It's been stated here already. You can write whatever you want into it. It doesn't matter. What matters is that the compiler realizes there's a dead store go

It's been stated here already. You can write whatever you want into it. It doesn't matter. What matters is that the compiler realizes there's a dead store going into it, i.e. that the data is thrown away after it's written. So it can optimize out any write, since no conforming program can read that data after it's thrown away.