performance tuning: only do GADT if a type param ref T is invariant

liufengyun · liufengyun · commit 5bc9fcbd08c7 · 2017-11-20T13:50:41.000+01:00
diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
@@ -814,7 +814,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
   def checkGADT(tp: Type): Boolean = {
     new TypeAccumulator[Boolean] {
       override def apply(b: Boolean, tp: Type): Boolean = tp match {
-        case tref: TypeRef if tref.symbol.is(TypeParam) => true
+        case tref: TypeRef if tref.symbol.is(TypeParam) && variance == 0 => true
         case tp => b || foldOver(b, tp)
       }
     }.apply(false, tp)

Original file line number	Diff line number	Diff line change
`@@ -814,7 +814,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {`
`814`	`814`	`def checkGADT(tp: Type): Boolean = {`
`815`	`815`	`new TypeAccumulator[Boolean] {`
`816`	`816`	`override def apply(b: Boolean, tp: Type): Boolean = tp match {`
`817`		`- case tref: TypeRef if tref.symbol.is(TypeParam) => true`
	`817`	`+ case tref: TypeRef if tref.symbol.is(TypeParam) && variance == 0 => true`
`818`	`818`	`case tp => b \|\| foldOver(b, tp)`
`819`	`819`	`}`
`820`	`820`	`}.apply(false, tp)`