Compute the def-use list on-demand by walking the dominator tree.

runtime/vm/flow_graph_allocator.cc

 // 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.
 
 #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 84 matching lines @@
         GrowableArray<Value*>* values = current->env()->values_ptr();
 
         for (intptr_t i = 0; i < values->length(); i++) {
           UseVal* use = (*values)[i]->AsUse();
           if (use == NULL) continue;
 
           Definition* def = use->definition();
 
           PushArgumentInstr* push_argument = def->AsPushArgument();
           if ((push_argument != NULL) && push_argument->WasEliminated()) {
-            // TODO(zerny): This should be unreachable if we could properly
-            // replace uses by values. (See RemovePushArguments in
-            // flow_graph_optimizer.cc).
-            (*values)[i] = push_argument->value();
+            (*values)[i] = push_argument->value()->CopyValue();
             continue;
           }
 
           PhiInstr* phi = def->AsPhi();
           if ((phi != NULL) && !phi->is_alive()) {
             (*values)[i] = null_value;
             continue;
           }
         }
       } else {
@@ skipping 1914 matching lines @@
     OS::Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(flow_graph_, true);
     printer.PrintBlocks();
     OS::Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart