volatile: is NOT a frill, i

[Guy Harris]

> I have some hope of seeing decent cross-procedural and global analysis
> in production C compilers in my lifetime ;-}. In which case, the
> compiler may be able to prove that user_interrupt is not modified
> by any function called...

Or it may not, given that "sleep" may be dynamically bound and therefore the
compiler may have no way of knowing what procedure "sleep" is, and therefore
has to limit its cross-procedural analysis.