http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58970
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Bernd Edlinger from comment #7)
> (In reply to Jakub Jelinek from comment #6)
> > That doesn't look safe, negative rbitpos is not necessarily undefined
> > behavior.
> > Can't you get the same with say
> > struct S { unsigned char s : 1; };
> >
> > ...
> > void function(struct S *p)
> > {
> > p[-1].s = 0;
> > }
>
> no. I checked that. This is folded quite differently:
>
> MEM[(struct S *)p_1(D) + -1B].s = 0;
>
> and there is no ICE in this case.
But this is really nothing the expansion code should rely on to detect if the
code is undefined behavior or not.
