Fixes for checked mode and change buildbot script to run dart2js tests in checked mode also.

lib/compiler/implementation/ssa/optimize.dart

 // Copyright (c) 2011, 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.
 
 interface OptimizationPhase {
   String get name();
   void visitGraph(HGraph graph);
 }
 
 class SsaOptimizerTask extends CompilerTask {
@@ skipping 524 matching lines @@
       }
     } else if (expressionType.isArray()) {
       if (element === compiler.listClass
           || Elements.isListSupertype(element, compiler)) {
         return graph.addConstantBool(true);
       } else {
         return graph.addConstantBool(false);
       }
     // TODO(karlklose): remove the hasTypeArguments check.
     } else if (expressionType.isUseful()
+               && !expressionType.canBeNull()
                && !compiler.codegenWorld.rti.hasTypeArguments(type)) {
       Type receiverType = expressionType.computeType(compiler);
       if (receiverType !== null) {
         if (compiler.types.isSubtype(receiverType, type)) {
           return graph.addConstantBool(true);
         } else if (expressionType.isExact()) {
           return graph.addConstantBool(false);
         }
       }
     }
     return node;
   }
 
   HInstruction visitTypeConversion(HTypeConversion node) {
     HInstruction value = node.inputs[0];
     Type type = node.propagatedType.computeType(compiler);
     if (type.element === compiler.dynamicClass
         || type.element === compiler.objectClass) {
       return value;
     }
     HType combinedType = value.propagatedType.intersection(node.propagatedType);
     return (combinedType == value.propagatedType) ? value : node;
   }
 
   HInstruction visitInvokeDynamicGetter(HInvokeDynamicGetter node) {
     HInstruction receiver = node.inputs[0];
     if (!receiver.propagatedType.isUseful()) return node;
+    if (receiver.propagatedType.canBeNull()) return node;
     Type type = receiver.propagatedType.computeType(compiler);
     if (type === null) return node;
     Element field = compiler.world.locateSingleField(type, node.name);
     if (field === null) return node;
     Modifiers modifiers = field.modifiers;
     bool isFinalOrConst = false;
     if (modifiers != null) {
       isFinalOrConst = modifiers.isFinal() || modifiers.isConst();
     }
     return new HFieldGet(field, node.inputs[0], isFinalOrConst: isFinalOrConst);
   }
 
   HInstruction visitInvokeDynamicSetter(HInvokeDynamicSetter node) {
     HInstruction receiver = node.inputs[0];
     if (!receiver.propagatedType.isUseful()) return node;
+    if (receiver.propagatedType.canBeNull()) return node;
     Type type = receiver.propagatedType.computeType(compiler);
     if (type === null) return node;
     Element field = compiler.world.locateSingleField(type, node.name);
     if (field === null) return node;
     return new HFieldSet(field, node.inputs[0], node.inputs[1]);
   }
 
   HInstruction visitStringConcat(HStringConcat node) {
     DartString folded = const LiteralDartString("");
     for (int i = 0; i < node.inputs.length; i++) {
@@ skipping 540 matching lines @@
         // the if block terminates. So any use of the instruction
         // after the join block should be changed to the new
         // instruction.
         changeUsesDominatedBy(ifUser.joinBlock, input, convertedType);
       }
       // TODO(ngeoffray): Also change uses for the then block on a HType
       // that knows it is not of a specific Type.
     }
   }
 }