Avoid HeapObject check in HStoreNamedField.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index e15d4a69875fcbe108a369927a7a496ffd36b9e1..e1b9e5f159095eccedde4ea3da55f89173e5b131 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2327,15 +2327,7 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
   LOperand* temp = (!is_in_object || needs_write_barrier ||
       needs_write_barrier_for_map) ? TempRegister() : NULL;
 
-  LInstruction* result = new(zone()) LStoreNamedField(obj, val, temp);
-  if (!instr->access().IsExternalMemory() &&
-      instr->field_representation().IsHeapObject() &&
-      (val->IsConstantOperand()
-       ? HConstant::cast(instr->value())->HasSmiValue()
-       : !instr->value()->type().IsHeapObject())) {
-    result = AssignEnvironment(result);
-  }
-  return result;
+  return new(zone()) LStoreNamedField(obj, val, temp);
 }