[kbenson]

> When using a new version of a compiler, and existing code stops working, it is often a compiler error. When different compilers give different results, it is often a compiler error.

To be fair, sometimes that's because the compiler became more strict and your code had an error that wasn't being caught. Sometimes it's the compiler taking a more liberal stance on what "undefined behavior" is for performance reasons. In both cases, that would still a programmer error (and I think those are likely the more common case than an actual compiler error).