Add intersection of disjoint masks to the TypeMask implementation.

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

 // Copyright (c) 2012, 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.
 
 part of ssa;
 
 abstract class OptimizationPhase {
   String get name;
   void visitGraph(HGraph graph);
 }
@@ skipping 545 matching lines @@
           return graph.addConstantBool(true, constantSystem);
         } else if (expressionType.isExact()) {
           return graph.addConstantBool(false, constantSystem);
         }
       }
     }
     return node;
   }
 
   HInstruction visitTypeConversion(HTypeConversion node) {
+    // TODO(kasperl): This needs cleaning up. We shouldn't be creating
+    // HType objects for malformed types.
+    if (node.isMalformedCheckedModeCheck) return node;
     HInstruction value = node.inputs[0];
     DartType type = node.instructionType.computeType(compiler);
     if (identical(type.element, compiler.dynamicClass)
         || identical(type.element, compiler.objectClass)) {
       return value;
     }
     if (value.instructionType.canBeNull() && node.isBooleanConversionCheck) {
       return node;
     }
     HType combinedType =
@@ skipping 970 matching lines @@
     HBasicBlock block = user.block;
     block.addAfter(user, interceptor);
     block.rewrite(user, interceptor);
     block.remove(user);
 
     // The interceptor will be removed in the dead code elimination
     // phase. Note that removing it here would not work because of how
     // the [visitBasicBlock] is implemented.
   }
 }