In LoadOptimizer::EmitPhis check for environment uses of phis.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, 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.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 3363 matching lines @@
 
     return true;
   }
 
   // Phis have not yet been inserted into the graph but they have uses of
   // their inputs.  Insert the non-redundant ones and clear the input uses
   // of the redundant ones.
   void EmitPhis() {
     for (intptr_t i = 0; i < phis_.length(); i++) {
       PhiInstr* phi = phis_[i];
-      if ((phi->input_use_list() != NULL) && !EliminateRedundantPhi(phi)) {
+      if (phi->HasUses() && !EliminateRedundantPhi(phi)) {
         phi->mark_alive();
         phi->block()->InsertPhi(phi);
       } else {
         for (intptr_t j = phi->InputCount() - 1; j >= 0; --j) {
           phi->InputAt(j)->RemoveFromUseList();
         }
       }
     }
   }
 
@@ skipping 973 matching lines @@
 
   if (FLAG_trace_constant_propagation) {
     OS::Print("\n==== After constant propagation ====\n");
     FlowGraphPrinter printer(*graph_);
     printer.PrintBlocks();
   }
 }
 
 
 }  // namespace dart