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package dotty.tools.dotc
package transform
import ast.{Trees, tpd}
import core._, core.Decorators._
import Contexts._, Trees._, StdNames._, Symbols._
import DenotTransformers._, TreeTransforms._, Phases.Phase
import ExtensionMethods._, TreeExtractors._, ValueClasses._
/** This phase elides unnecessary value class allocations
*
* For a value class V defined as:
* class V(val underlying: U) extends AnyVal
* we avoid unnecessary allocations:
* new V(u1) == new V(u2) => u1 == u2
* (new V(u)).underlying() => u
*/
class VCElideAllocations extends MiniPhaseTransform with IdentityDenotTransformer {
import tpd._
override def phaseName: String = "vcElideAllocations"
override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[ElimErasedValueType])
override def transformApply(tree: Apply)(implicit ctx: Context, info: TransformerInfo): Tree =
tree match {
// new V(u1) == new V(u2) => u1 == u2
// (We don't handle != because it has been eliminated by InterceptedMethods)
case BinaryOp(NewWithArgs(tp1, List(u1)), op, NewWithArgs(tp2, List(u2)))
if (tp1 eq tp2) && (op eq defn.Any_==) && isDerivedValueClass(tp1.typeSymbol) =>
// == is overloaded in primitive classes
applyOverloaded(u1, nme.EQ, List(u2), Nil, defn.BooleanType)
// (new V(u)).underlying() => u
case ValueClassUnbox(NewWithArgs(_, List(u))) =>
u
case _ =>
tree
}
}
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