Alternative fix

Author: liufengyun

compiler/src/dotty/tools/dotc/Run.scala

@@ -202,7 +202,6 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
           Stats.trackTime(s"$phase ms ") {
             val start = System.currentTimeMillis
             val profileBefore = profiler.beforePhase(phase)
-            ctx.typerState.constraint = OrderingConstraint.empty
             units = phase.runOn(units)
             profiler.afterPhase(phase, profileBefore)
             if (ctx.settings.Xprint.value.containsPhase(phase))

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -4537,7 +4537,7 @@ object Types {
 
     override def tryNormalize(using Context): Type = reduced.normalized
 
-    def reduced(using Context): Type = {
+    def reduced(using Context): Type = inContext(ctx.fresh.setExploreTyperState()) {
 
       def contextInfo(tp: Type): Type = tp match {
         case tp: TypeParamRef =>