dart2js cps: Fix some analyzer hints in the CPS backend.

pkg/compiler/lib/src/cps_ir/bounds_checker.dart

 // Copyright (c) 2015, 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 dart2js.cps_ir.bounds_checker;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart' show Pass;
 import 'octagon.dart';
 import '../constants/values.dart';
@@ skipping 475 matching lines @@
 
   @override
   void visitGetLength(GetLength node) {
     valueOf[node] = getLength(node.object.definition, currentEffectNumber);
   }
 
   @override
   void visitBoundsCheck(BoundsCheck node) {
     if (node.checks == BoundsCheck.NONE) return;
     assert(node.index != null); // Because there is at least one check.
-    Primitive object = node.object.definition;
     SignedVariable length = node.length == null
         ? null
         : getValue(node.length.definition);
     SignedVariable index = getValue(node.index.definition);
     if (node.hasUpperBoundCheck) {
       if (isDefinitelyLessThan(index, length)) {
         node.checks &= ~BoundsCheck.UPPER_BOUND;
       } else {
         makeLessThan(index, length);
       }
@@ skipping 225 matching lines @@
     }
     return node.body;
   }
 }
 
 /// Lattice representing the known (weak) monotonicity of a loop variable.
 ///
 /// The lattice bottom is represented by `null` and represents the case where
 /// the loop variable never changes value during the loop.
 enum Monotonicity { NotMonotone, Increasing, Decreasing, }