>
> How can this be a bug in our code? Wraparound of unsigned values is
> well-defined.


True, it is well-defined, but it was not intended for sure, hence it's a
100% bug. Eli's term of "undefined behavior" was an exaggeration I think.

I don't think the compiler is justified in making this optimization.
> Since when is an infinite loop undefined behavior? GCC has no right to
> alter program semantics in this case, loop unrolling or no.


I would agree here, throwing out wrapped loop is just too much even though
such loop was unintended. GCC should have either left it alone since it is
infinite or make a warning. I think this case is still worth showing to GCC
developers.