scala.tools.nsc.transform.TailCalls

# TailCallElimination

#### class TailCallElimination extends Global.Transformer

A Tail Call Transformer

Source
  TailCalls.scala
Version

  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: `Uncurry` has been run already, and no multiple parameter lists exit.

Linear Supertypes
Global.Transformer, Global.Transformer, AnyRef, Any
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Inherited

1. TailCallElimination
2. Transformer
3. Transformer
4. AnyRef
5. Any

Implicitly

1. by any2stringadd
2. by StringFormat
3. by Ensuring
4. by ArrowAssoc

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### Instance Constructors

1. #### new TailCallElimination(unit: Global.CompilationUnit)

### Type Members

1. #### class ClonedTailContext extends TailContext

2. #### class DefDefTailContext extends TailContext

3. #### sealed trait TailContext extends AnyRef

### Value Members

1. #### final def !=(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

2. #### final def ##(): Int

   Definition Classes
     AnyRef → Any

3. #### def +(other: String): String

   Implicit information
     This member is added by an implicit conversion from TailCallElimination to any2stringadd[TailCallElimination] performed by method any2stringadd in scala.Predef.
   Definition Classes
     any2stringadd

4. #### def ->[B](y: B): (TailCallElimination, B)

   Implicit information
     This member is added by an implicit conversion from TailCallElimination to ArrowAssoc[TailCallElimination] performed by method ArrowAssoc in scala.Predef.
   Definition Classes
     ArrowAssoc
   Annotations
     @inline()

5. #### final def ==(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

6. #### object EmptyTailContext extends TailContext

7. #### final def asInstanceOf[T0]: T0

   Definition Classes
     Any

8. #### def atOwner[A](owner: Global.Symbol)(trans: ⇒ A): A

   Definition Classes
     Transformer

9. #### def clone(): AnyRef

   Attributes
     protected[java.lang]
   Definition Classes
     AnyRef
   Annotations
     @throws( ... )

10. #### def currentClass: Global.Symbol

    Attributes
      protected
    Definition Classes
      Transformer

11. #### def currentMethod: Global.Symbol

    Attributes
      protected
    Definition Classes
      Transformer

12. #### var currentOwner: Global.Symbol

    Attributes
      protected[scala]
    Definition Classes
      Transformer

13. #### def ensuring(cond: (TailCallElimination) ⇒ Boolean, msg: ⇒ Any): TailCallElimination

    Implicit information
      This member is added by an implicit conversion from TailCallElimination to Ensuring[TailCallElimination] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

14. #### def ensuring(cond: (TailCallElimination) ⇒ Boolean): TailCallElimination

    Implicit information
      This member is added by an implicit conversion from TailCallElimination to Ensuring[TailCallElimination] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

15. #### def ensuring(cond: Boolean, msg: ⇒ Any): TailCallElimination

    Implicit information
      This member is added by an implicit conversion from TailCallElimination to Ensuring[TailCallElimination] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

16. #### def ensuring(cond: Boolean): TailCallElimination

    Implicit information
      This member is added by an implicit conversion from TailCallElimination to Ensuring[TailCallElimination] performed by method Ensuring in scala.Predef.
    Definition Classes
      Ensuring

17. #### final def eq(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

18. #### def equals(arg0: Any): Boolean

    Definition Classes
      AnyRef → Any

19. #### def finalize(): Unit

    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )

20. #### def formatted(fmtstr: String): String

    Implicit information
      This member is added by an implicit conversion from TailCallElimination to StringFormat[TailCallElimination] performed by method StringFormat in scala.Predef.
    Definition Classes
      StringFormat
    Annotations
      @inline()

21. #### final def getClass(): Class[_]

    Definition Classes
      AnyRef → Any

22. #### def hashCode(): Int

    Definition Classes
      AnyRef → Any

23. #### final def isInstanceOf[T0]: Boolean

    Definition Classes
      Any

24. #### final def ne(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

25. #### def noTailTransform(tree: Global.Tree): Global.Tree

26. #### def noTailTransforms(trees: List[Global.Tree]): collection.immutable.List[Global.Tree]

27. #### final def notify(): Unit

    Definition Classes
      AnyRef

28. #### final def notifyAll(): Unit

    Definition Classes
      AnyRef

29. #### final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
      AnyRef

30. #### def toString(): String

    Definition Classes
      AnyRef → Any

31. #### def transform(tree: Global.Tree): Global.Tree

    Definition Classes
      TailCallElimination → Transformer

32. #### def transform(tree: Global.Tree, nctx: TailContext): Global.Tree

    Rewrite this tree to contain no tail recursive calls

33. #### def transformCaseDefs(trees: List[Global.CaseDef]): List[Global.CaseDef]

    Definition Classes
      Transformer

34. #### def transformIdents(trees: List[Global.Ident]): List[Global.Ident]

    Definition Classes
      Transformer

35. #### def transformMemberDefs(trees: List[Global.MemberDef]): List[Global.MemberDef]

    Definition Classes
      Transformer

36. #### def transformModifiers(mods: Global.Modifiers): Global.Modifiers

    Definition Classes
      Transformer

37. #### def transformStats(stats: List[Global.Tree], exprOwner: Global.Symbol): List[Global.Tree]

    Definition Classes
      Transformer

38. #### def transformTemplate(tree: Global.Template): Global.Template

    Definition Classes
      Transformer

39. #### def transformTrees(trees: List[Global.Tree]): List[Global.Tree]

    Definition Classes
      Transformer

40. #### def transformTypeDefs(trees: List[Global.TypeDef]): List[Global.TypeDef]

    Definition Classes
      Transformer

41. #### def transformUnit(unit: Global.CompilationUnit): Unit

    Definition Classes
      TailCallElimination → Transformer

42. #### def transformValDef(tree: Global.ValDef): Global.ValDef

    Definition Classes
      Transformer

43. #### def transformValDefs(trees: List[Global.ValDef]): List[Global.ValDef]

    Definition Classes
      Transformer

44. #### def transformValDefss(treess: List[List[Global.ValDef]]): List[List[Global.ValDef]]

    Definition Classes
      Transformer

45. #### val treeCopy: Global.TreeCopier

    Definition Classes
      Transformer

46. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

47. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

48. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

49. #### def yesTailTransform(tree: Global.Tree): Global.Tree

50. #### def →[B](y: B): (TailCallElimination, B)

    Implicit information
      This member is added by an implicit conversion from TailCallElimination to ArrowAssoc[TailCallElimination] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
      ArrowAssoc

### Inherited from Global.Transformer

### Inherited from AnyRef

### Inherited from Any

### Inherited by implicit conversion any2stringadd from TailCallElimination to any2stringadd[TailCallElimination]

### Inherited by implicit conversion StringFormat from TailCallElimination to StringFormat[TailCallElimination]

### Inherited by implicit conversion Ensuring from TailCallElimination to Ensuring[TailCallElimination]

### Inherited by implicit conversion ArrowAssoc from TailCallElimination to ArrowAssoc[TailCallElimination]

### Ungrouped