IfConverted should unuse inputs of the join it removes.

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 6281 matching lines @@
           pred->set_block_id(block->block_id());
 
           // If v1 and v2 were defined inside eliminated blocks pred1/pred2
           // move them out to the place before inserted IfThenElse instruction.
           EliminateTrivialBlock(pred1, v1->definition(), if_then_else);
           EliminateTrivialBlock(pred2, v2->definition(), if_then_else);
 
           // Update use lists to reflect changes in the graph.
           phi->UnuseAllInputs();
           branch->UnuseAllInputs();
+          block->UnuseAllInputs();
 
           // The graph has changed. Recompute dominators and block orders after
           // this pass is finished.
           changed = true;
         }
       }
     }
   }
 
   if (changed) {
@@ skipping 235 matching lines @@
 
   // Insert materializations at environment uses.
   const Class& cls = Class::Handle(alloc->constructor().Owner());
   for (intptr_t i = 0; i < exits.length(); i++) {
     CreateMaterializationAt(exits[i], alloc, cls, *fields);
   }
 }
 
 
 }  // namespace dart