test/files/run/t5313.scala


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import scala.tools.partest.IcodeComparison

object Test extends IcodeComparison {
  override def printIcodeAfterPhase = "dce"

  override def extraSettings: String = super.extraSettings + " -optimize"

  override def code =
    """class Foo {
      def randomBoolean = scala.util.Random.nextInt % 2 == 0
      def bar = {
        var kept1 = new Object
        val result = new java.lang.ref.WeakReference(kept1)
        kept1 = null // we can't eliminate this assignment because result can observe
                   // when the object has no more references. See SI-5313
        kept1 = new Object // but we can eliminate this one because kept1 has already been clobbered
        var erased2 = null // we can eliminate this store because it's never used
        val erased3 = erased2 // and this
        var erased4 = erased2 // and this
        val erased5 = erased4 // and this
        var kept2: Object = new Object // ultimately can't be eliminated
        while(randomBoolean) {
          val kept3 = kept2
          kept2 = null // this can't, because it clobbers kept2, which is used
          erased4 = null // safe to eliminate
          println(kept3)
        }
        var kept4 = new Object // have to keep, it's used
        try
          println(kept4)
        catch {
          case _ : Throwable => kept4 = null // have to keep, it clobbers kept4 which is used
        }
        var kept5 = new Object
        print(kept5)
        kept5 = null // can't eliminate it's a clobber and it's used
        print(kept5)
        kept5 = null // can eliminate because we don't care about clobbers of nulls
        while(randomBoolean) {
          var kept6: AnyRef = null // not used, but have to keep because it clobbers the next used store
                                   // on the back edge of the loop
          kept6 = new Object // used
          println(kept6)
        }
        result
      }
    }""".stripMargin

  override def show() {
    val storeLocal = "STORE_LOCAL"
    val lines1 = collectIcode() filter (_ contains storeLocal) map (x => x.drop(x.indexOf(storeLocal)))
    println(lines1 mkString "\n")
  }
}