Optimise away local lazy vals that are not used

[nicolasstucki]

Compiling the following code with -optimise

object Test {
  def main(args: Array[String]): Unit = {
    lazy val foo = 1
  }
}

currently produces

 class Test$ extends Object { 
    def <init>(): Unit = 
      {
        super()
        ()
      }
    def main(args: String[]): Unit = 
      {
        lazy var foo$lzy1: dotty.runtime.LazyInt = new dotty.runtime.LazyInt()
        ()
      }
    private def foo$lzyINIT1$1(foo$lzy1$1: dotty.runtime.LazyInt): Int = 
      scala.Int.unbox(
        foo$lzy1$1.synchronized(
          scala.Int.box(
            if foo$lzy1$1.initialized() then foo$lzy1$1.value() else 
              {
                foo$lzy1$1.initialized_=(true)
                foo$lzy1$1.value_=(1)
                foo$lzy1$1.value()
              }
          )
        )
      )
    private lazy <accessor> def foo$1(foo$lzy1$2: dotty.runtime.LazyInt): Int = 
      if foo$lzy1$2.initialized() then foo$lzy1$2.value() else 
        Test.foo$lzyINIT1$1(foo$lzy1$2)
  }

The optimizer should be able to eliminate the declaration of foo$lzy1. Hopefully before the creation of foo$lzyINIT1$1 and foo$1.

[smarter]

Is this really useful? Just have a warning "Unused val foo" and the user can remove the code himself :).

[nicolasstucki]

It might become unused after some other optimization. This lazy val could also have been generated by the compiler in a phase that is not able to do escape analysis.