Value class equality boxes

[odersky]

Minimized example

Compile the following with -Xprint:elimErasedValueType

class ApproxState(private val bits: Int) extends AnyVal

object Main {
  val FreshApprox: ApproxState = new ApproxState(4)
  var approx: ApproxState = FreshApprox
  println(approx == FreshApprox)
}

Output

The last statement compiles to:

    println(
      scala.Boolean.box(
        new ApproxState(Main.approx()).==(new ApproxState(Main.FreshApprox()))
      )
    )

Expectation

No boxing

[smarter]

The culprit is this line in VCElideAllocations:

!defn.Any_equals.overridingSymbol(tp1.typeSymbol.asClass).exist

Which is as documented:

new V(u1) == new V(u2) => u1 == u2 provided V does not redefine equals

But value classes of course have to define equals, I think this is supposed to check that the equals in question is not synthetic.

[odersky]

Yes, I think that's right. Fix forthcoming...