Remove dead phis as soon as they are discovered.

runtime/vm/flow_graph.h

 // 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.
 
 #ifndef VM_FLOW_GRAPH_H_
 #define VM_FLOW_GRAPH_H_
 
 #include "vm/growable_array.h"
 #include "vm/intermediate_language.h"
 #include "vm/parser.h"
@@ skipping 149 matching lines @@
   void RenameRecursive(
       BlockEntryInstr* block_entry,
       GrowableArray<Definition*>* env,
       GrowableArray<PhiInstr*>* live_phis);
 
   void InsertPhis(
       const GrowableArray<BlockEntryInstr*>& preorder,
       const GrowableArray<BitVector*>& assigned_vars,
       const GrowableArray<BitVector*>& dom_frontier);
 
-  void MarkLivePhis(GrowableArray<PhiInstr*>* live_phis);
+  void RemoveDeadPhis(GrowableArray<PhiInstr*>* live_phis);
 
   void ReplacePredecessor(BlockEntryInstr* old_block,
                           BlockEntryInstr* new_block);
 
   // DiscoverBlocks computes parent_ and assigned_vars_ which are then used
   // if/when computing SSA.
   GrowableArray<intptr_t> parent_;
   GrowableArray<BitVector*> assigned_vars_;
 
   intptr_t current_ssa_temp_index_;
   intptr_t max_block_id_;
 
   // Flow graph fields.
   const ParsedFunction& parsed_function_;
   const intptr_t num_copied_params_;
   const intptr_t num_non_copied_params_;
   const intptr_t num_stack_locals_;
   GraphEntryInstr* graph_entry_;
   GrowableArray<BlockEntryInstr*> preorder_;
   GrowableArray<BlockEntryInstr*> postorder_;
   GrowableArray<BlockEntryInstr*> reverse_postorder_;
   bool invalid_dominator_tree_;
   ConstantInstr* constant_null_;
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_H_