Sorry for the confusion, I meant to say yes it is needed.
I just duplicated the TODO comment found on [other](https://github.com/dawgfoto/dmd/blob/f97ef37f4ee4bcd39e9962dd7366877a186635af/src/backend/ptrntab.c#L135) REX.W instructions, it means we're missing a way to explicitly encode REX.W in the table and rely on the codegen to emit the prefix because the _64_bit flag is set.