SI-12499 performance regression in patmat.

src/compiler/scala/tools/nsc/transform/patmat/Logic.scala

@@ -120,7 +120,7 @@ trait Logic extends Debugging {
       def apply(ps: Prop*)           = create(ps)
       def create(ps: Iterable[Prop]) = ps match {
         case ps: Set[Prop] => new And(ps)
-        case _             => new And(ps.to(scala.collection.immutable.ListSet))
+        case _             => new And(ps.to(scala.collection.immutable.Set))
       }
     }
 
@@ -129,7 +129,7 @@ trait Logic extends Debugging {
       def apply(ps: Prop*)           = create(ps)
       def create(ps: Iterable[Prop]) = ps match {
         case ps: Set[Prop] => new Or(ps)
-        case _             => new Or(ps.to(scala.collection.immutable.ListSet))
+        case _             => new Or(ps.to(scala.collection.immutable.Set))
       }
     }
 

test/files/neg/t12499.check

@@ -0,0 +1,8 @@
+t12499.scala:455: warning: Cannot check match for unreachability.
+The analysis required more space than allowed.
+Please try with scalac -Ypatmat-exhaust-depth 60 or -Ypatmat-exhaust-depth off.
+  implicit val converter: Thing[Phantom.TypeA] => String = {
+                                                           ^
+error: No warnings can be incurred under -Werror.
+1 warning
+1 error