https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71701
--- Comment #1 from Pedro Alves <palves at redhat dot com> ---
I tried to reduce this manually, but failed. My attempt made gcc warn about
the original variable in my test case:
strtok.c: In function ‘main’:
strtok.h:30:10: warning: ‘saveptr’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
while (*__s == __sep)
^~~~
It may be that glibc's use of __extension__ / __builtin_constant_p is what
triggers this.
