I tried check.c and check_bad.c using xlc-v11 (on my POWER6) - and the
results were the same as in Pablo's entry.

On the gcc119 host - using the v13 compiler, check_bad does not crash.
Not gotten to testing xlc-v16 yet.

I have seen lots of options today - wheile researching, so probably,
yes. Just do not know it off the top.

Atm - testing "master" build using xlc-v11 and xlc-v13.

On 06/07/2020 18:13, David Edelsohn wrote:
> David Edelsohn <dje.gcc@gmail.com> added the comment:
>
> I don't believe that this is an XLC bug, but I suspect that it is undefined behavior / implementation-defined behavior.
>
> I suspect that this is tripping over AIX/XLC null behavior. AIX specifically and intentionally maps the first page of memory at address 0 to allow the compiler to speculate through NULL pointers. The compiler probably is speculating in this case and the second element is not defined.
>
> There is some option to disable this speculation in XLC.
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue41215>
> _______________________________________
>