }
+    }
+  }
+
+  def f2() = {
+    for (x <- g(true) ; y <- g(true) ; z <- g(true)) yield {
+      for (x <- g(true) ; y <- g(true) ; z <- g(true)) yield {
+        g(true) map { _ =>
+          (null: Any) match {
+            case Some(x: Int) => x
+            case _            => 5
+          }
+        }
+      }
+    }
+  }
+
+  def main(args: Array[String]): Unit = {
+    println(f1())
+    println(f2())
+  }
+}