[Bug rtl-optimization/108117] Wrong instruction scheduling on value coming from abnormal SSA

["fxue at os dot amperecomputing.com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108117

--- Comment #8 from Feng Xue <fxue at os dot amperecomputing.com> ---
(In reply to Andrew Pinski from comment #7)
> (In reply to Feng Xue from comment #6)
> > (In reply to Andrew Pinski from comment #2)
> > > https://en.cppreference.com/w/c/program/setjmp
> > 
> > I think that most programmers are not aware of this, neither I for sure.
> > Usage of volatile here is not that intuitive as for purpose of
> > multi-execution synchronization
> 
> You should read up on
> https://en.cppreference.com/w/cpp/utility/program/signal too.

From viewpoint of programmer, setjmp/longjmp is somewhat similar to C++
exception handling, which happens in one logical execution context, while
signal implies two  unrelated contexts.

In another angle, because gcc already model control flow and SSA web for
setjmp/longjmp, explicit volatile specification is not really needed. But
signal mechanism is kind of asynchronous exception, for which it is impractical
for compiler to do that, so volatile is must.