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An expression containing nested casts would type the same tree 2^N
times where N is the number of nested casts. This was particularly
visible in Vector.scala where one can find a six-cast expression.
It's currently line "why was six afraid of seven", aka line 789.
display5((index >> 25) & 31)
.asInstanceOf[Array[AnyRef]]((index >> 20) & 31)
.asInstanceOf[Array[AnyRef]]((index >> 15) & 31)
.asInstanceOf[Array[AnyRef]]((index >> 10) & 31)
.asInstanceOf[Array[AnyRef]]((index >> 5) & 31)
.asInstanceOf[Array[AnyRef]](index & 31)
.asInstanceOf[T]
Compiling Vector.scala, before/after.
< #unique types : 10805
> #unique types : 9722
< #created tree nodes : 26716
> #created tree nodes : 25647
I found a similar bug about a year ago in 39f01d4f48. It's
interesting to consider how little defense we have against bugs
of this nature - visually non-obvious differences in tree
traversal can have spectacular impact on complexity.
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