[Interpreter] Implement ForIn in bytecode graph builder.

src/interpreter/bytecode-generator.cc

Index: src/interpreter/bytecode-generator.cc
diff --git a/src/interpreter/bytecode-generator.cc b/src/interpreter/bytecode-generator.cc
index 22972537abcbccb0e72a702ba07e9e4eb12a011a..af5111e4fcc8e5fc35bbb9ddf6ef762e6b6f31d7 100644
--- a/src/interpreter/bytecode-generator.cc
+++ b/src/interpreter/bytecode-generator.cc
@@ -851,7 +851,6 @@ void BytecodeGenerator::VisitForInAssignment(Expression* expr,
 
 void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   EffectResultScope statement_result_scope(this);
-
   if (stmt->subject()->IsNullLiteral() ||
       stmt->subject()->IsUndefinedLiteral(isolate())) {
     // ForIn generates lots of code, skip if it wouldn't produce any effects.
@@ -865,34 +864,33 @@ void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   VisitForAccumulatorValue(stmt->subject());
   loop_builder.BreakIfUndefined();
   loop_builder.BreakIfNull();
-
   Register receiver = execution_result()->NewRegister();
+  // BytecodeGenerator emits a cast here as the BytecodeGraphBuilder
+  // only supports a single de-opt point per bytecode. So whilst the
+  // ast-graph-builder does the cast (semantically) inside
+  // ForInPrepare we need to cast first in case it de-opts.

[Benedikt Meurer, 2015/12/18 07:55:50]

Same here. I'm not sure what that comment is supposed to say.
Also it's not really a "cast", but a "type conversion".

   builder()->CastAccumulatorToJSObject();
+  loop_builder.BreakIfNull();
   builder()->StoreAccumulatorInRegister(receiver);
-  builder()->CallRuntime(Runtime::kGetPropertyNamesFast, receiver, 1);
-  builder()->ForInPrepare(receiver);
-  loop_builder.BreakIfUndefined();
-
-  Register for_in_state = execution_result()->NewRegister();
-  builder()->StoreAccumulatorInRegister(for_in_state);
+  Register cache_type = execution_result()->NewRegister();
+  Register cache_array = execution_result()->NewRegister();
+  Register cache_length = execution_result()->NewRegister();
+  builder()->ForInPrepare(receiver, cache_type, cache_array, cache_length);
 
   // Check loop termination (accumulator holds index).
-  Register index = receiver;  // Re-using register as receiver no longer used.
+  Register index = execution_result()->NewRegister();
   builder()->LoadLiteral(Smi::FromInt(0));
+  builder()->StoreAccumulatorInRegister(index);
   loop_builder.LoopHeader();
   loop_builder.Condition();
-  builder()->StoreAccumulatorInRegister(index).ForInDone(for_in_state);
+  builder()->ForInDone(index, cache_length);
   loop_builder.BreakIfTrue();
-  builder()->ForInNext(for_in_state, index);
+  builder()->ForInNext(receiver, cache_type, cache_array, index);
   loop_builder.ContinueIfUndefined();
-
   VisitForInAssignment(stmt->each(), stmt->EachFeedbackSlot());
   Visit(stmt->body());
-
-  // TODO(oth): replace CountOperation here with ForInStep.
   loop_builder.Next();
-  builder()->LoadAccumulatorWithRegister(index).CountOperation(
-      Token::Value::ADD, language_mode_strength());
+  builder()->ForInStep(index);
   loop_builder.JumpToHeader();
   loop_builder.LoopEnd();
 }