Main sharing of TypeBoundsTree bounds through (un)pickling

Author: odersky

compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala

@@ -102,7 +102,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   REFINEDtpt     Length underlying_Term refinement_Stat*
                   APPLIEDtpt     Length tycon_Term arg_Term*
                   POLYtpt        Length TypeParam* body_Term
-                  TYPEBOUNDStpt  Length low_Term high_Term
+                  TYPEBOUNDStpt  Length low_Term high_Term?
                   ANNOTATEDtpt   Length underlying_Term fullAnnotation_Term
                   ANDtpt         Length left_Term right_Term
                   ORtpt          Length left_Term right_Term

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -552,7 +552,10 @@ class TreePickler(pickler: TastyPickler) {
           withLength { pickleParams(tparams); pickleTree(body) }
         case TypeBoundsTree(lo, hi) =>
           writeByte(TYPEBOUNDStpt)
-          withLength { pickleTree(lo); pickleTree(hi) }
+          withLength {
+            pickleTree(lo);
+            if (hi ne lo) pickleTree(hi)
+          }
         case Hole(idx, args) =>
           writeByte(HOLE)
           withLength {

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -1038,7 +1038,9 @@ class TreeUnpickler(reader: TastyReader,
               val body = readTpt()
               LambdaTypeTree(tparams, body)
             case TYPEBOUNDStpt =>
-              TypeBoundsTree(readTpt(), readTpt())
+              val lo = readTpt()
+              val hi = if (currentAddr == end) lo else readTpt()
+              TypeBoundsTree(lo, hi)
             case HOLE =>
               readHole(end)
             case _ =>