Set previous instruction pointers when building the graph.

runtime/vm/flow_graph_optimizer.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_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 3116 matching lines @@
       }
 
       if (join != NULL) {
         // Replace the branch with a jump to the reachable successor.
         // Drop the comparison, which does not have side effects as long
         // as it is a strict compare (the only one we can determine is
         // constant with the current analysis).
         GotoInstr* jump = new GotoInstr(join);
         Instruction* previous = branch->previous();
         branch->set_previous(NULL);
-        previous->set_next(jump);
+        previous->LinkTo(jump);
         // Replace the false target entry with the new join entry. We will
         // recompute the dominators after this pass.
-        join->set_next(next);
+        join->LinkTo(next);
       }
     }
   }
 
   graph_->DiscoverBlocks();
   GrowableArray<BitVector*> dominance_frontier;
   graph_->ComputeDominators(&dominance_frontier);
   graph_->ComputeUseLists();
 
   if (FLAG_trace_constant_propagation) {
     OS::Print("\n==== After constant propagation ====\n");
     FlowGraphPrinter printer(*graph_);
     printer.PrintBlocks();
   }
 }
 
 
 }  // namespace dart