Implement is-checks against type variables.

sdk/lib/_internal/compiler/implementation/universe/universe.dart

Index: sdk/lib/_internal/compiler/implementation/universe/universe.dart
diff --git a/sdk/lib/_internal/compiler/implementation/universe/universe.dart b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
index 0b78d6337c6c7bee64d0737244b981d6d94decfb..1e33b8e41573e8851b40d52cd33af407b72821fe 100644
--- a/sdk/lib/_internal/compiler/implementation/universe/universe.dart
+++ b/sdk/lib/_internal/compiler/implementation/universe/universe.dart
@@ -88,6 +88,42 @@ class Universe {
   bool hasFieldSetter(Element member, Compiler compiler) {
     return fieldSetters.contains(member);
   }
+
+  /**
+   * Compute type arguments of classes that potentially use their type

[ngeoffray, 2013/02/26 14:11:37]

Why potentially? We know they are for the resolution universe, as well as for
the codegen universe.

[karlklose, 2013/02/27 10:12:58]

I meant it may use it, if the method containing it is called. rephrased.

+   * variables in is-checks and add the is-checks that they imply.
+   *
+   * This function must be called after all is-checks have been registered.
+   *
+   * TODO(karlklose): move these computations into a function producing an
+   * immutable datastructure.
+   */
+  void addImplicitChecks(Iterable<ClassElement> classesUsingChecks) {
+    if (!classesUsingChecks.isEmpty) {

[ngeoffray, 2013/02/26 14:11:37]

How about:
if (classesUsingChecks.isEmpty) return;

Also, please add a comment on why you're doing this check.

[karlklose, 2013/02/27 10:12:58]

Done.

+      // Find all instantiated types that are a subtype of a class that uses
+      // one of its type arguments in an is-check and add the arguments to the
+      // set of is-checks.
+      // TODO(karlklose): replace this with code that uses a subtype lookup
+      // datastructure in the world.
+      for (DartType type in instantiatedTypes) {
+        if (type.kind != TypeKind.INTERFACE) {
+          continue;
+        }
+        InterfaceType classType = type;
+        for (ClassElement cls in classesUsingChecks) {
+          // We need the type as instance of its superclass anyway, so we just
+          // try to compute the substitution; if the result is [:null:], the
+          // classes are not related.
+          InterfaceType instance = classType.asInstanceOf(cls);
+          if (instance == null) continue;
+          Link<DartType> typeArguments = instance.typeArguments;
+          for (DartType argument in typeArguments) {
+            isChecks.add(argument);
+          }
+        }
+      }
+    }
+  }
 }
 
 class SelectorKind {