Current C2 intrinsic code makes Opaque a "relaxed" plain load/store with regards to single copy atomicity.

  bool requires_atomic_access = false;
  switch (kind) {
      case Relaxed:
      case Opaque:
          requires_atomic_access = AlwaysAtomicAccesses;
          break;

This contradicts the intent of making Opaque similar to std::atomic...(..., memory_order_relaxed), which is single copy atomic.