The C1 shared code for generating the intrinsics for the Unsafe.getXXX and Unsafe.putXXX is:

void LIRGenerator::do_UnsafeGetObject(UnsafeGetObject* x) {
  ...
  if (x->is_volatile() && os::is_MP()) __ membar_acquire();
  get_Object_unsafe(reg, src.result(), off.result(), type, x->is_volatile());
  if (x->is_volatile() && os::is_MP()) __ membar();
}

void LIRGenerator::do_UnsafePutObject(UnsafePutObject* x) {
  ...
  if (x->is_volatile() && os::is_MP()) __ membar_release();
  put_Object_unsafe(src.result(), off.result(), data.result(), type, x->is_volatile());
}

Note that "get" has a final membar(), but it is the "put" that needs it.

Also "get" should be "load; acquire" not "acquire; load"