[Interpreter] Add ForInPrepare runtime function which returns a ObjectTriple.

src/interpreter/interpreter.cc

 // Copyright 2015 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.
 
 #include "src/interpreter/interpreter.h"
 
 #include "src/code-factory.h"
 #include "src/compiler.h"
 #include "src/compiler/interpreter-assembler.h"
 #include "src/factory.h"
@@ skipping 1680 matching lines @@
 }
 
 
 // ForInPrepare <cache_type> <cache_array> <cache_length>
 //
 // Returns state for for..in loop execution based on the object in the
 // accumulator. The registers |cache_type|, |cache_array|, and
 // |cache_length| represent output parameters.
 void Interpreter::DoForInPrepare(compiler::InterpreterAssembler* assembler) {
   Node* object = __ GetAccumulator();
-  Node* result = __ CallRuntime(Runtime::kInterpreterForInPrepare, object);
+  Node* result_triple = __ CallRuntime(Runtime::kForInPrepare, object);
+
+  // Set output registers:
+  //   0 == cache_type, 1 == cache_array, 2 == cache_length
   for (int i = 0; i < 3; i++) {
-    // 0 == cache_type, 1 == cache_array, 2 == cache_length
-    Node* cache_info = __ LoadFixedArrayElement(result, i);
+    Node* cache_info = __ Projection(i, result_triple);
     Node* cache_info_reg = __ BytecodeOperandReg(i);
     __ StoreRegister(cache_info, cache_info_reg);
   }
-  __ SetAccumulator(result);
+
   __ Dispatch();
 }
 
 
 // ForInNext <receiver> <cache_type> <cache_array> <index>
 //
 // Returns the next enumerable property in the the accumulator.
 void Interpreter::DoForInNext(compiler::InterpreterAssembler* assembler) {
   Node* receiver_reg = __ BytecodeOperandReg(0);
   Node* receiver = __ LoadRegister(receiver_reg);
@@ skipping 34 matching lines @@
   Node* index_reg = __ BytecodeOperandReg(0);
   Node* index = __ LoadRegister(index_reg);
   Node* result = __ CallRuntime(Runtime::kForInStep, index);
   __ SetAccumulator(result);
   __ Dispatch();
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8