dart2js cps: Add instruction for null checks.

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library tree_ir_builder;
 
 import '../common.dart';
 import '../constants/values.dart';
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
 import '../elements/elements.dart';
@@ skipping 89 matching lines @@
   Variable getVariable(cps_ir.Primitive primitive) {
     return primitive2variable.putIfAbsent(primitive,
         () => new Variable(currentElement, primitive.hint));
   }
 
   /// Obtains a reference to the tree Variable corresponding to the IR primitive
   /// referred to by [reference].
   /// This increments the reference count for the given variable, so the
   /// returned expression must be used in the tree.
   Expression getVariableUse(cps_ir.Reference<cps_ir.Primitive> reference) {
-    if (thisParameter != null && reference.definition == thisParameter) {
+    cps_ir.Primitive prim = reference.definition.effectiveDefinition;
+    if (thisParameter != null && prim == thisParameter) {
       return new This();
     }
-    return new VariableUse(getVariable(reference.definition));
+    return new VariableUse(getVariable(prim));
+  }
+
+  Expression getVariableUseOrNull(
+        cps_ir.Reference<cps_ir.Primitive> reference) {
+    return reference == null ? null : getVariableUse(reference);
   }
 
   Label getLabel(cps_ir.Continuation cont) {
     return labels.putIfAbsent(cont, () => new Label());
   }
 
   Variable addFunctionParameter(cps_ir.Parameter parameter) {
     return getVariable(parameter);
   }
 
@@ skipping 365 matching lines @@
     return new LiteralMap(
         node.dartType,
         new List<LiteralMapEntry>.generate(node.entries.length, (int index) {
           return new LiteralMapEntry(
               getVariableUse(node.entries[index].key),
               getVariableUse(node.entries[index].value));
         })
     );
   }
 
-  FunctionDefinition makeSubFunction(cps_ir.FunctionDefinition function) {
-    return createInnerBuilder().buildFunction(function);
-  }
-
   Expression visitReifyRuntimeType(cps_ir.ReifyRuntimeType node) {
     return new ReifyRuntimeType(
         getVariableUse(node.value), node.sourceInformation);
   }
 
   Expression visitReadTypeVariable(cps_ir.ReadTypeVariable node) {
     return new ReadTypeVariable(
         node.variable,
         getVariableUse(node.target),
         node.sourceInformation);
@@ skipping 123 matching lines @@
         return new ForeignStatement(
             node.codeTemplate,
             node.type,
             arguments,
             node.nativeBehavior,
             node.dependency);
       };
     }
   }
 
+  visitNullCheck(cps_ir.NullCheck node) => (Statement next) {
+    return new NullCheck(
+        condition: getVariableUseOrNull(node.condition),
+        value: getVariableUse(node.value),
+        selector: node.selector,
+        next: next,
+        sourceInformation: node.sourceInformation);
+  };
+
   Expression visitGetLazyStatic(cps_ir.GetLazyStatic node) {
     // In the tree IR, GetStatic handles lazy fields because we do not need
     // as fine-grained control over side effects.
     return new GetStatic(node.element, node.sourceInformation);
   }
 
   @override
   NodeCallback visitYield(cps_ir.Yield node) {
     return (Statement next) {
       return new Yield(getVariableUse(node.input), node.hasStar, next);
@@ skipping 41 matching lines @@
     --enclosingFunctions;
   }
 
   @override
   visitInterpolatedNode(js.InterpolatedNode node) {
     if (enclosingFunctions > 0) {
       found = true;
     }
   }
 }