Avoid generating skolems just to return true

Co-authored-by: Guillaume Martres <[email protected]>

Author: dwijnand

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

@@ -1731,20 +1731,6 @@ class Definitions {
     else sys.error(s"Not a primitive value type: $tp")
   }.typeRef
 
-  def unboxedType(tp: Type)(using Context): TypeRef = {
-    val cls = tp.classSymbol
-    if (cls eq BoxedByteClass)         ByteType
-    else if (cls eq BoxedShortClass)   ShortType
-    else if (cls eq BoxedCharClass)    CharType
-    else if (cls eq BoxedIntClass)     IntType
-    else if (cls eq BoxedLongClass)    LongType
-    else if (cls eq BoxedFloatClass)   FloatType
-    else if (cls eq BoxedDoubleClass)  DoubleType
-    else if (cls eq BoxedUnitClass)    UnitType
-    else if (cls eq BoxedBooleanClass) BooleanType
-    else sys.error(s"Not a boxed primitive value type: $tp")
-  }
-
   /** The JVM tag for `tp` if it's a primitive, `java.lang.Object` otherwise. */
   def typeTag(tp: Type)(using Context): Name = typeTags(scalaClassName(tp))
 

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -512,18 +512,15 @@ class SpaceEngine(using Context) extends SpaceLogic {
       if converted == null then tp else ConstantType(converted)
     case _ => tp
 
-  def adaptType(tp1: Type, tp2: Type): Type = trace(i"adaptType($tp1, $tp2)", show = true) {
-    def isPrimToBox(tp: Type, pt: Type) =
-      tp.classSymbol.isPrimitiveValueClass && (defn.boxedType(tp).classSymbol eq pt.classSymbol)
-    if      isPrimToBox(tp1, tp2) then defn.boxedType(tp1).narrow   //  1  <:< Integer => (<skolem> : Integer) <:< Integer = true
-    else if isPrimToBox(tp2, tp1) then defn.unboxedType(tp1).narrow // ONE <:< Int     => (<skolem> : Int)     <:< Int     = true
-    else convertConstantType(tp1, tp2)
-  }
+  def isPrimToBox(tp: Type, pt: Type) =
+    tp.classSymbol.isPrimitiveValueClass && (defn.boxedType(tp).classSymbol eq pt.classSymbol)
 
   /** Is `tp1` a subtype of `tp2`?  */
   def isSubType(tp1: Type, tp2: Type): Boolean = trace(i"$tp1 <:< $tp2", debug, show = true) {
     if tp1 == constantNullType && !ctx.explicitNulls then tp2 == constantNullType
-    else adaptType(tp1, tp2) <:< tp2
+    else
+      isPrimToBox(tp1, tp2) || isPrimToBox(tp2, tp1) ||
+      convertConstantType(tp1, tp2) <:< tp2
   }
 
   def isSameUnapply(tp1: TermRef, tp2: TermRef): Boolean =

compiler/test/dotty/tools/dotc/transform/SpaceEngineTest.scala

@@ -15,5 +15,5 @@ class SpaceEngineTest extends DottyTest:
 
     val BoxedIntType = BoxedIntClass.typeRef
 
-    assertEquals(BoxedIntType, e.adaptType(IntType, BoxedIntType).widenSingleton)
-    assertEquals(IntType,      e.adaptType(BoxedIntType, IntType).widenSingleton)
+    assertTrue(e.isPrimToBox(IntType, BoxedIntType))
+    assertFalse(e.isPrimToBox(BoxedIntType, IntType))