[Interpreter] Implement ForIn in bytecode graph builder.

src/interpreter/control-flow-builders.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/control-flow-builders.h"
 
 namespace v8 {
 namespace internal {
 namespace interpreter {
 
@@ skipping 72 matching lines @@
 
 void BlockBuilder::EndBlock() {
   builder()->Bind(&block_end_);
   SetBreakTarget(block_end_);
 }
 
 
 LoopBuilder::~LoopBuilder() { DCHECK(continue_sites_.empty()); }
 
 
+void LoopBuilder::LoopHeader() {
+  // Jumps from before the loop header into the loop violate ordering
+  // requirements of bytecode basic blocks. The only entry into a loop
+  // must be the loop header. Surely breaks is okay? Not if nested
+  // and misplaced between the headers.
+  DCHECK(break_sites_.empty() && continue_sites_.empty());
+  builder()->Bind(&loop_header_);
+}
+
+
 void LoopBuilder::EndLoop() {
   // Loop must have closed form, i.e. all loop elements are within the loop,
   // the loop header precedes the body and next elements in the loop.
   DCHECK(loop_header_.is_bound());
   builder()->Bind(&loop_end_);
   SetBreakTarget(loop_end_);
   if (next_.is_bound()) {
     DCHECK(!condition_.is_bound() || next_.offset() >= condition_.offset());
     SetContinueTarget(next_);
   } else {
@@ skipping 20 matching lines @@
 
 
 void SwitchBuilder::SetCaseTarget(int index) {
   BytecodeLabel& site = case_sites_.at(index);
   builder()->Bind(&site);
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8