Implement is-checks against type variables.

sdk/lib/_internal/compiler/implementation/ssa/builder.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/builder.dart b/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
index f0f844a85e402be7e059f65aa7a0ee8f865a79cd..b630968073d3ec1590576ecd222e7b61149b7537 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
@@ -2582,14 +2582,10 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
   // TODO(karlklose): change construction of the representations to be GVN'able
   // (dartbug.com/7182).
   List<HInstruction> buildTypeArgumentRepresentations(DartType type) {
-    HInstruction createForeignArray(String code, inputs) {
-      return createForeign(code, HType.READABLE_ARRAY, inputs);
-    }
-
     // Compute the representation of the type arguments, including access
     // to the runtime type information for type variables as instructions.
     HInstruction representations;
-    if (type.element.isTypeVariable()) {
+    if (type.kind == TypeKind.TYPE_VARIABLE) {
       return <HInstruction>[addTypeVariableReference(type)];
     } else {
       assert(type.element.isClass());
@@ -2601,7 +2597,8 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
           HInstruction runtimeType = addTypeVariableReference(variable);
           inputs.add(runtimeType);
         });
-        HInstruction representation = createForeignArray(template, inputs);
+        HInstruction representation =
+            createForeign(template, HType.READABLE_ARRAY, inputs);
         add(representation);
         arguments.add(representation);
       }
@@ -2633,6 +2630,7 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
         isNot = true;
       }
       DartType type = elements.getType(typeAnnotation);
+      compiler.enqueuer.codegen.registerIsCheck(type);
       if (type.isMalformed) {
         String reasons = Types.fetchReasonsFromMalformedType(type);
         if (compiler.enableTypeAssertions) {
@@ -2642,16 +2640,23 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
         }
         return;
       }
-      if (type.element.isTypeVariable()) {
-        // TODO(karlklose): remove this check when the backend can deal with
-        // checks of the form [:o is T:] where [:T:] is a type variable.
-        stack.add(graph.addConstantBool(true, constantSystem));
-        return;
-      }
 
       HInstruction instruction;
-      if (type.element.isTypeVariable() ||
-          RuntimeTypeInformation.hasTypeArguments(type)) {
+      if (type.kind == TypeKind.TYPE_VARIABLE) {
+        List<HInstruction> representations =
+            buildTypeArgumentRepresentations(type);
+        assert(representations.length == 1);
+        HInstruction runtimeType = addTypeVariableReference(type);
+        Element helper =
+            compiler.findHelper(const SourceString('objectIsSubtype'));
+        HInstruction helperCall = new HStatic(helper);
+        add(helperCall);
+        List<HInstruction> inputs = <HInstruction>[helperCall, expression,
+                                                   runtimeType];
+        instruction = new HInvokeStatic(inputs, HType.BOOLEAN);
+        add(instruction);
+
+      } else if (RuntimeTypeInformation.hasTypeArguments(type)) {
 
         void argumentsCheck() {
           HInstruction typeInfo = getRuntimeTypeInfo(expression);
@@ -2680,7 +2685,8 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
         void classCheck() { push(new HIs(type, <HInstruction>[expression])); }
 
         SsaBranchBuilder branchBuilder = new SsaBranchBuilder(this, node);
-        branchBuilder.handleLogicalAndOr(classCheck, argumentsCheck, isAnd: true);
+        branchBuilder.handleLogicalAndOr(classCheck, argumentsCheck,
+                                         isAnd: true);
         instruction = pop();
       } else {
         instruction = new HIs(type, <HInstruction>[expression]);