Check that environments assigned via AssignEnvironment are actually used.

src/lithium-codegen.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 50 matching lines @@
   virtual void GenerateBodyInstructionPre(LInstruction* instr) {}
   virtual void GenerateBodyInstructionPost(LInstruction* instr) {}
 
   virtual void EnsureSpaceForLazyDeopt(int space_needed) = 0;
   virtual void RecordAndWritePosition(int position) = 0;
 
   int GetNextEmittedBlock() const;
 
   void RegisterWeakObjectsInOptimizedCode(Handle<Code> code);
 
+  // Check that an environment assigned via AssignEnvironment is actually being
+  // used. Redundant assignments keep things alive longer than necessary, and
+  // consequently lead to worse code, so it's important to minimize this.
+  void CheckEnvironmentUsage();
+
  protected:
   enum Status {
     UNUSED,
     GENERATING,
     DONE,
     ABORTED
   };
 
   LPlatformChunk* const chunk_;
   MacroAssembler* const masm_;
   CompilationInfo* const info_;
   Zone* zone_;
   Status status_;
   int current_block_;
   int current_instruction_;
   const ZoneList<LInstruction*>* instructions_;
   int last_lazy_deopt_pc_;
 
   bool is_unused() const { return status_ == UNUSED; }
   bool is_generating() const { return status_ == GENERATING; }
   bool is_done() const { return status_ == DONE; }
   bool is_aborted() const { return status_ == ABORTED; }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_LITHIUM_CODEGEN_H_