Add functions for setting an environment and rebinding a use.

runtime/vm/flow_graph_allocator.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_allocator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/intermediate_language.h"
 #include "vm/il_printer.h"
 #include "vm/flow_graph.h"
@@ skipping 102 matching lines @@
             continue;
           }
 
           PhiInstr* phi = def->AsPhi();
           if ((phi != NULL) && !phi->is_alive()) {
             it.SetCurrentValue(new Value(constant_null));
             continue;
           }
         }
       } else {
-        current->set_env(NULL);
+        current->RemoveEnvironment();
       }
     }
   }
 }
 
 
 void FlowGraphAllocator::ComputeInitialSets() {
   const intptr_t block_count = postorder_.length();
   for (intptr_t i = 0; i < block_count; i++) {
     BlockEntryInstr* block = postorder_[i];
@@ skipping 2377 matching lines @@
     OS::Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(flow_graph_, true);
     printer.PrintBlocks();
     OS::Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart