[Bug c/115326] __builtin_sub_overflow reports incorrect overflow value

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115326

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think this is just invalid testcase.
The compiler is told that *a is const, but it is changed through a different
lvalue.