Use native behavior for dead code elimination

pkg/compiler/lib/src/native/behavior.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.
 
 part of native;
 
 /// This class is a temporary work-around until we get a more powerful DartType.
 class SpecialType {
   final String name;
   const SpecialType._(this.name);
@@ skipping 13 matching lines @@
   static const NativeThrowBehavior MAY_THROW_ONLY_ON_FIRST_ARGUMENT_ACCESS =
       const NativeThrowBehavior._(1);
   static const NativeThrowBehavior MAY = const NativeThrowBehavior._(2);
   static const NativeThrowBehavior MUST = const NativeThrowBehavior._(3);
 
   final int _bits;
   const NativeThrowBehavior._(this._bits);
 
   bool get canThrow => this != NEVER;
 
+  /// Does this behavior always throw a noSuchMethod check on a null first
+  /// argument before any side effect or other exception?
+  // TODO(sra): Extend NativeThrowBehavior with the concept of NSM guard
+  // followed by other potential behavior.
+  bool get isNullNSMGuard => this == MAY_THROW_ONLY_ON_FIRST_ARGUMENT_ACCESS;
+
+  /// Does this behavior always act as a null noSuchMethod check, and has no
+  /// other throwing behavior?
+  bool get onlyNullNSMGuard => this == MAY_THROW_ONLY_ON_FIRST_ARGUMENT_ACCESS;

[floitsch, 2015/04/13 08:07:14]

nit: isOnlyNullNSMGuard

[sra1, 2015/04/13 23:59:05]

Done.

+
+  /// Returns the behavior if we assume the first argument is not null.
+  NativeThrowBehavior get onNonNull {
+    if (this == MAY_THROW_ONLY_ON_FIRST_ARGUMENT_ACCESS) return NEVER;
+    return this;
+  }
+
   String toString() {
     if (this == NEVER) return 'never';
     if (this == MAY) return 'may';
     if (this == MAY_THROW_ONLY_ON_FIRST_ARGUMENT_ACCESS) return 'null(1)';
     if (this == MUST) return 'must';
     return 'NativeThrowBehavior($_bits)';
   }
 }
 
 /**
@@ skipping 675 matching lines @@
         MessageKind.GENERIC,
         {'text': "Type '$typeString' not found."});
     return const DynamicType();
   }
 
   static _errorNode(locationNodeOrElement, compiler) {
     if (locationNodeOrElement is Node) return locationNodeOrElement;
     return locationNodeOrElement.parseNode(compiler);
   }
 }