Generators return boxed values

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index a20d468bae4721f681b6efdcafb185c7bc54e83e..24591657927d0eeacfa290c578a2df53400ccffc 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1924,11 +1924,12 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       Label resume;
       __ CompareRoot(result_register(), Heap::kTheHoleValueRootIndex);
       __ j(not_equal, &resume);
-      __ pop(result_register());
       if (expr->yield_kind() == Yield::SUSPEND) {
-        // TODO(wingo): Box into { value: VALUE, done: false }.
+        EmitReturnIteratorResult(false);
+      } else {
+        __ pop(result_register());
+        EmitReturnSequence();
       }
-      EmitReturnSequence();
 
       __ bind(&resume);
       context()->Plug(result_register());
@@ -1939,19 +1940,8 @@ void FullCodeGenerator::VisitYield(Yield* expr) {
       VisitForAccumulatorValue(expr->generator_object());
       __ Move(FieldOperand(result_register(),
                            JSGeneratorObject::kContinuationOffset),
-              Smi::FromInt(JSGeneratorObject::kGeneratorClosed));
-      __ pop(result_register());
-      // TODO(wingo): Box into { value: VALUE, done: true }.
-
-      // Exit all nested statements.
-      NestedStatement* current = nesting_stack_;
-      int stack_depth = 0;
-      int context_length = 0;
-      while (current != NULL) {
-        current = current->Exit(&stack_depth, &context_length);
-      }
-      __ Drop(stack_depth);
-      EmitReturnSequence();
+              Smi::FromInt(0));
+      EmitReturnIteratorResult(true);
       break;
     }
 
@@ -2058,6 +2048,63 @@ void FullCodeGenerator::EmitGeneratorResume(Expression *generator,
 }
 
 
+void FullCodeGenerator::EmitReturnIteratorResult(bool done) {
+  Label gc_required;
+  Label allocated;
+
+  STATIC_ASSERT(HeapObject::kMapOffset == 0);
+  STATIC_ASSERT(JSObject::kPropertiesOffset == kPointerSize);
+  STATIC_ASSERT(JSObject::kElementsOffset == 2 * kPointerSize);
+  STATIC_ASSERT(JSObject::kHeaderSize == 3 * kPointerSize);
+  STATIC_ASSERT(JSGeneratorObject::kResultValuePropertyIndex == 0);
+  STATIC_ASSERT(JSGeneratorObject::kResultDonePropertyIndex == 1);
+
+  const int size = 5 * kPointerSize;
+  __ Allocate(size, rax, rcx, rdx, &gc_required, TAG_OBJECT);
+
+  __ bind(&allocated);
+  // The object is now in rax.  Initialize its map, value, and done fields.
+  Handle<Map> map(isolate()->native_context()->iterator_result_map());
+  __ Move(rbx, map);
+  __ pop(rcx);
+  __ Move(rdx,
+          done
+          ? isolate()->factory()->true_value()
+          : isolate()->factory()->false_value());
+  __ movq(FieldOperand(rax, 0 * kPointerSize), rbx);  // map
+  __ Move(FieldOperand(rax, 1 * kPointerSize),        // properties
+          isolate()->factory()->empty_fixed_array());
+  __ Move(FieldOperand(rax, 2 * kPointerSize),        // elements
+          isolate()->factory()->empty_fixed_array());
+  __ movq(FieldOperand(rax, 3 * kPointerSize), rcx);  // value
+  __ movq(FieldOperand(rax, 4 * kPointerSize), rdx);  // done?
+
+  // Only the value field needs a write barrier, as the other values are in the
+  // root set.
+  __ RecordWriteField(rax, 3 * kPointerSize, rcx, rdx, kDontSaveFPRegs);
+
+  if (done) {
+    // Exit all nested statements.
+    NestedStatement* current = nesting_stack_;
+    int stack_depth = 0;
+    int context_length = 0;
+    while (current != NULL) {
+      current = current->Exit(&stack_depth, &context_length);
+    }
+    __ Drop(stack_depth);
+  }
+
+  EmitReturnSequence();
+
+  __ bind(&gc_required);
+  __ Push(Smi::FromInt(size));
+  __ CallRuntime(Runtime::kAllocateInNewSpace, 1);
+  __ movq(context_register(),
+          Operand(rbp, StandardFrameConstants::kContextOffset));
+  __ jmp(&allocated);
+}
+
+
 void FullCodeGenerator::EmitNamedPropertyLoad(Property* prop) {
   SetSourcePosition(prop->position());
   Literal* key = prop->key()->AsLiteral();