Here is another case where the optimizer in scala 2.11.x is generating incorrect code:

class Bust(val x: Long) {
  def sameDirection(y: Long): Boolean = 
    (y == 0 || x == 0 || ((y > 0) == (x > 0)))
}

object Bust {
  def main(args: Array[String]) {
    val b = new Bust(1L)
    assert(!b.sameDirection(-1L))
  }
}

This should clearly run without error, but the assertion fails in 2.11.x when -optimise is specified. It works fine if -optimise is left off, and it works fine in scala 2.10.x.

I also tried this with the latest scala nightly build (scala-2.11.8-7492bda-nightly), but it still fails.