Mark phi as producing a smi value if it is dominated by SmiChecks over its operands.

runtime/vm/flow_graph_optimizer.h

 // 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.
 
 #ifndef VM_FLOW_GRAPH_OPTIMIZER_H_
 #define VM_FLOW_GRAPH_OPTIMIZER_H_
 
 #include "vm/intermediate_language.h"
 #include "vm/flow_graph.h"
 
@@ skipping 10 matching lines @@
   virtual ~FlowGraphOptimizer() {}
 
   void ApplyICData();
 
   void OptimizeComputations();
 
   void EliminateDeadPhis();
 
   void SelectRepresentations();
 
+  void PropagateSminess();
+
   virtual void VisitStaticCall(StaticCallInstr* instr);
   virtual void VisitInstanceCall(InstanceCallInstr* instr);
   virtual void VisitRelationalOp(RelationalOpInstr* instr);
   virtual void VisitEqualityCompare(EqualityCompareInstr* instr);
   virtual void VisitBranch(BranchInstr* instr);
 
   // TODO(fschneider): Once we get rid of the distinction between Instruction
   // and computation, this can be made private again.
   void InsertBefore(Instruction* instr,
                     Definition* defn,
@@ skipping 107 matching lines @@
  private:
   static void OptimizeRecursive(
       BlockEntryInstr* entry,
       DirectChainedHashMap<Definition*>* map);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_