Optimize comparing types in mergeRefinedOrApplied

Author: noti0na1

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

@@ -244,44 +244,36 @@ object TypeOps:
 
     def mergeRefinedOrApplied(tp1: Type, tp2: Type): Type = {
       def fail = throw new AssertionError(i"Failure to join alternatives $tp1 and $tp2")
-      def fallback = tp2 match
+
+      tp2 match
         case AndType(tp21, tp22) =>
-          mergeRefinedOrApplied(tp1, tp21) & mergeRefinedOrApplied(tp1, tp22)
+          return mergeRefinedOrApplied(tp1, tp21) & mergeRefinedOrApplied(tp1, tp22)
         case _ =>
-          fail
-      tp1 match {
+
+      if tp1 eq tp2 then tp1
+      else tp1 match
         case tp1 @ RefinedType(parent1, name1, rinfo1) =>
-          tp2 match {
+          tp2 match
             case RefinedType(parent2, `name1`, rinfo2) =>
               tp1.derivedRefinedType(
                 mergeRefinedOrApplied(parent1, parent2), name1, rinfo1 | rinfo2)
-            case _ => fallback
-          }
+            case _ => fail
         case tp1 @ AppliedType(tycon1, args1) =>
-          tp2 match {
+          tp2 match
             case AppliedType(tycon2, args2) =>
               tp1.derivedAppliedType(
                 mergeRefinedOrApplied(tycon1, tycon2),
                 TypeComparer.lubArgs(args1, args2, tycon1.typeParams))
-            case _ => fallback
-          }
+            case _ => fail
         case tp1 @ TypeRef(pre1, _) =>
-          tp2 match {
+          tp2 match
             case tp2 @ TypeRef(pre2, _) if tp1.name eq tp2.name =>
               tp1.derivedSelect(pre1 | pre2)
-            case _ => fallback
-          }
-        case tp1: TypeParamRef =>
-          tp2 match {
-            case tp2: TypeParamRef
-            if (tp1.binder eq tp2.binder) && (tp1.paramNum == tp2.paramNum) =>
-              tp1
-            case _ => fallback
-          }
+            case _ => fail
         case AndType(tp11, tp12) =>
           mergeRefinedOrApplied(tp11, tp2) & mergeRefinedOrApplied(tp12, tp2)
+        case tp1: TypeParamRef if tp1 == tp2 => tp1
         case _ => fail
-      }
     }
 
     def approximateOr(tp1: Type, tp2: Type): Type = {