Avoid generating empty else.

lib/compiler/implementation/ssa/variable_allocator.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.
 
 /**
  * The [LiveRange] class covers a range where an instruction is live.
  */
 class LiveRange {
   final int start;
   // [end] is not final because it can be updated due to loops.
@@ skipping 316 matching lines @@
 
   void addCopy(HInstruction source, HInstruction destination) {
     copies.add(new Copy(source, destination));
   }
 
   void addAssignment(HInstruction source, HInstruction destination) {
     assignments.add(new Copy(source, destination));
   }
 
   String toString() => 'Copies: $copies, assignments: $assignments';
+  bool isEmpty() => copies.isEmpty() && assignments.isEmpty();
 }
 
 /**
  * Contains the mapping between instructions and their names for code
  * generation, as well as the [CopyHandler] for each basic block.
  */
 class VariableNames {
   final Map<HInstruction, String> ownName;
   final Map<HBasicBlock, CopyHandler> copyHandlers;
   /**
@@ skipping 216 matching lines @@
       if (!needsName(input)) {
         names.addAssignment(predecessor, input, phi);
       } else {
         names.addCopy(predecessor, input, phi);
       }
     }
 
     namer.allocateName(phi);
   }
 }