spurious dead code warning with an irrefutable extractor in withFilter

[scabug]

class A
object A {
  def unapply(a: A): Some[A] = Some(a) // Change return type to Option[A] and the warning is gone
}

object Test {
  for (A(a) <- List(new A)) yield a // spurious dead code warning.
}

// List(new A()).withFilter(((check$ifrefutable$2) => check$ifrefutable$2: @scala.unchecked match {
//  case A((a @ _)) => true
//  case _ => false // this is dead code, but it's compiler generated.
// }))

I'm pretty sure the regression is explained by the combination of:

scala/scala@cbd0205
and
scala/scala@dfbaaa1

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7183?orig=1
Reporter: @retronym
Affected Versions: 2.10.1-RC1

[scabug]

@retronym said:
scala/scala#2168

[scabug]

@retronym said:
If you want to defer this change, we must at least revert cbd02059 in 2.10.1 IMO.

[scabug]

@gkossakowski said:
Elevated to blocker as it blocks 2.10.1 release.