Singleton typed args/results don't interfere with tailcalls #6420
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At one point the literal types PR modified the semantics of asInstanceOf to check for equality of the target value with the value embedded in the singleton type. This interacted badly with mkAttributedCastHack in Tailcalls, dotta@c2534bf because the inserted casts could end up referring to a non-existent Symbol which would be needed to implement the equality check during Erasure. The fix at the time was to make the use of a singleton type as a method argument or result type disqualify the method from having the tailcall optimization applied. A later decision by the SIP committee decided for unrelated reasons that an asInstanceOf test should not perform an equality check, so this disqualification became unnecessary. It was not removed, however. This came to light because singleton types are used as method argument and result types in methods which are expected to have the tail call optimizatino applied, resulting in, scala/scala-dev#467 We fix that here by doing what should have been done earlier: removing the disqualification.
retronym
approved these changes
Mar 13, 2018
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At one point the literal types PR modified the semantics of
asInstanceOfto check for equality of the target value with the value embedded in the singleton type. This interacted badly withmkAttributedCastHackinTailcalls, because the inserted casts could end up referring to a non-existent symbol which would be needed to implement the equality check during erasure.The fix at the time was to make the use of a singleton type as a method argument or result type disqualify the method from having the tailcall optimization applied. A later decision by the SIP committee decided for unrelated reasons that an
asInstanceOftest should not perform an equality check, so this disqualification became unnecessary. It was not removed, however.This came to light because singleton types are used as method argument and result types in methods which are expected to have the tail call optimization applied, resulting in scala/scala-dev#467. We fix that here by doing what should have been done earlier: removing the disqualification.
Fixes scala/scala-dev#467.