Constant propagator should revisit phis when it visits predecessor block.

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 194 matching lines @@
   bool IsUnknown(const Object& value) {
     return value.raw() == unknown_.raw();
   }
   bool IsNonConstant(const Object& value) {
     return value.raw() == non_constant_.raw();
   }
   bool IsConstant(const Object& value) {
     return !IsNonConstant(value) && !IsUnknown(value);
   }
 
+  void VisitSuccessorPhis(BlockEntryInstr* block);
+
   virtual void VisitBlocks() { UNREACHABLE(); }
 
 #define DECLARE_VISIT(type) virtual void Visit##type(type##Instr* instr);
   FOR_EACH_INSTRUCTION(DECLARE_VISIT)
 #undef DECLARE_VISIT
 
   FlowGraph* graph_;
 
   // Sentinels for unknown constant and non-constant values.
   const Object& unknown_;
@@ skipping 10 matching lines @@
 
   // Worklists of blocks and definitions.
   GrowableArray<BlockEntryInstr*> block_worklist_;
   GrowableArray<Definition*> definition_worklist_;
 };
 
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_OPTIMIZER_H_