title: Opt-in tail call support in the JVM on a per-language base?
body: <p>While it doesn't look like that tail call optimization will ever be added as a common optimization technique, especially after Sun was bought, wouldn't it be technically possible to let languages running on the VM decide themselves if their compiler emits <code>tailcall</code> instructions in the byte code?</p>
  
  <p>E. g. Java, Groovy can decide not to use the instruction, while more functional languages like Scala or Clojure can emit it and the HotSpot VM will only optimize the ones marked with <code>tailcall</code>?</p>