VM: Improve phi-elimination to improve code inside of try-catch.

runtime/vm/intermediate_language.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_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 1966 matching lines @@
 
   void set_reaching_defs(BitVector* reaching_defs) {
     reaching_defs_ = reaching_defs;
   }
 
   virtual bool MayThrow() const { return false; }
 
   // A phi is redundant if all input operands are the same.
   bool IsRedundant() const;
 
+  bool HasReplacement(Definition** replacement) const;
+
   void set_induction_variable_info(InductionVariableInfo* info) {
     loop_variable_info_ = info;
   }
 
   InductionVariableInfo* induction_variable_info() {
     return loop_variable_info_;
   }
 
   PRINT_TO_SUPPORT
 
@@ skipping 6292 matching lines @@
   LocationSummary* Name::MakeLocationSummary(Zone* zone, bool opt) const {    \
     UNIMPLEMENTED();                                                          \
     return NULL;                                                              \
   }                                                                           \
   void Name::EmitNativeCode(FlowGraphCompiler* compiler) { UNIMPLEMENTED(); }
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_