Normalize type masks to use the least upper instantiated subclass/type.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 2dec2eea53a8afd213efbd081024c1e94aea7938..151ca61ce61253bef3d3591ffea371280fe9b630 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -3247,7 +3247,7 @@ class SsaBuilder extends ast.Visitor
     });
 
     TypeMask type =
-        new TypeMask.nonNullExact(coreClasses.functionClass, compiler.world);
+        new TypeMask.nonNullSubtype(closureClassElement, compiler.world);

[sigurdm, 2015/11/03 13:06:50]

?

[Johnni Winther, 2015/11/03 13:20:02]

Why not notNullExact?

[herhut, 2015/11/04 10:42:20]

Hmm, not sure this works. I know that we introduce classes for closures and that
technically they are all subtypes of Function. However, all of this happens
after resolution and during type inference IIRC. Do we update the required
information?

if so, notNullExact would be more precise. We know here that it is an instance
of exactly that class.

[Johnni Winther, 2015/11/06 13:43:23]

Update the closed world for the latter.

     push(new HForeignNew(closureClassElement, type, capturedVariables)
         ..sourceInformation = sourceInformationBuilder.buildCreate(node));
 
@@ -5074,7 +5074,12 @@ class SsaBuilder extends ast.Visitor
             : inferred;
       } else if (element.isGenerativeConstructor) {
         ClassElement cls = element.enclosingClass;
-        return new TypeMask.nonNullExact(cls.thisType.element, compiler.world);
+        if (cls.isAbstract) {
+          // An error will be thrown.
+          return new TypeMask.nonNullEmpty();
+        } else {
+          return new TypeMask.nonNullExact(cls.thisType.element, compiler.world);

[sigurdm, 2015/11/03 13:06:50]

long line

[Johnni Winther, 2015/11/06 13:43:23]

Done.

+        }
       } else {
         return TypeMaskFactory.inferredReturnTypeForElement(
             originalElement, compiler);