https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64689
--- Comment #2 from Philipp Gschwandtner <philipp.gschwandtner at uibk dot ac.at> --- Thanks for the quick reply, it's an excerpt from a larger code and I wasn't aware that it's actually not C-compliant. Maybe gcc bug submission guidelines should include compiling/running with -fsanitize to check for issues like that.
