Weird optimization bug

[François-Xavier Coudert]

Hi Ignacio,

I'm sorry that I don't have enough time to write a full answer, but
here is the short version:

> So, I would say it was a too-sensitive-to-optimization thing

You would be right.

> but fixing it with a WRITE tells me it must be a bug

The WRITE hides the optimization opportunity to the compiler, which is
why the behaviour is then identical to the unoptimized case.

FX