Implement PrimitiveOrNull types.

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 534 matching lines @@
         } else if (expressionType.isExact()) {
           return graph.addConstantBool(false);
         }
       }
     }
     return node;
   }
 
   HInstruction visitTypeConversion(HTypeConversion node) {
     HInstruction value = node.inputs[0];
-    // If the union of the types is still the input type then
-    // no conversion is required.
-    HType combinedType = value.propagatedType.union(node.propagatedType);
+    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;
     Type type = receiver.propagatedType.computeType(compiler);
     if (type === null) return node;
     if (!compiler.world.isOnlyFields(type, node.name)) return node;
     return new HFieldGet(node.name, node.inputs[0]);
@@ skipping 504 matching lines @@
         }
         user.changeUse(input, newInput);
       }
     }
   }
 
   void visitIs(HIs instruction) {
     HInstruction input = instruction.expression;
     HType convertedType =
         new HType.fromBoundedType(instruction.typeExpression, compiler);
-    if (convertedType === null) return;
 
     List<HInstruction> ifUsers = <HInstruction>[];
     List<HInstruction> notIfUsers = <HInstruction>[];
 
     for (HInstruction user in instruction.usedBy) {
       if (user is HIf) {
         ifUsers.add(user);
       } else if (user is HNot) {
         for (HInstruction notUser in user.usedBy) {
           if (notUser is HIf) notIfUsers.add(notUser);
@@ skipping 17 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.
     }
   }
 }