Don't emit code for HContext values with no uses.

src/x64/lithium-x64.cc

 // Copyright 2011 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 1171 matching lines @@
 
 
 LInstruction* LChunkBuilder::DoPushArgument(HPushArgument* instr) {
   ++argument_count_;
   LOperand* argument = UseOrConstant(instr->argument());
   return new LPushArgument(argument);
 }
 
 
 LInstruction* LChunkBuilder::DoContext(HContext* instr) {
-  return DefineAsRegister(new LContext);
+  return instr->HasNoUses() ? NULL : DefineAsRegister(new LContext);
 }
 
 
 LInstruction* LChunkBuilder::DoOuterContext(HOuterContext* instr) {
   LOperand* context = UseRegisterAtStart(instr->value());
   return DefineAsRegister(new LOuterContext(context));
 }
 
 
 LInstruction* LChunkBuilder::DoGlobalObject(HGlobalObject* instr) {
@@ skipping 940 matching lines @@
   LOperand* key = UseOrConstantAtStart(instr->key());
   LOperand* object = UseOrConstantAtStart(instr->object());
   LIn* result = new LIn(key, object);
   return MarkAsCall(DefineFixed(result, rax), instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64