Fix for a smi stores optimization on x64 with a test case.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 9073ac36ca9983aa3e51550cb137b882370a511d..09ac767953b730b6abd4fb851aaa704ab5cb13b5 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -6534,7 +6534,6 @@ class HStoreNamedField V8_FINAL : public HTemplateInstruction<3> {
         write_barrier_mode_(UPDATE_WRITE_BARRIER),
         has_transition_(false),
         store_mode_(store_mode) {
-    if (!FLAG_smi_x64_store_opt) store_mode_ = INITIALIZING_STORE;
     // Stores to a non existing in-object property are allowed only to the
     // newly allocated objects (via HAllocate or HInnerAllocatedObject).
     ASSERT(!access.IsInobject() || access.existing_inobject_property() ||
@@ -6723,7 +6722,6 @@ class HStoreKeyed V8_FINAL
       is_uninitialized_(false),
       store_mode_(store_mode),
       new_space_dominator_(NULL) {
-    if (!FLAG_smi_x64_store_opt) store_mode_ = INITIALIZING_STORE;
     SetOperandAt(0, obj);
     SetOperandAt(1, key);
     SetOperandAt(2, val);