[turbofan] Canonicalize return sequence for JSFunctions.

src/compiler/code-generator.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_CODE_GENERATOR_H_
 #define V8_COMPILER_CODE_GENERATOR_H_
 
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/instruction.h"
 #include "src/deoptimizer.h"
@@ skipping 154 matching lines @@
     int pc_offset;
   };
 
   friend class OutOfLineCode;
 
   Frame* const frame_;
   Linkage* const linkage_;
   InstructionSequence* const code_;
   CompilationInfo* const info_;
   Label* const labels_;
+  Label return_label_;
   RpoNumber current_block_;
   SourcePosition current_source_position_;
   MacroAssembler masm_;
   GapResolver resolver_;
   SafepointTableBuilder safepoints_;
   ZoneVector<HandlerInfo> handlers_;
   ZoneDeque<DeoptimizationState*> deoptimization_states_;
   ZoneDeque<Handle<Object>> deoptimization_literals_;
   size_t inlined_function_count_;
   TranslationBuffer translations_;
   int last_lazy_deopt_pc_;
   JumpTable* jump_tables_;
   OutOfLineCode* ools_;
   int osr_pc_offset_;
   bool needs_frame_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_CODE_GENERATOR_H