message: fix handle_insert_order_at_merge when two regs are same
  Summary: Fix handle_insert_order_at_merge when two regs are same so that the sort can work properly.
diff: @@ -420,6 +420,7 @@ void AliasedRegisters::handle_insert_order_at_merge(
  // return false if they compare equal or if b occurs before a.
  // `a` and `b` only index into this, not other.
  + if (a == b) return false;
  const Value& val_a = this->m_graph[a];
  const Value& val_b = this->m_graph[b];
  auto other_a = other.find(val_a);
  