> you upgrade your compiler, and you see some mysterious new backtraces showing up in the crash reporter, then it's entirely possible your compiler is buggy.

IME, there are two more likely causes of this, that are kind of rooted in the same cause:

1. Your code depended on a compiler bug to function, the bug is fixed, and now your code is broken

2. Your code depended on an undefined part of the language semantics, the compiler changed from doing one undefined thing to another, and now your code is broken