Drop unique hashing for superId bitsets

Reason: (1) There are few sets: When compiling doty itself, 1.2K sets total, hashed to 500 uniques. (2) Bitset comparison is expensive because it relies on a double inclusion test. (This should be fixed in the Scala stdlib).

2 files changed, 1 insertions, 8 deletions

diff --git a/src/dotty/tools/dotc/core/Contexts.scala b/src/dotty/tools/dotc/core/Contexts.scala
index c7e0784c8..859475cd5 100644
--- a/src/dotty/tools/dotc/core/Contexts.scala
+++ b/src/dotty/tools/dotc/core/Contexts.scala
@@ -420,13 +420,6 @@ object Contexts {
       lastSuperId
     }
 
-    // SymDenotations state
-    /** A table where unique superclass bits are kept.
-     *  These are bitsets that contain the superclass ids of all base classes of a class.
-     *  Used to speed up isSubClass tests.
-     */
-    private[core] val uniqueBits = new util.HashSet[BitSet]("superbits", 1024)
-
     // Types state
     /** A table for hash consing unique types */
     private[core] val uniques = new util.HashSet[Type]("uniques", initialUniquesCapacity) {
diff --git a/src/dotty/tools/dotc/core/SymDenotations.scala b/src/dotty/tools/dotc/core/SymDenotations.scala
index 1bb912059..b377817f9 100644
--- a/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -872,7 +872,7 @@ object SymDenotations {
           to
       }
       myBaseClasses = classSymbol :: addParentBaseClasses(classParents, Nil)
-      mySuperClassBits = ctx.uniqueBits.findEntryOrUpdate(seen.toImmutable)
+      mySuperClassBits = seen.toImmutable
     }
 
     /** A bitset that contains the superId's of all base classes */