scala.tools.nsc.transform.TailCalls
Rewrite this tree to contain no tail recursive calls
(tailCallElimination: StringAdd).self
(tailCallElimination: StringFormat).self
(tailCallElimination: ArrowAssoc[TailCallElimination]).x
(Since version 2.10.0) Use leftOfArrow instead
(tailCallElimination: Ensuring[TailCallElimination]).x
(Since version 2.10.0) Use resultOfEnsuring instead
A Tail Call Transformer
1.1
What it does:
Finds method calls in tail-position and replaces them with jumps. A call is in a tail-position if it is the last instruction to be executed in the body of a method. This is done by recursing over the trees that may contain calls in tail-position (trees that can't contain such calls are not transformed). However, they are not that many.
Self-recursive calls in tail-position are replaced by jumps to a label at the beginning of the method. As the JVM provides no way to jump from a method to another one, non-recursive calls in tail-position are not optimized.
A method call is self-recursive if it calls the current method and the method is final (otherwise, it could be a call to an overridden method in a subclass). Furthermore, If the method has type parameters, the call must contain these parameters as type arguments. Recursive calls on a different instance are optimized. Since 'this' is not a local variable, a dummy local val is added and used as a label parameter. The backend knows to load the corresponding argument in the 'this' (local at index 0). This dummy local is never used and should be cleand up by dead code elimination (when enabled).
This phase has been moved before pattern matching to catch more of the common cases of tail recursive functions. This means that more cases should be taken into account (like nested function, and pattern cases).
If a method contains self-recursive calls, a label is added to at the beginning of its body and the calls are replaced by jumps to that label.
Assumes:
Uncurryhas been run already, and no multiple parameter lists exit.