optimize isSubType by checking nullType first

liufengyun · liufengyun · commit 5dccc29a5624 · 2018-04-06T09:41:58.000+02:00
diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
@@ -379,7 +379,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
 
   /** Is `tp1` a subtype of `tp2`?  */
   def isSubType(tp1: Type, tp2: Type): Boolean = {
-    val res = tp1 <:< tp2 && (tp1 != nullType || tp2 == nullType)
+    val res = (tp1 != nullType || tp2 == nullType) && tp1 <:< tp2
     debug.println(s"${tp1.show} <:< ${tp2.show} = $res")
     res
   }

Original file line number	Diff line number	Diff line change
`@@ -379,7 +379,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {`
`379`	`379`
`380`	`380`	/** Is `tp1` a subtype of `tp2`? */
`381`	`381`	`def isSubType(tp1: Type, tp2: Type): Boolean = {`
`382`		`- val res = tp1 <:< tp2 && (tp1 != nullType \|\| tp2 == nullType)`
	`382`	`+ val res = (tp1 != nullType \|\| tp2 == nullType) && tp1 <:< tp2`
`383`	`383`	`debug.println(s"${tp1.show} <:< ${tp2.show} = $res")`
`384`	`384`	`res`
`385`	`385`	`}`